Patent Publication Number: US-2022219365-A1

Title: Slide mechanism, fixing mold, movable mold and molding mold

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sliding mechanism as well as an undercut processing mechanism, a gate cutting mechanism, a gate pulling mechanism, and a molding mold or molding die including the same. 
     Description of Related Art 
     For use in molding dies which mold a molded product including an undercut portion, many undercut processing mechanisms have been developed in accordance with shapes of undercut portions. For example, well-known processing mechanisms include: a processing mechanism having a slide core structure used for a molded product including a hole in a lateral face thereof; and a processing mechanism having a loose core structure used for a molded product including a projection on an inner side of a core thereof. 
     Further, there is an undercut processing mechanism capable of being compactly incorporated into a mold (for example, see Patent Document 1). The undercut processing mechanism as described in Patent Document 1 includes a slider which supports an undercut molding core, a base member which is slidably coupled to the slider, and a holder, and the undercut processing mechanism is configured to operate in conjunction with an ejector mechanism to move the slider and demold an undercut. 
     RELATED DOCUMENT 
     Patent Document 
     [Patent Document 1] JP Laid-open Patent Publication No. 2011-068040 
     SUMMARY OF THE INVENTION 
     As mentioned above, there are various mechanisms for moving a molding core in an undercut processing mechanism. Such a mechanism for moving a core member is also used in, besides an undercut processing mechanism, a gate cutter which cuts a gate inside an injection molding die as well as a cutter which cuts a processing target in a molding die. 
     If the size of a sliding mechanism for moving a core member such as an undercut molding core, a gate cutter, and a cutter for cutting a processing target can be reduced, a molding die including these components can also be made compact. Further, a sliding mechanism capable of moving a core member in at least two different directions with a simple structure may be employed in various applications. 
     An object of the present invention is to provide: a sliding mechanism capable of moving a slider in at least two different directions with a simple structure; an undercut processing mechanism, a gate cutting mechanism, and a gate pulling mechanism including the sliding mechanism; a fixed die, a movable die, and a molding die including the same; as well as a molded product. 
     The present invention provides a sliding mechanism including: a slider; and a guide body including a guide unit configured to guide the slider in predetermined directions. The slider is guided by the guide unit to move in the predetermined directions. The predetermined directions at least include a first direction and a second direction which are different from each other, and the guide unit at least includes: a first guide unit configured to guide the slider in the first direction; and a second guide unit configured to guide the slider in the second direction. 
     The sliding mechanism according to the present invention may further include an engaging member configured to slidably engage with the slider, and an engaging member guide unit configured to guide the engaging member such that the slider can advance and retract. 
     In the sliding mechanism according to the present invention, the guide body may include the engaging member guide unit. 
     In the sliding mechanism according to the present invention, the guide body may be a holder. 
     The sliding mechanism according to the present invention may be assembled as a single unit. 
     In the sliding mechanism according to the present invention, the guide unit may be capable of moving the slider in the first direction and subsequently in the second direction or in the second direction and subsequently in the first direction. 
     In the sliding mechanism according to the present invention, the first direction may extend in one of four shapes including a linear shape, a linear shape having a partially curved part, a curved shape, and a curved shape having a partially linear part, and the second direction may extend in one of four shapes including a linear shape, a linear shape having a partially curved part, a curved shape, and a curved shape having a partially linear part. 
     In the sliding mechanism according to the present invention, the slider may include an engagement unit configured to slidably engage with the guide unit, wherein the engagement unit may include: a first engagement unit configured to slidably engage with the first guide unit; and a second engagement unit configured to slidably engage with the second guide unit. 
     In the sliding mechanism according to the present invention, the guide unit may include a recessed groove, and the engagement unit may include a click or a protrusion or a protruding line configured to be slidably fitted into the recessed groove. 
     In the sliding mechanism according to the present invention, the guide unit may include a click or a protrusion or a protruding line, and the engagement unit may include a recessed groove configured to slidably receive the click or the protrusion or the protruding line. 
     In the sliding mechanism according to the present invention, the engagement unit may include two or more sliding surfaces configured to come into surface contact with the guide unit, or two or more sliding sides configured to come into line contact with the guide unit, or three or more sliding points configured to come into point contact with the guide unit. 
     The present invention provides an undercut processing mechanism including the sliding mechanism, the undercut processing mechanism being configured to remove, from an undercut portion of a molded product, a molding core configured to mold the undercut portion. 
     In the undercut processing mechanism according to the present invention, the guide body may be a holder, the slider may be a sliding piece including the molding core, and the guide unit may be configured to guide the sliding piece such that the molding core is removed from the undercut portion, and the molding core avoids collision with another member. 
     The undercut processing mechanism according to the present invention may be assembled as a single unit. 
     The present invention provides a gate cutting mechanism including the sliding mechanism, the gate cutting mechanism being configured to cut a gate connected to a molded product. 
     In the gate cutting mechanism according to the present invention, the guide body may be a holder, the slider may be a sliding piece including a cutter configured to cut the gate, and the guide unit may be configured to guide the sliding piece such that the cutter cuts the gate, and the cutter after cutting the gate is moved away from the gate. 
     The gate cutting mechanism according to the present invention may include a sliding piece including a cutter configured to cut the gate and a pressing unit configured to press an area in the vicinity of the gate of the molded product so as to prevent the area in the vicinity of the gate from moving when the cutter cuts the gate, wherein the guide body may be a holder, the slider may be a pressing unit, and the guide unit may be configured to guide the pressing unit so as to prevent the area in the vicinity of the gate from moving when the cutter cuts the gate and to guide the pressing unit such that the pressing unit is moved away from the molded product after the cutter cuts the gate. 
     In the gate cutting mechanism according to the present invention, the guide body may be a holder, the slider may be a cutting piece configured to cut the gate, and the guide unit may be configured to guide the cutting piece such that the cutting piece cuts the gate, and the cutting piece after cutting the gate is moved away from the gate, or a runner connected to the gate, or a part of the runner. 
     The gate cutting mechanism according to the present invention may be assembled as a single unit. 
     The present invention provides a gate pulling mechanism including the sliding mechanism as claimed in any one of claims  1  to  11 , the gate pulling mechanism being configured to pull a gate connected to a molded product to apply a load to the gate, or to extend the gate, or to crack the gate, or to tear the gate. 
     In the gate pulling mechanism according to the present invention, the guide body may be a holder, the slider may be a pulling piece configured to pull the gate, the guide unit may be configured to guide the pulling piece such that the pulling piece applies a load to the gate, or extends the gate, or cracks the gate, or tears the gate, and the guide unit may further be configured to guide the pulling piece such that the pulling piece after applying the load to the gate, or extending the gate, or cracking the gate, or tearing the gate is moved away from the gate, or a runner connected to the gate, or a part of the runner. 
     The gate pulling mechanism according to the present invention may be assembled as a single unit. 
     The present invention provides a fixed die or a movable die including the sliding mechanism, or the undercut processing mechanism, or the gate cutting mechanism, or the gate pulling mechanism. 
     The present invention provides a molding die including the sliding mechanism, or the undercut processing mechanism, or the gate cutting mechanism, or the gate pulling mechanism. 
     The present invention provides a molded product molded by the fixed die, or the movable die, or the molding die. 
     Effects of the Invention 
     According to the present invention, it is possible to provide a sliding mechanism capable of moving a slider in at least two different directions with a simple structure; an undercut processing mechanism, a gate cutting mechanism, and a gate pulling mechanism including the sliding mechanism; a fixed die, a movable die, and a molding die including the same; as well as a molded product. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an operation of a sliding mechanism  1  according to a first embodiment of the present invention; 
         FIG. 2  is an exploded view showing features of the sliding mechanism  1  according to the first embodiment of the present invention; 
         FIG. 3  illustrates an exemplary application of the sliding mechanism  1  according to the first embodiment of the present invention; 
         FIG. 4  illustrates an operation of a sliding mechanism  50  according to a second embodiment of the present invention; 
         FIG. 5  is an exploded view showing features of the sliding mechanism  50  according to the second embodiment of the present invention; 
         FIG. 6  is a cross-sectional view of a molding die  100  including an undercut processing mechanism  101  according to a third embodiment of the present invention in a mold closed state; 
         FIG. 7  is a cross-sectional view of the molding die  100  including the undercut processing mechanism  101  according to the third embodiment of the present invention after mold opening; 
         FIG. 8  is a cross-sectional view of the molding die  100  including the undercut processing mechanism  101  according to the third embodiment of the present invention during a process of ejecting a molded product P; 
         FIG. 9  is a cross-sectional view of the molding die  100  including the undercut processing mechanism  101  according to the third embodiment of the present invention during the process of ejecting the molded product P; 
         FIG. 10  is an exploded view showing features of the undercut processing mechanism  101  according to the third embodiment of the present invention; 
         FIG. 11  is a cross-sectional view of a molding die  200  including a gate cutting mechanism  201  according to a fourth embodiment of the present invention in a mold closed state; 
         FIG. 12  is a cross-sectional view of the molding die  200  including the gate cutting mechanism  201  according to the fourth embodiment of the present invention during a process of opening the mold; 
         FIG. 13  is a cross-sectional view of the molding die  200  including the gate cutting mechanism  201  according to the fourth embodiment of the present invention during the process of opening the mold; 
         FIG. 14  is a cross-sectional view of the molding die  200  including the gate cutting mechanism  201  according to the fourth embodiment of the present invention after mold opening; 
         FIG. 15  is a cross-sectional view of the molding die  200  including the gate cutting mechanism  201  according to the fourth embodiment of the present invention during a process of ejecting a molded product P; 
         FIG. 16  is an exploded view showing features of the gate cutting mechanism  201  according to the fourth embodiment of the present invention; 
         FIG. 17  is an exploded view showing features of a gate cutting mechanism  202 , which is a variant of the gate cutting mechanism  201  according to the fourth embodiment of the present invention; 
         FIG. 18  illustrates an operation of a molding die  300  including a gate cutting mechanism  301  according to a fifth embodiment of the present invention; 
         FIG. 19  illustrates an operation of the molding die  300  including the gate cutting mechanism  301  according to the fifth embodiment of the present invention; 
         FIG. 20  illustrates an operation of the molding die  300  including the gate cutting mechanism  301  according to the fifth embodiment of the present invention; 
         FIG. 21  illustrates an operation of the molding die  300  including the gate cutting mechanism  301  according to the fifth embodiment of the present invention; 
         FIG. 22  illustrates an operation of the molding die  300  including the gate cutting mechanism  301  according to the fifth embodiment of the present invention; 
         FIG. 23  is an exploded view showing features of a gate cutting mechanism  301  according to the fifth embodiment of the present invention; 
         FIG. 24  is a cross-sectional view showing a main part of a molding die  400  including the gate cutting mechanism  401  according to a sixth embodiment of the present invention in a mold closed state; 
         FIG. 25  is a cross-sectional view showing the main part of the molding die  400  including the gate cutting mechanism  401  according to the sixth embodiment of the present invention during a process of opening the mold; 
         FIG. 26  is a cross-sectional view showing the main part of the molding die  400  including the gate cutting mechanism  401  according to the sixth embodiment of the present invention during the process of opening the mold; 
         FIG. 27  is an exploded view showing features of the gate cutting mechanism  401  according to the sixth embodiment of the present invention; 
         FIG. 28  is a cross-sectional view showing a main part of a molding die  500  including a gate cutting mechanism  501  according to a seventh embodiment of the present invention in a mold closed state; 
         FIG. 29  is a cross-sectional view showing the main part of the molding die  500  including the gate cutting mechanism  501  according to the seventh embodiment of the present invention during a process of opening the mold; 
         FIG. 30  is a cross-sectional view showing the main part of the molding mold  500  including the gate cutting mechanism  501  according to the seventh embodiment of the present invention during the process of opening the mold; 
         FIG. 31  is an exploded view showing features of the gate cutting mechanism  501  according to the seventh embodiment of the present invention; 
         FIG. 32  is an exploded view showing features of a sliding mechanism  6  according to an eighth embodiment of the present invention; 
         FIG. 33  illustrates an exemplary application of the sliding mechanism  6  according to the eighth embodiment of the present invention; 
         FIG. 34  is an exploded view showing features of an undercut processing mechanism  103  according to a ninth embodiment of the present invention; 
         FIG. 35  is a cross-sectional view of a molding die  102  including the undercut processing mechanism  103  according to the ninth embodiment of the present invention in a mold closed state; 
         FIG. 36  is a cross-sectional view of the molding die  102  including the undercut processing mechanism  103  according to the ninth embodiment of the present invention after mold opening; 
         FIG. 37  is a cross-sectional view of the molding die  102  including the undercut processing mechanism  103  according to the ninth embodiment of the present invention during a process of ejecting a molded product P; 
         FIG. 38  is a cross-sectional view of the molding die  102  including the undercut processing mechanism  103  according to the ninth embodiment of the present invention during the process of ejecting the molded product P; 
         FIG. 39  is a cross-sectional view of the molding die  102  including the undercut processing mechanism  103  according to the ninth embodiment of the present invention during the process of ejecting the molded product P; 
         FIG. 40  is an exploded view showing features of an undercut processing mechanism  105  according to a tenth embodiment of the present invention; 
         FIG. 41  is a cross-sectional view of a molding die  104  including the undercut processing mechanism  105  according to the tenth embodiment of the present invention in a mold closed state; 
         FIG. 42  is a cross-sectional view of the molding die  104  including the undercut processing mechanism  105  according to the tenth embodiment of the present invention after mold opening; 
         FIG. 43  is a cross-sectional view of the molding die  104  including the undercut processing mechanism  105  according to the tenth embodiment of the present invention during a process of ejecting a molded product P; 
         FIG. 44  is a cross-sectional view of the molding die  104  including the undercut processing mechanism  105  according to the tenth embodiment of the present invention during the process of ejecting the molded product P; 
         FIG. 45  is a cross-sectional view of the molding die  104  including the undercut processing mechanism  105  according to the tenth embodiment of the present invention during the process of ejecting the molded product P; 
         FIG. 46  is an exploded view showing features of an undercut processing mechanism  107  according to an eleventh embodiment of the present invention; 
         FIG. 47  is a cross-sectional view of a molding die  106  including the undercut processing mechanism  107  according to the eleventh embodiment of the present invention in a mold closed state; 
         FIG. 48  is a cross-sectional view of the molding die  106  including the undercut processing mechanism  107  according to the eleventh embodiment of the present invention after mold opening; 
         FIG. 49  is a cross-sectional view of the molding die  106  including the undercut processing mechanism  107  according to the eleventh embodiment of the present invention during a process of ejecting a molded product P; 
         FIG. 50  is a cross-sectional view of the molding die  106  including the undercut processing mechanism  107  according to the eleventh embodiment of the present invention during the process of ejecting the molded product P; 
         FIG. 51  is an exploded view showing features of an undercut processing mechanism  109  according to a twelfth embodiment of the present invention; 
         FIG. 52  is a cross-sectional view of a molding die  108  including the undercut processing mechanism  109  according to the twelfth embodiment of the present invention in a mold closed state; 
         FIG. 53  is a cross-sectional view of the molding die  108  including the undercut processing mechanism  109  according to the twelfth embodiment of the present invention after mold opening; 
         FIG. 54  is a cross-sectional view of the molding die  108  including the undercut processing mechanism  109  according to the twelfth embodiment of the present invention during a process of ejecting a molded product P; 
         FIG. 55  is a cross-sectional view of the molding die  108  including the undercut processing mechanism  109  according to the twelfth embodiment of the present invention during the process of ejecting the molded product P; 
         FIG. 56  is a cross-sectional view of the molding die  108  including the undercut processing mechanism  109  according to the twelfth embodiment of the present invention during the process of ejecting the molded product P; 
         FIG. 57  is an exploded view showing features of an undercut processing mechanism  111  according to a thirteenth embodiment of the present invention; 
         FIG. 58  is a cross-sectional view of a molding die  110  including the undercut processing mechanism  111  according to the thirteenth embodiment of the present invention in a mold closed state; 
         FIG. 59  is an exploded view showing features of an undercut processing mechanism  112  according to a fourteenth embodiment of the present invention; 
         FIG. 60  includes a left-side view, a front view, and a right-side view of a sliding piece  179  including a molding core  191  for the undercut processing mechanism  112  according to the fourteenth embodiment of the present invention; 
         FIG. 61  illustrates an operation of the undercut processing mechanism  112  according to the fourteenth embodiment of the present invention; 
         FIG. 62  is an exploded view showing features of an undercut processing mechanism  113  according to a fifteenth embodiment of the present invention; 
         FIG. 63  includes a left-side view, a front view, a right-side view, and a bottom view of a sliding piece  194  including the molding core  191  for the undercut processing mechanism  113  according to the fifteenth embodiment of the present invention; 
         FIG. 64  illustrates an operation of the undercut processing mechanism  113  according to the fifteenth embodiment of the present invention; 
         FIG. 65  is a cross-sectional view of a molding die  800  including a gate tearing mechanism  801  according to a sixteenth embodiment of the present invention in a mold closed state; 
         FIG. 66  is a cross-sectional view of the molding die  800  including the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention during a process of opening the mold; 
         FIG. 67  is a cross-sectional view of the molding die  800  including the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention after mold opening; 
         FIG. 68  is an exploded view showing features of the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention; 
         FIG. 69  is a cross-sectional view of a molding die  900  including the gate tearing mechanism  901  according to a seventeenth embodiment of the present invention in a mold closed state; 
         FIG. 70  is a cross-sectional view of a molding die  1000  including a gate tearing mechanism  1001  according to an eighteenth embodiment of the present invention in a mold closed state; 
         FIG. 71  is a cross-sectional view of a molding die  1100  including a gate tearing mechanism  1101  according to a nineteenth embodiment of the present invention in a mold closed state; 
         FIG. 72  is a perspective view illustrating an operation of a gate tearing mechanism  1201  according to a twentieth embodiment of the present invention; 
         FIG. 73  is a perspective view illustrating an operation of the gate tearing mechanism  1201  according to the twentieth embodiment of the present invention; 
         FIG. 74  is a perspective view illustrating an operation of the gate tearing mechanism  1201  according to the twentieth embodiment of the present invention; 
         FIG. 75  is a perspective view illustrating an operation of the gate tearing mechanism  1201  according to the twentieth embodiment of the present invention; 
         FIG. 76  is an exploded view showing features of the gate tearing mechanism  1201  according to the twentieth embodiment of the present invention; 
         FIG. 77  is a perspective view illustrating an operation of a gate tearing mechanism  1301  according to a twenty-first embodiment of the present invention; 
         FIG. 78  is a perspective view illustrating an operation of the gate tearing mechanism  1301  according to the twenty-first embodiment of the present invention; 
         FIG. 79  is a perspective view illustrating an operation of the gate tearing mechanism  1301  according to the twenty-first embodiment of the present invention; 
         FIG. 80  is an exploded view showing features of the gate tearing mechanism  1301  according to the twenty-first embodiment of the present invention; 
         FIG. 81  is a perspective view illustrating an operation of a gate tearing mechanism  1401  according to a twenty-second embodiment of the present invention; 
         FIG. 82  is a perspective view illustrating an operation of the gate tearing mechanism  1401  according to the twenty-second embodiment of the present invention; 
         FIG. 83  is a perspective view illustrating an operation of a gate tearing mechanism  1501  according to a twenty-third embodiment of the present invention; 
         FIG. 84  is a perspective view illustrating an operation of the gate tearing mechanism  1501  according to the twenty-third embodiment of the present invention; 
         FIG. 85  is a perspective view illustrating an operation of the gate tearing mechanism  1501  according to the twenty-third embodiment of the present invention; 
         FIG. 86  is a perspective view illustrating an operation of the gate tearing mechanism  1501  according to the twenty-third embodiment of the present invention; and 
         FIG. 87  is an exploded view showing features of the gate tearing mechanism  1501  according to the twenty-third embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  illustrates an operation of a sliding mechanism  1  according to a first embodiment of the present invention.  FIG. 2  is an exploded view showing features of the sliding mechanism  1  according to the first embodiment of the present invention.  FIG. 1  illustrates the sliding mechanism  1  as viewed from the front; for the sake of convenience, in the following description, the “left” side corresponds to the left side in Chart (A) of  FIG. 1 , and the “upper” side corresponds to the upper side in Chart (A) of  FIG. 1 . The X direction, Y direction, and Z direction in the drawings and the specification correspond to the X-axis direction, Y-axis direction, and Z-axis direction of a three-dimensional rectangular coordinate system, respectively. In the present specification, the +X direction means a direction indicated by an arrow on the X axis in the drawings, and the −X direction means a direction opposite to the direction indicated by the arrow on the X axis. The same applies to the +Y direction, −Y direction, +Z direction, and −Z direction. 
     The sliding mechanism  1  according to the first embodiment of the present invention includes a slider capable of moving in a first direction and subsequently in a second direction. The first direction and the second direction are predetermined directions, and the first direction is different from the second direction. Hereinafter, the features will be specifically described with reference to  FIG. 1  and  FIG. 2 . 
     The sliding mechanism  1  includes a first piece  11 , a second piece  21 , and a guiding body  31  which guides the first piece  11  and the second piece  21 . In the present embodiment, the second piece  21  corresponds to a slider; and the guiding body  31  corresponds to a guide body. As described later, a guiding groove  38  corresponds to a guide unit; a first guiding part  39  corresponds to a first guide unit; and a second guiding part  42  corresponds to a second guide unit. A click  23  corresponds to an engagement unit; a first sliding surface of the click  23  corresponds to a first engagement unit; and a second sliding surface of the click  23  corresponds to a second engagement unit. 
     The guiding body  31  has a channel-shaped or U-shaped transverse section and includes a rectangular bottom plate  32  and side walls  33 ,  35  at opposite ends of the rectangular bottom plate  32 . Inner surfaces  34 ,  36  of the left side wall  33  and the right side wall  35  are parallel to each other. The left-side-wall inner surface  34  and the right-side-wall inner surface  36  function as guides for the first piece  11 . The bottom plate  32  includes a dog-legged guiding groove  38  on an inner surface of the bottom plate  32 . 
     The guiding groove  38  is a recessed groove and includes a first guiding part  39  which guides the second piece  21  in a primary direction (i.e., first direction) and a second guiding part  42  which guides the second piece  21  in a secondary direction (second direction). In the present embodiment, the first direction extends diagonally upward to the right, and the second direction extends diagonally upward to the left. The first guiding part  39  and the second guiding part  42  are connected to each other, and a center axis M 1  of the first guiding part  39  and a center axis M 2  of the second guiding part  42  intersect with each other. The first guiding part  39  includes opposite side surfaces  40 ,  41  that are parallel to each other, and the second guiding part  42  includes opposite side surfaces  43 ,  44  that are parallel to each other. 
     The first piece  11  has a cuboid shape and includes left and right side faces  12 ,  13  that are parallel to each other. A width W 1  between the left and right side faces  12 ,  13  is substantially equal to a width W between the left- and right-side-wall inner surfaces  34 ,  36  of the guiding body  31 . Thus, when the first piece  11  is placed on the guiding body  31 , the left and right side faces  12 ,  13  come into contact with the left- and right-side-wall inner surfaces  34 ,  36  of the guiding body  31 . 
     The second piece  21  is a columnar member having a rectangular cross section and includes a back face  22  including the click  23  configured to be fitted into the guiding groove  38  in the guiding body  31 . The click  23  protrudes from the back face  22  and, therefore, may be considered as a protrusion. The click  23  has a height (thickness) substantially equal to a depth of the guiding groove  38 . The click  23  has a rhombic shape when the back face  22  of the second piece  21  is viewed straightforwardly, and includes four side surfaces  24 ,  25 ,  26 ,  27 . The side surface  24  and the side surface  25  are parallel to each other, and the side surface  26  and the side surface  27  are parallel to each other. In the present embodiment, the click  23  is an engagement unit configured to slidably engage with the guiding groove  38  and is arranged such that when the click  23  is fitted into the guiding groove  38 , a longitudinal direction of the second piece  21  is parallel to a longitudinal direction of the guiding body  31 . 
     The opposite side surfaces  24 ,  25  of the click  23  serve as first sliding surfaces, and the opposite side surfaces  26 ,  27  of the click  23  serve as second sliding surfaces. The first sliding surfaces slidably come into contact with the opposite side surfaces  40 ,  41  of the first guiding part  39  of the guiding groove  38  in the guiding body  31 . The second sliding surfaces slidably come into contact with the opposite side surfaces  43 ,  44  of the second guiding part  42  of the guiding groove  38  in the guiding body  31 . 
     An operation of the sliding mechanism  1  will be described with reference to  FIG. 1 . In the following description, the first piece  11  is an input end, and the second piece  21  is an output end. The click  23  is fitted into the first guiding part  39 , and the first piece  11  is placed on the guiding body  31  such that the first piece  11  comes into contact with a bottom face of the second piece  21 . In this state, the opposite side faces  12 ,  13  of the first piece  11  are slidably in contact with the opposite side-wall inner surfaces  34 ,  36  of the guiding body  31 , and the first sliding surfaces of the click  23  are slidably in contact with the opposite side surfaces  40 ,  41  of the first guiding part  39  (see Chart (A) of  FIG. 1 ). 
     When the first piece  11  is pushed upward (i.e., in the Y direction), the first piece  11  ascends while the opposite side faces  12 ,  13  slide on the opposite side-wall inner surfaces  34 ,  36  of the guiding body  31 , which serve as guides. The second piece  21  is pushed out by the first piece  11  and moves along the first guiding part  39  in the first direction (diagonally upward to the right), while the first sliding surfaces of the click  23  slide on the opposite side surfaces  40 ,  41  of the first guiding part  39 , with the first guiding part  39  of the guiding body  31  serving as a guide. 
     When the second piece  21  is pushed out by the first piece  11 , and the side surface  26  of the click  23  reaches a point where the side surface  26  comes into contact with the side surface  44  of the second guiding part  42 , the side surface  24  of the click  23  leaves the side surface  40  of the first guiding part  39 , which the side surface  24  has been in contact with (see Chart (B) of  FIG. 1 ). When the first piece  11  is pushed up from this state, the second piece  21  moves along the second guiding part  42  in the second direction (diagonally upward to the left), while the second sliding surfaces of the click  23  slide on the opposite side surfaces  43 ,  44  of the second guiding part  42 , with the second guiding part  42  serving as a guide. 
       FIG. 3  shows a changeover switch  2  which employs the sliding mechanism  1  according to the first embodiment of the present invention. Features corresponding to the features of the sliding mechanism  1  of the first embodiment as shown in  FIG. 1  and  FIG. 2  are denoted with like reference numerals, and description thereof is omitted. 
     The changeover switch  2  includes a first terminal  4   a  connected to the first piece  11  through a lead wire  3   a  and a second terminal  4   b  connected to the first piece  11  through a lead wire  3   b . In the middle of the lead wires  3   a ,  3   b , a first lamp  5   a  and a second lamp  5   b  are arranged. The first piece  11  and the second piece  21  have conductivity, and the first piece  11  includes a battery (not illustrated) therein. 
     The first terminal  4   a  is located at a position where an upper end portion of the second piece  21  comes into contact when the click  23  on the second piece  21  reaches a tip end portion (upper right) of the first guiding part  39  of the guiding groove  38 . On the other hand, the second terminal  4   b  is located at a position where the upper end portion of the second piece  21  comes into contact when the click  23  on the second piece  21  reaches a tip end portion (upper left) of the second guiding part  42  of the guiding groove  38 . In the present embodiment, the first terminal  4   a  is arranged in such a position that the second piece  21  comes in contact with the first terminal  4   a  when moved to a rightmost position, and the second terminal  4   b  is arranged in such a position that the second piece  21  comes in contact with the second terminal  4   b  when moved to a leftmost position. 
     In the changeover switch  2  having the above constitution, when the second piece  21  is pushed up through the first piece  11 , and the upper end portion of the second piece  21  comes into contact with the first terminal  4   a , a circuit is formed to turn on the first lamp  5   a . When the second piece  21  is pushed up further, the upper end portion of the second piece  21  leaves the first terminal  4   a , so that the first lamp  5   a  is turned off. When the second piece  21  is pushed up to a highest position, the upper end portion of the second piece  21  comes into contact with the second terminal  4   b , so that the second lamp  5   b  is turned on. 
     As discussed above, the sliding mechanism  1  of the first embodiment, the guiding body  31  includes the guiding groove  38  which guides the second piece  21  in two different directions, and therefore, the second piece  21  can be surely moved in the two different directions. Since the sliding mechanism  1  of the present embodiment is constructed such that the first piece  11  ejects the second piece  21  with the click  23  fitted into the recessed guiding groove  38  in the guiding body  31 , the sliding mechanism  1  has a simple structure and thus can be realized easily. 
     The click  23  to be fitted into the recessed guiding groove  38  includes: first sliding surfaces which slide on the side surfaces  40 ,  41  when moving in the first guiding part  39  of the guiding groove  38 ; and second sliding surfaces which slide on the side surfaces  43 ,  44  when moving in the second guiding part  42  of the guiding groove  38 . The first sliding surfaces are constituted by the opposing two side surfaces  24 ,  25 , and the second sliding surfaces are constituted by the opposing two side surfaces  26 ,  27 , so that two surfaces of the click  23  make surface contact in each case, i.e., when the click moves in the first guiding part  39  or in the second guiding part  42 . Thus, the second piece  21  can be moved stably without rattling. 
     Further, since the guiding body  31  includes a guide for guiding the first piece  11  which is different from the guiding groove  38  for guiding the second piece  21 , the second piece  21  can be easily moved in the first direction and subsequently in the second direction through the first piece  11 . 
     In the sliding mechanism  1 , the directions of the first guiding part  39  and the second guiding part  42  are not limited to specific directions. In the present embodiment, the first guiding part  39  extends diagonally upward to the right, and the second guiding part  42  extends diagonally upward to the left. However, the second guiding part  42  may extend diagonally upward to the right at a different angle from the angle at which the first guiding part  39  extends. Further, one of the first guiding part  39  and the second guiding part  42  may extend in a direction corresponding to a direction in which the first piece  11  is pushed up (i.e., in the Y direction). These also apply to a sliding mechanism  50  according to a second embodiment as described later as well as in other embodiments. 
     The first guiding part  39  and the second guiding part  42  of the guiding groove  38  may not necessarily be linear lines, and may be circular arcs or a combination of a circular arc and a linear line. In short, the first direction and the second direction may extend in one of four shapes including a linear shape, a linear shape having a partially curved part, a curved shape, and a curved shape having a partially linear part. The guiding groove  38  may further include a third guiding part subsequently to the second guiding part  42 , or the guiding groove may include four or more guiding parts. These also apply to the sliding mechanism  50  according to the second embodiment as well as in other embodiments. 
     The configuration of the click  23  to be fitted into the guiding groove  38  is not limited to that of the present embodiment. In the present embodiment, the first sliding surfaces of the click  23  make surface contact with the opposite side surfaces  40 ,  41  of the first guiding part  39  of the guiding groove  38 . However, this may be achieved through line contact or point contact. In the case of line contact, it is only necessary that one or more sides of the click  23  come into contact with each of the opposite side surfaces  40 ,  41  of the first guiding part  39  of the guiding groove  38 . In the case of point contact, it is only necessary that one or more points of the click  23  come into contact with each of the opposite side surfaces  40 ,  41  of the first guiding part  39  of the guiding groove  38 , and three points of the click  23  in total come into contact with the opposite side surfaces  40 ,  41 . The same applies to the second guiding part  42  of the guiding groove  38 . These also apply to the sliding mechanism  50  according to the second embodiment as well as in other embodiments. 
     The sliding mechanism  1  may include a coupling mechanism having a dovetail groove structure between an upper face  14  of the first piece  11  and a bottom face  28  of the second piece  21 . Specifically, one of the upper face  14  of the first piece  11  and the bottom face  28  of the second piece  21  may include a protruding line (dovetail-groove protruding line), and the other may include a dovetail groove which slidably receives the protruding line. In the sliding mechanism having such a configuration, the first piece  11  corresponds to a coupling member; the second piece  21  corresponds to a slider; the guiding body  31  corresponds to a guide body; and the left- and right-side-wall inner surfaces  34 ,  36  of the guiding body  31  correspond to a coupling member guide unit. 
     The opposite side faces  12 ,  13  of the first piece  11  and the opposite side-wall inner surfaces  34 ,  36  of the guiding body  31  may be constructed as a coupling mechanism having a dovetail groove structure through a protruding line (dovetail-groove protruding line) and a dovetail groove. Further, the guiding groove  38  and the click  23  may be coupled together through a protruding line (dovetail-groove protruding line) and a dovetail groove. Such a structure prevents the components from being disassembled, and therefore, the sliding mechanism  1  can be easily assembled into a single unit. These also apply to the sliding mechanism  50  according to the second embodiment as well as in other embodiments. 
       FIG. 4  illustrates an operation of the sliding mechanism  50  according to the second embodiment of the present invention.  FIG. 5  is an exploded view showing features of the sliding mechanism  50  according to the second embodiment of the present invention. Features corresponding to the features of the sliding mechanism  1  of the first embodiment as shown in  FIG. 1  and  FIG. 2  are denoted with like reference numerals, and description thereof is omitted. 
       FIG. 4  is a front view of the sliding mechanism  50 . For the sake of convenience, in the following description, the “left” side corresponds to the left side in Chart (A) of  FIG. 4 , and the “upper” side corresponds to the upper side in Chart (A) of  FIG. 4 . 
     As with the sliding mechanism  1  of the first embodiment, the sliding mechanism  50  according to the second embodiment of the present invention includes a slider capable of moving in a first direction and subsequently in a second direction. The first direction and the second direction are predetermined directions, and the first direction is different from the second direction (see  FIG. 5 ). Hereinafter, the features will be specifically described with reference to  FIG. 4  and  FIG. 5 . 
     The sliding mechanism  50  includes a first piece  11 , a second piece  61 , and a guiding body  81  which guides the first piece  11  and the second piece  61 . In the present embodiment, the second piece  61  corresponds to a slider; and the guiding body  81  corresponds to a guide body. As described later, a guiding groove  88  and an upper inner surface  87  of the guiding body  81  correspond to a guide unit; a first guiding part  89  corresponds to a first guide unit; and a side surface  93  of a second guiding part  92  and the upper inner surface  87  of the guiding body  81  correspond to a second guide unit. A click  63  and a side face  73  of the second piece  61  correspond to an engagement unit; a first sliding surface of the click  63  corresponds to a first engagement unit; and an inclined surface  68  of the click  63  and the side face  73  of the second piece  61  correspond to a second engagement unit. 
     The guiding body  81  has a channel-shaped or U-shaped transverse section and includes a rectangular bottom plate  82  and side walls  83 ,  85  at opposite ends of the rectangular bottom plate  82 . The left side wall  83  has a linear shape in a front view, and the right side wall  85  includes an upper part protruding to the left. A lower inner surface  86  of the right side wall  85  located below a center of the right side wall extends parallel to an inner surface  84  of the left side wall  83 , and the upper inner surface  87  of the right side wall  85  is an inclined surface which is inclined toward an upper left side. The left-side-wall inner surface  84  and the right-side-wall inner surface  86  serve as guides for the first piece  11 . A guiding groove  88  is located on an inner surface of the bottom plate  82 . 
     The guiding groove  88  is a recessed groove and includes a first guiding part  89  which guides the second piece  61  in a primary direction (i.e., first direction) and a second guiding part  92  which guides the second piece  61  in a secondary direction (second direction). In the present embodiment, the first direction corresponds to the Y direction, and the second direction extends diagonally upward to the left. The first guiding part  89  and the second guiding part  92  are connected to each other, and a center axis M 1  of the first guiding part  89  and a center axis M 2  of the second guiding part  92  intersect with each other (see  FIG. 5 ). The first guiding part  89  includes a left side surface  90  and a right side surface  91  that are parallel to each other. Similarly, the second guiding part  92  includes a left side surface  93  and a right side surface  94  that are parallel to each other. 
     The left side surface  93  of the second guiding part  92  is connected to the left side surface  90  of the first guiding part  89  at substantially middle position in a height direction of the bottom plate  82  (i.e., Y direction), and the right side surface  94  of the second guiding part  92  is connected to the right side surface  91  of the first guiding part  89  at an upper position in the height direction of the bottom plate  82  (i.e., Y direction). For this reason, the right side surface  94  of the second guiding part  92  is shorter than the left side surface  93  of the second guiding part  92 . Further, the right side surface  94  of the second guiding part  92  is flush with the upper inner surface  87  of the right side wall  85 . 
     Since the first piece  11  has the same configuration as that of the first piece  11  of the sliding mechanism  1  of the first embodiment, description thereof is omitted. 
     The second piece  61  is a columnar member having a rectangular cross section and includes an upper part that is bent diagonally upward to the left in a front view. Opposite lower side faces  71 ,  72  of the second piece  61  located below a center of the second piece  61  are parallel to each other, and opposite upper side faces  73 ,  74  of the second piece  61  are parallel to each other. A bending angle θ 1  of the second piece  61  (see Chart (B) of  FIG. 4 ) is the same as an intersecting angle θ 2  (see  FIG. 5 ) between the center axis M 1  of the first guiding part  89  and the center axis M 2  of the second guiding part  92  of the guiding groove  88 . 
     The second piece  61  includes, on a lower part of a back face  62  thereof, a click  63  configured to be fitted into the first guiding part  89  of the guiding groove  88  on the guiding body  81 . The click  63  protrudes from the back face  62  and, therefore, may be considered as a protrusion. The click  63  has a height (thickness) substantially equal to a depth of the first guiding part  89  of the guiding groove  88 . The click  63  has a pentagonal shape when the back face  62  of the second piece  61  is viewed straightforwardly, and includes an inclined surface  68  in a lower part of the right side surface of the click  63 . 
     The click  63  includes five side faces  64 ,  65 ,  66 ,  67 ,  68 . The opposing side faces  64 ,  65  of the click  63  are parallel to each other. The side face  64  is flush with the lower side face  71  of the second piece  61 , and the side face  65  is flush with the lower side face  72  of the second piece  61 . The side faces  64 ,  65  of the click  63  serve as first sliding surfaces. The first sliding surfaces slidably come into contact with the opposite side surfaces  90 ,  91  of the first guiding part  89  of the guiding groove  88  in the guiding body  81 . 
     The inclined side face  68  of the click  63  is parallel to the upper side faces  73 ,  74  of the second piece  61 . When the click  63  of the second piece  61  is fitted into the second guiding part  92  of the guiding groove  88 , the inclined side face  68  of the click  63  comes into contact with the left side surface  93  of the second guiding part  92 . At the same time, the upper side face  73  of the second piece  61  comes into contact with the upper, right side surface  87  of the part of the guiding body  81 . The inclined side face  68  of the click  63  and the upper side face  73  of the second piece  61  serve as second sliding surfaces which slidably come into contact with the left side surface  93  of the second guiding part  92  and the upper, right side surface  87  of the guiding body  81 , respectively. 
     An operation of the sliding mechanism  50  will be described with reference to  FIG. 4 . In the following description, the first piece  11  is an input end, and the second piece  61  is an output end. The click  63  is fitted into the first guiding part  89 , and the first piece  11  is placed on the guiding body  81  such that the first piece  11  comes into contact with a bottom face of the second piece  61 . In this state, the opposite side faces  12 ,  13  of the first piece  11  are slidably in contact with the opposite side-wall inner surfaces  84 ,  86  of the guiding body  81 , and the first sliding surfaces of the click  63  are slidably in contact with the opposite side surfaces  90 ,  91  of the first guiding part  89  (see Chart (A) of  FIG. 4 ). 
     When the first piece  11  is pushed upward (i.e., in the Y direction), the first piece  11  moves upward while the opposite side faces  12 ,  13  slide on opposite side-wall inner surfaces  84 ,  86  of the guiding body  81 , which serve as guides. The second piece  61  is pushed out by the first piece  11  and moves along the first guiding part  89  in the first direction (i.e., Y direction), while the first sliding surfaces of the click  63  slide on the opposite side surfaces  90 ,  91  of the first guiding part  89 , with the first guiding part  89  of the guiding body  81  serving as a guide. 
     When the second piece  61  is pushed out by the first piece  11 , and the upper side face  73  reaches a point where the side face  73  comes into contact with the upper, right side surface  87  of the guiding body  81 , the side face  65  of the click  63  leaves the side surface  90  of the first guiding part  89 , which the side face  65  has been in contact with (see Chart (B) of  FIG. 4 ). When the first piece  11  is pushed up from this state, the second piece  61  moves in the second direction (diagonally upward to the left), while the side face  68  of the click  63  slides on the left side surface  93  of the second guiding part  92 , and the side face  73  of the second piece  61  slides on the upper, right side surface  87  of the guiding body  81 , with the second guiding part  92  and the upper, right side surface  87  of the guiding body  81  serving as guides (see Chart (C) of  FIG. 4 ). 
     Where the sliding mechanism  50  of the second embodiment and the sliding mechanism  1  of the first embodiment are compared, they differ in the mechanisms for guiding the second piece in the second direction. In the sliding mechanism  1  of the first embodiment, the second piece  21  is guided by the second guiding part  42  of the guiding groove  38  of the guiding body  31  to move in the second direction. The second guiding part  42  of the guiding groove  38  is located on a same plane as the first guiding part  39  of the guiding groove  38 , and the click  23  includes the first sliding surfaces and the second sliding surfaces which slide on the side surfaces of the guiding groove  38 . 
     On the other hand, in the sliding mechanism  50  of the second embodiment, the second piece  61  is guided by the left side surface  93  of the second guiding part  92  of the guiding groove  88  of the guiding body  81  and the upper, right side surface  87  of the guiding body  81  to move in the second direction. That is, in the sliding mechanism  50  of the second embodiment, the guiding groove  88  and the side surfaces of the guiding body  81  operate in conjunction with each other to guide the second piece  61  in the second direction. Although the second guiding part  92  of the guiding groove  88  is located on a same plane as the first guiding part  89  of the guiding groove  88 , the upper, right side surface  87  of the guiding body  81  has a different height from that of the first guiding part  89  of the guiding groove  88 . Further, the sliding mechanism  50  of the second embodiment also differs from the sliding mechanism  1  of the first embodiment in that the side face  73  of the second piece  61  serves as a sliding surface in addition to the click  63 . 
     As discussed above, the sliding mechanism  50  of the second embodiment shares a common point with the sliding mechanism  1  of the first embodiment in that the second piece can be moved in two different directions essentially by the guiding groove, although they have different mechanisms for guiding the second piece  61  in the second direction. In addition, the click  61  provides essentially the same effects and advantages as those of the click  21  of the sliding mechanism  1 . 
     The sliding mechanism  50  may include a coupling mechanism having a dovetail groove structure between the upper face  14  of the first piece  11  and the bottom face  69  of the second piece  61 . Specifically, a protruding line (dovetail-groove protruding line) may be located on one of the upper face  14  of the first piece  11  and the bottom face  69  of the second piece  61 , and a dovetail groove which slidably receives the protruding line may be located on the other. In the sliding mechanism having such a constitution, the first piece  11  corresponds to a coupling member; the second piece  61  corresponds to a slider; the guiding body  81  corresponds to a guide body; and the left- and right-side-wall inner surfaces  84 ,  86  of the guiding body  81  correspond to a coupling member guide unit. 
       FIG. 6  is a cross-sectional view of a molding mold or molding die  100  including an undercut processing mechanism  101  according to a third embodiment of the present invention in a mold closed state, and  FIG. 7  is a cross-sectional view of the molding die  100  after mold opening.  FIG. 8  and  FIG. 9  show cross-sectional views of the molding die  100  including the undercut processing mechanism  101  according to the third embodiment of the present invention during a process of ejecting a molded product P.  FIG. 10  is an exploded view showing features of the undercut processing mechanism  101  according to the third embodiment of the present invention. Features corresponding to the features of the sliding mechanism  1  of the first embodiment as shown in  FIG. 1  and  FIG. 2  are denoted with like reference numerals, and description thereof is omitted. 
     As with a known injection molding die, the molding die  100  of the third embodiment of the present invention includes: a fixed mold or fixed die  600  which molds an external surface of the molded product P; a movable mold or movable die  700  which molds an internal surface of the molded product P; and further the undercut processing mechanism  101 . For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  600  in  FIG. 6 , and the “lower” side means the side of the movable die  700  in  FIG. 6 . In the following description, the “left” side corresponds to the left side in  FIG. 6 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     The fixed die  600  includes a cavity  606  for molding the external surface of a molded product P. The movable die  700  includes: a movable mold plate  711  including a core  712  for forming an internal surface of the molded product P; a movable attachment plate  750 ; a spacer block  751 ; two ejector mount plates  762 ; an ejector pin  763 ; a return pin  765 ; a spring  767 ; and an ejector rod  768 . The ejector mount plates  762 , the ejector pin  763 , the ejector rod  768  and the like are assembled into an ejector mechanism  760 . The ejector mechanism  760  is a single-stage ejecting mechanism. 
     After the processes of molding and cooling, the molding die  100  is opened, and the ejector mount plates  762  move in a demolding direction of the molded product P (upward direction or Y direction in  FIG. 6 ) to approach the movable mold plate  711 , so that the ejector pin  763  operates to eject the molded product P. Since such a constitution and an operation are the same as those in a known molding die, description thereof is omitted. 
     In the present embodiment, an undercut portion P 1  is a protruding portion P 1  which protrudes from an end portion of the molded product P toward an inner side of the molded product P and extends in a direction which intersects with the demolding direction of the molded product P (i.e., Y direction). The molded product P in the present embodiment also includes a protruding portion P 2  which is located ahead in a direction in which the undercut portion P 1  is demolded (i.e., X direction) and protrudes toward the inner side of the molded product P. The shapes of the molded product P, the protruding portion P 1 , and the protruding portion P 2  are not limited to specific ones. The material of the molded product P is not limited to a synthetic resin such as a plastic or the like, either, and may be a metal such as iron, copper, aluminum or the like. 
     The undercut processing mechanism  101  molds the undercut portion P 1  when the molded product P is molded, and is removed from the undercut portion P 1  upon ejection of the molded product P in a synchronized manner with the ejector mechanism  760 , so that the molded product P can be demolded from the molding die  100 . The undercut processing mechanism  101  of the present embodiment employs the sliding mechanism  1  of the first embodiment. 
     The undercut processing mechanism  101  includes: a holder  121  which is incorporated in and is fixed to the movable mold plate  711 ; a sliding piece  171  including, at a tip end of the sliding piece  171 , a molding core  191  which molds the undercut portion P 1  of the molded product P; and a retaining piece  161  which slidably retains the sliding piece  171   
     The holder  121  of the present embodiment corresponds to the guiding body  31  of the sliding mechanism  1  of the first embodiment; the sliding piece  171  including the molding core  191  at the tip end thereof corresponds to the second piece  21 ; and the retaining piece  161  corresponds to the first piece  11 . Also, in the present embodiment, the sliding piece  171  corresponds to a slider; and the holder  121  corresponds to a guide body. As described later, a guiding groove  141  corresponds to a guide unit; a first guiding part  145  corresponds to a first guide unit; and a second guiding part  148  corresponds to a second guide unit. A click  180  corresponds to an engagement unit; a first sliding surface of the click  180  corresponds to a first engagement unit; and a second sliding surface of the click  180  corresponds to a second engagement unit. The retaining piece  161  and the sliding piece  171  are slidably coupled together through a dovetail groove structure. The retaining piece  161  corresponds to a coupling member, and left- and right-side-wall inner surfaces  127 ,  130  of the holder  121  correspond to a coupling member guide unit. 
     The holder  121  is fitted into a recessed part  714  which opens on a bottom face  713  of the movable mold plate  711 , and is incorporated in and fixed to the movable mold plate  711  through the fixed plate  715 . The holder  121  houses the sliding piece  171  and the retaining piece  161 , and restricts a movement direction of the sliding piece  171  and the retaining piece  161 . As used herein, the expression that the holder  121  houses the sliding piece  171  and the retaining piece  161  may include a case where the holder  121  houses the entirety of the sliding piece  171  and the retaining piece  161  as well as a case where the holder  121  partially houses the sliding piece  171  and the retaining piece  161 . 
     The holder  121  includes two half holder members  125  of a same shape which are assembled together, and has a box-like column shape which defines an inner space therein with an open upper end face and an open lower end face (see  FIG. 10 ). The holder  121  may be constituted by a plurality of divided members or be integrated with the movable mold plate  711 . The holder  121  includes an inner surface  127  of a left side wall  126  and an inner surface  130  of a right side wall  129  which function as guides for the retaining piece  161 . The holder  121  includes guiding grooves  141  which guide the sliding piece  171  on a front-face-wall inner surface and on a back-face-wall inner surface  135  of the holder  121 . 
     Each guiding groove  141  is a recessed groove and includes a first guiding part  145  which guides the sliding piece  171  in the first direction and a second guiding part  148  which guides the sliding piece  171  in the second direction. The first guiding part  145  is inclined with respect to a mold opening direction of the molding die  100  (i.e., Y direction), and the second guiding part  148  is parallel to a mold opening direction of the molding die  100  (i.e., Y direction). The first guiding part  145  and the second guiding part  148  are connected to each other, and a center axis M 1  of the first guiding part  145  and a center axis M 2  of the second guiding part  148  intersect with each other (see  FIG. 10 ). 
     The first guiding part  145  guides the sliding piece  171  diagonally upward to the left (i.e., in the first direction) such that the molding core  191  attached to the sliding piece  171  is removed from the undercut portion P 1  in a synchronized manner with the ejector mechanism  760 . In this regard, the direction in which the molding core  191  is removed from the undercut portion P 1  means a direction in which the molding core  191  is removed from the undercut portion P 1  without deforming or damaging the undercut portion P 1 . 
     The center axis M 1  of the first guiding part  145  is defined depending on the shape of the undercut portion P 1  of the molded product P, in particular, on an extent of projection of the undercut portion P 1  in the X direction and a stroke of an ejection pin  745 , so that the molding core  191  can be removed from the undercut portion P 1  of the molded product P upon ejection of the molded product P. 
     The second guiding part  148  guides the molding core  191  such that the molding core  191  which has been removed from the undercut portion P 1  does not collide with the protruding portion P 2  which is located ahead in a removal direction of the undercut portion P 1  (i.e., X direction). In the present embodiment, the second guiding part  148  is arranged so as to guide the molding core  191  in the mold opening direction (i.e., second direction or Y direction). This makes it possible to prevent the molding core  191  from moving in the X direction and to avoid collision of the molding core with the protruding portion P 2 . 
     In the present embodiment, the center axis (guiding direction) M 2  of the second guiding part  148  is parallel to the mold opening direction of the molding die  100  (i.e., Y direction). However, the arrangement of the center axis M 2  is not limited to this arrangement. As long as the molding core  191  which has been removed from the undercut portion P 1  can avoid collision with the protruding portion P 2  and can be kept removed from the undercut portion P 1 , the center axis M 2  of the second guiding part  148  may not necessarily coincide with the mold opening direction of the molding die  100  (i.e., Y direction). 
     The retaining piece  161  has a cuboid shape and includes a bottom face to which the ejection pin  745  fixed to the ejector mount plates  762  is connected. The retaining piece  161  is housed in the holder  121 . The retaining piece  161  is ejected by the ejection pin  745  and is guided on the left-side-wall inner surface  127  and the right-side-wall inner surface  130  to move in the demolding direction (i.e., Y direction), with a left side face  165  and a right side face  166  of the retaining piece slidably in contact with the left-side-wall inner surface  127  and the right-side-wall inner surface  130  of the holder  121 . 
     The retaining piece  161  includes an upper face including a protruding line (dovetail-groove protruding line)  168  extending in the X direction. The protruding line  168  extends parallel to the direction in which the undercut portion P 1  is demolded, and a dovetail groove  176  at a lower end of a body  175  of the sliding piece  171  slidably comes into engagement with the protruding line  168 , so as to guide the sliding piece  171  such that the molding core  191  is removed from the undercut portion P 1 . 
     The sliding piece  171  includes the linear body  175  having a rectangular cross section, and the body  175  includes a tip end portion to which the molding core  191  is attached and a lower end including the dovetail groove  176  which slidably engages with the protruding line  168  of the retaining piece  161 . The protruding line (dovetail-groove protruding line)  168  of the retaining piece  161  and the dovetail groove  176  of the sliding piece  171  constitute a dovetail groove structure for slidable coupling. The sliding piece  171  also includes clicks  180  on a part of the front face and on a part of the back face of the sliding piece  171 , the clicks  180  being configured to be fitted into the guiding grooves  141  of the holder  121 . Each click  180  corresponds to the click  23  on the second piece  21  of the sliding mechanism  1  of the first embodiment. The clicks  180  have a rectangular cross section and extend from middle parts of the body  175  to the lower end of the body  175  in a protruding manner on a front face and a back face of the sliding piece. Therefore, the clicks  180  may be considered as protruding lines. 
     Until the molding core  191  is removed from the undercut portion P 1 , left side faces  181  and right side faces  182  of the clicks  180  are in contact with left side surfaces  146  and right side surfaces  147  of the first guiding parts  145  of the guiding grooves  141  in the holder  121 , respectively. Upper side faces  183  and lower side faces  184  of the clicks  180  come into contact with left side surfaces  149  and right side surfaces  150  of the second guiding parts  148  of the guiding grooves  141  in the holder  121 , respectively, in order to guide the molding core  191  which has been removed from the undercut portion P 1  in the demolding direction (i.e., Y direction). The opposite left side faces  181  and right side faces  182  of the clicks  180  serve as first sliding surfaces, and the opposite upper side faces  183  and lower side faces  184  of the clicks  180  serve as second sliding surfaces. 
     The molding core  191  is a block member having a shape matching a part of the molded product P including the undercut portion P 1  and is fixed to an upper end face of the sliding piece  171  by screwing or the like. The shape of the molding core  191  depends on the shape of the molded product P. The molding core  191  may be integrated with the sliding piece  171 . 
     An operation and effects of the molding die  100  of the present embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding in the molding die  100 . When molding the molded product P, the sliding piece  171  is housed in the holder  121 , and the molding core  191  is placed so as to mold an undercut portion P 1  of the molded product P (see  FIG. 6 ). In the molding die  100 , parting faces (PL faces) of the fixed die  600  and the movable die  700  are fitted together to define a cavity part, and a molten material is injected into the cavity to mold the molded product P. 
     Once the steps of injecting and cooling the molten material are completed, the process proceeds to steps of opening the mold and taking out the molded product P. In the steps of opening the mold and taking out the molded product, the molding die  100  operates as follows. 
     After the mold is opened (see  FIG. 7 ), the ejector rod  768  is pushed up through a non-illustrated ejection device, and the ejector mount plates  762  move upward (i.e., in the Y direction). In association therewith, the ejector pin  763  which is disposed so as to stand on the ejector mount plates  762  ejects the molded product P in the Y direction (see  FIG. 8 ). 
     At the same time, the retaining piece  161  housed in the holder  121  is ejected by the ejection pin  745  and is moved in the Y direction to the same extent as the ejector pin  763 . In association with the movement of the retaining piece  161  in the Y direction, the sliding piece  171  is moved from a molding position as shown in  FIG. 6  along the first guiding parts  145  of the holder  121 , while the first sliding surfaces of the clicks  180  slide on the left side surfaces  146  and the right side surfaces  147  of the first guiding parts  145  of the guiding groove  141  in the holder  121 . Thus, the molding core  191  is moved simultaneously in the Y direction and the X direction away from the undercut portion P 1 . 
     When the ejector mount plates  762  are moved upward by ΔH 1  from a mold clamped state, the upper side faces  183  of the clicks  180  of the sliding piece  171  come into contact with the left side surfaces  149  of the second guiding parts  148  of the guiding grooves  141  in the holder  121 . At this point, the molding core  191  attached to the sliding piece  171  is completely removed from the undercut portion P 1  (see  FIG. 8 ). As for the sliding piece  171 , the upper side faces  183  of the clicks  180  are in contact with the left side surfaces  149  of the second guiding parts  148  of the holder  121 , and the right side faces  182  of the clicks  180  are separated from the right side surfaces  147  of the first guiding parts  145  of the guiding grooves  141  in the holder  121 . 
     When the ejector mount plates  762  are moved upward by ΔH 1  from the mold clamped state, the molded product P has not reached a position where the molded product P can be taken out (see  FIG. 8 ). Therefore, the ejector mount plates  762  continue to move upward, and the ejector pin  763  in contact with an inner side of the molded product P continues to eject the molded product P. The retaining piece  161  also moves upward in a same manner, and the sliding piece  171  moves upward while the second sliding surfaces of the clicks  180  slide on the left and right side surfaces  149 ,  150  of the second guiding parts  148  of the guiding grooves  141  in the holder  121 . 
     Since the center axes M 2  of the second guiding parts  148  of the guiding grooves  141  of the holder  121  are parallel to the Y direction, the molding core  191  moves upward without moving in the +X direction or the −X direction. Although the molded product P includes the protruding portion P 2  which is located ahead in the removal direction of the undercut portion P 1  (i.e., +X direction), the molding core  191  does not collide with the protruding portion P 2  because the molding core  191  does not move in the +X direction. Further, since the molding core  191  does not move in the −X direction, either, the undercut portion P 1  will not be caught on the molding core  191  when the molded product P is taken out (see  FIG. 9 ). Thus, the molded product P can be taken out without damage. 
     After the molded product P is taken out, the molding die  100  is clamped again in order to mold a next molded product P. Upon mold clamping, the entire movable die  700  is moved in the upward direction in  FIG. 9 , and the ejector mount plates  762  are moved in the downward direction in  FIG. 9 . As for the undercut processing mechanism  101 , the retaining piece  161  is moved in an opposite direction to the previous direction in conjunction with the movement of the movable die  700 , and an upper face of the molding core  191  becomes flush with an upper face of the core  712 . Once the mold clamping is completed, a molding material is injected, and a next molded product P is molded. An operation of the molding die  100  from a mold open state to a mold clamped state is essentially the same as a conventional molding die including an undercut processing mechanism. 
     As described above, the molding die  100  and the undercut processing mechanism  101  can achieve compact and simple configurations and allow an undercut portion P 1  to be demolded easily and reliably because in conjunction with an operation of taking out the molded product P from the molding die  100 , the retaining piece  161  moves upward while sliding inside the holder  121 , and the sliding piece  171  is guided by the holder  121  to move such that the molding core  191  is removed from the undercut portion P 1 . 
     In addition, the molding die  100  and the undercut processing mechanism  101  can further allow even a molded product P, including a protruding portion P 2  which is located ahead in the direction of demolding an undercut portion P 1 , to be demolded easily and reliably because after the molding core  191  is moved so as to demold the undercut portion P 1 , the molding core  191  is moved in the demolding direction (i.e., Y direction) in conjunction with the operation of taking out the molded product P. 
     Moreover, the undercut processing mechanism  101  can be incorporated into the molding die  100  with the sliding piece  171  and the retaining piece  161  housed in the holder  121 , and therefore, the undercut processing mechanism can have a compact configuration and be easily attached to the molding die  100 . In particular, the holder  121 , the retaining piece  161 , the sliding piece  171 , and the molding core  191  can be assembled into a single independent unit; the undercut processing mechanism  101  as a single unit can be more easily attached to the molding die  100 . 
       FIG. 11  is a cross-sectional view of a molding die  200  including a gate cutting mechanism  201  according to a fourth embodiment of the present invention in a mold closed state, and  FIG. 12  is a cross-sectional view of the molding die  200  during a process of opening the mold.  FIG. 13  is a cross-sectional view of the molding die  200  including the gate cutting mechanism  201  according to the fourth embodiment of the present invention during the process of opening the mold;  FIG. 14  is a cross-sectional view of the molding die  200  after mold opening; and  FIG. 15  is a cross-sectional view of the molding die  200  during a process of ejecting a molded product P.  FIG. 16  is an exploded view showing features of the gate cutting mechanism  201  according to the fourth embodiment of the present invention. Features corresponding to the features of the molding die  100  and the undercut processing mechanism  101  according to the third embodiment of the present invention as shown in  FIG. 6  to  FIG. 10  are denoted with like reference numerals, and description thereof is omitted. 
     As with the molding die  100 , the molding die  200  includes: a fixed die  602  which molds an external surface of a molded product P; a movable die  702  which molds an internal surface of the molded product P; and further a gate cutting mechanism  201  which cuts a gate G. For the sake of convenience, in the following description, the “upper” side means the side of the fixed mold  602  in  FIG. 11 , and the “lower” side means the side of the movable mold  702  in  FIG. 11 . In the following description, the “left” side corresponds to the left side in  FIG. 11 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     As with the fixed die  600  of the third embodiment, the fixed die  602  includes a fixed mold plate  605  including a cavity  606  for molding the external surface of the molded product P. The fixed mold plate  605  includes, adjacent to the cavity  606 , a housing part  608  which houses the gate cutting mechanism  201 . The housing part  608  is arranged so as to penetrate the fixed mold plate  605  in a vertical direction. The fixed mold plate  605  also includes a recessed part  612  on a bottom face  610  thereof, which receives a spring  218  for advancing and retracting a movable piece  205 . 
     As with the movable die  700 , the movable die  702  includes a movable mold plate  711  including a core  712  which molds the inner surface of the molded product P. The movable mold plate  711  includes a housing part  720  which receives the movable piece  205 . The movable piece  205  is fitted into the housing part  720  to shape a runner R. The movable mold plate  711  includes, in addition to an insertion hole through which the ejector pin  763  is inserted to push out (eject) the molded product P, an insertion hole through which an ejector pin  746  is inserted to push out (eject) a material left in the runner R after cutting the gate G. 
     The movable piece  205  has a cuboid shape and includes a recessed part  208  which opens on an upper face of the movable piece  205  and receives a lower part of the holder  221 . The movable piece  205  also includes a recessed part  210  for attaching a coupling pin  215 , the recessed part extending from a bottom part to an upper part of the movable piece  205 ; and a through hole extending from the upper face of the movable piece  205  to the recessed part  210 . The diameter of the through hole is smaller than the diameter of the recessed part  210 . 
     The movable piece  205  is coupled to the fixed mold plate  605  through the coupling pin  215 . The coupling pin  215  includes a pin body having a smaller diameter than that of the through hole connecting to the recessed part  210  and, at a tip end portion of the pin body, a flange  216  having a smaller diameter than that of the recessed part  210 . The coupling pin  215  is inserted into the through hole connecting to the recessed part  210  such that the flange  216  is located within the recessed part  210 , and a base end portion of the coupling pin  215  is fixed to the bottom of the recessed part  612 . The spring  218  for pushing out the movable piece  205  is inserted onto the coupling pin  215  and is attached so as to be housed in the recessed part  612 , with a lower end of the spring in contact with an upper face  206  of the movable piece  205 . 
     The housing part  720  is a substantially rectangular recessed part in a front view (see  FIG. 15 ) and includes a recessed part  724  which shapes the runner R on the left side of a bottom face  722  of the housing part  720  (see  FIG. 15 ). Further, a cushioning material  212  for protecting a tip end portion  293  of a cutter  291  is attached to the core  712  which is into contact with an upper left end of the housing part  720  (see  FIG. 15 ). The cushioning material  212  is made of a material softer than the tip end portion  293  of the cutter  291 , such as soft iron. 
     The gate cutting mechanism  201  is operable to cut the gate G connecting the molded product P to the runner R. The gate cutting mechanism  201  can cut the gate G with the cutter  291  in conjunction with a mold opening operation of the molding die  200 , and move the cutter  291  after cutting the gate G away from the gate G, so that a material left in the runner R can be removed. The gate cutting mechanism  201  of the present embodiment employs the sliding mechanism  1  of the first embodiment. 
     The gate cutting mechanism  201  includes: the cutter  291  which cuts the gate G; a sliding piece  271  which is coupled to the cutter  291  to slide the cutter  291 ; and a retaining piece  261  which slidably retains the sliding piece  271 ; and a holder  221  which houses the retaining piece  261  in an advanceable and retractable manner. 
     The sliding piece  271  of the present embodiment corresponds to the second piece  21  of the sliding mechanism  1  of the first embodiment; the retaining piece  261  corresponds to the first piece  11 ; and the holder  221  corresponds to the guiding body  31 . Also, in the present embodiment, the sliding piece  271  corresponds to a slider, and the holder  221  corresponds to a guide body. As described later, a guiding groove  241  corresponds to a guide unit; a first guiding part  245  corresponds to a first guide unit; and a second guiding part  248  corresponds to a second guide unit. A click  280  corresponds to an engagement unit; a first sliding surface of the click  280  corresponds to a first engagement unit; and a second sliding surface of the click  280  corresponds to a second engagement unit. The retaining piece  261  and the sliding piece  271  are slidably coupled together through a dovetail groove structure. The retaining piece  261  corresponds to a coupling member, and left- and right-side-wall inner surfaces  227 ,  230  of the holder  221  correspond to a coupling member guide unit. 
     The holder  221  houses the retaining piece  261  in an advanceable and retractable manner, and guides the retaining piece  261  in the vertical direction. Further, the holder  221  guides the sliding piece  271  such that the cutter  291  attached to the sliding piece  271  cuts the gate G, and the cutter  291  after cutting the gate G is moved away from the gate G. The holder  221  includes two half holder members  225  of a same shape which are assembled together, and has a box-like column shape which defines an inner space therein with an open upper face and an open lower face. The holder  221  may be constituted by a plurality of divided members or be integrated with the fixed mold plate  605 . 
     The holder  221  shares a common point with the holder  121  of the third embodiment in that the sliding piece  271  is guided in the first direction and subsequently in the second direction. In contrast, the holder  221  has a different configuration from the holder  121  of the third embodiment in that the sliding piece  271  including the cutter  291  is slidably housed. 
     The holder  221  includes a left side wall  226  which is shorter than a back face wall  234  of the holder  221  and is opened below the left side surface thereof. This opening allows the cutter  291  to move in and out. At a lower part of the left side wall  226 , there is a stepped portion  228  which protrudes inward. At a lower part of a right side wall  229 , there is also a stepped portion  231  which protrudes inward. A left-side-wall inner surface  227  and a right-side-wall inner surface  230  serve as guides for the retaining piece  261 , and the left and right stepped portions  228 ,  231  serve as stoppers for the retaining piece  261 . As with the holder  121  of the third embodiment, the holder  221  includes guiding grooves  241  for guiding the sliding piece  271  on a front-face-wall inner surface and a back-face-wall inner surface  235  of the holder. 
     Each guiding groove  241  is a recessed groove and has a dog-legged shape when the back-face-wall inner surface  235  is viewed straightforwardly (see  FIG. 16 ). Each guiding groove  241  includes a first guiding part  245  which guides the sliding piece  271  in the first direction and a second guiding part  248  which guides the sliding piece  271  in the second direction. The first guiding part  245  is inclined diagonally upward to the right such that an upper part thereof is located on the right side with respect to a lower part thereof. The second guiding part  248  is inclined diagonally upward to the left such that an upper part thereof is located on the left side with respect to a lower part thereof. The first guiding part  245  and the second guiding part  248  are connected to each other, and a center axis M 1  of the first guiding part  245  and a center axis M 2  of the second guiding part  248  intersect with each other (see  FIG. 16 ). 
     The first guiding part  245  guides the sliding piece  271  such that the cutter  291  coupled to the sliding piece  271  cuts the gate G in a synchronized manner with the ejector mechanism  760 . On the other hand, the second guiding part  248  guides the sliding piece  271  such that the cutter  291  after cutting the gate G is moved away from the gate G in a synchronized manner with the ejector mechanism  760 . 
     The holder  221  is attached to the housing part  608  such that a lower end of the left side wall  226  is flush with the bottom face  610  of the fixed mold plate  605 . For this reason, a lower part of the holder  221  including the opening for the cutter  291  to move in and out projects downward from the bottom face  610  of the fixed mold plate  605 . The part of the holder  221  which projects downward from the bottom face  610  of the fixed mold plate  605  can be accommodated in the recessed part  208  of the movable piece  205  when the mold is closed. 
     The retaining piece  261  has a cuboid shape and includes a protruding line (dovetail-groove protruding line)  268  extending in the X direction on the bottom face of the retaining piece  261 . The protruding line  268  slidably comes into engagement with a dovetail groove  276  at an upper end of a body  275  of the sliding piece  271 , and guides the cutter  291  attached to the sliding piece  271  in the +X direction and the −X direction. The retaining piece  261  also includes recessed parts  263  which open on an upper face  262  of the retaining piece  261 . The recessed parts  263  serve as housing parts for springs  270  which push out the retaining piece  261  downward. There are two recessed parts  263 . 
     A left side face  265  and a right side face  266  of the retaining piece  261  are slidably in contact with the left-side-wall inner surface  227  and the right-side-wall inner surface  230  of the holder  221 , and the retaining piece  261  advances and retract in the demolding direction (i.e., Y direction) in conjunction with opening and closing of the molding die  200 . 
     The sliding piece  271  includes the linear body  275  having a rectangular cross section, and the body  275  includes a middle part to which the cutter  291  is attached and an upper end including the dovetail groove  276  which slidably comes into engagement with the protruding line  268  of the retaining piece  261 . The protruding line (dovetail-groove protruding line)  268  of the retaining piece  261  and the dovetail groove  276  of the sliding piece  271  constitute a dovetail groove structure for slidable coupling. The sliding piece  271  also includes clicks  280  which are configured to be fitted into the guiding grooves  241  of the holder  221 . The clicks  280  are located at middle parts of the body  275  in a protruding manner on a front face and a back face of the sliding piece  271 . Therefore, the clicks  280  may be considered as protruding lines. 
     Left side faces  281  and right side faces  282  of the clicks  280  serve as first sliding surfaces which are in contact with the left side surfaces  246  and right side surfaces  247  of the first guiding parts  245  of the holder  221 , respectively, until the cutter  291  cuts the gate G. Upper side faces  283  and lower side faces  284  of the clicks  280  serve as second sliding surfaces which come into contact with right side surfaces  250  and left side surfaces  249  of the second guiding parts  248  of the holder  221 , respectively, in order to move the cutter  291  after cutting the gate G away from the gate G. 
     The cutter  291  has a rod shape and includes a base end fixed to the sliding piece  271  and a blade for cutting the gate G at the tip end portion  293 . The cutter  291  is removably attached to the sliding piece  271 . Although the cutter  291  may be integrated with the sliding piece  271 , the cutter  291  is preferably removable from the sliding piece  271 , so that only the cutter  291  can be replaced when the blade has worn out. 
     The gate cutting mechanism  201  having the above constitution is incorporated into the holder  221 , with the cutter  291  attached to the sliding piece  271 , and the dovetail groove  276  of the sliding piece  271  receiving the protruding line  268  of the retaining piece  261 . In this state, the clicks  280  of the sliding piece  271  are fitted into the guiding grooves  241  of the holder  221 , and the cutter  291  protrudes from the opening at the left side face of the holder  221 . The gate cutting mechanism  201  including the respective pieces and the springs  270  incorporated therein is fitted into the housing part  608  in the fixed mold plate  605 , and is fixed to the fixed mold plate  605  through the fixed plate  615 . 
     An operation and effects of the molding die  200  and gate cutting mechanism  201  of the present embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding in the molding die  200 . 
     In a mold closed state, the upper face  206  of the movable piece  205  is in contact with the bottom face  610  of the fixed mold plate  605 , and the bottom face  207  of the movable piece  205  is in contact with a bottom  722  of the housing part  720  in the movable mold plate  711 . Thus, the runner R is shaped. As for the gate cutting mechanism  201 , a bottom part of the holder  221  and a bottom part of the sliding piece  271  are in contact with a bottom of recessed part  208  of the movable piece  205 , and the sliding piece  271  is located at a highest lift position with respect to the holder  221 . Then, the clicks  280  are located in the first guiding parts  245 , and the tip end portion  293  of the cutter  291  is located at a slightly rightward position with respect to the gate G (see  FIG. 11 ). 
     When the mold is closed, parting faces (PL faces) of the fixed die  602  and the movable die  702  are fitted together to define a cavity part. Then, a molten resin is injected from a non-illustrated injection device, and the resin passes through a sprue (not illustrated), then through the runner R and the gate G and fills in the cavity part. After a pressure holding step and a cooling step, the mold is opened, and a molded product P is taken out. The processes of opening the mold and taking out the molded product P are performed according to the following procedure. 
     Once the movable mold  702  retracts and the mold starts to open, a gap (space) is created between the bottom face of the holder  221  and the bottom of the recessed part  208  of the movable piece  205 . Thus, the spring  270  extends, so that the retaining piece  261  is pushed out downward. The sliding piece  271  slidably coupled to the retaining piece  261  moves downward along the first guiding parts  245 , while the first sliding surfaces slide in the first guiding parts  245  of the guiding grooves  241  in the holder  221 . Since the first guiding parts  245  are inclined downward to the left, the cutter  291  attached to the sliding piece  271  moves in the X direction while moving downward. 
     In conjunction with mold opening, the sliding piece  271  descends, and when the lower side faces  284  of the clicks  280  come into contact with the left side faces  249  of the second guiding parts  248  of the guiding grooves  241 , the gate G is completely cut by the cutter  291  (see  FIG. 12 ). As the gap further increases between the fixed die  602  and the movable die  702  increases, the sliding piece  271  moves along the second guiding parts  248 , while the second sliding surfaces slide in the second guiding part  248  of the guiding grooves  241 , and the cutter  291  moves in the −X direction so as to move away from the gate G (see  FIG. 13 ). When the bottom part of the retaining piece  261  comes into contact with the left and right stepped portions  228 ,  231  of the holder  221 , the sliding piece  271  stops descending, and the cutter  291  also stops moving. 
     When the flange  216  of the coupling pin  215  comes into contact with a ceiling surface of the recessed part  210  of the movable piece  205 , the movable piece  205  is integrated with the fixed die  602 . Thereafter, the holder  221  and the movable piece  205  have a fixed positional relation. When a necessary space to remove the resin left in the runner R is secured between the movable piece  205  and the movable mold plate  711  (see  FIG. 14 ), the ejector mount plates  762  move upward. Thus, the molded product P is ejected by the ejector pin  763 , and the resin left in the runner R is ejected by the ejector pin  746  (see  FIG. 15 ). 
       FIG. 17  is an exploded view showing features of a gate cutting mechanism  202 , which is a variant of the gate cutting mechanism  201  of the molding die  200  according to the fourth embodiment of the present invention. Features corresponding to the features of the gate cutting mechanism  201  as shown in  FIG. 16  are denoted with like reference numerals, and description thereof is omitted. 
     The difference between the gate cutting mechanism  202  and the gate cutting mechanism  201  is the shape of the first guiding parts of the guiding grooves  241  in the holder  221 . Correspondingly, the shapes of left side faces  285  and right side faces  286  of the clicks  280  of the sliding piece  271 , which serve as the first sliding surfaces, also differ from those in the gate cutting mechanism  201 . 
     The first guiding parts  245  of the guiding grooves  241  of the gate cutting mechanism  201  have the linear center axes M 1  and the linear left and right side surfaces  246 ,  247 , whereas the first guiding parts  252  of the guiding grooves  241  of the gate cutting mechanism  202  have slightly curved center axes M 1  and slightly curved left and right side surfaces  253 ,  254 . Correspondingly, the left side faces  285  and the right side faces  286  of the clicks  280  of the sliding piece  271 , which serve as the first sliding surface, are also curved. 
     Although, as with the gate cutting mechanism  201 , the second guiding parts  248  of the guiding grooves  241  of the gate cutting mechanism  202  extend linearly, the second guiding parts  248  may also be curved. As described above, the first guiding parts and the second guiding parts of the guiding grooves  241  may have a linear shape, or a curved shape, or a combination of a linear shape and a curved shape. 
     As described above, the molding die  200  and the gate cutting mechanism  201 ,  202  can achieve compact and simple configurations and can operate such that the gate G can be cut easily and reliably prior to taking out the molded product P. In addition, the cutter  291  after cutting the gate G is moved away from the gate G in conjunction with mold opening, so that the cutter  291  does not interfere when the molded product P is taken out. 
     Further, the molding die  200  moves the movable piece  205  in conjunction with mold opening and allows a material left in the runner to be removed, and therefore, the molding die  200  is highly convenient for use. Moreover, the gate cutting mechanism  201 ,  202  can be incorporated into the molding die  200  with the sliding piece  271  and the retaining piece  261  housed in the holder  221 , and therefore, the gate cutting mechanism  201 ,  202  can have a compact configuration and be easily attached to the molding die  200 . In particular, the holder  221 , the retaining piece  261 , the sliding piece  271 , and the cutter  291  can be assembled into a single independent unit; the gate cutting mechanism  201 ,  202  as a single unit can be more easily attached to the molding die  200 . 
       FIG. 18  to  FIG. 22  illustrate operations of a molding die  300  including a gate cutting mechanism  301  according to a fifth embodiment of the present invention.  FIG. 23  is an exploded view showing features of the gate cutting mechanism  301  according to the fifth embodiment of the present invention. Features corresponding to the features of the sliding mechanism  1  according to the first embodiment of the present invention as shown in  FIG. 1  and  FIG. 2  are denoted with like reference numerals, and description thereof is omitted. For the sake of convenience, in the following description, the “upper” side means the side of the molded product P in  FIG. 18 , and the “lower” side means the side of the molding die  300  in  FIG. 18 . In the following description, the “left” side corresponds to the left side in  FIG. 18 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     The molding die  300  includes a gate cutting mechanism  301  which cuts a gate G. The gate cutting mechanism  301  is operable to cut a gate G connecting a molded product P to a runner R, and employs the sliding mechanism  1  of the first embodiment. The gate cutting mechanism  301  is incorporated in the housing part  305  of the molding die  300 . The housing part  305  is arranged so as to penetrate the molding die  300  in the vertical direction and includes a bottom part closed by another member. 
     The gate cutting mechanism  301  includes: a first cutter  391  which cuts the gate G; a second cutter  395 ; a sliding piece  371  including the first cutter  391 ; a retaining piece  361  which slidably holds the sliding piece  371 ; and a holder  321  which houses the retaining piece  361  in an advanceable and retractable manner. 
     The sliding piece  371  of the present embodiment corresponds to the second piece  21  of the sliding mechanism  1  of the first embodiment; the retaining piece  361  corresponds to the first piece  11 ; and the holder  321  corresponds to the guiding body  31 . In the present embodiment, the sliding piece  371  corresponds to a slider; the holder  321  corresponds to a guide body; the guiding groove  38  corresponds to a guide unit; the first guiding part  39  corresponds to a first guide unit; and the second guiding part  42  corresponds to a second guide unit. A click  23  corresponds to an engagement unit; a first sliding surface of the click  23  corresponds to a first engagement unit; and a second sliding surface of the click  23  corresponds to a second engagement unit. The retaining piece  361  and the sliding piece  371  are slidably coupled together through a dovetail groove structure. The retaining piece  361  corresponds to a coupling member, and a left-side-wall inner surface  327  of the holder  321  and a left side face  311  of a middle piece  310  correspond to a coupling member guide unit. 
     The holder  321  shares a common point with the guiding body  31  of the sliding mechanism  1  of the first embodiment in that the sliding piece  371  is guided in the first direction and subsequently in the second direction, and in that the retaining piece  361  is guided in the demolding direction (i.e., Y direction). In contrast, the holder  321  differs in the structure from the guiding body  31  in that the middle piece  310  including a runner R at a middle part thereof is attached to the holder  321 . 
     The holder  321  includes a channel-shaped member  322  having a channel-shaped or U-shaped transverse section and a flat plate (not illustrated) which provides a front face wall for closing a front side (fore side) of the channel-shaped member  322 , and has a box-like column shape which defines an inner space therein with an open upper face and an open lower face. The holder  321  may include two half holder members of a same shape which are assembled together as in other embodiments, or be constituted by a plurality of divided members, or be integrated with the molding die  300 . 
     The channel-shaped member  322  includes a rectangular back face wall  334  and side walls  326 ,  329  at opposite ends of the rectangular back face wall  334 . The middle piece  310  is a linear member having a rectangular transverse section and is attached on a rightward position on a back-face-wall inner surface  335  of the channel-shaped member  322 . The left-side-wall inner surface  327  of the channel-shaped member  322  is parallel to the left side face  311  of the middle piece  310 , and the right-side-wall inner surface  330  of the channel-shaped member  322  is parallel to the right side face  312  of the middle piece  310 . 
     The left-side-wall inner surface  327  of the channel-shaped member  322  and the left side face  311  of the middle piece  310  serve as guides for the retaining piece  361 , and the right-side-wall inner surface  330  of the channel-shaped member  322  and the right side face  312  of the middle piece  310  serve as guides for the second cutter  395 . Guiding grooves  38  are located on the back-face-wall inner surface  335  of the channel-shaped member  322  and a front-face-wall inner surface (not illustrated) which closes the front side of the channel-shaped member  322 , each guiding groove having a dog-legged shape when the back-face-wall inner surface  335  is viewed straightforwardly. The guiding grooves  38  have a same basic configuration as that of the guiding groove  38  in the holder  31  of the first embodiment, and guide the sliding piece  371 . 
     The first guiding parts  39  of the guiding grooves  38  guide the sliding piece  371  such that the first cutter  391  in the sliding piece  371  cuts the gate G. On the other hand, the second guiding part  42  guides the sliding piece  371  such that the first cutter  391  in the sliding piece  371  after cutting the gate G is moved away from the gate G. 
     The retaining piece  361  has a cuboid shape and includes lock grooves  367  in upper parts of the front face wall  363  and the back face wall, the lock grooves  367  being configured to slidably lock or engage clicks  377  in a dovetail groove  376  at a lower end of the sliding piece  371 . Each lock groove  367  includes, at a position slightly below an upper face of the retaining piece  361 , a first lock groove  368  which extends parallel to the X direction from a left end to a middle part of the retaining piece  361  and a second lock groove  369  which continues from the first lock groove  368  and extends diagonally downward to the right. An upper part of the retaining piece  361  including the first lock groove  368  is constructed as a protruding line (dovetail-groove protruding line). 
     The retaining piece  361  is ejected in the Y direction through the ejection pin  745 , while the left side face  365  and the right side face  366  are slidably in contact with the left-side-wall inner surface  327  of the holder  321  and the left side face  311  of the middle piece  310 . 
     The middle piece  310  includes a runner R connected to the gate G at an upper part thereof. The middle piece  310  includes inclined surfaces  313 ,  314  at left and right upper ends. The left inclined surface  313  is inclined at a same angle as that of an inclined surface of the first cutter  391 , and the right inclined surface  314  is inclined at a same angle as that of an inclined surface at a tip end portion of the second cutter  395  (see  FIG. 18 ). Further, the middle piece  310  is coupled to an ejector pin  746  configured to remove a material left in the runner R after the molded product P is taken out. 
     The sliding piece  371  includes a substantially triangular body  375  with an inclined right side in a front view. The sliding piece  371  includes the first cutter  391  at an upper right end of the body  375  and the dovetail groove  376  at a lower end of the body  375 , which are configured to be slidably locked into the lock grooves  367  of the retaining piece  361 . The protruding line (dovetail-groove protruding line) of the retaining piece  361  and the dovetail groove  376  of the sliding piece  371  constitute a dovetail groove structure for slidable coupling. The sliding piece  371  also includes the clicks  23  configured to be fitted into the guiding grooves  38  of the holder  321 . The clicks  23  are located at lower positions on the front face side and the back face side of the body  375  in a protruding manner. Therefore, the clicks  23  may be considered as protruding lines. The clicks  23  have a same basic configuration as that of the click  23  on the second piece  21  of the sliding mechanism  1  of the first embodiment and includes first sliding surfaces which slidably come into contact with the first guiding parts  39  of the guiding grooves  38  and second sliding surfaces which slidably come into contact with the second guiding parts  42  of the guiding grooves  38 . 
     The first cutter  391  is integrated with the body  375  at an upper right end portion of the body  375  of the sliding piece  371 , and a tip end portion  393  of the first cutter  391  is a blade for cutting the gate G. In the present embodiment, the sliding piece  371  is integrated with the first cutter  391 . However, the sliding piece  371  and the first cutter  391  may be constituted as separate members and be coupled together. 
     The second cutter  395  is a columnar body having a rectangular cross section and includes a blade  396  for cutting the gate G at an upper left end portion of the second cutter  395 . The width W 3  of the second cutter  395  is substantially equal to a width W 4  between the right side face  312  of the middle piece  310  of the holder  321  and the right-side-wall inner surface  330  of the holder  321 . When the second cutter  395  is fitted into the holder  321 , the left side face  397  slidably comes into contact with the right side face  312  of the middle piece  310 , and the right side face  398  slidably comes into contact with the right-side-wall inner surface  330  of the holder  321 . An ejection pin  747  is coupled to a bottom face of the second cutter  395 . 
     The gate cutting mechanism  301  having the above constitution is incorporated into the holder  321 , with the clicks  377  of the dovetail groove  376  of the sliding piece  371  fitted into the lock groove  367  of the retaining piece  361 . The second cutter  395  is incorporated into the holder  321  and is fitted into the housing part  305  in the molding mold  300  to be fixed therein. 
     An operation and effects of the molding die  300  and the gate cutting mechanism  301  of the present embodiment will be described. 
     During molding, the retaining piece  361  is located at lowermost end of the holder  321 , and the sliding piece  371  slidably coupled to the retaining piece  361  is also at a lowermost position. The first cutter  391  and the second cutter  395  are separated to a maximum extent, and both of the first cutter  391  and the second cutter  395  are located away from the gate G (see  FIG. 18 ). 
     When the molded product P is taken out, the ejection pins  745 ,  747  and the ejector pin  746  are pushed up simultaneously by a same distance. At the same time, the sliding piece  371  including the first cutter  391  at the upper right tip end portion thereof is guided by the first guiding parts  39  to move upward to the right, while the first sliding surfaces of the clicks  23  slide in the first guiding parts  39  of the guiding grooves  38 . On the other hand, the second cutter  395  is guided by the right side face  312  of the middle piece  310  and the right-side-wall inner surface  330  of the holder  321  to move in the Y direction. 
     Thus, the first cutter  391  moves to the right (i.e., in the −X direction), and the first cutter  391  and the second cutter  395  cut the gate G. At this point, the clicks  377  of the dovetail groove  376  of the sliding piece  371  are located at rightmost positions in the first lock grooves  368  of the retaining piece  361 . The clicks  23  on the sliding piece  371  are located in the first guiding parts  39  of the guiding grooves  38  (see  FIG. 19 ). 
     When the ejection pins  745 ,  747  and the ejector pin  746  are pushed up further, the molded product P is pushed up by the second cutter  395 , and with the gate G cut, the runner R is also pushed up by the ejector pin  746 . On the other hand, the sliding piece  371  is guided by the first guiding parts  39  of the guiding grooves  38  to move to the upper right side, while the clicks  377  of the dovetail groove  376  enter the second lock grooves  369  of the retaining piece  361 . Since the second lock grooves  369  extend downward to the right, the first cutter  391  moves in the upward direction (i.e., Y direction) to a lesser extent than that of the second cutter  395 . Thus, the tip end portion  393  of the first cutter  391  moves so as to enter a lower side of the blade  396  of the second cutter  395  (see  FIG. 20 ). This makes it possible to cut the gate G reliably. 
     When the ejection pins  745 ,  747  and the ejector pin  746  are pushed up further, the clicks  23  of the sliding piece  371  enter the second guiding parts  42  of the guiding grooves  38 . Since the second guiding parts  42  extend upward to the left, when the clicks  23  enter the second guiding parts  42  of the guiding grooves  38 , the clicks  377  of the dovetail groove  376  enter the first lock grooves  368  of the retaining piece  361 . Thus, the positions of the first cutter  391  and the second cutter  395  are aligned, and the molded product P is pushed up by the first cutter  391  and the second cutter  395 . At the same time, a material (molding material) left in the runner R after the gate G is cut is also pushed up by the ejector pin  746  (see  FIG. 21 ). Then, the sliding piece  371  is guided by the second guiding parts  42  of the guiding grooves  38  to move to the upper left side, so that the first cutter  391  is moved away from the second cutter  395  (see  FIG. 22 ). 
     The above operation makes it possible to take out the molded product P from the molding die  300  and also to remove, from the runner R, a molding material left in the runner R after the gate G is cut. 
     As described above, the molding die  300  and the gate cutting mechanism  301  can achieve compact and simple configurations and can operate such that the gate G can be cut easily and reliably in conjunction with taking out the molded product P. Further, the molding die  300  allows a material left in the runner R to be removed, and therefore, the molding die  300  is highly convenient for use. 
     Moreover, the gate cutting mechanism  301  can be incorporated into the molding die  300  with the sliding piece  371  including the first cutter  391 , the second cutter  395 , and the retaining piece  361  housed in the holder  321 , and therefore, the gate cutting mechanism  301  can have a compact configuration and be easily attached to the molding die  300 . In particular, the sliding piece  371  including the first cutter  391 , the second cutter  395 , the retaining piece  361 , and the holder  321  can be assembled into a single independent unit; the gate cutting mechanism  301  as a single unit can be more easily attached to the molding die  300 . 
       FIG. 24  is a cross-sectional view showing a main part of a molding die  400  including a gate cutting mechanism  401  according to the sixth embodiment of the present invention when the mold is closed.  FIG. 25  and  FIG. 26  show cross-sectional views showing the main part of the molding die  400  including the gate cutting mechanism  401  according to the sixth embodiment of the present invention during a process of opening the mold.  FIG. 27  is an exploded view showing features of the gate cutting mechanism  401  of the sixth embodiment of the present invention. Features corresponding to the features of the molding die  200  including the gate cutting mechanism  201  according to the fourth embodiment of the present invention as shown in  FIG. 11  to  FIG. 17  are denoted with like reference numerals, and description thereof is omitted. 
     As with the molding die  200  of the fourth embodiment, the molding die  400  includes: a fixed die  603  which molds an external surface of a molded product P; a movable die  703  which molds an internal surface of the molded product P; and further a gate cutting mechanism  401  which cuts a gate G. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  603  in  FIG. 24 , and the “lower” side means the side of the movable die  703  in  FIG. 24 . In the following description, the “left” side corresponds to the left side in  FIG. 24 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     As with the fixed die  602  of the fourth embodiment, the fixed die  603  includes a fixed mold plate  605  including a cavity  606  for molding the external surface of the molded product P. The fixed mold plate  605  includes, adjacent to the cavity  606 , a housing part  608  which houses the gate cutting mechanism  401 . The housing part  608  is arranged so as to penetrate the fixed mold plate  605  in the vertical direction and includes a step in an upper part of the housing part  608 . A guide piece  630  which guides a sliding piece  471  is attached at a rightward position on a bottom face of the housing part  608  of the fixed mold plate  605 . 
     As with the movable die  702  of the fourth embodiment, the movable die  703  includes a movable mold plate  711  including a core  712  which molds the inner surface of the molded product P. A part of the movable mold plate  711  which shapes a runner R and a gate G connected to the molded product P is constructed as a recessed part, so that a space is defined between this part and the bottom face  610  of the fixed mold plate  605 . 
     The gate cutting mechanism  401  is operable to cut a gate G connecting a molded product P to a runner R and includes: a cutter  491  which cuts the gate G; a sliding piece  471  which is coupled to the cutter  491  to slide the cutter  491 ; a retaining piece  461  which slidably retains the sliding piece  471 ; a holder  421  which houses the retaining piece  461  in an advanceable and retractable manner; and a movable piece  405  which presses the molded product P. The gate cutting mechanism  401  of the present embodiment employs the sliding mechanism  1  of the first embodiment. 
     The movable piece  405  of the present embodiment corresponds to the second piece  21  of the sliding mechanism  1  of the first embodiment; the retaining piece  461  corresponds to the first piece  11 ; and the holder  421  corresponds to the guiding body  31 . In the present embodiment, the movable piece  405  corresponds to a slider, and the holder  421  corresponds to a guide body. As described later, a first guiding groove  441  corresponds to a guide unit; a first guiding part  445  corresponds to a first guide unit; and a second guiding part  448  corresponds to a second guide unit. Protruding lines  412 ,  413 ,  414  (not illustrated),  415  correspond to an engagement unit; first sliding surfaces of the protruding lines  412 ,  413 ,  415  correspond to a first engagement unit; and second sliding surfaces of the protruding lines  412 ,  413 ,  415  correspond to a second engagement unit. The retaining piece  461  and the movable piece  405  are slidably coupled together through a dovetail groove structure. The retaining piece  461  corresponds to a coupling member, and left- and right-side-wall inner surfaces  427 ,  430  of the holder  421  correspond to a coupling member guide unit. 
     The holder  421  includes two half holder members  425  of a same shape which are assembled together, each half holder member having a channel-shaped or U-shaped cross section, so as to have a box-like column shape which defines an inner space therein with an open upper face and an open lower face. The holder  421  may be constituted by a plurality of divided members or be integrated with the fixed mold plate  605 . The holder  421  corresponds to the guiding body  31  of the sliding mechanism  1  of the first embodiment and, as with the guiding body  31 , guides the movable piece  405 , which corresponds to the second piece  21  of the sliding mechanism  1  of the first embodiment, in the first direction and subsequently in the second direction. 
     Further, the holder  421  houses the retaining piece  461 , which corresponds to the first piece  11  of the sliding mechanism  1  of the first embodiment, in an advanceable and retractable manner and guides the retaining piece  461  in the vertical direction. The holder  421  also guides the cutter  491  attached to the sliding piece  471  such that the cutter  491  cuts the gate G, and the cutter  491  after cutting the gate G is moved away from the gate G. 
     The holder  421  includes a left side wall  426  which is shorter than a back face wall  434  of the holder  421  and is opened below the left side face. This opening allows the cutter  491  and a presser  407  for the movable piece  405  to move out. A right side wall  429  of the holder is also shorter than the back face wall  434 , and the holder  421  is opened below the right side face. The right side wall  429  includes a stepped portion  431  protruding inward at a lower position on the right side wall  429 . A left-side-wall inner surface  427  and a right-side-wall inner surface  430  serve as guides for the retaining piece  461 , and the stepped portion  431  on the right side serves as a stopper for the retaining piece  461 . An inner side of the stepped portion  431  of the right side wall  429  is an inclined surface  432  which is inclined downward to the right. 
     As with the guiding body  31  of the first embodiment, the holder  421  includes first guiding grooves  441  which guides the movable piece  405  on a front-face-wall inner surface (not illustrated) and a back-face-wall inner surface  435 . Each first guiding groove  441  is a recessed groove and includes a first guiding part  445  which guides the movable piece  405  in the first direction and second guiding parts  448  which guide the movable piece  405  in the second direction. The first guiding part  445  is parallel to the left side wall  426  so as to extend along the left side wall  426  and guides the movable piece  405  in the Y direction (i.e., first direction). There are two second guiding parts  448  arranged in the vertical direction and inclined diagonally downward to the right, and the second guiding parts  448  guide the movable piece  405  diagonally downward to the right (i.e., in the second direction). The axes of the two second guiding parts  448  arranged in the vertical direction extend parallel to each other and intersect with the axis of the first guiding part  445 . The second guiding parts  448  are connected to the first guiding part  445  (see  FIG. 27 ). 
     The holder  421  includes second guiding grooves  452  which guide the sliding piece  471  on the front-face-wall inner surface (not illustrated) and the back-face-wall inner surface  435 . Each second guiding groove  452  is a recessed groove and is inclined such that an upper part of the second guiding groove  452  is located at a middle leftward position, and a lower part of the second guiding groove  452  is located below the right side wall  429 . The second guiding grooves  452  guide the sliding piece  471  such that the cutter  491  coupled to the sliding piece  471  cuts the gate G and further guides the sliding piece  471  such that the cutter  491  after cutting the gate G is moved away from the gate G. 
     The holder  421  is attached to the housing part  608  through a lock pin  455  such that an upper face  495  of the cutter  491  is flush with the bottom face  610  of the fixed mold plate  605  when the mold is clamped. Therefore, a lower part of the holder  421  including the opening for the cutter  491  to move in and out projects downward from the bottom face  610  of the fixed mold plate  605  (see  FIG. 25 ). 
     The retaining piece  461  has a cuboid shape and includes a dovetail groove line  467  extending in the X direction at a middle part of the bottom face in the Z direction. The retaining piece  461  also includes protruding lines (dovetail-groove protruding lines)  468 ,  469  located on the front face side and the back face side and extending in the X direction on the opposite sides of the dovetail groove line  467  (see  FIG. 27 ). The dovetail groove line  467  slidably receives a protruding line (dovetail-groove protruding line)  476  of the sliding piece  471 , and the protruding lines  468 ,  469  are slidably fitted with front and back clicks  408 ,  409  of the movable piece  405 , respectively. The retaining piece  461  also includes a recessed part  463  which opens on an upper face  462  of the retaining piece  461  and houses a spring  470 . The spring  470  ejects the retaining piece  461  downward. 
     The retaining piece  461  advances and retracts in a demolding direction (i.e., Y direction) in conjunction with opening and closing of the molding die  400 , while the left side face  465  and the right side face  466  are slidably in contact with the left-side-wall inner surface  427  and the right-side-wall inner surface  430  of the holder  421 . 
     The sliding piece  471  includes a body  475  including: a cuboid-shaped part  472 ; a triangular-shaped part  473  which is connected to a right end of the cuboid-shaped part  472  and has a triangular shape in a front view; and a prismatic column part  474  which is connected to an upper face  478  of the cuboid-shaped part  472  and a left side face of the triangular-shaped part  473 . The cuboid-shaped part  472  includes, at a left end thereof, a recessed part  477  which shapes a runner R. The cuboid-shaped part  472  also includes, at a middle part of the upper face  478 , an attaching part  479  for attaching the cutter  491 . 
     The triangular-shaped part  473  of the body  475  has a triangular shape such that a lower part thereof is wider than an upper part thereof in a front view, and is disposed perpendicular to the cuboid-shaped part  472 . An upper end of the triangular-shaped part  473  is located above the upper face  478  of the cuboid-shaped part  472 , and a bottom face of the triangular-shaped part  473  is flush with a bottom face of the cuboid-shaped part  472 . The triangular-shaped part  473  includes, at right ends of front face and a back face of the triangular-shaped part  473 , protruding lines  480  extending along a right side face of the triangular-shaped part  473 . The protruding lines  480  are slidably fitted into second guiding grooves  452  of the holder  421 . 
     The body  475  includes a protruding portion  481  having a triangular shape in a front view, at a right bottom part of the triangular-shaped part  473 . The protruding portion  481  includes a left side face  482  which is an inclined surface and serves as a lock click configured to be locked to a pulling piece  730  attached to the movable mold plate  711 . 
     An upper end of the prismatic column part  474  of the body  475  is at a same height as an upper end of the triangular-shaped part  473 , and there is a protruding line (dovetail-groove protruding line)  476  protruding upward from the upper end of the prismatic column part  474  of the body  475 . The protruding line  476  extends parallel to the X direction (see  FIG. 27 ). A width (in the Z direction) of the prismatic column part  474  of the body  475  is smaller than a width (in the Z direction) of the cuboid-shaped part  472  and the triangular-shaped part  473 . 
     The cutter  491  has a flat plate shape and includes, in the vicinity of a tip end portion thereof, a through hole  492  which shapes a gate G. The through hole  492  is tapered so as to have a smaller dimension on a side connected to a cavity part than on a side connected to a runner R, and a left side surface of the through hole  492  is a blade for cutting the gate G. The inclined part which makes the through hole  492  wider on the side of the runner R than on the side of the cavity part serves as a withdrawal space for a molding material left in the runner R after the gate G is cut. These features make it possible to cut the gate G reliably and clearly. 
     The base end portion  493  of the cutter  491  is fixed to the attaching part  479  on the upper face  478  of the cuboid-shaped part  472  of the sliding piece  471 . Once the cutter  491  is attached to the sliding piece  471 , the through hole  492  is located above the recessed part  477  at the left end of the cuboid-shaped part  472 , so that the through hole  492  is communicated with the recessed part  477 . Thus, a flow path is defined which connects the runner R, the gate G, and further the cavity part. 
     The movable piece  405  is configured to press a part of the molded product P adjacent to the gate G so as to prevent the molded product P from being pulled by the cutter  491  to move when the cutter  491  attached to the sliding piece  471  slides to cut the gate G. The movable piece  405  includes a body  406  having a prismatic column shape, and the body  406  integrally includes a presser  407  which protrudes to the left side at a lower part of the body  406 . The presser  407  has a flat plate shape. 
     The movable piece  405  includes, at an upper part of the body  406 , a pair of the front and back clicks  408 ,  409  which protrude from the upper face of the movable piece  405 . The click  408  is located on an upper part of a front face wall  410  of the movable piece  405  and extends parallel to the X direction, and the click  409  is located in an upper part of a back face wall  411  of the movable piece  405  and extends parallel to the X direction. The protruding lines  468 ,  469  of the retaining piece  461  and the clicks  408 ,  409  of the movable piece  405  constitute a dovetail groove structure for slidable coupling. The movable piece  405  also includes, in a right side face of the body  406 , a recessed part  416  which slidably receives the prismatic column part  474  of the sliding piece  471 . 
     The movable piece  405  includes upper and lower protruding lines  412 ,  413  on the front face wall  410  as well as an upper protruding line (not illustrated) and a lower protruding line  415  on the back face wall  411 . The upper protruding line  412  and the upper protruding line (not illustrated) correspond to each other in terms of the shape, position, and angle. Similarly, the lower protruding line  413  and the lower protruding line  415  correspond to each other in terms of the shape, position, and angle. 
     The upper and lower protruding lines  412 ,  413 ,  415  correspond to the clicks  280  of the gate cutting mechanism  201  of the fourth embodiment and are slidably fitted into the first guiding grooves  441 . Each protruding line includes left and right wall surfaces which serve as first sliding surfaces, and upper and lower wall surfaces which serve as second sliding surfaces. With reference to the protruding line  413  as an example, the left side face  417  and the right side face  418  serve as the first sliding surfaces, and the upper side face  419  and the lower side face  420  serve as the second sliding surfaces. 
     In the gate cutting mechanism  401  having the above constitution, the protruding line  476  of the sliding piece  471  with the cutter  491  attached thereto is fitted into the dovetail groove  467  of the retaining piece  461 , and further the clicks  408 ,  409  of the movable piece  405  are fitted so as to be engaged with the front and back protruding lines  468 ,  469  of the retaining piece  461 . In this state, when the prismatic column part  474  of the sliding piece  471  is fitted into the recessed part  416  of the movable piece  405 , the bottom face of the presser  407  of the movable piece  405  slidably comes into contact with the upper face  478  of the prismatic column part  474  of the sliding piece  471  and the upper face  495  of the cutter  491 . 
     With the retaining piece  461 , the sliding piece  471 , and the movable piece  405  coupled to each other, they are incorporated into the holder  421  and are fixed to the housing part  608  of the fixed die  603 . 
     An operation and effects of the molding die  400  and the gate cutting mechanism  401  of the present embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding in the molding die  400 . 
     When the mold is closed, the sliding piece  471  is arranged such that a tip end of the cutter  491  is fitted into the recessed part  726  of the movable mold plate  711 , and the bottom face of the body  475  of the sliding piece  471  is in contact with the upper face of the movable mold plate  711 . Further the lock click  481  of the sliding piece  471  is locked to the pulling piece  730 , and a lower part of the right side face of the sliding piece  471  is in contact with the guide piece  630 . As for the movable piece  405 , the left side face of the body  406  is in contact with the left-side-wall inner surface  427  of the holder  421 , the right side face of the body  406  is in contact with the left side face of the triangular-shaped part  473  of the sliding piece  471 , and a tip end of presser  407  is located within the cavity (see  FIG. 24 ). The protruding lines  480  of the sliding piece  471  are fitted into the second guiding grooves  452 , and the protruding lines  412 ,  413 ,  415  of the movable piece  405  are fitted into the first guiding parts  445  of the first guiding grooves  441 . 
     In this state, the runner R, the gate G, and the cavity part are communicated with each other. The cavity part is a space for molding the molded product P to be shaped by the cavity  606  of the fixed die  603  and the core  712  of the movable die  703  when the mold is closed. When the mold is closed, a molten resin is injected from a non-illustrated injection device, and the resin passes through a sprue (not illustrated) in the fixed die  603 , and then through the runner R and the gate G and fills in the cavity part. After a pressure holding step and a cooling step, the molded product P is taken out. The processes of opening the mold and taking out the molded product P are performed according to the following procedure. 
     Once the movable die  703  retracts and the mold starts to open, the retaining piece  461  is pushed downward (i.e., in the −Y direction) by the spring  470 . The sliding piece  471  slidably coupled to the retaining piece  461  is guided by the second guiding grooves  452  and moves diagonally downward to the right with respect to the holder  421 . Thus, the cutter  491  attached to the sliding piece  471  slides in the −X direction with respect to the movable mold plate  711 , and the blade in the through hole  492  moves across the gate G to cut the gate G connected to the molded product P (see  FIG. 25 ). 
     At the same time, the movable piece  405  slidably coupled to the retaining piece  461  is guided by the first guiding parts  445  of the first guiding grooves  441  in the holder  421  to move downward (i.e., in the −Y direction). Unlike the sliding piece  471 , the movable piece  405  does not move in the +X direction or in the −X direction, so that the movable piece  405  remains in the same state with respect to the molded product P as it was at the time of the mold closed state (see  FIG. 25 ). 
     Thus, the gate G can be cut with the molded product P pressed by the presser  407  of the movable piece  405  (see  FIG. 25 ). In addition, as the cutter  491  slides rightward (i.e., in the −X direction), the through hole  492  also pulls the resin in the runner R rightward (i.e., in the −X direction). Thus, the resin in the runner R can be easily removed from the runner R. 
     When the movable mold  703  retracts further, the movable piece  405  is guided by the second guiding parts  448  of the first guiding grooves  441  to be guided downward to the right. Thus, the presser  407  of the movable piece  405  is moved away from the molded product P. Then, the molded product P is ejected by an ejector pin (not illustrated) such that it can be taken out. 
     As described above, the molding die  400  and the gate cutting mechanism  401  can achieve compact and simple configurations and can operate such that the gate G can be cut easily and reliably prior to taking out the molded product P. In particular, the gate G is cut with a part of the molded product P adjacent to the gate G pressed by the movable piece  405 , and therefore, the gate G can be cut reliably and clearly. Further, the molding die  400  can move the movable piece  405  in conjunction with mold opening to allow a material left in the runner R to be removed, and therefore, the molding die  400  is highly convenient for use. 
     Moreover, the gate cutting mechanism  401  can be incorporated into the molding die  400  with the sliding piece  471 , the movable piece  405 , and the retaining piece  461  housed in the holder  421 , and therefore, the gate cutting mechanism  401  can have a compact configuration and be easily attached to the molding die  400 . In particular, the holder  421 , the retaining piece  461 , the sliding piece  471 , and the movable piece  405  can be assembled into a single independent unit; the gate cutting mechanism  401  as a single unit can be more easily attached to the molding die  400 . 
       FIG. 28  is a cross-sectional view showing a main part of a molding die  500  including a gate cutting mechanism  501  according to a seventh embodiment of the present invention in a mold closed state.  FIG. 29  and FIG. show cross-sectional views showing the main part of the molding die  500  including the gate cutting mechanism  501  according to the seventh embodiment of the present invention during a process of opening the mold.  FIG. 31  is an exploded view showing features of the gate cutting mechanism  501  according to the seventh embodiment of the present invention. Features corresponding to the features of the molding die  400  including the gate cutting mechanism  401  according to the sixth embodiment of the present invention as shown in  FIG. 24  to  FIG. 27  are denoted with like reference numerals, and description thereof is omitted. 
     As with the molding die  400  of the sixth embodiment, the molding mold  500  includes: a fixed die  603  which molds an external surface of a molded product P; a movable die  703  which molds an internal surface of the molded product P; and further a gate cutting mechanism  501  which cuts a gate G. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  603  in  FIG. 28 , and the “lower” side means the side of the movable die  703  in  FIG. 28 . In the following description, the “left” side corresponds to the left side in  FIG. 28 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     Since the fixed die  603  of the seventh embodiment has a same configuration as that of the fixed die  603  of the sixth embodiment, the features are denoted with like reference numerals, and description thereof is omitted. Similarly, since the movable die  703  of the seventh embodiment has a same configuration as that of the movable mold  703  of the sixth embodiment, the features are denoted with like reference numerals, and description thereof is omitted. 
     The gate cutting mechanism  501  is operable to cut a gate G connecting a molded product P to a runner R and includes: a cutter  591  which cuts the gate G; a sliding piece  571  which is coupled to the cutter  591  to slide cutter  591 ; a retaining piece  561  which slidably retains the sliding piece  571 ; a holder  521  which houses the retaining piece  561  in an advanceable and retractable manner; and a movable piece  505  which presses the molded product P. The gate cutting mechanism  501  of the present embodiment employs the sliding mechanism  50  of the second embodiment. 
     The movable piece  505  of the present embodiment corresponds to the second piece  61  of the sliding mechanism  50  of the second embodiment; the retaining piece  561  corresponds to the first piece  11 ; and the holder  521  corresponds to the guiding body  81 . In the present embodiment, the movable piece  505  corresponds to a slider, and the holder  521  corresponds to a guide body. The retaining piece  561  is slidably coupled to the movable piece  505 . The retaining piece  561  corresponds to a coupling member, and left- and right-side-wall inner surfaces  527 ,  530  of the holder  521  correspond to a coupling member guide unit. 
     The holder  521  includes two half holder members  525  ( 525   a ,  525   b ) of a same shape which are assembled together, each half holder member having a channel-shaped or U-shaped cross section, and the holder has a box-like column shape which defines an inner space therein with an open upper face and an open lower face. The holder  521  may be constituted by a plurality of divided members or be integrated with the fixed mold plate  605 . The holder  521  corresponds to the guiding body  81  of the sliding mechanism  50  of the second embodiment and, like the guiding body  81 , guides the movable piece  505 , which corresponds to the second piece  61  of the sliding mechanism  50  of the second embodiment, in the first direction and subsequently in the second direction. 
     Further, the holder  521  houses the retaining piece  561 , which corresponds to the first piece  11  of the sliding mechanism  50  of the second embodiment, in an advanceable and retractable manner, and guides the retaining piece  561  in the vertical direction. The holder  521  also guides the cutter  591  attached to the sliding piece  571  such that the cutter  591  cuts the gate G, and the cutter  591  after cutting the gate G is moved away from the gate G. 
     The holder  521  includes stepped portions  528  ( 528   a ,  528   b ) protruding inward at lower parts of right side walls  526  ( 526   a ,  526   b ) of the holder  521 , and lower inner surfaces of the stepped portions  528  are inclined surfaces  531  ( 531   a ,  531   b ). Right-side-wall inner surfaces  527  ( 527   a ,  527   b ) and left-side-wall inner surfaces  530  ( 530   a ,  530   b ) serve as guides for the retaining piece  561 , and the stepped portions  528  serve as stoppers for the retaining piece  561 . 
     As with the guiding body  81  of the second embodiment, the holder  521  includes a first guiding groove  541  which guides the movable piece  505  on a front-face-wall inner surface  533  of the holder  521 . The first guiding groove  541  is a recessed, inclined linear groove which has an upper part located on the right and a lower part located on the left when the front-face-wall inner surface  533  is viewed straightforward. The left-side inner wall surface  530   a  of the front face wall of the holder  521  and the inclined surface  531   a  of the front-face-wall stepped portion  528   a  of the holder  521  serve as a first guide unit which guides the movable piece  505  in the first direction. A side surface  542  of the first guiding groove  541  and the inclined surface  531   a  of the front-face-wall stepped portion  528   a  of the holder  521  serve as a second guide unit which guides the movable piece  505  in the second direction. 
     The holder  521  also includes a second guiding groove  552  which guides the sliding piece  571  on a back-face-wall inner surface  535  of the holder  521 . The second guiding groove  552  is a recessed, inclined linear groove which has an upper part located on the left and a lower part located on the right when the back-face-wall inner surface  535  is viewed straightforward. The second guiding groove  552  guides the sliding piece  571  such that the cutter  591  coupled to the sliding piece  571  cuts the gate G, and further guides the sliding piece  571  such that the cutter  591  after cutting the gate G is moved away from the gate G. 
     The holder  521  is attached to the housing part  608  in the fixed mold plate  605  through the lock pin  455 . When the holder  521  is attached to the housing part  608 , a bottom part of the holder  521  is flush with the bottom face  610  of the fixed mold plate  605  (see  FIG. 28 ). 
     The retaining piece  561  has a block shape and includes a protruding line  567  (dovetail-groove protruding line) which extends from the left to the right, on a bottom face of the retaining piece  561  which extends downward to the right in a front view. The retaining piece  561  includes a cutout part  568  below a right side face  566  of the retaining piece  561 . The cutout part  568  can be locked to the stepped portions  528  of the holder  521 . The retaining piece  561  also includes a recessed part  563  which opens on an upper face  562  thereof and houses a spring  470  (see  FIG. 31 ). The spring  470  ejects the retaining piece  561  downward. 
     The retaining piece  561  advances and retracts in a demolding direction (i.e., Y direction) in conjunction with opening and closing of the molding die  500 , while the left side face  565  and the right side face  566  of the retaining piece  561  are slidably in contact with the left-side-wall inner surfaces  530  and the right-side-wall inner surfaces  527  of the holder  521 . 
     The sliding piece  571  includes a body  572  and a second lock body  580  fixed to an upper face  573  of the body  572 . The body  572  includes a recessed part  574  which shapes a runner R on the left side face of the body  572 . The body  572  also includes an attaching part  577  for attaching the cutter  591  at an upper left part of the body  572 , and an upper part of the attaching part  577  is a housing part for a presser plate  507  of the movable piece  505 . A right side face  575  of the body  572  is an inclined surface which extends diagonally downward to the right in a front view. 
     The second lock body  580  is a plate-like member having a thickness equivalent to approximately half a width (in the Z direction) of the body  572 . In a front view, an upper part of the second lock body  580  extends slightly downward to the right, and a right side face  582  of the second lock body  580  is also an inclined surface extending downward to the right. A left side face  583  of the second lock body  580  extends perpendicular to the bottom face of the second lock body  580 , and when attached to the body  572 , extends perpendicular to the upper face  573  of the body  572 . 
     The second lock body  580  includes, at an upper part of a front face  584  thereof, a recessed groove so as to form a click  585 . The click  585  is slidably locked to a back face of the protruding line  567  of the retaining piece  561 . The second lock body  580  also includes, on a back face thereof, a protruding line  586  extending along the right side face  582 . The protruding line  586  is slidably fitted into the second guiding groove  552  of the holder  521 . 
     The cutter  591  has a flat plate shape and includes, near a tip end portion thereof, a through hole  592  which shapes a gate G. The through hole  592  is tapered so as to have a smaller dimension on a side connected to a cavity part than on a side connected to the runner R, and a left side surface of the through hole  592  is a blade for cutting the gate G. The inclined part which makes the through hole  592  wider on the side of the runner R than on the side of the cavity part serves as a withdrawal space for a molding material left in the runner R after the gate G is cut. These features make it possible to cut the gate G reliably and clearly. 
     A base end portion of the cutter  591  is fixed to the attaching part  577  which is located at an upper left part of the body  572  of the sliding piece  571 . When the cutter  591  is attached to the sliding piece  571 , the through hole  592  is located above the recessed part  574  at a left end of the body  572 , and the through hole  592  is communicated with the recessed part  574 . Thus, a flow path is defined which connects the runner R, the gate G, and further the cavity part. 
     The movable piece  505  is configured to press a part of the molded product P adjacent to the gate G so as to prevent the molded product P from being pulled by the cutter  591  to move when the cutter  591  attached to the sliding piece  571  slides to cut the gate G. The movable piece  505  includes a presser plate  507  and a first lock body  510  attached to an upper face of the presser plate  507 . 
     The first lock body  510  is a plate-like member having a thickness equivalent to approximately half a width (in the Z direction) of the presser plate  507 , and an upper part of the first lock body  510  extends slightly downward to the right in a front view. A right side face  512  of the first lock body  510  is an inclined surface extending downward to the right, and the right side face  512  includes, at a lower part thereof, an inclined surface  514  which is set back with respect to an upper part and a middle part thereof in a front view. A left side face  511  of the first lock body  510  extends perpendicular to the bottom face of the first lock body  510 , and when attached to the presser plate  507 , extends perpendicular to an upper face  508  of the presser plate  507 . The inclined surface  514  and the left side face  511  correspond to a first engagement unit which slidably comes into engagement with a first guide unit. 
     The first lock body  510  includes, at an upper part of a back face thereof, a recessed groove so as to form a click  515 . The click  515  is slidably locked to a front face of the protruding line  567  of the retaining piece  561 . The first lock body  510  also includes, on a front face thereof, a protruding line  517  extending along the right side face  512 . The protruding line  517  is slidably fitted into a first guiding groove  542  of the holder  521 , and the protruding line  517  has a width L 2  smaller than a width L 1  of the first guiding groove  542 . The protruding line  517  and the right side face  512  correspond to a second engagement unit which slidably comes into engagement with a second guide unit. 
     The gate cutting mechanism  501  having the above constitution is fixed to the housing part  608  of the fixed die  603  in the following manner. The presser plate  507  of the movable piece  505  is fitted into an upper part of the attaching part  577  of the sliding piece  571  with the cutter  591  attached thereto, and the click  515  of the first lock body  510  and the click  585  of the second lock body  580  are fitted to the protruding line  567  of the retaining piece  561 , with the front face  584  of the second lock body  580  of the sliding piece  571  abutted with the back face of the first lock body  510  of the movable piece  505 . 
     With the retaining piece  561 , the sliding piece  571 , and the movable piece  505  coupled together, they are incorporated into the holder  521  and are fixed to the housing part  608  of the fixed die  604 . 
     An operation and effects of the molding die  500  and the gate cutting mechanism  501  of the present embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding in the molding die  500 . 
     When the mold is closed, the sliding piece  571  is arranged such that a tip end of the cutter  591  is fitted into the recessed part  708  of the movable mold plate  711 , and the protruding line  586  of the second lock body  580  is slidably fitted into the second guiding groove  552  of the holder  521 . Further, the right side face  575  of the body  572  of the sliding piece  571  is in contact with the guide piece  630 . The left side face  583  of the second lock body  582  of the sliding piece  571  is in contact with the left-side-wall inner surface  530   b  of the holder  521 . 
     As for the movable piece  505 , the bottom face of the presser plate  507  is in contact with the upper face of the cutter  591 , and a tip end of the presser plate  507  is located within the cavity part (see  FIG. 28 ). The bottom face of the first lock body  510  of the movable piece  505  is in contact with the upper face  573  of the body  572  of the sliding piece  571 , and the protruding line  517  is slidably fitted into the first guiding groove  541  of the holder  521 . In this state, the protruding line  517  is arranged such that a right side face thereof, when the first lock body  510  is viewed straightforwardly, is in contact with a right side surface  543  of the second guiding groove  541 , and the inclined surface  514  is in contact with the inclined surface  531   a  of the stepped portion  528  of the holder  521 . On the other hand, a left side face of the protruding line  517  is not in contact with and is separated from the left side surface  542  of the first guiding groove  541  (see  FIG. 28 ). The left side face  511  of the first lock body  510  of the movable piece  505  is in contact with the left-side-wall inner surface  530   a  of the holder  521 . 
     In this state, the runner R, the gate G, and the cavity part are communicated with each other. The cavity part is a space for molding the molded product P to be shaped by the cavity  606  of the fixed die  603  and the core  712  of the movable die  703  when the mold is closed. When the mold is closed, a molten resin is injected from a non-illustrated injection device, and the resin passes through a sprue (not illustrated) in the fixed die  603 , and then through the runner R and the gate G, and fills in the cavity part. After a pressure holding step and a cooling step, the molded product P is taken out. The process of opening the mold is performed according to the following procedure. 
     Once the movable die  703  retracts and the mold starts to open, the retaining piece  561  is pushed downward (i.e., in the −Y direction) by the spring  470 . The sliding piece  571  slidably coupled to the retaining piece  561  is guided by the second guiding groove  552  and moves diagonally downward to the right with respect to the holder  521 . Thus, the cutter  591  attached to the sliding piece  571  slides in the −X direction with respect to the movable mold plate  711 , and the blade in the through hole  592  moves across the gate G to cut the gate G connected to the molded product P (see  FIG. 29 ). 
     At the same time, the movable piece  505  slidably coupled to the retaining piece  561  moves downward (i.e., first direction, −Y direction) such that the left side face of the protruding line  517  of the first lock body  510  comes into contact with the left side surface  542  of the first guiding groove  541  of the holder  521 . At this point, unlike the sliding piece  571 , the movable piece  505  does not move in the +X direction or in the −X direction. This is because when the mold is clamped, the left side face of the protruding line  517  of the first lock body  510  of the movable piece  505  is separated from the left side surface  542  of the first guiding groove  541  of the holder  521  (see  FIG. 29 ). 
     Thus, the gate G can be cut with the molded product P pressed by the presser plate  507  of the movable piece  505  (see  FIG. 29 ). In addition, as the cutter  591  slides rightward (i.e., in the −X direction), the through hole  592  also pulls the resin in the runner R rightward (i.e., in the −X direction) after the gate G is cut. Thus, the resin in the runner R can be easily removed from the runner R. 
     When the movable die  703  retracts further, the movable piece  505  moves diagonally downward to the right, i.e., in the second direction, as the protruding line  517  of the first lock body  510  is guided by the first guiding groove  541 . At this time, the right side face  512  of the first lock body  510  is slidably in contact with the inclined surface  531   a  of the stepped portion  528   a  of the holder  521 , so that the movable piece  505  moves diagonally downward to the right without staggering. Thus, the presser plate  507  of the movable piece  505  is moved away from the molded product P. Then, the molded product P is ejected by an ejector pin (not illustrated) such that it can be taken out. 
     As described above, the molding die  500  and the gate cutting mechanism  501  can achieve compact and simple configurations and can operate such that the gate G can be cut easily and reliably prior to taking out the molded product P. In particular, the gate G is cut with a part of the molded product P adjacent to the gate G pressed by the movable piece  505 , and therefore, the gate G can be cut reliably and clearly. Further, the molding die  500  can move the movable piece  505  in conjunction with mold opening to allow a material left in the runner R to be removed, and therefore, the molding die  500  is highly convenient for use. 
     Moreover, the gate cutting mechanism  501  can be incorporated into the molding die  500  with the sliding piece  571 , the movable piece  505 , and the retaining piece  561  housed in the holder  521 , and therefore, the gate cutting mechanism  501  can have a compact configuration and be easily attached to the molding die  500 . In particular, the holder  521 , the retaining piece  561 , the sliding piece  571  including the cutter  591 , and the movable piece  505  can be assembled into a single independent unit; the gate cutting mechanism  501  as a single unit can be more easily attached to the molding die  500 . 
     Other embodiments of the sliding mechanism and the undercut processing mechanism according to the present invention will be described below. 
       FIG. 32  is an exploded view showing features of a sliding mechanism  6  according to an eighth embodiment of the present invention.  FIG. 33  shows a changeover switch  7  which employs the sliding mechanism  6  according to the eighth embodiment of the present invention. Features corresponding to the features of the sliding mechanism  1  and the changeover switch  2  of the first embodiment as shown in  FIG. 1  to  FIG. 3  are denoted with like reference numerals, and description thereof is omitted. 
     The sliding mechanism  6  according to the eighth embodiment of the present invention has a same basic configuration as that of the sliding mechanism  1  of the first embodiment. However, the shapes of the guiding groove  45  and the click  30  differ from the shapes of the guiding groove  38  and the click  23  of the first embodiment. Further, the upper face  14  of the first piece  11  and the bottom face  28  of the second piece  21  are coupled together through a dovetail groove structure. Specifically, a protruding line (dovetail-groove protruding line)  15  is located on the upper face  14  of the first piece  11 , and a dovetail groove  29  which slidably receives the protruding line  15  is located on the bottom face  28  of the second piece  21 . 
     In the present embodiment, the second piece  21  corresponds to a slider; the guiding body  31  corresponds to a guide body; the guiding groove  45  corresponds to a guide unit; the first guiding part  39  corresponds to a first guide unit; and the second guiding part  42  corresponds to a second guide unit. The click  30  corresponds to an engagement unit; a first sliding surface of the click  30  corresponds to a first engagement unit; and a second sliding surface of the click corresponds to a second engagement unit. The first piece  11  corresponds to a coupling member, and the left- and right-side-wall inner surfaces  34 ,  36  of the holder  31  correspond to a coupling member guide unit. 
     In the sliding mechanism  6  of the eighth embodiment, the guiding groove  45  includes four guiding parts, namely, a first guiding part  39  extending in a first direction, a second guiding part  42  extending in a second direction, a third guiding part  46  extending in a third direction, and a fourth guiding part  48  extending in a fourth direction. As with the guiding part of the first embodiment, the guiding parts are sequentially connected in the order of the first guiding part  39 , the second guiding part  42 , the third guiding part  46 , and the fourth guiding part  48 . The four guiding parts including their connection parts has a same width (which is a distance between left and right side surfaces). The first guiding part  39  and the third guiding part  46  of the guiding groove  45  are arranged such that their center axes M 1 , M 3  are parallel to each other. That is, the first direction is parallel to the third direction. In contrast, the second direction and the fourth direction differ from all other directions than themselves. 
     If, in the case where the guiding groove includes three or more guiding parts, the three or more guiding parts extend in two different directions (herein, parallel guiding directions are considered as a same direction), it is possible to use a same click  23  as that of the first embodiment. This applies to the case where the guiding groove  45  only includes the first guiding part  39 , the second guiding part  42 , and the third guiding part  46  in the sliding mechanism  6  according to the eighth embodiment of the present invention. 
     In the sliding mechanism  6  according to the eighth embodiment of the present invention, however, the guiding groove  45  includes the four guiding parts  39 ,  42 ,  46 ,  48 , and the second direction of the second guiding part  42  is different from the fourth direction  48 , so that the sliding mechanism  6  of the eighth embodiment includes three different guiding directions. Due to its configuration, the click  23  of the first embodiment is not applicable to an application with three different guiding directions. In such a case, the click  30  may be shaped in a cylindrical or columnar form, as shown in  FIG. 32  (B). A click having a round external shape in a transverse section and an outer diameter fittable into the guiding parts without a gap can be applicable to even an application with three or more guiding directions. 
     In Chart (A) of  FIG. 33 , the click  30  comes into line contact with the opposite side surfaces  40 ,  41  of the first guiding part  39  at two lines, namely, line A and line B in Chart (B) of  FIG. 32 . Thus, the line A and line B of the click  30  serve as first sliding surfaces. At an interface between the first guiding part  39  and the second guiding part  42  in Chart (B) of  FIG. 33 , the click comes into line contact at two lines, namely, line C and line D in Chart (B) of  FIG. 32 . Further, when moving in the second guiding part  42  in  FIG. 33 , the click  30  comes into line contact with the opposite side surfaces  43 ,  44  at two lines, namely, line E and line F in Chart (B) of  FIG. 32 . Thus, the line E and line F of the click  30  serve as second sliding surfaces. Since the third guiding part  46  is parallel to the first guiding part  39  as shown in  FIG. 33 , when the click moves in the third guiding part  46 , the click  30  comes into line contact at two lines, namely, line A and line B in Chart (B) of  FIG. 32 , as with the case of moving in the first guiding part  39 . Since the fourth guiding part  48  extends in a direction different from directions of the all other guiding parts as shown in  FIG. 33 , when the click  30  moves in the fourth guiding part  48 , the click  30  comes into line contact with the opposite side surfaces of the fourth guiding part  48 , at other lines than the line A, the line B, the line C, the line D, the line E, and the line F in Chart (B) of  FIG. 32 . 
     In the sliding mechanism  6  of the eighth embodiment, the first piece  11  and the second piece  21  are coupled together through a dovetail groove structure. Such a structure has advantages in that it prevents the constituting members from easily disassembled, so that the sliding mechanism  6  can be assembled into a single unit, and moreover, in that a posture of the second piece  21  can be maintained constant. 
     In the sliding mechanism  6  of the eighth embodiment, as with the first embodiment, if the upper face  14  of the first piece  11  and the bottom face  28  of the second piece  21  are simply brought into surface contact, the second piece  21  would be tilted to the left and right around the click  30  as a pivot point, when a force acts on a tip end portion  20  of the second piece  21  to move the tip end portion  20  to the left and right (+X direction, −X direction). In contrast, where the first piece  11  and the second piece  21  are coupled together through a dovetail groove structure, the opposite side faces  12 ,  13  of the first piece  11  are in surface contact with the left- and right-side-wall inner surfaces  34 ,  36  of the guiding body  31 , so that the second piece  21  will not be tilted to the left and right. 
     The changeover switch  7  as shown in  FIG. 33  can turn on and off a first lamp  5   a  to a third lamp  5   c  in the same manner as the changeover switch  2  as shown in  FIG. 3 . Since the guiding groove  45  includes the four guiding parts  39 ,  42 ,  46 ,  48 , the switch  7  can make a switchover to turn on and off four lamps. 
       FIG. 34  is an exploded view showing features of an undercut processing mechanism  103  according to a ninth embodiment of the present invention.  FIG. 35  is a cross-sectional view of a molding die  102  including the undercut processing mechanism  103  according to a ninth embodiment of the present invention when the mold is closed, and  FIG. 36  is a cross-sectional view of the molding die  102  after the mold is opened.  FIG. 37  to  FIG. 39  show cross-sectional views of the molding die  102  including the undercut processing mechanism  103  according to the ninth embodiment of the present invention during a process of ejecting a molded product P. Features corresponding to the features of the undercut processing mechanism  101  and the molding die  100  of the third embodiment as shown in  FIG. 6  to  FIG. 10  are denoted with like reference numerals, and description thereof is omitted. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  600  in  FIG. 35 , and the “lower” side means the side of the movable die  700  in  FIG. 35 . In the following description, the “left” side corresponds to the left side in  FIG. 35 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     The molding die  102  including the undercut processing mechanism  103  according to the ninth embodiment of the present invention has a same basic configuration as that of the molding die  100  including the undercut processing mechanism  101  according to the third embodiment of the present invention. The following description will mainly focus on differences from the molding die  100  including the undercut processing mechanism  101  of the third embodiment. 
     In the molding die  102  of the ninth embodiment, the shape of the molded product P, the shapes and positional relation of the undercut portion P 1  and the protruding portion P 2  are the same as those in the molding die  100  of the third embodiment. As with the undercut processing mechanism  101  of the third embodiment, the undercut processing mechanism  103  of the present embodiment employs the sliding mechanism  1  of the first embodiment. However, the undercut processing mechanism  103  of the present embodiment differs from the undercut processing mechanism  101  of the third embodiment in terms of the first direction and the second direction in which a sliding piece  172  including a molding core  191  at a tip end thereof, which corresponds to the second piece  21 , is guided. In association therewith, the configuration of a guiding groove  142  is different from that of the guiding groove  141  of the third embodiment. 
     In the molding die  102  of the ninth embodiment, a holder  122  corresponds to the guiding body  31  of the sliding mechanism  1  of the first embodiment; and the sliding piece  172  including the molding core  191  at the tip end thereof corresponds to the second piece  21 . The sliding piece  172  corresponds to a slider, and the holder  122  corresponds to a guide body. As described later, a guiding groove  142  corresponds to a guide unit; a first guiding part  145  corresponds to a first guide unit; and a second guiding part  148  corresponds to a second guide unit. A click  180  corresponds to an engagement unit; a first sliding surface of the click  180  corresponds to a first engagement unit; and a second sliding surface of the click  180  corresponds to a second engagement unit. The retaining piece  161  and the sliding piece  172  are slidably coupled together through a dovetail groove structure. The retaining piece  161  corresponds to a coupling member, and left- and right-side-wall inner surfaces  127 ,  130  of the holder  122  correspond to a coupling member guide unit. 
     The holder  122  is the same as the holder  121  of the third embodiment, except for the guiding grooves  142  which are located on the front-face-wall inner surface and the back-face-wall inner surface  135  of the holder  122  and guide the sliding piece  172 . Each guiding groove  142  is a recessed groove and includes a first guiding part  145  which guides the sliding piece  172  in the first direction and a second guiding part  148  which guides the sliding piece  171  in the second direction. 
     The first guiding part  145  is parallel to a mold opening direction of the molding die  102  (i.e., Y direction), and the second guiding part  148  is inclined with respect to the mold opening direction of the molding die  102  (i.e., Y direction). The first guiding part  145  and the second guiding part  148  are connected to each other, and a center axis M 1  of the first guiding part  145  and a center axis M 2  of the second guiding part  148  intersect with each other (see  FIG. 34 ). 
     The first guiding part  145  has a larger height h 1  (in the Y direction) than a height h 2  (in the Y direction) of each click  180  (see  FIG. 34 ). Therefore, when the mold is clamped, there is a space above each click  180 . The first guiding part  145  guides the molding core  191  attached to the sliding piece  172  such that the molding core  191  ejects the molded product P in the mold opening direction (i.e., first direction, Y direction) in a synchronized manner with the ejector mechanism  760 . The second guiding part  148  guides the sliding piece  172  diagonally upward to the left (i.e., in the second direction) such that the molding core  191  attached to the sliding piece  172  is removed from the undercut portion P 1 . In this regard, the direction in which the molding core  191  is removed from the undercut portion P 1  means a direction in which the molding core  191  is removed from the undercut portion P 1  without deforming or damaging the undercut portion P 1 . 
     The center axis M 2  of the second guiding part  148  is defined depending on the shape of the undercut portion P 1  of the molded product P, in particular, on an extent of projection of the undercut portion P 1  in the X direction and a stroke of an ejection pin  745 , so that the molding core  191  can be removed from the undercut portion P 1  of the molded product P upon ejection of the molded product P. The first guiding part  145  and the second guiding part  148  guide the molding core  191  such that the molding core  191  which has been removed from the undercut portion P 1  does not collide with the protruding portion P 2  which is located ahead in a removal direction of the undercut portion P 1  (i.e., X direction). 
     The sliding piece  172  has a same basic configuration as that of the sliding piece  171  of the third embodiment. Upper side faces  183  and lower side faces  184  of the clicks  180  come into contact with left side surfaces  151  of the first guiding parts  145  of the guiding grooves  142  in the holder  122  and a right-side-wall inner surface  130  of the holder  122 , respectively, in order to guide the molding core  191  in the demolding direction (i.e., Y direction). Until the molding core  191  is removed from the undercut portion P 1 , left side faces  181  and right side faces  182  of the clicks  180  are in contact with left side surfaces  149  and right side surfaces  150  of the second guiding parts  148  of the guiding grooves  142  in the holder  122 , respectively. The opposite upper side faces  183  and lower side faces  184  of the clicks  180  serve as first sliding surfaces, and the opposite left side faces  181  and right side faces  182  of the clicks  180  serve as second sliding surfaces. 
     An operation of the undercut processing mechanism  103  in the molding die  102  will be described. When the mold is clamped, the sliding piece  172  is arranged such that the left side faces  181  of the clicks  180  are in contact with the inclined surfaces  152  of the first guiding parts  145 , the upper side faces  183  are in contact with the left side surfaces  151  of the first guiding parts  145 , and the lower side faces  184  are in contact with the right-side-wall inner surfaces  130  of the holder  122  (see  FIG. 35 ). After the mold is opened (see  FIG. 36 ), the ejector rod  768  is pushed up through a non-illustrated ejection device, and the ejector mount plates  762  move upward (i.e., in the Y direction). In association therewith, the ejector pin  763  which is disposed so as to stand on the ejector mount plates  762  ejects the molded product P in the Y direction (see  FIG. 8 ). At the same time, the sliding piece  172  is also guided by the first guiding parts  145  so as to move upward, and the molding piece  191  ejects the molded product P in the Y direction (see  FIG. 37 ). 
     In association with the movement of the ejector mount plates  762 , once the right side faces  182  of the sliding piece  172  are moved to come into contact with the right side surfaces  150  of the second guiding parts  148 , the sliding piece  172  moves in the second direction along the second guiding parts  148 , while the left side faces  181  and the right side faces  182  of the clicks  180  slide on the left side surfaces  149  and the right side surfaces  150  of the second guiding parts  148 , respectively. Thus, the molding core  191  is moved simultaneously in the Y direction and the X direction away from the undercut portion P 1  (see  FIG. 38 ). 
     The first guiding parts  145  and the second guiding parts  148  of the guiding grooves  142  allow movement in the X direction to the extent that the molding core  191  does not collide with the protruding portion P 2  when the ejector mount plates  762  are moved to a highest position. Therefore, the molding core  191  does not collide with the protruding portion P 2  (see  FIG. 38 ). 
     The effects and advantages of the undercut processing mechanism  103  of the ninth embodiment and the molding die  102  including the same are essentially the same as those of the undercut processing mechanism  101  of the third embodiment and the molding die  100  including the same. 
     The undercut processing mechanism  103  can be incorporated into the molding die  102  with the sliding piece  172  and the retaining piece  161  housed in the holder  122 , and therefore, the undercut processing mechanism  103  can have a compact configuration and be easily attached to the molding die  102 . In particular, the holder  122 , the retaining piece  161 , the sliding piece  172 , and the molding core  191  can be assembled into a single independent unit; the undercut processing mechanism  103  as a single unit can be more easily attached to the molding die  102 . 
       FIG. 40  is an exploded view showing features of an undercut processing mechanism  105  according to a tenth embodiment of the present invention.  FIG. 41  is a cross-sectional view of a molding die  104  including an undercut processing mechanism  105  according to the tenth embodiment of the present invention when the mold is closed, and  FIG. 42  is a cross-sectional view of the molding die  104  after the mold is opened.  FIG. 43  to  FIG. 45  show cross-sectional views of the molding die  104  including the undercut processing mechanism  105  according to the tenth embodiment of the present invention during a process of ejecting a molded product P. Features corresponding to the features of the undercut processing mechanism  101  and the molding die  100  of the third embodiment as shown in  FIG. 6  to  FIG. 10  are denoted with like reference numerals, and description thereof is omitted. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  600  in  FIG. 41 , and the “lower” side means the side of the movable die  700  in  FIG. 41 . In the following description, the “left” side corresponds to the left side in  FIG. 41 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     As with the molding die  100  including the undercut processing mechanism  101  of the third embodiment, the molding die  104  including the undercut processing mechanism  105  according to the tenth embodiment of the present invention includes a fixed die  600  and a movable die  700  and is configured to mold a molded product P including an undercut portion P 4 . The following description will mainly focus on differences from the molding die  100  including the undercut processing mechanism  101  of the third embodiment 
     The molded product P to be molded by the molding die  104  of the tenth embodiment includes an undercut portion P 4  which is located at a middle right position and protrudes inward. The undercut portion P 4  has an inverted T shape and includes a tip end portion extending to the left and right. The molded product P also includes a protruding portion P 2  which is located leftward (in the +X direction) with respect to the undercut portion P 4  and protrudes inward and a protruding portion P 3  which is located rightward (i.e., in the −X direction) with respect to the undercut portion P 4  and protrudes inward. 
     As with the undercut processing mechanism  101  of the third embodiment, the undercut processing mechanism  105  of the present embodiment employs the sliding mechanism  1  of the first embodiment. However, due to the position and shape of the undercut portion P 4 , the undercut processing mechanism  105  of the present embodiment significantly differs from the undercut processing mechanism  101  of the third embodiment in terms of the structures and configurations of the molding core and the sliding piece. 
     In the molding die  104  of the tenth embodiment, a holder  123  corresponds to the guiding body  31  of the sliding mechanism  1  of the first embodiment, and sliding pieces  173   a ,  173   b  respectively including molding cores  191   a ,  191   b  at tip ends thereof correspond to the second piece  21 . The sliding pieces  173   a ,  173   b  correspond to a slider, and the holder  123  corresponds to a guide body. As described later, guiding grooves  143   a ,  143   b  correspond to a guide unit; first guiding parts  145   a ,  145   b  correspond to a first guide unit; and second guiding parts  148   a ,  148   b  correspond to a second guide unit. Clicks  180   a ,  180   b  correspond to an engagement unit; first sliding surfaces of the clicks  180   a ,  180   b  correspond to a first engagement unit; and second sliding surfaces of the click  180   a ,  180   b  correspond to a second engagement unit. The retaining piece  161  and the sliding pieces  173   a ,  173   b  are slidably coupled to each other. The retaining piece  161  corresponds to a coupling member, and left- and right-side-wall inner surfaces  127   a ,  127   b ,  130   a ,  130   b  of the holder  122  correspond to a coupling member guide unit. 
     The holder  123  includes two half holder members  125   a ,  125   b  which, when they are used, are assembled into a columnar shape such that guiding grooves  143   a ,  143   b  on the respective half holder members  125   a ,  125   b  are opposed to each other. The holder  123  has a same configuration as the holder  121  of the third embodiment, except for guiding grooves  143   a ,  143   b  which are located on a front-face-wall inner surface  135   a  and a back-face-wall inner surface  135   b  of the holder  123  and guide the sliding pieces  173   a ,  173   b.    
     Since the two half holder members  125   a ,  125   b  have a same shape and a same structure, their structure and the like will be described with reference to one half holder member  125   a . The letters “a” and “b” used with the reference numerals are intended to distinguish the two half holder members  125   a ,  125   b . Left side walls  126   a ,  126   b  of the holder  123  of the present embodiment have a same configuration as the left side wall  126  of the holder  121  of the third embodiment. 
     The guiding groove  143   a  is a recessed groove and includes a first guiding part  145   a  which guides the sliding piece  173   a  in the first direction and a second guiding part  148   a  which guides the sliding piece  173   a  in the second direction. The first guiding part  145   a  extends parallel to a mold opening direction of the molding die  104  (i.e., Y direction), and the second guiding part  148   a  is inclined with respect to the mold opening direction of the molding die  104  (i.e., Y direction). The first guiding part  145   a  and the second guiding part  148   a  are connected to each other, and a center axis M 1  of the first guiding part  145   a  and a center axis M 2  of the second guiding part  148   a  intersect with each other (see  FIG. 40 ). 
     The first guiding part  145   a  guides the sliding piece  173   a  such that a molding core  191   a  attached to the sliding piece  173   a  ejects the molded product P in the mold opening direction (i.e., first direction, Y direction) in a synchronized manner with the ejector mechanism  760 . The second guiding part  148   a  guides the sliding piece  173   a  diagonally upward to the right (i.e., in the second direction) such that the molding core  191   a  attached to the sliding piece  173   a  is removed from the undercut portion P 4 . In this regard, the direction in which the molding core  191   a  is removed from the undercut portion P 4  means a direction in which the molding core  191   a  is removed from the undercut portion P 4  without deforming or damaging the undercut portion P 4 . Note that the second guiding part  148   b  guides the sliding piece  173   b  diagonally upward to the left (i.e., in the second direction) such that the molding core  191   b  attached to the sliding piece  173   b  is removed from the undercut portion P 4 . 
     The center axis M 2  of the second guiding part  148   a  is defined depending on the shape of the undercut portion P 4  of the molded product P, in particular, on an extent of projection of the undercut portion P 4  in the X direction and a stroke of an ejection pin  745 , so that the molding core  191   a  can be removed from the undercut portion P 4  of the molded product P upon ejection of the molded product P. The first guiding part  145   a  and the second guiding part  148   a  guide the molding core  191   a  such that the molding core  191   a  which has been removed from the undercut portion P 4  does not collide with the protruding portion P 3  which is located ahead in a removal direction of the undercut portion P 4  (i.e., −X direction). Similarly, the first guiding part  145   b  and the second guiding part  148   b  guide the molding core  191   b  which has been removed from the undercut portion P 4  does not collide with the protruding portion P 2  which is located ahead in a removal direction of the undercut portion P 4  (i.e., +X direction). 
     In the present embodiment, there are two sliding pieces  173   a ,  173   b . Since the two sliding pieces  173   a ,  173   b  have a same shape and a same structure, their structure and the like will be described with reference to one sliding piece  173   a . The letters “a” and “b” used with the reference numerals are intended to distinguish the two sliding pieces  173   a ,  173   b . For example, the click  180   a  of the sliding piece  173   a  of the present embodiment has a same configuration as the click  180  of the sliding piece  171  of the third embodiment. 
     The sliding piece  173   a  has a same basic configuration as that of the sliding piece  171  of the third embodiment. An upper side face  183   a  and a lower side face  184   a  of the click  180   a  come into contact with a left side surface  146   a  and a right side surface  147   a  of the first guiding part  145   a  of the guiding groove  143   a  in the half holder member  125   a , respectively, in order to guide the molding core  191   a  in the demolding direction (i.e., Y direction). Until the molding core  191   a  is removed from the undercut portion P 4 , a left side face  181   a  and a right side face  182   a  of the click  180   a  are in contact with a right side surface  150   a  and a left side surface  149   a  of the second guiding part  148   a  of the guiding groove  143   a  in the holder  125   a , respectively. The opposite upper side face  183   a  and lower side face  184   a  of the click  180   a  serve as first sliding surfaces, and the opposite left side face  181   a  and right side face  182   a  of the click  180   a  serve as second sliding surfaces. 
     The sliding piece  173   a  includes the click  180   a  only on the front face of the sliding piece  173   a  when the sliding piece  173   a  incorporated into the molding die  104  is viewed straightforwardly, and the sliding piece  173   a  does not include a click on the back face thereof. Similarly, the sliding piece  173   b  includes the click  180   b  only on the back face of the sliding piece  173   b  when the sliding piece  173   b  incorporated into the molding mold  104  is viewed straightforwardly, and the sliding piece  173   b  does not include a click on the front face thereof (see  FIG. 44 ). 
     The sliding piece  173   a  includes, at a lower part of the back face, a recessed groove  177   a  which comes into engagement with the protruding line  168  of the retaining piece  161 . The back face refers to a face opposite to the face on which the click  180   a  is located. The sliding piece  173   b  includes, at a lower part of the front face, a recessed groove  177   b  which comes into engagement with the protruding line  168  of the retaining piece  161 . The front face refers to a face opposite to the face on which the click  180   b  is located. 
     The molding core  191   a  and the molding core  191   b  include recessed grooves  192   a ,  192   b , respectively, for molding the undercut portion P 4 . 
     The holder  123 , the retaining piece  161 , the sliding piece  173   a  including the molding core  191   a , and the sliding piece  173   b  including the molding core  191   b  having the above constitution are incorporated into the holder  123 , with the recessed groove  177   a  of the sliding piece  173   a  receiving the front face of the protruding line  168  of the retaining piece  161 , and the recessed groove  177   b  of the sliding piece  173   b  receiving the back face of the protruding line  168  of the retaining piece  161 . 
     An operation of the undercut processing mechanism  105  in the molding die  104  will be described. After the mold is opened (see  FIG. 42 ), the ejector rod  768  is pushed up through a non-illustrated ejection device, and the ejector mount plates  762  move upward (i.e., in the Y direction). In association therewith, the ejector pin  763  which is disposed so as to stand on the ejector mount plates  762  ejects the molded product P in the Y direction. At the same time, the sliding pieces  173   a ,  173   b  are ejected by the first retaining piece  161  and is guided by the first guiding parts  145  so as to move upward, and the molding cores  191   a ,  191   b  eject the molded product P in the Y direction (see  FIG. 43 ). 
     In association with the movement of the ejector mount plates  762 , once the upper side face  183   a  of the click  180   a  of the sliding piece  173   a  is moved to come into contact with the right side surface  150   a  of the second guiding part  148   a , the sliding piece  173   a  thereafter moves in the second direction along the second guiding part  148   a , while the left side face  181   a  and the right side face  182   a  of the click  180   a  slide on the right side surface  150   a  and the left side surface  149   a  of the second guiding part  148   a , respectively. Thus, the molding core  191   a  is moved simultaneously in the Y direction and the −X direction away from the undercut portion P 4  (see  FIG. 44 ). 
     Similarly, in association with the movement of the ejector mount plates  762 , once the upper side face  183   b  of the click  180   b  of the sliding piece  173   b  is moved to come into contact with the right side surface  150   b  of the second guiding part  148   b , the sliding piece  173   b  thereafter moves in the second direction along the second guiding part  148   b , while the left side face and the right side face of the click  180   b  slide on the right side surface  150   b  and the left side surface  149   b  of the second guiding part  148   b , respectively. Thus, the molding core  191   b  is moved simultaneously in the Y direction and the +X direction away from the undercut portion P 4  (see  FIG. 44 ). 
     The first guiding parts  145   a ,  145   b  and the second guiding parts  148   a ,  148   b  of the guiding grooves  143   a ,  143   b  allow movement in the X direction to the extent that the molding cores  191   a ,  191   b  do not collide with the protruding portions P 3 , P 2  when the ejector mount plates  762  are moved to a highest position. In the present embodiment, the sliding pieces  173   a ,  173   b  incorporated into the molding die  104  move equally in a laterally symmetrical manner. However, the two sliding pieces  173   a ,  173   b  may move to different extents. In the present embodiment, the protruding portions P 3 , P 2  of the molded product P are other members for the molding cores  191   a ,  191   b  to avoid collision with. Also in other embodiments, a protruding portion of the molded product P is another member for the molding core  191  to avoid collision with. 
     As described above, the molding die  104  and the undercut processing mechanism  105  can achieve compact and simple configurations and can operate such that in conjunction with an operation of taking out the molded product P from the molding die  104 , the retaining piece  161  moves upward while sliding inside the holder  123 , and the sliding pieces  173   a ,  173   b  are guided by the holder  123  such that the molding cores  191   a ,  191   b  are removed from the undercut portion P 4 . Therefore, the undercut portion P 4  can be demolded easily and reliably. In addition, even where the molded product P includes the protruding portions P 2 , P 3  which are located ahead in the direction(s) of demolding the undercut portion P 4 , the molded product P can be demolded reliably without collision with the protruding portions P 2 , P 3 . 
     The undercut processing mechanism  105  can be incorporated into the molding die  104  with the sliding pieces  173   a ,  173   b  and the retaining piece  161  housed in the holder  123 , so that the undercut processing mechanism can have a compact configuration and be easily attached to the molding die  104 . In particular, the holder  123 , the retaining piece  161 , the sliding pieces  173   a ,  173   b , and the molding cores  191   a ,  191   b  can be assembled into a single independent unit; the undercut processing mechanism  105  as a single unit can be more easily attached to the molding die  104 . 
       FIG. 46  is an exploded view showing features of an undercut processing mechanism  107  according to an eleventh embodiment of the present invention.  FIG. 47  is a cross-sectional view of a molding die  106  including the undercut processing mechanism  107  according to the eleventh embodiment of the present invention when the mold is closed, and  FIG. 48  is a cross-sectional view of the molding die  106  when the mold is opened.  FIG. 49  and  FIG. 50  show cross-sectional views of the molding die  106  including the undercut processing mechanism  107  according to the eleventh embodiment of the present invention during a process of ejecting a molded product P. Features corresponding to the features of the undercut processing mechanism  101  and the molding die  100  of the third embodiment as shown in  FIG. 6  to  FIG. 10  are denoted with like reference numerals, and description thereof is omitted. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  600  in  FIG. 47 , and the “lower” side means the side of the movable die  700  in  FIG. 47 . In the following description, the “left” side corresponds to the left side in  FIG. 47 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     As with the molding die  100  including the undercut processing mechanism  101  of the third embodiment, the molding die  106  including the undercut processing mechanism  107  according to the eleventh embodiment of the present invention includes a fixed die  600  and a movable die  700  and is configured to mold a molded product P including undercut portions P 5   a , P 5   b . The following description will mainly focus on differences from the molding die  100  including the undercut processing mechanism  101  of the third embodiment. 
     The molded product P to be molded by the molding die  106  of the eleventh embodiment includes, at the center of the molded product P, two undercut portions P 5   a , P 5   b  which are located apart from each other. The undercut portion P 5   a  which is located leftward in a front view has an inversed L shape and includes a protrusion extending in the −X direction at a lower end thereof. On the other hand, the undercut portion P 5   b  which is located rightward in a front view has an L shape and includes a protrusion extending in the +X direction at a lower end thereof. 
     As with the undercut processing mechanism  101  of the third embodiment, the undercut processing mechanism  107  of the present embodiment employs the sliding mechanism  1  of the first embodiment. However, due to the positions and shapes of the undercut portions P 5   a , P 5   b , the undercut processing mechanism  107  of the present embodiment significantly differs from the undercut processing mechanism  101  of the third embodiment in terms of the structures and configurations of the molding core and the sliding piece. 
     In the molding die  106  of the eleventh embodiment, a holder  124  corresponds to the guiding body  31  of the sliding mechanism  1  of the first embodiment, and sliding pieces  174   a ,  174   b  respectively including molding cores  191   a ,  191   b  at their tip ends correspond to the second piece  21 . The sliding pieces  174   a ,  174   b  correspond to a slider, and the holder  124  corresponds to a guide body. As described later, guiding grooves  144   a ,  144   b  correspond to a guide unit; first guiding parts  145   a ,  145   b  correspond to a first guide unit; and second guiding parts  148   a ,  148   b  correspond to a second guide unit. Clicks  180   a ,  180   b  correspond to an engagement unit; first sliding surfaces of the clicks  180   a ,  180   b  correspond to a first engagement unit; and second sliding surfaces of the clicks  180   a ,  180   b  correspond to a second engagement unit. The retaining piece  161  and the sliding pieces  174   a ,  174   b  are slidably coupled together through a dovetail groove structure. The retaining piece  161  corresponds to a coupling member, and left- and right-side-wall inner surfaces  127 ,  130  of the holder  124  correspond to a coupling member guide unit. 
     The holder  124  includes a pair of half holder members  125  which are assembled into a columnar shape when used. The holder  124  has a same configuration as the holder  121  of the third embodiment, except for guiding grooves  144   a ,  144   b  which are located on a front-face-wall inner surface and a back-face-wall inner surface  135  of the holder  124  and guide the sliding pieces  174   a ,  174   b.    
     On each of the front-face-wall inner surface and the back-face-wall inner surface  135  of the holder  124 , the guiding grooves  144   a ,  144   b  are located in a laterally symmetrical manner with a gap therebetween. Each guiding groove  144   a  is a recessed groove and includes a first guiding part  145   a  which guides the sliding piece  174   a  in the first direction and a second guiding part  148   a  which guides the sliding piece  174   a  in the second direction. The first guiding part  145   a  is inclined with respect to a mold opening direction of the molding die  106  (i.e., Y direction), and the second guiding part  148   a  is parallel to the mold opening direction of the molding die  106  (i.e., Y direction). The first guiding part  145   a  and the second guiding part  148   a  are connected to each other, and a center axis M 1  of the first guiding part  145   a  and a center axis M 2  of the second guiding part  148   a  intersect with each other (see  FIG. 46 ). 
     The first guiding part  145   a  guides the sliding piece  174   a  diagonally upward to the right (i.e., in the first direction) such that the molding core  191   a  attached to the sliding piece  174   a  is removed from the undercut portion P 5   a  in a synchronized manner with the ejector mechanism  760 . In this regard, the direction in which the molding core  191   a  is removed from the undercut portion P 5   a  means a direction in which the molding core  191   a  is removed from the undercut portion P 5   a  without deforming or damaging the undercut portion P 5   a . The second guiding part  148   a  guides the sliding piece  174   a  such that the molding core  191   a  attached to the sliding piece  174   a  ejects the molded product P in the mold opening direction (second direction, Y direction) in a synchronized manner with the ejector mechanism  760 . 
     The center axis M 1  of the first guiding part  145   a  is defined depending on the shape of the undercut portion P 5   a  of the molded product P, in particular, on an extent of projection of the undercut portion P 5   a  in the −X direction and a stroke of an ejection pin  745 , so that the molding core  191   a  can be removed from the undercut portion P 5   a  of the molded product P upon ejection of the molded product P. The first guiding part  145   a  and the second guiding part  148   a  guide the molding core  191   a  such that the molding core  191   a  which has been removed from the undercut portion P 5   a  does not collide with the molding core  191   b . The molding core  191   b  is another member for the molding core  191   a  to avoid collision with, whereas the molding core  191   a  is another member for the molding core  191   b  to avoid collision with. 
     The guiding groove  144   b  only differs from the guiding groove  144   a  in the direction of the first guiding part  145   b  and has otherwise a same configuration as the guiding groove  144   a . Therefore, it is only necessary to substitute the letter “a” with the letter “b” of the reference signs in the above description. 
     In the present embodiment, there are two sliding pieces  174   a ,  174   b . Since the two sliding pieces  174   a ,  174   b  have a same shape and a same structure, their structure and the like will be described with reference to one sliding piece  174   a . The letters “a” and “b” used with the reference numerals are intended to distinguish the two sliding pieces  174   a ,  174   b . For example, a click  180   a  of the sliding piece  174   a  and a click  180   b  of the sliding piece  174   b  of the present embodiment have a same configuration as the click  180  of the sliding piece  171  of the third embodiment. 
     The sliding piece  174   a  has a same basic configuration as that of the sliding piece  171  of the third embodiment. An upper side face  183   a  and a lower side face  184   a  of each click  180   a  come into contact with a left side surface  149   a  and a right side surface  150   a  of the second guiding part  148   a  of the guiding groove  144   a  in the holder  124 , respectively, in order to guide the molding core  191   a  in the demolding direction (i.e., Y direction). Until the molding core  191   a  is removed from the undercut portion P 5   a , a left side face  181   a  and a right side face  182   a  of that click  180   a  are in contact with a left side surface  146   a  and a right side surface  147   a  of the first guiding part  145   a  of the guiding groove  144   a  in the holder  124 , respectively. The opposite upper side face  183   a  and lower side face  184   a  of the click  180   a  serve as second sliding surfaces, and the opposite left side face  181   a  and right side face  182   a  of the click  180   a  serve as first sliding surfaces. 
     The molding core  191   a  and the molding core  191   b  include recessed grooves  192   a ,  192   b  for molding the undercut portions P 5   a , P 5   b , respectively. 
     The holder  124 , the retaining piece  161 , the sliding piece  174   a  including the molding core  191   a , and the sliding piece  174   b  including the molding core  191   b  having the above constitution are incorporated into the holder  124 , with dovetail grooves  176   a ,  176   b  receiving the protruding line  168  of the retaining piece  161 . 
     An operation of the undercut processing mechanism  107  in the molding die  106  will be described. After the mold is opened (see  FIG. 48 ), the ejector rod  768  is pushed up through a non-illustrated ejection device, and the ejector mount plates  762  move upward (i.e., in the Y direction). In association therewith, the ejector pin  763  which is disposed so as to stand on the ejector mount plates  762  ejects the molded product P in the Y direction. At the same time, the retaining piece  161  also moves upward (i.e., in the Y direction). 
     The sliding piece  174   a  engaged with the retaining piece  161  moves in the first direction along the first guiding parts  145   a , while the left side faces  181   a  and the right side faces  182   a  of the clicks  180   a  slide on the left side surfaces  146   a  and the right side surfaces  147   a  of the first guiding parts  145   a , respectively. Thus, the molding core  191   a  is moved simultaneously in the Y direction and the −X direction and is removed from the undercut portion P 5   a . Similarly, the sliding piece  174   b  moves in the first direction along the first guiding parts  145   b , while the left side faces  181   b  and the right side faces  182   b  of the clicks  180   b  slide on the left side surfaces  146   b  and the right side surfaces  147   b  of the first guiding parts  145   b , respectively. Thus, the molding core  191   b  is moved simultaneously in the Y direction and the +X direction and is removed from the undercut portion P 5   b  (see  FIG. 49 ). 
     In association with the movement of the ejector mount plates  762 , once the upper side faces  183   a  of the clicks  180   a  of the sliding piece  174   a  are moved to come into contact with the right side surfaces  150   a  of the second guiding parts  148   a , the sliding piece  174   a  moves in the second direction along the second guiding parts  148   a , while the upper side faces  183   a  and the lower side faces  184   a  of the clicks  180   a  slide on the right side surfaces  150   a  and the left side surfaces  149   a  of the second guiding parts  148   a , respectively. Thus, the molding core  191   a  moves in the Y direction. 
     Similarly, in association with the movement of the ejector mount plates  762 , once the upper side faces  183   b  of the clicks  180   b  of the sliding piece  174   b  are moved to come into contact with the left side surfaces  149   b  of the second guiding parts  148   b , the sliding piece  174   b  moves in the second direction along the second guiding parts  148   b , while the upper side faces  183   b  and the lower side faces  184   b  of the clicks  180   b  slide on the left side surfaces  149   b  and the right side surfaces  150   b  of the second guiding parts  148   b , respectively. Thus, the molding core  191   b  moves in the Y direction. 
     The first guiding parts  145   a ,  145   b  and the second guiding parts  148   a ,  148   b  of the guiding grooves  144   a ,  144   b  allow movement in the X direction to the extent that the molding cores  191   a ,  191   b  do not collide with each other when the ejector mount plates  762  are moved to a highest position (see  FIG. 50 ). In the present embodiment, the sliding pieces  174   a ,  174   b  incorporated into the molding die  106  move equally in a laterally symmetrical manner. However, the two sliding pieces  174   a ,  174   b  may move to different extents. 
     As described above, the molding die  106  and the undercut processing mechanism  107  can achieve compact and simple configurations and can operate such that in conjunction with an operation of taking out the molded product P from the molding die  106 , the retaining piece  161  moves upward while sliding inside the holder  124 , and the sliding pieces  174   a ,  174   b  are guided by the holder  124  to move such that the molding cores  191   a ,  191   b  are removed from the undercut portions P 5   a , P 5   b . Therefore, the undercut portions P 5   a , P 5   b  can be demolded easily and reliably. In addition, the two sliding pieces  174   a ,  174   b  are configured to avoid colliding with each other after the undercut portions P 5   a , P 5   b  are demolded. 
     The undercut processing mechanism  107  can be incorporated into the molding die  106  with the sliding pieces  174   a ,  174   b  and the retaining piece  161  housed in the holder  124 , and therefore, the undercut processing mechanism  107  can have a compact configuration and be easily attached to the molding die  106 . In particular, the holder  124 , the retaining piece  161 , the sliding pieces  174   a ,  174   b , and the molding cores  191   a ,  191   b  can be assembled into a single independent unit; the undercut processing mechanism  107  as a single unit can be more easily attached to the molding die  106 . 
       FIG. 51  is an exploded view showing features of an undercut processing mechanism  109  according to a twelfth embodiment of the present invention.  FIG. 52  is a cross-sectional view of a molding die  108  including the undercut processing mechanism  109  according to the twelfth embodiment of the present invention when the mold is closed, and  FIG. 53  is a cross-sectional view of the molding die  108  when the mold is opened.  FIG. 54  and  FIG. 55  show cross-sectional views of the molding die  108  including the undercut processing mechanism  109  according to the twelfth embodiment of the present invention during a process of ejecting a molded product P.  FIG. 56  shows the molded product P ejected from the molding die  108  including the undercut processing mechanism  109  according to the twelfth embodiment of the present invention. Features corresponding to the features of the undercut processing mechanism  101  and the molding die  100  of the third embodiment as shown in  FIG. 6  to FIG. are denoted with like reference numerals, and description thereof is omitted. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  600  in  FIG. 52 , and the “lower” side means the side of the movable die  700  in  FIG. 52 . In the following description, the “left” side corresponds to the left side in  FIG. 52 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     As with the molding die  100  including the undercut processing mechanism  101  according to the third embodiment of the present invention, the molding die  108  including the undercut processing mechanism  109  according to the twelfth embodiment of the present invention includes a fixed die  600 , a movable die  700 , and the undercut processing mechanism  109  and is configured to mold a molded product P including an undercut portion. However, the undercut processing mechanism  109  has a different structure. The following description will mainly focus on differences from the molding die  100  including the undercut processing mechanism  101  of the third embodiment. 
     In the molding die  108  of the twelfth embodiment, the shape of the molded product P, the shapes and positional relation of the undercut portion P 1  and the protruding portion P 2  are the same as those in the molding die  100  of the third embodiment. As with the undercut processing mechanism  101  of the third embodiment, the undercut processing mechanism  109  of the present embodiment guides a sliding piece  178  including a molding core  191  at a tip end thereof, which corresponds to the second piece  21 , in the first direction and the second direction. However, the undercut processing mechanism  109  includes a first guide unit and a second guide unit which are different from those of the undercut processing mechanism  101 , for guiding the sliding piece  178  in the first direction and the second direction, respectively. 
     In the molding die  108  of the twelfth embodiment, a holder  131  corresponds to the guiding body  31  of the sliding mechanism  1  of the first embodiment, and the sliding piece  178  including the molding core  191  at the tip end thereof corresponds to the second piece  21 . The sliding piece  178  corresponds to a slider, and the holder  131  corresponds to a guide body. Left and right side walls of the holder  131  correspond to a first guide unit, and a knock pin  169  and an inclined surface  134  of the holder  131  correspond to a second guide unit. The retaining piece  161  and the sliding piece  178  are slidably coupled together through a dovetail groove structure. The retaining piece  161  corresponds to a coupling member, and left- and right-side-wall inner surfaces  127 ,  130  of the holder  131  correspond to a coupling member guide unit. 
     The holder  131  includes a pair of holder halves  132  are assembled into a columnar shape when used. The holder  131  does not include a guiding groove for guiding the sliding piece  178  but, instead, includes a knock pin  169  attached to an inside of the holder  131 . The knock pin  169  has a cylindrical shape and is located at an upper right part of the holder  131  in a front view. In the holder  131 , the left-side-wall inner surface  127  and the right-side-wall inner surface  130  guide the sliding piece  178  in the mold opening direction (i.e., Y direction), which is the first direction, and the inclined surface  134  at the upper left part of the holder  131  and the knock pin  169  guide the sliding piece  178  in the upper left direction, which is the second direction. Here, the first direction is parallel to the mold opening direction (i.e., Y direction), and the second direction is inclined with respect to the mold opening direction (i.e., Y direction). 
     The knock pin  169  guides the sliding piece  178  diagonally upward to the left (second direction) such that the molding core  191  attached to the sliding piece  178  is removed from the undercut portion P 1 . In this regard, the direction in which the molding core  191  is removed from the undercut portion P 1  means a direction in which the molding core  191  is removed from the undercut portion P 1  without deforming or damaging the undercut portion P 1 . 
     The position of the knock pin  169  is defined depending on the shape of the undercut portion P 1  of the molded product P, in particular, on an extent of projection of the undercut portion P 1  in the X direction and a stroke of an ejection pin  745 , so that the molding core  191  can be removed from the undercut portion P 1  of the molded product P upon ejection of the molded product P. Also, the knock pin  169  guides the molding core  191  such that the molding core  191  which has been removed from the undercut portion P 1  does not collide with the protruding portion P 2  which is located ahead in a removal direction of the undercut portion P 1  (i.e., X direction). 
     The sliding piece  178  does not include a click. Instead, an upper side face  185  and a lower side face  184  of a body  175  of the sliding piece  178  serve as first sliding surfaces, and a left side face  186  and a right side face  187  of the body  175  serve as second sliding surface. Until the sliding piece  178  comes into contact with the knock pin  169 , the upper side face  185  and the lower side face  184  are in contact with the left-side-wall inner surface  127  and the right-side-wall inner surface  130  of the holder  131  and guide the molding core  191  in the first direction. After the body  175  comes into contact with the knock pin  169 , the left side face  186  and the right side face  187  of the body  175  of the sliding piece  178  guide the molding core  191  in the second direction, with the left side face  186  slidably in contact with the inclined surface  134  of the holder  131  and the right side face  187  slidably in contact with the knock pin  169 . 
     An operation of the undercut processing mechanism  109  in the molding die  108  will be described. When the mold is clamped, the upper side face  185  and the lower side face  184  of the body  175  of the sliding piece  178  are in contact with the left-side-wall inner surface  127  and the right-side-wall inner surface  130  of the holder  131 , respectively (see  FIG. 52 ). After the mold is opened (sec  FIG. 53 ), the ejector rod  768  is pushed up through a non-illustrated ejection device, and the ejector mount plates  762  move upward (i.e., in the Y direction). In association therewith, the ejector pin  763  which is disposed so as to stand on the ejector mount plates  762  ejects the molded product P in the Y direction. In this case, the sliding piece  178  is also guided by the opposite side wall inner surfaces of the holder  131  so as to move upward, and the molding core  191  ejects the molded product P in the Y direction (see  FIG. 54 ). 
     In association with the movement of the ejector mount plates  762 , once the right side face  187  of the body of the sliding piece  178  is moved to come into contact with the knock pin  169 , the sliding piece  178  moves in the second direction, while the right side face  187  of the body slides on the knock pin  169 , and the left side face  186  of the body slides on the inclined surface  134  of the holder  131 . Thus, the molding core  191  is moved simultaneously in the Y direction and the X direction away from the undercut portion P 1 . The position of the knock pin  169  is defined so as to allow movement in the X direction to the extent that the molding core  191  does not collide with the protruding portion P 2  when the ejector mount plates  762  are moved to a highest position. Therefore, the molding core  191  does not collide with the protruding portion P 2 . 
     The effects and advantages of the undercut processing mechanism  109  of the twelfth embodiment and the molding die  108  including the same are essentially the same as those of the undercut processing mechanism  101  of the third embodiment and the molding mold  100  including the same. 
     The undercut processing mechanism  109  can be incorporated into the molding die  108  with the sliding piece  178  and the retaining piece  161  housed in the holder  131 , and therefore, the undercut processing mechanism  109  can have a compact configuration and be easily attached to the molding die  108 . In particular, the holder  131  including the knock pin  169 , the retaining piece  161 , the sliding piece  178 , and the molding core  191  can be assembled into a single independent unit; the undercut processing mechanism  109  as a single unit can be more easily attached to the molding die  108 . 
       FIG. 57  is an exploded view showing features of an undercut processing mechanism  111  according to a thirteenth embodiment of the present invention.  FIG. 58  is a cross-sectional view of a molding die  110  including the undercut processing mechanism  111  according to the thirteenth embodiment of the present invention in a mold closed state. Features corresponding to the features of the undercut processing mechanism  109  and the molding die  108  of the twelfth embodiment as shown in  FIG. 51  to  FIG. 56  are denoted with like reference numerals, and description thereof is omitted. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  600  in  FIG. 58 , and the “lower” side means the side of the movable die  700  in  FIG. 58 . In the following description, the “left” side corresponds to the left side in  FIG. 58 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     The molding die  110  including the undercut processing mechanism  111  according to the thirteenth embodiment of the present invention shares many common points with the undercut processing mechanism  109  and the molding die  108  of the twelfth embodiment, like for example in that the molding core  191  attached to the sliding piece  178  includes the knock pin  169  which guides the sliding piece  178  diagonally upward to the left (in the second direction) such that the molding core  191  is removed from the undercut portion P 1 . The following description will mainly focus on differences from the molding die  108  including the undercut processing mechanism  109  of the twelfth embodiment. 
     In the molding die  110  of the thirteenth embodiment, the shape of the molded product P, the shapes and positional relation of the undercut portion P 1  and the protruding portion P 2  are the same as those in the molding die  108  of the twelfth embodiment. The undercut processing mechanism  11  does not include an independent holder but includes a holder  776  integrated into a receiving body  770  attached to a movable mold plate  716 . A movable receiving plate  718  is attached to a bottom part of the movable mold plate  716 . 
     In the molding die  110  of the thirteenth embodiment, the holder  776  corresponds to the guiding body  31  of the sliding mechanism  1  of the first embodiment, the sliding piece  178  including the molding core  191  at a tip end thereof corresponds to the second piece  21 . The sliding piece  178  corresponds to a slider, and the holder  776  corresponds to a guide body. Left and right side walls of the holder  776  correspond to a first guide unit, and the knock pin  169  and an inclined surface at an upper left part of the holder  776  correspond to a second guide unit. The retaining piece  161  and the sliding piece  178  are slidably coupled together through a dovetail groove structure. The retaining piece  161  corresponds to a coupling member, and left- and right-side-wall inner surfaces of the holder  776  correspond to a coupling member guide unit. 
     The receiving body  770  includes a core  773  for molding an inner surface of a molded product P at an upper part of a body  772  of the receiving body  770 , and a recessed part  774  for molding the protruding portion P 2  of the molded product P on an upper face of the receiving body  770 . The receiving body  770  is fitted into a recessed part  717  in the movable mold plate  716  and is fixed to the movable mold plate  716  through the movable receiving plate  718  with flanges  775  at a bottom part of the body  772  engaged with the recessed part  717 . 
     The holder  776  penetrates the body  772  in the vertical direction. The holder  772  includes, at an upper part thereof, a recessed part  778  connected to the holder  772 . The recessed part  778  is a receiving hole which receives the molding core  191 , and the molding core  191  is slidably received into the recessed part  778  without a gap. The receiving body  770  also includes an attachment hole  780  to which the knock pin  169  is attached and a through hole  782  through which the ejector pin  763  is inserted. 
     Since the holder  776  has a same basic configuration as and same effects as those of the holder  131  of the undercut processing mechanism  109  of the twelfth embodiment, description thereof is omitted. Since the position and the effect of the knock pin  169  are also the same as those of the knock pin  169  of the undercut processing mechanism  109  of the twelfth embodiment, description thereof is omitted. The sliding piece  178  of the present embodiment is identical to the sliding piece  178  of the undercut processing mechanism  109  of the twelfth embodiment. 
     The movable receiving plate  718  is attached to the bottom part of the movable mold plate  716  so as to support the receiving body  770 . The movable receiving plate  718  includes a through hole  719  which allows the retaining piece  161  to freely move therethrough. 
     The operation, effects and advantages of the molding die  110  and the undercut processing mechanism  111  are essentially the same as those of the molding die  108  and the undercut processing mechanism  109  of the twelfth embodiment. 
     The undercut processing mechanism  111  can be incorporated into the molding die  110  with the sliding piece  178  and the retaining piece  161  housed in the holder  776 , and therefore, the undercut processing mechanism  111  can have a compact configuration and be easily attached to the molding die  110 . In particular, the receiving body  770  including the holder  776  including the knock pin  169 , the retaining piece  161 , the sliding piece  178 , and the molding core  191  can be assembled into a single independent unit; the undercut processing mechanism  111  as a single unit can be more easily attached to the molding die  110 . 
       FIG. 59  is an exploded view showing features of an undercut processing mechanism  112  according to a fourteenth embodiment of the present invention. Charts (A), (B), and (C) of  FIG. 60  show a left-side view, a front view, and a right-side view, respectively, of a sliding piece  179  including the molding core  191  of the undercut processing mechanism  112  according to the fourteenth embodiment of the present invention.  FIG. 61  illustrates an operation of the undercut processing mechanism  112  according to the fourteenth embodiment of the present invention. Features corresponding to the features of the undercut processing mechanism  101  and the molding die  100  of the third embodiment as shown in  FIG. 6  to  FIG. 10  are denoted with like reference numerals, and description thereof is omitted. In the following description, it should be understood that instead of the undercut processing mechanism  101 , the undercut processing mechanism  112  is incorporated into the molding die  100 . In the present embodiment, the “left” side means a far side in the X direction and corresponds to the left side in Chart (A) of  FIG. 61 . 
     The undercut processing mechanism  112  is configured to mold the undercut portion P 1  when the molded product P is molded, and to be removed from the undercut portion P 1  upon ejection of the molded product P in a synchronized manner with the ejector mechanism  760 , so that the molded product P can be demolded from the molding die. The undercut processing mechanism  112  of the present embodiment employs the sliding mechanism  1  of the first embodiment. 
     The undercut processing mechanism  112  includes: a holder  136 ; the sliding piece  179  including, at the tip end thereof, the molding core  191  which molds the undercut portion P 1  of the molded product P; and the retaining piece  161  which slidably retains the sliding piece  179 . As with the undercut processing mechanism  101  of the third embodiment, the undercut processing mechanism  112  of the present embodiment guides sliding piece  179  including a molding core  191  at a tip end thereof, which corresponds to the second piece  21 , in the first direction and the second direction. However, the undercut processing mechanism  112  includes a first guide unit and a second guide unit which are different from those of the undercut processing mechanism  101 , for guiding the sliding piece in the first direction and the second direction, respectively. 
     The holder  136  of the present embodiment corresponds to the guiding body  31  of the sliding mechanism  1  of the first embodiment; the sliding piece  179  including the molding core  191  at the tip end thereof corresponds to the second piece  21 ; and the retaining piece  161  corresponds to the first piece  11 . In the present embodiment, the sliding piece  179  corresponds to a slider, and the holder  136  corresponds to a guide body. As described later, guiding grooves  153 ,  154 ,  155  ( 155   a ,  155   b ) correspond to a guide unit; the guiding groove  153  and the guiding groove  154  correspond to a first guide unit; and the guiding groove  155  corresponds to a second guide unit. The body  175  of the sliding piece  179  corresponds to a first engagement unit, and clicks  188  ( 188   a ,  188   b ) correspond to a second engagement unit. The retaining piece  161  and the sliding piece  179  are slidably coupled together through a dovetail groove structure. The retaining piece  161  corresponds to a coupling member, and left- and right-side-wall inner surfaces  127 ,  130  of the holder  136  correspond to a coupling member guide unit. 
     The holder  136  includes two half holder members  137  of a same shape which are assembled together. In the holder  136 , the inner surface  127  of the left side wall  126  and the inner surface  130  of the right side wall  129  serve as guides for the retaining piece  161 , and the holder  136  includes guiding grooves  153 ,  154 ,  155  for guiding the sliding piece  179  on the front-face-wall inner surface and the back-face-wall inner surface  135 . 
     The guiding grooves  153  and the guiding grooves  154  are recessed grooves for guiding the sliding piece  179  in the first direction and guide the sliding piece  179  in the Y direction. The guiding grooves  153  and the guiding grooves  154  extend parallel to the mold opening direction of the molding die  100  (i.e., Y direction) on the front-face-wall inner surface and the back-face-wall inner surface  135  of the holder  136 . The guiding grooves  154  are located at above the guiding grooves  153  and connect to the guiding grooves  153  seemingly without a step in a front view. The guiding grooves  154 , however, have a smaller groove depth than that of the guiding grooves  153 , and there is stepped portions at the interface  156  between the guiding grooves  154  and the guiding grooves  153  (see  FIG. 59 ). 
     The guiding grooves  153  and the guiding grooves  154  have a width W 5  which is approximately half of the width of the front-face-wall inner surface and the back-face-wall inner surface  135  of the holder  136 . Right side surfaces of the guiding grooves  153  and of the guiding grooves  154  are flush with the right-side-wall inner surface  130  of the holder  136  when the holder  136  is viewed straightforwardly (see  FIG. 61 ). 
     The guiding grooves  155  ( 155   a ,  155   b ) are recessed grooves for guiding the sliding piece  179  in the second direction and guides the sliding piece  179  diagonally upward to the left. The guiding grooves  155  are located next to the guiding grooves  153  and the guiding grooves  154  to the left on the front-face-wall inner surface and the back-face-wall inner surface  135  of the holder  136  in a front view. Of the guiding grooves  155 , the guiding grooves  155   a  are located at middle positions in the Y direction, and the guiding grooves  155   b  are located at upper positions in the Y direction. 
     The two guiding grooves  155   a ,  155   b  are arranged such that in a front view, the left sides of the grooves  155   a ,  155   b  are on the left-side-wall inner surface  127  of the holder  136 , and the right sides of the grooves  155   a ,  155   b  connect to the guiding grooves  153 . Upper sides of the guiding grooves  155   b  linearly meet lower sides of the guiding grooves  154  in a front view. The guiding grooves  155   a ,  155   b  have a groove depth equal to that of the guiding grooves  153 . 
     The sliding piece  179  includes the linear body  175  having a rectangular cross section, and the body  175  includes a tip end portion to which the molding core  191  is attached and a lower end including the dovetail groove  176  which slidably engages with the protruding line  168  of the retaining piece  161 . The body  175  has a slightly smaller thickness in an upper part than the rest of the body and is stepped in a side view (see  FIG. 60 ). The step of the body  175  has a height equal to that of the step at the interfaces  156  between the guiding grooves  154  and the guiding grooves  153 . 
     The body  175  of the sliding piece  179  has a width W 6  substantially equal to a width W 5  of the guiding grooves  153 , and the sliding piece  179  can be slidably fitted into the guiding grooves  153 ,  154  without a gap (see Chart (B) of  FIG. 61 ). The sliding piece  179  moves in the Y direction, which is the first direction, while sliding on the left side surfaces  157  of the guiding grooves  153 , the left side surfaces  158  of the guiding grooves  154  and further the right-side-wall inner surface  130  of the holder  136  as sliding surface. 
     The sliding piece  179  includes, on a front face and a back face of the body  175 , clicks  188  ( 188   a ,  188   b ) which are fitted into the guiding grooves  155  ( 155   a ,  155   b ). The clicks  188   a  are located at lower positions in the Y direction, and the clicks  188   b  are located at middle positions in the Y direction. The clicks  188   a ,  188   b  are arranged so as to define recessed grooves above and below the respective clicks  188   a ,  188   b . Therefore, the clicks  188   a ,  188   b  may be considered as protruding lines. 
     The clicks  188  ( 188   a ,  188   b ) have a height (thickness) equal to the depth of the guiding grooves  155  ( 155   a ,  155   b ). The clicks  188  ( 188   a ,  188   b ) are inclined so as to be parallel to the guiding grooves  155  ( 155   a ,  155   b ) when the body  175  and the holder  136  are viewed straightforwardly. Each click  188   a  has a width substantially equal to a width of each guiding groove  155   a , so that the clicks  188   a  can be slidably fitted into the guiding grooves  155   a  without a gap. Similarly, each click  188   b  has a width substantially equal to a width of each guiding groove  155   b , so that the clicks  188   b  can be slidably fitted into the guiding grooves  155   b  without a gap. 
     An operation of the undercut processing mechanism  112  will be described. When the mold is clamped, a left side face  189  of the body  175  of the sliding piece  179  is in contact with the left side surfaces  157  of the guiding grooves  153  and the left side surfaces  158  of the guiding grooves  154 , and the right side face  190  of the body  175  is in contact with the right-side-wall inner surface  130  of the holder  131  (see Chart (A) of  FIG. 61 ). In the undercut processing mechanism  112 , when the mold is clamped, the left and right side faces  189 ,  190  of the body  175  of the sliding piece  179  are in contact with the guiding grooves  153 ,  154  and the holder  131  over a wide area in the vertical direction, so that the sliding piece  179  will not be displaced, even when a large load is applied to the molding core  191  laterally (in the ±X directions). 
     When the retaining piece  161  is ejected in the Y direction, the retaining piece  161  moves in the Y direction, while the left-side-wall inner surface  127  and the right-side-wall inner surface  130  of the holder  136  serve as guides. The sliding piece  179  coupled to the retaining piece  161  moves in the Y direction, while the left side surfaces  157  of the guiding grooves  153 , the left side surfaces  158  of the guiding grooves  154 , and the right-side-wall inner surface  130  of the holder  136  serve as guides (see Chart (B) of  FIG. 61 ). 
     Once the sliding piece  179  is moved, and upper sides  193  of the clicks  188   b  of the sliding piece  179  come into contact with the interfaces  156  of the holder  136  (see Chart (B) of  FIG. 61 ), the sliding piece  179  moves upward to the left, while the clicks  188   a  are guided by the guiding grooves  155   a , and the clicks  188   b  are guided by the guiding grooves  155   b  (see Chart (C) of  FIG. 61 , Chart (D) of  FIG. 61 ). 
     The operation, effects and advantages of the undercut processing mechanism  112  and the molding die  100  incorporating the same are essentially the same as those of the molding die  100  and the undercut processing mechanism  101  of the third embodiment. 
     The undercut processing mechanism  112  can be incorporated into the molding die with the sliding piece  179  and the retaining piece  161  housed in the holder  136 , and therefore, the undercut processing mechanism  112  can have a compact configuration and be easily attached to the molding die. In particular, the holder  136 , the retaining piece  161 , the sliding piece  179 , and the molding core  191  can be assembled into a single independent unit; the undercut processing mechanism  112  as a single unit can be more easily attached to the molding die. 
       FIG. 62  is an exploded view showing features of an undercut processing mechanism  113  according to a fifteenth embodiment of the present invention. Charts (A), (B), (C), and (D) of  FIG. 63  show a left-side view, a front view, a right-side view, and a bottom view, respectively, of a sliding piece  194  including the molding core  191  of the undercut processing mechanism  113  according to the fifteenth embodiment of the present invention.  FIG. 64  illustrates an operation of the undercut processing mechanism  113  according to the fifteenth embodiment of the present invention. Features corresponding to the features of the undercut processing mechanism  101  and the molding die  100  of the third embodiment as shown in  FIG. 6  to  FIG. 10  are denoted with like reference numerals, and description thereof is omitted. In the following description, it should be understood that instead of the undercut processing mechanism  101 , the undercut processing mechanism  113  is incorporated into the molding die  100 . In the present embodiment, the “left” side means a far side in the X direction and corresponds to the left side in Chart (A) of  FIG. 64 . 
     As with the undercut processing mechanism  101  of the third embodiment, the undercut processing mechanism  113  is attached to the molding die  100  and is configured to mold the undercut portion P 1  when the molded product P is molded, and to be removed from the undercut portion P 1  upon ejection of the molded product P in a synchronized manner with the ejector mechanism  760 , so that the molded product P can be demolded from the molding die. The undercut processing mechanism  113  of the present embodiment employs the sliding mechanism  1  of the first embodiment. 
     The undercut processing mechanism  113  includes: a holder  138 ; a sliding piece  194  including, at a tip end thereof, a molding core  191  which molds an undercut portion P 1  of a molded product P; and a retaining piece  161  which slidably retains the sliding piece  194 . As with the undercut processing mechanism  101  of the third embodiment, the undercut processing mechanism  113  of the present embodiment guides the sliding piece  194  including the molding core  191  at the tip end thereof, which corresponds to the second piece  21 , in the first direction and the second direction. However, the undercut processing mechanism  113  includes a first guide unit and a second guide unit which are different from those of the undercut processing mechanism  101 , for guiding the sliding piece  194  in the first direction and the second direction, respectively. 
     The holder  138  of the present embodiment corresponds to the guiding body  31  of the sliding mechanism  1  of the first embodiment; the sliding piece  194  including the molding core  191  at the tip end thereof corresponds to the second piece  21 ; and the retaining piece  161  corresponds to the first piece  11 . In the present embodiment, the sliding piece  194  corresponds to a slider, and the holder  138  corresponds to a guide body. As described later, guiding grooves  159  ( 159   a ,  159   b ),  160 ,  162  ( 162   a ,  162   b ) and an inclined surface  164  correspond to a guide unit; the guiding grooves  159 , the guiding grooves  160  and the inclined surfaces  164  correspond to a first guide unit; and the guiding grooves  162  corresponds to a second guide unit. A body  175  of the sliding piece  194  corresponds to a first engagement unit, and clicks  195  ( 195   a ,  195   b ) correspond to a second engagement unit. The retaining piece  161  and the sliding piece  194  are slidably coupled together through a dovetail groove structure. The retaining piece  161  corresponds to a coupling member, and left- and right-side-wall inner surfaces  127 ,  130  of the holder  138  correspond to a coupling member guide unit. 
     The holder  138  includes two half holder members  139  of a same shape which are assembled together. In the holder  138 , the inner surface  127  of the left side wall  126  and the inner surface  130  of the right side wall  129  serve as guides for the retaining piece  161 , and the holder  138  includes guiding grooves  159  ( 159   a ,  159   b ),  160 ,  162  ( 162   a ,  162   b ) which guide the sliding piece  194  on the front-face-wall inner surface and the back-face-wall inner surface  135 . The holder  138  also includes an inclined surface  164  at an upper end of the left side wall  126 , and the inclined surface  164  serves as a guide which guides the sliding piece  194  in the first direction. 
     The guiding grooves  159  and the guiding grooves  160  are recessed grooves which guide the sliding piece  194  in the first direction and are located on the front-face-wall inner surface of the back-face-wall inner surface  135  of the holder  136  to guide the sliding piece  194  diagonally upward to the left. The guiding grooves  160  are located between the guiding grooves  159   a  and the guiding grooves  159   b  and linearly connect to these grooves seemingly without a step in a front view. The guiding grooves  159   a  and the guiding grooves  159   b  has a same groove depth, and the guiding grooves  160  have a smaller groove depth than that of the guiding grooves  159 , so that there are stepped portions  163  at interfaces between the guiding grooves  159   a  and the guiding grooves  160  and interfaces between the guiding grooves  159   b  and the guiding grooves  160  (see  FIG. 62 ). 
     The guiding grooves  162  ( 162   a ,  162   b ) are recessed grooves which guide the sliding piece  194  in the second direction and are located on the front-face-wall inner surface and the back-face-wall inner surface  135  of the holder  136  to guide the sliding piece  194  in the Y direction. When the holder  136  is viewed straightforwardly, the guiding grooves  162  are located on both sides of the guiding grooves  160 , so that the guiding grooves  162   a  are located on the right of the guiding grooves  160 , and the guiding grooves  162   b  are located on the left of the guiding grooves  160 . The guiding grooves  162   a  have a groove depth equal to that of the guiding grooves  159   a , and the guiding grooves  162   a  and the guiding grooves  159   a  are connected to each other without a step. Similarly, the guiding grooves  162   b  have a groove depth equal to that of the guiding grooves  159   b , and the guiding grooves  162   b  and the guiding grooves  159   b  are connected to each other without a step. 
     The sliding piece  194  includes the linear body  175  having a rectangular cross section, and the body  175  includes a tip end portion to which the molding core  191  is attached and a lower end including the dovetail groove  176  which slidably engages with the protruding line  168  of the retaining piece  161 . The body  175  includes two clicks  195   a ,  195   b  on each of a front face and a back face thereof (see  FIG. 62 ). The clicks  195   a  are located at lower parts of the body  175 , and the clicks  195   b  are located at upper parts of the body  175 . The clicks  195   a  and the clicks  195   b  are separated from each other. 
     The clicks  195   a  and the clicks  195   b  have a same click height, and the clicks  195   a ,  195   b  are shaped so as to define recessed parts adjacent to the clicks. Therefore, the clicks  195   a ,  195   b  may be considered as protruding lines. The clicks  195   a  are configured to be slidably fitted into the guiding grooves  162   a  without a gap, and the clicks  195   b  are configured to be slidably fitted into the guiding grooves  162   b  without a gap. 
     Next to the clicks  195   b  to the right, there is stepped portions  196  which are a step lower than the clicks  195   b . Each stepped portions  196  is constructed such that a sum of a height of the stepped portion  196  and a height of a guiding groove  160  in the holder  138  corresponds to a height of each click  195   a ,  195   b.    
     An operation of the undercut processing mechanism  113  will be described. When the mold is clamped, the sliding piece  194  is placed such that the lower side face  184  of the body  175  is in contact with the right-side-wall inner surface  130  of the holder  138 , the clicks  195   a  of the body  175  are fitted into the guiding grooves  159   a , the clicks  195   b  of the body  175  are fitted into the guiding grooves  159   b , and the stepped portions  196  are fitted into the guiding grooves  160  without a gap (see Chart (A) of  FIG. 64 ). In the undercut processing mechanism  113 , when the mold is clamped, the respective parts of the body  175  of the sliding piece  194  are in contact with the holder  138 , the guiding grooves  159   a ,  159   b , the guiding grooves  160 , and further the inclined surface  164  over a wide area in the vertical direction, so that the sliding piece  194  will not be displaced, even when a large load is applied to the molding core  191  laterally (in the f X directions). 
     When the retaining piece  161  is ejected in the Y direction, the retaining piece  161  moves in the Y direction, while the left-side-wall inner surface  127  and the right-side-wall inner surface  130  of the holder  138  serve as guides. The sliding piece  194  slidably coupled to the retaining piece  161  moves in the upper left direction, which is the first direction, while the guiding grooves  159   a ,  159   b , the guiding grooves  160 , and further the inclined surface  164  serve as guides (see Chart (B) of  FIG. 64 ). 
     Once the sliding piece  194  is moved, and left side faces  197  of the clicks  195   a  of the sliding piece  194  come into contact with the stepped portions  163  of the guiding grooves  160  of the holder  138  (see Chart (B) of  FIG. 64 ), the sliding piece  194  moves in the Y direction, while the clicks  195   a  are guided by the guiding grooves  162   a  and the clicks  195   b  are guided by the guiding grooves  162   b  (see Chart (C) of  FIG. 64 ). 
     The operation, effects and advantages of the undercut processing mechanism  113  and the molding die  100  including the same are essentially the same as those of the molding die  100  and the undercut processing mechanism  101  of the third embodiment. 
     The undercut processing mechanism  113  can be incorporated into the molding die with the sliding piece  194  and the retaining piece  161  housed in the holder  138 , and therefore, the undercut processing mechanism  113  can have a compact configuration and be easily attached to the molding die. In particular, the holder  138 , the retaining piece  161 , the sliding piece  194 , and the molding core  191  can be assembled into a single independent unit; the undercut processing mechanism  113  as a single unit can be more easily attached to the molding die. 
       FIG. 65  is a cross-sectional view of a molding die  800  including a gate tearing mechanism  801  according to a sixteenth embodiment of the present invention in a mold closed state.  FIG. 66  is a cross-sectional view of the molding die  800  including the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention during a process of opening the mold, and  FIG. 67  is a cross-sectional view of the molding die  800  when the mold is opened.  FIG. 68  is an exploded view showing features of the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention. Features corresponding to the features of the molding die  200  and the gate cutting mechanism  201  according to the fourth embodiment of the present invention as shown in  FIG. 11  to  FIG. 16  are denoted with like reference numerals, and description thereof is omitted. 
     As with the molding die  200 , the molding die  800  includes: a fixed die  602  which molds an external surface of a molded product P; a movable die  702  which molds an internal surface of the molded product P; and further a gate tearing mechanism  801  which tears a gate G. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  602  in  FIG. 65 , and the “lower” side means the side of the movable die  702  in  FIG. 65 . In the following description, the “left” side corresponds to the left side in  FIG. 65 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     The fixed die  602  includes a fixed mold plate  605  and a receiving body  607  including a cavity  606  for shaping the outer surface of the molded product P. The fixed mold plate  605  includes, in a bottom face  610  thereof, a recessed part  612  which receives a spring  849  which maintains a position of a driving piece  841  as described later. The receiving body  607  has a toppled L shape in a front view and includes a lower right end which extends downward (i.e., in the −Y direction) and partly defines a runner groove which shapes a runner R. 
     The movable die  702  includes: a movable mold plate  711 ; a receiving body  721  including a core which shapes the inner surface of the molded product P; and a movable receiving plate  718 . The movable mold plate  711  includes a recessed part  728  which has a substantially rectangular shape in a front view and is configured to receive components of the gate tearing mechanism  801  such as a holder  851  (see  FIG. 66 ). 
     The gate tearing mechanism  801  is operable to tear a gate G connecting a molded product P to a runner R and is configured to tear the gate G by a tearing piece in conjunction with opening of the molding die  800  and thereafter to move the tearing piece away from the gate G and the runner R so as to allow a material left in the runner R to be removed. The gate tearing mechanism  801  of the present embodiment employs the sliding mechanism  1  of the first embodiment. 
     The gate tearing mechanism  801  includes: a tearing piece  803  which tears a gate G; a retaining piece  821  which is slidably coupled to the tearing piece  803  to slide the tearing piece  803 ; a driving piece  841  which is slidably coupled to the retaining piece  821  to slide the retaining piece  821 ; and a holder  851  which houses the retaining piece  821  and the like in an advanceable and retractable manner. 
     The tearing piece  803  of the present embodiment corresponds to the second piece  21  of the sliding mechanism  1  of the first embodiment; the retaining piece  821  corresponds to the first piece  11 ; and the holder  851  corresponds to the guiding body  31 . In the present embodiment, the tearing piece  803  corresponds to a slider, and the holder  851  corresponds to a guide body. As described later, a guiding groove  856  corresponds to a guide unit; a first guiding part  857  corresponds to a first guide unit; and a second guiding part  858  corresponds to a second guide unit. A click  812  corresponds to an engagement unit; a first sliding surface of the click  812  corresponds to a first engagement unit; and a second sliding surface of the click  812  corresponds to a second engagement unit. The retaining piece  821  and the tearing piece  803  are slidably coupled together through a dovetail groove structure. The retaining piece  821  corresponds to a coupling member, and a guiding groove  871  of the holder  851  corresponds to a coupling member guide unit. 
     The holder  851  houses the retaining piece  821  in an advanceable and retractable manner and guides the retaining piece  821  laterally (in the +X direction and the −X direction). Further, the holder  851  guides the retaining piece  803  such that the tearing piece  803  tears the gate G, and the tearing piece  803  after tearing the gate G is moved away from the gate G and the runner R. The holder  851  includes two half holder members  852  of a substantially same shape which are assembled together so as to have a box-like column shape which defines an inner space therein and is open on a left side face and a left part of an upper face of the holder  851  with respect to the center. The holder  851  may be constituted by a plurality of divided members or be integrated with the movable mold plate  711 . 
     As with the holder  221  of the fourth embodiment, the holder  851  guides the tearing piece  803  in the first direction and subsequently in the second direction. The opening on the left side face of the holder  851  allows the tearing piece  803  and the retaining piece  821  to move in and out. The half holder member  852  constituting a back face side of the holder  851  includes a recessed part  865  which opens on the left side face of the holder  851 . The recessed part  865  is a space which receives a block member  830  attached to the retaining piece  821 . The holder  851  includes, in a right part of the upper face thereof, an insertion hole through which a support pin  846  coupled to the driving piece  841  is inserted. 
     The holder  851  includes guiding grooves  856  which guide the tearing piece  803  on a front-face-wall inner surface  853  and a back-face-wall inner surface  854  of the holder  851 . The holder  851  also includes guiding grooves  871  which guide the retaining piece  821  and guiding grooves  875  which guide the driving piece  841  on the front-face-wall inner surface  853  and the back-face-wall inner surface  854 . 
     The guiding grooves  856  are recessed grooves located at upper left positions on the front-face-wall inner surface  853  and the back-face-wall inner surface  854 , each guiding grooves  856  having a dog-legged shape (see  FIG. 68 ). There are two guiding grooves  856  arranged next to each other in the lateral direction in each half holder member. Each guiding groove  856  includes a first guiding part  857  which guides the tearing piece  803  in the first direction and a second guiding part  858  which guides the tearing piece  803  in the second direction. The first guiding part  857  extends in the vertical direction (i.e., Y direction), and the second guiding part  858  is inclined diagonally downward to the right such that a lower part of the second guiding part  858  is located on the right side. The first guiding part  857  and the second guiding part  858  are connected to each other, and a center axis of the first guiding part  857  and a center axis of the second guiding part  858  intersect with each other (see  FIG. 68 ). 
     The first guiding part  857  guides the tearing piece  803  such that the tearing piece  803  tears the gate G in conjunction with mold opening. On the other hand, the second guiding part  858  guides the tearing piece  803  such that the tearing piece  803  after tearing the gate G is moved away from the gate G and the runner R in conjunction with mold opening. 
     The guiding grooves  871  are recessed grooves located at lower ends of the front-face-wall inner surface  853  and the back-face-wall inner surface  854  and extend in a horizontal direction (i.e., X direction) (see  FIG. 68 ). The guiding grooves  871  slidably receive protruding lines  828  of the retaining piece  821  and guide the retaining piece  821  in the horizontal direction (i.e., X direction) in conjunction with mold opening. 
     The guiding grooves  875  are recessed grooves located at right ends of the front-face-wall inner surface  853  and the back-face-wall inner surface  854  and extend in the vertical direction (i.e., Y direction) (see  FIG. 68 ). The guiding grooves  875  slidably receive the protruding lines  844  of the driving piece  841  and guide the driving piece  841  in the vertical direction (i.e., Y direction) in conjunction with mold opening. 
     The tearing piece  803  is configured to tear a gate G and is a substantially triangular body which is shaped, in a front view, as an upper half of a cuboid member cut along a diagonal thereof with a lower half removed and includes a bottom face inclined diagonally upward to the right. The tearing piece  803  includes a protruding line (dovetail-groove protruding line)  805  on a bottom face thereof. The protruding line  805  slidably comes into engagement with a dovetail groove  824  on a left inclined surface  822  of the sliding piece  821 . 
     The tearing piece  803  includes a first groove part  807  located at a middle position on a left side face of the tearing piece  803  and a second groove part  808  located above the first groove part  807  and communicated with the first groove part  807 . The first groove part  807  and the second groove part  808  serve as runner grooves which shape a runner R. The first groove part  807  has a trapezoidal shape, and a back face wall of the tearing piece  803  includes a trapezoidal cutout so as to connect to the first groove part  807 . On the other hand, there is no cutout on a front face wall  804  of the tearing piece  803 , and a part of the front face wall  804  located at the first groove part  807  serves as a flashboard. 
     The second groove part  808  is most recessed at the middle and includes inclined surfaces so as to expand toward the upper face, front face and back face of the tearing piece  803 . The upper face connected to the second groove part  808  includes a slight cutout so as to define a recess  810 . The recess  810  shapes the gate G. 
     The tearing piece  803  includes clicks  812  to be fitted the guiding grooves  856  of the holder  851 . The clicks  812  are located on upper parts of the front face wall  804  and the back face wall in a protruding manner. Therefore, the clicks  812  may be considered as protruding lines. The clicks  812  are adapted to the guiding grooves  856  of the holder  851 , and there are two such clicks  812  on each of the front face wall  804  and the back face wall. Although there may be a single pair of such a click  812  and a guiding groove  856 , provision of two pairs of the clicks  812  and the guiding grooves  856  makes it possible to move the tearing piece  803  more reliably and more precisely, further to distribute a force applied to the clicks  812  and to prevent rotation of the tearing piece  803 . 
     Left side faces  813  and right side faces  814  of the clicks  812  serve as first sliding surfaces which come into contact with left side surfaces and right side surfaces of the first guiding parts  857  of the holder  851 , respectively. Upper side faces  815  and lower side faces  816  of the clicks  812  serve as second sliding surfaces which come into contact with upper side surfaces and lower side surfaces of the second guiding parts  858  of the holder  851 , respectively, in order to move the tearing piece  803  after tearing the gate G away from the gate G and the runner R. 
     The retaining piece  821  is configured to move the tearing piece  803  to tear the gate G and has a substantially trapezoidal shape in a front view. The retaining piece  821  includes a left side face  822  and a right side face  823  formed as inclined surfaces. The left inclined surface  822  includes a dovetail groove  824  which slidably receives the protruding line (dovetail-groove protruding line)  805  of the tearing piece  803 , and the right inclined surface  823  includes a dovetail groove  825  which slidably receives a protruding line (dovetail-groove protruding line)  845  of the driving piece  841 . The retaining piece  821  also includes, at lower ends of a front face wall  827  and a back face wall thereof, protruding lines  828  which are slidably fitted into the guiding grooves  871  of the holder  851 . 
     The retaining piece  821  includes a block member  830  on the back face side of the retaining piece  821 . The block member  830  has a rectangular shape having a height about half the height of the retaining piece  821  and includes an inclined surface  831  at a front upper part thereof. When the mold is clamped (closed), the inclined surface  831  connects to the first groove part  807  of the tearing piece  803  to define a part of the runner groove. 
     The driving piece  841  is configured to move the retaining piece  821  such that the tearing piece  803  tears the gate G and is a triangular body which is shaped, in a front view, as an upper half of a cuboid member cut along a diagonal thereof with a lower half removed and includes a bottom face inclined diagonally upward to the left. The driving piece  841  includes protruding lines  844  which extend in the vertical direction (i.e., Y direction) at right ends of a front face wall  842  and a back face wall  843  of the driving piece  841  and are slidably fitted into the guiding grooves  875  of the holder. The driving piece  841  also includes, on the left inclined surface, a protruding line (dovetail-groove protruding line)  845  which slidably engages with the dovetail groove  825  on the right inclined surface  823  of the sliding piece  821 . 
     A support pin  846  extending upward (i.e., in the Y direction) is attached to an upper face of the driving piece  841 . The support pin  846  has a flange  848  at an upper part thereof, and a spring  849  is fitted between the upper face of the driving piece  841  and the flange  848  with the support pin  846  inserted through the spring  849 . 
     The gate tearing mechanism  801  having the above constitution is incorporated into the holder  851  such that the protruding line  805  of the tearing piece  803  is fitted into the dovetail groove  824  of the retaining piece  821 , the protruding line  845  of the driving piece  841  is fitted into the dovetail groove  825  of the retaining piece  821 , and the support pin  846  protrudes from the holder  851 . In this state, the clicks  812  of the tearing piece  803  are fitted into the guiding grooves  856  of the holder  851 , the protruding lines  828  of the retaining piece  821  are fitted into the guiding grooves  871  of the holder  851 , and the protruding lines  844  of the driving piece  841  are fitted into the guiding grooves  875  of the holder  851 . The gate tearing mechanism  801  incorporating the respective pieces is fitted into the recessed part  728  of the movable mold plate  711 , and the holder  851  is fixed to the movable mold plate  711 . 
     An operation and effects of the molding die  800  and the gate tearing mechanism  801  of the present embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding in the molding die  800 . 
     When the mold is closed, the tearing piece  803  is located at a leftmost position (in the X direction), and the left side face of the tearing piece  803  is in contact with the receiving body  721 . The lower right end of the receiving body  607  is in contact with the upper face  832  of the block member  830 . These parts shape a runner R and a gate G. When the mold is closed, the retaining piece  821  is located at a leftmost position (in the X direction). When the mold is closed, an upper end  847  of the support pin  846  is in contact with the bottom face  613  of the recessed part  612 , and the driving piece  841  is a lowermost position. Also, the spring  849  is in a most compressed state with the support pin  846  inserted therethrough (see  FIG. 65 ). 
     When the mold is closed, parting faces (PL faces) of the fixed die  602  and the movable die  702  are fitted together to define a cavity part. Then, a molten resin is injected from a non-illustrated injection device, and the resin passes through a sprue (not illustrated), then through the runner R and the gate G and fills in the cavity part. After a pressure holding step and a cooling step, the mold is opened, and a molded product P is taken out. The processes of opening the mold and taking out the molded product P are performed according to the following procedure. 
     Once the movable die  702  retracts and the mold starts to open, the holder  851  of the gate tearing mechanism  801  descends in the −Y direction integrally with the movable die  702 . On the other hand, the driving piece  841  slidably fitted into the holder  851  remains at the same position as the position when the mold is closed because the spring  849  acts so as to push up the flange  848 . For this reason, when the mold starts to open, the driving piece  841  ascends relative to the holder  851  (see  FIG. 66 ). 
     When the driving piece  841  ascends relative to the holder  851 , the retaining piece  821  engaged with the driving piece  841  is guided by the guiding grooves  871  to move to the right (i.e., in the −X direction). Further, when the retaining piece  821  moves to the right (i.e., in the −X direction), the tearing piece  803  engaged with the retaining piece  821  is guided by the first guiding parts  857  of the guiding grooves  856  to move in the −Y direction (see  FIG. 66 ). Thus, the gate G is torn, and further the resin in the runner R is pulled back. 
     When the tearing piece  803  descends to tear the gate G, the block member  830  moves rightward (i.e., in the −X direction), so that a space is created between the block member  830  and the receiving body  721 . Further, a space is also created between the upper face  832  of the block member  830  and the bottom face of the receiving body  607 . Therefore, the resin in the runner R which is pulled back as the gate G is torn can be withdrawn to the space. Thus, it is possible to prevent breakage of the resin in the runner R and simplify the recovery mechanism for the resin. 
     After the tearing piece  803  tears the gate G in conjunction with mold opening, as the gap further increases between the fixed die  602  and the movable die  702 , the tearing piece  803  moves along the second guiding parts  858 , while the second sliding surfaces slides in the second guiding parts  858  of the guiding grooves  856 . Thus, the tearing piece  803  moves in the −X direction so as to secure a necessary space to remove the resin which is torn and left in the runner R (see  FIG. 67 ). Then, a non-illustrated ejector mount plate moves up, and the molded product P and the resin left in the runner R are ejected by the ejector pin. 
     As described above, the molding die  800  and the gate tearing mechanism  801  can achieve compact and simple configurations and can operate such that the gate G can be torn easily and reliably prior to taking out the molded product P. In addition, the tearing piece  803  after tearing the gate G is moved away from the gate G and the runner R in conjunction with mold opening, so that the molded product P and the material left in the runner R can be easily removed. In particular, the gate tearing mechanism  801  can tear the gate G without breaking the material in the runner R, and therefore, the mechanism for removing the material left in the runner R is simplified. 
     Further, the gate tearing mechanism  801  can be incorporated into the molding die  800  with the tearing piece  803 , the retaining piece  821 , and the driving piece  841  housed in the holder  851 , and therefore, the gate tearing mechanism  801  can have a compact configuration and be easily attached to the molding die  800 . In particular, the holder  851 , the tearing piece  803 , the retaining piece  821 , and the driving piece  841  can be assembled into a single independent unit; the gate cutting mechanism  801  as a single unit can be more easily attached to the molding die  800 . 
       FIG. 69  is a cross-sectional view of a molding die  900  including a gate tearing mechanism  901  according to a seventeenth embodiment of the present invention in a mold closed state. Features corresponding to the features of the molding die  800  and the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention as shown in  FIG. 65  to  FIG. 68  are denoted with like reference numerals, and description thereof is omitted. The following description will mainly focus on differences from the molding die  800  and the gate tearing mechanism  801  of the sixteenth embodiment of the present invention. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  602  in  FIG. 69 , and the “lower” side means the side of the movable die  702  in  FIG. 69 . In the following description, the “left” side corresponds to the left side in  FIG. 69 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     The configuration and operation of the molding die  900  of the seventeenth embodiment are essentially the same as those of the molding die  800  of the sixteenth embodiment. The gate tearing mechanism  901  of the seventeenth embodiment also has a same basic configuration as that of the gate tearing mechanism  801  of the sixteenth embodiment. However, in the gate tearing mechanism  901 , the configuration of a driving piece  941  which slides a retaining piece  821  is different from that of the driving piece  841 . In association therewith, the configuration of a holder  951  which houses the retaining piece  821  in an advanceable and retractable manner is partly different from that of the holder  851 . 
     As with the gate tearing mechanism  801  of the sixteenth embodiment, the gate tearing mechanism  901  is configured to tear a gate G by a tearing piece  803  in conjunction with opening the molding die  900  and then to move the tearing piece  803  away from the gate G and a runner R so as to allow a material left in the runner R to be removed. The gate tearing mechanism  901  of the present embodiment also employs the sliding mechanism  1  of the first embodiment. The tearing piece  803  and the retaining piece  821  are identical to those of the sixteenth embodiment. 
     The driving piece  841  of the sixteenth embodiment maintains its own position when the mold is opened, using the support pin  846  attached to the upper part of the driving piece  841  and the spring  849  which is inserted by the support pin  846 , whereas the driving piece  941  includes a plate member extending in the Z direction on an upper face thereof and maintains its own position using a spring  943  disposed below the plate member. The configuration of the driving piece  941  is otherwise the same as that of the driving piece  841 . 
     The holder  951  has substantially the same configuration as that of the holder  851  of the sixteenth embodiment, except that an entire upper face of the holder  951  is open, unlike the holder  851 . In addition, the holder  951  includes a recessed part which receives the plate member of the driving piece  941  at an upper right end on a front face wall thereof and, similarly, a recessed part which receives the plate member of the driving piece  941  at an upper right end on a back face wall thereof. The configuration of the holder  951  is otherwise the same as that of the holder  851 . 
     The gate tearing mechanism  901  having the above constitution is arranged such that the protruding line  805  of the tearing piece  803  is fitted into the dovetail groove  824  of the retaining piece  821 , and the protruding line  845  of the driving piece  941  is fitted into the dovetail groove  824  of the retaining piece  821 . The clicks  812  of the tearing piece  803  are fitted into the guiding grooves  856  of the holder  951 , the protruding lines  828  of the retaining piece  821  are fitted into the guiding grooves  871  of the holder  951 , and the protruding lines  844  of the driving piece  941  are fitted into the guiding grooves  875  of the holder  951  (see  FIG. 65  to  FIG. 68 ). The gate tearing mechanism  901  incorporating the respective pieces is fitted into the recessed part  728  of the movable mold plate  711 , and the holder  951  is fixed to the movable mold plate  711 . 
     An operation and effects of the molding die  900  and the gate tearing mechanism  901  of the seventeenth embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding in the molding die  900 . Since the operation and effects of the molding die  900  and the gate tearing mechanism  901  of the seventeenth embodiment are essentially the same as those of the molding die  800  and the gate tearing mechanism  801  of the sixteenth embodiment, only important points will be described with reference to  FIG. 65  to  FIG. 68 . 
     When the mold is closed, the tearing piece  803  is located at a leftmost position (in the X direction), and the left side face of the tearing piece  803  is in contact with the receiving body  721 . Also, the lower right end of the receiving body  607  is in contact with the upper face  832  of the block member  830 . These parts shape a runner R and a gate G. When the mold is closed, the retaining piece  821  is located at a leftmost position (in the X direction). When the mold is closed, the driving piece  941  is arranged such that a ceiling face of the plate member is in contact with the bottom face  610  of the fixed mold plate  605 , and the spring  943  is in a most compressed state (see  FIG. 69 ). When the mold is opened, the spring  943  acts so as to push up the plate member of the driving piece  941  slidably fitted into the holder  951 . Accordingly, even when the mold starts to open, the driving piece  941  maintains the same position as before mold opening and thus moves upward relative to the holder  951 . 
     The processes of molding a molded product P, tearing a gate G, and taking out the molded product P and a resin left in a runner R are performed in the same manner as those in the molding die  800  and the gate tearing mechanism  801  of the sixteenth embodiment. 
     The molding die  900  and the gate tearing mechanism  901  have essentially the same effects, advantages and characteristics as those of the molding die  800  and the gate tearing mechanism  801 . However, the gate tearing mechanism  901  has an advantage that processing to the fixed die  602  is not particularly necessary when incorporating the fixed die  602  into the molding die  900 . 
       FIG. 70  is a cross-sectional view of a molding die  1000  including a gate tearing mechanism  1001  according to an eighteenth embodiment of the present invention in a mold closed state. Features corresponding to the features of the molding die  800  and the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention as shown in  FIG. 65  to  FIG. 68  as well as the molding die  900  and the gate tearing mechanism  901  according to the seventeenth embodiment of the present invention as shown in  FIG. 69  are denoted with like reference numerals, and description thereof is omitted. The following description will mainly focus on differences from the molding dies  800 ,  900  and the gate tearing mechanisms  801 ,  901  of the sixteenth and seventeenth embodiments of the present invention. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  602  in  FIG. 70 , and the “lower” side means the side of the movable die  702  in  FIG. 70 . In the following description, the “left” side corresponds to the left side in  FIG. 70 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     The molding die  1000  of the eighteenth embodiment has essentially the same configuration and operation as those of the molding die  800  of the sixteenth embodiment. The gate tearing mechanism  1001  of the eighteenth embodiment also has a same basic configuration as that of the gate tearing mechanism  801  of the sixteenth embodiment but differs from the gate tearing mechanism  801  in terms of a driving unit which slides a retaining piece  1021 . In association therewith, the configurations of the retaining piece  1021  and a holder  1051  are partly different from those of the retaining piece  821  and the holder  851 . 
     As with the gate tearing mechanism  801  of the sixteenth embodiment, the gate tearing mechanism  1001  is configured to tear a gate G by a tearing piece  803  in conjunction with opening the molding die  1000  and then to move the tearing piece  803  away from the gate G and a runner R so as to allow a material left in the runner R to be removed. The gate tearing mechanism  1001  of the present embodiment also employs the sliding mechanism  1  of the first embodiment. The tearing piece  803  is identical to that of the sixteenth embodiment. 
     As with the retaining piece  821 , the retaining piece  1021  is configured to slide the tearing piece  803 . Unlike the retaining piece  821 , the retaining piece  1021  does not include a dovetail groove on a right inclined surface  823  thereof. The right inclined surface  823  of the retaining piece  1021  is slidably in contact with an inclined surface  1044  of a locking block  1041 . The retaining piece  1021  has a same configuration as the retaining piece  821 , except that there is no dovetail groove on the right inclined surface  823 . 
     In the present embodiment, a driving unit which slides the retaining piece  1021  is a gas spring  1080 . The gas spring  1080  is a known gas spring including a cylinder body and an expandable rod  1082  attached to the cylinder body. The gas spring  1080  is attached to a recessed part  729  in the receiving body  721  such that an advancing and retracting direction of the rod  1082  coincides with a sliding direction of the retaining piece  1021 , and a tip end of the rod  1082  is in contact with a front face of the block member  830 . 
     The locking block  1041  is slidably in contact with the retaining piece  1021  and is configured to position the retaining piece  1021  when the mold is closed and to restrict movement (slide) of the retaining piece  1021  when the mold is being opened. The locking block  1041  is a block-like member which is shaped by diagonally cutting a left part of a cuboid member off to shape a left side face of the locking block  1041  as an inclined surface  1044  inclined downward to the right. When the locking block  1041  is incorporated into the holder  1051 , the inclined surface  1044  is slidably in contact with the right inclined surface  823  of the retaining piece  1021 . 
     An upper part of the locking block  1041  is fitted into the recessed part  612  of the fixed mold plate  605 , and the locking block  1041  is fixed to the fixed mold plate  605  by a fixing bolt  1046 . When attached to the fixed mold plate  605 , the locking block  1041  mostly projects downward. 
     The holder  1051  has a same configuration as the holder  951 , except that the holder  1051  does not include the guiding grooves  875  and a recessed part for receiving a plate member. 
     The gate tearing mechanism  1001  having the above constitution is incorporated into the holder  1051  with the protruding line  805  of the tearing piece  803  fitted into the dovetail groove  824  of the retaining piece  1021 . In this state, the clicks  812  of the tearing piece  803  are fitted into the guiding grooves  856  of the holder  1051 , and the protruding lines  828  of the retaining piece  1021  are fitted into the guiding grooves  871  of the holder  1051  (see FIG.  65  to  FIG. 68 ). With the tearing piece  803  and the retaining piece  1021  incorporated into the holder  1051 , the gate tearing mechanism  1001  is fitted into the recessed part  728  of the movable mold plate  711 , and the holder  1051  is fixed to the movable mold plate  711 . 
     An operation and effects of the molding die  1000  and the gate tearing mechanism  1001  of the eighteenth embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding in the molding die  1000 . Since the operation and effects of the molding die  1000  and the gate tearing mechanism  1001  of the eighteenth embodiment are essentially the same as those of the molding die  800  and the gate tearing mechanism  801  of the sixteenth embodiment, only important points will be described. 
     When the mold is closed, the tearing piece  803  is located at a leftmost position (in the X direction), and the left side face of the tearing piece  803  is in contact with the receiving body  721 . Also, the lower right end of the receiving body  607  is in contact with the upper face  832  of the block member  830 . These parts shape a runner R and a gate G. When the mold is closed, the retaining piece  1021  is in contact with the receiving body  721 . The gas spring  1080  is arranged such that the tip end of the rod  1082  is in contact with the front face of the block member  830 . As the mold is being opened, the movable die  702  descends to create a gap between the movable die  702  and the fixed die  602 , and the retaining piece  1021  is pushed by the gas spring  1080  to move in the −X direction. In this state, the right inclined surface  823  of the retaining piece  1021  is slidably in contact with the inclined surface  1044  of the locking block  1041 . 
     The processes of molding a molded product P, tearing a gate G, and taking out the molded product P and a resin left in a runner R are performed in the same manner as those in the molding die  800  and the gate tearing mechanism  801  of the sixteenth embodiment. The molding die  1000  and the gate tearing mechanism  1001  have essentially the same effects, advantages and characteristics as those of the molding die  800  and the gate tearing mechanism  801 . 
       FIG. 71  is a cross-sectional view of a molding die  1100  including a gate tearing mechanism  1101  according to a nineteenth embodiment of the present invention in a mold closed state. Features corresponding to the features of the molding die  800  and the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention as shown in  FIG. 65  to  FIG. 68  are denoted with like reference numerals, and description thereof is omitted. The following description will mainly focus on differences from the molding die  800  and the gate tearing mechanism  801  of the sixteenth embodiment of the present invention. For the sake of convenience, in the following description, the “upper” side means the side of the fixed die  602  in  FIG. 71 , and the “lower” side means the side of the movable die  702  in  FIG. 71 . In the following description, the “left” side corresponds to the left side in  FIG. 71 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     The molding die  1100  of the nineteenth embodiment has essentially the same configuration and operation as those of the molding die  800  of the sixteenth embodiment. The gate tearing mechanism  1001  of the nineteenth embodiment also has a same basic configuration and a same operation as those of the gate tearing mechanism  801  of the sixteenth embodiment but differs from the driving piece  841  in terms of a driving piece  1141  which slides the retaining piece  821 . In association therewith, the configuration of a holder  1151  partly differs from that of the holder  851 . 
     As with the gate tearing mechanism  801  of the sixteenth embodiment, the gate tearing mechanism  1101  is configured to tear a gate G by a tearing piece  803  in conjunction with opening the molding die  1100  and then to move the tearing piece  803  away from the gate G and a runner R so as to allow a material left in the runner R to be removed. The gate tearing mechanism  1101  of the present embodiment also employs the sliding mechanism  1  of the first embodiment. The tearing piece  803  and the retaining piece  821  are identical to those of the sixteenth embodiment. The block member  830  also have a same basic configuration as that of the block member  830  of the sixteenth embodiment but additionally includes a recessed part  835  which houses a spring  1180  on a left side face of the block member  830 . 
     As with the driving piece  841 , the driving piece  1141  is configured to move the retaining piece  821  such that the tearing piece  803  tears a gate G. The driving piece  1141  has a triangular shape in a front view and includes, at right ends of a front face wall and a back face wall of the driving piece  1141 , protruding lines  844  which are slidably fitted into guiding grooves of the holder  1151 . Each protruding line  844  is arranged such that an upper part thereof is located rightward with respect to a lower part thereof in a front view. The driving piece  1141  also includes, on the left inclined surface thereof, a protruding line (dovetail-groove protruding line) which slidably come into engagement with the dovetail groove  825  on the right inclined surface  823  of the sliding piece  821 . 
     The driving piece  1141  integrally includes a hook  1142  having a toppled L shape on an upper face of the driving piece  1141 . The hook  1142  includes a base part connected to the upper face of the driving piece  1141  and a horizontal part connected to the base part and is arranged such that a tip end  1143  of the horizontal part is directed to the left. 
     The driving piece  1141  is locked to a locking hook  1145  attached to the fixed mold plate  605 . The locking hook  1145  is a hook having a toppled L shape and is fixed to a recessed part  620  in the fixed mold plate  605 . The locking hook  1145  is fixed to the recessed part  620  such that a tip end  1146  of a horizontal part thereof is directed to the right and the horizontal part is located lower than the base part (see  FIG. 71 ). For this reason, there is a space above the horizontal part of the locking hook  1145 . 
     When the mold is clamped, the driving piece  1141  is locked such that the horizontal part of the hook  1142  is placed on the horizontal part of the locking hook  1145 . The recessed part  620  has a longer length (in the X direction) than a sum of lengths of the locking hook  1145  and the hook  1142 . Therefore, when the driving piece  1141  locked to the locking hook  1145  is moved to the right (i.e., in the −X direction) to a maximum extent possible, the driving piece  1141  can be disengaged from the locking hook  1145  and also be moved out from the fixed mold plate  605 . 
     The holder  1151  has a same basic configuration as that of the holder  851  but differs from the holder  851  in that the holder  1151  has an entirely open upper face. The guiding grooves  875  which slidably receive the protruding lines  844  of the driving piece  1141  are adapted to the protruding lines  844  of the driving piece  1141  and extend diagonally upward to the right in a front view. The holder  1151  also includes an inclined surface  1152  extending along the guiding grooves  875 . The inclined surface  1152  is slidably in contact with the right inclined surface of the driving piece  1141 . Except for the above points, the holder  1151  has a same configuration as the holder  851 . 
     The spring  1180  pushes out the retaining piece  821  in the −X direction. 
     The gate tearing mechanism  1101  having the above constitution is incorporated into the holder  1151  with the protruding line  805  of the tearing piece  803  fitted into the dovetail groove  824  of the retaining piece  821 , and the protruding line of the driving piece  1141  fitted into the dovetail groove  825  of the retaining piece  821 . In this state, the clicks  812  of the tearing piece  803  are fitted into the guiding grooves  856  of the holder  1151 ; the protruding lines  828  of the retaining piece  821  are fitted into the guiding grooves  871  of the holder  1151 ; and the protruding lines  844  of the driving piece  1141  are fitted into the guiding grooves  875  of the holder  1151  (see  FIG. 65  to  FIG. 68 ). The gate tearing mechanism  1101  incorporating the respective pieces is fitted into the recessed part  728  of the movable mold plate  711 , and the holder  1151  is fixed to the movable mold plate  711 . 
     An operation and effects of the molding die  1100  and the gate tearing mechanism  1101  of the nineteenth embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding in the molding die  1100 . Since the operation and effects of the molding die  1100  and the gate tearing mechanism  1101  of the nineteenth embodiment are essentially the same as those of the molding die  800  and the gate tearing mechanism  801  of the sixteenth embodiment, only important points will be described. 
     When the mold is closed, the tearing piece  803  is located at a leftmost position (in the X direction), and the left side face of the tearing piece  803  is in contact with the receiving body  721 . Also, the lower right end of the receiving body  607  is in contact with the upper face  832  of the block member  830 . These parts shape a runner R and a gate G. When the mold is closed, the hook  1142  of the driving piece  1141  is locked to the locking hook  1145 . Since the hook  1142  is locked to the locking hook  1145 , it is possible to drive the respective pieces with a larger force than a force of the spring  1180 . The spring  1180  is in a compressed state, and a tip end of the spring  1180  is in contact with the receiving body  721 . 
     As the mold is being opened, the movable die  702  descends to create a gap between the movable die  702  and the fixed die  602 , and the driving piece  1141  moves upward relative to the holder  1151 , so that the retaining piece  821  slidably engaged with the driving piece  1141  moves in the −X direction. Although the spring  1180  is expanded in association with mold opening, the spring  1180  continues to push the retaining piece  821  in the −X direction. 
     When the retaining piece  821  moves rightward (i.e., in the −X direction), the tearing piece  803  engaged with the retaining piece  821  is guided by the first guiding parts  857  of the guiding grooves  856  to move in the −Y direction. Thus, the gate G is torn, and further the resin in the runner R is pulled back. When the tearing piece  803  descends to tear the gate G, the block member  830  moves rightward (i.e., in the −X direction), so that a space is created between the block member  830  and the receiving body  721 . Further, a space is also created between the upper face  832  of the block member  830  and the bottom face  613  of the receiving body  607 . Therefore, the resin in the runner R which is pulled back as the gate G is tom can be withdrawn to the space. 
     After the tearing piece  803  tears the gate G in conjunction with mold opening, as the gap further increases between the fixed die  602  and the movable die  702 , the tearing piece  803  moves along the second guiding parts  858 , while the second sliding surfaces slide in the second guiding parts  858  of the guiding grooves  856 . Thus, the tearing piece  803  moves in the −X direction so as to secure a necessary space to remove the resin which is torn and left in the runner R. Then, a non-illustrated ejector mount plate moves up, and the molded product P and the resin left in the runner R are ejected by the ejector pin. 
     Since the driving piece  1141  moves diagonally upward to the right along the guiding grooves  875  of the holder  1151 , when the gap increases between the fixed die  602  and the movable die  702  in conjunction with mold opening, the hook  1142  is disengaged from the locking hook  1145 . The driving piece  1141  disengaged from the locking hook  1145  moves integrally with the movable mold plate  711  through the holder  1151 . Even when the driving piece  1141  is disengaged from the locking hook  1145 , the respective pieces remain at same positions because the spring  1180  continuously pushes the retaining piece  821  in the −X direction. 
     The molding die  1100  and the gate tearing mechanism  1101  have essentially the same effects, advantages and characteristics as those of the molding die  800  and the gate tearing mechanism  801 . 
       FIG. 72  to  FIG. 75  are perspective views illustrating operations of a gate tearing mechanism  1201  according to a twentieth embodiment of the present invention.  FIG. 76  is an exploded view showing features of the gate tearing mechanism  1201  according to the twentieth embodiment of the present invention. For the sake of convenience, in the following description, the “upper” side means the side of the molded product P in  FIG. 72 , and the “lower” side means the side of the guiding piece  1271  in  FIG. 72 . In the following description, the “left” side corresponds to the left side in  FIG. 72 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     As with the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention, the gate tearing mechanism  1201  according to the twentieth embodiment of the present invention is incorporated into and used in a molding die including a fixed die which molds an external surface of a molded product P and a movable die which molds an internal surface of the molded product P. Such a molding die which includes the fixed die and the movable die and is capable of being used with the gate tearing mechanism  1201  incorporated therein is not limited to a particular type. 
     As with the gate tearing mechanism  801 , the gate tearing mechanism  1201  is operable to tear a gate G connecting a molded product P to a runner R and is configured to tear a gate G by a tearing piece  1203  in conjunction with opening the molding die and then to move the tearing piece  1203  away from the gate G and a runner R so as to allow a material left in the runner R to be removed. The gate tearing mechanism  1201  of the present embodiment also employs the sliding mechanism  1  of the first embodiment. 
     The gate tearing mechanism  1201  includes a tearing piece  1203  which tears a gate G; a retaining piece  1221  which is slidably engaged with the tearing piece  1203  to slide the tearing piece  1203 ; a holder  1251  which partially houses the tearing piece  1203  and the retaining piece  1221  and slides the retaining piece  1221 ; and a guiding piece  1271  which guides the retaining piece  1221  (see  FIG. 76 ). 
     The tearing piece  1203  of the present embodiment corresponds to the second piece  21  of the sliding mechanism  1  of the first embodiment; the retaining piece  1221  corresponds to the first piece  11 ; and the holder  1251  corresponds to the guiding body  31 . In the present embodiment, the tearing piece  1203  corresponds to a slider, and the holder  1251  corresponds to a guide body. As described later, a guiding groove  1256  corresponds to a guide unit; a first guiding part  1257  corresponds to a first guide unit; and a second guiding part  1258  corresponds to a second guide unit. A click  1212  corresponds to an engagement unit; a first sliding surface of the click  1212  corresponds to a first engagement unit; and a second sliding surface of the click  1212  correspond to a second engagement unit. The retaining piece  1221  and the tearing piece  1203  are slidably engaged with each other. The retaining piece  1221  corresponds to an engaging member, and the guiding piece  1271  corresponds to an engaging member guide unit. 
     The tearing piece  1203  is configured to shape a gate G and to tear the gate G. The tearing piece  1203  includes a protrusion  1210  which extends in the Z direction at an upper tip end of the tearing piece  1203  and is configured to shape the gate G. The protrusion  1210  is tapered toward a tip end thereof (in the X direction). The tip end of the tearing piece  1203  is located on a side on which the protrusion  1210  is located, which corresponds to the left side in  FIG. 76 . At an upper part opposite from the protrusion  1210 , the tearing piece  1203  includes the clicks  1212  which are slidably fitted into the guiding grooves  1256  of the holder  1251 . The clicks  1212  are located on upper parts of a front face wall  1204  and a back face wall of the tearing piece  1203  in a protruding manner. Therefore, the clicks  1212  may be considered as protruding lines. 
     A left side face  1213  and a right side face  1214  of each click  1212  serve as first sliding surfaces which come into contact with a left side surface and a right side surface of a corresponding first guiding part  1257  of the guiding grooves  1256  of the holder  1251 , respectively. An upper side face  1215  and a lower side face  1216  of a click  1212  serve as second sliding surfaces which come into contact with an upper side surface and a lower side surface of a second guiding part  1258  of the guiding groove  1256  of the holder  1251  in order to move the tearing piece  1203  after tearing the gate G away from the gate G and the runner R. 
     The tearing piece  1203  includes a protruding portion  1206  extending in the −X direction below the protrusion  1210 . The protruding portion  1206  includes, at an upper part thereof, an L-shaped recessed part  1208  which serves as a part of a runner groove which shapes the runner R. A bottom face of the protruding portion  1206  is an inclined surface  1209 . The inclined surface  1209  inclines downward to the front and slidably comes into contact with an inclined surface  1222  of the retaining piece  1221 . A bottom face of the tearing piece  1203  is an inclined surface which is inclined toward the front, and a protruding line  1205  is located at a lower end of the front face wall  1204  and extends along the bottom face. The protruding line  1205  is slidably fitted into a recessed groove of the retaining piece  1221 . 
     The retaining piece  1221  is configured to move the tearing piece  1203  so as to tear the gate G. The retaining piece  1221  has an inclined surface  1222  as a left side face, and the inclined surface  1222  includes a recessed part  1224  which is shaped in a chased manner and slidably receives a lower part of the tearing piece  1203 . The recessed part  1224  extends upward to the right and includes, on a side thereof, a recessed groove (not illustrated) which receives the protruding line  1205  of the tearing piece  1203 . The inclined surface  1209  of the tearing piece  1203  slidably comes into contact with the inclined surface  1222 . 
     The retaining piece  1221  also includes a protruding portion  1230  which protrudes frontward at an upper part of the front face wall  1227 . The protruding portion  1230  and the inclined surface  1222  defines a recessed part  1231  which receives the protruding portion  1206  of the tearing piece  1203 . The protruding portion  1230  is a closing part which closes an upper part of the recessed part  1208  of the protruding portion  1206  which is fitted into the recessed part  1231 . 
     The retaining piece  1221  includes a right side face as an inclined surface which is inclined downward to the right, and includes protruding lines  1225 ,  1226  extending along the right side face on the front face wall  1227  and the back face wall of the retaining piece  1221 . The protruding lines  1225 ,  1226  are slidably fitted into guiding grooves  1259  of the holder  1251 . The retaining piece  1221  includes, at a bottom part thereof, a dovetail groove which slidably receives a protruding line (dovetail-groove protruding line)  1273  of the guiding piece  1271 . 
     The guiding piece  1271  is slidably coupled to the retaining piece  1221  and guides the retaining piece  1221 . The guiding piece  1271  is shaped by a flat plate-like member and a protruding line (dovetail-groove protruding line)  1273  located on an upper face of the flat plate-like member. When the gate tearing mechanism  1201  is incorporated into the molding die, the guiding piece  1271  is fixed to the movable die. The guiding piece  1271  of the present embodiment includes a bolt insertion hole  1274  for fixing the guiding piece  1271  to the movable die. 
     The holder  1251  partially houses the tearing piece  1203  and the retaining piece  1221  and guides the tearing piece  1203  such that the tearing piece  1203  tears the gate G and the tearing piece  1203  after tearing the gate G is moved away from the gate G and the runner R. The holder  1251  includes two half holder members  1252  of a substantially same shape which are assembled together. The holder  1251  may be constituted by a plurality of divided members or be integrated with the fixed die. 
     The holder  1251  includes a body  1253  having a substantially cuboid shape and a flange  1254  which is located at an upper part of the body  1253  and is integrated to the body  1253 . The body  1253  is open on a left side face thereof and includes a housing part  1260  therein which partially houses the tearing piece  1203  and the retaining piece  1221 . The housing part  1260  narrows down to the right (to the rear) and includes an inclined surface  1261  extending downward to the right thereinside. The second guiding part  1258  of the guiding groove  1256  and guiding grooves  1259  extend along the inclined surface  1261 . 
     The holder  1251  includes the guiding grooves  1256  which guide the tearing piece  1203  at a center upper part and a back-face-wall inner surface  1263  of the holder  1251 . The guiding groove  1256  located on the back-face-wall inner surface  1263  has a dog-legged shape and includes a first guiding part  1257  which guides the tearing piece  1203  in the first direction and a second guiding part  1258  which guides the tearing piece  1203  in the second direction. The first guiding part  1257  extends in the vertical direction (i.e., Y direction), and the second guiding part  1258  is inclined diagonally downward to the right such that a lower part thereof is located on the right. The first guiding part  1257  and the second guiding part  1258  are connected to each other, and a center axis of the first guiding part  1257  and a center axis of the second guiding part  1258  intersect with each other (see  FIG. 76 ). On the other hand, the guiding groove  1256  located at the center upper part only includes a first guiding part  1257  which guides the tearing piece  1203  in the first direction 
     The first guiding parts  1257  guide the tearing piece  1203  such that the tearing piece  1203  tears the gate G in conjunction with mold opening. On the other hand, the second guiding part  1258  guides the tearing piece  1203  such that the tearing piece  1203  after tearing the gate G is moved away from the gate G and the runner R in conjunction with mold opening. The second guiding part  1258  of the guiding groove  1256  on the back-face-wall inner surface  1263  also serves as a guiding groove  1259  which slidably receives the protruding line  1226  of the retaining piece  1221 . Another guiding groove  1259  which receives the protruding line  1225  of the retaining piece  1221  is located on a front-face-wall inner surface  1262  of the holder  1251 . These two guiding grooves  1259  guide movement of the retaining piece  1221 . 
     The holder  1251  also includes a stopper receiving hole  1266  which houses a stopper  1267  for preventing movement of the retaining piece  1221 . The stopper receiving hole  1266  opens on the upper face  1264  and includes a lower end communicated with the housing part  1260 . The flange  1254  includes a bolt insertion hole  1274  for fixing the holder  1251  to the fixed die. 
     The stopper  1267  is a bottomed cylindrical member which prevents movement of the retaining piece  1221  and includes a spring  1268  placed therein. The stopper  1267  is slidably inserted into the stopper receiving hole  1266  such that a lower end of the stopper  1267  projects into the housing part  1260 . Once the retaining piece  1221  retracts, and a movement restricting part (not illustrated) on the retaining piece  1221  hits the stopper  1267 , the movement is prevented. 
     The spring  1268  is placed in the stopper  1267  and presses the stopper  1267  downward (i.e., in the −Y direction) when the gate tearing mechanism  1201  is incorporated into the molding die. 
     An operation and effects of the gate tearing mechanism  1201  of the present embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding when the gate tearing mechanism  1201  is incorporated into a molding die similar to that as shown in  FIG. 65  which includes the fixed die  602  and the movable die  702 . Features corresponding to the features of the fixed die  602  and the movable die  702  as shown in  FIG. 65  are denoted with like reference numerals, and description thereof is omitted. 
     The gate tearing mechanism  1201  is incorporated into the holder  1251  with the protruding line  1205  of the tearing piece  1203  fitted into the dovetail groove of the retaining piece  1221 , and the protruding portion  1206  of the tearing piece  1203  fitted into the recessed part  1231  of the retaining piece  1221 . In this state, the clicks  1212  of the tearing piece  1203  are fitted into the first guiding parts  1257  of the guiding grooves  1256  of the holder  1251 , and the protruding line  1225  and the protruding line  1226  of the retaining piece  1221  are fitted into the guiding grooves  1259  of the holder  1251 . 
     The holder  1251  is arranged such that the flange  1254  is fixed to the fixed mold plate  605 , and when the mold is closed, the body  1253  of the holder  1251  is located in the recessed part  728  of the movable die  702 . The guiding piece  1271  is fixed to the bottom face of the recessed part  728  of the movable die  702 . 
     When the mold is closed, the tearing piece  1203  is at a position for shaping a gate G and a runner R. The retaining piece  1221  is also located next to the tearing piece  1203  to shape the runner R. At this point, the tearing piece  1203  and the retaining piece  1221  are projected to a maximum extent from the holder  1251  (see  FIG. 72 ). 
     When the mold is closed, parting faces (PL faces) of the fixed die  602  and the movable die  702  are fitted together to define a cavity part. Then, a molten resin is injected from a non-illustrated injection device, and the resin passes through a sprue (not illustrated), then through the runner R and the gate G and fills in the cavity part. After a pressure holding step and a cooling step, the mold is opened, and a molded product P is taken out. The processes of opening the mold and taking out the molded product P are performed according to the following procedure. 
     Once the movable die  702  retracts and the mold starts to open, the retaining piece  1221  slidably coupled to the guiding piece  1271  and the tearing piece  1203  slidably engaged with the retaining piece  1221  descend along with the movable die  702 . On the other hand, the holder  1251  remains in the same position because it is fixed to the fixed die  602 . Therefore, when the mold starts to open, the holder  1251  ascends relative to the tearing piece  1203  and the retaining piece  1221  (see  FIG. 73 ). 
     At the same time, the clicks  1212  of the tearing piece  1203  are guided in the first guiding parts  1257  of the guiding grooves  1256  and move in the −Y direction with respect to the molded product P. Thus, the gate G is torn, and the resin in the runner R is pulled back. The protruding line  1225  of the retaining piece  1221  is guided by the second guiding part  1258  of the guiding groove  1256 . At the same time, since the retaining piece  1221  is slidably engaged with the guiding piece  1271 , the retaining piece  1221  retracts toward the side of the holder  1251  without changing its height position relative to the molded product P (see  FIG. 73 ). 
     When the tearing piece  1203  descends to tear the gate G, if the retaining piece  1221  descends along with the tearing piece  1203 , and the protruding portion  1230  pushes the runner R down, a shearing force would act on the resin in the runner R, resulting in breakage of the runner R. In the gate tearing mechanism  1201  of the present embodiment, however, when the tearing piece  1203  descends to tear the gate G, the retaining piece  1221  has retracted and is away from the runner R, so that only the tearing piece  1203  pushes the runner R down. When the tearing piece  1203  pushes down the runner R in such a state, the runner R deflects, so that it is possible to prevent breakage of the runner R (see  FIG. 73 ). 
     After the tearing piece  1203  tears the gate G in conjunction with mold opening, as the gap further increases between the fixed die  602  and the movable die  702 , the tearing piece  1203  moves along the second guiding part  1258 , while the second sliding surfaces of the click  1212  slide in the second guiding part  1258  of the guiding groove  1256 . Thus, the tearing piece  1203  moves away from the runner R (see  FIG. 74 ). When the movable die  702  descends further, the retaining piece  1221  is disengaged from the guiding piece  1271 , and the retaining piece  1221  is connected to the holder  1251  together with the tearing piece  1203 . Thus, a necessary space is secured to take out the molded product P and the resin which is torn and left in the runner R (see  FIG. 75 ). Then, a non-illustrated ejector mount plate moves up, and the molded product P and the resin left in the runner R are ejected by the ejector pin. 
     As described above, the gate tearing mechanism  1201  can achieve a compact and simple configuration and can operate such that the gate G can be torn easily and reliably prior to taking out the molded product P. In addition, the tearing piece  1203  after tearing the gate G is moved away from the gate G and the runner R in conjunction with mold opening, so that the molded product P and the material left in the runner R can be easily removed. In particular, the gate tearing mechanism  1201  can tear the gate G without breaking the material in the runner R, and therefore, the mechanism for removing the material left in the runner R is simplified. 
     Further, the gate tearing mechanism  1201  can be incorporated into the molding die with the tearing piece  1203  and the retaining piece  1221  housed in the holder  1251 , and therefore, the gate tearing mechanism  1201  can have a compact configuration and be easily attached to the molding die. In particular, the holder  1251 , the tearing piece  1203 , the retaining piece  1221 , and the guiding piece  1271  can be assembled into a single independent unit; the gate cutting mechanism  1201  as a single unit can be more easily attached to the molding die. 
       FIG. 77  to  FIG. 79  are perspective views illustrating operations of a gate tearing mechanism  1301  according to a twenty-first embodiment of the present invention.  FIG. 80  is an exploded view showing features of the gate tearing mechanism  1301  according to the twenty-first embodiment of the present invention. For the sake of convenience, in the following description, the “upper” side means the side of the molded product P in  FIG. 77 , and the “lower” side means the side of the spring  1380  in  FIG. 77 . In the following description, the “left” side corresponds to the left side in  FIG. 77 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     As with the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention, the gate tearing mechanism  1301  according to the twenty-first embodiment of the present invention is incorporated into and used in a molding die including a fixed die which molds an external surface of a molded product P and a movable die which molds an internal surface of the molded product P. Such a molding die which includes the fixed die and the movable die and is capable of being used with the gate tearing mechanism  1301  incorporated therein is not limited to a particular type. 
     As with the gate tearing mechanism  1201 , the gate tearing mechanism  1301  is operable to tear a gate G connecting a molded product P to a runner R and is configured to tear a gate G by a tearing piece  1303  in conjunction with opening the molding die and then to move the tearing piece  1303  away from the gate G and a runner R so as to allow a material left in the runner R to be removed. The gate tearing mechanism  1301  of the present embodiment also employs the sliding mechanism  1  of the first embodiment. 
     The gate tearing mechanism  1301  includes a tearing piece  1303  which tears a gate G; a retaining piece  1321  which is slidably engaged with the tearing piece  1303  to slide the tearing piece  1303 ; a driving piece  1341  which is slidably engaged with the retaining piece  1321  to slide the retaining piece  1321 ; and a holder  1351  which houses the retaining piece  1321  and the like in an advanceable and retractable manner (see  FIG. 80 ). 
     The tearing piece  1303  of the present embodiment corresponds to the second piece  21  of the sliding mechanism  1  of the first embodiment; the retaining piece  1321  corresponds to the first piece  11 ; and the holder  1351  corresponds to the guiding body  31 . In the present embodiment, the tearing piece  1303  corresponds to a slider, and the holder  1351  corresponds to a guide body. As described later, a guiding groove  1356  corresponds to a guide unit; a first guiding part  1357  corresponds to a first guide unit; and a second guiding part  1358  corresponds to a second guide unit. A click  1312  corresponds to an engagement unit; a first sliding surface of the click  1312  corresponds to a first engagement unit; and a second sliding surface of the click  1312  corresponds to second engagement unit. The retaining piece  1321  and the tearing piece  1303  are slidably engaged with each other. The retaining piece  1321  corresponds to an engaging member, and a recessed groove  1371  of the holder  1351  corresponds to an engaging member guide unit. 
     The tearing piece  1303  is configured to shape a gate G and tearing the gate G. The tearing piece  1303  includes a protrusion  1310  which extends in the Z direction at an upper tip end of the tearing piece  1303  and is configured to shape the gate G. The protrusion  1310  is tapered toward a tip end thereof. The tip end of the tearing piece  1303  is located on a side on which the protrusion  1310  is located, which corresponds to the left side in  FIG. 80 . On a back face wall  1307  of the tearing piece  1303 , there are two clicks  1312  which are slidably fitted into two guiding grooves  1356  in the holder  1351 . The two clicks  1312  are located on the back face wall  1307  in a protruding manner. Therefore, the clicks  1312  may be considered as protruding lines. Although there may be a single pair of such a click  1312  and a guiding groove  1356 , provision of two pairs of the clicks  1312  and the guiding grooves  1356  makes it possible to move the tearing piece  1303  more reliably and more precisely, further to distribute a force applied to the clicks  1312  and to prevent rotation of the tearing piece  1303 . 
     Left side faces  1313  and right side faces  1314  of the clicks  1312  serve as first sliding surfaces which come into contact with left side surfaces and right side surfaces of the first guiding parts  1357  of the guiding grooves  1356  of the holder  1351 . Upper side faces  1315  and lower side faces of the clicks  1312  serve as second sliding surfaces which come into contact with upper side surfaces and lower side surfaces of the second guiding parts  1358  of the guiding grooves  1356  of the holder  1351  in order to move the tearing piece  1303  after tearing the gate G away from the gate G and a runner R. 
     The tearing piece  1303  includes a recessed part  1308  extending in the X direction below the protrusion  1310 . The recessed part  1308  includes a bottom face which is an inclined surface  1309  extending downward to the front. The tearing piece  1303  includes a bottom face which is an inclined surface inclined toward the front and a front face including a protruding line  1305  which is located at a lower end of the front face and extends along the bottom face (see  FIG. 80 ). The protruding line  1305  is slidably fitted into a recessed groove  1331  of the retaining piece  1321 . 
     The retaining piece  1321  is configured to move the tearing piece  1303  to tear the gate G. The retaining piece  1321  includes a recessed part  1334  on the front side (see  FIG. 80 ). A bottom face of the recessed part  1334  is an inclined surface  1322  extending downward to the front. The recessed part  1344  is arranged such that when the tearing piece  1303  is incorporated into the retaining piece  1321 , the recessed part  1344  is connected to the recessed part  1308  of the tearing piece  1303 . The recessed part  1334  has a same size and a same shape as those of the recessed part  1308  of the tearing piece  1303  and is arranged such that when the tearing piece  1303  is incorporated into the retaining piece  1321 , the inclined surface  1322  of the recessed part  1334  of the retaining piece  1321  is flush with the inclined surface  1309  of the recessed part  1308  of the tearing piece  1303 . The recessed part  1308  and the recessed part  1334  serve as runner grooves. 
     The retaining piece  1321  includes, on back face wall thereof, a recessed groove  1331  which extends upward to the right and slidably receives the protruding line  1305  of the tearing piece  1303 . The retaining piece  1321  includes a right side face  1323  as an inclined surface extending downward to the right and a recessed groove  1325  on a front face thereof. The recessed groove  1325  slidably receives a protruding line of the driving piece  1341 . The retaining piece  1321  also includes, at lower parts of a front face wall  1327  and a back face wall thereof, protruding lines  1328  which are slidably fitted into recessed grooves  1371  of the holder  1351 . 
     The retaining piece  1321  includes a spring receiving hole  1330  which is located on a front face  1329  below the inclined surface  1322  of the retaining piece  1321  and receives the spring  1380 . The spring  1380  has one end in contact with the movable die and the other end in contact with a bottom face of the spring receiving hole  1330  and pushes the retaining piece  1321  toward the driving piece  1341 . 
     The driving piece  1341  is configured to move the retaining piece  1321  such that the tearing piece  1303  tears the gate G. A left side face  1342  of the driving piece  1341  is an inclined surface, and the left side face  1342  is slidably in contact with a left side surface of the recessed groove  1325  of the retaining piece  1321 . The driving piece  1341  also includes a protruding line which extends along the left side face  1342  and is slidably fitted into the recessed groove  1325  of the retaining piece  1321 . A right side face  1343  of the driving piece  1341  is also slightly inclined, and the driving piece  1341  is tapered toward a bottom thereof in a front view. 
     The driving piece  1341  includes, on an upper face thereof, an attaching part  1345  for attaching the driving piece  1341  to the fixed die. With the attaching part  1345  fitted into a recessed part in the fixed mold plate, the driving piece  1341  is fixed thereto by a fixing screw or the like. When the driving piece  1341  is attached to the fixed mold plate, a lower part of the driving piece  1341  with respect to the attaching part  1345  projects from the fixed mold plate. 
     The holder  1351  houses the retaining piece  1321  in an advanceable and retractable manner. Further, the holder  1351  guides the tearing piece  1303  such that the tearing piece  1303  tears the gate G and the tearing piece  1303  after tearing the gate G is moved away from the gate G and the runner R. The holder  1351  includes two half holder members  1352   a ,  1352   b  which are assembled together so as to have a box-like column shape which defines an inner space therein with an open left side face and an open upper face. The holder  1351  may be constituted by a plurality of divided members or be integrated with the movable mold plate  711  (see  FIG. 65 ). 
     The opening on the left side face of the holder  1351  allows the tearing piece  1303  and the retaining piece  1321  to move in and out. The opening on the upper face of the holder  1351  allows the driving piece  1341  to move in and out. 
     The holder  1351  includes, on a back-face-wall inner surface  1354  thereof, a guiding groove  1356  which guides the tearing piece  1303 . The holder  1351  further includes, at lower parts of a front-face-wall inner surface  1353  and the back-face-wall inner surface  1354  thereof, guiding grooves (recessed grooves)  1371  which guide the retaining piece  1321 . The holder  1351  includes a right inner wall surface  1375  which is an outwardly inclined surface extending upward. The right inner wall surface  1375  comes into contact with the right side face  1343  of the driving piece  1341 . 
     Each guiding grooves  1356  is a recessed groove located at an upper left position on the back-face-wall inner surface  1354  and has a reversed L shape (see  FIG. 80 ). There are two such guiding grooves  1356  arranged next to each other in the lateral direction. Each guiding groove  1356  includes a first guiding part  1357  which guides the tearing piece  1303  in the first direction and a second guiding part  1358  which guides the tearing piece  1303  in the second direction. The first guiding part  1357  extends in the vertical direction (i.e., Y direction), and the second guiding part  1358  extends in the horizontal direction (lateral direction) such that a far end thereof is located on the right side. The first guiding part  1357  and the second guiding part  1358  are connected to each other, and a center axis of the first guiding part  1357  and a center axis of the second guiding part  1358  intersect with each other (see  FIG. 80 ). 
     The first guiding part  1356  guides the tearing piece  1303  such that the tearing piece  1303  tears the gate G in conjunction with mold opening. On the other hand, the second guiding part  1357  guides the tearing piece  1303  such that the tearing piece  1303  after tearing the gate G is moved away from the gate G and the runner R in conjunction with mold opening. 
     The guiding grooves  1371  are recessed grooves located at lower ends of the front-face-wall inner surface  1353  and the back-face-wall inner surface  1354  and extend in the horizontal direction (i.e., X direction) (see  FIG. 80 ). The guiding grooves  1371  receive the protruding lines  1328  of the retaining piece  1321  and guide the retaining piece  1321  in the horizontal direction (i.e., lateral direction) in conjunction with mold opening. 
     The holder  1351  also includes, at a left tip end of the half holder member  1352   a , a runner groove  1372  which defines a part of the runner R. 
     An operation and effects of the gate tearing mechanism  1301  of the present embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding when the gate tearing mechanism  1301  is incorporated into a molding die similar to that as shown in  FIG. 65  which includes the fixed die  602  and the movable die  702 . Features corresponding to the features of the of the fixed die  602  and the movable die  702  as shown in  FIG. 65  are denoted with like reference numerals, and description thereof is omitted. 
     The gate tearing mechanism  1301  is incorporated into the holder  1351  with the protruding line  1305  of the tearing piece  1303  fitted into the recessed groove  1331  of the retaining piece  1321 , and the protruding line of the driving piece  1341  fitted into the recessed groove  1325  of the retaining piece  1321 . In this state, the clicks  1312  of the tearing piece  1303  are fitted into the first guiding parts  1357  of the guiding grooves  1356  of the holder  1351 , and the protruding lines  1328  of the retaining piece  1321  are fitted into the guiding grooves  1371  of the holder  1351 . 
     The holder  1351  is incorporated into and fixed to the recessed part  728  in the movable mold plate  711 . When the holder  1351  is fixed to the movable mold plate  711 , an upper face  1360  of the holder  1351  is flush with the upper face of the movable mold plate  711 . The attaching part  1345  of the driving piece  1341  is incorporated into and fixed to the recessed part  612  in the fixed mold plate  605 . When the driving piece  1341  is fixed to the fixed mold plate  605 , the driving piece  1341  except for a fixing part  1345  thereof projects from the bottom face  610  of the fixed mold plate  605 . 
     When the mold is closed, the tearing piece  1303  is located at a position where the tearing piece  1303  shapes the gate G and the runner R. The retaining piece  1321  is also located next to the tearing piece  1303  so as to shape the runner R (see  FIG. 77 ). When the mold is closed, parting faces (PL faces) of the fixed die  602  and the movable die  702  are fitted together to define a cavity part. Then, a molten resin is injected from a non-illustrated injection device, and the resin passes through a sprue (not illustrated), then through the runner R and the gate G and fills in the cavity part. After a pressure holding step and a cooling step, the mold is opened, and a molded product P is taken out. The processes of opening the mold and taking out the molded product P are performed according to the following procedure. 
     Once the movable die  702  retracts and the mold starts to open, the retaining piece  1321  as well as the tearing piece  1303  slidably engaged with the retaining piece  1321  in the holder  1351  descend along with the movable die  702 . On the other hand, the driving piece  1341  remains in the same position because it is fixed to the fixed die  602 . Therefore, when the mold starts to open, the driving piece  1341  ascends relative to the retaining piece  1321  (see  FIG. 78 ). 
     Thus, the retaining piece  1321  is guided by the guiding grooves  1371  of the holder  1351  to retract. The tearing piece  1303  slidably engaged with the retaining piece  1321  moves in the −Y direction as the retaining piece  1321  retracts. More specifically, the clicks  1312  of the tearing piece  1303  are guided by the first guiding parts  1357  of the guiding grooves  1356  and move in the −Y direction with respect to the molded product P. Thus, the gate G is torn, and the resin in the runner R is pulled back (see  FIG. 78 ). 
     After the tearing piece  1303  tears the gate G in conjunction with mold opening, as the gap further increases between the fixed die  602  and the movable die  702 , the tearing piece  1303  moves along the second guiding parts  1358 , while the second sliding surfaces of the clicks  1312  slide in the second guiding parts  1358  of the guiding grooves  1356 . Thus, the tearing piece  1303  moves away from the runner R. When the movable mold  702  descends further, a necessary space is secured to take out the molded product P and the resin which is torn and left in the runner R (see  FIG. 79 ). Then, a non-illustrated ejector mount plate moves up, and the molded product P and the resin left in the runner R are ejected by the ejector pin. Even when the driving piece  1341  is disengaged from the retaining piece  1321 , the retaining piece  1321  and the tearing piece  1302  remain at same positions because the spring  1380  pushes the retaining piece  1321 . 
     As described above, the gate tearing mechanism  1301  can achieve a compact and simple configuration and can operate such that the gate G can be torn easily and reliably prior to taking out the molded product P. In addition, the tearing piece  1303  after tearing the gate G is moved away from the gate G and the runner R in conjunction with mold opening, so that the molded product P and the material left in the runner R can be easily removed. In particular, the gate tearing mechanism  1301  can tear the gate G without breaking the material in the runner R, so that the mechanism for removing the material left in the runner R is simplified. 
     Further, the gate tearing mechanism  1301  can be incorporated into the molding die with the tearing piece  1303  and the retaining piece  1321  housed in the holder  1351 , and therefore, the gate tearing mechanism  1301  can have a compact configuration and be easily attached to the molding die. In particular, the holder  1351 , the tearing piece  1303 , the retaining piece  1321 , and the driving piece  1341  can be assembled into a single independent unit; the gate cutting mechanism  1301  as a single unit can be more easily attached to the molding die. 
       FIG. 81  and  FIG. 82  are perspective views illustrating operations of a gate tearing mechanism  1401  according to a twenty-second embodiment of the present invention. The gate tearing mechanism  1401  according to the twenty-second embodiment of the present invention has a same basic configuration as that of and shares many common points with the gate tearing mechanism  1201  according to the twentieth embodiment of the present invention. Features corresponding to the features of the gate tearing mechanism  1201  according to the twentieth embodiment of the present invention as shown in  FIG. 72  to  FIG. 76  are denoted with like reference numerals, and description thereof is omitted. For the sake of convenience, in the following description, the “upper” side means the side of the flange  1454  of the holder  1451  in  FIG. 81  and the “lower” side means the side of the guiding piece  1471  in  FIG. 81 . In the following description, the “left” side corresponds to the left side in  FIG. 81 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     As with the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention, the gate tearing mechanism  1401  according to the twenty-second embodiment of the present invention is incorporated into and used in a molding die including a fixed die which molds an external surface of a molded product P and a movable die which molds an internal surface of the molded product P. Such a molding die which includes the fixed die and the movable die and is capable of being used with the gate cutting mechanism  1401  incorporated therein is not limited to a particular type. 
     The gate cutting mechanism  1401  is operable to cut a gate G connecting a molded product P to a runner R and is configured to tear a gate G by a cutting piece  1403  in conjunction with opening the molding die and then to move the cutting piece  1403  away from the gate G and a runner R so as to allow a material left in the runner R to be removed. The gate cutting mechanism  1401  of the present embodiment also employs the sliding mechanism  1  of the first embodiment. 
     The gate cutting mechanism  1401  includes: a cutting piece  1403  which cuts a gate G; a retaining piece  1421  which is slidably engaged with the cutting piece  1403  to slide the cutting piece  1403 ; a holder  1451  which partially houses the cutting piece  1403  and the retaining piece  1421  and slides the retaining piece  1421 ; and a guiding piece  1471  which guides the retaining piece  1421  (see  FIG. 81 ). 
     The cutting piece  1403  of the present embodiment corresponds to the second piece  21  of the sliding mechanism  1  of the first embodiment; the retaining piece  1421  corresponds to the first piece  11 ; and the holder  1451  corresponds to the guiding body  31 . In the present embodiment, the cutting piece  1403  corresponds to a slider; and the holder  1451  corresponds to a guide body. As described later, a guiding groove corresponds to a guide unit; a first guiding part corresponds to a first guide unit; and a second guiding part corresponds to a second guide unit. A click  1212  of the cutting piece  1403  corresponds to an engagement unit; a first sliding surface of the click  1212  corresponds to a first engagement unit; and a second sliding surface of the click  1212  corresponds to a second engagement unit. The retaining piece  1421  and the cutting piece  1403  are slidably engaged with each other. The retaining piece  1421  corresponds to an engaging member, and the guiding piece  1471  corresponds to an engaging member guide unit. 
     The cutting piece  1403  is configured to shape a gate G and to cut the gate G. The cutting piece  1403  includes, at an upper tip end thereof, a narrow recessed part for shaping a gate G and an L-shaped recessed part which serves as a part of a runner groove for shaping a runner R. The side of the tip end of the cutting piece  1403  corresponds to the left side in  FIG. 81 . At upper parts of the cutting piece  1403  opposite from the tip end side, the cutting piece  1403  includes the clicks  1212  which are slidably fitted into the guiding grooves  1256  of the holder  1451 . The clicks  1212  are located at upper parts of a front face wall and a back face wall of cutting piece  1403  in a protruding manner. Therefore, the clicks  1212  may be considered as protruding lines. 
     The clicks  1212  have the same structure as the clicks  1212  as shown in  FIG. 76 , and left side faces  1213  and right side faces  1214  of the clicks  1212  serve as first sliding surfaces which come into contact with left side surfaces and right side surfaces of first guiding parts  1257  of guiding grooves  1256  of the holder  1451 . Upper side faces  1215  and lower side faces  1216  of the clicks  1212  serve as second sliding surfaces which come into contact with upper side surfaces and lower side surfaces of second guiding parts  1258  of the guiding groove  1256  of the holder  1451  in order to move the cutting piece  1403  after cutting the gate G away from the gate G and the runner R (see  FIG. 76 ). 
     A bottom face of the cutting piece  1403  is an inclined surface inclined downward to the front, and the cutting piece  1403  includes, at a lower end thereof, a protruding line  1405 . The protruding line  1405  is slidably fitted into a recessed groove of the retaining piece  1421 . Above the protruding line  1405 , the cutting piece  1403  includes an inclined surface  1409  which is parallel to the protruding line  1405  and is slidably into contact with a left side face of the retaining piece  1421 . 
     The retaining piece  1421  is configured to move the cutting piece  1403  so as to cut the gate G. The left side face of the retaining piece  1421  is an inclined surface  1422  which includes a recessed groove  1427  which slidably receives the protruding line  1405  of the cutting piece  1403 . The inclined surface  1422  of the retaining piece  1421  is slidably in contact with the inclined surface  1409  of the cutting piece  1403 . 
     The structure of a right side face of the retaining piece  1421  is similar to that of the right side face of the retaining piece  1221 . Referring to  FIG. 76 , the right side face of the retaining piece  1421  is an inclined surface which is inclined downward to the right, and the protruding lines  1225 ,  1226  are located on the front face wall  1227  and the back face wall and extend along right side face. The protruding lines  1225 ,  1226  are slidably fitted into the second guiding parts  1258  of the guiding grooves  1256  of the holder  1451 . 
     The retaining piece  1421  includes an inversed L-shaped click  1428  at a right bottom part thereof. Between a bottom face  1429  of the retaining piece  1421  and the click  1428 , there is a recessed part which slidably receives a protrusion  1473  at a rear end of the guiding piece  1471 . 
     The guiding piece  1471  includes, at the rear end thereof, the protrusion  1473  which comes into engagement with the click  1428  of the retaining piece  1421 , and guides the retaining piece  1421  through the protrusion  1473 . When the gate cutting mechanism  1401  is incorporated into the molding die, the guiding piece  1471  is fixed to the movable die. 
     The holder  1451  partially houses the cutting piece  1403  and the retaining piece  1421  and guides the cutting piece  1403  such that the cutting piece  1403  cuts the gate G and the cutting piece  1403  after cutting the gate G is moved away from the gate G and the runner R. The holder  1451  includes two half holder members  1452  of a substantially same shape which are assembled together. The holder  1451  may be constituted by a plurality of divided members or be integrated with the fixed die. 
     The holder  1451  has a same configuration as the holder  1251 . The holder  1451  will be described with reference to  FIG. 76 . The holder  1451  includes a body  1453  having a substantially cuboid shape and a flange  1454  integrated with the body  1453  at an upper part of the body  1453 . The body  1453  is open on a left side face thereof and includes a housing part  1260  therein which partially houses the cutting piece  1403  and the retaining piece  1421 . The housing part  1260  narrows to the right and includes an inclined surface  1261  which is inclined downward to the right inside the housing part  1260 . The second guiding parts  1258  of the guiding grooves  1256  extend along the inclined surface  1261 . 
     The holder  1451  includes the guiding grooves  1256  which guide the cutting piece  1403  on the front-face-wall inner surface  1262  and the back-face-wall inner surface  1263  of the holder  1451 . Each guiding groove  1256  has a dog-legged shape and includes a first guiding part  1257  which guides the cutting piece  1403  in the first direction and a second guiding part  1258  which guides the cutting piece  1403  in the second direction. The first guiding part  1257  extends in the vertical direction (i.e., Y direction), and the second guiding part  1258  is inclined diagonally downward to the right such that a lower part thereof is located on the right. The first guiding part  1257  and the second guiding part  1258  are connected to each other, and a center axis of the first guiding part  1257  and a center axis of the second guiding part  1258  intersect with each other (see  FIG. 76 ). 
     The first guiding parts  1257  guide the cutting piece  1403  such that the cutting piece  1403  cuts the gate G in conjunction with mold opening. On the other hand, the second guiding parts  1258  guide the cutting piece  1403  such that the cutting piece  1403  after cutting the gate G is moved away from the gate G and the runner R in conjunction with mold opening. The second guiding parts  1258  also receive the protruding lines  1225 ,  1226  of the retaining piece  1421  and guide movement of the retaining piece  1421 . 
     The holder  1451  includes a stopper receiving hole  1266  which houses a stopper  1267  for preventing movement of the retaining piece  1421 . The stopper insertion hole  1266  opens on the upper face  1264  and includes a lower end communicated with the housing part  1260  (see  FIG. 76 ). The flange  1454  includes a bolt insertion hole  1466  for fixing the holder  1451  to the fixed die. 
     The stopper  1267  is a bottomed cylindrical member which prevents movement of the retaining piece  1421  and includes a spring  1268  placed therein. The stopper  1267  is slidably inserted into the stopper receiving hole  1266  such that a lower end of the stopper  1267  projects into the housing part  1260 . Once the retaining piece  1421  retracts, and a movement restricting part (not illustrated) on the retaining piece  1421  hits the stopper  1267 , the movement is prevented. 
     The spring  1268  is placed in the stopper  1267  and presses the stopper  1267  downward (i.e., in the −Y direction) when the gate cutting mechanism  1401  is incorporated into the molding mold. 
     An operation and effects of the gate cutting mechanism  1401  of the present embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding when the gate cutting mechanism  1401  is incorporated into a molding die similar to that as shown in  FIG. 65  which includes the fixed die  602  and the movable die  702 . Features corresponding to the features of the of the fixed die  602  and the movable die  702  as shown in  FIG. 65  are denoted with like reference numerals, and description thereof is omitted. 
     The gate cutting mechanism  1401  is incorporated into the holder  1451  with the protruding line  1405  of the cutting piece  1403  fitted into the recessed groove  1427  of the retaining piece  1421 . In this state, the clicks  1212  of the cutting piece  1403  are fitted into the first guiding parts  1257  of the guiding grooves  1256  of the holder  1451 , and the protruding lines  1225 ,  1226  of the retaining piece  1421  are fitted into the second guiding parts  1258  of the guiding grooves  1256  of the holder  1451  (see  FIG. 76 ). The holder  1451  is arranged such that the flange  1454  of the holder  1451  is fixed to the fixed mold plate  605 , and when the mold is closed, the body  1453  of the holder  1451  is located in the recessed part  728  of the movable die  702 . The guiding piece  1471  is fixed to the bottom face of the recessed part  728  of the movable die  702 , and the protrusion  1473  is engaged with the click  1428  of the retaining piece  1421 . 
     When the mold is closed, the cutting piece  1403  is at a position for shaping a gate G and a runner R (see  FIG. 81 ). When the mold is closed, parting faces (PL faces) of the fixed die  602  and the movable die  702  are fitted together to define a cavity part. Then, a molten resin is injected from a non-illustrated injection device, and the resin passes through a sprue (not illustrated), then through the runner R and the gate G and fills in the cavity part. After a pressure holding step and a cooling step, the mold is opened, and a molded product P is taken out. The processes of opening the mold and taking out the molded product P are performed according to the following procedure. 
     Once the movable die  702  retracts and the mold starts to open, the retaining piece  1421  slidably engaged with the guiding piece  1471  and the cutting piece  1403  slidably engaged with the retaining piece  1421  descend along with the movable die  702 . On the other hand, the holder  1451  remains in the same position because it is fixed to the fixed die  602 . Therefore, when the mold starts to open, the holder  1451  ascends relative to the cutting piece  1403  and the retaining piece  1421  (see  FIG. 82 ). 
     At the same time, the clicks  1212  of the cutting piece  1403  are guided by the first guiding parts  1257  of the guiding grooves  1256  in the holder  1451  and move in the −Y direction with respect to the molded product P. Thus, the gate G is torn as a shearing force acts thereto, and the resin in the runner R is pulled back. The retaining piece  1421  is guided by the second guiding parts of the guiding grooves in the holder  1451 . At the same time, the click  1428  slidably comes into contact with the protrusion  1473  of the guiding piece  1471 , so that the retaining piece  1421  retracts toward the side of the holder  1451  without largely changing a height position relative to the molded product P (see  FIG. 82 ). 
     In the gate cutting mechanism  1401  of the present embodiment, when the cutting piece  1403  descends to cut the gate G, the runner R is pushed down. Since the cutting piece  1403  includes the recessed part for shaping the gate G and the L-shaped recessed part which serves as a part of a runner groove for shaping a runner R, a space is creased below the runner R when the cutting piece  1403  descends. This allows the runner R to deflect, so that it is possible to prevent breakage of the runner R (see  FIG. 82 ). 
     After the cutting piece  1403  cuts the gate G in conjunction with mold opening, as the gap further increases between the fixed die  602  and the movable die  702 , the cutting piece  1403  moves along the second guiding parts  1258 , while the second sliding surfaces of the clicks  1212  slide in the second guiding parts  1258  of the guiding grooves  1256  of the holder  1451 . Thus, the cutting piece  1403  moves away from the runner R. When the movable die  702  descends further, the retaining piece  1421  is disengaged from the guiding piece  1471 , and the retaining piece  1421  is connected to the holder  1451  together with the cutting piece  1403 . Thus, a necessary space is secured to take out the molded product P and the resin which is tom and left in the runner R. Then, a non-illustrated ejector mount plate moves up, and the molded product P and the resin left in the runner R are ejected by the ejector pin. 
     As described above, the gate cutting mechanism  1401  can achieve a compact and simple configuration and can operate such that the gate G can be cut easily and reliably prior to taking out the molded product P. In addition, the cutting piece  1403  after cutting the gate G is moved away from the gate G and the runner R in conjunction with mold opening, so that the molded product P and the material left in the runner R can be easily removed. In particular, the gate cutting mechanism  1401  can cut the gate G without breaking the material in the runner R, so that the mechanism for removing the material left in the runner R is simplified. 
     Further, the gate cutting mechanism  1401  can be incorporated into the molding die with the cutting piece  1403  and the retaining piece  1421  housed in the holder  1451 , and therefore, the gate cutting mechanism  1401  can have a compact configuration and be easily attached to the molding die. In particular, the holder  1451 , the cutting piece  1403 , the retaining piece  1421 , and the guiding piece  1471  can be assembled into a single independent unit; the gate cutting mechanism  1401  as a single unit can be more easily attached to the molding die. 
       FIG. 83  to  FIG. 86  are perspective views illustrating operations of a gate tearing mechanism  1501  according to a twenty-third embodiment of the present invention.  FIG. 87  is an exploded view showing features of the gate tearing mechanism  1501  according to the twenty-third embodiment of the present invention. The gate tearing mechanism  1501  according to the twenty-third embodiment of the present invention has a same basic configuration as and shares many common points with the gate tearing mechanism  1201  according to the twentieth embodiment of the present invention. Features corresponding to the features of the gate tearing mechanism  1201  according to the twentieth embodiment of the present invention as shown in  FIG. 72  to  FIG. 76  are denoted with like reference numerals, and description thereof is omitted. For the sake of convenience, in the following description, the “upper” side means the side of the molded product P in  FIG. 83 , and the “lower” side means the side of the ejector pin  1601  in  FIG. 83 . In the following description, the “left” side corresponds to the left side in  FIG. 83 , and the “right” side means the opposite side, unless otherwise specifically noted. 
     As with the gate tearing mechanism  801  according to the sixteenth embodiment of the present invention, the gate tearing mechanism  1501  according to the twenty-third embodiment of the present invention is incorporated into and used in a molding die including a fixed die which molds an external surface of a molded product P and a movable die which molds an internal surface of the molded product P. Such a molding die which includes the fixed die and the movable die and is capable of being used with the gate tearing mechanism  1501  incorporated therein is not limited to a particular type. 
     The gate tearing mechanism  1501  is operable to tear a gate G connecting a molded product P to a runner R and is configured to tear a gate G by a tearing piece  1503  in conjunction with opening the molding die and then to move the tearing piece  1503  away from the gate G and a runner R so as to allow a material left in the runner R to be removed. The gate tearing mechanism  1501  of the present embodiment also employs the sliding mechanism  1  of the first embodiment. 
     The gate tearing mechanism  1501  includes: a tearing piece  1503  which tears a gate G; a retaining piece  1521  which is slidably engaged with the tearing piece  1503  to slide the tearing piece  1503 ; a driving piece  1541  which is engaged with the retaining piece  1521  to retract the retaining piece  1521 ; a holder  1551  which partially houses and guides the retaining piece  1521  and the driving piece  1541 ; and a tearing piece holder  1571  which guides the tearing piece  1503  (see  FIG. 87 ). 
     The tearing piece  1503  of the present embodiment corresponds to the second piece  21  of the sliding mechanism  1  of the first embodiment; the retaining piece  1521  corresponds to the first piece  11 ; and the tearing piece holder  1571  corresponds to the guiding body  31 . In the present embodiment, the tearing piece  1503  corresponds to a slider, and the tearing piece holder  1571  corresponds to a guide body. As described later, a guiding groove  1256  corresponds to a guide unit; a first guiding part corresponds to a first guide unit; and a second guiding part corresponds to a second guide unit. A click  1212  corresponds to an engagement unit; a first sliding surface of the click  1212  corresponds to a first engagement unit; and a second sliding surface of the click  1212  corresponds to a second engagement unit. The retaining piece  1521  and the tearing piece  1503  are slidably engaged with each other. The retaining piece  1521  corresponds to an engaging member, and a guiding groove  1556  in the holder  1551  corresponds to an engaging member guide unit. 
     The tearing piece  1503  is configured to shape a gate G and cutting the gate G. In the present embodiment, the gate tearing mechanism  1501  includes two tearing piece  1503  in order to adapt to a molding die which molds two molded products P. The two tearing piece  1503  have the same structure and the same size. Each tearing piece  1503  includes a protruding portion  1507  at an upper part thereof and a narrow recessed part  1510  at a side of the protruding portion  1507 , the recessed part  1510  being configured to shape a gate G. A left side face  1506  below the protruding portion  1507  serves as a part of a runner groove for shaping a runner R. The left side face  1506  includes, at a lower part thereof, a recessed groove  1511  extending in the Z direction. The recessed groove  1511  is engaged with a protruding line  1523  of the retaining piece  1521 . 
     A side face wall  1504 , which is located on a back face side when the protruding portion  1507  of each tearing piece  1503  is viewed straightforwardly, includes a click  1212  which is slidably fitted into a guiding groove  1256  of the tearing piece holder  1571 . The click  1212  is located on the side face wall  1504  in a protruding manner. Therefore, the click  1212  may be considered as a protruding line. 
     These clicks  1212  have the same structure as that of the clicks  1212  as shown  FIG. 76 , left side faces  1213  and right side faces  1214  of the clicks  1212  serve as first sliding surfaces which come into contact with left side surfaces and right side surfaces of first guiding parts  1257  of guiding grooves  1256  of the tearing piece holder  1571 . Upper side faces  1215  and lower side faces  1216  of the clicks  1212  serve as second sliding surfaces which come into contact with upper side surfaces and lower side surfaces of second guiding parts  1258  of guiding grooves  1256  of the tearing piece holder  1571  in order to move the tearing piece  1503  after tearing the gate G away from the gate G and the runner R (see  FIG. 76 ). 
     A back face wall  1505 , which is also located on the back face side when the protruding portion  1507  of each tearing piece  1503  is viewed straightforwardly, is an inclined surface which inclines downward to the rear (to the side opposite to the protruding portion  1507 ). The back face wall  1505  slidably comes into contact with an inclined surface located on the front side of the tearing piece holder  1571 . A side face of the tearing piece  1503  which is opposite to the side face wall  1504  in a plan view slidably comes into contact with a protruding portion  1572  of the tearing piece holder  1571 . The tearing piece  1503  also includes an inclined surface  1512  which is located below the recessed groove  1511  and slidably comes into contact with an inclined surface of the retaining piece  1521 . 
     The tearing piece holder  1571  engages with the two tearing pieces  1503  and guides them such that the two tearing pieces  1503  simultaneously tear the gates G and the tearing pieces  1503  after tearing the gates G are moved away from the gates G and the runner R. The tearing piece holder  1571  includes a protruding portion  1572  on the front face side thereof, and inclined surfaces located on both sides of the protruding portion  1572  slidably come into contact with side faces of the tearing pieces  1503  which are opposite to the side face walls  1504  in a plan view. 
     The protruding portion  1572  includes, at a tip end portion thereof, a recessed part  1581  which defines a part of a sprue. On opposite sides of the protruding portion  1572 , a runner R connected to the sprue is shaped, and a bottom face of the protruding portion  1572  serves as a part of a runner groove which shapes the runner R. 
     On opposite side-face inner walls  1573  of the tearing piece holder  1571 , there are the guiding grooves  1256  which slidably receive the clicks  1212  of the tearing piece  1503 . Each guiding groove  1256  has a dog-legged shape and includes a first guiding part  1257  which guides the tearing piece  1503  in the first direction and a second guiding part  1258  which guides the tearing piece  1503  in the second direction. The first guiding part  1257  extends in the vertical direction (i.e., Y direction), and the second guiding part  1258  is inclined diagonally downward. The first guiding part  1257  and the second guiding part  1258  are connected to each other, and a center axis of the first guiding part  1257  and a center axis of the second guiding part  1258  intersect with each other (see  FIG. 87 ). 
     The first guiding part  1257  guides the tearing piece  1503  such that the tearing piece  1503  tears the gate G in conjunction with mold opening. On the other hand, the second guiding part  1258  guides the tearing piece  1503  such that the tearing piece  1503  after tearing the gate G is moved away from the gate G and the runner R in conjunction with mold opening. 
     The tearing piece holder  1571  also includes stopper insertion holes which house stoppers  1577  for preventing movement of the tearing pieces  1503 . Each stopper insertion hole opens on the upper face  1574  and includes a lower end which penetrates a front inclined surface  1580  of the holder  1571 . 
     Each stopper  1577  is a bottomed cylindrical member which prevents movement of the tearing piece  1503  and includes a spring  1578  placed therein. The stoppers  1577  are slidably inserted into the stopper insertion holes such that lower ends of the stoppers  1577  project from the front inclined surface  1580 . Once the tearing pieces  1503  retract, and movement restricting parts (not illustrated) on the tearing pieces  1503  hit the stoppers  1577 , the movement is prevented. 
     The springs  1578  are placed in the stoppers  1577  and press the stoppers  1577  downward (i.e., in the −Y direction) when the gate tearing mechanism  1501  is incorporated into the molding mold. 
     The retaining piece  1521  is configured to move the tearing pieces  1503  such that the tearing pieces  1503  tear the gates G. The retaining piece  1521  includes an inclined surface  1522  at an upper part of a right side face thereof as shown in  FIG. 87  and a protruding line  1523  extending in the Z direction which is shaped by a recessed part located below the inclined surface  1522 . The protruding line  1523  is slidably fitted into the recessed grooves  1511  of the two tearing pieces  1503 . The inclined surface  1522  of the retaining piece  1521  serves as a part of the runner groove for shaping the runner R. At a lower part of the right side face of the retaining piece  1521 , there is an inclined surface  1524  which slidably comes into contact with the inclined surfaces  1512  of the tearing pieces  1503 . 
     A left side face of the retaining piece  1521  is an inclined surface  1525  extending downward to the left, and the inclined surface  1525  includes a dovetail groove  1526  which slidably receives a click  1545  of the driving piece  1541 . The retaining piece  1521  includes, on a front-face outer wall  1527  and a back-face outer wall thereof, protruding lines  1528  which extend in the X direction and are slidably fitted into guiding grooves (recessed grooves)  1556  in the holder  1551 . 
     The holder  1551  partially houses the retaining piece  1521  and the driving piece  1541  and guides the tearing pieces  1503  such that the tearing pieces tear  1503  the gates G and the tearing pieces  1503  after tearing the gates G are moved away from the gates G and the runner R. The holder  1551  includes two half holder members  1552  of a same shape and a same size which are assembled together so as to have a box-like column shape with an open right side face and an open upper face. The holder  1551  may be constituted by a plurality of divided members or be integrated with the movable mold plate  711 . 
     The holder  1551  includes guiding grooves  1556  which guide the retaining piece  1521  on a front-face-wall inner surface  1554  and a back-face-wall inner surface  1553  thereof. The guiding grooves  1556  are recessed grooves extending in the horizontal direction (i.e., X direction) and am configured to receive the protruding lines  1528  on the retaining piece  1521  to guide the retaining piece  1521  in the horizontal direction (i.e., X direction) in conjunction with mold opening. A left-side inner wall surface  1557  of the holder  1551  is an outwardly inclined surface extending upward. The left-side inner wall surface  1557  comes into contact with a left side face  1543  of the driving piece  1541 . The holder  1551  also includes, on a bottom face thereof, a recessed part  1558  which receives a ball plunger  1560 . 
     The driving piece  1541  is configured to move the retaining piece  1521  such that the tearing pieces  1503  tear the gates G. A right side face of the driving piece  1541  is an inclined surface  1542 , and the inclined surface  1542  slidably comes into contact with the left side face  1525  of the retaining piece  1521 . The driving piece  1541  also includes a click  1545  which extends along the inclined surface  1542  and is slidably fitted into the recessed groove  1526  of the retaining piece  1521 . The click  1545  is located on the inclined surface  1542  in a protruding manner. Thus, the click  1545  may be considered as a protruding line. The left side face  1543  of the driving piece  1541  is also slightly inclined, and the driving piece  1541  narrows to a lower part thereof in a front view. 
     With the driving piece  1541  fitted into a recessed part in the fixed mold plate, the driving piece  1541  is fixed thereto by a fixing screw or the like. When the driving piece  1541  is attached to the fixed mold plate, the inclined surface  1542  and the click  1545  project from the fixed mold plate. 
     An operation and effects of the gate tearing mechanism  1501  of the present embodiment will be described with reference to an exemplary case where a molded product P is molded by injection molding when the gate tearing mechanism  1501  is incorporated into a molding die similar to that as shown in  FIG. 65  which includes the fixed die  602  and the movable die  702 . Features corresponding to the features of the of the fixed die  602  and the movable die  702  as shown in  FIG. 65  are denoted with like reference numerals, and description thereof is omitted. 
     A process of incorporating the respective pieces of the gate tearing mechanism  1501  will be described blow. The two tearing pieces  1503  are arranged such that the respective recessed grooves  1511  receives the protruding line  1523  of the retaining piece  1521 , and the two tearing pieces  1503  are engaged with the retaining piece  1521 . The clicks  1212  of the two tearing pieces  1503  are fitted into the first guiding parts  1257  of the guiding grooves  1256  of the tearing piece holder  1571 , and the two tearing pieces  1503  are engaged with the tearing piece holder  1571 . The tearing piece holder  1571  is fixed to the fixed mold plate  605 . 
     In this state, the protruding lines  1528  of the retaining piece  1521  are fitted into the guiding grooves  1556  of the holder  1551 . An upper part of the driving piece  1541  is fixed to the fixed mold plate  605 , and the click  1545  is fitted into the dovetail groove  1526  of the retaining piece  1521 . In this state, the left side face  1543  of the driving piece  1541  is in contact with the left-side inner wall surface  1557  of the holder  1551 . The holder  1551  is fixed to the recessed part  728  of the movable die  702 . 
     When the mold is closed, the tearing pieces  1503  are located at positions where the tearing pieces  1503  shape the gates G and the runner R. When the mold is closed, parting faces (PL faces) of the fixed die  602  and the movable die  702  are fitted together to define a cavity part. Then, a molten resin is injected from a non-illustrated injection device, and the resin passes through a sprue (not illustrated), then through the runner R and the gates G and fills in the cavity part. After a pressure holding step and a cooling step, the mold is opened, and molded products P are taken out. The processes of opening the mold and taking out the molded products P are performed according to the following procedure. 
     Once the movable die  702  retracts and the mold starts to open, the holder  1551  and the retaining piece  1521  engaged with the holder  1551  descend along with the movable die  702 . On the other hand, the driving piece  1541  and the tearing piece holder  1571  remain in the same positions because they are fixed to the fixed die  602 . Therefore, when the mold starts to open, the driving piece  1541  and the tearing piece holder  1571  ascend relative to the tearing pieces  1503  and the retaining piece  1521  (see  FIG. 84 ). 
     When the driving piece  1541  ascends relative to the holder  1551 , the retaining piece  1521  retracts (in the X direction). In association therewith, the tearing pieces  1503  engaged with the retaining piece  1521  are guided by the first guiding parts  1257  of the guiding grooves  1256  of the tearing piece holder  1571  and moves in the −Y direction with respect to the molded product P. Thus, the gates G are torn, and the resin in the runner R is pulled back (see  FIG. 84 ). 
     After the tearing pieces  1503  tear the gates G in conjunction with mold opening, as the gap further increases between the fixed die  602  and the movable die  702 , the tearing pieces  1503  move along the second guiding parts  1258 , while the second sliding surfaces of the clicks  1212  slide in the second guiding part  1258  of the guiding grooves  1256  of the tearing piece holder  1571 . Thus, the tearing pieces  1503  move away from the runner R. When the tearing pieces  1503  move in the −X direction and come into contact with the stoppers  1577 , the tearing pieces  1503  stop moving. The retaining piece  1521  is fixed in position because of the ball plunger  1560  attached to the holder  1551 . Thus, an original state can be recovered smoothly when the mold is cramped (closed). Instead of the ball plunger  1560 , it is possible to use a plate spring or any other elastic body. 
     When the movable die  702  descends further, the tearing pieces  1503  are disengaged from the retaining piece  1521 , and the tearing pieces  1503  are locked to the tearing piece holder  1571  (see  FIG. 85 ). Thus, a necessary space is secured to take out the molded products P and the resin which is torn and left in the runner R. Then, a non-illustrated ejector mount plate moves up, the resin left in the runner R is ejected by the ejector pin  1601 , and the molded products P are also ejected by a non-illustrated ejector pin. 
     As described above, the gate tearing mechanism  1501  can achieve a compact and simple configuration and can operate such that the gates G can be torn easily and reliably prior to taking out the molded products P. The gate tearing mechanism  1501  can be suitably used in a molding which molds two molded products P. In addition, the tearing pieces  1503  after tearing the gates G are moved away from the gates G and the runner R in conjunction with mold opening, so that the molded products P and the material left in the runner R can be easily removed. In particular, the gate tearing mechanism  1501  can tear the gates G without breaking the material in the runner R, so that the mechanism for removing the material left in the runner R is simplified. 
     Further, the gate tearing mechanism  1501  can be incorporated into the molding die with the two tearing pieces  1503 , the retaining piece  1521 , and the driving piece  1541  housed in the holder  1551 , and therefore, the gate tearing mechanism  1501  can have a compact configuration and be easily attached to the molding die. In particular, the holder  1551 , the tearing pieces  1503 , the retaining piece  1521 , the driving piece  1541 , and the tearing piece holder  1571  can be assembled into a single independent unit; the gate tearing mechanism  1501  as a single unit can be more easily attached to the molding die. 
     As described above, the sliding mechanisms, the undercut processing mechanisms, the gate cutting mechanisms, the gate tearing mechanisms, the fixed dies, the movable dies, and the molding dies according to the present invention are described with reference to the sliding mechanisms, the undercut processing mechanisms, the gate cutting mechanisms, the gate tearing mechanisms, the fixed dies, the movable dies, and the molding dies according to the first to the twenty-third embodiments. However, the present invention is not limited to the above embodiments, and modification may be made without departing the scope of the present invention. 
     In the gate tearing mechanism of the sixteenth embodiment, the tearing piece is moved away from the gate and the runner after tearing the gate. Alternatively, the mechanism may be configured such that the tearing piece is moved away from a part of the runner after tearing the gate. This is applicable to the gate tearing mechanisms according to other embodiments. The gate cutting mechanisms may also be configured such that the cutting piece, or the cutter, or the like is moved away from a part of the runner. 
     The gate tearing mechanisms according to the above embodiments are configured to tear a gate, in other words, to break a gate. Depending on the application, however, it may be required to apply a load to a gate, to extend a gate, or to crack a gate. Depending on the application, it may be required to move a piece away from a gate or a runner or a part of a runner after applying a load to the gate, extending the gate, or cracking the gate 
     A mechanism which applies a load to a gate, or extends a gate, or cracks a gate may employ any of the gate tearing mechanisms according to the above embodiments. It is only necessary to replace the tearing piece of the gate tearing mechanism with a pulling piece which applies a load to a gate, or extends a gate, or cracks a gate, and such a mechanism can be considered as a gate pulling mechanism. In addition, since an operation of tearing a gate is considered as an aspect of an operation of pulling a gate, the gate pulling mechanism is a generalized concept including the gate tearing mechanism, and thus the gate tearing mechanism according to the present invention may be considered as a gate pulling mechanism according to the present invention. 
     The undercut processing mechanisms, the gate cutting mechanisms, and the gate tearing mechanisms according to the above embodiments employ cylindrical holders. However, holders useable in the undercut processing mechanisms, the gate cutting mechanisms, and the gate tearing mechanisms according to the present invention are not limited to cylindrical holders. Holders useable in the undercut processing mechanisms, the gate cutting mechanisms, and the gate tearing mechanisms according to the present invention are only required to be capable of housing respective pieces such as a retaining piece in an advanceable and retractable manner and of including a guide unit such as a guiding groove. In addition, housing respective pieces such as a retaining piece may include partially housing them, and housing may be considered as retainment. For example, a component having a shape and structure similar to those of the channel-shaped guiding body of the first embodiment may be used as a holder. 
     Further, fixing positions of the holders, the driving pieces, or the like are not limited to those of the above embodiments. For example, in the gate tearing mechanism according to the twenty-first embodiment, the holder is fixed to the movable mold plate. However, it is only necessary that the holder is fixed to the movable die or a member which integrally moves with the movable die. Similarly, in the gate tearing mechanism according to the twenty-first embodiment, the driving piece is fixed to the fixed mold plate. However, it is only necessary that the driving piece is fixed to the fixed die or a member which integrally moves with the fixed die. These also apply to other embodiments and to any other members than the holders and the driving pieces. 
     In the third embodiment, the undercut processing mechanism is incorporated into the movable die. However, the undercut processing mechanism may be incorporated into the fixed die. Similarly, the undercut processing mechanisms, the gate cutting mechanisms, and the gate tearing mechanisms according to other embodiments of the present invention may be incorporated into the fixed die or the movable die in a reverse manner. 
     The driving mechanisms and driving sources for the undercut processing mechanisms, the gate cutting mechanisms, the gate tearing mechanisms according to the present invention are not limited to those of the present embodiments. Two or more undercut processing mechanisms according to the present invention may be incorporated into a single molding die. A combination of an undercut processing mechanism according to the present invention and a gate cutting mechanism or a gate tearing mechanism according to the present invention may be incorporated into a single molding die. 
     In the description of the undercut processing mechanism  112  according to the fourteenth embodiment of the present invention and the undercut processing mechanism  113  according to the fifteenth embodiment of the present invention, they are described as being incorporated into the molding die  100 . However, molding dies capable of incorporating and being used with the undercut processing mechanism  112  according to the fourteenth embodiment of the present invention and the undercut processing mechanism  113  according to the fifteenth embodiment of the present invention are not limited to the molding die  100 . 
     In the previously described embodiments of the present invention, a spring and a gas spring are used as pressing members. However, a different pressing member may be used instead of a spring and a gas spring. Further, a spring may be used in place of a gas spring, or a gas spring may be used in place of a spring in a reverse manner. Other pressing members may include elastic bodies other than springs, ball plungers for position fixing, or any other mechanisms or members may be used alternatively. 
     In the first embodiment, a recessed groove is used as a guide unit, and a click is used as an engagement unit which engages with the guide unit. However, a protruding line may be used as a guide unit, and a recessed groove may be used as an engagement unit which engages with the guide unit. This also applies to other embodiments. In the above embodiments, a coupling structure (coupling mechanism) using a protruding line (dovetail-groove protruding line) and a dovetail groove is described. The arrangement of the protruding line (dovetail-groove protruding line) and the dovetail groove may be reversed. A coupling structure (coupling mechanism) using a dovetail-groove protruding line and a dovetail groove is an aspect of an engagement structure (engagement mechanism) including a protruding line or a protrusion or a click and a groove for guiding it and is encompassed in the engagement structure (engagement mechanism). Therefore, the first piece  11  of the first embodiment may be considered as an engaging member, and the left- and right-side-wall inner surfaces  34 ,  36  of the guiding body  31  may be considered as an engaging member guide unit. This is applicable to other embodiments of the present invention. An engagement structure (engagement mechanism) including a protruding line or a protrusion or a click and a groove for guiding it may not necessarily be a dovetail groove structure (dovetail groove mechanism). 
     In the sliding mechanisms, the undercut processing mechanisms, the gate cutting mechanisms, and the gate tearing mechanisms according to the present invention, the cross sectional shapes of inclined grooves, protruding lines, fitting parts, engaging parts, or locking parts which are brought to be fitted or engaged with each other are not limited to rectangular shapes as illustrated. The cross sectional shapes may be round, triangular, or the like. In the sliding mechanisms, the undercut processing mechanisms, the gate cutting mechanisms, and the gate tearing mechanisms according to the present invention, respective guide units and restricting units for the holders, the retaining pieces, and the sliding pieces are not limited to those of the above embodiments. For example, a linear guide or the like may be used. 
     In the gate cutting mechanisms, the gate tearing mechanisms, and the molding dies including the same according to the present invention, the gate G is not limited to a particular type. The gate may be of any type such as a side gate, an overlap gate, a submarine gate. In addition, the runner may be of any type such as a cold runner and even a hot runner. 
     In the gate tearing mechanism according to the twenty-third embodiment of the present invention, the ejector pin fixed to the ejector mount plate is used to take out the molded products P and the resin left in the runner R. However, the molded products P or the material left in the runner R is not necessarily taken out by the ejector pin. Instead of the ejector pin, a robot arm or a human hand may be used. This is applicable to other gate tearing mechanisms and gate cutting mechanisms. 
     In the sliding mechanisms, the undercut processing mechanisms, the gate cutting mechanisms, the gate tearing mechanisms, and the molding dies according to the present invention, the respective components may have chamfering, round chamfering, or the like at corners or side ridges. 
     Materials of the respective components used in the sliding mechanisms, the undercut processing mechanisms, the gate cutting mechanisms, the gate tearing mechanisms, and the molding dies according to the present invention are not limited to particular materials. Suitable materials may be employed which are equivalent to those used for components of known undercut processing mechanisms, gate cutting mechanisms, gate tearing mechanisms, and molding dies. It should be noted that for sliding surfaces of the respective components, it is preferable to use a material having good slidability or a surface processed material so as to have good slidability. 
     The sliding mechanisms, the undercut processing mechanisms, the gate cutting mechanisms, the gate tearing mechanisms, and the molding dies according to the present invention may be applied to sliding mechanisms, undercut processing mechanisms, gate cutting mechanisms, gate tearing mechanisms, and molding dies which open horizontally, or vertically, or in other directions. 
     The undercut processing mechanisms, the gate cutting mechanisms, the gate tearing mechanisms, and the molding dies according to the present invention may suitably used in, besides injection molding dies, other molding die such as die-cast molds as well as mold press molding dies. 
     Each of the sliding mechanisms, the undercut processing mechanisms, the gate cutting mechanisms, and the gate tearing mechanisms according to the present invention can be assembled into an independent single unit. Therefore, such a sliding mechanism may be considered as a slide device; such an undercut processing mechanism may be considered as an undercut processing device; such a gate cutting mechanism may be considered as agate cutting device; such a gate tearing mechanism may be considered as a gate tearing device; and such a gate pulling mechanism may be considered as a gate pulling device. 
     The above embodiments are described with reference to the examples where the sliding mechanisms according to the present invention are employed in the undercut processing mechanisms, the gate cutting mechanisms, the gate tearing mechanisms, and the gate pulling mechanisms. However, the sliding mechanisms according to the present invention may also be used as a cutter mechanism or a cutting device which cuts a processing target. The sliding mechanisms according to the present invention may also be incorporated, as a sliding mechanism or a slide device, into other devices than the molding dies, such as a conveying device and a processing device. 
     Although the present invention has been described in terms of the preferred examples thereof with reference to the drawings, those skilled in the art would readily arrive at various changes and modifications in view of the present specification without departing from the scope of the invention. Accordingly, such changes and modifications are included within the scope of the present invention defined by the appended claims. 
     REFERENCE NUMERALS 
     
         
           1 ,  6 ,  50  . . . sliding mechanism 
           11  . . . first piece 
           15  . . . protruding line 
           21 ,  61  . . . second piece 
           23 ,  30 ,  63  . . . click 
           24 ,  64  . . . side face 
           25 ,  65  . . . side face 
           26 ,  68  . . . side face 
           27  . . . side face 
           29  . . . dovetail groove 
           31 ,  81  . . . guiding body 
           34 ,  84  . . . left-side-wall inner surface 
           36 ,  86  . . . right-side-wall inner surface 
           38 ,  45 ,  88  . . . guiding groove 
           39 ,  89  . . . first guiding part 
           40 ,  90  . . . side surface 
           41 ,  91  . . . side surface 
           42 ,  92  . . . second guiding part 
           43 ,  93  . . . side surface 
           44  . . . side surface 
           46  . . . third guiding part 
           48  . . . fourth guiding part 
           68  . . . side face 
           73  . . . side face 
           87  . . . upper inner surface 
           100 ,  102 ,  104 ,  106 ,  108 ,  110 ,  800 ,  900 ,  1000 ,  1100  . . . molding die 
           101 ,  103 ,  105 ,  107 ,  109  . . . undercut processing mechanism 
           111 ,  112 ,  113  . . . undercut processing mechanism 
           121 ,  122 ,  123 ,  124 ,  131 ,  136 ,  138  . . . holder 
           127 ,  127   a ,  127   b ,  227 ,  327 ,  427 ,  527   a  . . . left-side-wall inner surface 
           130 ,  130   a ,  130   b ,  230 ,  330 ,  430  . . . right-side-wall inner surface 
           134 ,  164  . . . inclined surface 
           141 ,  142 ,  143   a ,  143   b ,  144   a ,  144   b  . . . guiding groove 
           153 ,  154 ,  155   a ,  155   b ,  159 ,  159   a ,  159   b  . . . guiding groove 
           160 ,  162   a ,  162   b ,  856 ,  1256 ,  1356  . . . guiding groove 
           145 ,  145   a ,  145   b ,  245 ,  252 ,  857 ,  1257 ,  1357  . . . first guiding part 
           146 ,  146   a ,  146   b ,  157 ,  158 ,  246  . . . left side surface 
           147 ,  147   a ,  147   b ,  187 ,  247  . . . right side surface 
           148 ,  148   a ,  148   b ,  248 ,  858 ,  1258 ,  1358  . . . second guiding part 
           149 ,  151 ,  249 ,  253 ,  311  . . . left side surface 
           150 ,  150   a ,  150   b ,  250 ,  254  . . . right side surface 
           161 ,  261 ,  361 ,  461 ,  561 ,  821 ,  1021 ,  1221 ,  1321 ,  1421 ,  1521  . . . retaining piece 
           168 ,  268 ,  567  . . . protruding line 
           169  . . . knock pin 
           171 ,  172 ,  173   a ,  173   b ,  174   a ,  174   b ,  178 ,  179  . . . sliding piece 
           176 ,  176   a ,  176   b ,  276 ,  376 ,  467  . . . dovetail groove 
           177   a ,  177   b  . . . recessed groove 
           179 ,  194 ,  271 ,  371 ,  471 ,  571  . . . sliding piece 
           180 ,  180   a ,  180   b ,  181   a ,  181   b  . . . click 
           188   a ,  188   b ,  195   a ,  195   b ,  280  . . . click 
           181 ,  181   a ,  186 ,  189 ,  190 ,  197 ,  281 ,  285  . . . left side face 
           182 ,  182   a ,  187 ,  282 ,  286  . . . right side face 
           183 ,  183   a ,  183   b ,  185 ,  283  . . . upper side face 
           184 ,  184   a ,  184   b ,  284  . . . lower side face 
           191 ,  191   a ,  191   b  . . . molding core 
           200 ,  300 ,  400 ,  500  . . . molding die 
           201 ,  202 ,  301 ,  401 ,  501 ,  1401  . . . gate cutting mechanism 
           221 ,  321 ,  421 ,  521 ,  776 ,  851 ,  1051 ,  1151 ,  1251 ,  1351 ,  1451  . . . holder 
           241 ,  871 ,  1556  guiding groove 
           291 ,  491 ,  591  . . . cutter 
           367  . . . lock groove 
           391  . . . first cutter 
           395  . . . second cutter 
           405 ,  505  . . . movable piece 
           407  . . . presser 
           408 ,  409  . . . click 
           412 ,  413 ,  415  . . . protruding line 
           417  . . . left side face 
           418  . . . right side face 
           419  . . . upper side face 
           420  . . . lower side face 
           441  . . . first guiding groove 
           445  . . . first guiding part 
           448  . . . second guiding part 
           468 ,  469  . . . protruding line 
           507  . . . presser plate 
           512  . . . right side face 
           514  . . . inclined surface 
           531 ,  531   a  . . . inclined surface 
           541  . . . first guiding groove 
           542  . . . left side surface 
           543  . . . right side surface 
           600 ,  602 ,  603  . . . fixed die 
           700 ,  702 ,  703  . . . movable die 
           801 ,  901 ,  1001 ,  1101 ,  1201 ,  1301 ,  1501  . . . gate tearing mechanism 
           803 ,  1203 ,  1303 ,  1503  . . . tearing piece 
           812 ,  1212 ,  1312  . . . click 
           828 ,  1273 ,  1328 ,  1528  . . . protruding line 
           841 ,  941  . . . driving piece 
           1271  . . . guiding piece 
           1371  . . . recessed groove 
           1403  . . . cutting piece 
           1571  . . . tearing piece holder 
         P . . . molded product 
         P 1 , P 4 , P 5   a , P 5   b  . . . undercut portion 
         P 2 , P 3  . . . protruding portion 
         G . . . gate 
         R . . . runner