Research on the mechanism of ultrasonic-assisted underwater laser wet welding of 304 stainless steel

The dynamic evolution of cavitation bubbles in underwater wet laser welding significantly influences the laser beam. To mitigate the adverse effects of cavitation bubbles, an ultrasonic-assisted underwater laser wet welding method is proposed. This work reports an experimental study of ultrasonic-assisted underwater laser welding 304 stainless steel at varying welding speeds, different water layer thicknesses, and different ultrasonic powers. Additionally, the high-speed photography method was used to analyze the effect of ultrasound on the movement of cavitation bubbles, and a ray optics finite element model was employed to better understand the impact of cavitation positions on the laser beam. The results indicate that, under identical process parameters, the application of ultrasonic waves controls the movement of cavitation bubbles via acoustic flow. Consequently, the weld seam is more uniform, and the width and depth are increased effectively. In addition, without ultrasonic assistance, the weld seam width and depth decrease with higher welding speeds and decrease with the increase of the water layer thickness. With ultrasonic assistance, the weld seam width decreases while the depth increases at higher welding speeds. The weld seam width and depth increase with the increase of ultrasonic power. The weld width first decreases and then increases as the water layer thickness increases, and the weld seam depth shows a decreasing trend. These indicate that the dynamic evolution of cavitation bubbles has an important impact on the weld width and depth. This study can provide a reference for achieving better weld efficiency and geometry in underwater laser wet welding.