Date of Award

2019-01-01

Degree Name

Master of Science

Department

Mechanical Engineering

Advisor(s)

David Espalin

Abstract

Evolution in additive manufacturing, specifically in material extrusion, has resulted in large-scale machines capable of extruding thermoplastic-matrix composite materials in higher volumes to fabricate products for large-scale applications. As with small- and medium-scale material extrusion, the properties of the final product often correlate directly with the bevy of print parameters employed. The current research was performed to evaluate the effects of the screw speed and temperature on an ABS 20%wt. carbon fiber thermoplastic processed on a Big Area Additive Manufacturing (BAAM, Cincinnati Inc) machine. Five screw speeds (50, 150, 250, 350 and 400 rpm) and three extruder temperature profiles were selected (one profile based on manufacturer recommendations, and two profiles outside the recommendations wherein one was above and the other was below the recommended temperatures). For extruded and printed beads, qualitative and quantitative results are reported for void percentage, tensile strength, yield strength, modulus, mass loss due to off-gassing, specific gravity, and surface roughness. At lower screw speeds, small voids were identified throughout the entire radius of the specimens. This voids are the result of volatile off gassing or material degradation. At screw speeds of 250 rpm or more, larger voids were identified at the edges of the specimens. These voids are significantly larger than gas voids and are caused by air which is introduced due to the speed at which material is entering the barrel of the extruder. Results highlighted the need to understand and model internal voids in beads, as gas voids are not eliminated through the printing process. Although the use of higher temperatures allowed for an increased extruder output, they also resulted in a higher void content, also assumed to be a result of increased off-gassing. Overall, findings from this work can be used in academic and applied research in the area of large-scale additive manufacturing. This document also contains a section describing the controls for a non-standard CNC tool with a wire embedder end effector that was mounted into the BAAM system. This tool allows for the introduction of 3D printed electronics at large scale which in the past has only been reserved for small scale additive manufacturing systems.

Language

en

Provenance

Received from ProQuest

File Size

71 pages

File Format

application/pdf

Rights Holder

Xavier Jimenez Guzman

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