Freeform extrusion of high solids loading ceramic slurries. Part 1: Extrusion process control

Autores: Mason, M.S.|Huang, T.|Landers, R. G.|Leu, M. C.|Hilmas, G. E.
Fuente: Proceedings of the Freeform Fabrication Symposium, 2006

Part I of this paper provided a detailed description of a novel fabrication machine for high solids loading ceramic slurry extrusion processes and presented an empirical model of the ceramic extrusion process, viewing ram velocity as the input and extrusion force as the output. A constant extrusion force is desirable as it correlates with a constant material deposition rate and, thus, good part quality. The experimental results used to construct the model demonstrated that a constant ram velocity will not necessarily produce a constant extrusion force. In some instances the extrusion force increased until ram motor skipping occurred, and process disturbances, such as air bubble release and nozzle clogging, were often present. In this paper a feedback controller for the ceramic extrusion process is designed and experimentally implemented. The controller intelligently adjusts the ram motor velocity to maintain a constant extrusion force. Since there is tremendous variability in the extrusion process model, an on-off controller is utilized in these studies. Comparisons are made between parts fabricated with and without feedback control. It is demonstrated that the use of intelligent feedback control reduces the effect of process disturbances (i.e., air bubble release and nozzle clogging) and dramatically improves part quality.