Theoretical and experimental investigation of the deformation shape in press-braking bending considering surface residual stresses induced by milling operation

Abstract Press-braking bending is usually performed after face milling to obtain the specified curvature of variety mechanical parts, which is widely applied in the aircraft manufacturing. The surface layer residual stress on workpiece caused by milling has an important influence on subsequent forming. The influences of surface residual stress caused by milling operation on press-braking bending has been investigated analytically and experimentally in this study. The analytical model for springback prediction based on plane strain assumption is proposed using the material model of Mises yield criterion and Swift exponential hardening law, and takes into account of the effects of milling-induced residual stress. Three levels of residual stress are introduced in the test plates through milling operation with different cutting speed. The analytical results are compared with the bending experiments of 7050-T7451 Al-alloy plates. Results show that the accuracy of the contour obtained by the proposed model is improved when surface residual stress is considered. Furthermore, the influence of surface residual stress on springback is discussed. It is revealed that surface tensile residual stress increases springback and surface compressive residual stress contributes positively to the final shape of bent specimens.