Evolution of porosity and geometrical quality through the ceramic extrusion additive manufacturing process stages

Ceramic Extrusion Additive Manufacturing (CEAM) enables the die-less fabrication of small ceramic parts, with a process chain that includes four consecutive stages: the 3D printing, solvent de-binding, thermal de-binding, and sintering. The 3D printing process was implemented through Ephestus, a specially developed EAM machine for the manufacturing of parts from alumina feedstock. A test part was designed, and X-ray computed tomography (mu-CT) was used to quantify its characteristics through the processing stages of the EAM. The porosity distribution and the distribution of void size and shape were determined throughout the samples at each stage, using image analysis techniques. Furthermore, the evolution of some macroscopic quality properties was measured. The results show that both microscopic (porosity) and macroscopic (geometry, density) properties of the samples improve through the process stages. A vertical gradient of porosity is present in green and de-bound samples, with porosity decreasing with increasing sample height. After sintering, the vertical gradient of porosity disappears. The sphericity and the diameter of voids are negatively correlated and dispersed over a wide range in the green state. The sintering process has a homogenization effect on the void shape distribution. The geometrical deviation from the nominal designed dimensions and the surface quality of parts improves when moving from the green to the sintered state.