Mechanism of penetration depth increase in gas-jet-assisted keyhole laser welding

0.8 mm diameter of assisted gas jet nozzle was employed to straightly blow keyhole with the incidence angle of 45° to deepen keyhole and weld penetration. A series of experiments of CO₂ laser welding of stainless steel were carried out and the images of molten pool and keyhole were captured by high speed camera. The optimized range of incident point, nozzle positions and flow rates of assisted gas jet were obtained by using the contour map, and the maximum penetration depth increased by about 38% compared with the conventional laser welding. The experimental results shows that, when the gas jet is projected the keyhole center, the introduction of assisted gas jet with the suitable flow rate is not only to suppress the plasma, significantly expand the keyhole orifice, but also to change the flow direction of the plasma inside keyhole which leads to the change of the internal flow of the molten pool. When the gas jet is projected behind the keyhole with the incident area is away from keyhole, it extrudes the liquid metal to the keyhole orifice and the tail part of molten pool which would result in hump weld.