| 摘要 |
PROBLEM TO BE SOLVED: To prevent the formation of burrs on the outer periphery on the pin side in pin part by rough forging, to prevent the occurrence of defects on the surface of the pin and to obtain a crankshaft excellent in surface quality by making the shapes of a base stock and dies for rough forging at the time of manufacturing the crankshaft by die forging. SOLUTION: The die for rough forging is made into a shape in which the interval between the dies is released toward the outside on the pin side so that the burrs are not projected from the outer periphery 17-1 on the pin side in the pin part 17 after rough forging. In this way, the flow of metal to the pin side at the time of rough forging is promoted and the occurrence of the surface defects is suppressed. By making the part equivalent to the pin at the time of dividing the base stock for rough forging into a part equivalent to the pin and the other part in the longitudinal direction off-center on the pin side to the center axis in the longitudinal direction of the base stock and making the cross-sectional shape in the part equivalent to the pin of the base stock for rough forging proper, the flow of metal on the pin side is promoted and the occurrence of the surface defects is suppressed.
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