FORGING FORMATION METHOD FOR THREAD OF SCREW SHAFT

摘要

PURPOSE:To increase sharply the efficiency in screwing and to increase the strength as well by forming with forging a round bar by giving a rotary feeding between a pair of tapping dies providing on the forming surface the shape for forming a thread groove with forging. CONSTITUTION:The upper tapping die 1 provides the projection piece 1b which can form the thread groove having half the necessary pitch on the inner face 1a of the semicircular column which is equivalent to the radius of the aiming thread and the height of the projection piece 1b is made higher with the advancement toward the rear end. The inclination is preferrably taken as the steep inclination within the range of 0 deg.-10 deg. rather than the inclination of the necessary thread. The lower tapping die 2 is provided by advancing the projection piece 2b 180 deg. more than the projection piece 1b. The formation is performed by setting the round bar on the rotary device movable before and behind with the use of said tap. The screw having excellent quality can be produced extremely efficiently compared with the conventional machining.