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

Image Number 5 for United States Patent #5516376.

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 by a forging die having a first die element with a piercing punch entering into the central through hole of the hollow material from one side thereof and having a second die element with a piercing punch entering into the central through hole of the hollow material from another side thereof. The forging die forms teeth of the gear on the outer side of the hollow material while producing an annular flash in the central through hole of the hollow material between the piercing punches. A distance between the piercing punches in a closed condition of the forging die defines a thickness of the annular flash which is 0.3 mm or more and no greater than 1.3 times (130%) of a depth of the hardened surface layer. After that, the annular flash is removed from the forged body, and thermal refining is implemented to the forged body by quenching and tempering.

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