Effect of Laser Beam Oscillation on Thermal Behavior and Residual Stress in Multilayer Cu Foil Stacks to a Cu Tab Joint: A Numerical Investigation

Laser welding of multilayer copper foil stacks for lithium-ion battery tabs generates steep thermal gradients that can induce plastic deformation and residual stresses, potentially affecting joint integrity. This study numerically investigates the effect of laser beam oscillation on the thermo-mechanical behavior of a 60-layer Cu foil stack joined to a 0.3 mm Cu tab using a three-dimensional sequentially coupled finite element model. Line and wobble welding were compared using temperature-dependent material properties and a moving conical Gaussian heat source. Beam oscillation increased the predicted peak temperature from 2060 K to 2577 K while reducing the through-thickness temperature reduction from approximately 22.5% to 12.1%, indicating a more uniform thermal field. The dominant longitudinal residual stress decreased from approximately 225 MPa to 181 MPa, while the von Mises equivalent residual stress decreased from 199 MPa to 141 MPa, corresponding to a reduction of approximately 29%. These results demonstrate that beam oscillation redistributes thermal energy and mitigates localized residual-stress concentration, providing a numerical basis for optimizing laser welding of multilayer Cu battery-tab joints.