| 摘要 |
PROBLEM TO BE SOLVED: To drastically reduce a producing cost by simplifying a producing process and dispersing with an expensive die for forgoing conventionally used in the next process. SOLUTION: A plurality of projected line parts 50a-50c extended along the axial direction with a prescribed clearance along the peripheral direction, are arranged at the one end side of a punch 26. Further, a forming land part 54 having a prescribed width hand formed so as to round the one end side, a projecting part 58 having a prescribed width and rounding the other end side to form product precision of an internal shape, and a recessing parts 60 allowing warpage of the punch 26 between the forming land part 54 and the projecting part 58, are arranged in each projected line part 50a-50c.
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