Plume attenuation under high power Nd:YAG laser welding

Abstract

During high-power cw Nd:YAG laser welding a vapour plume is formed containing vaporised material ejected from the keyhole. The gas used as a plume control mechanism affects the plume shape but not its temperature, which has been found to be less than 3000K, independent of the atmosphere and plume control gases. In this study high-power (up to 8kW) cw Nd:YAG laser welding has been performed under He, Ar and N2 gas atmospheres, extending the power range previously studied. The plume was found to contain very small evaporated particles of diameter less than 50nm. Rayleigh and Mie scattering theories were used to calculate the attenuation coefficient of the incident laser power by these small particles. In addition the attenuation of a 9W Nd:YAG probe laser beam, horizontally incident across the plume generated by the high-power Nd:YAG laser, was measured at various positions with respect to the beam-material interaction point. Up to 40% attenuation of the probe laser power was measured at positions corresponding to zones of high concentration of vapour plume, shown by high-speed video measurements. These zones interact with the high-power Nd:YAG laser beam path and, can result in significant laser power attenuation.During high-power cw Nd:YAG laser welding a vapour plume is formed containing vaporised material ejected from the keyhole. The gas used as a plume control mechanism affects the plume shape but not its temperature, which has been found to be less than 3000K, independent of the atmosphere and plume control gases. In this study high-power (up to 8kW) cw Nd:YAG laser welding has been performed under He, Ar and N2 gas atmospheres, extending the power range previously studied. The plume was found to contain very small evaporated particles of diameter less than 50nm. Rayleigh and Mie scattering theories were used to calculate the attenuation coefficient of the incident laser power by these small particles. In addition the attenuation of a 9W Nd:YAG probe laser beam, horizontally incident across the plume generated by the high-power Nd:YAG laser, was measured at various positions with respect to the beam-material interaction point. Up to 40% attenuation of the probe laser power was measured at positions correspon...