| 摘要 |
PURPOSE:To reinforce effectively and surely by working the hole edge part of a round hole with the 2nd die having an elliptic conical working part further after the plastic work of the hole edge part of the round hole in advance by the plural projecting parts formed along the generating line on the outer periphery of a conical working part. CONSTITUTION:The 1st upper and lower dies 9-5, 9-6 having a conical working part at the tip and having four pieces of projecting parts 9-1-9-4 which run along the generating line thereof on the outer peripheral face of this working part are pressed to the hole edge and taper face and reinforced by causing a plastic flow in the 45 deg. direction of the hole edge. Then, the 2nd upper and lower dies 9-6, 9-6' having an elliptic conical working part are pressed to the hole edge and taper face and the 90 deg. direction not worked by the 1st die 9-5 is subjected to the plastic work. In this way the round hole edge part where stress is concentrated can easily be reinforced.
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