Study of the solidified thin layer on molten pool surface in laser deep penetration welding

Abstract

Morphology and temperature are two important features of molten pools in laser deep penetration welding. An experimental platform equipped with a high-speed camera and a two-color pyrometer was built to observe the variations in the morphology and temperature, and a floating layer on the surface of a molten pool was discovered. The floating layer’s morphology, temperature, and thickness were described, and there was a correlation between the morphology of the floating layer and the temperature distribution of the molten pool. The results revealed that the variation range of floating layer thickness is primarily related to three factors: the floating layer area, the molten pool’s temperature, and the inclination angle of the floating layer immersed in the molten pool. Surface tension is an important factor in allowing the solidified thin layer to float on the surface of the molten pool. During laser deep penetration welding, the floating layer area goes through three stages during laser welding: growth, reduction, and dynamic stabilization. Finally, the floating layer abbreviated as “STL”, is defined as the solidified thin layer. As the laser power increases, the STL area decreases and the weld reinforcement is lower. Weld reinforcement is linearly related to the STL area. In summary, this study’s results provide a theoretical foundation for predicting the welding quality in laser deep penetration welding in the future.