Numerical simulation of the dynamic characteristics of weld pool geometry with step-changes of welding parameters

The gas tungsten arc welding process is an uncertain nonlinear multivariable system. In order to control the welding process, the nonlinear dynamic relationship between the weld pool geometry reflecting the weld quality and the welding parameters must be developed. A three-dimensional numerical model is developed to investigate the dynamic characteristics of the weld pool geometry when the welding current and welding speed undergo a step-change. Under the welding conditions employed in this research, the transformation periods are about 4 s for a 20 A down step-change of welding current, and about 2 s for a 20 mm min^-1 up step-change of welding speed, respectively. At the initial stage during the step-change of welding current and welding speed, the responses of weld pool geometry are quicker, but they slow down subsequently until the weld pool reaches a new quasi-steady state. Welding experiments were conducted to verify the simulation results. It was found that the predicted weld pool geometries agree with the measured ones.