Droplet transfer characteristics in high-power laser–MAG hybrid welding: Influence of energy parameters

High-power laser–arc hybrid welding experiments were performed on Q345 low-alloy steel with a thickness of 10 mm, and the effects of energy parameters such as laser power, arc power, laser–arc distance, and welding speed on the droplet transfer behavior were investigated using a high-speed imaging system. The distance between the position of the droplet falling into the molten pool and the keyhole was statistically analyzed to determine the effect of the change in the droplet transfer behavior on welding stability. Results revealed that a strong reactive force from metal vapor was generated as the laser power exceeded 6.5 kW, causing the droplet transfer trajectory to shift, which enhanced welding stability. The stability of the keyhole became worse when the laser power was increased to 9.5 kW. As the arc power increased from 4096 to 6860 W, the droplet transfer mode appeared as a mixed transfer mode dominated by globular droplet transfer, projected droplet transfer, and spray droplet transfer. A single-spray droplet transfer mode was discerned when the arc power exceeded 7394 W. In this regard, the increased arc power will enhance the stability of the welding process. Excessively large or small values will lead to poor welding stability, with the former attributed to the strong mutual interference between the laser and arc and the latter ascribed to the weakened attraction of the laser to the arc. Moreover, arc stability and droplet transfer frequency decreased with an increasing welding speed.