Numerical Analysis of Nitrogen Atmosphere Mixing in GTA Welding

Mixing behaviors of the nitrogen into the arc plasma in GTA welding is studied by numerical analysis. The whole region consisted of a tungsten cathode, an arc, a shield nozzle and a water cooled cupper anode is treated in the unified two-dimensional numerical model. Simulation results show that the argon arc has higher shielding gas concentration compared with the helium arc. Additionally, it is assumed that the shielding gas concentration in the arc plasma is affected by the shielding gas density and the diffusion coefficient. Lower gas density reduces the shielded area and higher diffusion coefficient increases the nitrogen mixture in plasma region of high temperature range. The reduction of shielding gas concentration in helium arcs, especially, is caused by the higher diffusion coefficient of the helium plasma.