| 摘要 |
PURPOSE:To enable a yoke to be processed without producing a crack and the like by causing the bottom of its raw material to be in a plastic deformation with a boss-forming punch so that there is provided a recessed part equivalent to an opening which is thin in its wall thickness, and subsequently punching the recessed part with a pierce punch. CONSTITUTION:A recessed part 11 is provided on part, equivalent to an opening 8, of the bottom 6 of a work piece W, whose side is processed in a U-shaped form. In this process, a boss-forming punch 23A is used to apply a press working to the bottom 6 of the work piece W so that the wall thickness of the recessed part 11 is made thinner. Subsequently, said recessed part 11 is punched with a pierce punch 24A. Further, the bore diameter of the pierce punch 24A is almost equal to that of the opening 8, and moreover, in order to cope with said punching operation, an acceptor mold 24B is also provided with a by-pass port which can accept the remaining work piece W after the recessed part 11 is punched. Hereby, at the time when a yoke is processed, the opening is not punched before the final stage in the processing is reached, and accordingly, the peripheral part of a soket can be processed precisely.
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