Abstract:
Provided is a highly versatile casting mold in which weight and manufacturing cost can be reduced, and whereby flash can be suppressed. A plate-shaped base part having a flat attachment face to which a back face of a fixed-cavity mold is attached is provided to a fixed mold constituting a casting mold. A portion of the base part in contact with the back face of the fixed-cavity mold has an attachment part body for supporting the fixed-cavity mold, and a pressure increasing means for increasing the pressure imparted to the fixed-cavity mold via the attachment part body in a state in which the mold is closed.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a casting die assembly (casting mold) including a plate-shaped base having a flat attachment surface to which the rear surface of a cavity die is attached. 
       BACKGROUND ART 
       [0002]    One known type of casting die assembly is made up from a fixed die and a movable die, each having a thick die block with a recess defined therein, and a cavity die that is fitted in the recess (see FIG. 5 of Japanese Laid-Open Patent Publication No. 61-226159). The casting die assembly is highly costly to manufacture because it is necessary to bore the recess highly precisely. The casting die assembly also is problematic in that it is heavy, since the die block with the recess defined therein is thick. Further, the casting die assembly is not versatile in use, due to the fact that the cavity die and the recess must be complementary in shape to each other. 
         [0003]    To solve the aforementioned problems, there has been proposed a casting die assembly including dies, each of which has a flat attachment surface on which the rear surface of a cavity die is mounted (see, for example, Japanese Laid-Open Patent Publication No. 61-226159). Since the dies of the proposed casting die assembly do not require a recess for a cavity die to be fitted therein, the casting die assembly is relatively low in cost and weight, and is highly versatile in use. 
       SUMMARY OF INVENTION 
       [0004]    If each of the dies disclosed in Japanese Laid-Open Patent Publication No. 61-226159 is formed into a plate shape in order to reduce the weight thereof, then the die is reduced in rigidity and tends to be deformed easily when the casting die assembly is closed. When the dies are deformed, the cavity dies also are deformed in a corresponding manner. Therefore, a gap tends to be formed between the cavity die of the fixed die and the cavity die of the movable die, which connects the cavity to the exterior of the casting die assembly. The gap allows molten metal that is poured into the cavity to leak out, thereby producing a phenomenon called “metal spits” that is liable to produce burrs on the cast product. 
         [0005]    It is an object of the present invention to provide a casting die assembly, which is relatively low in cost and weight, is highly versatile in use, and prevents burrs from being produced on cast products. 
         [0006]    According to the present invention, there is provided a casting die assembly including a first die and a second die, which face each other and are configured to be movable toward and away from each other, wherein at least one of the first die and the second die includes a cavity die and a plate-shaped base having a flat attachment surface to which a rear surface of the cavity die is attached, and wherein the base includes a region held in contact with the rear surface of the cavity die. The region includes a support configured to support the cavity die, and a pressure boosting unit configured to increase a pressure applied through the support to the cavity die when the first die and the second die are combined with each other. 
         [0007]    With the casting die assembly according to the present invention, when the first die and the second die are combined, the pressure boosting unit increases the pressure applied through the support to the cavity die, thereby minimizing deformation of the portion of the cavity die that is supported by the support. Since any gap connecting the cavity formed by the cavity die to the exterior of the casting die assembly is prevented from being formed upon closure of the casting die assembly, i.e., when the first die and the second die are combined with each other, burrs on the cast product are minimized. Further, since the rear surface of the cavity die is attached to the flat attachment surface of the plate-shaped base, the base does not require a recess in which the cavity die is fitted. Consequently, it is possible to reduce the manufacturing cost and weight of the casting die, and the casting die assembly can be made versatile in use. 
         [0008]    In the above casting die assembly, the pressure boosting unit may have a deformable portion, which is less rigid than the support, the deformable portion being configured to be elastically deformed to become convex away from the cavity die when the first die and the second die are combined with each other. 
         [0009]    With the above arrangement, when the first die and the second die are combined, the deformable portion is elastically deformed in a convex manner away from the cavity die, such that an elastic force (restoring force) of the deformable portion acts on the support. Therefore, when the first die and the second die are combined with each other, pressure applied to the cavity die through the support is increased to an appropriate level. 
         [0010]    In the casting die assembly, the deformable portion may be thinner than the support. Consequently, the deformable portion effectively is made elastically deformable while the support is made less deformable. Therefore, burrs on the cast product are minimized efficiently. 
         [0011]    In the casting die assembly, the deformable portion may have a through hole therein. In this manner, the rigidity of the deformable portion becomes smaller than the rigidity of the support, thereby making the deformable portion more elastically deformable. 
         [0012]    In the casting die assembly, the pressure boosting unit may have a hole therein. Therefore, it is possible for the contact area of the cavity die with the base to be reduced without changing the contact area of the cavity die with the support. Consequently, the pressure applied through the support to the cavity die can be increased to an appropriate level. 
         [0013]    The casting die assembly may further include a plurality of ejector pins configured to remove a cast product from the cavity die, and the hole may be large enough for the ejector pins to be inserted therein. 
         [0014]    With the above arrangement, the hole is large enough for the ejector pins to be inserted therein. Therefore, even if the layout of the ejector pins is changed depending on the shape of the cast product, the ejector pins can be inserted in the hole. In other words, the hole doubles as a hole through which the ejector pins can be inserted. Stated otherwise, there is no need for a new main die body to be produced responsive to changes made in the layout of the ejector pins. Consequently, the manufacturing cost of the casting die assembly is prevented from increasing, even if differently shaped products are cast. 
         [0015]    In the above casting die assembly, the support may be disposed around the pressure boosting unit, and the pressure boosting unit may be disposed behind a cavity-forming portion of the cavity die. Accordingly, deformation of the portion of the cavity die that is positioned around the cavity-forming portion is minimized. Therefore, burrs on the cast product are minimized efficiently. 
         [0016]    The casting die assembly may further include a flange that projects from the base toward the cavity die and abuts against a side surface of the cavity die, and a joint member configured to join the flange and the cavity die to each other. 
         [0017]    With the above arrangement, since the cavity die and the flange are joined to each other by the joint member, the cavity die is prevented from becoming displaced in position with respect to the base upon thermal expansion and contraction of the cavity die. The cavity die is thermally expandable away from the flange, so that the flange and the cavity die are prevented from becoming damaged when the cavity die undergoes thermal expansion. 
         [0018]    In the casting die assembly, the flange may have a first surface facing the cavity die, and the first surface may have a first recess in which a portion of a sprue sleeve or a portion of a sprue pin is disposed. The cavity die may have a second surface facing the flange, and the second surface may have a second recess in which another portion of the sprue sleeve or another portion of the sprue pin is disposed. When the sprue sleeve or the sprue pin is disposed in the first recess and the second recess, the cavity die may be positioned with respect to the base along a direction perpendicular to the direction in which the flange projects, and perpendicular to the direction in which the first surface faces. 
         [0019]    Accordingly, the cavity die can easily be positioned with respect to the base along a direction perpendicular to the direction in which the flange projects and perpendicular to the direction in which the first surface faces. Therefore, since the sprue sleeve or the sprue pin can be used as a positioning member, it is unnecessary for a new dedicated positioning member to be provided, thus resulting in a reduction in the number of parts. Since positional displacement of the cavity die with respect to the base is prevented, the dimensional accuracy of a cast product can be increased. 
         [0020]    In the casting die assembly, in the hole, a reinforcement member may be provided by being fixed to the rear surface of the cavity die. With this arrangement, the reinforcement member can prevent the cavity die from being excessively deformed during the casting process. As a result, the dimensional accuracy of a cast product can be increased. 
         [0021]    In the casting die assembly, the reinforcement member may be formed by stacking a plurality of metal plates. With this arrangement, by changing the number of stacked metal plates, the rigidity of the reinforcement member can be adjusted easily. 
         [0022]    With the casting die assembly according to the present invention, when the first die and the second die are combined, the pressure applied by the pressure boosting unit to the cavity die through the support is increased, thereby minimizing burrs on the cast product. Since the base, which serves as a main die body, is shaped as a plate, it is possible to reduce the manufacturing cost and weight of the casting die assembly, and the casting die assembly can be made versatile in use. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0023]      FIG. 1  is a vertical cross-sectional view, partially omitted from illustration, of a casting die assembly according to a first embodiment of the present invention, with the casting die assembly being shown in an open state; 
           [0024]      FIG. 2  is a perspective view of a fixed die of the casting die assembly, with a front side of the fixed die being shown; 
           [0025]      FIG. 3  is a perspective view of the fixed die shown in  FIG. 2 , with a rear side of the fixed die being shown; 
           [0026]      FIG. 4  is an exploded perspective view of the fixed die shown in  FIG. 2 ; 
           [0027]      FIG. 5  is a perspective view of a main fixed die body of the fixed die, with a rear side of the main fixed die body being shown; 
           [0028]      FIG. 6  is a rear elevational view of the main fixed die body shown in  FIG. 5 ; 
           [0029]      FIG. 7  is a perspective view of a movable die, a slide die, and a slide mechanism of the casting die assembly, as viewed from a front side thereof; 
           [0030]      FIG. 8  is a perspective view of the movable die shown in  FIG. 7 , with a rear side of the movable die being shown; 
           [0031]      FIG. 9  is an exploded perspective view of the movable die shown in  FIG. 7 ; 
           [0032]      FIG. 10  is a perspective view of a main movable die body of the movable die, with a rear side of the main movable die body being shown; 
           [0033]      FIG. 11  is a rear elevational view of the main movable die body shown in  FIG. 10 ; 
           [0034]      FIG. 12  is a vertical cross-sectional view, partially omitted from illustration, of the casting die assembly shown in  FIG. 1 , with the casting die assembly being shown in a closed state; 
           [0035]      FIG. 13  is a perspective view of a main die body according to a modification of the present invention; 
           [0036]      FIG. 14  is a vertical cross-sectional view, partially omitted from illustration, of a casting die assembly according to a second embodiment of the present invention, with the casting die assembly being shown in an open state; 
           [0037]      FIG. 15  is a rear elevational view of a main fixed die body of a fixed die shown in  FIG. 14 ; 
           [0038]      FIG. 16  is a rear elevational view of a main movable die body of a movable die shown in  FIG. 14 ; and 
           [0039]      FIG. 17  is a vertical cross-sectional view, partially omitted from illustration, of a modification of the casting die assembly shown in  FIG. 14 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0040]    Casting die assemblies according to preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. 
       First Embodiment 
       [0041]    Firstly, a casting die assembly  10  according to a first embodiment of the present invention will be described below. The casting die assembly  10  is a die assembly for use in a die casting process. Further, as shown in  FIG. 1 , the casting die assembly  10  includes a fixed die (first die)  12  and a movable die (second die)  14 , which face each other and are movable toward and away from each other, and a slide die  16  and a slide mechanism  18  (see  FIG. 7 ), which are mounted on the movable die  14 . Upon closure of the casting die assembly  10 , the fixed die  12 , the movable die  14 , and the slide die  16  jointly define a cavity C (see  FIG. 12 ), which is complementary in shape to a cast product. 
         [0042]    First, structural details of the fixed die  12  will be described below. As shown in  FIGS. 1 through 4 , the fixed die  12  has a main fixed die body  20 , a fixed cavity die  22  constructed from a plate mounted on the main fixed die body  20 , and an ejector mechanism  24  for ejecting a cast product out of the fixed cavity die  22 . The main fixed die body  20  includes a plate-shaped base  26 , and a flange  28  that projects from the base  26  toward the fixed cavity die  22 . 
         [0043]    The base  26 , which is substantially rectangular as viewed in front elevation, has a longitudinal end from which the flange  28  projects. Thus, the main fixed die body  20  is substantially L-shaped as viewed in side elevation. The base  26  has a sleeve placement hole  32  defined substantially centrally widthwise (transversely) in one end thereof. An injection sleeve  30  ( FIG. 1 ) for introducing molten metal is disposed in the sleeve placement hole  32 . The base  26  has a flat attachment surface (flat surface)  34  held in contact with the fixed cavity die  22 . The attachment surface  34  is flat over the entire surface. The flat attachment surface  34  is greater in size than a flat rear surface  36  ( FIG. 1 ) of the fixed cavity die  22 . 
         [0044]    As shown in  FIG. 4 , the base  26  includes a plurality of (four as illustrated) through holes  38  defined in a central region thereof, and a plurality of (four as illustrated) pin holes  40  defined in a region around the through holes  38 . The ejector mechanism  24  has ejector pins  90 , to be described later, which are inserted respectively in the through holes  38 , and return pins  92 , to be described later, which are inserted respectively in the pin holes  40 . A plurality of mounting bolts  42  for fastening the fixed cavity die  22  are mounted on the base  26 . Other details of the base  26  will be described later. 
         [0045]    The flange  28  extends over the full width of the base  26 . The flange  28  projects from the base  26  by a given length that is substantially the same as the thickness of the fixed cavity die  22 . The flange  28  has a pair of positioning pins  46 ,  48  mounted on a tip end face thereof. The positioning pins  46 ,  48  are transversely spaced from each other. The flange  28  has a first surface  50  that faces toward the flat attachment surface  34 , i.e., toward the fixed cavity die  22  combined with the main fixed die body  20 , and a first recess  54  defined in the first surface  50  for receiving a portion of a sprue sleeve  52 . The sprue sleeve  52  is joined end-to-end with the injection sleeve  30  for guiding molten metal from the injection sleeve  30  into the cavity C. 
         [0046]    According to the present embodiment, the sprue sleeve  52  is of a tubular shape, although the sprue sleeve  52  may be of any desired shape. The first recess  54 , which is positioned substantially centrally widthwise in the flange  28 , is shaped in a complementary manner to one-half of the outer shape of the sprue sleeve  52 . According to the present embodiment, the first recess  54  is of a semicircular transverse shape, although the first recess  54  may be of any desired shape. The flange  28  also has a pair of insertion holes  60 ,  62  defined therein for insertion of a pair of respective joint bolts (joint members)  56 ,  58  that serve to interconnect the flange  28  and the fixed cavity die  22 . The insertion holes  60 ,  62  extend along the longitudinal direction of the base  26 , and open at the first surface  50  on both sides of the first recess  54 . 
         [0047]    The fixed cavity die  22 , which extends along the longitudinal direction of the base  26 , is of a substantially rectangular shape as viewed in front elevation. The fixed cavity die  22  is attached to the main fixed die body  20  while remaining in contact with the flat attachment surface  34  of the base  26  and the first surface  50  of the flange  28 . The fixed cavity die  22  has a second surface  64 , which faces toward the flange  28 . The second surface  64  has a second recess  66  defined therein, which receives the other portion of the sprue sleeve  52 . 
         [0048]    The second recess  66  is positioned substantially centrally widthwise (transversely) in the fixed cavity die  22 , and is shaped in a complementary manner to one-half of the outer shape of the sprue sleeve  52 . According to the present embodiment, the second recess  66  is of a semicircular transverse shape, although the second recess  66  may be of any desired shape. The second surface  64  of the fixed cavity die  22  has a pair of bolt holes  68 ,  70  defined therein on both sides of the second recess  66  for receiving the respective joint bolts  56 ,  58  in a threaded manner therein. 
         [0049]    The fixed cavity die  22  has a mating surface  72  located remotely from the base  26 . The mating surface  72  includes a concave cavity-forming portion  74 , and a clearance  76  that prevents the mating surface  72  from interfering with the slide die  16  (see  FIG. 7 ). The fixed cavity die  22  has a plurality of through holes  78  for insertion of respective ejector pins  90  therein, and a plurality of pin holes  80  for insertion of respective return pins  92  therein. The through holes  78  open toward the cavity-forming portion  74 , whereas the pin holes  80  open toward the mating surface  72 . The mating surface  72  has a pair of positioning holes (bushings)  82 ,  84  defined in respective diagonal corners thereof. 
         [0050]    The ejector mechanism  24  has a square ejector plate  88  disposed behind the main fixed die body  20 . The ejector pins  90  are fixed to a central region of the ejector plate  88 , and the return pins  92  are fixed to respective corners of the ejector plate  88 . The ejector plate  88  can be pressed toward the base  26  by a non-illustrated pressing means. The ejector pins  90 , which serve to eject a cast product from the cavity-forming portion  74  when pressed by the ejector plate  88 , extend through respective through holes  38 , which are defined in the main fixed die body  20 , and extend through respective through holes  78 , which are defined in the fixed cavity die  22 . The return pins  92 , which serve to return the pressed ejector pins  90  to their initial non-pressed positions, extend through respective pin holes  40 , which are defined in the main fixed die body  20 , and extend through the respective pin holes  80 , which are defined in the fixed cavity die  22 . 
         [0051]    As shown in  FIGS. 4 and 5 , the base  26  includes a substantially rectangular channel defined substantially centrally widthwise in a rear surface thereof, and which extends from the other longitudinal end of the base  26  terminating short of the sleeve placement hole  32 . The base  26  also includes a pair of slits  94 ,  96 , which are defined on opposite sides of the sleeve placement hole  32 , and extend from the base  26  longitudinally toward one end thereof remote from the channel. 
         [0052]    The channel, which is defined in the base  26 , forms the base  26  into a pair of side blocks  98 ,  100 , a portal-shaped wall  102  in which the sleeve placement hole  32  is defined, and a thin-walled attachment plate  104  that extends between the side blocks  98 ,  100  and is joined to one end of the wall  102  remote from the sleeve placement hole  32 . The ejector plate  88  is disposed in the channel behind the attachment plate  104  (see  FIG. 3 ). 
         [0053]    The attachment plate  104  includes a main attachment plate body (support)  114 , which lies between the side blocks  98 ,  100  behind the channel, and a thin-walled panel (pressure boosting unit, deformable portion)  116  disposed inside and formed thinner than the main attachment plate body  114 . In other words, the main attachment plate body  114  is positioned around the thin-walled panel  116 . 
         [0054]    The thin-walled panel  116  is positioned behind the concave cavity-forming portion  74  of the fixed cavity die  22  (see  FIG. 1 ). The main attachment plate body  114  has the pin holes  40  defined therein, and the thin-walled panel  116  has the through holes  38  defined therein. The thin-walled panel  116  is lower in rigidity than the main attachment plate body  114 . More specifically, the rigidity of the thin-walled panel  116  is such that, when the casting die assembly  10  is closed, the thin-walled panel  116  is elastically deformed to become convex away from the fixed cavity die  22 . Thus, the thin-walled panel  116  is more elastically deformable than the main attachment plate body  114 . 
         [0055]    As shown in  FIGS. 4 and 6 , the base  26  includes a region T 1 , i.e., the region indicated by the two-dot-and-dash lines shown in  FIGS. 4 and 6 , which is referred to as a first contact region and is in contact with the flat rear surface  36  of the fixed cavity die  22 . The region T 1  includes the main attachment plate body  114  and the thin-walled panel  116 , both of which support the fixed cavity die  22 . 
         [0056]    In the fixed die  12  as above, the fixed cavity die  22  is installed on the main fixed die body  20  in the following manner. First, the fixed cavity die  22  is placed on the main fixed die body  20  such that the flat rear surface  36  of the fixed cavity die  22  is brought into contact with the flat attachment surface  34  of the base  26 , and the first surface  50  of the flange  28  is brought into contact with or abutment against the second surface  64  of the fixed cavity die  22 . 
         [0057]    At this time, the sprue sleeve  52  is disposed in the first recess  54  and the second recess  66 , thereby positioning the fixed cavity die  22  with respect to the main fixed die body  20  along the transverse direction of the base  26 . 
         [0058]    Thereafter, the mounting bolts  42  mounted on the base  26  are threaded into respective bolt holes, not shown, defined in the flat rear surface  36  of the fixed cavity die  22 . In addition, the joint bolts  56 ,  58  are inserted respectively through the insertion holes  60 ,  62  in the flange  28  and threaded into the respective bolt holes  68 ,  70  in the fixed cavity die  22 . As a result, the fixed cavity die  22  is fastened to the main fixed die body  20 . 
         [0059]    The movable die  14  will be described below. As shown in  FIGS. 1 and 7  through  9 , the movable die  14  includes a main movable die body  120 , a movable cavity die  122  constructed from a plate that is mounted on the main movable die body  120 , an ejector mechanism  124 , and a pair of support blocks  126 ,  128 . The main movable die body  120  includes a plate-shaped base  130 , and a flange  132  that projects from the base  130  toward the movable cavity die  122 . 
         [0060]    The base  130 , which is substantially rectangular when viewed in front elevation, has a longitudinal end from which the flange  132  projects. Thus, the main movable die body  120  is substantially L-shaped as viewed in side elevation. The base  130  has a flat attachment surface (flat surface)  134 , which is held in contact with the movable cavity die  122 , and is greater in size than a flat rear surface  136  ( FIG. 1 ) of the movable cavity die  122 . 
         [0061]    As shown in  FIG. 9 , the base  130  has a plurality of (five as illustrated) through holes  138  defined in a central region thereof. The ejector mechanism  124  has ejector pins  190 , which are inserted respectively into the through holes  138 . Plural mounting bolts  142  are mounted on the base  130 , which serve to fasten the movable cavity die  122 . Other details of the base  130  will be described later. 
         [0062]    The flange  132  extends over the full width of the base  130 . The flange  132  projects from the base  130  by a given length, which is substantially the same as the thickness of the movable cavity die  122 . The flange  132  has a pair of positioning holes (positioning bushings)  146 ,  148  defined in a tip end face thereof for receiving the respective positioning pins  46 ,  48  on the flange  28  of the fixed die  12 . The flange  132  includes a first surface  150 , which faces toward the flat attachment surface  134 , i.e., toward the movable cavity die  122  combined with the main movable die body  120 , and a first recess  154 , which is defined in the first surface  150  for receiving a portion of a sprue pin  152 . The sprue pin  152  serves to guide molten metal into the cavity C. 
         [0063]    The sprue pin  152  may be of any desired shape, although according to the present embodiment, the sprue pin  152  is in the form of a cylinder with an axial groove defined in the outer circumferential surface thereof. Upon closure of the casting die assembly  10 , the sprue pin  152  is inserted into the sprue sleeve  52  of the fixed die  12 , thereby forming a sprue runner  156  (see  FIG. 12 ) between the sprue pin  152  and the sprue sleeve  52 . The first recess  154  is positioned substantially centrally widthwise in the flange  132 , and is shaped in a complementary manner to one-half of the outer shape of the sprue pin  152 . According to the present embodiment, the first recess  154  is of a semicircular transverse shape, although the first recess  154  may be of any desired shape. 
         [0064]    The flange  132  also has a pair of insertion holes  162 ,  164  defined therein into which a pair of respective joint bolts (joint members)  158 ,  160  are inserted for interconnecting the flange  132  and the movable cavity die  122 . The insertion holes  162 ,  164  extend along the longitudinal direction of the base  130 , and open at the first surface  150  on both sides of the first recess  154 . 
         [0065]    The movable cavity die  122  extends along the longitudinal direction of the base  130 , and is mounted on the main movable die body  120  while remaining in contact with the flat attachment surface  134  of the base  130  and the first surface  150  of the flange  132 . The movable cavity die  122  is in the shape of a rectangle, with one corner thereof beveled into a slanted surface on which the slide mechanism  18  is fixed (see  FIG. 7 ). The movable cavity die  122  has a second surface  166 , which faces toward the flange  132 , and has a second recess  168  defined therein that receives the other portion of the sprue pin  152 . 
         [0066]    The second recess  168  is positioned substantially centrally widthwise (transversely) in the movable cavity die  122 , and is shaped in a complementary manner to one-half of the outer shape of the sprue pin  152 . According to the present embodiment, the second recess  168  is of a semicircular transverse shape, although the second recess  168  may be of any desired shape. The second surface  166  of the movable cavity die  122  has a pair of bolt holes  170 ,  172  defined therein on both sides of the second recess  168  into which the respective joint bolts  158 ,  160  are threaded and received. 
         [0067]    The movable cavity die  122  has a mating surface  174 , which is located remotely from the base  130 . The mating surface  174  has a convex cavity-forming portion  176 . The movable cavity die  122  includes a plurality of (five as illustrated) through holes  178  into which the respective ejector pins  190  are inserted and received. The through holes  178  open at the cavity-forming portion  176 . The mating surface  174  includes a pair of positioning pins  182 ,  184 , which are disposed in respective diagonal corners thereof for insertion into the respective positioning holes  82 ,  84  of the fixed cavity die  22 . 
         [0068]    The ejector mechanism  124  has a rectangular ejector plate  188 , which is disposed behind the main movable die body  120 , the ejector pins  190 , which are fixed to a central region of the ejector plate  188 , and a plurality of projection limiting pins  192 . The ejector pins  190  extend through the respective through holes  138 , which are defined in the main movable die body  120 , and the respective through holes  178 , which are defined in the movable cavity die  122 . By coming into contact with the rear surface of the main movable die body  120 , the projection limiting pins  192  serve to limit the length by which the ejector pins  190  project from the movable cavity die  122 . 
         [0069]    The support blocks  126 ,  128  extend along the longitudinal direction of the base  130 , and are spaced transversely from each other behind the base  130 . The ejector plate  188  is supported by the support blocks  126 ,  128  for movement along the thicknesswise direction thereof. The support blocks  126 ,  128  may be hollowed out in order to reduce the weight of the support blocks  126 ,  128 . 
         [0070]    As shown in  FIGS. 10 and 11 , the base  130  has a substantially rectangular channel defined substantially centrally in a widthwise direction in the rear surface of the base  130  and which extends over the full length of the base  130 . The channel, which is defined in the base  130 , makes the base  130  into a pair of side blocks  202 ,  204 , and a thin-walled attachment plate  206  that extends between the side blocks  202 ,  204  centrally in the base  130 . The support block  126  is fixed to a rear surface of the side block  202 , whereas the support block  128  is fixed to a rear surface of the side block  204 . 
         [0071]    The attachment plate  206  has a square recess defined substantially centrally in a rear surface thereof. The square recess, which is defined in the attachment plate  206 , makes the attachment plate  206  into a main attachment plate body (support)  212 , and a thin-walled panel (pressure boosting unit, deformable portion)  214 , which is disposed on and formed thinner than the main attachment plate body  212 . In other words, the main attachment plate body  212  is positioned around the thin-walled panel  214 . As shown in  FIG. 10 , the rear surface of the main attachment plate body  212  has a dent  216 , which is defined substantially centrally widthwise in one end portion of the main attachment plate body  212 , and is joined to the channel behind the thin-walled panel  214 . The thickness of the portion of the main attachment plate body  212  in which the dent  216  is defined is greater than the thickness of the thin-walled panel  214 . 
         [0072]    The thin-walled panel  214  is positioned behind the cavity-forming portion  176  (see  FIG. 1 ). The thin-walled panel  214  has a plurality of through holes  138  defined therein. The thin-walled panel  214  is lower in rigidity than the main attachment plate body  212 . More specifically, the thin-walled panel  214  is sufficiently rigid, such that when the casting die assembly  10  is closed, the thin-walled panel  214  is elastically deformed to become convex in a direction away from the movable cavity die  122 . Accordingly, the thin-walled panel  214  is made more elastically deformable than the main attachment plate body  212 . 
         [0073]    As shown in  FIGS. 9 and 11 , the base  130  includes a region T 2 , i.e., the region indicated by the two-dot-and-dash lines shown in  FIGS. 9 and 11 , which is referred to as a second contact region and is in contact with the flat rear surface  136  of the movable cavity die  122 . The region T 2  includes the main attachment plate body  212  and the thin-walled panel  214 , both of which support the movable cavity die  122 . 
         [0074]    In the movable die  14  as above, the movable cavity die  122  is installed on the main movable die body  120  in the following manner. First, the movable cavity die  122  is placed on the main movable die body  120  such that the flat rear surface  136  of the movable cavity die  122  is brought into contact with the flat attachment surface  134  of the base  130 , and the first surface  150  of the flange  132  is brought into contact with or abutment against the second surface  166  of the movable cavity die  122 . 
         [0075]    At this time, the sprue pin  152  is disposed in the first recess  154  and the second recess  168 , thereby positioning the movable cavity die  122  with respect to the main movable die body  120  along the transverse direction of the base  130 . 
         [0076]    Thereafter, the mounting bolts  142  mounted on the base  130  are threaded into respective bolt holes, not shown, defined in the flat rear surface  136  of the movable cavity die  122 . In addition, the joint bolts  158 ,  160  are inserted respectively through the insertion holes  162 ,  164  in the flange  132 , and threaded into the respective bolt holes  170 ,  172  in the movable cavity die  122 . As a result, the movable cavity die  122  becomes fastened to the main movable die body  120 . 
         [0077]    As shown in  FIGS. 7 and 9 , the slide die  16 , which serves as a die for forming the cavity C, is smaller and lighter in weight than the fixed die  12  and the movable die  14 . The slide mechanism  18 , in a state of being fixedly mounted on the movable cavity die  122 , supports the slide die  16  for movement toward and away from the cavity-forming portion  176  of the movable die  14 . 
         [0078]    The casting die assembly  10  according to the present embodiment basically is constructed as described above. Operations and advantages of the casting die assembly  10  will be described below. 
         [0079]    For performing a die casting process using the casting die assembly  10 , the movable die  14  initially is displaced toward the fixed die  12 . The positioning pins  46 ,  48  of the main fixed die body  20  are inserted into the positioning holes  146 ,  148  in the main movable die body  120 . At this time, the main fixed die body  20  and the main movable die body  120  are positioned with respect to each other. The positioning pins  182 ,  184  of the movable cavity die  122  are inserted into the positioning holes  82 ,  84  in the fixed cavity die  22 . At this time, the movable cavity die  122  and the fixed cavity die  22  are positioned with respect to each other. 
         [0080]    Upon further displacement of the movable die  14  toward the fixed die  12 , the respective distal ends of the return pins  92  of the fixed die  12  are pushed by the mating surface  174  of the movable cavity die  122 , thereby retracting the ejector plate  88  and the ejector pins  90  of the fixed die  12  to their initial positions. Further, the ejector plate  188  and the ejector pins  190  of the movable die  14  are retracted to their initial positions by an actuating means, not shown. 
         [0081]    The mating surface  174  of the movable cavity die  122  and the mating surface  72  of the fixed cavity die  22  are brought into contact with each other. A non-illustrated actuator of the slide mechanism  18  is operated to move the slide die  16  forwardly toward the cavity-forming portion  176 . Following movement thereof, the fixed cavity die  22 , the movable cavity die  122 , and the slide die  16  jointly define the cavity C. 
         [0082]    Thereafter, the movable die  14  is pressed against the fixed die  12  in order to apply a predetermined die closing force between the movable cavity die  122  and the fixed cavity die  22 . At this time, the outer circumferential portion of the main movable die body  120  is pressed against the fixed die  12 . 
         [0083]    When the movable die  14  is pressed against the fixed die  12 , as shown in  FIG. 12 , the plate-shaped base  26  of the main fixed die body  20  is elastically deformed, so as to become convex toward the ejector plate  88 . Since the rigidity of the thin-walled panel  116  is smaller than the rigidity of the main attachment plate body  114 , the thin-walled panel  116  flexes more greatly than the main attachment plate body  114 . 
         [0084]    Since the elastic force (restoring force) of the thin-walled panel  116  acts on the main attachment plate body  114  around the thin-walled panel  116 , the main attachment plate body  114  applies an increased pressing force to the fixed cavity die  22 . Consequently, the portion of the fixed cavity die  22  that is supported by the main attachment plate body  114  is deformed less than other portions of the fixed cavity die  22 . According to the present embodiment, in particular, inasmuch as the thin-walled panel  116  is disposed behind the cavity-forming portion  74 , deformation of the portion of the fixed cavity die  22  that is positioned around the cavity-forming portion  74  is minimized. 
         [0085]    Similarly, when the movable die  14  is pressed against the fixed die  12 , a reaction from the fixed die  12  elastically deforms the plate-shaped base  130  of the main movable die body  120 , so as to become convex toward the ejector plate  188 . Since the rigidity of the thin-walled panel  214  is smaller than the rigidity of the main attachment plate body  212 , the thin-walled panel  214  flexes more greatly than the main attachment plate body  212 . 
         [0086]    Since the elastic force (restoring force) of the thin-walled panel  214  acts on the main attachment plate body  212  around the thin-walled panel  214 , the main attachment plate body  212  applies an increased pressing force to the movable cavity die  122 . Consequently, the portion of the movable cavity die  122  that is supported by the main attachment plate body  212  is deformed less than other portions of the movable cavity die  122 . According to the present embodiment, in particular, inasmuch as the thin-walled panel  214  is disposed behind the cavity-forming portion  176 , deformation of the portion of the movable cavity die  122  that is positioned around the cavity-forming portion  176  is minimized. 
         [0087]    Therefore, upon closure of the casting die assembly  10 , the movable cavity die  122  and the fixed cavity die  22  are kept in high intimate contact with each other. In other words, a gap through which the cavity C communicates with the outside is not formed between the movable cavity die  122  and the fixed cavity die  22 . Accordingly, when an unillustrated molten metal supply source is operated in order to pour molten metal into the cavity C, the introduced molten metal does not leak outside of the cavity C, thereby preventing metal spits from being produced. 
         [0088]    When the molten metal introduced into the cavity C has solidified into a cast product, the movable die  14  is moved away from the fixed die  12 , and the slide die  16  is retracted by the slide mechanism  18 . If the cast product is stuck to the fixed cavity die  22 , then the ejector plate  88  of the fixed die  12  is pressed toward the base  26  by a non-illustrated pressing means, thereby causing the ejector pins  90  to project from the cavity-forming portion  74  in order to remove the cast product from the fixed cavity die  22 . On the other hand, if the cast product is stuck to the movable cavity die  122 , then the ejector plate  188  of the movable die  14  is pressed toward the base  130  by a non-illustrated pressing means, thereby causing the ejector pins  190  to project from the cavity-forming portion  176  in order to remove the cast product from the movable cavity die  122 . Thus, upon removal thereof from the casting die assembly  10 , the cast product has a minimum of burrs, and hence exhibits high dimensional accuracy. At this time, the die casting process using the casting die assembly  10  is finished. 
         [0089]    According to the present embodiment, when the movable die  14  and the fixed die  12  are combined, i.e., upon closure of the casting die assembly  10 , the thin-walled panel  116  of the main fixed die body  20  is elastically deformed so as to become convex toward the ejector plate  88 , i.e., away from the fixed cavity die  22 . Consequently, the elastic force (restoring force) of the thin-walled panel  116  acts on the main attachment plate body  114 , so as to apply an increased pressing force by the main attachment plate body  114  to the fixed cavity die  22 . Stated otherwise, when the movable die  14  and the fixed die  12  are combined, the thin-walled panel  116  boosts the pressure that is applied through the main attachment plate body  114  to the fixed cavity die  22 . Therefore, deformation of the portion of the fixed cavity die  22 , which is supported on the main attachment plate body  114 , is minimized. 
         [0090]    Similarly, when the movable die  14  and the fixed die  12  are combined, i.e., upon closure of the casting die assembly  10 , the thin-walled panel  214  of the main movable die body  120  is elastically deformed to become convex away from the movable cavity die  122 . Thus, the thin-walled panel  214  makes it possible to increase the pressure applied to the movable cavity die  122  through the main attachment plate body  212 . Therefore, deformation of the portion of the movable cavity die  122 , which is supported on the main attachment plate body  212 , is minimized. Any gap connecting the cavity C to the exterior of the casting die assembly  10  is prevented from being formed upon closure of the casting die assembly  10 , and therefore, burrs on the cast product are minimized. 
         [0091]    Since the flat rear surface  36  of the fixed cavity die  22  is attached to the flat attachment surface  34  of the plate-shaped base  26  of the main fixed die body  20 , the main fixed die body  20  does not require a recess for fitting of the fixed cavity die  22  therein. Likewise, since the flat rear surface  136  of the movable cavity die  122  is attached to the flat attachment surface  134  of the plate-shaped base  130  of the main movable die body  120 , the main movable die body  120  does not require a recess for fitting of the movable cavity die  122  therein. Consequently, the cost and weight of the casting die assembly  10  can be reduced, and the casting die assembly  10  can be made versatile in use. 
         [0092]    According to the present embodiment, since the thin-walled panel  116  of the main fixed die body  20  is thinner than the main attachment plate body  114 , the thin-walled panel  116  effectively is made elastically deformable while the main attachment plate body  114  is made less deformable. Similarly, since the thin-walled panel  214  of the main movable die body  120  is thinner than the main attachment plate body  212 , the thin-walled panel  214  effectively is made elastically deformable while the main attachment plate body  212  is made less deformable. Therefore, burrs on the cast product are minimized efficiently. 
         [0093]    According to the present embodiment, the thin-walled panel  116  of the main fixed die body  20  is positioned behind the cavity-forming portion  74 , and the main attachment plate body  114  is positioned around the thin-walled panel  116 . Therefore, deformation of the portion of the fixed cavity die  22  around the cavity-forming portion  74  is reduced to an appropriate level. In addition, the thin-walled panel  214  of the main movable die body  120  is positioned behind the cavity-forming portion  176 , and the main attachment plate body  212  is positioned around the thin-walled panel  214 . Therefore, similarly, deformation of the portion of the movable cavity die  122  around the cavity-forming portion  176  is reduced to an appropriate level. As a result, burrs on the cast product are minimized more effectively. 
         [0094]    According to the present embodiment, the through holes  38  are defined in the thin-walled panel  116  of the main fixed die body  20 , thereby making the thin-walled panel  116  more elastically deformable. Similarly, the through holes  138  are defined in the thin-walled panel  214  of the main movable die body  120 , thereby making the thin-walled panel  214  more elastically deformable. 
         [0095]    According to the present embodiment, since the fixed cavity die  22  and the flange  28  are joined to each other by the joint bolts  56 ,  58 , the fixed cavity die  22  is prevented from becoming positionally displaced with respect to the main fixed die body  20  when the fixed cavity die  22  is subjected to thermal expansion and contraction. The fixed cavity die  22  expands thermally away from the flange  28 , i.e., in the direction in which the first surface  50  faces, so that upon thermal expansion of the fixed cavity die  22 , the main fixed die body  20  (the flange  28 ) and the fixed cavity die  22  are prevented from being damaged. 
         [0096]    Likewise, since the movable cavity die  122  and the flange  132  are joined to each other by the joint bolts  158 ,  160 , the movable cavity die  122  is prevented from becoming positionally displaced with respect to the main movable die body  120  when the movable cavity die  122  is subjected to thermal expansion and contraction. The movable cavity die  122  expands thermally away from the flange  132 , i.e., in the direction in which the first surface  150  faces, so that upon thermal expansion of the movable cavity die  122 , the main movable die body  120  (the flange  132 ) and the movable cavity die  122  are prevented from being damaged. 
         [0097]    According to the present embodiment, a portion of the sprue sleeve  52  is disposed in the first recess  54  in the flange  28  of the main fixed die body  20 , and the other portion of the sprue sleeve  52  is disposed in the second recess  66  in the fixed cavity die  22 . Accordingly, the fixed cavity die  22  is easily positioned widthwise with respect to the main fixed die body  20 , i.e., in a direction perpendicular to the direction in which the flange  28  projects, and perpendicular to the direction which the first surface  50  faces. The sprue sleeve  52 , which is used as a positioning member, makes it unnecessary to provide a new dedicated positioning member, thereby resulting in a reduction in the number of parts. Since the fixed cavity die  22  is prevented from becoming positionally displaced with respect to the main fixed die body  20 , the dimensional accuracy of the cast product can be increased. 
         [0098]    According to the present embodiment, a portion of the sprue pin  152  is disposed in the first recess  154  in the flange  132  of the main movable die body  120 , whereas the other portion of the sprue pin  152  is disposed in the second recess  168  of the movable cavity die  122 . Accordingly, the movable cavity die  122  is easily positioned widthwise with respect to the main movable die body  120 , i.e., in a direction perpendicular to the direction in which the flange  132  projects, and perpendicular to the direction in which the first surface  150  faces. The sprue pin  152 , which is used as a positioning member, makes it unnecessary to provide a new dedicated positioning member, thereby resulting in a reduction in the number of parts. Further, since the movable cavity die  122  is prevented from becoming positionally displaced with respect to the main movable die body  120 , the dimensional accuracy of the cast product can be increased. 
         [0099]    The present embodiment is not limited to the above structural details. Each of the main fixed die body  20  and the main movable die body  120  may be replaced with a main die body  230  according to the modification shown in  FIG. 13 . The main die body  230  has a plate-shaped base  232  and a flange  234 . A plurality of first grooves  236  are defined in a rear portion of the base  232 . The first grooves  236  extend over the full length of the base  232  and are arrayed along the transverse direction thereof. The main die body  230  also has a plurality of second grooves  238 , which extend over the full width of the base  232  and are arrayed along the longitudinal direction thereof. The first grooves  236  are positioned substantially centrally in the base  232  along the transverse direction thereof, whereas the second grooves  238  are positioned substantially centrally in the base  232  along the longitudinal direction thereof. As illustrated in  FIG. 13 , each of the first grooves  236  and the second grooves  238  are V-shaped in cross-section, although the grooves may be of any desired cross-sectional shape. 
         [0100]    The main die body  230 , which is constructed in the foregoing manner, is less rigid in a crossing region (pressure boosting unit, deformable portion)  242  where the first grooves  236  and the second grooves  238  cross each other than in other regions thereof. More specifically, the base  232  has a region T 3 , which is held in contact with the rear surface of a cavity die (the fixed cavity die  22  or the movable cavity die  122 ). Additionally, the region T 3  includes an attachment plate body (support)  240  for supporting the cavity die and the crossing region  242 , which is less rigid than the attachment plate body  240 . 
         [0101]    Upon closure of the casting die assembly  10 , the crossing region  242  becomes elastically deformed in a convex manner away from the cavity die. Therefore, the main die body  230  offers the same advantages as those of the embodiment described above. 
       Second Embodiment 
       [0102]    A casting die assembly  10 A according to a second embodiment of the present invention will be described below with reference to  FIGS. 14 through 17 . Parts of the casting die assembly  10 A according to the second embodiment, which are identical to those of the casting die assembly  10  according to the first embodiment, are denoted by identical reference characters, and such features will not be described in detail below. 
         [0103]    As shown in  FIGS. 14 through 16 , the casting die assembly  10 A according to the second embodiment includes a fixed die (first die)  12   a  and a movable die (second die)  14   a . The fixed die  12   a  has a main fixed die body  20   a  including a base  26   a . The base  26   a  includes an attachment plate  302  having a square hole (pressure boosting unit)  300  defined therein, which is provided instead of the thin-walled panel  116  described above, and a main attachment plate body (support)  114 . The hole  300  is of a size that is large enough for the ejector pins  90  to be inserted therein. 
         [0104]    The movable die  14   a  includes a main movable die body  120   a  including a base  130   a . The base  130   a  includes an attachment plate  306  having a square hole (pressure boosting unit)  304  defined therein, which is provided instead of the thin-walled panel  214  described above, and a main attachment plate body (support)  212 . The hole  304  is of a size that is large enough for the ejector pins  190  to be inserted therein. 
         [0105]    According to the present embodiment, since the main fixed die body  20   a  has the hole  300  therein, it is possible for the contact area of the fixed cavity die  22  with the base  26   a  to be reduced without changing the contact area of the fixed cavity die  22  with the main attachment plate body  114 . Consequently, the pressure applied through the main attachment plate body  114  (first contact region T 1 ) to the fixed cavity die  22  can be increased to an appropriate level. 
         [0106]    Similarly, since the main movable die body  120   a  has the hole  304  therein, it is possible for the contact area of the movable cavity die  122  with the base  130   a  to be reduced without changing the contact area of the movable cavity die  122  with the main attachment plate body  212 . Consequently, the pressure applied through the main attachment plate body  212  (second contact region T 2 ) to the movable cavity die  122  can be increased to an appropriate level. 
         [0107]    According to the present embodiment, the hole  300  is large enough for the ejector pins  90  to be inserted therein, and the hole  304  is large enough for the ejector pins  190  to be inserted therein. Therefore, even if the layout of the ejector pins  90 ,  190  is changed depending on the shape of a product to be cast, the ejector pins  90 ,  190  can still be inserted in the holes  300 ,  304 . In other words, the hole  300  doubles as a hole through which the ejector pins  90  can be inserted, and the hole  304  doubles as a hole through which the ejector pins  190  can be inserted. Stated otherwise, there is no need for a new main fixed die body and a new main movable die body to be produced responsive to changes made in the layout of the ejector pins  90 ,  190 . Consequently, the cost of the casting die assembly  10 A is prevented from increasing, even if differently shaped products are cast. 
         [0108]    The present embodiment is not limited to the above structure. For example, as shown in  FIG. 17 , in the hole  300  of the base  26   a  of the main fixed die body  20   a , a reinforcement member (metal member)  310  may be provided by being fixed to the rear surface  36  of the fixed cavity die  22  through a plurality of unillustrated bolts or the like, in order to prevent deformation of the fixed cavity die  22  during the casting process. 
         [0109]    The reinforcement member  310  is formed by stacking a plurality of metal plates  312 . In this case, the rigidity of the reinforcement member  310  can be easily adjusted by changing the number of stacked metal plates  312 . Incidentally, the shape, the material, and the thickness of each metal plate  312  can be set arbitrarily. 
         [0110]    The metal plates  312  are joined together in a stacked state by use of the bolts through which the metal plates  312  are fixed to the rear surface  36  of the fixed cavity die  22 . Accordingly, each of the metal plates  312  has a plurality of unillustrated insertion holes through which the respective bolts are inserted. As is obvious from  FIG. 17 , each of the metal plates  312  has a plurality of through holes  314  through which the respective ejector pins  90  are inserted. 
         [0111]    Further, for example, in a case that an insert die is placed in the fixed cavity die  22  and the flange of the insert die is placed in the hole  300  such that the flange of the insert die is in contact with the rear surface  36  of the fixed cavity die  22 , a recess or a hole for receiving the flange of the insert die preferably should be formed in one of the metal plates  312  that is positioned closest to the fixed cavity die  22 . Owing thereto, the reinforcement member  310  can be placed in contact with the rear surface  36  of the fixed cavity die  22  reliably. Thus, deformation of the fixed cavity die  22  during the casting process can be prevented effectively. 
         [0112]    The reinforcement member  310  may be formed by a single metal plate  312 . In this case, a plurality of metal plates  312  having different plate thicknesses are provided in advance, and one metal plate  312  having the most appropriate thickness for a casting condition, etc. is selected from among the metal plates  312 . 
         [0113]    On the other hand, in the hole  304  of the base  130   a  of the main movable die body  120   a , a reinforcement member (metal member)  316  may be provided by being fixed to the rear surface  136  of the movable cavity die  122  through a plurality of unillustrated bolts, in order to prevent deformation of the movable cavity die  122  during the casting process. 
         [0114]    The reinforcement member  316  is formed by stacking a plurality of metal plates  318 . In this case, the rigidity of the reinforcement member  316  can be easily adjusted by changing the number of stacked metal plates  318 . Incidentally, the shape, the material, and the thickness of each metal plate  318  can be set arbitrarily. 
         [0115]    The metal plates  318  are joined together in a stacked state by use of the bolts through which the metal plates  318  are fixed to the rear surface  136  of the movable cavity die  122 . Accordingly, each of the metal plates  318  has a plurality of unillustrated insertion holes through which the respective bolts are inserted. As is obvious from  FIG. 17 , each of the metal plates  318  has a plurality of through holes  320  through which the respective ejector pins  190  are inserted. 
         [0116]    For example, in a case that an insert die is placed in the movable cavity die  122  and the flange of the insert die is placed in the hole  304  such that the flange of the insert die is in contact with the rear surface  136  of the movable cavity die  122 , a recess or a hole for receiving the flange of the insert die preferably should be formed in one of the metal plates  318  that is positioned closest to the movable cavity die  122 . Owing thereto, the reinforcement member  316  can be placed in contact with the rear surface  136  of the movable cavity die  122  reliably. Thus, deformation of the movable cavity die  122  during the casting process can be prevented effectively. 
         [0117]    The reinforcement member  316  may be formed by a single metal plate  318 . In this case, a plurality of metal plates  318  having different plate thicknesses are provided in advance, and one metal plate  318  having the most appropriate thickness for a given casting condition, etc. is selected from among the metal plates  318 . 
         [0118]    According to the modification shown in  FIG. 17 , the reinforcement member  310  is provided in the hole  300  of the base  26   a , while being fixed to the rear surface  36  of the fixed cavity die  22 . Thus, the reinforcement member  310  can prevent the fixed cavity die  22  from being excessively deformed during the casting process. As a result, the dimensional accuracy of a cast product can be increased. Further, the reinforcement member  310  is formed by stacking a plurality of metal plates  312 , and thus the number of stacked metal plates  312  is changed, whereby the rigidity of the reinforcement member  310  can be adjusted easily. 
         [0119]    As with the above, the reinforcement member  316  is provided in the hole  304  of the base  130   a , while being fixed to the rear surface  136  of the movable cavity die  122 . Thus, the reinforcement member  316  can prevent the movable cavity die  122  from being excessively deformed during the casting process. As a result, the dimensional accuracy of a cast product can be increased. Further, the reinforcement member  316  is formed by stacking a plurality of metal plates  318 , and thus the number of stacked metal plates  318  is changed, whereby the rigidity of the reinforcement member  316  can be adjusted easily. 
         [0120]    The present invention is not limited to the above embodiments. It is a matter of course that various changes and modifications can be made to the embodiments without departing from the scope of the invention as set forth in the appended claims.