During lithium-ion battery packing, joining between battery cases and tabs is challenging for manufacturers due to dissimilar materials of the battery case and the tab, as well as their thicknesses. Laser welding, which has proven to produce a good weld with high productivity and low electrical resistance, is introduced to weld these materials. The weld was conducted with nanosecond-pulsed fiber laser and the effect of laser powers on mechanical and electrical properties as well as microstructure of the joint is investigated. The weld bead at the low laser power exhibited several blowholes on the surface, while the formation of voids including centerline and root cavities was observed through the cross-section. Moreover, the phenomenon of upward penetration (UP) was observed in all laser powers and recoil pressure which was generated by metal evaporation was supposed to cause the formation of an upward flow of the lower material. A hardness test was performed on both horizontal and vertical directions through the fusion zone. Additionally, the increase of upward penetration (UP) resulted in higher strength and lower electrical resistance of the weld.

The efficiency of any laser materials processing depends on the efficient energy transfer from the laser to a substrate. One of the critical factors in the process is the spatial distribution or the “mode” of the laser beam. Although an inverse Bremsstrahlung initiates the photon to electron energy transfer, a major part of the process is transport phenomena created by the absorbed energy. A mathematical model for transport phenomena during laser materials interaction is developed that includes multiple reflections, capillary and thermocapillary forces, recoil pressure, temperature distribution, melt pool flow, and phase changes. This model simulates interaction between a CO2 laser (λ = 10.6 μm) with four different spatial distributions and iron. The results of a simulation for fundamental understanding of this laser-material interaction are presented in this paper. First, overall keyhole behaviors are compared in terms of response time, penetration hole geometry, and absorptivity. Furthermore, a dimensionless parameter is developed to examine keyhole collapse quantitatively. Finally, velocity, temperature, and, intensity fields are analyzed.