Research On The Characteristics And Droplet Transfer Behavior Of Laser-MIG Arc Pulse Coordinated Hybrid Welding

When the heat sources of laser and arc are close to each other and the arc is guided,the traditional continuous laser-pulsed MIG hybrid welding will hinder the droplet transfer on the one hand,and it is easy to have a phenomenon such as "multiple pulses form a large drop".On the other hand,due to the influence of vaporized metal at the end of the wire,the laser plasma tends to increase height and expand,so the laser energy will lose a lot.Therefore,in order to ensure a smooth transfer of the droplets,the distance between two heat sources is generally increased,but this will reduce the hybrid welding interaction and penetration effect.Aiming at the above problems,this paper proposed a pulsed laser-pulsed MIG arc synchronous coordinated hybrid welding method to improve the behavior of droplet transfer and suppress the splash and laser plasma expansion by controlling the pulse phase matching of two heat sources.A set of signal acquisition and trigger synchronization control system was established.At the same time,the plasma and droplet transfer behavior of the hybrid welding process was observed by high-speed camera.The main research results are as follows:The dynamic behavior and interaction of continuous laser plasma and pulsed MIG plasma were studied.The results showed that the laser plasma expanded and increased height during the rising and falling period of the arc current.During the period of peak arc current,the particle density in plasma above the keyhole was very high.These would affect the transmission efficiency of laser energy.During the period of base arc current,the wire vaporized the metal less,and the laser plasma did not appear to expand and increase height.Combined with the waveform change of the hybrid welding arc current and voltage signals,it was found that during the period of pulsed MIG arc ignition,the arc would first interact with the high-power laser plasma.Since the actual arc length was large due to the interaction at the beginning of the peak period,the arc voltage became high.This leaded to a reduction in arc current.Therefore,the Joule heat of the molten wire was reduced,and it was easy to have a phenomenon such as "multiple pulses form a large drop".The droplet force model of laser-pulsed MIG hybrid welding was established.It was found that in the peak period,the anti-phase mode hybrid welding added low-power laser would reduce the amount of metal vapor emission and reduce the force of metal vapor reaction that hindered the droplet transfer.At the same time,it would reduce the electrical charge flow effect,so that the direction of the electromagnetic force is more biased toward the axis of the wire.And it would reduce the arc length to make the arc shape more divergent at the peak.These would promote the transfer of the droplet along the wire axis and reduce the splash.At the same time,in the anti-phase coupling mode,the droplets would fly into the molten pool in the front of the keyhole,avoiding the influence of the laser beam on the droplets in flight.The effect of distance between laser and arc on weld formation and quality was investigated.It was found that as the distance between the heat sources increased,the area of the arc plasma decreased and the degree of expansion of the laser plasma decreased.As the distance between laser and arc increased from 3mm to 7mm,the penetration depth of continuous laser-pulsed MIG hybrid welding increased first and then decreased,while the optimized anti-phase mode hybrid welding has been reduced.It showed that when the distance between laser and arc was small,adding high-power laser during the peak of the arc current would cause loss of laser energy.At the same time,the welded joint of the anti-phase mode hybrid welding had lower heat input,and the columnar crystals of welded joint were thinner and shorter.The effects of different coupling methods on weld porosity defects were investigated.The results showed that the continuous laser-pulsed MIG hybrid weld had a high porosity,reaching 1.92%.The porosity of optimized anti-phase mode hybrid welding was only 0.36%.It has been found that the addition of pulsed lasers with optimized regulation can suppress the expansion of the laser plasma above the keyhole,and to some extent avoid the generation of pores.