HOT FORGING METHOD AND HOT FORGING DIE OF PREFORM PROCESS

PROBLEM TO BE SOLVED: To provide a hot forging method that can suppress an increase of a forming load.SOLUTION: A hot forging method performs: preform step S40 of forming any one of burrs W31 of both sides in the lateral direction of a preform compact W30 in a position higher than that of a height-direction center C of a crankshaft W50, forming other burrs W31 at both sides in the lateral direction in the position lower than that of the height-direction center C of the crankshaft W50, and forming the burrs W31 by replacing the relationship of the height position of at both sides in the lateral direction in two or more positions along a longitudinal direction of the preform compact W30; and finishing step S50 of pushing down the burrs W31 of the preform compact W30 formed in the position higher than that of the height-direction center C of the crankshaft W50 with a finishing forming die 40, and pushing up the burrs W31 of the preform compact W30 formed in the position lower than that of the height-direction center C of the crankshaft W50 with the finishing forming die 40. 【課題】成形荷重の増大を抑制できる熱間鍛造方法を提供する。【解決手段】荒地成形体Ｗ３０の短手方向両側のいずれか一方のバリＷ３１を、クランクシャフトＷ５０の高さ方向中央部Ｃよりも高い位置に形成し、短手方向両側の他方のバリＷ３１を、クランクシャフトＷ５０の高さ方向中央部Ｃよりも低い位置に形成し、荒地成形体Ｗ３０の長手方向に沿った複数の位置において、短手方向両側の高さ位置の関係を入れ替えてバリＷ３１を形成する荒地工程Ｓ４０と、クランクシャフトＷ５０の高さ方向中央部Ｃよりも高い位置に形成した荒地成形体Ｗ３０のバリＷ３１を、仕上成形型４０で押し下げるとともに、クランクシャフトＷ５０の高さ方向中央部Ｃよりも低い位置に形成した荒地成形体Ｗ３０のバリＷ３１を、仕上成形型４０で押し上げる仕上工程Ｓ５０とを行う。【選択図】図８