Characterization of molten pool behavior and humping formation tendency in high-speed gas tungsten arc welding

The humping defect which easily forms in high-current and high-speed gas tungsten arc welding (GTAW) severely deteriorates the homogeneity of weld properties. However, the complicated and multi-coupled transport phenomena in molten pool make the quantitative characterization of humping formation tendency difficult. In this paper, dimensionless groups containing characteristic heat and fluid-flow variables of molten pool are determined based on Buckingham π-theorem. These groups with clear physical implication correspond to important and peculiar molten pool behaviors during humping formation, and they can be combined to evaluate humping formation tendency. Scaling analysis is then employed to study the molten pool behaviors in high-speed GTAW, in which the analytical equations between characteristic molten pool variables and process variables are formulated. The scaling laws are well verified and calibrated by numerical data from a numerical heat transfer and fluid flow model. The dimensionless groups and scaling equations show an explicit relation between process variables and humping formation tendency. The proposed methodology has low computational intensity, and can be easily applied to give a quantitative description of humping formation tendency at different welding parameters and to predict humping formation.