Development of extrusion on demand for ceramic freeze-form extrusion fabrication processes

Freeze-form Extrusion Fabrication (FEF) is a Solid Freeform Fabrication method. It involves the deposition of a ceramic paste in a layer by layer manner to construct a three dimensional structure. The ceramic paste used in this process consists of a high solids loading of ceramic powder mixed with water and a nominal amount of an aqueous organic binder. These characteristics make the process environmentally friendly. Also the absence of dies or molds in the process makes it suitable for fabrication of materials like ceramics. In the past, parts have been fabricated with continuous extrusion of a ceramic paste. In FEF, Extrusion on Demand (EOD) refers to the ability to control the start and stop paste extrusion on command. Extrusion on Demand makes possible the fabrication of parts with complex geometries and internal features. The extrusion force is an important aspect to be controlled for the successful implementation of EOD in FEF. A general tracking controller with integral action is implemented to allow precise tracking of the reference force. Two possible methods of achieving EOD by controlling extrusion force and fine tuning process parameters have been discussed. Experiments are conducted to tune the controller and process parameters. Working ranges for all process parameters have been established. Three dimensional ceramic structures have been fabricated by using the parameter values obtained from the experiments --Abstract, page iv