Method of and apparatus for manufacturing a gear with a central through hole

摘要

A hardened surface layer is formed in the region of inner and outer surfaces of a hollow material having a central through hole, then the hollow material is hot-forged into a hollow gear-like forged body 7 by a forging die 1 having a first die element 2 with a piercing punch 4 entering into the central through hole of the hollow material from one side and having a second die element 3 with a piercing punch 5 entering into the central through hole from the other side. The forging die 1 forms gear teeth 7a while producing an annular flash 7c in the central through hole between the piercing punches 4, 5. The distance between the piercing punches 4, 5 in a closed condition of the forging die 1 defines a thickness of the annular flash which is at least 0.3 mm and at most 1.3 times the depth of the hardened surface layer. After that, the annular flash 7c is removed from the forged body 7, and thermal refining (quenching and tempering) is carried out.