Fig. 1. Schematic of experimental setup

Fig. 2. System interface. (a) Operation card module; (b) data display module; (c) signal waveform display module; (d) data processing and playback module

Fig. 3. Program chart of process parameter saving module

Fig. 4. Program chart of plasma image display and processing

Fig. 5. Program chart of data saving

Fig. 6. Program chart of data extraction

Fig. 7. Plasma morphology during laser-MIG hybrid welding

Fig. 8. Images after morphological processing and bifurcation removal processing. (a) Original image; (b) Otsu method; (c) spots removing; (d) smoothing; (e) thinning; (f) the result of bifurcation removal algorithm based on path tracing

Fig. 9. Logical diagram of proposed algorithm

Fig. 10. Results of identification. (a) Weld filler wire and workpiece; (b) action point of arc on the workpiece

Fig. 11. Laser path and laser transmission distance in plasma. (a) Laser path; (b) laser transmission distance in plasma

Fig. 12. Front surface morphology of aluminium alloy weld seam formed with laser-MIG hybrid welding

Fig. 13. Monitoring results of continuous 200 frames of plasma images

Fig. 14. Eight frames of plasma images in the same period

Fig. 15. DLTP value of eight frames of plasma images in the same period