Process control of pulsed laser enhanced metal transfer behavior in CO2 gas shielded welding

Spot pressure, as an arc repelling force, hinders the metal transfer process and has a negative effect on welding process stability in CO2 gas shielded welding. In addition, the direction of the spot pressure changes uncontrollably with the deflection of the droplet. Therefore, it is particularly critical to provide an additional force to improve droplet transfer characteristics without disturbing the arc stability. To this end, a new approach of the pulsed laser enhanced metal transfer (PLE-MT) process in CO2 gas shielded welding was proposed to control metal transfer behavior. The results demonstrate that: different from the uncontrollable deflection of droplets caused by laser incident on the solid–liquid interface (S-L-I) of the droplet, the irradiation of solid-state welding wire (S-W) can fundamentally solve the droplet deflection problem. The cut droplet can enter into the molten pool smoothly along the axis, and the change of the incident height does not significantly change the droplet's detachment velocity. The droplet’s detachment time at three different laser incident heights (0.5, 1, and 1.5 mm) remained almost unchanged, all of which were about 6–8 ms. When the wire feeding speed is 4 m/min and the voltage is 25 V, after laser irradiation is added, the metal transfer frequency increases from 5 to 25 Hz. The droplet transfer mode changes from SC transfer to spray transfer, and it avoids the short-circuit spatter. However, the metal evaporation mass produced by laser heating liquid droplet or welding wires is about 3.5% of the droplet mass. Under the condition of direct current electrode negative (DCEN), although the melting efficiency of the wire can be effectively improved, the droplet will be repelled until the arc is extinguished, and the stability of the arc will also deteriorate due to the rise of the arc. The irradiation of the pulsed laser can impede the climb of the droplet (cut off the droplet when its size is small before the arc climbs up), promote metal transfer, and improve the stability of the welding process in DCEN. While expanding the process interval of CO2 welding, an efficient spatter-free, low-pollution metal transfer process was obtained under a relatively small current through the PLE-CO2 welding process.