Effect of Weld Pool Flow and Keyhole Formation on Weld Penetration in Laser-MIG Hybrid Welding within a Sensitive Laser Power Range

The weld penetration variation in laser-MIG hybrid welding under sensitive laser power range was investigated by welding experiments and CFD (computational fluid dynamics) simulation. During this investigation, joints of AH36 sheets were welded with varying laser powers by the laser-MIG hybrid welding process. In addition, the CFD model was established based on experimental parameters and measurement results. Moreover, surface tension, electromagnetic force, buoyancy, recoil pressure, evaporative condensation, evaporative heat exchange, melt drop transfer, and other factors were considered. The influence of various factors on molten pool depth and keyhole depth were studied, including temperature, velocity, and flow direction of liquid metal. The results show that the weld-forming effect is better at the laser power is 7.5 kW in the range of sensitive laser power. After the keyhole is formed, its depth gradually entered the stage of linear increase, oscillation increase, and oscillation balance. Increasing the laser power can effectively shorten the time of the two growth stages and allow the keyhole to enter the balance stage earlier. During the oscillation balance state of the keyhole, the molten metal under the keyhole flowed to the molten pool root in the reverse direction of welding; it can also promote weld penetration.