Additive friction stir deposition (AFSD) is an emerging solid-state metal additive manufacturing technology that uses deformation bonding to create near-net shape 3D components. As a developing technology, a deeper understanding of the processing science is necessary to establish the process-structure relationships and enable improved control of the as-printed microstructure and material properties. AFSD provides a unique opportunity to explore the friction stir fundamentals via direct observation of the material during processing. This work explores the relationship between the processing parameters (e.g., tool rotation rate Ω, tool velocity V, and material feed rate F) and the thermomechanical history of the material by process monitoring of i) the temperature evolution, ii) the force evolution, and iii) the interfacial contact state between the tool and deposited material. Empirical trends are established for the peak temperature with respect to the processing conditions for Cu and Al-Mg-Si, but a key difference is noted in the form of the power law relationship: Ω/V for Cu and Ω2/V for Al-Mg-Si. Similarly, the normal force Fz for both materials correlates to V and inversely with Ω. For Cu both parameters show comparable influence on the normal force, whereas Ω is more impactful than V for Al-Mg-Si. On the other hand, the torque Mz trends for Al-Mg-Si are consistent with the normal force trends, however for Cu there is no direct correlation between the processing parameters and the torque. These distinct relationships and thermomechanical histories are directly linked to the contact states observed during deformation monitoring of the two material systems. In Cu, the interfacial contact between the material and tool head is characterized by a full slipping condition (δ=1). In this case, interfacial friction is the dominant heat generation mechanism and compression is the primary deformation mechanism. In Al-Mg-Si, the interfacial contact is characterized by a partial slipping/sticking condition (0<δ<1), so both interfacial friction and plastic energy dissipation are important mechanisms for heat generation and material deformation. Finally, an investigation into the contact evolution at different processing parameters shows that the fraction of sticking is critically dependent on the processing parameters which has many implications on the thermomechanical processing history. / Doctor of Philosophy / Additive manufacturing or three-dimensional (3D) printing technologies have been lauded for their ability to fabricate complex geometries and multi-material parts with reduced material waste. Of particular interest is the use of metal additive manufacturing for repair and fabrication of industrial and structural components. This work focuses on characterizing the thermomechanical processing history for a developing technology Additive Friction Stir Deposition (AFSD). AFSD is solid-state additive manufacturing technology that uses frictional heat and mechanical mixing to fabricate 3D metal components. From a fundamental materials science perspective, it is imperative to understand the processing history of a material to be able to predict the performance and properties of a manufactured part. Through the use of infrared imaging, thermocouples, force sensors, and video monitoring this work is able to establish quantitative relationships between the equipment processing parameters and the processing history for Cu and Al. This work shows that there is a fundamental difference in how these two materials are processed during AFSD. In the future, these quantitative relationships can be used to validate modeling efforts and improve manufacturing quality of parts produced via friction stir techniques.

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Grâce à la fabrication additive, il est aujourd'hui possible de fabriquer de nouvelles géométries. Les perspectives offertes par les moyens de fabrications conventionnelles et additives sont très différentes. Des propositions de design très contraintes peuvent devenir beaucoup plus libres avec la fabrication additive. Cette liberté qu'elle offre fait émerger une multitude de possibilités. Dans ce manuscrit, nous nous sommes focalisés sur un type particulier de structures (les octetruss) ainsi que sur les moyens de fabrication EBM (Electron Beam Melting) de la société ARCAM. Les travaux présentés dans cette thèse ont été réalisés au sein des laboratoires G-SCOP et SIMAP ainsi qu'en partenariat avec l'entreprise POLY-SHAPE. Ce manuscrit est articulé autour de trois principaux points.Il s'agit tout d'abord de faire émerger des structures treillis lors du processus de conception. Pour cela, deux approches existantes sont détaillées. La première met en œuvre l'optimisation topologique et la seconde s'appuie sur le concept de matériau équivalent. Ensuite deux méthodologies permettent de faire émerger des zones dans lesquelles l'intégration de structures treillis est adaptée. La première consiste à réaliser les différentes zones en s'appuyant sur un champ de contraintes issu d'un calcul Eléments Finis, la seconde se base sur un résultat d'optimisation topologique pour établir les différentes zones. Cette seconde méthodologie est appliquée à un cas d'étude industriel.Ensuite nous étudions comment remplir les différentes zones avec des structures treillis adaptées en nous focalisant tout d'abord sur leur génération. Un accent particulier est porté sur l'intersection des différents barreaux par la mise en place de sphères. Une méthodologie permettant de générer des arrondis est également proposée. Une étude est menée sur l'ensemble des paramètres et informations à considérer pour intégrer une structure treillis à une zone donnée. Cette étude conduit à une proposition de méthodologie qui est appliquée à un cas d'étude industriel.Enfin, les aspects liés à la fabrication sont pris en compte. Pour cela, nous considérons différentes limites du moyen de fabrication EBM pour des structures treillis comme les dimensions maximales réalisables ou les problématiques thermiques. Une étude consistant à prédire la dépoudrabilité des pièces est réalisée. Enfin, des essais mécaniques sont effectués. Nos résultats sont comparés à ceux obtenus dans d'autres travaux. L'impact des arrondis sur le comportement mécanique d'une pièce est discuté. / Thanks to additive manufacturing, it is now possible to manufacture new geometric shapes. The prospects offered by the methods of conventional and additive manufacturing are very different. Highly constrained design proposals can become much freer with additive manufacturing. The freedom it offers brings forward a multitude of possibilities. In this manuscript, we focused on a particular type of structures (the octetruss) as well as the use of EBM (Electron Beam Melting) of ARCAM as a means of manufacturing. The work presented in this thesis was carried out in the laboratories G-SCOP and SIMAP as well as in partnership with the company POLY-SHAPE. This manuscript focuses on three main points.The first of which is the action of emergence of lattice structures during the design process. For this, two existing approaches are detailed. The first uses topological optimization and the second is based on the concept of equivalent material. Following these, there are two methodologies used to identify areas in which the integration of lattice structures is possible and appropriate. The first consists of creating the different zones by relying on a stress field resulting from a finite element calculation, the second establishes the different zones using a topological optimization result. This second methodology is applied to an industrial case study.Secondly, we study how to fill the different areas with appropriate lattice structures by focusing first on their generation. Particular emphasis is placed on the intersection of the various bars by the establishment of spheres. A methodology for generating rounded-shape is also proposed. A study is carried out on all the parameters and information in order to integrate a lattice structure to a given area. This study leads to a proposed methodology that is applied to an industrial case study.Finally, aspects related to manufacturing are taken into account. For this, we consider different limits of the EBM manufacturing and what they mean for lattice structures; such as maximum achievable dimensions or thermal problems. A study to predict powder removal in order to extract the fabricated structure is performed. Mechanical tests are carried out. Our results are compared to those obtained in other works. The impact of curve on the mechanical behavior of a product is discussed.

Metal additive manufacturing (AM) can produce complex parts that were once considered impossible or too costly to fabricate using conventional machining techniques, making AM machines an exceptional tool for rapid prototyping, one-off parts, and labor-intensive geometries. Due to the growing popularity of this technology, especially in the defense and medical industries, more researchers are looking into the physics and mechanics behind the AM process. Many factors and parameters contribute to the overall quality of a part, one of them being the powder bed itself. So far, little investigation has been dedicated to the behavior of the powder in the powder bed during the lasering process. A powder spreading machine that simulates the powder bed fusion process without the laser was designed by Lawrence Livermore National Laboratory and was built as a platform to observe powder characteristics. The focus for this project was surface roughness and particle size distribution (PSD), and how dose rate and coating speed affect the results. Images of the 316L stainless steel powder on the spreading device at multiple layers were taken and processed and analyzed in MATLAB to access surface quality of each region. Powder from nine regions of the build plate were also sampled and counted to determine regional particle size distribution. As a comparison, a simulation was developed to mimic the adhesive behavior of the powder, and to observe how powder distributes powder when spread.

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Introduction: Production systems go through changes over time and there are different factors driving the change. Metal Additive manufacturing (AM) could be a factor with industries that already havetaken interest in the manufacturing technique. Qualification and standards of manufacturing guide consistent product quality and could face challenges when implementing AM. However,most publications about metal AM are currently posted from a material point of view. This requires more publications with comprehensive overviews of metal AM and dive deeper into metal AMs industry applications, limitations and challenges. Purpose: The purpose of this thesis is to identify challenges that may arise in the implementation of AM. The intention is also to compare the conventional method of sand casting with AM for metal production targeted at excavators. This is accomplished by specifically highlighting the metallurgical benefits of AM. Research Questions: RQ1: What challenges arise when qualifying AM products for excavators? RQ2: What are the metallurgical benefits of an AM produced product in comparison to a Sand Casted product for excavator bucket teeth? Method: An inductive approach has been taken, with a literature, empirical and case study conducted.The construction of the theoretical framework used information from scientific articles and books. The findings of the empirical study arrived from information gathered through observations and experimentation, with help and interpretation from the case companies. The empirical findings will assist in answering the research questions. The case study consisted of metallurgical testing in form of porosity analysis, microstructure examination, hardness- and chemical composition test. Conclusion: Several challenges were discovered that will impact the qualification of AM products. These can affect the results derived from the case study, providing incorrect data. It can however be seen as beneficial as it provides knowledge of how to reduce or eliminate their impact withfuture analyses.The AM products tested, displayed positive metallurgical properties in comparison with sand casted products. A standout trait was the consistency in the dimension and density of the AM products, displaying how AM can create nearly identical products.

Additive friction stir deposition (AFSD) is a newly developed solid-state metal additive manufacturing (AM) technology that adds a material feeding mechanism to the friction stir principle (Yu et al.., 2018). As a newly developed process, the development of a sound understanding of the process mechanics is necessary and may shed light on both limiting factors and new opportunities. This work explores the fundamental modes of deformation through an analytical decomposition of three flow components: 1) radial spreading, 2) rotating, and 3) traversing shear flow. The analytical models provide 'back-of-the-envelope' estimates of mechanical requirements (machine torque, for example), and straightforward algebraic equations for estimating the peak strain rate associated with deformation and the expected residence time of material underneath the AFSD tool head. A more complex, but preliminary, numerical modeling approach is then presented to models the steady state material flow as a fully coupled non-Newtonian fluid with rate and temperature dependent properties. Additionally, a transient thermal model is presented which captures the thermal history of the material along a dynamic printing trajectory. The numerical models provide insight into the pressure distribution underneath the AFSD tool, which impacts deformation bonding conditions at the interface, and suggest that temperature differences under the tool may be as high as 70℃. Several interface fracture experiments reveal a well-bonded center region, with high ductility and energy dissipation, and a poorly bonded outer edge region. Novel characterization work has been presented showing evidence of a nearly uniform 50μm thick shear layer on the top surface of a deposit. Analysis of the Prandtl number suggests that this shear layer is a consequence of a thin thermal boundary layer, which in the presence of frictional shear stress, becomes a thermo-mechanical boundary layer with a distinct flow regime from the bulk. Further characterization shows viscous mixing patterns in the wake of tool pins, and incomplete bonding at the edges of the deposition track. An additional application is presented for AFSD – selective area cladding of thin sheet metal. Substrates as thin as 1.4mm were clad without localized deformation, which is dependent on the clamping configuration of the substrate. Cladding quality, interface integrity, and certain failure modes are identified for thin cladding operations. In-situ monitoring and ex-situ laser scanning shows the slow evolution of thermal distortion during cooling of the cladding-on-sheet system. Finally, residual stress and strain estimates are made using curvature methods for bi-layer specimens extracted from the cladding. / Doctor of Philosophy / Additive manufacturing of metal components (colloquially called "3D printing") has generated significant interest and excitement as the manufacturing method of the future, where new materials with complex shapes and functionalities may unlock new possibilities for commerce and industry. Metal 3D printing also gives us new methods to repair aging and damaged structures, providing opportunities to extend the life of existing infrastructure. This work is centrally focused on understanding the most important factors and physical principles at play during a particular metal additive manufacturing process, additive friction stir deposition (ASFD). AFSD uses deformation to heat and bond materials together, building on the principles of friction welding and forge welding. A fundamental understanding of the process mechanics will allow for a better understanding of the current limits and potential opportunities this new technology can provide. Using a combination of analytical analysis, numerical modeling, and experiments, this work aims to provide a deeper understanding of the material flow, thermal fields, and mechanical forces associated with depositing material by AFSD, which may be insightful for new materials, tunable material properties, and may lead to new machine design opportunities.

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The analytical modelling of complex turbulent airflow remains one of the great unsolved mysteries of physics, but in this paper two widely used Reynolds Averaged Navier-Stokes models (k-$\epsilon$ and k-$\omega$ SST) are compared while designing a heat exchanger for the KTH Formula Student electric race car. CAD software was used to design lattices for the heat exchanger core and theorise about how to increase heat transfer while also taking into account the utilisation of metal additive manufacturing. The models were then analysed using Computational Fluid Dynamics to determine their characteristics as well as the effects of the two turbulence models.  It was found that the first iteration of the second design performed best in terms of pressure drop and generating turbulent kinetic energy closely followed by the second iteration of the second design and the second iteration of the first design. When comparing the turbulence models the results indicated agreement with their theoretical foundations. The first model overestimating turbulent kinetic energy relative to the second, which picked up more detail of near-wall turbulence thanks to better boundary layer formulation. Future work includes improving the simulation setup, correlating the results with wind tunnel testing and further evaluating more complex designs.