METHOD FOR MANUFACTURING CAST CRANKSHAFT

摘要

This cast crankshaft manufacturing method includes a preliminary molding step for molding a burr-free rough raw material (31) formed in the shape of a crankshaft having excess portions (Aaa, Aba) that protrude from the outer periphery at both sides in the vicinity of a pin section (P) of a crank arm section (A); a die-casting step for molding a cast material (32) with burrs by pressing the rough raw material (31) by using a pair of first metal molds; and a burr removing step for removing burrs (32a) from the cast material (32). In the die-casting step, the thicknesses of two side portions (Aa, Ab) of the arm section (A) are increased by deforming the excess portions (Aaa, Aba) of the arm section (A) by means of the first metal molds while a surface of the arm section (A) on a journal section (J) side is held by being pressed by a second metal mold (20). By doing so, it is possible to obtain a lightweight cast crankshaft with sufficient rigidity in a simple manner while enhancing the yield ratio.