Laser-directed energy deposition (L-DED) is a type of additive manufacturing (AM) technology that allows the manufacture of complex geometry components in a layer-by-layer way and can be considered an emerging manufacturing technique. The process efficiency and properties of produced parts are closely linked to its parameters, i.e., laser power, deposition speed, material flow rate and, inert gas flows. These operational parameters usually are different depending on the machine and material employed. The best combination of process parameters is fundamental to obtain the best characteristics together with process sustainability for each manufactured component. At the present work, an L-DED head and a powder feeding system are combined in a particular machine to deposit Inconel 625 on a substrate made of AISI 304 stainless steel. A combination of analytical studies, CFD simulations, and experimental tests was carried out, finding a process setting that offers a higher concentration of particles, quality depositions, and optimal cooling rates, reducing gas and material consumption during the process. After some in-situ tests, the best results were employed to fabricate thin wall structures and solid components. The specimens were characterized by laser confocal microscopy, roughness, and Vickers microhardness measurements, finding exciting results with a significant reduction in gas consumption and metal powder usage.

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.

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