Extrusion freeforming of ceramics through fine nozzles

Thermoplastic suspensions of 55 vol.% zirconia in a wax-based vehicle were extruded through a range of fine nozzles with diameters from 76 to 510 μm. Fixed pressure extrusion under a maximum nitrogen gas pressure of 350 kPa and an extrusion temperature of 175 °C were used. The ability of unfiltered suspensions to flow in fine nozzles depended critically on the mixing method. Ceramic latticework in the form of structures suitable for bone substitute scaffolds were created by extrusion freeforming, a process also known as fused deposition modelling (FDM) or fused deposition of ceramics (FDC). However, precisely ordered deposition could not be obtained by fixed pressure extrusion with a 55 vol.% suspension because of rate variations due to slight mixing inhomogeneities. The quality of welds was examined. Heat transfer considerations show that the use of thermoplastic suspensions is not ideal for fine (<100 μm dia.) filament work because the fibres solidify before folding and welding.