Numerical simulation of powder flow field on coaxial powder nozzle in laser metal direct manufacturing

In the laser metal direct manufacturing, gas-solid two-phase flow theory is adopted to simulate the flow field of powders in coaxial nozzle to fabricate complex parts of compact structure. The separate model in FLUENT is used to evaluate the concentration distribution rule and the focusing characteristics of the powder flow field. The results indicate that the focal concentrations of the coaxial powder nozzle in radial direction and axial direction are approximately obeyed by the Gaussian distribution. When the cone angle of coaxial nozzle is invariable, the cone ring gap is smaller, the focal point concentration in the powder flow field is bigger; the focus radius is smaller, the focal distance is also smaller, and the gathering characteristic is better. When the cone ring gap of the coaxial powder nozzle is invariable, the cone angle getting too big or too small is harmful for powder gathering. When other conditions are invariable, extreme protective gas velocity (too large or too small) is harmful for powder gathering. When the protective gas velocity approaches to 6 m/s, the gathering characteristic of the coaxial nozzle achieves its best performance.