Date of Award

2021-05-01

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Advisor(s)

David Espalin

Abstract

Material extrusion additive manufacturing (AM) technology is one of the most commonly used technology to fabricate functional prototypes and end-use application parts with custom design. The evolution of the extrusion technology led this particular AM process to grow in many aspects such as new materials development, new design thinking, fabrication of parts in multiscale length, and manufacturing of monolithic parts with multiple functionalities. The research presented in this Dissertation results in the creation of knowledge in material extrusion AM technology with the length scale of production-grade to large-scale 3D printing machine those were used to enable the fabrication of multimaterial and composite materials for multifunctional application.Multimaterial fabrication technology was demonstrated using production-grade machines by introducing discrete materials. 3D printed high current-carrying wire embedded plastic parts were fabricated in a Multi3D foundry system. As fabricated and heat-treated parts were characterized both thermally and electrically to understand the impact of porosity in high current carrying embedded electronics application. Electrical breakdown result showed that insulation of the heat-treated specimens were increased significantly. In addition, heat-treated specimens showed reduced void content in the part and increase heat dissipation. In another project of multi-material structure fabrication, continuous carbon fibers were embedded into 3D printed plastic parts using ultrasonic energy. Fiber-reinforced plastic parts were not only showed improved mechanical strength but also demonstrated the ability to work as structural health monitoring devices using piezoresistivity property. While the multimaterial fabrication requires separate feedstocks, short fiber-reinforced composite materials 3D printing offers a great benefit to fabricate mechanically reinforced parts with multifunctionality. The scaled-up manufacturing concept in AM platform gave birth to the large-scale pellet extrusion 3D printer. Compared to filament-driven production grade machines, pellet extrusion system is a relatively new technology. It became very attractive to the large-scale molds and tooling manufacturing community due to the usage of relatively low-cost pellet feedstock. However, some challenges associated with material-specific parameters development hindering the growth for widespread application. In this Dissertation, 3D printing of composites in a large-scale machine was demonstrated by creating knowledge in process, structure, and property relationship. A set of thermophysical and rheological characterizations were performed to understand the behavior of short fiber-reinforced composite materials. In-situ thermal imaging was performed to understand thermal history during 3D printing in a large-scale machine. Mechanical characterization such as dual cantilever beam testing was performed to understand the relationship of interlayer bond strength and printing temperatures.

Language

en

Provenance

Received from ProQuest

File Size

144 p.

File Format

application/pdf

Rights Holder

Kazi Md Masum Billah

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