| 摘要 |
PROBLEM TO BE SOLVED: To improve the durability of a punch by avoiding stress concentration developed to a specific portion of the punch caused by fluid action of the material when a track groove is formed by performing a backward extrusion-formation. SOLUTION: When the backward extrusion-formation is applied with the punch 30 having three projecting parts 46 and recessing parts 48, separated at the same angle along the circular direction and extended along the axial line direction, one pair of tapered surfaces 38a, 38b connected with a first to third rectangular inclining surfaces 36a-36c formed at the tip end part of the projecting part 46 of the punch 30 abutted on a head parts of a secondary forming product and inclined at a prescribed angle along the circular direction to the first to third rectangular inclining surfaces 36a-36c, are arranged. COPYRIGHT: (C)2006,JPO&NCIPI
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