LIQUID PHASE MIGRATION IN EXTRUSION OF AQUEOUS ALUMINA PASTE FOR FREEZE-FORM EXTRUSION FABRICATION

摘要

Freeze-form Extrusion Fabrication (FEF) is an additive manufacturing technique that extrudes highly ceramic loaded aqueous paste along 3D contours for complex ceramic part fabrication. The phenomenon of liquid phase migration (LPM) in paste extrusion process will result in variation of liquid content in paste and consequently problems in processing and non-uniform properties of ceramic parts. It is necessary to understand the LPM phenomenon in FEF process. In this paper, the effect of liquid phase migration on extrusion of aqueous alumina paste was investigated for FEF process. The water content and extrusion force data were collected for a series of ram velocities. According to the extrusion force profiles, the extrusion process can be divided into four stages: compaction stage, transient stage, steady stage and dead zone stage. The results show that ram velocity is the key parameter for occurrence of liquid phase migration phenomenon and there is a velocity threshold above which the liquid phase migration will not happen.