| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to reduce, when forming a primary metal fitting molded article with cold forging, the types of molds required for the formation of the tip-side annular portion of the molded article if the thread diameter of the primary metal fitting for a spark plug is the same, then even if the longitudinal position of the inwardly protruding annular portion, which is a second inside step portion, is different or the screw length is somewhat different, as long as the outer diameter of the tip-side annular portion provided at the screw tip, and the longitudinal dimension thereof, are the same.SOLUTION: Prior to formation of a tip-side annular portion 32, a body 30e being molded, in which a second inside step portion 44 is formed, is loaded from the tip side into a mold 201f having tip-side annular portion forming parts 205f, 206f; an annular tip-facing surface 243f of a punch 240f is pressed from behind into the inside of the body 30e being molded to press the second inside step portion 44 by the annular tip-facing surface 243f; and the tip portion of the molded body 30e is pressed against the tip-side annular portion forming parts 205f, 206f to forwardly extrusion-mold the tip-side annular portion 32. A primary metal fitting molded article 30f is thus obtained by the molding steps. |
