High-resolution thermal imaging for melt pool dynamics studies in TIG welding process

Abstract

Challenges in terms of reliability still surround thermal measurement methods in welding processes. However, the temperature distribution within the weld pool can provide important resources for understanding behaviors and explaining phenomena. This work aims to study the effect of gravity on the temperature distribution within the weld pool under different welding positions using an in-house developed equipment. First, a combination of optical settings and a calibration procedure were established. Experiments were carried out with the same welding parameters under flat, horizontal, vertical upward, and vertical downward positions. The thermal field from the backside of fully penetrated thin plates was accessed using the TIG process. The device allowed a well-delimited and detailed weld pool thermal field assessment. Dimensionless numbers were quantified, and Marangoni shear stress was plotted on the weld pool surface. Along the transversal weld pool direction, a symmetrical heat distribution was stated in the flat position, while an asymmetrical one was observed in the others. The Marangoni effect played a crucial role in all the experiments, emerging as the dominant driving force in 1G and 2G positions. It governed the fluid flow within the weld pool by influencing temperature gradients over time, which, in turn, altered the direction and magnitude of shear stress on the free surface. Notably, in the 2G position, the observed asymmetry in the weld pool features may be attributed to the combined effects of buoyancy and Marangoni forces acting together. Finally, through the developed equipment, it was possible to evaluate the impacts of gravity on the heat distribution within the weld pool and demonstrate its contribution to dynamics studies.