Numerical analysis of internal flow of molten pool in pulsed gas tungsten arc welding using a fully coupled model with free surface

A fully electromagnetic, fluid flow and heat transfer coupled model with free surface is proposed to analyze the internal flow of weld pool with the strong interaction of arc plasma in pulsed gas tungsten arc welding. Governing equations are solved in the whole domain including the tungsten cathode, arc plasma and weld pool without simplifications; the level set method, the Marangoni effect and the local thermodynamic equilibrium (LTE) diffusion approximation are used to treat the interface between the plasma arc and weld pool. The originality of this paper is providing a fully coupled model both with free surface and varying surface tension gradient to reveal the oscillating behaviour of arc plasma and internal flow of molten pool in a pulsed - GTAW process, especially with high peak current and low frequency. By considering the pulsed current ranging from 80 A to 400 A with oscillating frequency of 10 Hz and validating the model with experiments, the fully coupled model shows that the multiphysics-based simulation methodology could reveal the physical essence of periodically expansion and compression of arc plasma and fluctuations of molten pool subjected to pulsed current, The dynamic variations (the current density, electric potential, magnetic flux density, temperature, arc flow and internal flow of weld pool) and driving mechanisms of internal melt flow (The Marangoni effect due to varying surface tension gradient, Lorentz force, arc pressure, shear stress) are quantitatively analyzed, the computed arc plasma behaviour and molten pool profiles are in reasonable agreement with the corresponding experimental and calculating results, revealing that the arc plasma and the molten pool both have a very fast response to the varying current as a whole electromagneto-hydrodynamic system, while the internal flow of molten pool also exhibits nonlinear characteristics as a result of the Marangoni effect. (C) 2020 Published by Elsevier Ltd.