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The Effect of Gas Composition on Plasma Behaviour and Droplet Transfer in Hybrid CO2 Laser Pulsed Gas Metal Arc Welding (GMAW-P)
W. Zhang, X-M. Hua, W. Liao, F. Li and M. Wang

In hybrid CO2 laser pulsed gas metal arc welding (GMAW-P) the shielding gas is applied to isolate the molten metal from the ambient air, suppress the laser-induced plasma, remove the plume out of the keyhole, and stabilize the metal transfer. In this study a shielding gas consisting of He and Ar was used, and the effect of composition on the welding phenomena, such as behaviours of plasma generation and droplet transfer were investigated. High-speed video observation was used to investigate the welding phenomena of plasma shape and droplet transfer. Optical emission spectroscopy system was used to characterize the plasma temperature and electron number density distribution. It was found the increase of He content in the mixtures results in: (i) the arc plasma was changed from expand outward and downward to the side of the laser induced plasma; (ii) the droplets deviated from the wire axis, approached to the keyhole and were then blown away by the plasma plume from the keyhole resulting in a lot of spatters attached on the bead surfaces; and (iii) the plasma temperature distribution became more shrinkage. To obtain a relatively ideal welding process, 50% He content should be more appropriate.

Keywords: CO2 laser, pulsed gas metal arc welding (GMAW-P), steel, hybrid welding, laser-induced plasma, shielding gas, droplet transfer

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