"Γ"shaped arc and its promotion method in Tri-Arc dual wire welding
The Tri-Arc dual wire welding achieves a high de-position 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 pa-per,the formation mechanism of the"Γ"-shaped arc and the heat input regulation mechanism are investigated first.The res-ults 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 forma-tion of"Γ"shape in the coupled arc.In this case,the M-arc does not touch the workpiece,rendering a lower heat input dur-ing 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 el-evating the welding torch.Simultaneously,the length of the conductive nozzle should be increased to maintaining a con-stant distance between the tip of the conductive nozzle and the workpiece.When the length of the conductive nozzle is in-creased from 30 mm to 35 mm,as the welding torch is elev-ated,the duration of the"Γ"shaped arc phase gradually ex-tends.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 re-duced the weld bead width-to-height ratios and weld penetra-tion.
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