| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem of an end material or a crack while forming a through-hole in a pipe material used as an automobile structural member. SOLUTION: In the pipe material 1 for the automobile structural member with the circular through-hole 2 formed for infiltrating a coating or a rust-proofing liquid to the inside or discharging it therefrom, the through-hole is formed by bending the end material 22 connected with a pipe surface 11 by a bending edge 21 to the inside with the bending edge 21 as an axis. The through-hole 2 is punched in the pipe surface 11 by a through-hole forming punch in a cylindrical shape using the edge of a flat circular front end surface as a blade, having a chamfer formed by notching a part of the blade in the circumferential direction, and extending to the side face, in a range excluding the chamfer. Then, the end material 22 connected with the pipe surface 11 by the bending edge 21 remaining in the range of the chamfer is bent to the inside with the bending edge 21 as the axis, thereby forming the through-hole 2. COPYRIGHT: (C)2008,JPO&INPIT
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