<p>While metal 3D additive manufacturing processes such as Powder Bed Fusion (PBF) are being actively investigated for manufacturing of novel parts, the reduced mechanical properties of 3D printed parts continues to be a significant concern. Specifically, the presence of voids and non-uniform particle density in the powder bed prepared prior to energy deposition severely impacts the print quality. This work presents simulations-based analysis of the powder bed spreading process for different configurations of the initial powder pile. The performance of a number of heterogeneous powder pile configurations with particles of two and three different sizes is investigated using Discrete Element Modelling (DEM) simulations. Through force chain analysis and void fraction computation, it is shown that stacking smaller-sized particles under larger-sized particles prior to spreading results in significant improvement in powder bed density and reduction in void fraction of the powder bed. Additionally, it is shown that granular convection induced by a churner mechanism leads to further reduction in void fraction, with the best performance occurring at a specific rotational speed. It is shown that this optimal speed occurs due to two competing physical mechanisms related to the rotation of the churner. This work offers useful practical insights towards improving the quality of the powder bed preparation process in metal 3D printing.</p>