Aqueous-based extrusion of high solids loading ceramic pastes: Process modeling and control

A novel fabrication method known as aqueous-based extrusion fabrication (ABEF) has been developed for the manufacture of ceramic-based components in an environmentally friendly fashion. The method is based on the extrusion of ceramic pastes using water as the medium. This paper describes a machine developed for the extrusion of high solids loading ceramic pastes, investigates the dynamic behavior of the extrusion process, and develops and implements a feedback controller to regulate the extrusion force. The results demonstrate that aqueous-based ceramic extrusion processes have a very slow dynamic response, as compared to other non-compressible fluids such as water. A substantial amount of variation exists in aqueous-based ceramic extrusion processes, most notably during the transient period, and a constant ram velocity may either produce a relatively constant steady-state extrusion force or it may cause the extrusion force to steadily increase until the ram motor skips. It is demonstrated that the use of feedback control reduces the effects of process disturbances (i.e., agglomerate breakdown and air bubble release) and variations in the process as the material in the reservoir decreases, substantially decreases the time to obtain a desired extrusion force level, and dramatically improves part quality.