Effect of Coaxial Powder Nozzle Jet Process Parameters on Single-Track Geometry for Laser Beam Directed Energy Deposition Process

The major challenges faced by powder-based laser beam directed energy deposition are the powder efficiency and the part quality assurance. One of the main ways to quantify the quality of a printed part is its geometry. This paper aims to study the influence of gas and powder process parameters on the geometry of single deposited tracks using 316L stainless steel in powder-based laser beam directed energy deposition. The gas and powder settings are defined as the carrier and shielding gas volumetric flow rate, the powder mass flow rate, and the particle diameter. The track geometry is evaluated based on the deposition width, deposition height, area of deposition, contact angle, dilution depth, and degree of dilution. The single tracks are printed using the MiCLAD in-house hybrid directed energy deposition machine developed by the Additive Manufacturing Research Group of the Vrije Universiteit Brussel. Their geometry is evaluated by means of laser triangulation and micrographs of single-track transversal cross sections and differences in results are highlighted. The overall results show that powder mass flow rate and particle diameter range are the main parameters affecting the track's geometry and powder efficiency. The shielding and carrier gas volumetric flow rates show an effect on the geometry, but no clear tendencies can be retrieved. This highlights the presence of a complex relationship between powder mass flow rate, shielding, and carrier gas volumetric flow rate. The ratio shielding/carrier volumetric mass flow rate is revealed to be an essential factor impacting the printing process.