The overall goal of this research work is to enhance the capabilities of large-format, polymer material extrusion, additive manufacturing (AM) systems. Specifically, the aims of this research are to (1) Construct, and develop a robust workflow for, a large-format, robotic, AM system; (2) Develop an algorithm for determining and relaying proper rotation commands for 5 degree of freedom (DoF) multi-axis deposition; and (3) Create a method for printing a removable support material in large-format AM. The development and systems-integration of a large-format, pellet-fed, polymer, material extrusion (ME), AM system that leverages an industrial robotic arm is presented. The robotic arm is used instead of the conventional gantry motion stage due to its multi-axis printing ability, ease of tool changes for multi-material deposition and/or subtraction, and relatively small machine footprint. A novel workflow is presented as a method to control the robotic arm for layer-wise fabrication of parts, and several machine modifications and workflow enhancements are presented to extend the multi-axis manufacturing capabilities of the robot. This workflow utilizes existing AM slicers to simplify the motion path planning for the robotic arm, as well as allowing the workflow to not be restricted to a single robotic deposition system. To enable multi-axis deposition, a method for generating tool orientations and resulting deposition toolpaths from a geometry's STL file was developed for 5-DoF conformal printing and validated via simulation using several different multi-DOF robotic arm platforms. Furthermore, this research proposes a novel method of depositing a secondary sacrificial support material was created for large-format AM to enable the fabrication of complex geometries with overhanging features. This method employs a simple tool change to deposit a secondary, water-soluble polymer at the interfaces between the part and supporting structures. In addition, a means to separate support material into smaller sections to extend the range of geometries able to be manufactured via large-format AM is presented. The resultant method was used to manufacture a geometry that would traditionally be considered unprintable on conventional large-format AM systems. / Master of Science / Additive manufacturing (AM), also known as 3D printing, is a method of manufacturing objects in a layer-by-layer technique. Large-format AM is typically defined as an AM system that can create an object larger than 1 m3. There are only a few manufacturers in the world of these systems, and all currently are built on gantry-based motion stages that only allow movement of the printer in three principal axes (X, Y, Z). The primary goal of this thesis is to construct a large-format AM system that uses a robotic arm to enable printing in any direction or orientation. The use of an industrial robotic arm enables printing in multiple planes, which can be used to print structures without support structures, print onto curved surfaces, and to purt with curved layers which produces a smoother external part surface. The design of the large-format AM system was validated through successful printing of objects as large as 1.0x0.5x1.2 m, simultaneous printing of a sacrificial support material to enable overhanging features, and through completing multi-axis printing. To enable multi-axis printing, an algorithm was developed to determine the proper toolpath location and relative orientation to the part surface. Using a part's STL file as input, the algorithm identifies the normal vector at each movement command, which is then used to calculate the required tool orientation. The tool orientations are then assembled with the movement commands to complete the multi-axis toolpath for the robot to perform. Finally, this research presents a method of using a second printing tool to deposit a secondary, water-soluble material to act as supporting structures for overhanging and bridging part features. While typical 3D printers can generally print sacrificial material for supporting overhangs, large-format printers produce layers up to 25 mm wide, rendering any support material impossible to remove without post-process machining. This limits the range of geometries able to be printed to just those with no steep overhangs, or those where the support material is easily reachable by a tool for removal. The solution presented in this work enables the large scale AM processes to create complex geometries.

<p>Extrusion Deposition Additive Manufacturing (EDAM) is a process in which fiber-filled thermoplastic polymers pellets get molten in the extruder and deposited onto a build plate in a layer-by-layer basis. The use of short fiber composite for EDAM has enabled large-scale 3D printing structures and tools for traditional composite manufacturing processes. Successful EDAM production critically depends on the understanding of the process-structure-property relationship. Especially on the bonding between the beads which is of paramount importance in additive manufacturing since it affects primarily the fracture and strength characteristics of the printed part. Bonding is influenced mainly by the temperature history and the contact between the beads. Both of which is dependent on the fiber orientation within the bead induced by the flow deformation that occurs according to the printing parameters. This study aims to investigate and model the complex relationship between the printing conditions and inter-bead bonding in the lateral direction.</p> <p>A framework was developed to facilitate this aim, and it contains a fusion bonding model that couples the time-temperature history and the bead-to-bead contact interface. Four deposition parameters were studied: the nozzle height, ratio of the print velocity to extrudate velocity, bead-to-bead spacing, and layer time. First, a deposition flow model was developed, utilizing the anisotropic viscous flow model and smooth particle hydrodynamic finite element formulation, to predict the fiber orientation state across the deposited bead and the bead-to-bead interface for the given set of deposition parameters. Next, the effect of printing conditions on the temperature history of the bead was discovered by utilizing the heat transfer process simulation in ADDITIVE3D. Third, the experimental characterization procedure for mode I fracture toughness in the lateral direction was developed, and the fracture toughness was characterized using linear elastic fracture mechanics principles. Lastly, the phenomenological model for non-isothermal lateral fusion bonding was characterized using the bead contact interface, temperature history, and fracture toughness properties. This work showed a comprehensive effort in fusion bonding modeling while also presented a valuable process-structure-property-performance relationship in EDAM.  Guidance on the selection of printing conditions and strategy can be made using the developed model to print higher-strength parts.  </p>

Over the 1980’s, the introduction of Additive Manufacturing (AM) technologies has provided alternative methods for the fabrication of complex three-dimensional (3D) synthetic bone tissue implant scaffolds. However, implants are still unable to provide post surgery feedback. Implants often loosen due to mismatched mechanical properties of implant material and host bone. The aim of this PhD research is to fabricate an integrated strain gauge that is able to monitor implant strain for diagnosis of the bone healing process. The research work presents a method of fabricating electrical resistance strain gauge sensors using rapid and mask-less process by experimental development (design of experiment) using the nScrypt 3Dn-300 micro dispensing direct write (MDDW) system. Silver and carbon electrical resistance strain gauges were fabricated and characterised. Carbon resistive strain gauges with gauge factor values greater than 16 were measured using a proven cantilever bending arrangement. This represented a seven to eight fold increase in sensitivity over commercial gauges that would be glued to the implant materials. The strain sensor fabrication process was specifically developed for directly fabricating resistive strain sensor structures on synthetic bone implant surface (ceramic and titanium) without the use of glue and to provide feedback for medical diagnosis. The reported novel approach employed a biocompatible parylene C as a dielectric layer between the electric conductive titanium and the strain gauge. Work also showed that parylene C could be used as an encapsulation material over strain gauges fabricated on ceramic without modifying the performance of the strain gauge. It was found that the strain gauges fabricated on titanium had a gauge factor of 10.0±0.7 with a near linear response to a maximum of 200 micro strain applied. In addition, the encapsulated ceramic strain gauge produced a gauge factor of 9.8±0.6. Both reported strain gauges had a much greater sensitivity than that of standard commercially available resistive strain gauges.

The objective of the report is to investigate the feasibility and reliability of additive friction stir manufacturing of 7055 aluminum alloy. This is a technique in which multiple lap welds are performed to create a three-dimensional part out of relatively thin plate aluminum. To accomplish this, a four inch stack of 7055 aluminum alloy lap welds must be created. The solid weld nugget is then machined out of the center of the welded stack to create ASTM approved subsize tensile coupons. Rockwell hardness, yield strength, ultimate tensile strength, and percent elongation information is gathered from the tensile coupons to investigate the effectiveness of the additive friction stir manufacturing process. The data shows that the additive manufactured material experiences a significant reduction in strength and percent elongation while not showing any significant response to heat treatment. Suggestions are made regarding possible changes to the weld schedule that could improve the material properties of the additive manufactured aluminum.

Additive manufacturing (AM) is a novel near-net-shape manufacturing technology which deposited a component layer by layer directly from 3D CAD files. This rapid and complex weld pool process may introduce short and long range microstructure heterogeneities, which can potentially impact on the local mechanical properties of AM components. The present research thus focuses on the quantitatively analysing the microstructural heterogeneity, by the development and application of methods for the SEBM and WAAM Ti-6Al-4V parts. An additive manufacturing microstructure quantification tool, 'AMMQ', has been developed that combines automatic high resolution SEM image mapping with batch image analysis, to enable efficient quantification over large areas at the required resolution. It was found that the microstructural variation could be described by two key parameters, namely: the mean alpha plate spacing and mean β circularity of the retained β phase. The former corresponds to the combined effect of the rate of solid-state phase transformation upon cooling through the β transus in the first sub-Tβ thermal cycles followed by coarsening, whereas the latter attributes to a spheroidisation effect during subsequent re-heating and annealing below the β transus. The microstructure analysis algorithms showed adequate consistency for the possible varying imaging conditions, and for the different AM Ti-6Al-4V microstructure morphologies. In the SEBM specimens, a layer-scale periodicity in β phase circularity was detected, and a systematic drift of 'hot/cold regions was seen in the geometric specimens. Numerical modelling using a Rosenthal's model showed that the varied cooling conditions with respect to layer depth could be responsible for the layer-wise heterogeneity. Moreover, it has been shown that there is a direct linkage between thermal input, microstructure, and porosity density, as lack of fusion defects were detected in regions of low heat input, as inferred from local alpha plate measurements. This heterogeneity can firstly attribute to the SEBM control themes which were not optimised. Secondly, the heat dissipation condition for each geometry could also have affected the accumulated heat received for each volume of a part. In the WAAM specimens, a periodic microstructure pattern was consistently seen in the steady-state regions, where three typical microstructure morphologies were present: fine basketweave, colony alpha, and coarse basketweave. Micro-hardness mapping and in-situ tensile strain analysis were performed to investigate the microstructural influence on mechanical properties. It was found that both the hardness distribution and the tensile strain distribution was a function of the microstructural heterogeneity and that thin bands within each deposited layer with a colony alpha morphology appeared to be the main region of weakness within the deposited microstructures. Otherwise, the local hardness and tensile strength varied inversely to the local mean alpha plate spacing as expected. Finally, two important microstructure evolution mechanisms were proposed: i) alpha plate coarsening by the joining of neighbouring β layer as β phase volume fraction increases as the temperature approaches Tβ; ii) formation of the colony alpha by regrowth from a small fraction of alpha remnants at temperatures very close to Tβ.

The 21st century demand for innovation is leading towards a revolution in the way products are perceived. This will have a major impact on manufacturing technologies as current product innovation is constrained by the available manufacturing processes, which function independently. One of the most significant developments is the emergence of hybrid manufacturing technologies integrating various individual manufacturing processes. Hybrid processes utilise the advantages of the independent processes whilst minimising their weaknesses as well as extending application areas. Despite the fact that the drawbacks of the individual processes have been significantly reduced, the application of state of the art hybrid technology has always been constrained by the capabilities of their constituent processes either from technical limitations or production costs. In particular, it is virtually impossible to machine complex parts due to limited cutting tool accessibility. By contrast, additive manufacturing (AM) techniques completely solve the tool accessibility issue, but this increased flexibility and automation is achieved by compromising on part accuracy and surface quality. Furthermore, the shape and size of raw materials have to be specific for each hybrid process. More importantly, process planning methods capable of effectively utilising manufacturing resources for hybrid processes are highly limited. In this research, a hybrid process, entitled iAtractive, combining additive, subtractive and inspection processes is proposed. An experimental methodology has been designed and implemented, by which a generative reactionary process planning algorithm (GRP2A) and feature-based decision-making logic (FDL) is developed. GRP2A enables a complex part to be accurately manufactured as one complete unit in the shortest production time possible. FDL provides a number of manufacturing strategies, allowing existing parts to be reused and transformed into final parts with additional features and functionalities. A series of case studies have been manufactured from zero and existing parts, demonstrating the efficacy of the iAtractive process and the developed GRP2A and FDL, which are based on a manual process. The major contribution to knowledge is the new vision for a hybrid process, which is not constrained by the capability of the individual processes and raw material in terms of shape and size. It has been demonstrated that the hybrid process together with GRP2A and FDL provides an effective solution to flexibly and accurately manufacture complex part geometries as well as remanufacture existing parts.

3D printing has revolutionised traditional manufacturing methods, opening up and distributing design and production of low cost, custom objects to virtually anyone. Tailoring of print material and part geometry allows for the benefits of this technology to reach multiple engineering and scientific fields, given appropriate design. A multidisciplinary approach concerning development of new print materials and methods was undertaken with the aim of further expansion and application of 3D printing towards electrochemical applications. Specific requirements of materials used in this domain, such as conductivity and chemical stability, led to development of functional printable carbon composites, compatible with consumer grade 3D printers. This allows facile production of cheap, reusable, disposable, electrodes for analytical applications, demonstrating heavy metal detection in aqueous media and allowing further tailoring to specific applications to be easily implemented. A new method for printing of cellulose solutions was developed, with post processing of printed parts resulting in biocompatible, porous, conductive structures. When used as electrodes in microbial fuel cells, improved power and current output over traditionally used carbon cloth electrodes was achieved. Other developments resulting from this work applicable to other fields include a novel trajectory generation method based on exponential functions which can be applied to practically any robotic system, as well as improvements to the production process of metal alloy filaments for 3D printing of metallic components.

Three-dimensional, additive printing has emerged as an exciting new technology for the design and manufacture of small spacecraft systems. Using 3-D printed thermoplastic materials, hybrid rocket fuel grains can be printed with nearly any cross-sectional shape, and embedded cavities are easily achieved. Applying this technology to print fuel materials directly into a CubeSat frame results in an efficient, cost-effective alternative to existing CubeSat propulsion systems. Different 3-D printed materials and geometries were evaluated for their performance as propellants and as structural elements. Prototype "thrust columns" with embedded fuel ports were printed from a combination of acrylonitrile utadiene styrene (ABS) and VeroClear, a photopolymer substitute for acrylic. Gaseous oxygen was used as the oxidizer for hot-fire testing of prototype thrusters in ambient and vacuum conditions. Hot-fire testing in ambient and vacuum conditions on nine test articles with a combined total of 25 s burn time demonstrated performance repeatability. Vacuum specific impulse was measured at over 167 s and maximum thrust of individual thrust columns at 9.5 N. The expected ΔV to be provided by the four thrust columns of the consumable structure is approximately 37 m/s. With further development and testing, it is expected that the consumable structure has the potential to provide a much-needed propulsive solution within the CubeSat community with further applications for other small satellites.

Laser Sintering, a method of additive manufacturing, is used in the production of concept models, functional prototypes, and end-use production parts. As the technology has transitioned from a product development tool to an accepted production technique, functional qualities have become increasingly important. Tension properties reported for popular polyamide sintering materials are comparable to the molded properties with the exception of elongation. Reported strains for laser sintered polyamide are in the 15-30% range with 200-400% strains reported for molding. (CES Edupack n.d.) The primary contributors to poor mechanical properties in polyamide materials used during Selective Laser Sintering® are studied. Methods to quantify decreased mechanical properties are compared against each other and against mechanical properties of components fabricated using multiple process parameters. Of primary interest are Ultimate Tensile Strength (UTS) and Elongation at Break (EOB) of tensile specimens fabricated under conditions that produce varying degrees of ductile and brittle fracture. / text

Background: The applications for rapid prototyping have expanded dramatically over the last 20 years. In recent years, additive manufacturing has been intensely investigated for surgical implants, tissue scaffolds, and organs. There is, however, scant literature to date that has investigated the viability of 3D printing of surgical instruments. Materials and Methods: Using a fused deposition manufacturing (FDM) printer, an army/ navy surgical retractor was replicated from polylactic acid (PLA) filament. The retractor was sterilized using standard FDA approved glutaraldehyde protocols, tested for bacteria by PCR, and stressed until fracture in order to determine if the printed instrument could tolerate force beyond the demands of an operating room. Results: Printing required roughly 90 minutes. The instrument tolerated 13.6 kg of tangential force before failure, both before and after exposure to the sterilant. Freshly extruded PLA from the printer was sterile and produced no PCR product. Each instrument weighed 16g and required only $0.46 of PLA. Conclusions: Our estimates place the cost per unit of a 3D printed retractor to be roughly 1/10th the cost of a stainless steel instrument. The PLA Army/ Navy is strong enough for the demands of the operating room. Freshly extruded PLA in a clean environment, such as an OR, would produce a sterile, ready to use instrument. Due to the unprecedented accessibility of 3D printing technology world wide, and the cost efficiency of these instruments, there are far reaching implications for surgery in some underserved and less developed parts of the world.