Abstract:
A molding method uses a fluid-pressure generating unit form generating high fluid pressures that allows high-precision molding of complex shapes. The high fluid pressure is generated with a piston disposed in communication with a molding cavity. The high fluid pressure is imposed on a raw material workpiece to push the workpiece into a cavity causing the workpiece to conform to the shape of the cavity thereby producing an article of desired shape.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method for molding metals using high fluid pressure. As used herein, “fluid pressure” can include that of oil pressure, water pressure, or the like. “Method for molding” is used to indicate that fluid pressure is applied to a raw material to perform a molding of same into article shape. 
     Conventionally, articles having complex shapes including gears and the like have been molded using a female/male mold unit, i.e., a die and an punch. An example of this is described in Japanese laid-open patent publication number 5-154598. 
     In Japanese laid-open patent publication number 5-154598, a metal raw material is placed in a die. A punch is used to perform molding. In the molding operation, the punch and the metal raw material come into contact under high pressure so that resistance is generated between the two. This resulted in the fluidity of the metal material not always being adequately matched with the shape of the cavity. 
     This problem is not restricted to the molding operation disclosed in Japanese laid-open patent publication number 5-154598. It applies to all similar types of molding that use a die and a punch. 
     Japanese laid-open patent publication number 10-175028 and Japanese laid-open patent publication number 10-296347 are examples of conventional technology in which molding is performed using fluid pressure. In the former, a hydroform method involves a metal pipe, e.g., a copper pipe, placed in a split mold. An internal pressure, applied to the pipe, in the direction of the axis of the pipe, molds the pipe into a predetermined shape to form an article in the form of a bellows-pipe. In the latter publication, a fluid-pressure bulge processing method is presented. Internal pressure from fluid in a metal pipe is combined with axial compression of the metal pipe in order to expand a section of the metal pipe. 
     In both of these technologies, hollow piton-shaped members are disposed on either side of the metal pipe, which serves as the raw material. The piston-shaped members feed pressurized oil to the inner diameter of the metal pipe and push the metal pipe from both ends. These piston-shaped members are inserted into holes disposed in a split mold. The hollow section of the piston-shaped member serves as an oil passage through which the pressurized oil is fed. A sealing member is generally mounted to the outer diameter section of the piston-shaped member to prevent the fluid from leaking. 
     Due to its purpose, the sealing member must be flexible, so its resistance to pressure is limited. For example, such a sealing member generally cannot withstand a fluid pressure of approximately 2000 Mpa. Thus, high-pressure molding, using this method has not been conventionally possible. In both of these technologies, a high degree of process ability is provided by using the piston-shaped members to press from both ends of the raw material. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provided a molding method using a fluid-pressure generating unit capable of generating high pressures that allows high-precision molding of complex shapes that conventional methods could not produce. 
     A piston for generating high fluid pressure is disposed in the bore passage of a metal mold, the bore passage being in registry with an entry to a cavity in the metal mold so that a workpiece at least partly in the cavity can have a high fluid pressure, produced with the piston, imposed on it. This pressure imposed on the workpiece causes the raw metal material thereof to be pushed into the cavity and to assume in said cavity an article shape having an external configuration corresponding to an internal geometry of said cavity thereby forming an article of desired shape. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a vertical cross-sectional view of the upper mold part used in a first embodiment of the invention. 
     FIG. 1 b  is a vertical cross-section view of the lower mold part used with the FIG. 1 a  upper mold part, a workpiece being shown with at least a part thereof set in place in a forming cavity of the lower mold part. 
     FIG. 2 is a vertical cross-section view wherein the upper and lower mold parts have been moved to bring an upper block in the upper mold part into contact with a lower block on the lower mold part. 
     FIG. 3 is a vertical cross-section view similar to FIG. 2 showing a workpiece that has been formed by pressing the workpiece into the cavity formed in the lower block. 
     FIG. 4 is a vertical cross-section view depicting how a workpiece is made according to a second embodiment of the invention into a molded article having a hole therein. 
     FIG. 5 is a vertical cross-section depicting making of a workpiece according to a third embodiment of the invention. 
     FIG. 6 is a plan view showing of a representative horizontal geometry of the lower block cavity in the FIGS. 1-3 mold unit. 
     FIGS. 7 a  and  7   b  are respective elevation views of is a workpiece and the molded article made from said workpiece in accordance with the first embodiment of the invention. 
     FIGS. 8 a  and  8   b  are respective elevation views of the workpiece and molded article made therefrom by the second embodiment of the invention. 
     FIGS. 9 a  and  9   b  are the workpiece and the molded article made therefrom in accordance with a the third embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 a  and  1   b,  a first embodiment of the invention will be described for molding a solid workpiece to provide a solid molded article. In this embodiment, a solid workpiece is molded to provide a solid molded article. FIG. 1 a  shows an upper mold part  1  which is mounted on a slide of a press (not shown). FIG. 1 shows a lower mold  2  part that is mounted on a bolster of the press (not shown). The upper mold part  1  and the lower mold part  2  form a mold unit. A work piece  7  (FIG. 7 a ) is molded with this mold to form a molded article  12  (FIG. 7 b ). 
     A piston  3 , an upper block  4 , a guide  5 , and pine  6  are disposed on the upper mold part  1 . These members are raised and lowered in tandem with the slide of the press. This piston moves in a bore passage  32  in upper block  4 . The upper block  4  is guided by the guide  5 . The upper block  4  is actuated is driven by the pins  6  so that it can be raised and lowered freely. 
     A lower block  10 , a counter-punch  9 , and a knock-out pin  11  are disposed on the lower mold part  2 . The counter punch  9  is mounted inside the lower block  10 . The counter punch  9  actuated by the knock-out pin  11  so that it can be raised and lowered freely. As seen from FIG. 6, the lower block  10  is formed with a cavity  8  having a horizontal cross-section shape as depicted in that figure although other shapes could be used as desired. 
     The workpiece  7  is set on the lower block  10  disposed at least partly in cavity  8 . Referring to FIG.  2  and FIG. 3, molding is performed according to the sequence next described. With reference to FIG. 2, when the slide is lowered, the upper mold  1  part descends and the upper block  4  and the lower block  10  are pressed tightly against each other. The force to press together the upper block  4  and the lower block  10  comes from the pins  6 . The outer dimensions of the workpiece  7  are set to prevent gaps from forming between the inner surface of the bore cavity  32  and the upper block  4  and the workpiece outer surface. A top portion of the workpiece  7  is located in bore passage  32  of the upper block  4 . At this point, a fluid is fed into the space of bore passage  32  below piston  3 . The fluid disposing above a top part of the workpiece  7  in contact therewith. 
     Referring to FIG. 3, as the piston  3  descends further the fluid will become compressed by the piston  3  to form a high fluid-pressure in chamber  21 . The pressure is raised to at least not less than twice the deformation resistance of the workpiece raw material. The high fluid-pressure imposed on the workpiece causes the material of the workpiece to flow into cavity  8  and thereby to form the molded article  12 . The high pressure causes the workpiece external surface to conform in shape to the internal geometry of the cavity. It is understood that the pressure forces the workpiece to fully fill cavity  8 , leaving no voids. 
     Then, the slide is raised and the upper mold  1  part ascends. The molded article  12  left on the lower block  10  is pushed out from the lower block  10  by the counter-punch  9  and the knock-out pin  11 . 
     Referring to FIG. 4, there is shown a second embodiment. This embodiment differs from the first embodiment in that a mandrel  15  is used to form a molded article  14  having a hole. Otherwise, the technique employed is identical to that used in the first embodiment. 
     Referring to FIG. 4, a piston  13 , a mandrel  15 , an upper block  4 , a guide  5 , and pins  6  are disposed on the upper mold  1 . These members are raised and lowered in tandem with the slide of the press. The upper block  4  is guided by the guide  5  and is actuated by pins  6  so that it can be raised and lowered freely. The mandrel  15  is fixed to the piston  13 . 
     The lower block  10  includes a counter-punch  16  with a hold and a plurality of knock-out pins  17  disposed on the lower mold part  2 . The counter-punch  9  is mounted in the lower block  10 . The counter-punch  9  is actuated by the knock-out pins  17  to allow it to be freely raised and lowered. The counter-punch  16  includes a hold therein to avoid interfering with the mandrel  15 . The lower block  10  as noted earlier above is formed with the horizontal cross-section shape of FIG.  6 . 
     A workpiece  19  (not shown in the figure) is set on the lower block  10 . When the slide is lowered, the upper mold part  1  descends and the upper block  4  and the lower block  10  are pressed tightly together. The force pressing the upper block  4  and the lower block  10  tightly together is generated by the pins  6 . The dimensions of the workpiece  19  are set to prevent a gap from forming between the inner surface of the opening of the upper block  4  and the outer surface of the workpiece  19  as well as between the outer surface of the mandrel  15  and the inner surface of the opening of the workpiece  19 . The workpiece  19  is pressed into the cavity of the upper block  4  as the mandrel  15  is pushed into the hole of the workpiece  19 . At this point, a fluid is fed into the space below the piston  3  formed between the upper block  4  and the mandrel  15 . 
     As the piston  13  descends further, the fluid is compressed by the piston  13 , the cavity in upper block becoming a high fluid-pressure chamber  32 . The workpiece is caused to flow into the cavity  8  by this high fluid pressure, and the molded article  14  be formed. 
     The slide is then raised and the upper mold part  1  ascends. The molded article  14  left on the lower block  10  is pushed off of the lower block  10  by the counter-punch  16  and the knock-out pins  17 . 
     Referring to FIG. 5, a third embodiment of the of the invention is described. This embodiment differs from the second embodiment described above in that a gap is formed between a workpiece  20  (shown in FIG. 9 a ) and the mandrel  15 . Other aspects of the structures are the same in FIGS. 1-4. 
     Referring to FIG. 5, a gap is present between the workpiece  20  and the mandrel  15 , and in this embodiment the gap causes the fluid from the high fluid-pressure chamber  21  to invest the hole in the workpiece as well. Thus, the workpiece material defining the hole expands, resulting in the formation of a molded article  18  having a widened central hole therein, as shown in FIG.  5 . 
     Referring to FIGS. 7 a  and  7   b,  FIGS. 8 a  and  8   b,  and FIGS. 9 a  and  9   b,  there is shown the relationship between the raw material workpieces and the formed molded articles made in the respective ones of the first, second, and third embodiments of the invention. 
     In the present invention, there is no direct contact between a metal raw material and a punch. Thus, the flow of the metal raw material is not obstructed by resistance generated by the friction between the two. This makes it possible to provide articles with complex shapes. Furthermore, since pressure at least twice the deformation resistance of the metal raw material can be used, articles with complex shapes and requiring high precision can be provided.