| Characterized with high temperature resistance, high hardness and strength, structuralceramics are widely applied in the area of mechanics, aerospace, while it is very difficult toprocess ceramics by the traditional processing methods. It is a promising way to useSelective Laser Sintering (SLS) to form complex ceramic green parts, regardless of thedefects such as their porosity and low density. Combined with Cold Isostatic Pressing (CIP)and the following Solid State Sintering (SSS), the compound process can form complexceramic components with high density. At present, the research regarding this area is in theinitial stage, and the current research didn’t pay attention to the control of forming accuracyof the compound process, as well as apply the promising research method of numericalsimulation into the compound method.This paper will explore and improve the compound process of SLS/CIP/SSS tomanufacture high density alumina parts with high purity, and innovatively realize the fullprocess simulation of the compound process. The study mainly focuses on the followingaspects and makes corresponding achievements：(1) An alumina/epoxy resin E-06composite powder was made by mixing the matrixmaterial and the binder, namely granulated alumina powder with its size of80-120m andepoxy resin E06powder respectively, and the binder accounts for8%of the compositepowder in weight. Besides, the SLS process parameters were optimized and eventuallycomplex alumina green parts were produced with high strength and density.(2) The influence of CIP and SSS process parameters on densification and partperformance was studied, and the key process parameters were optimized as follows: CIPpressure of320MPa, dwell time of5min, SSS sintering temperature of1600℃, holding timeof4h, heating rate of5℃/h. Finally, pure alumina components were produced with theirdensity up to94.5%by the optimal compound process, which is a breakthrough in theproduction of the ceramic components by using the same methods in the world. In addition, gear components and components with channel structures were successfully made throughthe compound process, which proves the feasibility of manufacturing high density ceramicparts with complex structures by the SLS/CIP/SSS process.(3) Based on the finite element analysis platform of Abaqus, the deformation, sizecontraction and densification behavior were predicted during CIP process of cuboid and gearSLSed components on the basis of modified Cam-Clay model and Drucker-Prager/Cap(DPC) model. The simulation results agree well with the experimental results, and therelative errors between experimental and simulation results based on the two models are lessthan2.26%and1.7%, respectively. It proves the feasibility and accuracy of simulating theCIP process the alumina parts.(4) Based on the CIP simulation of SLSed parts, the effects of rubber bags on CIPprocess were studied and the forming accuracy of CIP was enhanced by optimizing the partstructure. The results show that rubber bags have shielding effects on the densificationprocess of CIP, which leads to the part distortion and weakens the homogenization of densitydistribution. Adding fillets to part structure can reduce deformation, improve the formingaccuracy of CIP process and facilitate the homogenization of the density distribution.Additionally, the optimal fillet size can be gained by simulation methods, thus optimizing theshaping accuracy and performance.(5) The modified SOVS model was developed, embedded into the subroutines ofAbaqus in this paper. The densification process, deformation, contraction and grain growthof CIPed parts during SSS process were simulated by this model, which builds the linksbetween macroscopic phenomena and microscopic variation. The relative error betweenexperimental and simulative results was less than1.5%, proving that this model canprecisely predict the deformation and contraction during SSS process. The results indicatethat SSS can narrow the relative density differences of the sintered parts. Finally, themaximum and maximum predicted grain size turns out to be2.556μm and2.008μm. And theexperimental mean grain size is calculated as2.42μm by certain calculation software, which is close to the simulation results. It proves that this model can accurately simulate the graingrowth of CIPed parts during SSS, providing reliable reasons to the research ofmicrostructure evolution and properties of sintered parts.Above all, this paper proves the feasibility of applying this SLS/CIP/SSS compoundprocess to manufacture high density ceramic parts with complex structures. Furthermore, thepaper has also innovatively fulfilled the full process numerical simulation of the compoundprocess. The simulation can not only accurately predict the deformation, size contraction,densification behavior and the microstructure evolution of SLSed parts during the process ofCIP and SSS, but also provide the effective and efficient guidance to the part structure andprocess optimization, thus enhancing the forming accuracy of the whole compound processfor the purpose of near net shaping. This study can also lay theoretical and technicalfoundation of the compound process to manufacture the hard-to-process ceramic parts. |
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