Research On Molding Process And Modification Of Polystyrene Based On Selective Laser Sintering

There are many advantages for the PS(Polystyrene) parts which are made by the SLS(selective laser sintering) technology, such as high molding precision and short molding period etc. Therefore it is widely used in rapid investment casting field. However, it is not suitable for sintering complex parts of large size, cantilever parts or thin wall parts due to their low intensity. In this study, the SLS prototyping mechanism of PS powders, optimization of prototyping process and material modification were analysed systematically, moreover, some experiments related to this research were carried out to provide more evidence and actual data. The experiments data show that the quality of the sintered parts was improved, which has important significance for applications of PS powders in rapid casting.First of all, according to the SLS prototyping process characteristics, the related thermal parameters of PS(glass-transition temperature and decomposition temperature) were measured through DSC/TG experiments. the PS powders' molding mechanism based on SLS were analysed in term of thermal process between the material and the laser. The material properties, energy accumulation and process parameters were analyzed to avoid the defects occouring during the sintering process. Besides, the comprehensive analysis was studied to confirm the SLS process parameters. The 3 dimensional variation rules in each orientations(length,width and height) of the PS parts via the experimental study was made under different processing parameters. The optimal scopes of the other process parameters were determined by dimensional accuracy of the height direction as the indicator. The suitable scale of sintering temperature was calculated and verified via the experimental study.Secondly, the rules of the dimensional error and intensity variation under the interaction of different parameters were summarized, furthermore, the causes were analysed through a series of prototyping experiments. The internal morphology of the parts was observed by scanning electric microscope, and the porosity was calculated. The main process parameters(laser power, layer thickness, scanning speed and scanning interval) were selected to carry out orthogonal experiment, the optimal process parameters combination was obtained with variance components method by dimensional accuracy and intensity as indicators. Through the experimental study on support scanning(support types, support layers), the formation quality was improved effectively.Finally, to address the low intensity of PS powders parts, some work on blending modification between PS powders and organic polymer materials was completed. Several studies on modification theory of PS powders, the selection of organic polymer materials, proportion of materials, the treatment methods of materials and the selection of process parameters were made thoroughly. At last, the proportion and preparation method of both modified material PS/PA and PS/PE wax/PTEE wax were obtained by systematic experiments which are compared with the pure PS powders' sintered parts, the intensity of these two modified materials are obviously increased.