| 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, and bend-facilitating lines G are provided at positions corresponding to bent lines in the 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 the plate thickness direction and by pressing a punch into a space between a pair of dies 17. Next, in a third step, a plug 20 having an outer peripheral shape that is the same as the final closed cross-sectional shape is placed on the bottom portion of the workpiece, which has been formed in the second step, and the bottom portion and the left and right side wall portions are bent along the bend-facilitating lines by pressing the bottom portion and the left and right side wall portions against an outer periphery of the plug. |
