To provide a method where a polygon and closed state tube in viewing a cross-section crossing by a right angle to a feeding direction of a band bar is produced continuously and the obtained tube is made precisely without being brittle caused on the metallic fatigue.
A metallic band bar (work) W is fed by every constant length between a die body, a core metal, a punch and a straightening punch, and feed bending to press the work W with them synchronizing with the above is executed. In this time, at first from an inlet neighborhood to a central neighborhood, among scheduling ridge lines L1 to L4 to exist extending to the feeding direction S in the work W composing the ridge lines L5 to L8 of a tube W1, the ridge lines from L1, L2 nearby both end parts e1, e2 orderly to the central part L3, L4 are bent gradually. After then, the obtained rough tube W0 is straightened from inside and outside near the outlet.
FUTAHASHI IWAO
OGAWA HIDEO
AMINO HIROYUKI
SUZUKI HIROTSUGU
AMINO KK