Study on forming mechanism of appearance defects in rotating arc narrow gap horizontal GMAW

In horizontal position welding process, the key problem is the poor weld formation and weld defects induced by the downward motion of the molten metal. Base on the research results of welding process, droplet transfer, molten pool behavior, temperature field, reasons, and solutions of the typical weld appearance defects in rotating arc narrow gap horizontal GMAW are studied. The causes and mechanisms of the defects of sagging surface, under cut, and convex surface are explored. The relationship of the defects and the welding parameters is established. The main causes of the appearance defects can be classified into three categories. The first one is the excessive heat input of the welding process, the second one is unstable welding process, and the third one is the mismatch between the fusion area of base metal and filling metal. Finally, the optimum welding parameters of rotating arc narrow gap horizontal welding are determined.