METHOD OF PRODUCING THREAD-ROLLING DIE

摘要

A method of producing a thread-rolling die used for producing multiple-threaded bolts, such as double-threaded bolts, having a loosening prevention function. A first cutting tool (10) has a shape of a coarse pitch thread with a flat crest. The tool (10) is fed into a thread-rolling die material (30) to a depth less than the maximum height of a projection (6), so that a part of the die material (30) is cut and part of a coarse pitch thread on the die is formed. Here the projection (6) is part of a fine pitch thread cyclically formed on the coarse pitch thread, in a valley portion between adjacent coarse pitch threads, in correspondence with phase displacement between the fine pitch thread obtained by extending a fine pitch screw and the coarse pitch thread obtained by extending a coarse pitch screw. Further, a second cutting tool (25) with a fine pitch thread shape is adjusted to the shape of the projection (6) and fed into the die material (30) from a valley portion (5a) at part of the coarse pitch thread on the die. Thus the die material (30) is cut and the remaining portion of the coarse pitch thread on the die and the projection (6) are formed.