Fig. 1. Schematic of laser and arc position

Fig. 2. High-speed camera and DAQ system

Fig. 3. Variations of current and voltage under different laser powers. (a) 4 kW; (b) 4.5 kW; (c) 5 kW; (d) 5.5 kW

Fig. 4. Influence of laser power on the probability density of current and voltage. (a) Current; (b) voltage

Fig. 5. Schematic of droplet stress

Fig. 6. Short-circuit droplet transition process of Section A under 4 kW laser power

Fig. 7. One droplet every two pulses transition process under 5.5 kW laser power

Fig. 8. Droplet transition processes under different laser powers

Fig. 9. Influence of laser power on diameter of droplets and position of droplets falling into the molten pool. (a) D_w; (b) D

Fig. 10. Spatters formation process on the front keyhole wall. (a) Laser power is 4 kW; (b) laser power is 5.5 kW

Fig. 11. Spatters formation process on the rear keyhole wall

Fig. 12. Schematic diagram of spatters formation process on the keyhole wall

Fig. 13. Influence of laser power on the number of spatters on the keyhole wall