Numerical analysis of low-current arc characteristics in micro-TIG welding

A semi-empirical two-temperature (2-T) arc model is developed to study the near-electrode regions and thermal non-equilibrium characteristics of low-current arcs that employ pin-to-pin electrodes in micro-tungsten inert gas (TIG) welding. Special emphasis is given to accurately depict the electrodes-arc attachment area and the spatial distributions of plasma temperature in 1-4 A argon arcs. The conditions of thermal non-equilibrium, as well as the coupling of the arc plasma and the cathode, are considered. The simulated electron temperature distributions are in good agreement with the arc appearances captured by the high-speed camera, and the predicted arc voltage is only 1.8 V lower than the experimental data. In contrast to TIG welding arcs that operate at higher currents, the temperature contours of the low-current arc column are parallel but slightly expanded in the vicinity of the electrodes. As the arc current decreases, the near-cathode voltage drop increases substantially. The electron temperature in the center of the arc column is almost constant, while the heavy particle temperature drops significantly, causing the arc column to contract. The heat flux at the center of the anode surface does not change as the arc current increases, but it increases significantly outside the 0.25 mm radius.