An analytical model of beam attenuation and powder heating during coaxial laser direct metal deposition

In the laser direct metal deposition process, interaction between the laser beam and powder from a coaxial powder delivery nozzle alters the temperature of powder and the amount and spatial distribution of laser intensity reaching the deposition melt pool. These factors significantly affect the process and are also important input parameters for any finite element or analytical models of the melt pool and deposition tracks. The analytical model in this paper presents a method to calculate laser attenuation and powder temperatures at every point below such a nozzle. It is applicable to laser beams that are approximately parallel over the beam -powder interaction distance of any initial intensity distribution (Top Hat, Gaussian, TEM01* or other). The volume below the nozzle is divided into the region above the powder consolidation plane, where the powder stream is annular, and below it, where it is a single Gaussian stream, and expressions derived for each region. Modelled and measured results are reasonably matched. Results indicate that attenuation is more severe once the annular powder stream has consolidated into a single stream but is not zero before that point. The temperature of powder reaching any point is not constant but the mean value is a maximum at the centre of the stream.