Linking particle properties to layer characteristics: Discrete element modelling of cohesive fine powder spreading in additive manufacturing

Particle properties play a key role in determining the flowability of cohesive fine powders and consequently the quality of parts fabricated by additive manufacturing. However, how the characteristics of a spread powder layer are linked to particle properties remains not well understood, largely due to the limitations of available numerical models and characterisation approaches. This study thus established an efficient discrete element modelling framework to address these issues, combining GPU computing with a novel methodology for particle stiffness scaling. The validity of the DEM model was verified on both packing and spreading of cohesive fine powders. The effect of particle cohesion on the characteristics of a spread powder layer was systematically analysed for non-cohesive and weakly to strongly cohesive powders. The structure of spread powder layer was qualitatively illustrated and quantitatively evaluated by not only commonly used metrics, such as coordination number, packing density and surface profiles but also particle clustering and pore characteristics. While reducing particle cohesion leads to an enhanced powder flowability, different regimes were identified in the relationship between layer characteristics and particle cohesion. The results showed that powder spreadability has a complicated dependence on the strength of particle cohesion, where the underlying mechanisms can be understood in part via a dimensionless inertial length. These findings not only provide valuable metrics to quantitatively evaluate the quality of a spread powder layer, but also enable a better understanding of the physics underlying the spreading of cohesive fine powders.