Numerical investigation of the arc properties in gas tungsten arc-based additive manufacturing

During gas tungsten arc-based additive manufacturing (GTA-AM), the arc is burning between a tungsten electrode and a deposited wall. With the increases in the built height, the arc behaviour becomes much different from that in gas tungsten arc welding (GTAW), in which the workpiece is keeps flat relatively. In present research, the arc properties in GTA-AM process were investigated via a numerical model including the effect of the surrounding air; the arc properties and the air transport and distribution were exhibited; the effect of the arc current on the arc properties and the air diffusion were examined. It is found that the arc is burning astride the deposited wall, altering the arc shape and peripheries significantly. A backward flow forms near the side surface of the build due to the abrupt drop of the deposited wall surface; such flow results in the air transport from the surrounding region to the inner part of the arc. Consequently, a relatively high concentration of the air occurs adjacent to the built wall, which, to a large extent, is an important reason for the oxidation and the shielding effect degradation of the layer during WAAM. In addition, the coverage of the arc plasma over the wall extends with the increased arc current surveyed, while the air diffusion towards the wall becomes intensified and its concentration presents a huge surge in this region, implying an aggravated oxidation and worsen shielding of the wall. The numerical results were in fair agreement with the experimental ones obtained by shadowgraphy technique.