Parametric Optimization of a Cold Spray Nozzle

Cold spraying is increasingly attractive as an additive manufacturing technique as it retains the original properties of the feedstock and it can produce oxide-free deposits. Cold spray can use different metallic powders to produce additive layer manufacturing coats. A uniform particle distribution of uniform velocity is desirable to achieve a good quality metal deposition. Two aerospace design codes based on the Method of Characteristics (MOC) are used to define axisymmetric convergent-divergent cold spray nozzle shapes of smooth, S-type profile. The goal is to improve on the metal particle delivery of the Impact 5/11 type 40 commercial nozzle, which has conical walls. The nozzle inner wall parametric surface is varied by changing the nozzle inlet conical angle in the convergent, the throat radius of curvature, and the peak slope in the divergent. The effectiveness of the redesigned nozzles is tested numerically by Computational Fluid Dynamics (CFD), using a coupled Eulerian-Lagrangian formulation, in which the steady gas expansion is computed by a Reynolds-Averaged Navier-Stokes (RANS) Shear Stress Transport (SST) k-ω model and the particle motion is determined by the Discrete Phase Model (DPM). Then, the design performance is assessed by evaluating a multi-objective penalty function for the different nozzle shapes. The penalty function combines some of the most desirable characteristics in cold spraying, namely: a high particle impact velocity, a good spatial uniformity in this velocity, and a good uniformity of the radial distribution of the particles. Finally, the performance of the best performing cold spray nozzle shape within the parameter space investigated is compared with that of the commercial conical convergent-divergent nozzle. This study has shown the potential of this integrated, multi-objective, parametric design approach that can be built up in complexity to further improve the deposition performance of cold spray nozzles.