Numerical Simulation of MIG Weld Pool in Switch Back Welding

The authors proposed the switch back welding method to make the stable back beads in the first layer weld during one side multilayer welding. In the proposed welding method, the torch motion is important to control the weld pool, i.e., the welding torch is moved backward and forward like switch back. It is important to investigate the behavior of the weld pool to get the optimum welding parameters such as the traveling speed, the forward distance, the backward distance, the welding current and so on. There are many welding parameters. In order to find the optimum welding parameters, the numerical simulations are useful method instead of the welding experiments. Since the deposited metal is considered in the numerical models of the welding in the thick plates, the numerical analysis becomes complicated. In order to simplify the analysis, the authors discussed the numerical simulations of the welding in the thin metal plates because the effect of the deposited metal can be minimized. First, the fundamental welding experiments were carried out in MIG welding. By using the experimental results, the numerical models in the switch back welding are determined. Next, the behaviors of the temperature are investigated under the change of the traveling speed and the backward distance. If the traveling speed is constant in the switch back welding, the weld pool size may sometimes become big. In this case, the burn trough may take place due to the flow in the weld pool. When the traveling speed of the forward movement is faster than backward movement, the weld pool length becomes shorter than the case of the constant traveling speed. Moreover, if the backward distance is longer than half of the forward distance of the switch back welding, the authors can obtain continuous back bead regardless of the disturbance such as the variation of the arc length, i.e., the stability of the weld pool is increased. The switch back welding method is useful to make the stable back bead in the MIG welding.