PURPOSE: To reduce by half of process number in a forging process, reduce the machining cost and improve the life of die.
CONSTITUTION: In order to forge a part with steps having a first small diameter part 2, a large diameter part 4 and a second small diameter part 3 on a lower step part, a middle step part and an upper step part in its axial direction with one process, an annular taper hole 28 which connects to the upper end of a first small diameter hole 27 of a lower die 20 and inclines so that the diameter is made larger facing toward the upper side is preliminarily formed, and an annular taper surface 46 which inclines so that the diameter is made smaller facing toward the upper side is preliminarily formed. Then, the taper hole 28 promotes the flow of raw material into the first small diameter part 2, and the taper surface 46 promotes the flow of raw material into the second small diameter part 3.
ITO YOSHIMASA
TACHIBANA HIDEKI
TOMITA MIKIO
ITO KAZUYA
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