METHOD OF MANUFACTURING DOOR HINGE FOR AUTOMOBILE

摘要

Disclosed is a method of manufacturing a high-strength door hinge for an automobile from a tabular steel material at low cost, which comprises a pressing step in which a cylindrical bulging portion is formed at an end of the material in the breadth direction; a shaft-hole boring step in which a shaft hole is bored in the cylindrical bulging portion; and a shaft-hole finishing step. In the shaft-hole boring step, a shaft hole is bored using a first punch having a conical end and a first die having a clearance volume between the outer circumference of the cylindrical bulging portion and the inner wall of the die. The clearance volume has a size such that, during punching of the cylindrical bulging portion using the first punch, no punching debris is produced and the cylindrical bulging portion bulges outward at a hole portion to be formed between an end at which machining starts and a predetermined position and such that punching debris is produced and discharged from a hole portion to be formed when the first punch is located between the predetermined position and an end at which machining ends. In the shaft-hole finishing step, the shaft hole is finished from the end at which machining ends using a second die having substantially the same shape as the first die and a second punch having a conical or truncated conical end and a maximum diameter larger than that of the first punch.