Preparation and characterization of microencapsulated, finely divided ceramic materials for selective laser sintering

Selective Laser Sintering (SLS) is an established rapid prototyping and manufacturing process capable of fabricating solid objects via laser induced, thermal sintering of powdered thermoplastics. The focus of the present work was to advance SLS by introducing the capability of fabricating solid shapes from high temperature materials such as ceramics and metals. This was done using fugitive thermoplastic binders without modification to the present implementation. SLS processing of these composite powder systems yielded green shapes that could be post-processed by traditional means to give functional ceramic or metal objects.; An emulsion based poly(methylmethacrylate-co-n-butylmethacrylate) was developed as the binder system. The properties of this binder, including its glass transition temperature, viscosity, and decomposition mechanisms were tailored for application to SLS. Evaluation of the binder under ideal conditions showed polymer coated powders yielded greater green strengths than mixtures of polymer and powder. Polymers with melt flow indices of 5-15 g/10min at 200{dollar}spcirc{dollar}C and 0.49MPa produced the strongest green shapes by optimizing binder rheological and mechanical properties. Furthermore, incorporation of adhesion promoting functionalities into the binder backbone and matching of acid-base interactions between the binder and the powder substrate improved green strengths. A preferred terpolymer of di-methylamino-ethylmethacrylate at 2 wt. % increased green strengths more than 20%.; Application of the SLS process to polymer coated ceramic materials proved very successful. A number of material systems, including a spheroidized soda-lime glass and an irregular silicon carbide, were tested with the developed binder. Detailed work with both of these substrates yielded information pertinent to the processing of polymer coated powders. Green shapes with strengths {dollar}>{dollar}1.0MPa (150 psi), good accuracy, fine features, and no curl were easily fabricated from these and other material systems. However, analysis of fabricated specimens showed overall binder to degrade by 6-20 wt. %. This result was modeled with a 1-dimensional thermal diffusion equation coupled with measured decomposition rate kinetics. Model agreement with experimental results was very good. The model was used to evaluate the effects of SLS processing variables on the extent of polymer degradation in order to further optimize binder performance.