PURPOSE: To form simultaneously a bolt head part and a head recessed part, to make them light in weight, and to save a material, by forming a projecting part on the bottom face of a recessed part for forming a bolt head part of a header, and pressing this header against a blank material.
CONSTITUTION: A bolt forming blank material 12 is held by a holder 11 so that its upper end is projected from the upper face of the holder 11, subsequently, a header 13 is moved downward, and a bolt head part 16 and a bolt head recessed part 17 are brought to cold forming at the same time. In this case, since the tip of a projecting part 15 is formed semispherically, both the projecting part 15 and the blank material are not damaged, and a fiber flow becomes good.
FUJII TADAYOSHI
DOUNAI AKIYUKI
