Analysis of the Agglomeration of Powder in a Coaxial Powder Feeding Nozzle Used for Laser Energy Deposition

Abstract

To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique, the influence of several parameters must be carefully assessed. In the present study the problem is addressed by means of numerical simulations based on a DEM-CFD (Discrete Element Method and Discrete Element Method) coupled model. The influence of the powder flow concentration, powder flow focal length and the amount of powder at the nozzle outlet on the rate of convergence of the powder flow is considered. The role played by the nozzle outlet width, the angle between the inner and outer walls and the powder incident angle in determining the powder flow concentration is also considered. The results show that, with increasing of nozzle outlet width, the powder flow concentration per unit volume at the nozzle focal point undergoes a non-mono-tonic behaviour (it first increases and then decreases). When the nozzle outlet width δ is 1.00 mm, the powder flow concentration at the focal point is maximal and the powder flow convergence can be considered optimal. By increasing the angle between the inner and outer walls, the powder flow concentration related to the upper focus decreases, the focus diameter increases and the powder flow aggregation worsens. The powder flow concentration increases first and then decreases with increasing incident angle. When the incident angle θ is 30°, the powder flow exhibits the best agglomeration properties. When the outlet width is smaller, the angle between the inner and outer walls is larger, and when the incident angle is set at 30°, the powder flow concentration of the coaxial nozzle can be effectively improved.