| 摘要 |
PROBLEM TO BE SOLVED: To effectively prolong the life of projecting ribs which are provided on a die to draw vertical grooves while recessed vertical grooves are workable simply and surely in rectangular parts of a nut material in a series of heading processes. SOLUTION: In a pre-heading step, a tapered face is headed at the top of a columnar nut material having fixed dimensions and a recessed part 1c which is deeper than the vertical grooves to be formed on the rear end is headed and also the whole outer periphery or the side of the rear end of the outer periphery is formed into a polygonal shape. In the next heading step, the nut material 1<SB>2</SB>obtained in the pre-heading step is upset into the die hole 18a of a die 18 after taking the turnabout of 180°and drawn with a plurality of projecting ribs 19 which are projected radially inward on the die hole 18a, by performing the heading while relieving the drawn excess material so as to overhang in the recessed part of the polygonal part 1d, the vertical grooves 1e are formed on the face between respective polygonal parts 1d and, in a succeeding step, punching is performed to the nut material which is obtained in the preceding step. COPYRIGHT: (C)2011,JPO&INPIT
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