Doctoral Dissertations

Keywords and Phrases

additive manufacturing; direct energy deposition; laser metal deposition; multidimensional systems; norm optimal control; repetitive process control


"Additive manufacturing (AM) has garnered much attention in recent years, some calling it the fourth industrial revolution. It was first used to create rapid prototypes, although recent efforts have been made to advance the technology towards production of functional parts. This requires advancement in the materials used in AM, as well as the ability to produce quality parts repeatably. More specifically, direct energy deposition (DED) of metal powders is a process capable of producing and repairing parts with complex geometries; however, it is not widely used in industry due to challenges with quality control. In this process, metal powder is dispensed from a nozzle and a laser beam melts the incident powder particles and a portion of the underlying surface. The melt pool is translated along the desired toolpath and parts are constructed in a layer-by-layer fashion. Several process inputs determine the deposition quality, including powder feed rate, laser power and nozzle speed. These inputs, as well as the environmental conditions, are subject to random fluctuations that can cause geometric defects during deposition. Such defects often propagate through to subsequent layers and are amplified, rendering the final part unusable. The objective of this work is to improve the geometric accuracy of parts produced by metal powder DED by designing and implementing process feedback control. The strategy involves measuring the part height after each layer and adjusting the nozzle speed trajectory for the next layer according to a designed control law. The major contributions of this work are 1. the construction of an open-architecture metal powder DED system that is capable of implementing layer-to-layer control and 2. the development of controllers to improve part morphology accuracy in metal powder DED"--Abstract, p. iv


Bristow, Douglas A.
Landers, Robert G.

Committee Member(s)

Liou, Frank W.
Singler, John R.
Sarangapani, Jagannathan
Mishra, Sandipan


Mechanical and Aerospace Engineering

Degree Name

Ph. D. in Mechanical Engineering


Missouri University of Science and Technology

Publication Date

Fall 2021


xi, 91 pages

Note about bibliography

Includes_bibliographical_references_(pages 89-90)


© 2021 Michelle Gegel, All Rights Reserved

Document Type

Dissertation - Open Access

File Type




Thesis Number

T 12217