Theoretical and Experimental Investigation of Gas Flows, Powder Transport and Heating in Coaxial Laser Direct Metal Deposition (DMD) Process

The results of theoretical and experimental investigations of direct metal deposition (DMD) processes involving a CO 2 -laser with the power up to 5 kW and wave length of 10.6 μm are presented. The physical and mathematical model of multi-layer gas flows with gas-jet transportation of metal powder particles has been developed. To simulate the flows of carrier and shaping gases in annular channels of a triple coaxial nozzle, Navier-Stokes equations were applied for an axisymmetric flow. Thermodynamics and powder particles transport are calculated from a discrete-trajectory model with due regard to particle collision with solid walls of the transport nozzle. It is shown that particles may overheat on their way between the nozzle and substrate; the overheating depends on the trajectories by which particles move, on their size, and time of their retention in the laser-radiation region. The results of performed experimental researches on DMD processes visualization are presented. Some results of numerical simulation and experimental data are compared and analyzed.