Mechanical & Materials Engineering, Department of
First Advisor
Jeffrey Shield
Date of this Version
5-2023
Citation
Anderson, Mark. Point Heat Source Correlation to Microstructural Evolution in Advanced Manufacturing. 2023. University of Nebraska - Lincoln, PhD Dissertation.
Abstract
Although there are different ways that advanced manufacturing can be performed, the use of single-point heat sources has become the standard to control a final product’s properties. It is imperative to understand how the heat source used in the different advanced manufacturing processes affect the microstructure of interest. The intimate relationship between the heat source and microstructure allows for controlling and tailoring a part’s properties. Utilizing different microstructural analysis, the cross-correlation of various point heat sources to developed microstructure was conducted in this dissertation.
Laser powder bed fusion allows for unique print-to-part protocols, but the dynamics of the process makes it difficult to control microstructural evolution. The thermal history plays a large role in determining the final microstructure, and through accurate prediction of it, the processing parameters can be adjusted to produce a uniform microstructure. In this dissertation, the microstructure of two parts was examined. One part built with constant processing parameters, and a second part with adjusted laser power based on internal temperatures predicted using graph theory. The microstructure of the second part was determined to be uniform throughout the build, based on the primary dendrite arm spacing. The first part, built with constant processing parameters, had a significantly coarser microstructure.
The graph theory model was also used to predict the thermal history during wire-arc additive manufacturing. The final microstructures were used to confirm the graph theory models, with the grain size utilized to compare cooling rates extracted the graph theory model from different regions of the part. The correlation of grain size with extracted cooling rates resulted in an empirical relationship to predict microstructural evolution at different cooling rates, thereby allowing process design to obtain desired microstructures.
The final study utilized a multi-cross-sectional analysis of the destructive surface laser processing technique. The energy profile that was used in the laser processing was compared to the cross-sections of self-organized copper mounds and allowed for the construction of the ablation and protection formation mechanism occurring with the manufacturing process.
Advisor: Jeffrey Shield
Comments
A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Engineering (Materials Engineering), Under the Supervision of Professor Jeffrey Shield. Lincoln, Nebraska: May, 2023
Copyright © 2023 Mark A. Anderson