Mazda Motor Corporation

Shinya Kodama

Kyoso Ishida

Disclosed herein in dies for forging a gear-shaped part made of a sheet metal, comprising a cylindrical die for forming, in cooperation with a cylindrical punch, tooth portions and bottom land portions at a peripheral wall portion of a cup-shaped work integrally formed from the sheet metal, wherein ridges and grooves provided at the inner peripheral surface of the cylindrical die in the axial direction of the die in order to form the tooth portions and the bottom land portions are such that, in the direction from an insertion-side opening of the cylindrical die toward the depth of the die, the height of the ridges is gradually increased to a final height, then the width of the ridges is gradually increased to a final width, and thereafter the depth of the grooves is gradually decreased to a final depth. The part is forged sequentially stepwise in the order of the bottom land portions, side surfaces of the teeth and the crests of the teeth, namely, from inner to outer side, so that no irrational forces are applied to the work. Therefore, die wear at the terminal ends of the tooth portions of the part can be restrained, and it is possible to secure an effective tooth length and to contrive a compact form of the part. At the same time, an enhanced yield can be contrived through prevention of cracking, and the useful lives of the punch, the die and the like can be prolonged because no irrational forces are applied to the tools.

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Aki, Japan

Shinya Kodama