Patent ID: 9630238
Date: 2017-04-25
CPC Classifications: B21D,B21J

Claim:
1. A method of forming a plate-shaped workpiece into a closed cross-sectional structure, the structure including a bottom portion formed in a central part thereof in a width direction and extends in a longitudinal direction, left and right side wall portions located on both sides of the bottom portion in the width direction and rise in a height direction, and a pair of flange portions formed at ends of the left and right side wall portions in the height direction, comprising: a first step of press-forming the plate-shaped workpiece into a shape having first bend lines that extend in a longitudinal direction and portions that are separated by the first bend lines to correspond to the bottom portion, the left and right side wall portions, and the pair of flange portions such that the portion corresponding to the bottom portion includes a first bottom portion and a second bottom portion that incline in the height direction toward a second bend line that extends in the longitudinal direction along a boundary between the first and second bottom portions; a second step of bending the workpiece, which has been formed in the first step so that the portions corresponding to the left and right side wall portions face each other by clamping the portion corresponding to the first and second bottom portions between a first punch and a pad having a support surface in a plate-thickness direction to bend the plate-shaped workpiece along the second bend line to cause the first and second bottom portions to reverse the direction of the incline of the first and second bottom portions to incline in a direction opposite to the height direction toward the second bend line; and a third step of: pushing a pair of pressure cams having respective pressing surfaces inwardly, while the portion of the workpiece corresponding to the bottom portion formed in the second step is placed on the support surface of the pad, to move the portions corresponding to the left and right side wall portions closer to each other so that the portions corresponding to the pair of flange portions are butted against each other and to define a die cavity having the same shape as a final shape of the closed cross-sectional structure with the support surface of the pad and the pressing surfaces of the pair of pressure cams; and pressing the portions corresponding to the bottom portion and the left and right side wall portions against the support surface and the pressing surfaces that form the die cavity by further bending the workpiece at the first bend lines to depress the portions corresponding to the pair of flange portions toward the cavity using a depressing portion of a second punch disposed above the pair of flange portions.