The effect of interlayer drying on the ceramic paste extrusion process

Paste extrusion (PE) of aqueous ceramic materials can be assisted by layer-wise drying, enabling complex geometries such as overhangs or high aspect ratio (tall and thin) components. However, the removal of water volume causes shrinkage, the effects of which have not previously been studied in the context of PE. In the range of interlayer drying times investigated, a linear relationship between moisture content and shrinkage in the Z direction was found, up to a maximum shrinkage of 6.4 % at a drying time of 90 s, after which further shrinkage was negligible. Shrinkage in the XY plane was also negligible due to the boundary condition of substrate adhesion. In the case of multilayer parts, drying improved the shape accuracy but Z shrinkage was found to cause voids by altering the height and extrudate width in the next layer. The void fraction of complex parts produced with and without shrinkage compensation was found, using μCT, to decrease from 13.3 to 0.6 %. Therefore, this approach can be used to create high-quality components using PE, without necessarily optimising the material formulation for printability, facilitating uptake of novel materials in ceramic additive manufacturing.