A study on attenuation of a Nd:YAG laser power by co-axial and off-axial nozzle powder stream during cladding

Abstract

The effects of powder stream when using different feeding nozzles on the attenuation of the laser power were investigated theoretically and experimentally. The powder streams were recorded with a high speed camera. The average velocity of the particles was obtained using standard Particle Image Velocimetry (PIV) technique. These average velocities were computed at different powder feeding rates with an industrial ILT co-axial nozzle and an off-axial nozzle. Different carrier gas flow rates and pressures were used in the experiments. The recorded images were processed with ImageJ software to acquire the divergence of the powder streams. The attenuated laser power was computed with a simple model based on mass concentration. A power meter was used to measure the transmitted laser power for the experimental verification of the calculated attenuated laser power. A Nd:YAG laser beam of 4.8 mm spot size at focus was used at 1100 W. The calculated laser power transmitted through the powder stream, agrees with the experimental values within 5% of error margin. The results indicate that the attenuation of laser power is less with the off-axial nozzle as compared to co-axial nozzle under the same test conditions. Clad tracks were produced with two different types of feeding nozzles. The cross sections of clad tracks were prepared with standard metallographic procedures to investigate the geometry of the clad, dilution and the heat penetration. The relation between the geometry of a clad and corresponding transmitted laser power was investigated. The results indicate that there is a minimum threshold laser power that is required to produce clads with adequate metallic bonding.