A novel joining technology for hybrid busbars in electric vehicle batteries

Abstract

In this paper, a joining by forming technique is suggested to join aluminium and copper sheets, aimed at potential hybrid busbar manufacturing. The technique, called hole hemming, is performed through the deformation of the aluminium sheet to create a mechanical interlock with the copper sheet, requiring neither heat, welding, nor additional elements/materials. Initially, the feasibility of this joining process is assessed using an analytical model to determine the parameters required for achieving a mechanical interlock while avoiding fractures. The accuracy of the process windows developed by this model is validated through comparisons with experimental results and numerical simulations. In these simulations, the Modified Mohr-Coulomb criterion is employed to predict ductile damage. Furthermore, a new design incorporating branches in the aluminium sheet holes is introduced. This innovation allows for fracture-free joint manufacturing beyond the safe limits predicted by the analytical model, thereby expanding the range of feasible process parameters. Subsequently, the mechanical performance of joints with and without branches is evaluated through destructive shear and cross-tension tests at both room temperature and an elevated temperature of 120 °C, simulating the maximum service conditions for busbars. The results demonstrate that hole hemming effectively joins AA6082-T4 and Cu-ETP R240 sheets, validating the proposed designs. Specifically, the hybrid aluminium and copper joints exhibit a maximum shear strength of 4.35 kN and a displacement of 12.11 mm at room temperature. In cross-tension tests, the joints achieve a maximum strength of 1.73 kN and a displacement of 9.86 mm. Although performance slightly diminishes at elevated temperatures, it remains excellent for both destructive test configurations.