Enhancing the deposition profile in cold spray additive manufacturing by nozzle redesign

Cold spraying is increasingly attractive as an additive manufacturing technique as it retains the original properties of the feedstock and produces oxide-free deposits. Many cold spray facilities use conical convergent-divergent nozzles for accelerating the particles; this typically creates deposits with a triangular profile, rather than an even layer, and can decrease the deposition efficiency. In the current study, this build-up issue is addressed by an axisymmetric profiling of the nozzle walls. This redesign is achieved by application of two aerospace design codes based on the Method Of Characteristics (MOC). By Computational Fluid Dynamics (CFD), the performance of a current commercial cold spray nozzle is compared with that of the redesigned nozzle profile. The CFD model uses a coupled Eulerian-Lagrangian formulation where steady Reynolds-Averaged Navier–Stokes (RANS) SST k-ω model is used to resolve the dynamics of the continuous phase and the Discrete Phase Model (DPM) is used to compute the motion of the particles. The numerical predictions show the tangible benefit redesigning the cold spray nozzle by application of classical gas dynamics. The outcome is a new nozzle shape that delivers more radially uniform deposit profiles. A higher particle velocity is obtained at the same operating conditions/costs used by the industry standard nozzle.