Spreading Cohesive Powders

In many additive manufacturing processes, the 3D structure is built via solidification of sequential layers of powder. To create each layer, powder is spread over a horizontal surface. The layer properties are determined by the machine geometry, process conditions and powder properties. Discrete element modelling (DEM) can be used ro simulate the system. The inclusion of cohesive forces in DEM powders increases the complexity of the contact models and particle stiffness scaling is often used to decrease simulation time. This study uses an efficient GPU code to test a new scaling methodology and apply it to cohesive particle spreading. In this work we demonstrate the validity of proposed model, both for powder packing and for spreading of fine powders before the effect of powder cohesivity on spreading is then investigated. A wide range of cohesivity, quantified via Bond number, was studied, significant differences in the structure of the spread layer were noted and several regimes identified. In particular, significant clustering, and less uniform spreading, was observed with lower cohesivity, flowable, powders. The mechanisms behind the observations are discussed and a dimensionless inertial number proposed to help interpret the phenomena observed.