Layered extrusion forming a simple and green method for additive manufacturing ceramic core
Layered extrusion forming, a type of additive manufacturing technique, was applied in this study, using aqueous ceramic pastes to build near net shaped ceramic cores at room temperature. As an example, aqueous based pastes of alumina using methylcellulose (MC) as binder were prepared, and layered extrusion forming method was employed to fabricate green alumina cores. Afterwards, post sintering was carried out to obtain ceramic cores with high strength. Pastes with alumina solid loading varying from 30 to 52 vol. were dispersed by MC solutions and presented shear thinning rheological behaviors. Solid loading had a significant effect on the processing of layered extrusion formation. Alumina pastes with 30 to 46 vol. were not suitable for layered extrusion formation, while pastes with solid loading ranging from 48 to 52 vol. could be applied successfully to the layered extrusion forming process. Pastes composed of 2 wt. MC solution as binder and 50 vol. solid loading generated specimens with best shape retention and surface consistency, and the height of each layer extruded was equally distributed. The green specimens exhibited slightly smaller dimensions than the designed ones, and sintered specimens showed linear shrinkage. Sintered specimens presented homogeneous morphology, and no gap between extruded filaments was observed. Specimens sintered at 1600 degC for 180 mins possessed best comprehensive performances and low thermal expansion, which could meet the requirements of ceramic cores in alloys casting. The systematic study of layered extrusion forming indicates that this method is a promising method to fabricate ceramic cores.