A STUDY ON PARAMETER OPTIMIZATION WITH NUMERICAL HEAT-CONDUCTION MODEL FOR CIRCUMFERENTIAL GAS TUNGSTEN ARC (GTA) WELDING OF THIN PIPES

One of the important problems to be solved in welding engineering is to develop a mathematical method for the determination of optimum process parameters, In order to estimate the optimal process parameters in circumferential gas tungsten arc (GTA) welding of thin pipes, an objective was chosen to maintain a uniform bead width over the full circumferential joint, while the constraints consist of the capacity limit of the welding power source and equipment used. A transient three-dimensional finite difference model (FDM) of the heat conduction flow in the circumferential GTA welding of pipes was adopted for calculating the temperature field considering the temperature-dependent thermal properties of the workpiece, and consequently for determining the resultant bead width in circumferential welding of the pipe workpiece. An efficient optimization model for the numerical heat conduction flow was proposed to evaluate the optimal welding current with a given welding velocity for a required bead width. Its solution was obtained by employing the steepest descent method (SDM), where the initial value of the welding current was estimated by using the linear complementary problem (LCP), and the welding currents in the middle part of the pipe were interpolated by the least-squares approximation method of the second order. The experimental results of the bead formation showed that the developed mathematical model can be effectively applied to obtain the optimal welding condition in circumferential welding of thin pipes, especially thin pipes with a small diameter and high thermal conductivity.