| 摘要 |
PROBLEM TO BE SOLVED: To provide a burring-working method with which development of crack at the tip end part of a flange is prevented. SOLUTION: A preparatory prepared hole 6 having diameter d1 is formed by blanking a plate material 3 and a prepared hole 5 having diameter d2 is formed by blanking the hole 6 with scrap width w. Then, a through-hole 4 having the flange 8 having height (h) is formed to the plate material 3 by bending the hole 5. Therefore, as compared with the case of having no preparatory prepared hole, since the surface-state of the blanked cross section for the hole 5 is improved, the through-hole 4 having the flange 8 with higher height (h) than the conventional art can be formed without developing the crack 7 at the tip end part of the flange 8. COPYRIGHT: (C)2007,JPO&INPIT
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