Study of spatter net forming mechanism and penetration mode under flexible ring mode laser welding

Abstract

Flexible ring mode (FRM) laser technology can generate different powers by adjusting the power ratio of the inner and outer rings, and has great potential for welding copper and its alloys with high reflectivity. This paper used a high-speed photographic camera to monitor the behavior and spatter-forming process of molten pool on the front of red copper plate. The spattering behavior in different penetration modes and net forming mechanisms under FRM are revealed. The results show that full penetration causes the high-temperature vapor to escape from the upper and lower openings. More energy is absorbed by the molten pool and keyhole in the semi-penetration mode, forming an expansion zone and increasing the pool's instability. The outer ring laser of FRM reduces the temperature gradient, which can lower the surface tension gradient, making the flow of the molten pool smoother and the height and formation times of the liquid column lower and less, thereby reducing the spatter. Moreover, FRM laser produces a larger and more stable keyhole, making the escape of metal vapor easier and minimizing the kinetic energy. The reasons above bring the sound result of high yield rate, improved by 75%, comparing with pure Gaussian laser. This paper provides theoretical guidance for engineering researchers to understand the role of shaping laser beams in the welding of highly reflective materials.