METHOD OF BENDING PLATE MATERIAL AND DEVICE FOR INCREASING OR DECREASING RESIDUAL STRESS

PROBLEM TO BE SOLVED: To provide a method of performing bending work having a small warpage by increasing or decreasing residual stress on cut edges of a workpiece.SOLUTION: In the method of bending a plate material, by which a planar workpiece having cut edges cut by a cutting means on both opposed sides is bent between both cut edges, the workpiece is bent after increasing or decreasing the residual stress on both cut edges of the workpiece, which is caused when cutting the workpiece. In the method of bending the metal plate, bending moment Mrs which is produced on the bent ridge line of the workpiece by the residual stress on both cut edges of the workpiece is calculated, also the bending moment Mz which is produced on the bent ridge line by bending of the workpiece is calculated, a bending moment M produced during bending the workpiece is calculated by (Mrs-Mz) and the curvature z of a warpage in the longitudinal direction is calculated by the bending moment M and the residual stress is increased or decreased in order to settle the difference between these curvature z of camber and curvature z0 of warpage of the target value within an allowable range.