Closed-section structure forming method and closed-section structure forming apparatus

摘要

An object is to make it possible to easily form a plate-shaped material into a closed cross-sectional structure with high precision. In a first step of press-forming, a workpiece 1 is formed into a curved shape that has curvatures in the longitudinal direction and the width direction required for a final closed cross-sectional shape. Next, in a second step, the workpiece, which has been formed in the first step, is bent in such a direction that left and right side wall portions approach each other by clamping bottom portions 2 and 3 between a punch 15 and a pad 16 in a plate-thickness direction. Next, in a third step, a pair of flange portions 7 and 8 are butted against each other while the bottom portions of the workpiece, which has been formed in the second step, are placed on a pad; and a die cavity having the same shape as the final closed cross-sectional shape is defined between a support surface of the pad supporting the bottom portion and pressing surfaces of a pair of pressure cams pressing the left and right side wall portions. Then, the pair of flange portions are depressed toward the cavity using depressing portions 31 of a second punch disposed above the pair of flange portions.