Abstract:
A lightweight mold for press forming is presented. Molds are characterized in that design forming portions thereof, these design forming portions making contact with a workpiece at the time of press forming and thereby forming a target design on the workpiece, are constructed of rod shaped members (design forming rods). By having the design forming portions be constructed of rod shaped members, the weight of the mold is reduced. It is preferred that the molds are further provided with supporting rods which support the design forming rods, these rod members constituting a framework structure.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a mold for press forming. 
       BACKGROUND ART 
       [0002]    Many improvements for molds for press forming have been proposed. For example, Patent Document 1 proposes a device to make it easier to remove a formed workpiece from the mold. Patent Document 2 proposes a mold in which a part of the mold or a punch can be moved, and which can thereby accommodate differing press shapes without exchanging the entire mold. 
       CITATION LIST 
     Patent Literatures 
       [0003]    Patent Document 1: Japanese Patent Application Publication No. H6-269866 
         [0004]    Patent Document 2: Japanese Patent Application Publication No. H7-16670 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0005]    The present specification presents a technique for improving the mold from a viewpoint different from Patent Document 1 and Patent Document 2. The present specification presents a technique for reducing the weight of the mold. 
       Solution to the Technical Problem 
       [0006]    In one aspect of a mold taught in the present specification, a design forming portion of the mold is constructed with a rod shaped member. The design forming portion makes contact with a workpiece during a press forming process and thereby forms a target design on the workpiece. By having the design forming portion be constructed with the rod shaped member, the present invention reduces the weight of the mold. In other words, a design surface for forming the target design on the workpiece is configured of the rod shaped member. Below, the rod shaped member that constitutes the design forming portion is called a design forming rod or a first rod member. 
         [0007]    If a member that supports the first rod member (the design forming rod) is also configured of a rod member, the weight is further reduced. Below, the rod member that supports the first rod member is called a supporting rod or a second rod member. The design forming rod and the supporting rod constitute a framework structure. More preferably, with the novel mold taught in the present specification, the design forming rod and the supporting rod constitute a truss structure. The truss structure refers to a structure in which moment does not occur in the rod members, and only load in the axial direction occurs. High strength can be expected from the truss structure. Moreover, for the strength and rigidity of the rod members to withstand the load, the design forming rod and the supporting rod may constitute a Rahmen structure. Further, the Rahmen structure refers to a structure in which both load in the axial direction and moment occur in the rod members. 
         [0008]    In the press forming process, a high load is applied from a press machine to the design forming portion (the design forming rod). In order to support the design forming rod strongly, it is preferred that the supporting rod extends parallel to the direction of load applied by the press machine and that a center line of the supporting rod in its longitudinal direction passes through the first rod member. According to such a configuration, the load from the press machine is applied in the axial direction of the supporting rod. Since the rod member is resistant to load in the axial direction, this configuration has the advantage that the load resistance of the design forming rod (the design forming portion) is high. 
         [0009]    The mold for press forming requires a block for positioning the mold. Specifically, a block is required for fixing the mold to the press machine. In a more preferred aspect of the above mold, a block for positioning the mold may be connected to the second rod member. 
         [0010]    The mold is preferably manufactured by a casting process, in particular, by a full mold casting process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a schematic side view of a press machine. 
           [0012]      FIG. 2  shows a perspective view of a mold (an upper mold and a lower mold). 
           [0013]      FIG. 3  shows a cross-sectional view of the mold. 
           [0014]      FIG. 4  is a figure illustrating a modification of the mold. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0015]    An embodiment of a mold will be described with reference to figures. To aid understanding, the mold will be described together with a press machine.  FIG. 1  is a schematic side view of a press machine  50  having molds  2 ,  32 . The press machine  50  comprises a pair of molds, i.e., the upper mold  32  and the lower mold  2 . The lower mold  2  is fixed to a bolster  51  of the press machine  50 , and the upper mold  32  is fixed to a slider  52 . The slider  52  is moved up and down by an actuator  55  while being guided by supports  53 . Moreover, in addition to these parts, the press machine  50  comprises a clamp for retaining a workpiece W, although this clamp is not shown. The clamp is disposed at the sides of the molds  2 ,  32 . 
         [0016]      FIG. 2  shows a perspective view of the upper mold  32  and the lower mold  2 .  FIG. 3  shows a cross-sectional view of the upper mold  32  and the lower mold  2 .  FIG. 3  is equivalent to a cross-section along the line III-III of  FIG. 2 . Moreover, it should be noted that the bolster  51  supporting the lower mold  2  is shown in  FIG. 2 , but the slider  52  supporting the upper mold  32  is not shown. Further,  FIG. 3  shows the upper mold  32  having been lowered to a lowermost position, this being a state for forming the workpiece W into a target design. As shown in  FIGS. 2 and 3 , the molds  2 ,  32  form a flat metal sheet (the workpiece W) into a rectangular convex shape (a workpiece Wb). Moreover, a Z-axis of the coordinates in the figures indicates a direction of movement of the slider  52  (Le., the upper mold  32 ). The Z-axis direction also corresponds to the direction of load applied by the press machine  50 . 
         [0017]    The molds  2 ,  32  will be described. The lower mold  2  is configured of a design forming rod  4 , supporting rods  6 ,  8 ,  10 ,  12 , and positioning blocks  14 . The upper mold  32  is configured of a design forming rod  34 , supporting rods  36 ,  38 ,  40 , and positioning blocks  44 . The design forming rods  4 ,  34  correspond to design forming portions for forming the workpiece W into the target design. 
         [0018]    The structure of the lower mold  2  will be described. A rectangular base is formed by the supporting rods  8  and  10 , and the four supporting rods  6  extend parallel to one another in a perpendicular manner from the four corners of this base. The design forming rod  4  is fixed to upper ends of the four supporting rods  6 . The design forming rod  4 , in entirety, forms a rectangular ring with rounded corners. Further, a cross-section of the design forming rod  4  also forms a rectangle with rounded corners. A part of the cross-section of the design forming rod  4  (a part of a side surface of the design forming rod  4 ) conforms to a target shape. The supporting rod  12  is attached in order to reinforce the design forming rod  4 . As shown in  FIG. 3 , the vicinity of the center of the supporting rod  12  is bent, so as not to interfere with the workpiece W, toward a back side of the mold (the bolster  51  side). The positioning blocks  14  are connected to end parts of the two supporting rods  8  that extend parallel to one another. When viewing the lower mold  2  from a plan view, the four positioning blocks  14  are seen in four corners surrounding the design forming rod  4 . The positioning blocks  14  are parts for fixing the lower mold  2  to the bolster  51  of the press machine. The reference number  16  indicates bolts for fixing the positioning blocks  14  to the bolster  51 . 
         [0019]    The structure of the upper mold  32  will be described. A rectangular base is formed by the supporting rods  38  and  40 , and the four supporting rods  36  extend parallel to one another in a perpendicular manner from the four corners of this base. The design forming rod  34  is fixed to lower ends of the four supporting rods  36 . The positioning blocks  44  are connected to end parts of the two supporting rods  38  that extend parallel to one another. When viewing the upper mold  32  from a plan view, the four positioning blocks  44  are seen in four corners surrounding the design forming rod  4 . The positioning blocks  44  are parts for fixing the upper mold  32  to the slider  52  of the press machine  50 . The reference number  45  indicates through holes through which bolts  46  for fixing the positioning blocks  44  pass. 
         [0020]    The overall shape of the design forming rod  34  is similar to the shape of the design forming rod  4  of the lower mold  2 . However, the ring of the design forming rod  34  has a size larger than the ring of the design forming rod  4 . Specifically, the ring of the design forming rod  34  has the size with which the ring fits with an outside of the ring of the design forming rod  4  with a clearance which is the same as the thickness of the workpiece W. As described above, the workpiece W is sandwiched between the design forming rods  4  and  34 , load from above and below is applied, thus forming the target design on the workpiece W. The design forming rods  4 ,  34  make contact with the workpiece, but the supporting rods do not make contact with the workpiece W. That is, only the design forming rods  4 ,  34  make contact with the workpiece W, and form the workpiece into a target shape by using the load applied by the press machine  50 . 
         [0021]    As shown in  FIG. 2 , in the lower mold  2 , the design forming rod  4  and the supporting rods  6 ,  8 ,  10  constitute a Rahmen structure (a framework structure). Further, in the upper mold  32 , the design forming rod  34  and the supporting rods  36 ,  38 ,  40  constitute a Rahmen structure (a framework structure). The molds  2 ,  32  are almost entirely composed of the rod members. In particular, by having the design forming portions configured of the rod members (design forming rods), the weight can be reduced. 
         [0022]    As shown in  FIG. 3 , each supporting rod  6  extends parallel to the direction in which load is applied by the press machine (the Z-axis direction). A longitudinal center line CL 1  of each supporting rod  6  passes through the design forming rod  4 . By means of such a structure, the supporting rods  6  catch, as an axial thrust load, the load applied to the design forming rod  4  (the load applied by the press machine). The rod members have a high load resistance for axial thrust loads. Consequently, since the supporting rods  6  receive the load applied by the press machine as an axial thrust load, a high load resistance of the lower mold  2  is realized. 
         [0023]    The same applies for the upper mold  32 . That is, the supporting rods  36  extend parallel to the direction in which load is applied by the press machine (the Z direction), and a longitudinal center line CL 2  of each supporting rod  36  passes through the design forming rod  34 . Consequently, the supporting rods  36  of the upper mold  32  also catch, as the axial thrust load, the load which the design forming rod  34  receives from the press machine. The upper mold  32  also realizes a high load resistance. 
         [0024]    The molds  2 ,  32  are made by a casting process, specifically, by full mold casting. Consequently, evaporative patterns having the same shapes as the molds  2  and  32  shown in  FIG. 2  are made. The evaporative patterns are made from polystyrene foam. The entire evaporative pattern of the lower mold  2  (or the upper mold  32 ) may be made in one piece, or may be made as a plurality of separate pieces. 
         [0025]    One modification of the mold of the embodiment will be described.  FIG. 4  shows a modified lower mold  102 . In this lower mold  102 , a rod main body  107  (a part other than end joints) of each supporting rod consists of a part separate from the joint portions. Further, a reinforcing member  109  has been added at locations where the strength of the lower mold  102  tends to be insufficient. Each reinforcing member  109  is positioned along the diagonal of a lattice of the framework structure (a lattice surrounded by adjacent rod members). The reinforcing members may be attached at locations other than the locations shown in  FIG. 4 . The reinforcing members are positioned such that the amount of bending of each part when a scheduled load (or maximum load) is applied to the mold  102  is equal to or less than a predetermined permissible amount. Moreover, the location where the reinforcing member  109  is attached constitutes the truss structure (framework structure). By constituting the truss structure, the lower mold  102  can realize high strength while being lightweight. 
         [0026]    Notes concerning the molds  2 ,  32  of the embodiment will be given. The design forming rods ( 4 ,  34 ) correspond to one aspect of the first rod member. The supporting rods ( 6 ,  8 ,  10 ,  12 ,  36 ,  38 ,  40 ) correspond to one aspect of the second rod member. The cross-sectional shape of the design forming rods  4 ,  34 , in particular the shape of the rod end surface that makes contact with the workpiece W, must be made in a shape corresponding to the pressed shape (the target design) of the workpiece. The cross-sectional shape of the supporting rods ( 6 ,  8 ,  10 ,  12 ,  36 ,  38 ,  40 ) may be a shape other than round. The cross-sectional shape of the supporting rods may be oval or polygonal. The supporting rods need not be a straight line, but may be bent, like the supporting rod  12 , or may be curved. 
         [0027]    The molds  2 ,  32  have a framework structure that includes the design forming portion. Consequently, the molds  2 ,  32  also have the advantage that removal of the workpiece from the mold after press forming is easy. 
         [0028]    The overall shape of the mold, i.e., the shape of the framework structure, is not limited to the shape of the present embodiment. Further, the shape and number of the design forming rods is not limited to the mold of the present embodiment. For example, in order to achieve a complex press shape, the mold may comprise a plurality of design forming rods. 
         [0029]    Specific examples of the present invention are described above in detail, but these examples are merely illustrative and place no limitation on the scope of the claims. The technology described in the claims also encompasses various changes and modifications to the specific examples described above. The technical elements explained in the present specification or drawings provide technical utility either independently or through various combinations. The present invention is not limited to the combinations described at the time the claims are filed. Further, the purpose of the examples illustrated by the present specification or drawings is to satisfy multiple objectives simultaneously, and satisfying any one of those objectives gives technical utility to the present invention. 
       DESCRIPTION OF THE NUMERALS 
       [0030]      2 : Mold (Lower Mold),  4 ,  34 : Design Forming Rods (First Rod Members),  6 ,  8 ,  10 ,  12 ,  36 ,  38 ,  40 : Supporting Rods (Second Rod Members),  14 ,  44 : Positioning Blocks,  32 : Mold (Upper Mold),  50 : Press Machine,  51 : Bolster,  52 : Slider,  53 : Support,  55 : Actuator,  102 : Mold (Lower Mold),  107 : Rod Main Body,  109 : Reinforcing Member