Forging method, forged product and forging apparatus

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;
• inserting end portions of the raw material fixed to the fixing die with the end portions protruded from the fixing die 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, wherein when the guides have an average moving speed, G, from an initiation of the movement thereof, if t0(T, G satisfies a relational expression of:
• (L−X)/[(I0−L)/P−t0]≦G≦P(X1−X)/(I0−X1−Pt0),
• where P is an average moving speed of the punches from an initiation of a movement thereof, X0 is a buckling limit length at the cross-sectional area of the raw material before the upsetting, X1 is a buckling limit length at the cross-sectional area of the enlarged diameter portion of the raw material after the upsetting, X is an initial clearance between the guides and the fixing die (0≦X≦X0), t0 is a time lag from the initiation of the movement of the punches to the initiation of the movement of the guides (0≦t0), L is a length of the enlarged diameter portion of the raw material after the upsetting, I0 is a length of the raw material in the state prior to the upsetting required for the enlarged diameter portion, and T is an upsetting time from the initiation of the movement of the punches.