"Γ" shaped arc and its promotion method in Tri-Arc dual wire welding

The Tri-Arc dual wire welding achieves a high deposition rate and low heat input by redistributing the heat input through an intermediate third arc called M-Arc. The M-arc is coupled to the main arc and exhibits "Γ" and "μ" shapes and their mirror images throughout the dynamic cycle. In this paper, the formation mechanism of the "Γ"-shaped arc and the heat input regulation mechanism are investigated first. The results indicate that the "Γ" shape evolves from the "μ" shape, the oscillation of adhered molten droplets induces a variation in the distance between two wire ends, thereby facilitating the formation of "Γ" shape in the coupled arc. In this case, the M-arc does not touch the workpiece, rendering a lower heat input during welding than the "μ"-shaped arc. In order to enhance the low heat input effectiveness of the Tri-Arc dual wire welding, the alteration of the distance at two wire ends is achieved by elevating the welding torch. Simultaneously, the length of the conductive nozzle should be increased to maintaining a constant distance between the tip of the conductive nozzle and the workpiece. When the length of the conductive nozzle is increased from 30 mm to 35 mm, as the welding torch is elevated, the duration of the "Γ" shaped arc phase gradually extends. This extended duration effectively facilitates arc thermal distribution, consequently reducing the heat input during Tri-Arc dual wire welding. As a result, peak value of the highest temperature within the molten pool diminishes, thereby reduced the weld bead width-to-height ratios and weld penetration.