Manufacturing Commons^™

Processing Of Preceramic Polymers For Direct-Ink Writing, James W. Kemp

Doctoral Dissertations

Preceramic polymers are organosilicon polymers that, when pyrolyzed to above 1000°C, convert from a polymer to an amorphous ceramic. These polymers have been used for fiber spinning, polymer infiltration, and casting of materials but have recently gained interest for use as the feedstock material for additive manufacturing techniques. This work explores preceramic polymers being used for direct-ink writing (an additive manufacturing method) and many of the issues that occur with the polymers during curing and pyrolysis.

The first chapter of this dissertation provides a review of preceramic polymers, while the second and third chapters focus on the development of inks …

Structural Stability Of Thermosets During Material Extrusion Additive Manufacturing, Stian K. Romberg

Doctoral Dissertations

Over the past decade, the scale of polymer additive manufacturing has been revolutionized with machines that print massive thermoplastic parts with greater geometric complexity than can be achieved by traditional manufacturing methods. However, the heat required to print thermoplastics consumes energy and induces thermal gradients that can reduce manufacturing flexibility and final mechanical properties. With the ability to be extruded at room temperature and excellent compatibility with fibers and fillers, thermoset resins show promise to decrease the energy consumption, expand the manufacturing flexibility, and broaden the material palette offered by large-scale polymer additive manufacturing. However, structural instability in the uncured …

Innovations In Aligned And Overmolded Long Fiber Thermoplastic Composites, Shailesh P. Alwekar

Doctoral Dissertations

Long fiber thermoplastic (LFT) composite materials are increasingly used in high performance lightweight automotive, sporting, and industrial applications. LFT composites are processed with extrusion-compression molding (ECM) and/or injection molding (IM). Melt extrusion offers unique opportunities to align long fibers in a thermoplastic polymer melt. The properties of LFT materials are highly influenced by processing techniques which leads to different porosity content, fiber length distribution, and fiber orientation distribution. Hence, it is important to understand the various LFT processing techniques and their effect on mechanical, thermal, and microscopic properties.

The fundamental process-property relationships in LFT composites are investigated in this dissertation. …

Digital Cutting Force Modeling For Milling Operations, Timothy T. No

Doctoral Dissertations

Process improvement in milling through improved understanding of machining dynamics is an on-going research endeavor. The objective of this project is to advance digital modeling of the milling process by incorporating tool-specific geometry in the machining analysis. Structured light scanning will be used to perform tool geometry measurements and produce a 3D model. The 3D model data will include the spatial location of the cutting edges, as well as the rake and relief profiles from the tool cross section. The rake and relief profiles will be imported, together with the work material flow stress model, into a finite element analysis …

Transients In Plastic Instabilities During Thermo-Mechanical Reversals In An Additively Manufactured Ti6al4v, Sabina C. Kumar

Doctoral Dissertations

A complex interaction of process variables in an evolving geometry during Additive Manufacturing (AM), can bring about spatial and temporal transients of temperature and stress within each layer in a part. Although AM shares commonalities with conventional processing techniques such as casting, welding, and thermo-mechanical process, published literature has shown that the steady-state conditions are not strictly valid during AM process. Macro-scale fluctuations of thermal gradients (dT/dx: 10³ to 10⁷ K/m) combined with local changes in thermal expansion coefficients, crystallographic strains and localized stress-strain constitutive properties in conjunction with thermal cycles, can bring about a plastic strain gradient …

3d Printing Of Hybrid Architectures Via Core-Shell Material Extrusion Additive Manufacturing, Robert Cody Pack

Doctoral Dissertations

Biological materials often employ hybrid architectures, such as the core-shell motif present in porcupine quills and plant stems, to achieve unique properties and performance. Drawing inspiration from these natural materials, a new method to fabricate lightweight and stiff core-shell architected filaments is reported. Specifically, a core-shell printhead conducive to printing highly loaded fiber-filled inks, as well as a new low-density syntactic foam ink, are utilized to 3D-print core-shell architectures consisting of a syntactic epoxy foam core surrounded by a stiff carbon fiber-reinforced epoxy composite shell. Effective printing of test specimens and structures with controlled geometry, composition, and architecture is demonstrated …

Displacement-Based Dynamometer For Milling Force Measurement, Michael F. Gomez

Doctoral Dissertations

This project will study the design and testing of a low-cost dynamometer for milling dynamic force measurement. The monolithic design is based on constrained-motion/flexure-based kinematics, where force is inferred from displacement measured using a low-cost optical interrupter (i.e., a knife edge that partially interrupts the light beam in an emitter-detector pair). The time-dependent displacement of the dynamometer’s moving platform caused by the milling force is converted to the frequency domain, multiplied by the inverse of the dynamometer’s ideally single degree of freedom (SDOF) frequency response function (FRF), and converted back into the time-domain to obtain the time-dependent cutting force. The …

Process-Structure-Property Relationships In 3d-Printed Epoxy Composites Produced Via Material Extrusion Additive Manufacturing, Nadim S. Hmeidat

Doctoral Dissertations

Extrusion-based additive manufacturing (AM) technologies, such as direct ink writing (DIW), offer unique opportunities to create composite materials and novel multi-material architectures that are not feasible using other AM technologies. DIW is a novel 3D-printing approach in which viscoelastic inks, with favorable rheological properties, are extruded through fine nozzles and patterned in a filament form at room temperature.

Recent developments in DIW of polymer composites have led to expanding the range of materials used for printing, as well as introducing novel deposition strategies to control filler orientation and create improved functional/structural composite materials. Despite these substantial advancements, the successful and …

Development Of In-Situ Radiometric Inspection Methods For Quality Assurance In Laser Powder Bed Fusion, Cody S. Lough

Doctoral Dissertations

“Laser Powder Bed Fusion (LPBF) metal Additive Manufacturing (AM) fabricates 3D metal parts layer-by-layer. The process enables production of geometrically complex parts that are difficult to inspect with traditional methods. The LPBF parts experience significant geometry driven thermal variations during manufacturing. This creates microstructure and mechanical property inhomogeneities and can stochastically cause defects. Mission critical applications require part qualification by measuring the defects non-destructively. The layer-to-layer nature of LPBF permits non-intrusive measurement of radiometric signals for a part’s entire volume. These measurements provide thermal features that correlate with the local part health. This research establishes Optical Emission Spectroscopy (OES) and …