Method for manufacturing fastening screw and fastening screw

Abstract

An object of the present invention is to reduce the fastening time and to obtain a predetermined fastening force and to suppress the loosening of a screw. The solution of the present invention is to provide a method for manufacturing a fastening screw, which comprises: a preliminary upsetting step B for forging a front end of a blank wire 1 and forming a head 1a having a depression 1d in a condition, where a curve portion 1b remains in an outer periphery to be formed into a bearing surface of the fastening screw, by means of a die 21 having a protrusion 21b protruding from a flat end face 21a and a first punch 20 having a cup-shaped cavity 20a, the front end protruding from the protrusion 21b of the die 21; a finish upsetting step C for forging the head 1a and forming a recess 1c so that the depression 1d of the head 1a is not interfered with the recess 1c by the die 21 and a second punch 30 having a protrusion 30b for forming the recess 1c on the head 1a; and a thread forming step D for processing a shank 1e extending from the head 1 and forming threads on the shank 1e.

Dependencies are inferred from the claim text.