Numerical and Experimental Analysis of Gas Flow in a Coaxial Nozzle Applied to Directed Energy Deposition (DED)

create a melt pool on the substrate. A nozzle is used to carry metal powder within a gas flow until the melt pool, concentrating the flow at the same point. Coaxial nozzles usually have also a shield gas flow to prevent oxidation and an internal flow to protect the optical system. A right flow configuration must be selected to avoid high turbulence at the nozzle exit, leading to an efficient, inexpensive, and high-quality process. Due to the complexity of the process, CFD – Computer Fluid Dynamics are becoming necessary to understand the behaviour of those gas flows in DED processes. CFD can offer results close to reality and may allow an optimization of the whole nozzle designs, besides selecting the best gas flows for each application. The present work develops a CFD simulation of the gas flow behaviour in a coaxial nozzle with three internal annular channels (internal, carrier and shield). An initial set of gas flow was selected, based on previous experience of the manufacturer, and then improved. It searches for the low gas consumption, to form a focal point coinciding with the laser focus and a low velocity, which favours the deposition quality. To check the accuracy of the proposed CFD model, experimental measurements of gas velocity were performed and compared with simulated results.

Experimental and Numerical Analysis of the Powder Flow in a Multi-Channel Coaxial Nozzle of a Direct Metal Deposition System

The work explores the powder transport process, using numerical simulation to address the dynamics of the powder flow in an in-house built multi-channel coaxial nozzle of a direct metal deposition (DMD) system. The fluid turbulence is handled by the standard k–ɛ and k–ω turbulence models, and the results are compared in order to predict their suitability. An image-based technique using CMOS camera is adopted to determine the powder flow characteristics. The model is validated with the in-house experimental results and verified available results in the literature. The findings of this work confirms the application of the k–ω model for powder gas flow investigations in blown powder additive manufacturing (AM) processes due to its better predictive capability. The proposed model will assist in simulating the direct metal deposition process.