| 摘要 |
PURPOSE:To obtain a product whose burring height is highly by executing the ironing by increasing successively the ironing diameter from a punch leading-in tip part, and varying a plate thickness decrease rate of a burring part by one stroke. CONSTITUTION:As for a multistage burring punch having different outside diameter dimensions d1, d2 of straight parts 7, 8 which follow the leading-in tip part, and of d1<d2, an effective length l1 of the straight part 7 exceeds a burring height of a product, and an effective length l2 of the straight part 8 is l1<l2. Also, this punch has both the straight parts 7, 8, a burring working part consisting of a smooth and connected curve, a straight part 9 held and pressed in a punch plate and a collar 10. By using said punch, first of all, the first burring working is executed by the small diameter part of the tip part, and subsequently, the re-burring working is executed by one stroke by the large diameter part, the plate thickness decrease rate of the burring part is made large, and a dimension whose burring height is high is obtained.
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