PRESS-FORMING METHOD OF TUBULAR PART HAVING CROSS-SECTION OF IRREGULAR SHAPE

A method of press-forming a tubular part having a cross section of an irregular shape crushes a steel tube between an upper die and a lower die in order to form a V-shaped cross section. When the curvature radius of a tip of the upper die is defined as R 1 , the curvature radius of a bottom portion of the lower die corresponding to the tip of the upper die is defined as R 2 , and the wall thickness of the steel tube is defined as t; R 1 , R 2 , and t satisfy R 1 +2t=R 2 and 1.5t¤R 1 ¤3t.