Experimental and computational study of temperature- and angle-dependent laser absorption in keyhole welding of copper along non-linear paths

With the growing demand for electric mobility, copper is increasingly used in critical electric vehicle components. Laser welding is essential for joining these components but is challenged by copper’s high reflectivity and thermal conductivity. Molten pool simulations of laser welding are valuable to understand the complex interactions between the laser beam and material but the literature models are limited to linear paths. Moreover, there exists a significant variation in the laser absorption values in the literature, leading to uncertainty in prediction. In this study, laser absorptivity of copper is calculated from temperature- and angle-dependent Fresnel relations. The absorption values are implemented in an existing computational fluid dynamics solver that employs Volume of Fluid method to track melt pool surface and a ray tracing approach to account for multiple reflections within the keyhole. Two ring-core beam profiles are investigated experimentally for keyhole mode welding of a hairpin, with the laser traveling along an elliptical path on the hairpin top surface over multiple passes. Simulation results are extensively validated against experimental data including in-situ high speed videos and weld cross-sections at different locations along the non-linear path. The validation is essential to better quantify the uncertain parameters in laser welding including laser absorptivity, recoil pressure, and extent of turbulence. In addition to demonstrating the necessity of incorporating both temperature- and angle-dependent absorptivity for accurate process modeling of laser welding of copper, the simulation results reveal significant differences in laser absorption behavior and melt pool and keyhole evolution for the non-linear scan than a linear scan.