Numerical investigation of gas-disperse jet flows created by coaxial nozzles during the laser direct material deposition

The paper presents the results of modelling of powder transport during the laser direct material deposition, involving standard coaxial nozzles made by Trumpf and Precitec and radiation of a СО2-laser with the power up to 4 kW. The patterns of particle trajectories positions are shown in the space for various geometries of coaxial nozzles (the double and triple ones). It is shown that collisions of particles and walls of the transport channel impose the governing effect on the particle trajectories, geometry of the powder jet, and density of particle's distribution in the flow and on the substrate. Inelastic collisions with walls cause velocity decrease after the reflection, which has a positive effect on the powder flow profile and focusing. Heating of particles depends on the position of their trajectories and residence time in the high-intensity radiation area. It is also shown that the triple coaxial nozzle has wider options to control the gas-disperse flows than the double coaxial nozzle. The preferable position of the substrate, 20 ± 5 mm, is found by calculations; here, the focusing of the powder jet into the laser spot and heating of the super-alloy Ti-6Al-4V particles in the radiation field are optimal. The results can be used to improve the laser cladding and direct material deposition process.