Research Of Preparation And Properties Of Ciomosite Materials Used In Additive Manufacturing

Additive manufacturing are a series of additive modeling technologies which are different with traditional subtractive manufacturing.However their applications were limited by the unity and none-functional materials used in those filed.So this thesis aims to solve above problems and following three areas were studied.The thermal conductive Al₂O₃/PA12 composite filament was prepared with twin-screw extruder for application in fused deposition modeling（FDM）.The influences of filled amounts of Al₂O₃ and silane coupling agent 3-aminopropyl triethoxysilane（KH550）on the density,melt flow rate（MFR）,mechanical and thermal properties of Al₂O₃/PA12composite were investigated in this work.The composite with 70wt%Al₂O₃ possesses good mechanical performance and high thermal conductivity,and simultaneously its MFR satisfies the requirement for the FDM process.The addition of 0.5wt%KH550 in composite increases melt flow rate,improves mechanical performance and enhances thermal conductivity.The Al₂O₃/PA12 composite filament with 70wt%Al₂O₃ and0.5wt%KH550 was successfully applied in the FDM process of 3D printing.Although the mechanical performance of FDM samples does not reach the level of the conventional injection molding samples due to the existence of pores,the thermal conductivity of FDM samples,compared to pure PA12,is enhanced by 170%.The preparation of Al₂O₃/PA12 composite powder which used in the selective laser sintering（SLS）molding and the post-processing of the SLS specimen were discussed in this work.The composite powder was made by crushing melting-blended Al₂O₃/PA12 composite granules at low temperature.Mold ability of the composite powder for application in the SLS molding machine and the effect of the heat treat temperature on the density of the specimen were investigated,the combination of particles inside the specimen before and after the heat treatment were observed and compared.Al₂O₃/PA12 composite powder made by melting-blending and low temperature crushing can fit the requirement of SLS molding and the specimen with neat profile,good internal combination and a relative density of 74%could be obtained.After a heat treatment at 200℃,internal combination between particles were strengthened and the relative density of specimen increased to 84%.PA12 was dissolved in hydrothermal synthesis reactor at high temperature and high pressure.The PA12 powder was precipitated with the cooling process.The influence of concentration of dissolved,solution temperature,pH value,cooling process to the size and morphology of the PA12 powder were studied.The increase of dissolved concentration was benefited to PA12 microspheres by disarray fluffy to densification.Temperature rising was benefited to PA12 microspheres crystallized ball and densification,and the results of infrared spectroscopy showed that structures of PA12 microspheres prepared at different temperatures were not changed.The alkaline environment has no significant impact on morphology of PA12 microspheres,and the structures of the microspheres would be damaged under acidic condition.When the cooling speed was fast,the PA12 had no time to fully crystallized and formed a porous sphere instead.Perfectly spherical PA12 powder was obtained by thermal insulation at 100¹20℃.