Packing quality of powder layer during counter-rolling-type powder spreading process in additive manufacturing

Powder spreading is an essential procedure in powder-bed-based additive manufacturing, and the resultant packing quality of the powder layer has important effects on the quality of the final products. In this work, the counter-rolling-type powder spreading is investigated by experiments and numerical simulations. Non-invasive in-situ measurements are performed to evaluate the packing qualities of the powder layer such as surface roughness and packing density, where the effect of the spreading speed is studied. It is found that both the surface quality and packing density of the powder layer decrease with the increase of spreading speed. Besides, the sensitivity of the surface roughness of the powder layer increases with the spreading speed, i.e., the higher the spreading speed is, the more remarkably the surface quality decreases. Numerical simulations using the discrete element method are performed to investigate the dynamics of the powder spreading in terms of the velocity, contact force and coordination number of powder particles, providing new insight to the physical mechanisms underlying the counter-rolling-type powder spreading at particulate scale.