Segregation of 316L stainless steel powder during spreading in selective laser melting based additive manufacturing

Abstract

Understanding and controlling particle segregation during spreading are critical in improving the quality of the powder bed and the performance of final products in selective laser melting (SLM) based additive manufacturing. In this paper, the segregation of 316L stainless steel powders during spreading was investigated numerically by means of the discrete element method. The influences of particle size and distribution on the segregation behaviors and related properties of the powder bed were systematically analyzed. The segregation mechanisms were identified from the microscopic particulate scale based on particle velocity, motion trajectory, and mechanical behavior. Finally, corresponding solutions were proposed. Results show that for the powder with median diameter D50 = 45 μm of Gaussian distribution, the segregation behavior is less serious when the standard deviation ≤ 4 μm (i.e., the width of size distribution Wd ≤ 30 μm). However, when Wd > 30 μm, increasing Wd will lead to severe segregation. Compared with the powder size, Wd has less influence on the packing density and uniformity of the powder bed. Decreasing the particle size will aggravate segregation of the powder bed when D50 ≥ 35 μm and this phenomenon will be weakened when D50 < 35 μm. In the present work, the powder bed becomes more compact and uniform with the decrease of D50. Different mechanics of large and small particles lead to differences in their motion behaviors, causing segregation during spreading. For the powders with a fixed size distribution, the segregation behavior could be weakened by increasing the blade velocity appropriately. The results presented here will provide valuable references for superior powder spreading as well as printing in practical applications.