Modeling and comparison of the powder flow dynamics for tilted annular and discrete-outlet nozzles in laser directed energy deposition

The Laser Directed Energy Deposition (L-DED) process is gradually maturing as an Additive Manufacturing (AM) technique. It provides substantial advantages for the refurbishment, redesign or coating of high-value components, which in general, are also large in volume and mass. For such components, it becomes necessary the use of a positioner which keeps the nozzle in a normal orientation as it is displaced over the different components’ surfaces. There is little understanding on the implications of tilting the nozzle on the process efficiency, as well as on the impact of using different nozzle configurations. This work presents a detailed Computational Fluid Dynamics (CFD) analysis of the powder stream generated by two widely used types of powder-fed coaxial nozzles: annular and discrete three-outlet nozzle. For different cases of nozzle orientation, the effect of mass flow and volumetric gas flow on particle velocity and powder convergence, are analyzed. This is crucially contrasted when the two nozzle types are taken into account. Further to analyzing stream behavior, this work also presents process maps for predicting powder usage rates. It was found that the powder usage is significantly affected by the nozzle type, mass and gas setting. For instance, for the case of a narrow 1.0 mm–wide melt pool in a 90°tilt, the annular nozzle is able to achieve up to 75.0% of powder capture efficiency, whereas for the three-outlet nozzle, this usage drops to 36.0%.