| Ceramic stereolithography is a method of ceramic solid free-form fabrication accomplished by additive layer photopolymerization of a ceramic suspension. Process development and optimization entails a combined understanding of suspension rheology, light scattering, and photopolymerization, guided by fundamentals of ceramics processing. The formulation of a highly-loaded photopolymerizable ceramic suspension of submicron ceramic powders and stereolithography-compatible rheological and optical properties is discussed. Characterization of suspension rheology reveals influences of particle size, solids loading, and size polydispersity. Rheological models were fit to shear-thinning regimes to provide insight on the quality of the dispersion of the ceramic suspensions. The Farris effect was observed in bimodal ceramic suspensions, lending practical importance in that suspensions of higher total loading maybe achieved with minimal increase in viscosity. A general, quantitative relationship between the photon transport mean free path (l*) and resin sensitivity in multiple-scattering suspensions formulated for ceramic stereolithography is presented and experimentally demonstrated. Experiments to study photopolymerization kinetics of the suspension were developed to provide insight on monomer conversion as a function of depth. A design of experiments method was used to relate output part quality and build time to several user-selected stereolithography machine parameters. Fundamentals of binder burnout and sintering processes are reviewed, along with discussion of material influences and the empirical selection of binder burnout and sintering conditions for objects fabricated by ceramic stereolithography. Finally, the capability of automated fabrication of ceramic monoliths of high geometric complexity is applied to the design and fabrication of functional effective dielectric millimeter-wave devices, previously unobtainable without ceramic stereolithography. Results from this work may guide future users of ceramic stereolithography in process optimization and continual improvement and also provides a basis for future design of functional ceramic objects of arbitrary geometric complexity. |
