Patent ID: 8505941

Claim:
A method of manufacturing a torsion beam comprising: forming a portion of a tubular body into an approximately U-shape in cross section or an approximately V-shape in cross section by crushing a portion of the tubular body in the radial direction and, thereafter, bending the tubular body with a bottom line of the tubular body set as an inner side of bending so that a bending strain of 2 to 6% in a longitudinal direction of the tube on a tensile side is imparted to ear portions, wherein, by using a vertically movable ship-bottom-shaped upper die where upward tapered portions are contiguously formed with both ends of an upper horizontal portion, upper clamps which are arranged on both end sides of the upper die in a vertically movable manner, and a fixed lower die where downward tapered portions are contiguously formed with both ends of an lower horizontal portion, a portion of the tubular body is formed into an approximately U-shape in cross section or an approximately V-shape in cross section by crushing a portion of the tubular body in the radial direction by the upper die and the lower die and, thereafter, both tube end portions are clamped and bent by the upper clamps and the downward tapered portions of the lower die with the bottom line set as the inner side of bending and, due to the bending, a bending strain, of 2 to 6% in the tube longitudinal direction on a tensile side is imparted to the ear portions of gradually changing portions.