PRODUCTION METHOD FOR FORGED CRANK SHAFT

摘要

A production method for a forged crank shaft, including a die-forging step, a burr-removal step, and an excess thickness section-bending step. The die-forging step molds a finished forged material having burrs thereon and having a crankshaft shape molded therein, said crank shaft shape having excess thickness sections (Aaa, Aba) in the outer perimeter of both side sections (Aa, Ab) in the vicinity of a pin section (P) of a crank arm section (A), said excess thickness sections (Aaa, Aba) protruding from said outer perimeter. The burr-removal step removes burrs from the finished forged material molded in the die-forging step. In the excess thickness section-bending step, the excess thickness sections (Aaa, Aba) of the crank arm section are bent towards the surface on a journal section (J) of the crank arm section (A), by the insertion of a first U-shaped die (10) from the direction of eccentricity onto the crank shaft having had the burrs removed therefrom in the burr-removal step. As a result, a forged crank shaft that is lighter and has rigidity ensured can be easily obtained.