Filament-based material extrusion additive manufacturing (MEAM) is an established technique in additive manufacturing (AM). However, semicrystalline polymers, such as polypropylene (PP), have limited commercial use in MEAM processes in the past due to their rapid crystallization kinetics and the subsequent effect on the integrity of the generated structures. The rapid crystallization of PP can be controlled by formulating blends of PP with hydrocarbon resins to enable longer re-entanglement times for interlayer adhesion. While the topic of formulating PP blends/composites with other materials to improve the printability has been investigated, variation in properties of commercial PP grades, of similar molecular weight (MW) and molecular weight distribution (MWD), on printability is still to be investigated. Those commercial PP grades can have wide variation in properties such as Melt Flow Index (MFI), additive content, and polymer architecture which can impact material properties relevant to printability. To investigate the effect of properties of commercial PP on their printability and mechanical performance, different commercial PP grades, with different properties, are blended with a fixed loading of hydrogenated resins, and the consequent effects on the mechanical properties of MEAM generated PP structures are studied via mechanical analysis. Tensile strength and the extent of interlayer adhesion in the 3D printed blends are characterized through rheological measurements. These measurements emphasize the importance of the relative location of the storage/loss modulus crossover point via small oscillatory frequency sweeps. We specifically show that a relatively higher crossover frequency will correlate with improved interlayer adhesion and reduced warpage in printed structures. However, this improvement is accompanied by a tradeoff, resulting in inferior tensile strength and an increased degree of print orientation anisotropy. / Master of Science / Additive Manufacturing (AM), commonly known as 3D printing, is a transformative technology with high potential to revolutionize the manufacturing landscape. Polymers are widely used in AM for various applications. As a result, extensive research is conducted to enhance the printability and properties of printed polymer structures. Polypropylene (PP) exhibits desirable mechanical, optical, and chemical properties that make its use in AM attractive. Despite this potential, optimizing the use of PP in 3D printing remains challenging. Consequently, extensive research is underway to improve the printability of PP. However, the effects of including additives to enhance the properties of commercial PP grades are often overlooked. We demonstrate that the choice of commercial PP grade is crucial to the mechanical and structural properties of structures generated via AM. This was established by developing a systematic experimental procedure to assess the printability of various PP grades and to measure their key mechanical and structural properties.

Yes / This paper presents an improved mathematical model for calculation of distortion vectors of two aligned surface meshes. The model shows better accuracy when benchmarked to an existing model with exceptional mathematical conditions, such as sharp corners and small radii. The model was implemented into a developed distortion compensation digital tool and applied to an industrial component. The component was made of Inconel 718 and produced by laser powder bed fusion 3D printing technology. The digital tool was utilised to compensate the original design geometry by pre-distortion of its original geometry using the developed mathematical model. The distortion of an industrial component was reduced from approximately ±400 µm to ±100 µm for a challenging thin structure subjected to buckling during the build process.

Yes / Fused deposition modelling (FDM) 3D printing has shown the most immediate potential for on-demand dose personalisation to suit particular patient's needs. However, FDM 3D printing often involves employing a relatively large molecular weight thermoplastic polymer and results in extended release pattern. It is therefore essential to fast-track drug release from the 3D printed objects. This work employed an innovative design approach of tablets with unique built-in gaps (Gaplets) with the aim of accelerating drug release. The novel tablet design is composed of 9 repeating units (blocks) connected with 3 bridges to allow the generation of 8 gaps. The impact of size of the block, the number of bridges and the spacing between different blocks was investigated. Increasing the inter-block space reduced mechanical resistance of the unit, however, tablets continued to meet pharmacopeial standards for friability. Upon introduction into gastric medium, the 1 mm spaces gaplet broke into mini-structures within 4 min and met the USP criteria of immediate release products (86.7% drug release at 30 min). Real-time ultraviolet (UV) imaging indicated that the cellulosic matrix expanded due to swelling of hydroxypropyl cellulose (HPC) upon introduction to the dissolution medium. This was followed by a steady erosion of the polymeric matrix at a rate of 8 μm/min. The design approach was more efficient than a comparison conventional formulation approach of adding disintegrants to accelerate tablet disintegration and drug release. This work provides a novel example where computer-aided design was instrumental at modifying the performance of solid dosage forms. Such an example may serve as the foundation for a new generation of dosage forms with complicated geometric structures to achieve functionality that is usually achieved by a sophisticated formulation approach.

Doctor of Philosophy / The long-term goal of this dissertation is to develop quality assurance methodologies for parts made using metal additive manufacturing (AM). Additive manufacturing is becoming a prominent manufacturing process due to its ability to generate complex structures that would otherwise be impossible to produce using traditional machining. This freedom of complexity enables engineers to make more efficient components and reduce part counts in assemblies. However, the AM process tends to generate random flaws that require manufacturers to perform extensive testing on all manufactured samples to ensure part quality. Due to this extensive testing, manufacturers have been slow to adopt the AM process. Thus, the goal of this dissertation is to understand, monitor, and predict the quality of metal AM parts as they are being printed to remove the need for post-manufacturing testing – hence the phrase Born Qualified. To enable Born Qualified manufacturing with AM, the objective of this dissertation was to use sensors installed on AM machines to monitor part quality during the process. With this objective, this dissertation focused on: (1) using acoustic signal monitoring to determine the onset of process instabilities that would generate flaws; (2) monitoring the process with multiple sensors to determine the specific type of flaws formed; (3) developing novel methods to monitor the sub-surface effects; and (4) combining multiple streams of sensor data with thermal simulations to detect flaw formation along with mechanical and material properties of the manufactured parts.

This work created a manufacturing process and material system based on binder jetting Additive Manufacturing to process pure copper. In order to reduce the sintered part porosity and shape distortion during sintering, the powder bed voids were filled with smaller particles to improve the powder packing density. Through the investigation of a bimodal particle size powder bed and nanoparticle binders, this work aims to develop an understanding of (i) the relationship between printed part properties and powder bed particle size distribution, and (ii) the binder-powder interaction and printed primitive formation in binder jetting of metals. Bimodal powder mixtures created by mixing a coarse powder with a finer powder were investigated. Compared to the parts printed with the monosized fine powder constituent, the use of a bimodal powder mixture improved the powder flowability and packing density, and therefore increased the green part density (8.2%), reduced the sintering shrinkage (6.4%), and increased the sintered density (4.0%). The deposition of nanoparticles to the powder bed voids was achieved by three different metal binders: (i) a nanoparticles suspension in an existing organic binder, (ii) an inorganic nanosuspension, and (iii) a Metal-Organic-Decomposition ink. The use of nanoparticle binders improved the green part density and reduced the sintering shrinkage, which has led to an improved sintered density when high binder saturation ratios were used. A new binding mechanism based on sintering the jetted metal nanoparticles was demonstrated to be capable of (i) providing a permanent bonding for powders to improve the printed part structural integrity, and (ii) eliminating the need for organic adhesives to improve the printed part purity. Finally, the binder-powder interaction was studied by an experimental approach based on sessile drop goniometry on a powder bed. The dynamic contact angle of binder wetting capillary pores was calculated based on the binder penetration time, and used to describe the powder permeability and understand the binder penetration depth. This gained understanding was then used to study how the nanoparticle solid loading in a binder affect the binder-powder interactions and the printed primitive size, which provided an understanding for determining material compatibility and printing parameters in binder jetting. / PHD / The binder jetting Additive Manufacturing (AM) process can be used to fabricate net-shape metal parts with complex geometries by selectively inkjet printing a liquid binding agent into a powder bed, followed by post-process sintering of the printed green parts. Motivated by the need to create highly efficient thermal management systems, this work has established a binder jetting manufacturing process chain for fabricating components made of pure copper, a conductive and optically reflective material that is challenging to be processed by laser-based AM systems. In order to improve the performance metrics (e.g., mechanical strength, electrical and thermal conductivity) of the printed copper parts, an overall strategy to improve powder bed packing density by filling the powder bed voids with fine particles was investigated. Through the use of a bimodal powder mixture and a nanoparticle binder, the sintered density and structural integrity of the printed parts were improved. Via the investigation of these novel material systems created for binder jetting of copper, (i) the gaps in understanding the relationship between printed part properties and powder bed particle size distribution were filled, and (ii) an experimental approach to characterize and understand the binder-powder interaction and printed primitive formation was created to guide the selection of printing parameters in binder jetting.

Extrusion additive manufacturing technologies may be utilized to fabricate complex geometry devices. However, the success of these additive manufactured devices depends upon their ability to withstand the static and dynamic mechanical loads experienced in service. In this study, quasi-static tensile and cyclic fatigue tests were performed on ULTEM 9085 samples fabricated by fused deposition modeling (FDM). First, tensile tests were conducted following ASTM D638 on three different build orientations with default build parameters to determine the mechanical strength of FDM ULTEM 9085 with those supplied by the vendor. Next, different build parameters (e.g. contour thickness, number of contours, contour depth, raster thickness, and raster angle) were varied to study the effects of those parameters on mechanical strength. Fatigue properties were investigated utilizing the procedure outlined in ASTM D7791. S-N curves were generated using data collected at stress levels of 80%, 60%, 30% and 20% of the ultimate tensile stress with an R-ratio of 0.1 for the build orientation XZY. The contour thickness and raster thickness were increased to 0.030 in. to determine the effect of those two build parameters on tension-tension fatigue life. Next, the modified Goodman approach was used to estimate the fully reversed (R=-1) fatigue life. The initial data suggested that the modified Goodman approach was very conservative. Therefore, four different stress levels of 25%, 20%, 15% and 10% of ultimate tensile stress were used to characterize the fully reversed fatigue properties. Because of the extreme conservatism of the modified Goodman model for this material, a simple phenomenological model was developed to estimate the fatigue life of ULTEM 9085 subjected to fatigue at different R-ratios. / Master of Science / Additive manufacturing (AM) is a revolutionary technology that is dramatically expanding the current manufacturing capabilities. The additive process allows the designers to create virtually any geometry by constructing the parts in layers. The layer-to-layer build technique eliminates many of the limitations imposed by traditional manufacturing methods. For example, machining is a common manufacturing technique that is used to create highly complex parts by removing material from a billet. The process of removing material to create a part is called subtractive manufacturing. Subtractive manufacturing requires sufficient clearance for tool access, in addition to complicated mounting fixtures to secure the part. These constraints often force engineers to design less optimized geometries to account for the manufacturing limitations. However, additive manufacturing allows the user greater design freedoms without a significant increase in resources. This innovative construction technique will push the boundaries of cutting-edge designs by removing many restrictions associated with traditional manufacturing technologies. Additive manufacturing is a relatively recent technology that evolved from rapid prototyping techniques that were developed in the 1960s. Rapid prototyping is used to create rapid iterations of physical models. However, additive manufacturing aims at creating functional end-use products. The layer-to-layer build process still poses many research challenges before it will be accepted as a reliable manufacturing technique. One of the current limitations with AM technologies is the availability of material properties associated with AM materials. The layer-to-layer build process and the toolpath creates different material properties that are dependent on the orientation of the applied load. Thus, further research is recommended to provide designers with a greater understanding of the mechanical characteristics of additive manufactured materials such as ULTEM 9085. This objective of this research is to characterize the static strength and fatigue characteristics of ULTEM 9085. The first part of the thesis focused on investigating the effects of the following build parameters on the strength of the component: build orientation, contour thickness, number of contours, contour depth, raster thickness, and raster angle. The second portion of this investigation determined the effects of fluctuating loads on the fatigue life of ULTEM 9085. Overall, the results of this investigation can be used to design more effective components using extrusion additive manufacturing technologies.

Copper is a material of interest to Additive Manufacturing (AM) owing to its outstanding material properties, which finds use in enhanced heat transfer and electronics applications. Its high thermal conductivity and reflectivity cause challenges in the use of Powder Bed Fusion AM systems that involve supplying high-energy lasers or electron beams. This makes Binder Jetting a better alternative as it separates part creation (binding together of powders) from energy supply (post-process sintering). However, it is challenging to fabricate parts of high density using this method due to low packing density of powder while printing. This work aims to investigate the effects of Hot Isostatic Pressing (HIP) as a secondary post-processing step on the densification of Binder Jet copper parts. By understanding the effects of HIP, the author attempts to create parts of near-full density, and subsequently to quantify the effects of the developed process chain on the material properties of resultant copper parts. The goal is to be able to print parts of desired properties suited to particular applications through control of the processing conditions, and hence the porosity. First, 99.47% dense copper was fabricated using optimized powder configurations and process parameters. Further, the HIP of parts sintered to three densities using different powder configurations was shown to result in an improvement in strength and ductility with porosity in spite of grain coarsening. The strength, ductility, thermal and electrical conductivity were then compared to various physical and empirical models in the literature to develop an understanding of the process-property-performance relationship. / Master of Science / Additive Manufacturing (AM) is a technique of fabricating an object in a layer-wise fashion. The layer-based approach provides opportunity for the manufacture of highly complex shapes. Binder Jetting is an AM technology that creates parts by the selective jetting of a polymeric binder onto successive layers of powdered material. In the case of metals, the printing process is followed by sintering in an oven, which burns out the binder and densifies the part. However, this is typically not enough to remove all the porosity in a specimen. While this enables the fabrication of a variety of materials, the porosity in sintered parts can be a detriment to their properties. This work aims to investigate the use of post-process Hot Isostatic Pressing (HIP) to eliminate the remaining porosity. HIP is a technique of applying high pressures at high temperatures in an inert gas medium. The goal of this research is to scientifically understand and quantify the effect of HIP on sintered parts made via Binder Jetting. The research is carried out in the context of copper, which has unique mechanical, thermal and electrical conductance properties that could be influenced by the presence of pores. In this work, the effects of the Binder Jetting-Sintering-HIP process chain on the porosity, and consequently the material properties, of copper parts are quantified. Resolving the issue of porosity can enable the printing of copper parts for specialized applications from electronic components to rocket engines. Developing a quantitative understanding can pave the way to design specific processing conditions to fabricate not only fully dense copper parts with superior properties, but also parts of a designed level of porosity that have specific target material properties.

Digital light Projection based Additive Manufacturing (AM) enables fabrication of complex three-dimensional (3D) geometries for applications ranging from rapid prototyping jet parts to scaffolds for cell cultures. Despite the ability in producing complex, three-dimensional architectures, the state of art DLP AM systems is limited to a single homogenous photo-polymer and it requires a large volume of resin bath to begin with. Extensible Multi-material Stereolithography (EMSL) is a novel high-resolution projection stereolithography system capable of manufacturing hybrid 3D objects. This system provides new capabilities, allowing more flexible design criteria through the incorporation of multiple feedstock materials throughout the structure. With EMSL manufacturing ability, multi-material programmable negative Poissons ratio honeycomb reentrant structures are realized. Researchers have been studying auxetic structures over decades, the mechanical property control of auxetic structure mainly relies on geometry design in previous studies. Now with the help of EMSL system, other design variables associated with auxetic structures, such as material properties of local structural members, are added into design process. The additional variables are then proved to have significant effects on the material properties of the auxetic structures. The ability to accurately manufacture multi-material digital design will not only allow for novel mechanical and material researches in laboratory, but also extend the additive manufacturing technology to numerous future applications with characteristics such as multiple electrical, electromechanical and biological properties. The design and optimization of EMSL system realizes novel structures have not been producible, therefore it will stimulate new possibilities for future additive manufacturing development. / Master of Science / Since 1970s, stereolithography, one of the most commonly known additive manufacturing techniques nowadays, has been improving the ability we make things. Through the controllable and repeatable photo-polymerization process, stereolithography can manufacture three-dimensional (3D) physical objects with fast speed, high accuracy and highly detailed surface finish. Today, stereolithography is already widely used in various rapid prototyping and manufacturing areas including dental products, jewelry prototypes, structural and tooling components. While latest researches continuously push its resolution to smaller scale or wider areas, this process is still limited to single material manufacturing. To go beyond this manufacturing limitation, this thesis reports an Extensible Multimaterial Stereolithography (EMSL) system. This system takes advantages of the sequential projections from a digital light modulator, combined with several lowcost while efficient mechatronics components to enable printing at least two types of materials with distinct colors or mechanical properties. With the multi-material printing capability from EMSL, novel multi-material 3D auxetic structures, which have only been theoretical concepts, are successfully manufactured and tested. The reliability of EMSL process and properties of the new materials are investigated with experiments and numerical calculations. The system can be further extended to print multiple feedstock materials into one complex architectural assembly. By realizing multi-material manufacturing capability, EMSL has broaden the potential applications of additive manufacturing and it will enable the development of multiple research and application areas including metamaterial, micro-electromechanical systems and bio-medical implants.

Effective quality improvement in the manufacturing industry is continually pursued. There is an increasing demand for real-time fault detection, and avoidance of destructive post-process testing. Therefore, it is desirable to employ sensors for in-process monitoring, allowing for real-time quality assurance. Chapter 3 describes the application of sensor based monitoring to additive manufacturing, in which sensors are attached to a desktop model fused deposition modeling machine, to collect data during the manufacturing process. A design of experiments plan is conducted to provide insight into the process, particularly the occurrence of process failure. Subsequently, machine learning classification techniques are applied to detect such failure, and successfully demonstrate the future potential of this platform and methodology. Chapter 4 relates the application of online, image-based quantification of the surface quality of workpieces produced by cylindrical turning. Representative samples of cylindrical shafts, machined by turning under various conditions, are utilized, and an apparatus is constructed for acquiring images while the part remains mounted on a lathe. The surface quality of these specimens is analyzed, employing an algebraic graph theoretic approach, and preliminary regression modeling displays an average surface roughness (Ra) prediction error of less than 8%. Prediction occurs in less than 2 seconds, showing the capability for future application in a real-time, quality control setting. Both of these cases, in additive manufacturing and in turning, are validated using real experimental data and analysis, showing application of sensor-based online process monitoring in multiple manufacturing areas. / Master of Science / Effective quality improvement in the manufacturing industry is continually pursued, and there is an increasing demand for real-time quality monitoring. Therefore, it is desirable to employ sensors for in-process monitoring, allowing for real-time quality assurance. This is explored in two manufacturing areas. The first section of this work is in the area of additive manufacturing (“3D printing”), in which sensors are attached to a desktop model machine, to collect data during the printing process. Experiments are conducted to provide insight into how the process behaves, particularly the occurrence of printing failure. Machine learning classification techniques are then applied to detect such failure, and successfully demonstrate the future potential of this platform and methodology, for real-time monitoring of the process. The second section of this work relates to the conventional machining process of turning, and describes the application of image-based measurement of surface roughness. An apparatus is constructed for acquiring images, while the cylindrically turned shaft remains mounted on the lathe. The surface roughness is measured, and preliminary modeling displays an average surface roughness prediction error of less than 8%. This prediction occurs in less than 2 seconds, showing the capability for future application in a real-time, quality control setting. Both of these cases, in additive manufacturing and in turning, show the application of sensor-based monitoring in various manufacturing areas. This work provides a basis for future research and application, demonstrating how this sensor-based monitoring approach may be used for real-time quality monitoring in manufacturing.

Additive manufacturing is a growing field dominated by printing processes that soften and re-solidify material, depositing this material layer by layer to form the printed shape. Increasingly, researchers are pursuing new materials to enable fabrication of a wider variety of associated capabilities. This includes fabrication with high-viscosity materials of many new classes of material compositions, such as doping for magnetic or electrically conducting polymers. These additives complicate the materials deposition process by requiring complex, non-linear calibration to synchronize these new candidate materials with the additive manufacturing software and hardware. In essence, additive manufacturing is highly dependent on identifying the delicate balance between materials properties, hardware, and software-which is currently realized via a time-consuming and costly iterative calibration process. This thesis is concerned with reducing this cost of calibration, in particular by providing a time-based metric based on material viscosity for material retraction at the conclusion of each extrusion. It presents a novel non-contact method of determining the material retraction rate (during reversal of extrusion), by measuring the variation in laser intensity resulting from the deformation of the material reservoir due to change in material pressure. Commercially available laser measurement systems cost more than $20,000 and are limited to 1 μm at a 300 ms (3 Hz) sampling rate. The experimental setup presented in this thesis costs less than $100 and is capable of taking measurements of 1 - 2 μm at a 0.535 ms (1870 Hz) sampling rate. For comparison, the stepper motor driving the material extruder operates at 0.667 ms (1500 Hz). Using this experimental setup, an inverse correlation is shown to exist between the viscosity of a material and the rate at which the material is retracted. Using this correlation and a simplified material analysis process, one can approximate the retraction time necessary to calibrate new materials, thereby significantly improving initial estimated calibration settings, and thus reducing the number of calibration iterations required to ready a new material for additive manufacturing. In addition, the insight provided into the material response can also be used as the basis for future research into minimizing the calibration process. / Master of Science / Additive manufacturing is a growing field with an ever-expanding base of materials used in the printing process. Two types of material gaining popularity in the commercial and academic communities are pastes and liquids. These materials require a different method of printing, and users need to take into account other considerations, such as viscosity and pressure, for their precise control. Traditionally, a new material would require a time consuming or costly calibration process to properly print. To decrease the investment required for calibration, this thesis presents a new non-contact method of measuring the pressure of the liquids using a laser to detect a dimensional change in the size of the container. This measurement technique enables an initial calibration estimate that is closer to the optimal setting, potentially allowing for better printing results when working with new materials for additive manufacturing.