A study into the effects of gas flow inlet design of the Renishaw AM250 laser powder bed fusion machine using computational modelling

Previous work has highlighted the importance of the gas flow system in laser powder bed fusion (L-PBF) processes. Inhomogeneous gas flow experienced at the surface of the powder bed can cause variations in mechanical properties over a build platform, where insufficient removal of by-products which cause laser attenuation and redisposition of byproducts are believed to contribute to these variations. The current study analyses the gas flow experienced over a build platform in a Renishaw AM250 metal powder bed fusion machine via Hot Wire Anemometer (HWA) testing. Velocity profiles of the flow directly above the powder-bed and through the centre plane normal to the inlets have been categorized. These HWA results illustrate the inhomogeneity of the gas flow experienced over the build platform and from literature imply that there will be insufficient removal of by-products and hence variable build quality in specific areas of the build platform. A Computational Fluid Dynamics (CFD) model was created in ANSYS Fluent and validated against HWA results coupled with a Discrete Phase Model (DPM) representing the expulsion of spatter. Velocity contours of simulated against experimental are compared, where the results appear in good agreement. The multiphase CFD model was then used to explore the effects of changing inlet design parameters using a Design of Experiments (DOE) study based on an Optimal Space Filling (OSF) method. This was to understand the effect of design parameters on flow uniformity, local gas velocity over the processing area and spatter particulate accumulation within the build chamber. The initial design study found that flow uniformity could potentially be increased by 21.05% and spatter accumulation on the processing area could be reduced by 26.64%. In addition, this has given insight into important design considerations for future generation of L-PBF machines