| 摘要 |
PURPOSE:To obtain an accurate tooth form without increasing a molding load by providing a corner of a bottom of a hole for a preform with an escape groove and an upper surface of a lower punch with projections fitting to the escape grooves and filling the escape groove with a surplus of the preform. CONSTITUTION:An end of an opening of a cup form preform 10 is set on a lower punch 6 with the end of the aperture facing downward so as a protrusion 9 of the lower punch 6 fits into an escape groove 11. Subsequently, by lowering an upper punch 5 a bottom plate of the preform 10 is pinch-held by an upper punch 5 and a lower punch 6, and the lower punch restrains the internal periphery by the spring force of a spring 13 with the cup bottom being in a close contact. Under the condition that the bottom plate is restrained by the lower punch 6, when the upper punch 5 is lowered, an aperture end of the cup is extrusion-molded by passing a die-orifice, so that an internal tooth form is molded following a tooth form of an external periphery of the lower punch 6. In this instance, a surplus material occurred in the neighborhood of the bottom of the internal periphery of the cup is inserted to the escape groove 11, and this is inserted to a space between the lower punch and the cup bottom so that the accurate tooth form is shaped without having a gap between the two.
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