Date of Award

2012-01-01

Degree Name

Master of Science

Department

Mechanical Engineering

Advisor(s)

Ryan B. Wicker

Abstract

Over the last three decades, developments within the area of Additive Manufacturing (AM) have resulted in novel technologies capable of producing highly customized, complex part geometries in a fraction of the lead time required by traditional manufacturing methods (e.g., injection molding, metal casting). In particular, fused deposition modeling (FDM), a material extrusion AM process, can produce parts using production-grade thermoplastics like acrylonitrile butadiene styrene, polycarbonate, and polyetherimide. Additionally, non-commercial materials (e.g., polycaprolactone, ceramic loaded polymers, carbon nanotube loaded polymers) have been processed using FDM in part to demonstrate the potential diversity in material selection.

Recently, a myriad of personal 3D Printers using material extrusion processes have received much attention because they resemble the initial steps towards transforming AM technologies into a home consumer item. These steps were also taken during the 1980s by inkjet printing technologies when they were first entering the home consumer market. However, before inkjet printers became a home consumer item, challenges related to the controlled flow of inks and the clogging of print heads needed to be resolved. Synonymously, FDM technologies need to resolve issues related to part accuracy, surface roughness, build time, and mechanical properties before they can be fully adopted by industry and home consumers.

A multi-material, multi-technology (MMMT) FDM system was developed to enable experimental methods related to the FDM attributes in need of improvement. The MMMT FDM system consists of two legacy FDM systems, a pneumatic slide, and an overall control system. The FDM systems were modified so that they mimic a gantry system enabling a work piece to be transported between each FDM system. A build platform was attached to the pneumatic slide to enable the transportation of the workpiece. A software program named FDMotion was developed to control each FDM system and the pneumatic slide via a graphic user interface as well as provide in-process instructions to the user. The functional MMMT FDM system was used to explore build process variations, the effect of ultraviolet ozone surface treatments at every layer on mechanical properties, and the development of a novel heat treatment for multi-material parts produced via FDM. Additionally, the system was employed to demonstrate the fabrication of multi-colored parts as well as multi-material parts made from discrete similar and dissimilar thermoplastics.

The build process variation consisted of depositing fine contours to promote dimensional accuracy and reduce surface roughness while depositing larger internal fill rasters to decrease build time. The internal roads were four times thicker and five times wider than the outer roads. A 55% improvement in surface roughness was measured on a plane that was inclined 10° from vertical and a 35% reduction in build time was observed when fabricating a simple square prism (50.8mm by 50.8mm and 25.4mm tall). Additionally, a student's t-test confirmed that the tensile properties of tensile specimens were not significantly altered by the build process variation

Multi-material fabrication was demonstrated with the MMMT FDM system by depositing different materials (similar and dissimilar) into different layers and different regions within a layer. This fabrication method was performed to construct simple geometries requiring little to no support material as well as complex geometries that required support material for a majority of the layers.

An interlayer bond improvement strategy was explored in which an ultraviolet ozone (UV/O3) surface treatment was implemented before the deposition of a new layer. The UV/O3 treatment was intended to increase surface energy and reduce the local glass transition temperature, which in turn was expected to increase interlayer bonding. A design of experiments (DOE) and analysis of variance (ANOVA) was conducted using six UV/O3 exposure times (0, 0.5, 1.0, 1.5, 2.0, or 3.0 minutes) to determine their effect on surface energy and mechanical properties (ultimate tensile stress (UTS), strain at UTS, and modulus of elasticity). While the surface energy increased by 26% when exposing ABS P400 for 1 minute, the mechanical properties remained unchanged. The UV/O3 surface treatment, however, can be used to increase the surface energy and wettability of FDM-fabricated parts for adhesive bonding processes requiring clean and chemically active surfaces.

To improve the tensile properties of FDM-fabricated specimens, a novel multi-material fabrication method and heat treatment were developed; the result being an increase of 25% in ultimate tensile strength with minor dimensional changes. A shell-and-core configuration was used wherein the shell material (PC) exhibited a higher glass transition temperature (Tg) than that of the core (ABS). The specimens were heat-treated at a temperature above the Tg of the core material but below the Tg of the shell material. This heat treatment removed the interstices between roads of the core material while limiting dimensional changes of the shell material.

Language

en

Provenance

Received from ProQuest

File Size

110 pages

File Format

application/pdf

Rights Holder

David Espalin

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