Patent ID: 7681428

Claim:
A forging method for upsetting end portions of a raw material as diameter expansion scheduled portions, the forging method comprising: providing an upsetting apparatus having a fixing die for fixing a raw material having a bar shape, a plurality of guides each having an insertion passage for inserting and holding an end portion of the raw material in a buckling preventing state, and a plurality of punches each for axially pressing the end portion of the raw material inserted in and held by the insertion passage of the guide, wherein said fixing die comprises a raw material fixing and fitting dented portion; fitting an axial central portion of the raw material in said raw material fixing and fitting dented portion such that the end portions of the raw material protrude from the fixing die in opposite directions into the insertion passages of the guides, respectively; and moving the guides in a direction opposite to a moving direction of the punches, respectively, such that a length of each exposed portion of the raw material becomes equal to or less than a buckling limit length at a cross-sectional area of the exposed portion of the raw material while simultaneously axially pressing the end portions of the raw material with the punches in a state in which a part of a peripheral surface of each exposed portion of the raw material exposed between each of the guides and the fixing die is restrained or an entire peripheral surface of each exposed portion of the raw material is not restrained, to thereby simultaneously upset the end portions as diameter expansion scheduled portions of the raw material.