THREE DIMENSIONAL TRANSIENT HEAT TRANSFER ANALYSIS FOR GTA WELDING PROCESS

摘要

It has been well recognized that the geometry of weld pool plays a fundamental role in determining the mechanical properties of weld joints. The major variables in GTA welding affeting on the formation of weld pool including welding current, voltage, welding speed, arc length, and electrode tip angle. Besides these variables, GTA welding is subject to numerous disturbances and uncertainties within and between welding cycles. These can arise from: workpiece thickness tolerances, fluctuations in welding current, voltage, welding speed, arc length, and root opening. Any or all of these complicate automation, reduce weld quality, and drive up production cost. For this reason, studying interaction and correlation of process variables, disturbances and uncertainties affecting on the formation of weld pool for GTA welding remains a major challenge and goal. In this research, a series of experiment has been conducted to investigate the interaction and correlation of welding current, voltage, welding speed, and arc length affecting on the formation of weld pool. The arc length affecting on arc efficiency and heat distribution parameter are also examined and addressed in this paper. In addition to experimental study, a three-dimensional finite element model has been developed to analyze transient heat flow and to predict the formation of weld pool. The correlation between the parameters including welding current, voltage, welding speed, arc length, open-loop response and the characteristic geometry of weld pool are established. The 3-D FEM can calculate not only the transient thermal histories but also the sizes of weld pool in single-pass arc welding. In order to obtain good weld quality, this model will determine the effect of arc length to the formation of weld. Furthermore, the effects of welding parameters on the Gaussian heat source parameters (arc efficiency and heat distribution parameter) are also studied. The experimental calibration and verification are carried out to verify the numerical model. Experimental data are consistent and in quantitative agreement with values from FEM simulations.