During a laser welding operation, the assist gas isusually brought by a nozzle directed towards theinteraction zone with a given inclination angle. A fewtens liters per minute, and a several millimeters nozzleradius are the usual parameters of welders to assist alaser welding operation. Previous studies showed thatthe assist gas flow influenced laser mater interaction,process stability and weld quality. In this study, theparametric influence related to the shielding gas fortwo types of protections : Back Protection (noted BP,gas flow in the welding direction) and Front Protection(noted FP, gas flow in the opposed welding direction)were investigated through statistical analysis of weldbead seam cross sections. This analysis showssignificant differences between the two protections.The assist gas velocity effects on laser materinteraction and process stability for a FP is much betterthan for a BP: The FP comparatively to a BP canincrease by 15 % the penetration depth and reduce bymore than 40 % the penetration depth fluctuations. Themorphological weld bead seam characteristicfluctuations (as the spiking phenomena) were mainlyattributed to the plasma plume fluctuations. In additionthe BP ensures a better welding pool protection againstoxidation than the FP.
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