| 摘要 |
PURPOSE:To constrain the material flow on the punch surface and to prevent the generation of a crack at the piston forging time by forming the stepping part at a punch tip composing the forging die of the piston made of an Al alloy in plural steps. CONSTITUTION:The stepping part for forming the pin boss part of a piston main body is formed in two steps by a stepping parts 24 and 26 at the tip part 22 of a punch 2 in the forging die of the piston made of an Al alloy composed of the punch 2 and die. Since the both stepping parts 24, 26 are connected smoothly by the curve of small radius the flow of an Al alloy of a material on the surface of the punch 2 is constrained in the case of forging a piston by the Al alloy to prevent the generation of a crack on the Al alloy made piston at the time of forging.
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