Dynamic investigation on the powder spreading during selective laser melting additive manufacturing

In selective laser melting in additive manufacturing, powder spreading significantly affects the subsequent operating procedure as well as the quality of final products. Compared with large amount of previous work on powder spreading on a flat substrate surface before printing, in this article, 3D particulate scale dynamic simulations were carried out to study the spreading of 316 L stainless steel powder during printing by using discrete element method (DEM). The influences of various factors including processing parameters, blade shape, and the powder size on the quality of the spread powder bed were investigated in terms of both macroscopic packing density/uniformity and microstructure/micro dynamics. And optimized condition was identified. The mechanisms were also analyzed based on the powder behavior and forces caused by cooperative interaction between the formed zone (printed part) and the already packed powder layer. The results show that the blade moving speed can seriously influence the quality of the spread powder bed; normally the smaller the blade moving speed, the higher the powder bed quality, but the lower the working efficiency. Therefore, through comprehensive consideration, the proper blade moving speed is chosen to be 0.1 m/s. Increasing the blade gap height or decreasing the particle size (i.e., D = 30 pm) will increase the average relative packing density and structure uniformity. The angle of 15' for the blade is proved to be optimal for excellent powder spreading. Through simulation under optimized parameters, it can be found that the spread powder layer can be more uniform and much denser with high efficiency. And both macroscopic and microscopic analyzes indicate that the spread powder bed has desired structure and property. These findings can improve the fundamental understanding on the powder spreading and provide valuable references for the formation of high quality powder bed during 3D printing.