Patent Publication Number: US-2020290107-A1

Title: Stamping apparatus and stamping method

Description:
BACKGROUND 
     1. Field 
     The following description relates to a stamping apparatus and a stamping method. 
     2. Description of Related Art 
     Japanese Laid-Open Patent Publication No. 2003-117619 discloses a method for stamping a product having teeth on the outer circumference, in which a material is first pressed so that an intermediate product, the perimeter of which is connected to the material, is half-blanked. At the same time, pressure is applied to a central portion of the intermediate product to move the central portion toward the perimeter. Then, the intermediate product is forced back toward the material so that the perimeter of the intermediate product is detached from the material. Finally, the intermediate product is removed from the material, and the central portion of the intermediate product is punched out. As a result, the product is formed. 
     When stamping a product that requires accuracy in the sheared surface, a number of processing steps is performed to ensure the accuracy. Such a method is burdensome. 
     SUMMARY 
     It is an objective of the present disclosure to provide a stamping apparatus and a stamping method that increase productivity. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     In one general aspect, a stamping apparatus includes a die on which a workpiece is mounted, a punch arranged to approach and recede from the die and configured to punch out a product from the workpiece, a back-pressure device including a pushing member disposed in the die, the back-pressure device urging the pushing member toward the punch to apply back pressure to the workpiece, a lift-up mechanism configured to lift the workpiece above the die when the punch recedes from the die, and a delay device configured to delay lifting movement of the pushing member in relation to receding movement of the punch when the punch recedes from the die. 
     In another general aspect, a stamping method includes, when punching out a product from a workpiece by causing a punch to approach and recede from a die on which the workpiece is mounted, applying back pressure to the workpiece from a side opposite to the punch using a pushing member, and when the punch recedes from the die, lifting the workpiece above the die and delaying lifting movement of the pushing member in relation to receding movement of the punch. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a stamping apparatus and a stamping method according to an embodiment, illustrating the structure of the stamping apparatus. 
         FIG. 2  is a perspective view of a back-pressure device and a delay device of the embodiment of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of an upper die assembly of the embodiment in which section A shows a cross section that differs from that in  FIG. 1 . 
         FIG. 4A  is a bottom view of a switch member from a side of a rotation plate when the rotation plate is located in an opposing position. 
         FIG. 4B  is a bottom view of the switch member from a side of the rotation plate when the rotation plate is located in an accommodated position. 
         FIG. 5  is a cross-sectional view of the stamping method of the embodiment of  FIG. 1 , illustrating a state in which upper pins are in contact with lower pins. 
         FIG. 6  is a cross-sectional view of the stamping method of the embodiment of  FIG. 1 , illustrating a state in which the upper ends of the upper pins are accommodated in recesses of the switch member. 
         FIG. 7  is a cross-sectional view of the stamping method of the embodiment of  FIG. 1 , illustrating a state in which a metal core is inserted into a through hole of a workpiece. 
         FIG. 8  is a cross-sectional view of the stamping method of the embodiment of  FIG. 1 , illustrating a state in which a product is punched out from the workpiece by a punch. 
         FIG. 9  is a cross-sectional view of the stamping method of the embodiment of  FIG. 1 , illustrating a state in which the rotation plate is switched from the accommodated position to the opposing position. 
         FIG. 10  is a cross-sectional view of the stamping method of the embodiment of  FIG. 1 , illustrating a state in which the metal core is receded from the through hole of the workpiece. 
         FIG. 11  is a cross-sectional view of the stamping method of the embodiment of  FIG. 1 , illustrating a state in which the punch is receded from the workpiece. 
         FIG. 12  is a cross-sectional view of the stamping method of the embodiment of  FIG. 1 , illustrating a state in which the product is lifted by a lifter. 
     
    
    
     Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     This description provides a comprehensive understanding of the methods, apparatuses, and/or systems described. Modifications and equivalents of the methods, apparatuses, and/or systems described are apparent to one of ordinary skill in the art. Sequences of operations are exemplary, and may be changed as apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted. 
     Exemplary embodiments may have different forms, and are not limited to the examples described. However, the examples described are thorough and complete, and convey the full scope of the disclosure to one of ordinary skill in the art. 
     A stamping apparatus and a stamping method according to an embodiment will now be described with reference to  FIGS. 1 to 12 . 
     As shown in  FIG. 1 , the present embodiment of a stamping apparatus  10  is configured to punch out a product P from a plate-shaped workpiece  200 , which is conveyed from right to left in  FIG. 1 . The product P of the present embodiment is a gear having teeth on the outer circumference. In the description hereafter, the conveying direction of the workpiece  200  (sideward direction in  FIG. 1 ) is referred to as a conveying direction X. 
     The stamping apparatus  10  includes a lower die assembly  20  including a die  25  and an upper die assembly  50  including a punch  70 . The workpiece  200  is conveyed and mounted on the die  25 . The punch  70  is arranged to approach and recede from the die  25  in the vertical direction and configured to punch out the produce P from the workpiece  200 . The upper die assembly  50  is coupled to a slider (not shown) that reciprocates in the vertical direction and is arranged to approach and recede from the lower die assembly  20 . 
     The structure of the lower die assembly  20  will now be described. 
     Lower Die Assembly  20   
     As shown in  FIG. 1 , the lower die assembly  20  includes a die holder  22  disposed on a base  21  and a die plate  23  fixed to an upper portion of the die holder  22  to accommodate the die  25 . The die  25  has a gear forming portion on the inner circumferential surface. 
     Multiple (five, in the present embodiment) gas cylinders  31  (urging portions) are arranged in the die holder  22  and fixed to the base  21 . Each of the gas cylinders  31  includes a cylinder  31   a  and a piston rod  31   b  configured to reciprocate in the cylinder  31   a . The piston rod  31   b  projects upward. The space defined by the cylinder  31   a  and the piston rod  31   b  is filled with gas such as nitrogen. The piston rod  31   b  is urged upward by the pressure of the gas in the cylinder  31   a.    
     As shown in  FIGS. 1 and 2 , an intermediate portion  32  is plate-shaped and rhombic in a plan view and is coupled to the distal ends of the piston rods  31   b  of the gas cylinders  31 . The intermediate portion  32  is urged upward by the gas cylinders  31  and is in contact with the lower surface of the die plate  23 . 
     Multiple (six, in the present embodiment) support pins  33  project from a central portion of the intermediate portion  32  in the conveying direction X. The support pins  33  are inserted through respective through holes  23   a  formed in the die plate  23 . The upper ends of the support pins  33  are located in the die  25 . 
     The upper ends of the support pins  33  are coupled to a discoid base plate  34  disposed in the die  25 . 
     A pushing member  35  is disposed on the upper surface of the base plate  34 . The pushing member  35  has a center hole  35   a  and a gear forming portion on the outer circumferential surface. The center hole  35   a  is a stepped hole in which a lower part has a larger diameter than an upper part. 
     In the present embodiment, the gas cylinders  31 , the intermediate portion  32 , the support pins  33 , the base plate  34 , and the pushing member  35  configure a back-pressure device  30 . The back-pressure device  30  urges the pushing member  35  toward the punch  70  using the gas cylinders  31  to apply back pressure to the workpiece  200 . 
     As shown in  FIG. 1 , a lifter  37  is disposed in the center hole  35   a  of the pushing member  35  and urged by a compression spring  36  toward the punch  70  so that the lifter  37  retractably extends from the pushing member  35 . The lifter  37  has a cylindrical shape with a lower open end and a closed upper end, defining a recess  37   a.  The upper and lower ends of the compression spring  36  are coupled to the closed end surface of the recess  37   a  of the lifter  37  and the upper surface of the base plate  34 , respectively. A flange projects circumferentially outward from the lower end of the lifter  37  along the entire perimeter. The flange is in contact with the step in the center hole  35   a  of the pushing member  35  to stop removal of the lifter  37  from the pushing member  35 . 
     Two through holes  23   b  vertically extend through the die plate  23  at opposite sides of the die  25  in the conveying direction X. Each through hole  23   b  receives a lower pin  24 . The lower end of each lower pin  24  is opposed to the upper surface of the intermediate portion  32 . More specifically, the lower pins  24  are disposed at opposite sides of the intermediate portion  32  in the conveying direction X (refer to  FIG. 2 ). In the present embodiment, the lower pins  24  are coupled to the upper surface of the intermediate portion  32 . Therefore, the lower pins  24  are movable in the vertical direction in accordance with reciprocation of the piston rods  31   b  of the gas cylinders  31 . When the intermediate portion  32  is in contact with the lower surface of the die plate  23 , the upper ends of the lower pins  24  project from the upper surface of the die plate  23 . 
     A lift-up mechanism  40  is arranged on an upstream side (left side in  FIG. 1 ) of the lower die assembly  20  in the conveying direction X. The lift-up mechanism  40  is configured to lift the workpiece  200  above the die  25  when the punch  70  recedes from the die  25 , and more specifically, when the upper die assembly  50  recedes from the lower die assembly  20 . The lift-up mechanism  40  includes a base  41  coupled to the lower die assembly  20  and a clamp  43  clamping the workpiece  200  in the vertical direction. The base  41  includes a receptacle  42  that is open upward. A compression spring  44  is disposed in the receptacle  42 . The clamp  43  is urged upward by the compression spring  44  disposed in the receptacle  42 . 
     The structure of the upper die assembly  50  will now be described. 
     Upper Die Assembly  50   
     The upper die assembly  50  includes a top plate  51 , a housing  52 , a punch holder  80 , and a stripper backing  90 . The housing  52  is fixed to the lower surface of the top plate  51  and accommodates a gas cylinder  60 . The punch holder  80  holds the punch  70 . The stripper backing  90  presses the workpiece  200  onto the lower die assembly  20  and guides the punch  70  in the vertical direction. The gas cylinder  60  and the gas cylinders  31  have the same structure. 
     The structure of the punch  70  will now be described in detail. 
     Punch  70   
     The punch  70  is opposed to the pushing member  35 . The punch  70  has a gear forming portion on the outer circumferential surface. A through hole  70   a  vertically extends through a center portion of the punch  70 . A metal core  71  is inserted through the through hole  70   a  to extend vertically. The upper end of the metal core  71  is fixed to the punch holder  80 . 
     In the present embodiment, in a step prior to the step of punching out the product P using the stamping apparatus  10 , a through hole  201  is formed in a portion of the workpiece  200  that is to be punched out by the punch  70 . When punching out the product P, the metal core  71  is inserted through the through hole  201 . This limits deformation of the through hole  201  and allows the punch  70  to stably punch out the product P from the workpiece  200 . The through hole  201  has a smaller diameter than the lifter  37 . 
     Two holding pins  72  are disposed in opposite sides of the punch  70  in the conveying direction X to retractably extend from the lower surface of the punch  70 . The holding pins  72  are urged downward by compression springs  73  disposed in the punch  70 . The sum of urging forces of the holding pins  72  is greater than urging force of the lifter  37 . 
     Punch Holder  80   
     The punch holder  80  is coupled to a lower portion of the housing  52 . 
     The punch holder  80  includes an accommodation recess  80   a  that is open downward to accommodate the upper end of the punch  70 . The accommodation recess  80   a  has an upper surface including multiple (two, in the present embodiment) through holes  80   b  vertically extending through the punch holder  80 . 
     A pressing pin  53  is inserted through each of the through holes  80   b.  The upper end of each pressing pin  53  extends through the lower portion of the housing  52  and is coupled to the gas cylinder  60  in the housing  52 . The lower end of each pressing pin  53  is coupled to the upper end of the punch  70 . 
     The punch holder  80  is vertically movable relative to the punch  70 . When the punch holder  80  vertically moves relative to the punch  70 , the metal core  71  fixed to the punch holder  80  extends from the lower surface of the punch  70 . 
     Two through holes  80   c  vertically extend through the punch holder  80  at opposite sides of the punch holder  80  in the conveying direction X. Each through hole  80   c  is a stepped hole in which a lower part has a larger diameter than an upper part. Each through hole  80   c  receives an upper pin  81  so that the upper pin  81  is movable in the vertical direction. The upper pins  81  are coaxial with the lower pins  24  of the lower die assembly  20 . Each upper pin  81  has a vertically-central portion having a larger diameter than the other portion, defining an enlarged portion  81   a.  The portion of the upper pin  81  located below the enlarged portion  81   a  is inserted through a through hole  90   c,  which extends through the stripper backing  90 . A compression spring  82  is disposed between the upper end of the enlarged portion  81   a  of each upper pin  81  and the stepped portion of the corresponding through hole  80   c.  The upper pins  81  are urged downward by the compression springs  82  to retractably extend from the lower surface of the stripper backing  90 . In addition, when the lower end of the enlarged portion  81   a  of each upper pin  81  contacts the upper surface of the stripper backing  90 , downward movement of the upper pin  81  is restricted. Vertical movement of the upper die assembly  50  allows the lower ends of the upper pins  81  to contact and separate from the upper ends of the lower pins  24 . 
     In the present embodiment, in a step prior to the step of stamping the product P with the stamping apparatus  10 , through holes  202  are formed in portions of the workpiece  200  that are opposed to the lower pins  24  and the upper pins  81  so that the lower pins  24  and the upper pins  81  are inserted through the through holes  202 . 
     Stripper Backing  90   
     A punch guide hole  90   a  is formed in a central portion of the stripper backing  90  in the conveying direction X to guide the punch  70 . The lower surface of the stripper backing  90  includes an accommodation recess  90   b,  which is connected to the punch guide hole  90   a.    
     A stripper plate  91  is accommodated in the accommodation recess  90   b  to push the workpiece  200 , mounted on the die  25 , from above. The lower surface of the stripper plate  91  is substantially flush with the lower surface of the stripper backing  90 . 
     A punch guide hole  91   a  is formed in a central portion of the stripper plate  91  in the conveying direction X to guide the punch  70 . 
     The stripper backing  90  is coupled to a gas cylinder  61  by a coupling member  92 . The gas cylinder  61  is fixed to an upstream side of the lower surface of the top plate  51  in the conveying direction X. The coupling member  92  extends through the punch holder  80 . The gas cylinder  61  and the gas cylinders  31  have the same structure. 
     The lower surface of the stripper backing  90  has an upstream portion in the conveying direction X including an escape portion  93 . When the upper die assembly  50  is lowered, the escape portion  93  accommodates the upper portion of the clamp  43  of the lift-up mechanism  40 . 
     Switch Member  100   
     A cylindrical switch member  100  is disposed above the punch holder  80  to be rotational about an axis C extending vertically. The switch member  100  includes a base  102  and a rotation plate  103 . The rotation plate  103  is disposed on the lower surface of the base  102  to be rotational relative to the base  102  and has an opposing surface  104  opposed to the upper ends of the upper pins  81 . The switch member  100  has a central portion including a center hole  101  that vertically extends through the base  102  and the rotation plate  103 . 
     The lower portion of the housing  52 , which is fixed to the top plate  51 , is located in the center hole  101  of the switch member  100 . The switch member  100  is movable relative to the housing  52  in the vertical direction. 
     The upper surface of the base  102  is urged downward by multiple (eight, in the present embodiment) gas cylinders  62 , which are fixed to the lower surface of the top plate  51 . The gas cylinders  62  are disposed at intervals in the circumferential direction about the axis C. The gas cylinders  62  and the gas cylinders  31  have the same structure. 
     As shown in  FIGS. 1, 4A, and 4B , two recesses  105  are formed in portions of the opposing surface  104  of the rotation plate  103  to accommodate the upper ends of the upper pins  81 . 
     As shown in  FIGS. 4A and 4B , the recesses  105  are elongated holes radially extending about the axis C. The recesses  105  extend through the rotation plate  103 . 
     Multiple (four, in the present embodiment) receiving holes  106  are formed in the opposing surface  104  of the rotation plate  103  at equal intervals in the circumferential direction. The receiving holes  106 , which are elongated holes extending in the circumferential direction about the axis C, extend through the rotation plate  103 . 
     As shown in  FIG. 3  with section A, a through hole  80   d  is formed in the punch holder  80  in a portion corresponding to each receiving hole  106 . Four support rods  94  project from the upper surface of the stripper backing  90  and are inserted through the through holes  80   d.  The upper end of each support rod  94  is coupled to the lower surface of the base  102  in the corresponding receiving hole  106 . The support rods  94  maintain a fixed vertical distance between the stripper backing  90  and the switch member  100 . For the sake of convenience, in  FIG. 3 , section A shows a cross section of one of the support rods  94  and one of the receiving holes  106  of the upper die assembly  50 . This cross section differs from the portion shown in in  FIG. 1 . 
     As shown in  FIGS. 4A and 4B , the receiving holes  106  are elongated holes extending in the circumferential direction. Thus, when the support rods  94  are accommodated in the receiving holes  106 , rotation of the rotation plate  103  is allowed. 
     The rotation plate  103  has a circumferential portion on which a gear portion  107  is formed. 
     Drive Mechanism  110   
     As shown in  FIGS. 2, 4A, and 4B , the upper die assembly  50  includes a drive mechanism  110  configured to rotate the rotation plate  103  about the axis C. The drive mechanism  110  includes an elongated slide bar  111  extending in the conveying direction X and an air cylinder  113  that reciprocates the slide bar  111  in the conveying direction X. 
     The proximal end of the slide bar  111  is coupled to an output shaft  114  of the air cylinder  113 . A gear portion  112  is formed on a portion of the distal end of the slide bar  111  opposed to the rotation plate  103  to engage the gear portion  107  of the rotation plate  103 . Reciprocation of the slide bar  111  in the conveying direction X rotates the rotation plate  103  about the axis C. 
     As shown in  FIGS. 4A and 4B , the drive mechanism  110  switches the position of the rotation plate  103  between an opposing position in which the upper ends of the upper pins  81  are opposed to the opposing surface  104  and an accommodated position in which the upper ends are accommodated in the recesses  105 . 
     When the support rods  94  of the stripper backing  90  are accommodated in the receiving holes  106  of the rotation plate  103 , the position of the rotation plate  103  is switchable between the opposing position and the accommodated position. 
     In the present embodiment, the lower pins  24  of the lower die assembly  20 , the upper pins  81  of the upper die assembly  50 , the switch member  100 , and the drive mechanism  110  configure a delay device  120 . The delay device  120  is configured to restrict upward movement of the intermediate portion  32 , thereby delaying lifting movement of the pushing member  35  in relation to receding movement of the punch  70 , during a set period from when the punch  70  starts to retract from the die  25 . 
     The stamping method of punching out the product P from the workpiece  200  using the stamping apparatus  10  will now be described. 
     As shown in  FIG. 1 , the workpiece  200  is conveyed and placed between the lower die assembly  20  and the upper die assembly  50 . At this time, the workpiece  200  is held by the clamp  43  of the lift-up mechanism  40  at a position separated upward from the lower die assembly  20 . The position of the rotation plate  103  of the switch member  100  is set to the accommodated position. In addition, the upper end of the punch  70  is spaced apart by a gap from the upper surface of the accommodation recess  80   a  of the punch holder  80 . 
     Then, the slider (not shown) presses the top plate  51  of the upper die assembly  50  to lower the upper die assembly  50  toward the lower die assembly  20  and bring the stripper backing  90  into contact with the upper surface of the workpiece  200 . 
     At this time, the holding pins  72  of the punch  70  are in contact with the upper surface of the workpiece  200  and recede in the punch  70 . The upper pins  81  are inserted into the through holes  202  of the workpiece  200 . The upper portion of the clamp  43  of the lift-up mechanism  40  is received in the escape portion  93  of the stripper backing  90 . 
     As shown in  FIG. 5 , the upper die assembly  50  is further lowered, so that the upper ends of the lower pins  24  come into contact with the lower ends of the upper pins  81 . At this time, the clamp  43  moves downward against the urging force of the compression spring  44 . 
     As shown in  FIG. 6 , when the upper die assembly  50  is further lowered, the lower surface of the workpiece  200  comes into contact with the upper surface of the die  25 . As a result, the lifter  37  is forced downward and is entirely accommodated in the pushing member  35 . 
     In the state shown in  FIG. 5 , the upper pins  81 , which are accommodated in the punch holder  80  and movable in the vertical direction, are in contact with the lower pins  24 . Thus, downward movement of the upper pins  81  is restricted. In this state, the upper die assembly  50  is lowered. As a result, the components of the upper die assembly  50  excluding the upper pins  81  are moved downward relative to the upper pins  81 . As described above, since the position of the switch member  100  is set to the accommodated position, when the upper die assembly  50  is lowered, the upper ends of the upper pins  81  are received in the recesses  105  of the switch member  100  (refer to  FIG. 6 ). 
     In this state, the workpiece  200  is held between the upper die assembly  50  and the lower die assembly  20 , so that downward movement of the stripper backing  90  is restricted. 
     In the description hereafter, the vertical position of the punch  70  in this state is referred to as a preparation position. The preparation position corresponds to a set position of the present disclosure. When the punch  70  is located in the preparation position, the upper surface of the punch holder  80  is in contact with the opposing surface  104  of the rotation plate  103 . 
     As shown in  FIG. 3 , the coupling member  92  is disposed between the gas cylinder  61  and the stripper backing  90 . The switch member  100  and the support rods  94  are disposed between the stripper backing  90  and the gas cylinders  62 . In addition, as described above, the switch member  100  is vertically movable relative to the housing  52 , which is fixed to the top plate  51 . 
     Therefore, as shown in  FIG. 7 , when the top plate  51  is pressed by the slider, the top plate  51  is moved downward as the piston rods of the gas cylinder  61  and the gas cylinders  62  are retracted. At the same time, the punch holder  80  is pressed downward by the housing  52 . Since the coupling member  92  and the support rods  94  are inserted through the punch holder  80 , the punch holder  80  is moved downward together with the top plate  51  and the housing  52 . 
     As described above, when downward movement of the stripper backing  90  is restricted and the punch holder  80  is moved downward together with the top plate  51  and the housing  52 , the switch member  100  will not move downward in a stroke range in which the piston rods of the gas cylinder  61  and the gas cylinders  62  are retractable. 
     As described above, when the housing  52  and the punch holder  80  are moved downward together with the top plate  51 , the punch  70  is in contact with the workpiece  200 , so that downward movement of the punch  70  is restricted. The upper end of the punch  70  is coupled by the pressing pins  53  to the gas cylinder  60  in the housing  52 . When the top plate  51  is pressed by the slider, the top plate  51  is moved downward together with the housing  52  and the punch holder  80  as the piston rod of the gas cylinder  60  is retracted. 
     As a result, the metal core  71 , which is fixed to the punch holder  80 , projects from the lower surface of the punch  70  and is inserted into the through hole  201  of the workpiece  200 . At this time, the gap between the upper end of the punch  70  and the upper surface of the accommodation recess  80   a  of the punch holder  80  is filled. 
     As shown in  FIG. 8 , the top plate  51  is further pressed by the slider to lower the punch  70  to the bottom dead center. As the back-pressure device  30  applies back pressure to the workpiece  200 , the product P is punched out from the workpiece  200 . The bottom dead center of the punch  70  is a position where the lower surface of the punch  70  is slightly below the upper surface of the die  25 , that is, the lower surface of the workpiece  200 . Therefore, the workpiece  200  is spaced apart from the product P by a slight gap in the vertical direction. 
     At this time, the back-pressure device  30  is pressed downward by the punch  70  and thus is moved downward. Accordingly, the upper ends of the upper pins  81 , which are urged downward by the compression springs  82 , are removed from the recesses  105  of the switch member  100 . 
     Then, as shown in  FIG. 9 , the drive mechanism  110  is driven to set the position of the rotation plate  103  of the switch member  100  to the opposing position. As a result, the upper pins  81  and the lower pins  24 , which are in contact with each other, are held between the opposing surface  104  of the rotation plate  103  and the upper surface of the intermediate portion  32 . 
     Then, as shown in  FIG. 10 , the top plate  51  is lifted so that the metal core  71  recedes from the product P. At this time, the gas cylinder  61  and the gas cylinders  62 , which are fixed to the top plate  51 , are lifted together with the top plate  51 . However, the piston rods of the gas cylinder  61  and the gas cylinders  62  are in the retracted state. Therefore, until the gas cylinder  61  and the gas cylinders  62  are released from the retracted state, the stripper backing  90  continues to be pressed through the coupling member  92  and the support rods  94 . As a result, with the stripper backing  90  pressing the workpiece  200 , the punch holder  80  is lifted together with the housing  52  and the top plate  51 . Consequently, the metal core  71  recedes from the product P. 
     Then, as shown in  FIG. 11 , the top plate  51  is lifted until the upper surface of the punch holder  80  comes into contact with the opposing surface  104  of the rotation plate  103 , that is, until the punch  70  returns to the preparation position, so that the punch  70  recedes from the product P. At this time, the stripper backing  90  is pressing the workpiece  200 , and the support rods  94  are disposed between the stripper backing  90  and the switch member  100 . Therefore, the switch member  100  will not move upward. 
     The holding pins  72  of the punch  70  are urged downward by the compression springs  73 . When the punch  70  recedes from the product P, the holding pins  72  of the punch  70  project from the lower surface of the punch  70  and press the upper surface of the product P. 
     Although not shown in the drawings, the top plate  51  is lifted to separate the upper die assembly  50  from the lower die assembly  20  so that the product P is removed from the stamping apparatus  10 . Accordingly, the lift-up mechanism  40  lifts the workpiece  200  upward in contact with the lower surface of the stripper backing  90 . 
     At this time, the upper pins  81  move upward in accordance with the lifting of the upper die assembly  50 . The intermediate portion  32 , which is pressed by the upper pins  81  through the lower pins  24 , is moved upward by the urging force of the gas cylinders  31  until the intermediate portion  32  comes into contact with the lower surface of the die plate  23 . As a result, the pushing member  35  is moved upward to a position where the upper surface of the pushing member  35  is flush with the upper surface of the die  25 . As described above, since the workpiece  200  is spaced apart from the product P by a slight gap in the vertical direction, the product P remains on the pushing member  35 . 
     As described above, during the set period in which the punch  70  recedes from the bottom dead center to the preparation position, the delay device  120  delays lifting movement of the pushing member  35  in relation to receding movement of the punch  70 . As a result, the upper die assembly  50  including the upper pins  81 , the workpiece  200 , and the product P are moved upward while maintaining the vertical position relative to each other. 
     Then, as shown in  FIG. 12 , when the upper die assembly  50  is further lifted, the holding pins  72  are lifted upward together with the punch  70 , and the product P is lifted by the lifter  37  above the upper surface of the pushing member  35 . When the product P is lifted by the lifter  37 , the upper surface of the product P is pressed by the holding pins  72 . 
     Finally, the upper die assembly  50  is further lifted, and the product P is removed outside from the pushing member  35 . 
     As described above, the stamping apparatus  10  punches out the product P from the workpiece  200 . 
     The operation and advantages of the present embodiment will now be described. 
     (1) The stamping apparatus  10  includes the die  25 , the punch  70 , the back-pressure device  30 , the lift-up mechanism  40 , and the delay device  120 . The workpiece  200  is mounted on the die  25 . The punch  70  is arranged to approach and recede from the die  25  and configured to punch out the produce P from the workpiece  200 . The back-pressure device  30  includes the pushing member  35  disposed in the die  25  and urges the pushing member  35  toward the punch  70  so that back pressure is applied to the workpiece  200 . The lift-up mechanism  40  is configured to lift the workpiece  200  above the die  25  when the punch  70  recedes from the die  25 . The delay device  120  is configured to delay lifting movement of the pushing member  35  in relation to receding movement of the punch  70  when the punch  70  recedes from the die  25 . 
     When punching out the product P from the workpiece  200  using the die  25  and the punch  70 , the pushing member  35  disposed in the die  25  applies back pressure to the workpiece  200 . This increases the processing accuracy of the product P. 
     However, when punching out the product P from the workpiece  200  all at once, the back-pressure device  30  may push the product P back to the punched hole in the workpiece  200  formed by the punching-out of the product P, which is so-called push-back. Occurrence of push-back is undesirable particularly when the product P has a number of teeth on the outer circumference. 
     In this regard, with the configuration described above, when the punch  70  recedes from the die  25 , the lift-up mechanism  40  lifts the workpiece  200  above the die  25 . In addition, the delay device  120  delays lifting movement of the pushing member  35  in relation to receding movement of the punch  70 . As a result, the workpiece  200  is lifted while the product P, which is punched out from the workpiece  200 , remains on the pushing member  35  in the die  25 . Thus, even when the product P is punched out all at once from the workpiece  200 , occurrence of push-back is limited. This improves the productivity of stamping. 
     (2) The back-pressure device  30  includes the gas cylinders  31  (urging portion) upwardly urging the pushing member  35  and the intermediate portion  32  disposed between the pushing member  35  and the gas cylinders  31 . During the set period from when receding movement of the punch  70  starts, the delay device  120  restricts upward movement of the intermediate portion  32 , thereby delaying lifting movement of the pushing member  35  in relation to the receding movement of the punch  70 . 
     With this configuration, during the set period from when receding movement of the punch  70  starts, the delay device  120  restricts upward movement of the intermediate portion  32 , which is disposed between the gas cylinders  31  and the pushing member  35 , thereby delaying lifting movement of the pushing member  35  in relation to the receding movement of the punch  70 . Thus, the delay device  120  is configured independently from the back-pressure device  30 . This simplifies the structure of the back-pressure device  30 . 
     The back-pressure device  30  is configured to urge the pushing member  35  using the gas cylinders  31 . This dispenses with, for example, hydraulic control of a hydraulic cylinder. 
     (3) The delay device  120  includes the lower pins  24  and the upper pins  81 . The lower ends of the lower pins  24  are opposed to the upper surface of the intermediate portion  32 . The lower pins  24  are movable in the vertical direction. The lower ends of the upper pins  81  are configured to contact and separate from the upper ends of the lower pins  24 . The upper pins  81  move together with the punch  70  in the vertical direction. The delay device  120  further includes the switch member  100  and the drive mechanism  110 . While the switch member  100  moves together with the punch  70  in an approaching-receding direction of the punch  70 , the switch member  100  does not lift or lower when the punch  70  is located between the bottom dead center and the preparation position, which is located above the bottom dead center. The drive mechanism  110  is configured to move the switch member  100 . In the delay device  120 , during a period in which the punch  70  is punching out the product P, the switch member  100  is set to the accommodated position, and during a period in which the punch  70  recedes from the bottom dead center to the preparation position, the switch member  100  is set to the opposing position. Thus, the upper pins  81  and the lower pins  24  are in contact with each other and held between the opposing surface  104  of the rotation plate  103  and the upper surface of the intermediate portion  32 . 
     With this configuration, while the switch member  100  moves together with the punch  70  in the vertical direction, the switch member  100  does not lift or lower when the punch  70  is located between the bottom dead center and the preparation position, which is located above the bottom dead center. 
     While the punch  70  is punching out the product P, the switch member  100  is set to the accommodated position. This limits downward pressing of the upper surface of the intermediate portion  32  performed by the upper pins  81  and the lower pins  24 , which are in contact with each other, thereby limiting shortage of back pressure applied to the workpiece  200 . 
     During a period in which the punch  70  recedes from the bottom dead center to the preparation position, the switch member  100  is set to the opposing position. The upper pins  81  and the lower pins  24  are in contact with each other and held between the opposing surface  104  of the rotation plate  103  and the upper surface of the intermediate portion  32 . Thus, during a period from when receding movement of the punch  70  starts at the bottom dead center until the punch  70  recedes to the preparation position, the intermediate portion  32  continues to be pressed downward by the upper pins  81  and the lower pins  24 . 
     (4) The switch member  100  is rotational about the axis C extending in the vertical direction. The drive mechanism  110  rotates the switch member  100  about the axis C between the accommodated position and the opposing position. 
     This configuration reduces the space for moving the switch member as compared to, for example, a configuration including a switch member that slides in a direction orthogonal to the vertical direction to move between the accommodated position and the opposing position. This reduces the size of the stamping apparatus  10 . 
     (5) The lifter  37  is disposed in the pushing member  35  and is urged toward the punch  70  so that the lifter  37  retractably extends from the pushing member  35  to lift the product P above the upper surface of the pushing member  35 . 
     With this configuration, the product P is lifted above the upper surface of the pushing member  35 . This limits close contact of the product P with the pushing member  35 . As a result, the product P may be readily discharged. 
     Moreover, for example, when a protrusion is formed on the surface of the product P opposed to a pushing member, the upper surface of the pushing member will be provided with a recess for forming the protrusion or for receiving the protrusion. In this case, when the upper surface of the pushing member is lifted to the upper surface of the die  25 , the protrusion of the product P is fitted in the recess in the pushing member. This hampers discharging of the product P. 
     In this regard, with the configuration described above, the lifter  37  disposed in the pushing member  35  lifts the product P, which is punched out from the workpiece  200 , above the upper surface of the pushing member  35 . This allows the protrusion of the product P to be released from the recess of the pushing member  35 . Thus, the product P may be readily discharged. 
     (6) The holding pins  72  are disposed in the punch  70  to retractably extend from the punch  70  so when the product P is lifted by the lifter  37 , the holding pins  72  press the upper surface of the product P and hold the position of the product P. 
     With this configuration, when the product P is lifted by the lifter  37 , the holding pins  72  disposed in the punch  70  press the upper surface of the product P to hold the position of the product P. This also limits occurrence of push-back of the product P caused by the lifter  37 . 
     (7) When the punch  70  recedes from the die  25 , the workpiece  200  is lifted above the die  25 , and the lifting movement of the pushing member  35  is delayed in relation to the receding movement of the punch  70 . 
     The method obtains advantages corresponding to advantage (1) described above. 
     The present embodiment may be modified as follows. The present embodiment and the following modified examples can be combined as long as the combined modified examples remain technically consistent with each other. 
     The metal core  71  may be omitted. 
     The number and layout of the support pins  33  and the pressing pins  53  may be modified as necessary. 
     The number and layout of the holding pins  72  may be modified as necessary. 
     The holding pins  72  may be omitted. 
     The lifter  37  may be omitted. In this case, the product P remains on the upper surface of the pushing member  35 . 
     The gear portion  112  of the slide bar  111  in the drive mechanism  110  may be configured separately from the slide bar  111 . The gear portion  107  of the rotation plate  103  may be configured separately from the rotation plate  103 . 
     The drive mechanism  110  may rotate the switch member  100  using an actuator other than the air cylinder  113  such as a servomotor or an electromagnetic solenoid. 
     The switch member  100  may slide in a direction orthogonal to the vertical direction to move between the accommodated position and the opposing position. 
     The number and layer of the upper pins  81  and the lower pins  24  may be modified as necessary. 
     The upper pins  81  do not necessarily have to be urged by the compression springs  82 . 
     The delay device may restrict upward movement of the intermediate portion  32 , for example, using pins that are integrally formed by the upper pins  81  and the lower pins  24 . In this case, the pins may be disposed at opposite sides of the workpiece  200  in a width-wise direction that is orthogonal to both the vertical direction and the conveying direction X in order to avoid interference with the workpiece  200 . In this case, the through holes  202  may be omitted from the workpiece  200 . 
     The gas cylinders  31 ,  60 ,  61 , and  62  may be hydraulic cylinders or pneumatic cylinders. 
     The back-pressure device  30  may drive the pushing member  35  using an actuator such as a ball screw so that the pushing member  35  vertically lifts and lowers to apply back pressure to the workpiece  200 . 
     The range in application of the stamping apparatus  10  is not limited to the product P, which has gear teeth on the outer circumference. The stamping apparatus  10  of the present embodiment can be employed in producing products having various shapes as long as those are punched out of a plate-shaped workpiece. 
     Various changes in form and details may be made to the examples above without departing from the spirit and scope of the claims and their equivalents. The examples are for the sake of description only, and not for purposes of limitation. Descriptions of features in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if sequences are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined differently, and/or replaced or supplemented by other components or their equivalents. The scope of the disclosure is not defined by the detailed description, but by the claims and their equivalents. All variations within the scope of the claims and their equivalents are included in the disclosure.