This thesis presents a newly developed manufacturing method, based on cyber-physically enhanced hybrid machining, regarding an optical bench (OB) made of Ti6Al4V alloy for the Advanced Telescope for High-ENergy Astrophysics (ATHENA). The method includes sophisticated hybrid laser metal deposition equipment and state-of-the-art cryogenic machining hardware. The derived strategy combines localized energy input, preheating, heat treatment, intermediate stress relief and machining. This results in a complex thermal history and remaining residual stresses, representing a considerable challenge for final precision machining. The method targets first time right machining based on iterative machining, process data-based tool path correction and spatially resolved root cause research based on process data modeling.:II. Table of Contents I. Acknowledgement ............................................................ III II. Table of Contents ................................................................. I 1. Introduction ........................................................................ 1 1.1 Foreword .................................................................................... 1 1.2 Research Subject Lot Size One ....................................................... 2 1.2.1 Historical Perspective ................................................................. 2 1.2.2 Going Full Cycle ......................................................................... 3 2. State of the Art in Titanium Processing ............................... 4 2.1 Conventional Processing................................................................ 4 2.2 Additive Manufacturing ................................................................. 5 2.2.1 Introduction .............................................................................. 5 2.2.2 Powder Bed Fusion ..................................................................... 6 2.2.3 Direct Energy Deposition ............................................................. 8 3. Derivation of a Flexible Hybrid Manufacturing System ...... 11 3.1 The ATHENA OB – a Large Structural Space Component ..................11 3.2 Material Constraints ....................................................................12 3.3 Solidification and Microstructural Content .......................................17 3.4 Residual Stresses and Intrinsic Heat Treatment ..............................22 3.4.1 Transient Temperature Gradients ................................................22 3.4.2 Residual Stresses and Degree of Fixity ........................................24 3.4.3 In-situ Stress Relief and Plastic Deformation ................................28 3.4.4 In-situ Martensite Decomposition and Thermal Trade-off ...............30 3.5 Melt Pool Considerations in Laser Metal Deposition ..........................36 3.6 Concept of Flexible Hybrid Manufacturing Cell .................................43 3.7 Process and Equipment Review by ESA ..........................................45 4. Realization of a Flexible Manufacturing Cell ...................... 45 4.1 Additive Processing with Hybrid Laser Metal Deposition ....................45 4.1.1 Principle Hardware ....................................................................45 4.2 Novel Local Shielding Solution ......................................................47 4.2.1 Melt Pool Observation towards Process Data Model ........................51 4.2.2 Energy Source Coupling .............................................................57 4.3 Subtractive Processing with Cryogenic Milling .................................57 4.3.1 General Considerations for Subtractive Processing ........................57 4.3.2 Cryogenic Machining Approach ...................................................58 4.3.3 Cryogenic Machining from the Materials Viewpoint ........................60 4.3.4 Cryogenic Machining of Additively Manufactured Ti-6Al-4V .............62 4.3.5 Principle Hardware for Cryogenic Milling with CO2..........................66 4.3.6 Intelligent Tool Spindle Future Part of the Process Data Model ........69 4.3.7 Carbon Dioxide Weighing Equipment and Switching Station ............70 4.3.8 Protective Measures for Safe Use of Cryogenic CO2 .......................72 4.4 Handling System .........................................................................74 4.4.1 Framework Considerations .........................................................74 4.4.2 Twin Robot System in the Initial State .........................................76 4.4.3 Integration of the ATHENA Turntable ...........................................79 4.4.4 Robot Calibration ......................................................................81 4.5 Lighting for Visual Inspection ........................................................84 4.6 Critical Design Review by ESA .......................................................84 5. Implementation and Validation ......................................... 85 5.1 Powdery Filler Material Selection ...................................................85 5.2 Basic Parameter Set for Additive Manufacturing ..............................87 5.2.1 Operating Point Selection ...........................................................87 5.2.2 Characterization and evaluation ..................................................89 5.2.3 Substrate to Structure Transition ................................................95 5.3 Energy Source Coupling ...............................................................99 5.3.1 Process Development ................................................................99 5.3.2 As-built Surface Treatment ...................................................... 103 5.3.3 Heat Treatment ...................................................................... 104 5.3.4 Mechanical Testing .................................................................. 106 5.3.5 Fractured Surfaces .................................................................. 108 5.3.6 Microstructure ........................................................................ 110 5.3.7 Linear Expansion Coefficient ..................................................... 113 5.4 Cryogenic Milling ....................................................................... 114 5.4.1 Strategy Approach .................................................................. 114 5.4.2 Milling Implementation ............................................................ 116 5.4.3 Technical Cleanliness ............................................................... 120 5.4.4 Accuracy and Duration ............................................................. 122 5.4.5 Surface Roughness.................................................................. 122 5.5 Process Data Model ................................................................... 123 6. Final Discussion and Conclusions..................................... 130 6.1 Summary ................................................................................. 130 6.2 Conclusions .............................................................................. 131 6.3 Outlook .................................................................................... 132 III. List of Figures ...................................................................... I IV. List of Tables .................................................................. VIII V. References ......................................................................... IX VI. Symbols and Units ....................................................... XXXVI VII. Abbreviations .............................................................. XXXIX VIII. Annex I ............................................................................ XLI IX. Annex II ....................................................................... XLIII X. Annex III ....................................................................... XLIV XI. Annex IV.......................................................................... XLV XII. Annex V ......................................................................... XLVI XIII. Annex VI....................................................................... XLVII XIV. Annex VII ................................................................... XLVIII

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<p>This study is concerned with the predictive modeling of the machining and the mechanical behaviors of additive manufactured (AMed) Ti6AlV/TiC composites and Ti6Al4V, respectively, using microstructure-based hierarchical multiscale modeling. The predicted results could constitute as a basis for optimizing the parameters of machining and AM of the current materials.</p> <p>Through hierarchical flow of material behaviors from the atomistic, to the microscopic and the macroscopic scales, multiscale heterogeneous models (MHMs) coupled to the finite element method (FEM) are employed to simulate the conventional and the laser assisted machining (LAM) of Ti6AlV/TiC composites. In the atomistic level, molecular dynamics (MD) simulations are used to determine the traction-separation relationship for the cohesive zone model (CZM) describing the Ti6AlV/TiC interface. Bridging the microstructures across the scales in MHMs is achieved by representing the workpiece by macroscopic model with the microscopic heterogeneous structure including the Ti6Al4V matrix, the TiC particles, and their interfaces represented by the parameterized CZM. As a result, MHMs are capable of revealing the possible reasons of the peculiar high thrust forces behavior during conventional machining of Ti6Al4V/TiC composites, and how laser assisted machining can improve this behavior, which has not been conducted before.</p> <p>Extending MHMs to predict the mechanical behaviors of AMed Ti6Al4V would require including the heterogeneous microstructure at the grain level, which could be computational expensive. To solve this issue, the extended mechanics of structure genome (XMSG) is introduced as a novel multiscale homogenization approach to predict the mechanical behavior of AMed Ti6Al4V in a computationally efficient manner. This is realized by embedding the effects of microstructure heterogeneity, porosity growth, and crack propagation in the multiscale calculations of the mechanical behavior of the AMed Ti6Al4V using FEM. In addition, the XMSG can predict the asymmetry in the Young’s modulus of the AMed Ti6Al4V under tensile and compression loading as well as the anisotropy in the mechanical behaviors. The applicability of XMSG to fatigue life prediction with valid results is conducted by including the energy dissipations associated with cyclic loading/unloading in the calculations of the cyclic response of the material.</p>

Laser patterning techniques have shown in the last decades to be capable of producing functional surfaces on a large variety of materials. A particular challenge for these techniques is the treatment of additively manufactured parts with high roughness levels. The presented study reports on the surface modification of additive-manufactured components of Ti64 and Al–Mg–Sc (Scalmalloy), with the aim of implementing water- and ice-repellent properties. Different laser-based microstructuring techniques, using nanosecond and picosecond pulses, are combined to create multiscale textures with feature sizes between ≈800 nm and 21 μm. The wettability could be set to static water contact angles between 141° and 153° for Ti64 and Al–Mg–Sc, respectively. In addition, surface free energy is analyzed for different surface conditions.

Les exigences du secteur aéronautique incitent les constructeurs à intégrer une part croissante d'alliages de titane Ti6Al4V et de composites à fibres de carbone maintenues dans résine époxyde pour alléger les pièces de structures tout en conservant d'excellentes propriétés mécaniques. Ces matériaux sont empilés et percés en une seule opération au moment de l'assemblage des appareils. Les verrous technologiques et scientifiques sont complexes dès lors que l'opération de perçage a été réalisée à sec. Dans la partie titane, un bilan thermique complet de la zone de coupe est établi pour limiter la production de chaleur et éviter la diffusion vers la partie composite. Il est montré qu'un phénomène de retreint de la surface du trou sur le foret est responsable d'environ 50% de la consommation énergétique de l'opération. Les mécanismes de retour élastique et de retreint thermique ont pu être mis en évidence par démarche expérimentale et numérique. Une étude tribologique est menée dans les zones de contact pièce/outil et copeau/outil pour quantifier et modéliser les contributions mécaniques (coefficient de frottement) et thermiques (coefficient de partage de la chaleur) aux interfaces. Ces données seront utilisées pour la simulation des effets thermomécaniques induits sur la pièce et le foret. Dans la partie composite, une étude expérimentale macroscopique est menée en premier lieu pour enrichir les connaissances dans ces matériaux caractérisés par des comportements très hétérogènes. Puis une analyse de la coupe des fibres à l'échelle mésoscopique est proposée pour identifier les mécanismes à l'origine du refus de coupe et du délaminage. A l'issue de ces études un outil bi-compétence a pu être mis au point. L'optimisation de la géométrie des listels, l'apport d'un revêtement diamant CVD anti-abrasion et le choix de conditions de coupe adaptées à chacun des matériaux, garantissent le respect de la qualité et des contraintes environnementales de l'usinage à sec.

Tato práce se zabývá pokročilou technologií výroby personalizovaných kloubních implantátů metodou EBM za použití titanové slitiny Ti6Al4V-ELI a navrhuje nový unikátní design kolenního implantátu společně s metodologií jeho inserce, přičemž tato řešení jsou součástí patentové přihlášky č. PV 2020-459. Toto neinvazivní řešení náhrady kolenního kloubu je šetrnější k pacientovi, maximálně chrání jeho zdravé tkáně a kosti, navíc se dá předpokládat vyšší životnost implantátu ve srovnání s tradičními dostupnými řešeními. Byla uskutečněna výroba vzorků z materiálu Ti6Al4V-ELI metodou EBM, proveden rozbor jejich materiálových, mechanických, technologických a únavových vlastností. Dále byly popsány pokročilé metody zobrazování, úpravy a tvorby kloubních ploch a použity k vyvinutí nového designu personalizovaného kloubního implantátu společně s inovační technologií jeho inserce a nástroji potřebnými k její úspěšné realizaci. Toto nové řešení bylo úspěšně ověřeno mnoha testy i výrobou Ti6Al4V-ELI a CoCrMo prototypů implantátů metodou EBM. Proveditelnost a použití v praxi bylo konzultováno a schváleno odborníky v této oblasti.

Fatigue and fracture assisted by the environment are responsible for the majority of failures in implants. Due to low tribological properties of titanium alloys, the thermal oxidation technique has been evaluated to improve the surface hardness and consequently, to improves the tribological properties of Ti6Al4V alloy. However, despite improved tribological properties of the Ti6Al4V alloy, there is a tendency to reduction of the fatigue limit of the oxide layer. The combined action of body fluid and cyclic loads also need to be investigated. This study evaluated the effect of thermal oxidation in the fatigue limit of the Ti6Al4V in environment containing 0.9% NaCl. It was observed a reduction in the fatigue limit for thermally oxidized Ti6Al4V alloy and it is suggested that the reduction in fatigue properties of alloy is associated with the brittleness of oxide layer. / Os processos de fadiga e fraturas assistidas pelo ambiente são responsáveis pela maioria das falhas em implantes. Devido às baixas propriedades tribológicas do titânio e suas ligas, a técnica de oxidação térmica tem ganhado destaque por conferir um aumento da dureza superficial e consequentemente melhorar as propriedades tribológicas da liga Ti6Al4V. Entretanto apesar da melhoria das propriedades tribológicas existe uma tendência na redução do limite de fadiga quando há presença de uma camada de óxido na superfície da liga Ti6Al4V. Ainda a ação combinada de fluidos corpóreos e de carregamento precisa ser investigada. Neste estudo foi avaliado o efeito da oxidação térmica combinado a aplicação de carregamento cíclico ao ar e em meio contendo 0,9 % NaCl. Foi observada uma redução no limite de resistência à fadiga para a liga Ti6Al4V oxidada termicamente. O meio contendo 0,9 % de NaCl não influenciou significativamente a resistência em fadiga de corpos de prova oxidados termicamente e sugere-se que a redução nas propriedades de fadiga da liga está associada à fragilidade da camada de óxido.

Additive Manufacturing (AM) is an innovative manufacturing process which offers near-net shape fabrication of complex components, directly from CAD models, without dies or substantial machining, resulting in a reduction in lead-time, waste, and cost. For example, the buy-to-fly ratio for a titanium component machined from forged billet is typically 10-20:1 compared to 5-7:1 when manufactured by AM. However, the production rates for most AM processes are relatively slow and AM is consequently largely of interest to the aerospace, automotive and biomedical industries. In addition, the solidification conditions in AM with the Ti alloy commonly lead to undesirable coarse columnar primary β grain structures in components. The present research is focused on developing a fundamental understanding of the influence of the processing conditions on microstructure and texture evolution and their resulting effect on the mechanical properties during additive manufacturing with a Ti6Al4V alloy, using three different techniques, namely; 1) Selective laser melting (SLM) process, 2) Electron beam selective melting (EBSM) process and, 3) Wire arc additive manufacturing (WAAM) process. The most important finding in this work was that all the AM processes produced columnar β-grain structures which grow by epitaxial re-growth up through each melted layer. By thermal modelling using TS4D (Thermal Simulation in 4 Dimensions), it has been shown that the melt pool size increased and the cooling rate decreased from SLM to EBSM and to the WAAM process. The prior β grain size also increased with melt pool size from a finer size in the SLM to a moderate size in EBSM and to huge grains in WAAM that can be seen by eye. However, despite the large difference in power density between the processes, they all had similar G/R (thermal gradient/growth rate) ratios, which were predicted to lie in the columnar growth region in the solidification diagram. The EBSM process showed a pronounced local heterogeneity in the microstructure in local transition areas, when there was a change in geometry; for e.g. change in wall thickness, thin to thick capping section, cross-over’s, V-transitions, etc. By reconstruction of the high temperature β microstructure, it has been shown that all the AM platforms showed primary columnar β grains with a <001>β.