Fig. 1. Schematic of electrical signal acquisition and high-speed CCD camera system

Fig. 2. Comparison between electrical signal and high-speed CCD camera images of plasma plume during deep penetration welding at welding speed of 16 mm·s-1 and welding power of 1250 W

Fig. 3. Comparison between electrical signal and high-speed CCD camera images of plasma plume during deep penetration welding at welding speed of 12 mm·s-1 and welding power of 1250 W

Fig. 4. Comparison between electrical signal and high-speed CCD camera images of plasma plume during deep penetration welding at welding speed of 8 mm·s-1 and welding power of 1250 W

Fig. 5. Comparison between electrical signal and high-speed CCD camera images of plasma plume during deep penetration welding at welding speed of 12 mm·s-1 and welding power of 1150 W

Fig. 6. Comparison between electrical signal and high-speed CCD camera images of plasma plume during deep penetration welding at welding speed of 12 mm·s-1 and welding power of 1350 W

Fig. 7. PSD plot of electrical signal at welding speed of 16 mm·s-1 and welding power of 1250 W. (a) First segment; (b) second segment; (c) third segment; (d) fourth segment; (e) fifth segment; (f) sixth segment; (g) seventh segment; (h) eighth segment; (i) ninth segment

Fig. 8. Fluctuation frequency of electrical signal under different conditions. (a) Different welding speeds; (b) different welding powers