Influence of powder feed parameters on the powder stream in laser metal deposition (LMD) by high-speed and high-resolution imaging

Laser metal deposition (LMD) is a blown powder process used for the additive manufacturing of large components or the generation of functional geometries on semi-finished parts. In LMD laser intensity and powder mass flow distribution within the process zone must be precisely matched for a welding bead of predefined shape and a consistent layer quality. Therefore, the present work analyses the powder stream of a single injector that is commonly used for discrete coaxial nozzles in LMD. Several powder size classes are investigated in a range of 45 μm and 106 μm. The influence of carrier gas flow rate and powder mass flow rate variations on powder stream characteristics like particle velocity and propagation were determined up to a distance of 10 mm from the nozzle by high-speed imaging at a frequency of 30 kHz with a high spatial resolution. It was found that particle velocity depends mainly on carrier gas flow rate and particle size. Additionally, the measurement shows that the divergence increases for higher distances and higher particle sizes.