Study Of Pulsed Plasma-MIG Coupling Principle And Droplet Transfer

Plasma-MIG welding is composed of Plasma arc and MIG arc,this welding also has a high melting rate,and improves arc energy density.Protection of droplet and welding pool by plasma arc decreasesweld porosity,suitable forwelding sheet aluminum alloy at a high speed andThick aluminum alloy in a big penetration.In this paper,according to the principle of plasma-MIG complex welding,establish the plasma-MIG welding plantform under the existing conditions in the laboratory,and a data acquisition system that synchronizing the high-speed camera and arc variables is developed to precisely analyze the droplet transfer of Pulsed Plasma-MIG hybrid welding.Based on the existing research of plasma-MIG welding,studying the coupling principle of plasma-MIG welding in-depth,find that both arc works in DCEP,no matter how large the voltage difference between plasma arc and the wire in the plasma arc,no current flows into or out of the wire side,the main reason is that the wire surface is smooth and can not form a tip discharge.Analyze the composite properties of plasma arc and MIG arc,found that the plasma arc voltage in the composite arc was higher than that of the plasma arc welding alone,wire extension and arc of MIG have different potential characteristics,compared to a separate plasma arc welding,Further study found that the voltage of plasma arc surrounding the wire increases,the voltage of plasma arc surrounding the MIG arc decreases.So we can know the effect of the MIG arc on the static behavior of the plasma arc is mainly through the change in the melting position of the droplet;Changed the plasma current and melting position of the wire,we find that the effect of plasma arc on MIG arc is mainly through the change of heat input to the wire,and this coupling characteristic makes the welding process unstable to establish a new melting balance,the wire current fluctuation amplitude compared to the individual MIG welding reduced.Study on droplet transfer of plasma-MIG composite welding by synchronous acquisition system,droplet size is reduced by increasing the plasma current and maintaining the MIG current constant.Analysis the forth of droplet transfer,we find that the plasma drag forth generated by the plasma arc promotes the droplet transfer.The plasma current can effectively reduce the droplet temperature without passing the wire,and the plasma arc has a strong penetration capability and a great advantage in the thick plate welding.Thus we propose a new control method of droplet transfer,the plasma current is modulated into a pulse shape,using the plasma drag forth promote droplet transfer,heat input of wire and weld separately controlled,achieve the deep welding on aluminum alloy plate.Through a large number of experimental studies,one droplet with one pulse procedure of pulse plasma-MIG welding was found when the wire feed speed is 6.9m / min.The base metal is a 5083 aluminum alloy with a thickness of 8 mm,Welding current is 190 A,while welding speed is 0.18 m / min,the weld is penetrated;Feeding speed increased to 11.5m / min,find one droplet with one pulse procedure,welding current is 250 A,while welding speed is 0.35 m / min,the weld is penetrated.The experimental results show that the pulsed plasma-MIG composite welding has obvious advantages in weld penetration ability,but pulsed plasma arc is introduced,the process parameters are increased and the optimum welding process is difficult to find.