Rolling die for ball screw

摘要

A rolling die for a ball screw has: a cylindrical portion including a helical protrusion formed in an outer peripheral surface thereof for forming a helical ball groove in a raw material of a screw shaft of the ball screw; and a conical lead-in portion formed in one end portion of the cylindrical portion, the lead-in portion including a plurality of frustum-cone-shaped portions, wherein the contact angles of the frustum-cone-shaped portions with respect to the raw material of the screw shaft are each set so as to increase sequentially in the order starting at and from the frustum-cone-shaped portion adjoining the cylindrical portion.