Numerical study on powder stream characteristics of coaxial laser metal deposition nozzle

A 3D model was established to accurately simulate the internal and external powder stream characteristics of the coaxial discrete three‐beam nozzle for laser metal deposition. A k‐ε tur-bulence model was applied in the gas flow phase, and powder flow was coupled to the gas flow by a Euler‐Lagrange approach as a discrete phase model. The simulated powder stream morphology was in good agreement with the experimental results of CCD and high‐speed camera imaging. The simulation results showed that the length, diameter and shrinkage angle of the powder passage in the nozzle have different effects on the velocity and convergence characteristics of the powder stream. The influence of different particle size distribution and the inner laser shielding gas on the powder stream were also discussed in this study. By analyzing the powder stream caused by different incident directions of powder passage, and the collision process between powder and the inner wall, the basic principle of controlling powder stream convergence was obtained.