A more precise unified model to describe comprehensive multiphysics and multiphase phenomena in plasma arc welding

Abstract

Plasma technology involves complex and coupled electric, magnetic, thermal and hydrodynamical interaction. It’s important to understand all the multiphysics mechanism for a wider industrial application. A 3D unified model was established, which includes a combination of hydrodynamical equations, heat transfer equation and electromagnetic equations, to comprehensively describe the electro-thermal conversion, electromagnetic effect, heat transfer, gas-liquid two-phase flow and solid-liquid phase change in plasma arc welding (PAW). Volume of Fluid method was used to track the gas-liquid interface of plasma arc and liquid metal pool, and an enthalpy-porosity technique was used to deal with the solid-liquid phase change during the welding process. The transient evolutions of temperature field, flow field and keyhole in the entire PAW process were predicted, and the distribution of electric potential and current density was obtained. It is found that there are high potential drop and current density near the electrode tip, which generates very high arc temperature and arc velocity. Plasma arc gradually melts the metal, then pushes the liquid metal to flow upwards along the keyhole surface, and finally penetrates through the workpiece, forming a “reversed bugle-like” configuration. Experiment was conducted with a plasma arc welding system, and it is found that both weld pool and keyhole geometry predicted by the model generally agree with experimental results. The calculated electric potential and full-penetration time also coincide with the experiment. It’s for the first time to give a relatively accurate prediction of electric potential drop and full-penetration time in unified PAW models. The research provides a deep and fundamental understanding of the comprehensive electric-magnetic-thermal-hydrodynamical multiphysics and gas-liquid-solid multiphase interaction in PAW process.