Development of Freeze Form Extrusion Fabrication With Use of Sacrificial Material

Abstract

The development of freezeform extrusion fabrication (FEF) process to fabricate threedimensional (3D) ceramic parts with use of sacrificial material to build support sections during the fabrication process is presented in this paper. FEF is an environmentally friendly, additive manufacturing (AM) process that builds 3D parts in a freezing environment layerbylayer by computer controlled extrusion and deposition of aqueous colloidal pastes based on computeraided design (CAD) models. Methyl cellulose was identified as the support material, and alumina was used as the main material in this study. After characterizing the dynamics of extruding alumina and methyl cellulose pastes, a general tracking controller (GTC) was developed and applied to control the extrusion force in depositing both alumina and methyl cellulose pastes. The controller was able to reduce the time constant of the closedloop system by more than 65% in comparison to the openloop control system. Freezedrying was used to remove the water content after the part has been built. The support material was then removed in the binder burnout process. Finally, sintering was done to densify the ceramic part. The fabrication of a cubeshaped part with a square hole in each side that requires depositing the sacrificial material during the FEF process was demonstrated.