Effect of pulse frequency on droplet transfer and weld formation in local dry underwater welding

Abstract This paper presents the effect of pulse frequency on the droplet transfer behavior and weld formation in local dry underwater welding (LDUW) based on micro-drainage device. Three different droplet transfer modes: projected transfer, globular transfer and spherical repelled transfer, were observed in the LDUW at the pulse current frequency of 25 Hz to 200 Hz. With the increase of pulse frequency from 100 Hz to 150 Hz, the direction of electromagnetic force changes, and the projected transfer becomes the globular transfer. With the increase of pulse frequency from 150 Hz to 200 Hz, the droplet transfer changes from the globular transfer to the spherical repelled transfer. The droplet transfer frequency decreases with the increase of pulse frequency. The weld formation with no obvious defects and relatedly deeper weld penetration were obtained in the mode of projected transfer, while in the mode of globular transfer, it is opposite. It is necessary to avoid the globular transfer, which would lead to the poor weld formation and minimum weld penetration.