Control Mechanism of Droplet Transfer in Underwater Wet Pulsed Current Welding

The formation mechanism of repulsive transition in underwater wet welding was firstly analyzed. Affected by the aqueous environment, molten droplets during underwater welding are subjected to combined effect of multiple forces. The gas pressure, gas drag force, and plasma flow force acting on the droplet fluctuate dynamically with the generation location of arc bubbles and the position of cathode spots. These forces together serve as the main driving forces for the repulsive transition of the droplet. The surface tension impedes lateral detachment of the droplet from the wire tip, while gravity facilitates droplet separation from the wire tip to complete the transition. The influence of pulse frequency, duty cycle, and peak current on weld formation, droplet transfer, and welding stability in underwater wet welding was investigated using the orthogonal experimental method. The weld reinforcement variation coefficient was adopted to evaluate formation quality. The results indicate that optimal welding performance is obtained at a duty cycle from 15% to 20%, a peak current of 350 A, and a pulse frequency of approximately 20 Hz. By applying pulsed current during the peak current phase, the electromagnetic contraction force acting on the droplet is significantly enhanced, promoting droplet transfer and increasing the transition frequency.