Abstract: Based on the principles of energy and mass conservation as well as energy minimization theory within a whole system of fully-penetrated gas tungsten arc welding (GTAW) molten pool, the governing equations are derived to describe the pool surface-deformation on both sides. The solution scheme for determining the Lagrange parameter is given for the coupled upper and bottom pool surface-deformation equations which are unified with a single Lagrange parameter. Through predicting and analyzing the dynamic variation processes of both upper and bottom pool surface-deformation during the period from the weld pool formation to its quasi-steady state for GTAW stainless steel and low carbon steel, the variables are extracted to characterize and judge the condition whether the workpiece is penetrated or not. It lays foundation for realizing welds penetration control based on front-side vision inspection.

Key words: Lagrange parameter, Numerical analysis, Penetration control, Weld pool surface-deformation