Analysis of transient thermo-fluidic behavior of melt pool during spot laser welding of 304 stainless-steel

In this study, the transient evolution of temperature and velocity field, melt pool geometry (width, depth of penetration and melt pool volume), melting and solidification behavior during spot laser welding of 304 stainless-steel is presented. The transport phenomena associated with the melting and the solidification stage are appropriately accounted in the computational model. The predicted melt pool geometry shows a good agreement with the published and in-house experimental data for spot laser welding. Analysis of important dimensionless numbers revealed the significant role of melt pool convection on the heat transfer and the melt pool geometry. Thermal cycles at several strategic locations were also investigated during the melting and the solidification stage. To analyze the solidification behavior of the melt pool, the relevant solidification parameters such as temperature gradients, solidification rates, and cooling rates were described. With progress in solidification of the melt pool at the melt pool interface, the solidification rate increases while the temperature gradient decreases. Also, an attempt has been made to account the free surface deformation in the melt pool by developing a separate numerical model considering the free/deformable top surface. A qualitative and quantitative comparison of the melt pool characteristics obtained from the free/deformable and the flat top surface model has been carried out. The predicted depth of penetration of the melt pool with the free/deformable top surface is found to be slightly larger than that with the flat top surface.