A design method for prediction of dimensions of rectangular hollow sections formed in stretch bending

Local deformation of individual cross-sectional members is of great interest in bending of aluminium alloy extrusions for tight tolerance production such as automotive components. The primary concern is the impact of such distortions on manufacturability as well as the dimensional tolerances of the component. This paper presents analytical models for the determination of local post-buckling and suck-in deformations in stretch bending. The models are based on the deformation theory of plasticity combined with an energy method using appropriate shape functions. The analytical predictions are being verified with experimental results. Based on the present findings, a simplified design method for evaluation of bendability of sections in industrial forming operations is being proposed. The results show that the slenderness (b/t) and the width of the flange are the main parameters related to the bending radius at the onset of plastic buckling and the magnitude of local deformations, respectively. Material parameters have proven to be relatively more important to the former than to the latter. Although there is some discrepancy at tight nominal bend radii, the overall correlation between the experimental and theoretical results is surprisingly good. It is therefore concluded that the present method provides to be an efficient means to the evaluation of bendability of rectangular hollow sections.