Investigating the effect of temperature on powder spreading behaviour in powder bed fusion additive manufacturing process by Discrete Element Method

In this study, a Discrete Element Method (DEM)-based model was developed to simulate the powder spreading process in Powder bed Fusion (PBF) for Polyamide 6 (PA6) powder, which considered the spreading speed (3 mm/s and 30 mm/s) and temperature (25 °C and 110 °C) as parameters affecting the final spreading powder layer quality. The particle horizontal and vertical velocities were analysed in regions near the spreading blade, where at the lower spreading speed, particle velocities are far less compared to the higher spreading speed. The lower particle velocities lead to gently settling down and rearranging particles during spreading on the bed, allowing a uniform powder layer to form. Increasing the spreading speed led to an increase in shear stress and inertia number. At higher temperatures, shear stresses also rise while the inertia number is slightly reduced due to the greater cohesion between particles. The generated powder layer by the DEM model was analysed using the wavelet analysis technique and compared to experiments. The spreadability index of experiments can be estimated with less than 5% error using DEM simulations, though in an approximately consistent manner that captures the experimental trends of spreading speed and temperature. The packing fraction of simulated powder layers was investigated in the spreading direction. The DEM simulations show that packing fraction decreases as temperature or spreading speed are increased, with its variation across the bed increasing for higher spreading speeds. Increasing the spreading speed leads to greater motion and inertia number of particles and, consequently, it intensifies the particle ejection and results in many unfilled areas in the spread powder layer. Increasing temperature leads to an increase in cohesivity between particles, resulting in aggregates forming on the spread powder layer.