Role of recoil pressure, multiple reflections, and free surface evolution during laser keyhole welding

A three dimensional laser keyhole welding model is developed, featuring the self-consistent evolution of the liquid-vapor (L/V) interface together with full simulation of fluid flow and heat transfer. Important interfacial phenomena, such as free surface evolution, evaporation, kinetic Knudsen layer, homogeneous boiling and multiple re-flections, are considered and applied to the model. The level set approach is adopted to incorporate the L/V interface boundary conditions in the Navier-Stokes equation and energy equation. Both thermo-capillary force and recoil pressure, which are the major driving forces for the melt flow, are incorporated in the formulation. For melting and solidification processes at the solid-liquid (S/L) interface, the mixture continuum model has been employed. This paper presents the model formulation and discusses the effects of evaporation, free surface evolution and multiple reflections on a steady molten pool to demonstrate the relevance of these interfacial phenomena.