Numerical Research On Powder Paving Process Of Nylon Powder Selective Laser Sintering

Selective Laser Sintering(SLS) is a kind of rapid prototyping technology in which the 3D components are manufactured directly through the powder paving process layer by layer and scanning sintered process step by step. In recent years, because any complex geometrical shape of the components can be processed by SLS, it has been applied more and more widely in the field of industrial engineering. Compared with the traditional processing methods, SLS needn’t support component and has high material utilization. For any kinds of materials used in SLS, in order to get the sintered component with density uniform and good mechanical properties, the forming process parameters should be matched. Among them, the forming process parameters include powder paving process and sintering process. Nylon powder materials are one of the widely used materials by SLS. Its sintering process was widely researched by scholars. However, the study on its powder paving process was few. The powder paving process will directly affect the sintering process and density uniformity of powder bed, thus affect the density uniformity and mechanical performance parameters of sintered part. Therefore, the powder paving process of nylon powder will be studied by the experiment and discrete element method in this paper. The mechanism of powder microscopic parameters and roller parameters on powder density of forming area will be explored. The research was carried out through the following several aspects:(1) In SLS, the size distribution of nylon powder is in the range of 20 to 100 microns. The van der Waals force between the particles has become the main factor that affects its flow behavior. Therefore, the role of van der Waals force in contact model should be considered. The classical elastic and viscoelastic contact model were introduced firstly in this paper. After the comparison and analysis of its applicable occasions, the contact model appropriate to nylon powder was developed on the basis of the Hertz-Mindlin model. The contact model was established on the platform of EDEM-API which was applied in numerical simulation. Finally, the contact model was verified by the comparison of results from theory and EDEM calculation.(2) The microscopic shape of nylon powder was observed by the depth of field microscope and the particle size distribution was measured by laser particle size analyzer. The established nylon powder discrete element model is calibrated and verified through the direct shear test, the angle of repose, and revolution powder analyzer and the corresponding numerical simulation.(3) Based on the discrete element model, we analyzed the effect of the roller rotation speed, translation speed, the tiny vibration of the roller, roller radius, the particle size and size distribution in the process of powder paving on density uniformity of powder bed, and dense characteristics. The compressive force on the roller, and the effect of powder paving process on the printed part was also analyzed.(4) First of all, the particle shape, particle size and its distribution of the virgin powder and used powder was analyzed by the experiment. We studied the flowability of the virgin powder and used powder by angle of repose test. Then, the powder paving process in the process of SLS of the virgin powder, used powder and different proportion mixture powder of that two was studied by discrete element method. Finally, the sintering experiment was carried out. The density uniformity and dense characteristics after the powder paving process were analyzed. The surface roughness and mechanical performance parameters of sintering components were also studied.