Research On Some Key Techniques For Selective Laser Sintering Of PS/Al₂O₃ Nano-composites

Selective laser sintering (SLS) is one of the most attentive rapid prototyping techniques due to its suitability to process almost any powder material. It is going to exhibit high potential applications in many fields. This thesis presents the study on SLS of polystyrene/nano-Al2O3 powder mixture for bulk polymer/ Al2O3 nanocomposites. The main works are focused on such as the method for developing the powder mixture system, the behavior of interaction between nanoparticles and laser beam, the mechanisms of melting/solidification and densification in sintering process, the relationships between the quality of sintered part and the process parameters as well as energy density, the characteristics of the morphology and the mechanical properties of the sintered specimens.The experimental results revealed that the methods for surface treatment of nanoparticles are important to not only the dispersion of nanoparticles within the polymer matrix, but also the sintering behavior and the quality of the sintered parts. The serious congregation of nanoparticles leads to the sintered part with the partially incompact structure and the difference of surface polarity between polymer and inorganic nanoparticle results in a lot of voids within the sintered part. By means of the emulsion polymerization, the composite particles were made for overcoming above problems. These particles have the core-shell structure that each single nanoparticle is coated by polystyrene.The interactive mechanisms of nanoparticles with both laser beam and melting polymer were investigated. There are three kinds of behaviors for nanoparticles in the sintering process, that is"slightly splashing"under the laser beam,"diffusely moving"with the polymer melt pool expending, and"infiltrating"with liquid polymer into the cranks and voids in the consolidated layer. The above conclusions suggest that SLS process has the functions of subsequently breaking up the congregating nanoparticles, diffusing the gathering nanoparticles and promoting nanoparticles moving. These behaviors were identified by observing the SEM micrographs about the dispersion of nanoparticles within the specimens made from SLS processing and convention modeling.Based on large number of sintering experiments, the relationships between the physical density of sintered parts and the process parameters were analyzed. The optimum combinations of laser power and scanning speed were achieved. The difference...