Thermo-Mechanical Coupled Finite Element Analysis of Ultrasonic Metal Welding in Multilayer Copper Foil Stacks

Ultrasonic metal welding (UMW) is widely used for joining multilayer copper foil stacks in battery manufacturing due to its low heat input and short process time. However, in thin multilayer structures, repeated shear deformation and localized frictional heating can lead to excessive plastic deformation and microcracks, degrading weld quality. In this study, the thermo-mechanical behavior during UMW of multilayer copper foils was analyzed using two-dimensional plane strain finite element simulations. The Johnson-Cook plasticity model and temperature-dependent material properties were incorporated. The effects of varying clamping pressures and vibration amplitudes on temperature distribution, plastic strain, and stress fields at the weld interface were investigated. Results showed that higher clamping pressures and vibration amplitudes increased the heat generation and expanded the plastic deformation zone, promoting more uniform nugget formation. Optimal welding conditions for achieving consistent and reliable joints were identified through the simulation results. This work provides fundamental insights into the optimization of UMW parameters for multilayer copper foil structures, contributing to enhanced weld quality and mechanical reliability.