| 摘要 |
PROBLEM TO BE SOLVED: To provide a tapping screw form rolling die capable of forming a sharp tip by cutting off the tip of a rivet. SOLUTION: A fore-end tip cut-off face 4 extending from a lower end of a tip reducing face 3 of a thread form rolling face comprises a retraction face 4a inclined in the retracting direction and a projecting face 4b inclined at the angle of inclination smaller than that of the retracting face 4. Though the fore-end tip is also plastically formed simultaneously as the rivet tip is plastically formed, the fore-end tip is not hardened because the plastic hardening is performed by the retraction face 4a of less deformation in its initial stage, and excess metal is smoothly moved to the fore-end tip. When the fore-end reduction is completed by the fore-end reduction face 3, the fore-end tip cut-off face 4 forms the projecting face 4b, and the deformation of the fore-end tip is increased, and the fore-end tip is cut off from the tip of the rivet. In this condition, the fore-end tip is hardened, and the tip of the rivet is finely finished since the plastic forming of the tip of the rivet by the tip reduction face 3 is completed. COPYRIGHT: (C)2007,JPO&INPIT
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