Using the multi-wire GMAW processes for controlling the formation of humping

Three-dimensional numerical models are established to investigate the convection in multi-wire GMAW processes. A high-speed photography system is used to capture the transient images of the weld pools. Based on the simulation and experimental results, the humping formation and suppression mechanisms are discussed. The results show that both the Bpush-pull" and outward flow patterns exist in the multi-wire GMAW weld pools, which help decrease the momentum of the backward fluid flow and widen the weld width. In high-speed GMAW process, there are three main factors that cause the formation of humping: the high momentum of the backward fluid flow, the capillary instability, and the large variation of the capillary pressure of the liquid channel in the welding direction. In twin-wire GMAWprocess, the first two factors are suppressed, humping is disappeared, but the variation of the capillary pressure of the liquid channel in the welding direction is still large, which causes the weld width uneven. All of those three factors are suppressed in triple-wire GMAW process, so sound weld bead can be obtained; the distance between the middle wire and trailing wire has little influence on the weld bead formation.