INFLUENCE OF ROUGH SURFACE OF DEPOSITED AREA ON QUALITY OF POWDER SPREADING DURING SELECTIVE LASER MELTING: DISCRETE ELEMENT SIMULATIONS

The final quality of the printed products is greatly affected by the powder spreading in selective laser melting (SLM). However, little attention is paid on the influence of rough surface of deposited area on the quality of the powder spreading. Therefore, a rough deposited area is modeled as the new substrate for investigating the effect of surface morphology of the deposited substrate and processing parameters on the quality of powder bed during spreading using the discrete element method (DEM). The particle dynamic behavior and powder bed formation mechanism of metal powder on the surface of the deposited area during powder spreading are analyzed. The numerical results show that the quality of powder layer can be effectively improved by rotating the powder spreading direction to a certain angle along the laser scanning direction of the bottom layer, and the influence of the surface of deposited area can be significantly reduced by increasing the powder bed thickness. Reducing the hatch overlap rate can improve the retention capacity of particles in the deposited area, so that more particles are deposited in the deposited area, thereby increasing the packing density of the powder bed. But the powder collides with the rough surface of the deposited area causing more particles to splash. During spreading, the number of strong chains produced by the powder pile on the rough deposited area is more than that on the smooth deposited area due to the increase in roughness of the deposited area. Meanwhile, under the action of the roller, the force arch is destroyed and the particles are rearranged to form a dense powder layer. At the boundary of the deposited area, the generation of force arch will eventually lead to the appearance of vacancy defects in the powder layer at the boundary. The present study is helpful to improve the quality of powder bed during the powder spreading.