Fig. 1. Laser-MIG hybrid welding experimental system

Fig. 2. Flow chart of droplet transition feature extraction. (a) Original image; (b) preprocessed image; (c) arc ROI images; (d) binary images; (e) edge extraction images; (f) droplet images

Fig. 3. Schematic of droplet feature extraction

Fig. 4. Schematic of forces affecting droplet

Fig. 5. Analysis of droplet transition features. (a) Experiment 15#; (b) experiment 10#; (c) experiment 11#; (d) experiment 12#; (e) experiment 13#; (f) experiment 14#

Fig. 6. Distribution of droplet barycenter (experiment 10#)

Fig. 7. High-speed photographs of droplet transition (experiment 10#). (a) Steady state; (b) destabilization

Fig. 8. Effect of laser power on droplet transition features. (a) Effect on droplet velocity and position; (b) effect on droplet transition frequency and extreme of arc ROI area

Fig. 9. Weld surface formation. (a) Sound weld; (b) uneven width; (c) uneven height

Fig. 10. Analysis of weld surface formation. (a) Experiment 10#; (b) experiment 12#

Fig. 11. Three-dimensional time-frequency spectrum and top view. (a) Short-time Fourier transformation frequency spectrum; (b) logarithmic power spectrum after processing

Fig. 12. Effect of welding parameters on droplet transition. (a) Effect on droplet transition period; (b) effect on standard deviation of droplet transition period and spectral entropy of power spectrum

Fig. 13. PSD instantaneous spectral entropy. (a) Experiment 3#; (b) experiment 4#