Prediction of coupled 2D and 3D effects in springback of copper alloys after deep drawing

The aim of this study is to investigate the balance between 2D and 3D (or twist) springback of copper-based thin sheets after a deep drawing process. Such materials are widely used in the manufacturing of electric and electronic components, but getting an accurate final geometry is usually difficult due to springback. Three copper-based materials are considered in this study, and in a first step, the mechanical behavior is investigated with uniaxial loading-unloading tension, monotonic and cyclic simple shear and hydraulic bulge tests. In a second step, thin blanks made of these copper alloys are deformed in a U-bending process, in which they are intentionally misaligned by 2° from the tool symmetry axis; then, the deformed geometry is measured with a laser scanner and the 2D springback and twisting parameters are calculated. It is shown that pure copper and the copper-iron alloy exhibit a rather limited 2D springback but a significant twisting whereas the opposite trend is observed for the copper-beryllium alloy. Finite element simulations are carried out with isotropic and mixed hardening models, calibrated from the experimental database. The comparison of experimental and predicted punch forces, 2D springback data and twisting parameters shows the accuracy of the numerical simulations. Moreover, the distinct springback characteristics of the three copper-based materials are correctly predicted and the influence of the mechanical properties on the relative 2D and 3D contributions to springback is analyzed.