Effect of Four Process Parameters on Flexural Strength and Porosity of Metakaolin Ceramics Fabricated by Material Extrusion: Optimization and Predictive Models via Orthogonal Experiments

A high-strength metakaolin-based porous ceramics are fabricated using slurry-based material extrusion via optimizing four key process parameters, including nozzle internal diameter, height to diameter ratio, filling rate, and printing speed. The orthogonal experiments are used to adjust flexural strength and porosity, and the optimal process parameters are obtained by comprehensive scoring and range analysis methods. The predictive models of strength-parameters, porosity-parameters, and strength-porosity are established and validated. The results show that the optimal process parameters for high-strength and high-porosity ceramics are 0.51 mm nozzle internal diameter, 70% height to diameter ratio, 100% filling rate, and 15 mm s⁻¹ printing speed. The correctness and predictability of three predictive models are proved by two methods, which are the mutual validation and comparison between theoretical and actual values. And the error rates between theoretical and actual results are less than 7%. This work provides guidance for the rapid fabrication of ceramics with adjustable strength and porosity by material extrusion, and the established predictive models can pave the way for its wider application in the practice.