ORCID Identifier(s)

0000-0001-9984-856X

Graduation Semester and Year

2020

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Ankur Jain

Abstract

Additive manufacturing (AM) is a burgeoning method for manufacturing over the subtractive manufacturing methodologies. Among the various method of polymer additive manufacturing the fused deposition modeling (FDM) also known as 3D printing is the most popular technique. In this technique, a rastering extruder dispenses a thermoplastic material on to a bed at a temperature greater than its glass transition temperature to build the part. Due to the additive nature of the process, AM introduces several challenges related to functional properties such as strength, thermal conductivity, etc of the eventual part. Measurement of thermal conductivity of additively manufactured polymer samples in the filament rastering direction and the build direction is done. Experimental data indicate significant orthotropy in thermal conductivity, with the value in the build direction being much lower than in the raster direction. As significant anisotropy is found in build and raster direction, an effort has been made to reduce it by post-processing i.e thermal annealing. This work reports significant enhancement in build-direction thermal conductivity of polymer extrusion-based parts as a result of thermal annealing. Over 150% improvement is observed when annealed at 135 °C for 96 hours. A theoretical model based on Arrhenius kinetics for neck growth and a heat transfer model for the consequent impact on inter-layer thermal contact resistance is developed. The theoretical model may play a key role in developing practical thermal annealing strategies that account for the multiple constraints involved in annealing of polymer parts. The process of filament-to-filament adhesion during polymer extrusion additive manufacturing (AM) is critically influenced by temperature distribution around the filament. Infrared thermography-based measurement of the temperature distribution in the filament in the standoff region and an analytical model for heat transfer in this region are studied. The analytical model predicts an exponentially decaying temperature distribution, the nature of which is governed by the characteristic length, a parameter that combines multiple process parameters such as mass flow rate, filament diameter, heat capacity, and cooling conditions. While past works have reported side-view (x-z) temperature measurement using infrared thermography, A measurement of the in-plane (x-y) temperature field is done on the build plane by infrared thermography carried out from under the build plate using an infrared-transparent window and infrared right-angle prism mirror. Direct measurement of in-plane temperature distribution of build plate, filament, and pre-post heater is carried out with an infrared camera. A few key features revealed by measurements include symmetrical and asymmetrical temperature distributions for single and multi-line printing, respectively, upstream-downstream asymmetry, and the thermal influence between lines being limited only to the adjacent line.

Keywords

Additive manufacturing, Polymer extrusion, Temperature measurement, Infrared thermography, Thermal annealing, Thermal conductivity enhancement, Filament adhesion, Fused deposition modelling, ABS

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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