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Wire and arc additive manufacturing (WAAM) is a manufacturing method using a numerical controlled motion system and a welding system to additively manufacture three dimensional components. The motion system is programmed from three dimensional computer aided design model data (3D-CAD) of the intended geometry which is then sliced in to layers and welded on additively. There are seven process categories within additive manufacturing (AM), each with their own benefits and drawbacks. One of these process categories is directed energy deposition (DED) which uses an energy source to melt material onto a build plate. Instead of filling the build plate with material and selectively melting or sintering the material, DED only deposit material which is to be melted. WAAM is a process within the DED process category. BAE Systems Hägglunds manufactures relatively large components with requirements for mass reduction. Hägglunds has therefor invested in a WAAM laboratory, for testing and investigation on how to utilize this technology to their advantage. During the master thesis a geometrical correlation between the overhang angle and the material deposition on the edges of the overhangs has been found. A slicing strategy utilising this correlation has proven useful in combatting an issue where the top surface of a parallelepiped ends up unwantedly not parallel to the substrate plate. This master thesis has also increased the capability from 30° to 45° overhang angle. A numeric simulation of cooling times in the WAAM process has been developed. The simulation had a maximum error of one minute or about 69 % longer measured than simulated cooling time at worst case.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24849号 / 工博第5166号 / 新制||工||1987(附属図書館) / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 泉井, 一浩, 教授 松原, 厚, 教授 平山, 朋子 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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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.