Internal characteristic of droplet and its influence on the underwater wet welding process stability

Based on an X-ray imaging system, the characteristic of underwater wet welding droplets was revealed, which was deemed to be the essential factor contributing to the unstable underwater wet welding process. By observing the X-ray images, it is confirmed that the inflation-exhaustion process in the droplet occurred during the entire process from the droplet forming to entering into the molten pool. The void in the droplet leaded to lower gravity and greater repulsive force and deteriorated the welding process stability. On the one hand, the spatter-like droplet transfer mode was relatively easy to occur, increasing the frequency of the droplet repelled spatter. On the other hand, the arc easily broke and the arc stability was deteriorated. In addition, the droplet rupture process tended to promote the generation of gas escaping spatter. The process was effected by material gas solubility, the surface tension, the temperature according to the establishing force models.