PRODUCTION METHOD FOR FORGED CRANK SHAFT

摘要

A method for producing a forged crankshaft includes a die forging step, a trimming step, and an excess projecting portion crushing step. The die forging step forms a finish forged blank with flash, the finish forged blank including a shape of the crankshaft, in which crank arms (A) have excess projecting portions (Aaa, Aba) at outer peripheries of side portions (Aa, Ab) thereof near a crank pin (P), the excess projecting portions projecting from the outer peripheries. The trimming step removes the flash from the finish forged blank formed in the die forging step. The excess projecting portion crushing step crushes the excess projecting portions (Aaa, Aba) of the crank arms by pressing the crankshaft using a pair of first dies (10A, 10B), the crankshaft being obtained by removing the flash in the trimming step. With this method, it is possible to conveniently produce a forged crankshaft having reduced weight in combination with sufficient stiffness.