Numerical simulation of gas-solid two-phase flow field on coaxial powder nozzle in laser metal direct manufacturing

In the laser metal direct manufacturing, gas-solid two-phase flow theory is considered to simulate the inside and outside flow field of coaxial powder nozzle with carrying gas to obtain cladding parts of less characteristic size and compact structure. The separate model in FLUENT is used to evaluate the concentration distribution and the powder focusing characteristics of the powder flow field. The computed results indicate that the focal point concentration of the coaxial powder nozzle in radial direction and axial direction is approximately obeyed by the Gaussian distribution. When the cone angle of a coaxial powder nozzle is invariable, the cone ring gap is smaller, the focal point concentration in the powder flow field is bigger, the focus radius smaller, the focal distance also smaller, the gathering characteristic 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, choosing the best cone angle facilitates obtaining the best gathering characteristics. When other conditions are invariable, too large or too small protect gas velocity is harmful for powder gathering. When the protect gas velocity approaches to 6 m/s, the gathering characteristic of the coaxial powder nozzle achieves the best.