FORMING METHOD AND FORMING METAL DIE FOR METAL TUBE

PROBLEM TO BE SOLVED: To keep a shape of a metal tube by applying plastic deformation on the metal tube and then removing the stress gradient incurred inside and outside of the bending direction. SOLUTION: A forming metal die 3 is equipped with a plurality of projected beads 5 in a metal die product section 4, which form a plurality of ringed recessed grooves on the outer peripheral surface of a thin walled steel tube after bending. After the thin walled steel tube affected by spring-back due to bending is set into the metal die product section 4 of the forming metal die 3, the forming die 3 is then fastened to press-form a plurality of ringed grooves by a plurality of projected beads 5 in the forming die product section 4 on the outer peripheral surface of the thin walled steel tube. Thus, the spring back can be eliminated through plastic deformation applied to the wall surface of the thin walled steel tube mainly by bending. Also, the plastic deformation can improve cross-sectional rigidity of the thin walled steel tube and prevent occurrence of collapse caused by circumferential stress, so that a larger plastic deformation can be applied. COPYRIGHT: (C)2005,JPO&NCIPI