Method of producing polygonal closed cross-section structural component with a curved form and polygonal closed cross-section structural component produced by the method

A method of producing a polygonal closed cross-section structural component with a curved form along its longitudinal direction having plural ridge lines corresponding to corner portions of the polygonal closed cross-section and two flange portions extending in parallel to a flat face including a ridge line located at an innermost side in a radial direction of the curved form of the component along the longitudinal direction among the above ridge lines from a metal plate, comprising:

• press-forming the metal sheet into a gutter-shaped pre-processed part with a curved form along its longitudinal direction having plural ridge lines corresponding to the corner portions of the polygonal closed cross-section of the component in a cross-sectional form developed by cutting the component at a position corresponding to the ridge line located at the innermost side in the radial direction to provide a flange portion extending along the ridge line at the resulting respective ends, wherein each of the ridge lines corresponding to the corner portions has a radius of curvature equal to or smaller than a radius of curvature of the corresponding ridge line of the component to have a length equal to or shorter than the length of the corresponding ridge line;
• and
• press-forming the pre-processed part to deform inwardly in the cross-sectional direction at a position of one or more of the plural ridge lines to butt the ridge lines located at the innermost side and the flange portions to each other.