A computationally efficient model of convective heat transfer and solidification characteristics during keyhole mode laser welding

Abstract

Computationally efficient heat transfer models of keyhole mode laser welding ignore fluid flow in the gas, liquid, and the two phase solid-liquid regions. These models cannot be applied to high Peclet number systems where convective heat transfer affects weld pool geometry, cooling rate, and other weld attributes. Here we show that by synthesizing features of an existing model to determine keyhole shape and size with rigorous fluid flow and heat transfer calculations in the liquid and the two phase solid-liquid regions, important features of both high and low Peclet number systems can be satisfactorily simulated. The geometry of the keyhole is calculated by assuming thermal equilibrium at the gas/liquid interface and point by point heat balance at the keyhole wall. The heat transfer outside the vapor cavity is calculated by numerically solving the equations of conservation of mass, momentum, and energy. A vorticity based turbulence model is used to estimate the values of effective viscosity and effective thermal conductivity of the liquid metal in the weld pool. It is shown that the temperature profile and the weld pool shape and size depend strongly on the convective heat transfer for low thermal conductivity alloys like stainless steel. For high thermal conductivity aluminum alloys, on the other hand, convection does not play a significant role in determining the shape and size of the weld pool. The computed solidification parameters indicated that the solidification structure becomes less dendritic and coarser with the decrease in welding velocity. The results demonstrate that a numerically efficient convective heat transfer model of keyhole mode laser welding can significantly improve the current understanding of weld attributes for different materials with widely different thermal properties.