Study Of Twin-Wire Indirect Arc Welding Technology By Bypass Coupling

Twin-wire Indirect Arc Welding(TWIAW)is a novel welding technology.Compare with conventional Gas Metal Arc Welding(GMAW),the most obvious difference is that the workpiece doesn't connect to the electrode while the arc burns between two wires.The workpiece is melted by part of indirect arc heat and the superimposed droplet heat.This welding method has the advantages of high deposition efficiency and low heat input.However,it is easy to form lack of fusion due to the low heat input of workpiece.The bypass coupling technique was employed on TWIAW to improve its penetration in this paper.A new welding method called Bypass Coupling Twin-wire Indirect Arc Welding(BC-TWIAW)is proposed.By adding a bypass current to the base metal,an arc is formed between the base metal and one of the wires coupling with the indirect arc of the twin-wire.The penetration and the reinforcement can be well-controlled by adjusting the current between the workpiece and the wire.This welding method has the characteristic of high deposition efficiency while the heat input of the workpiece also can be controlled.The effect of the workpiece polarity to welding procedure is studied.When the workpiece is connected to the anode,the welding bead cannot be fused well under low welding current or little workpiece current in BC-TWIAW.When larger welding current is employed,although the welding efficiency is high,the welding process is unstable with large spatter and easy to form pores and incomplete fusion..When the workpiece is connected to the cathode,a well-formed welding bead could be obtained even under the low total welding current conditions.Cathode-wire current can be adjusted by changing cathode wire feeding speed.The deposition efficiency increases with the increase of cathode-wire current.Under the same total current condition,the deposition and dilution rates of twin-wire indirect arc welding with bypass coupling is about twice and a third those of conventional gas metal arc welding,respectively.With the increase of the cathode-wire current in BC-TWIAW,high-speed camera observation results indicated that the arc shape changes from bell shape to broom shape and then triangle shape to bell shape again,while the cathode droplet transfer mode changes from free transfer to contact transfer.The anode transfer mode always keeps globular transfer,while the transfer period increases a little.The repulsion force of the anode droplet to the cathode wire increases with the increase of the cathode-wire current.The corrosion resistance of austenitic strainless steel surfacing layer prepared by BC-TWIAW was investigated by electrochemical testing.The result shows that the surfacing layer has good pitting corrosion resistance and intergranular corrosion resistance.This is attributed to the small heat input of the welding process,the short residence time of the welding layer at high temperature can effectively avoid the precipitation of Cr23C6.Therefore,the surfacing layer has high corrosion resistance.