Masters Theses

Xiyue Zhao

Keywords and Phrases

Ram extrusion

Abstract

"Freeze-form Extrusion Fabrication (FEF) is an additive manufacturing technique that extrudes ceramic loaded aqueous pastes layer by layer below the paste freezing temperature for component fabrication. As the FEF is aimed at being conducted at low environmental temperatures, down to -20°C, it is necessary to investigate the effect of environmental temperature on the process. The advantages of fabrication at low temperature have been proved by experiments. Comparisons in terms of operation parameters, self-sustaining ability, and system dynamic response were performed at different environmental temperatures ranging from 20°C to -20°C.

It is commonly known in paste extrusion processes that due to unmodeled effects such as air bubble release, non-uniform water content, unpredictable agglomerate breakdown, etc., the throughput (extrusion rate) is difficult to control. Moreover, during the extrusion, the rheological characteristics of the paste changes due to liquid migration, resulting in a processing challenge. Because of these difficulties, additional paste extrusion research is still in progress. Traditional PID controllers based on off-line empirical models are inadequate to control the ram extrusion processes. The Recursive Least Square algorithm is used in this research to identify the dynamic responses of the FEF process in real time. An adaptive controller with a novel general tracking control strategy is designed and implemented to regulate the extrusion force in real time. Experimental results demonstrated the robust performance of the controller, allowing the extrusion force to track various types of reference signals, while traditional controllers could only maintain the extrusion force (pressure) at a constant level (operation point)."--Abstract, page iv.

Advisor(s)

Landers, Robert G.
Leu, M. C. (Ming-Chuan)

Committee Member(s)

Hilmas, Greg

Department(s)

Mechanical and Aerospace Engineering

Degree Name

M.S. in Mechanical Engineering

Sponsor(s)

Air Force Research Laboratory (Wright-Patterson Air Force Base, Ohio)

Publisher

University of Missouri--Rolla

Publication Date

Fall 2007

Journal article titles appearing in thesis/dissertation

  • Adaptive control of freeze-form extrusion fabrication processes
  • Experimental investigation of effect of environment temperature on freeze-form extrusion fabrication

Pagination

xi, 59 pages

Note about bibliography

Includes bibliographical references (page 17).

Rights

© 2007 Xiyue Zhao, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Subject Headings

Adaptive control systems
Ceramics -- Extrusion
Least squares
Solid freeform fabrication

Thesis Number

T 9369

Print OCLC #

261126144

Electronic OCLC #

225885955

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