Method of manufacturing curvilineal closed structure parts without flange and apparatus for the same

A method of manufacturing a closed structure part having a curvature and welded edges along a longitudinal direction of the part, and having a varying cross-sectional shape, from two metal plates, comprising:

• press forming each of the two metal plates, which is provided with a curvature along a longitudinal direction of a plate corresponding to the curvature of the part along the longitudinal direction and further provided with both ends in a width direction of the plate corresponding to the welded edges of the part such that a folding line is formed on an inner side in the width direction of the plate;
• forming a closed structure by stacking the two metal plates after the press forming on each other vertically such that their bulging sides face outwardly and mutually welding their left ends and right ends in the width direction along the longitudinal direction so as to form welded edges;
• and
• forming the closed structure into the part having a target shape by guiding and conveying the closed structure with a pair of left and right rotary rolls or, in addition thereto, a lower rotary roll thereunder while changing a distance between the left and right rotary rolls or, in addition thereto, moving the lower rotary roll up and down such that the closed structure has a three-dimensional shape by using the folding lines and the welded edges as origins.

An apparatus that manufactures a closed structure part having a curvature and welded edges along a longitudinal direction of the part and having a varying cross-sectional shape, from two metal plates, comprising:

• a press forming machine that press forms each of the two metal plates, which is provided with a curvature along the longitudinal direction of the plate corresponding to the curvature of the part along a longitudinal direction and provided with both ends in a width direction of the plate corresponding to the welded edges of the part such that a folding line is formed on an inner side in the width direction of the plate;
• a welding machine that forms a closed structure by stacking the two metal plates after the press forming on each other vertically such that their bulging sides face outwardly and mutually welding their left ends and right ends in the width direction along the longitudinal direction so as to form welded edges;
• and
• a roll forming machine that fours the closed structure into the part having a target shape by guiding and conveying the closed structure with a pair of left and right rotary rolls or, in addition thereto, a lower rotary roll thereunder while changing the distance between the left and right rotary rolls or, in addition thereto, moving the lower rotary roll up and down such that the closed structure has a three-dimensional shape by using the folding lines and the welded edges as origins.