Improving working limit in draw bending process of aluminum square tubes in large bending radius

Light-gauge aluminum alloy extruded sections are advantageous for reducing the weight of vehicles and automotive components. In general, a bending process is required for actual applications using these materials. However, the bending of hollow sections causes several types of undesirable deformation such as flattening and wrinkling. In a previous work, the effect of using a rigid mandrel for aluminum alloy square tubes to suppress flattening deformation was demonstrated. In another study, the effects of using a laminated mandrel and applying axial tension to annealed aluminum square tubes on the suppression of wrinkling were clarified. However, in those studies, the range of bending radii R was small (R=50-200mm) in comparison with those of industrial products. Therefore, it is necessary to obtain data for large-scale bending radii R for hardened aluminum square tubes. In this work, the draw bending process in the case of a large R (R=300-900mm) was investigated. Both axial tension and a laminated elastic mandrel were used in the experiment on improving the working limit. We also evaluated the effect of different cross sections on the undesirable deformation by FEA (finite element analysis). In this study, the possibility of improving the working limit of extruded aluminum square tubes was confirmed by both experiments and FEA.