Simulation and analysis of heat transfer and fluid flow characteristics of arc plasma in longitudinal magnetic field-tungsten inert gas hybrid welding

Abstract

In the present work, an axisymmetrical model based on the magnetohydrodynamics (MHD) is established to investigate the effect of external longitudinal magnetic field (LMF) on arc characteristics during the gas tungsten arc welding (GTAW) process. The profiles of temperature and voltage drop, distributions of axial velocity, shear stress, and arc pressure, etc., in the cases of different applied LMF strengths ranging from 0 to 0.06 T are simulated by utilizing the fluid dynamic theory coupled with Maxwell equations. In order to achieve more accurate values of heat transfer and fluid flow of arc plasma, we take the boundary layer of electrodes into consideration. The results show that the applied LMF could drive particles to rotate and expand the arc, and a negative pressure area appears at the center and induces an upward streaming of gas (i.e., anti-gravity flow) through the arc core with the effects of centrifugal force, concentrating the anodic energy to the cathode. When the magnetic induction strength is 0.06 T, vortexes are dramatically formed around the arc axis by the interaction between the anti-gravity flow from the arc center and outside downward flow from the arc fringes. Thus, the distribution of current density, anodic heat flux, and arc pressure shifts from the arc center to the periphery and forms a bimodal pattern. The various thermal fluxes and subsequent thermal efficiency are also quantitatively investigated for a better understanding of the effects of LMF on arc behaviors and the theoretical predictions show good agreement with the experimental results.