An improved simulation of heat transfer and fluid flow in plasma arc welding with modified heat source model

摘要

A three dimensional numerical model is developed to investigate the plasma arc welding (PAW) process, featured by the compound volumetric heat source movement and heat transfer with phase change in the weld pool, where fluid flow is driven by a combination of surface tension, electromagnetic and buoyancy forces. Based on the actual configuration of PAW welds, a modified heat source model is proposed to involve the key-holing effect of PAW. It is composed of a double-ellipsoidal volumetric heat source at the upper and a conical volumetric heat source at the lower. It is proven that the modified heat source model as well as fluid flow consideration can improve the PAW simulation. The predicted weld bead is in good agreement with the experimental results, along with the hump in the fusion line. The effect of fluid flow in molten pool is indicated to be non-negligible. In addition, the evolution of the weld pool is presented along with the temperature field and velocity field. A discussion is made on the process parameters such as plasma arc power and welding speed. It turns out that high plasma arc power or/and low welding speed is beneficial to complete joint penetration, but optimum process parameters are good choice to ensure both the high weld quality and complete joint penetration.