| 41. |
- Kisielewicz, Agnieszka
(författare)
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Towards multi-sensor monitoringand control of Directed Energy Deposition using a Laser Beam
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Under senare år har omfattande insatser gjorts för att främja mer hållbara flygtransporter i Europa. De konventionella tillverkningsmetoderna som används inom flyg- och rymdindustrin kräver betydande mängder råmaterial, vars utvinning, bearbetning och användning har negativa miljöeffekter. Därför finns det ett starkt incitament att utveckla nya, mer material-effektiva tillverkningsmetoder.Additiv tillverkning (AM), även känd som 3D-printining, har fördelen att direkt komma nära den slutliga formen på strukturer genom att lägga till material endast där det behövs, något som minimerar spill och förbättrar materialanvändningen. Dock utgör införandet av AM komponenter i säkerhetskritiska flyg- och rymdtillämpningar en betydande utmaning på grund av komplexiteten hos processerna. Denna komplexitet kan leda till tillverkningsvariationer som i sin tur kan resultera i defekter i de tillverkade strukturerna. Därför är framsteg inom automation genom utvecklingen av lösningar för övervakning och styrning under processens gång ett nödvändigt steg för att uppnå tillräcklig pålitlighet och repeterbarhet.Denna avhandling presenterar en utveckling av multisensorövervakning och styrning av Directed Energy Deposition (DED) med en laservärmekälla (LB). DED-LB är en avancerad teknik som möjliggör tillverkning av storskaliga metallkomponenter nära den slutliga formen. I detta arbete har lösningar undersökts för övervakning av DED-LB med tillsatspulver och tråd. För fallet med tillsatstråd kan denna kompletteras med resistiv förvärmning (så kallad hotwire), vilket ger möjlighet att ytterligare finjustera värmetillförseln och förbättra smältprocessen. För övervakningsändamål undersöktes tre olika in-situtekniker för processens stabilitet och varians. Maskinseende och elektriska givare användes för DED-LB med tillsatstråd (DED-LB/w), medan optisk spektroskopi användes för övervakning både av processen med tillsatspulver (DEDLB/p) samt med tråd. Ett multisensorsystem baserat på de tre teknologierna testades för DED-LB/w. Det kamerabaserade systemet gav tydliga indikationer på avvikelser från nominella processförhållanden.Spännings-och strömgivarnas signaler korrelerade med förändringar i processparametrar och återspeglade tydligt metallöverföringen. Spektrometersystemet indikerade förändringar relaterade till värmeöverföringen. Dessutom möjliggjorde analysen av erhållna spektra en detektering av förluster av viktiga legeringselement under DED-LB/p.Slutsatsen från resultaten understryker behovet av multisensorövervakning, eftersom det inte bara möjliggör detektering och skattning av processförändringar utan även en bättre förståelse av deras grundorsaker. Den presenterade ansatsen är ett viktigt bidrag i utvecklingen av ett framtida robust och feltolerant automatiskt styrsystem.
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| 42. |
- Kumara, Chamara
(författare)
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Microstructure Modelling of Additive Manufacturing of Alloy 718
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, additive manufacturing (AM) of Alloy 718 has received increasing interest in the field of manufacturing engineering owing to its attractive features compared to those of conventional manufacturing methods. The ability to produce complicated geometries, low cost of retooling, and control of the microstructure are some of the advantages of the AM process over traditional manufacturing methods. Nevertheless, during the building process, the build material undergoes complex thermal conditions owing to the inherent nature of the process. This results in phase transformation from liquid to solid and solid state. Thus, it creates microstructural gradients in the built objects, and as a result,heterogeneous material properties. The manufacturing process, including the following heat treatment that is used to minimise the heterogeneity, will cause the additively manufactured material to behave differently when compared to components produced by conventional manufacturing methods. Therefore, understanding the microstructure formation during the building and subsequent post-heat treatment is important, which is the objective of this work. Alloy 718 is a nickel-iron based super alloy that is widely used in the aerospace industry and in the gas turbine power plants for making components subjected tohigh temperatures. Good weldability, good mechanical properties at high temperatures, and high corrosion resistance make this alloy particularly suitablefor these applications. Nevertheless, the manufacturing of Alloy 718 components through traditional manufacturing methods is time-consuming and expensive. For example, machining of Alloy 718 to obtain the desired shape is difficult and resource-consuming, owing to significant material waste. Therefore, the application of novel non-conventional processing methods, such as AM, seems to be a promising technique for manufacturing near-net-shape complex components.In this work, microstructure modelling was carried out by using multiphase-field modelling to model the microstructure evolution in electron beam melting (EBM) and laser metal powder directed energy deposition (LMPDED) of Alloy 718 and x subsequent heat treatments. The thermal conditions that are generated during the building process were used as input to the models to predict the as-built microstructure. This as-built microstructure was then used as an input for the heat treatment simulations to predict the microstructural evolution during heat treatments. The results showed smaller dendrite arm spacing (one order of magnitude smaller than the casting material) in these additive manufactured microstructures, which creates a shorter diffusion length for the elements compared to the cast material. In EBM Alloy 718, this caused the material to have a faster homogenisation during in-situ heat treatment that resulting from the elevated powder bed temperature (> 1000 °C). In addition, the compositional segregation that occurs during solidification was shown to alter the local thermodynamic and kinetic properties of the alloy. This was observed in the predicted TTT and CCT diagrams using the JMat Pro software based on the predicted local segregated compositions from the multiphase-field models. In the LMPDED Alloy 718 samples, this resulted in the formation of δ phase in the interdendritic region during the solution heat treatment. Moreover, this resulted in different-size precipitation of γ'/γ'' in the inter-dendritic region and in the dendrite core. Themicro structure modelling predictions agreed well with the experimental observations. The proposed methodology used in this thesis work can be an appropriate tool to understand how the thermal conditions in AM affect themicro structure formation during the building process and how these as-built microstructures behave under different heat treatments.
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| 43. |
- Köhler, Veronica, 1974-
(författare)
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Co-Creators of Scope of Action : An exploration of the dynamic relationship between people, IT, and work in a nursing context
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Information Technology (IT) is today widespread in our work places, in our spare time and in our society overall. Implementations of IT in organizations come with high expectations on effectiveness, revenue, smoother work processes and so on. However, this simplified view on IT ignores the fact that it is the IT usage rather than the IT artifact per se that in the end decides the effect of an implementation of IT. Although the IT artifact certainly has been designed to support certain tasks and processes, the success or failure of the Information System (IS) in the end depends on the individuals' actions, which ultimately depend on their perceptions and interpretations of the IS. Thus, when technology is being implemented and becomes an IS in use, it becomes a part of work, and as such more of a social system than a technological one.The actual result of a design process does not solely consist of things or artifacts, but above all changed action patterns for the users. From this follows that we must consider design of artifacts as something more than merely the constructing of actual objects with functions and properties that are easily measured. Rather, a large part of all design activities has to do with design of conceivable social milieus, not artifacts. Thus, design may be defined as the suggesting and establishing of scope of action. The concept scope of action aims at describing the fact that the design of, and consequently the implementation of, a specific IT artifact always aims at creating a certain scope of action; some actions are made easier, others are made more difficult or even impossible. This scope of action has to some extent been deliberately designed, but these changes may on the other hand also be undesired and not predicted in advance. The complexity of this phenomenon is great and hard to grasp in advance. However, this does not mean that we can allow ourselves to ignore exploring this phenomenon more deeply. On the contrary, with a usage perspective on IS success or failure, scope of action becomes very important.Although the term scope of action may seem a rather intuitive concept, we need more concrete knowledge about its character in order to be able to understand IT usage, both when designing a new IT artifact and when studying or evaluating IT. Thus, our intuitive understanding of the concept needs to be complemented with theory on the ‘constituents’ and effects of this phenomenon. For this purpose, in this thesis nurses’ use of the Electronic Patient record (EPR) is being explored in order to gain an empirically derived understanding of the character of scope of action.The research findings highlight the emergent character of scope of action. It is obvious that an individual’s scope of action is not being created on one occasion, and above all not only by the IT artifact. Various co- creators such as the IT artifact, the usage and the social context create and re-create scope of action. Also, how the individual interprets and understands the IT artifact in IT usage will influence her scope of action. This since sensemaking and learning processes on both a personal and organizational level take place that are co-creators of the individual’s scope of action, at the same time as the individual’s knowledge and previous sensemaking and learning influences her use of the IT artifact.Thus, reasoning, thinking, learning, and the IT artifact co-evolve over time in adaptation and appropriation processes. This means that IT as a mediational means constitutes an important co-creator of scope of action. From this also follows that work integrated learning is an important co- creator of scope of action when using IT in a work setting, at the same time as work integrated learning is being influenced by the individual’s scope of action.Finally, in order to understand how scope of action emerges in use, merely focusing on structures is insufficient. Scope of action emerges as a product of interplay between complex processes involving artifacts, usage and context. This means that the user’s scope of action is co-created by both static structures as well as dynamic processes relating to the IT artifact, the organization, and the work practice. Thus, the IT artifact, and subsequently scope of action, must be must be understood in relation to the multi-aspectual context of which it is a part instead of merely in relation to the properties of the IT artifact per se.
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| 44. |
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| 45. |
- Magalhães, Ana, 1986-
(författare)
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Thermo-electric temperature measurements in friction stir welding : Towards feedback control of temperature
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Friction Stir Welding has seen a fast uptake in many industry segments. Mechanical properties superior to fusion welding, the ability to weld "unweldable" aluminium alloys and low distortion are often described as the main reasons for the fast industrial implementation of FSW. Most existing applications consist of long straight welding joints. Applications with complex weld geometries, however, are rarely produced by FSW. These geometries can induce thermal variations during the welding process, thus making it challenging to maintain a consistent weld quality. In-process adaptation of weld parameters to respond to geometrical variations and other environmental variants allow new design opportunities for FSW. Weld quality has been shown to be reliant on the welding temperature. However, the optimal methodology to control the temperature is still under development.The research work presented in this thesis focuses on some steps to take in order to reach the improvement of the FSW temperature controller, thus reach a better and consistent weld quality. In the present work different temperature methods were evaluated. Temperature measurements acquired by the tool-workpiece thermocouple (TWT) method were accurate and fast, and thereby enhanced suitable for the controller. Different environmental conditions influencing the material heat dissipation were imposed in order to verify the controller effect on the joint quality. In comparison with no controlled weld, the use of the controller enabled a fast optimization of welding parameters for the different conditions, leading to an improvement of the mechanical properties of the joint.For short weld lengths, such as stitch welds, the initial plunge and dwell stages occupy a large part of the total process time. In this work temperature control was applied during these stages. This approach makes the plunge and dwell stages more robust by preventing local material overheating, which could lead to a tool meltdown. The TWT method was demonstrated to allow a good process control during plunging and continuous welding. The approach proposed for control offers weld quality consistency and improvement. Also, it allows a reduction of the time required for the development of optimal parameters, providing a fast adaptation to disturbances during welding and, by decreasing the plunge time, provides a significant decrease on the process time for short welds.
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| 46. |
- Mahade, Satyapal, 1987-
(författare)
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Functional Performance of Gadolinium Zirconate/Yttria Stabilized Zirconia Multi-Layered Thermal Barrier Coatings
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Yttria stabilized zirconia (YSZ) is the state of the art ceramic top coat material used for TBC applications. The desire to achieve a higher engine efficiency of agas turbine engine by increasing the turbine inlet temperature has pushed YSZ toits upper limit. Above 1200°C, issues such as poor phase stability, high sinteringrates, and susceptibility to CMAS (calcium magnesium alumino silicates) degradation have been reported for YSZ based TBCs. Among the new materials,gadolinium zirconate (GZ) is an interesting alternative since it has shown attractive properties including resistance to CMAS attack. However, GZ has a poor thermo-chemical compatibility with the thermally grown oxide leading to poor thermal cyclic performance of GZ TBCs and that is why a multi-layered coating design seems feasible.This work presents a new approach of depositing GZ/YSZ multi-layered TBCs by the suspension plasma spray (SPS) process. Single layer YSZ TBCs were also deposited by SPS and used as a reference.The primary aim of the work was to compare the thermal conductivity and thermal cyclic life of the two coating designs. Thermal diffusivity of the YSZ single layer and GZ based multi-layered TBCs was measured using laser flash analysis (LFA). Thermal cyclic life of as sprayed coatings was evaluated at 1100°C, 1200°C and 1300°C respectively. It was shown that GZ based multi-layered TBCs had a lower thermal conductivity and higher thermal cyclic life compared to the single layer YSZ at all test temperatures. The second aim was to investigate the isothermal oxidation behaviour and erosion resistance of the two coating designs. The as sprayed TBCs were subjected toisothermal oxidation test at 1150°C. The GZ based multi-layered TBCs showed a lower weight gain than the single layer YSZ TBC. However, in the erosion test,the GZ based TBCs showed lower erosion resistance compared to the YSZ singlelayer TBC. In this work, it was shown that SPS is a promising production technique and that GZ is a promising material for TBCs.
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| 47. |
- Massouh, Bassam
(författare)
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Planning and Control of Safety-Aware Plug & Produce
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Plug & Produce manufacturing system is a visionary concept that promises to facilitate the seamless integration and adaptation of manufacturing resources and production processes. The Plug & Produce control system allows for the automatic addition and removal of manufacturing resources, minimizing human intervention. However, the reconfigurability and autonomous decision-making features of Plug & Produce control systems pose challenges to safety design and control functions.In contrast to conventional manufacturing systems with fixed layouts and processes, ensuring safety in Plug & Produce systems is complicated due to the complex risk assessment process, the difficulty of implementing non-restrictive safety measures covering all possible hazards, and the challenge of designing a reliable controller for consistent safe operation.This thesis addresses these challenges through various contributions. It introduces an automatic hazard identification method, considering emergent hazards after reconfiguration. A novel domain ontology is developed, incorporating safety models specific to Plug & Produce systems. The work also proposes a generic, model-based, and automatic risk assessment method, along with a method for the safe execution of plans based on the results of the risk assessment.The results of this research offer benefits to process planners, who are responsible for coordinating the manufacturing processes with product design in the Plug & Produce system. The proposed solution provides tools for process planners to validate their plans and reduces their safety-related responsibilities. The proposed safety assurance method seamlessly integrates into the multi-agent control of Plug & Produce, providing the control system with risk scenarios associated with process plans. This enables proactive and reliable control, effectively avoiding potential risks during system operation.
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| 48. |
- Mi, Yongcui, 1986-
(författare)
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Novel beam shaping and computer vision methods for laser beam welding
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Laser beam welding has been widely applied in different industrial sectors due to its unique advantages. However, there are still challenges, such as beam positioning in T-joint welding, and gap bridging in butt joint welding,especially in the case of varying gap width along a joint. It is expected that enabling more advanced control to a welding system, and obtaining more in-depth process knowledge could help to solve these issues. The aim of this work is to address such welding issues by a laser beam shaping technology using a novel deformable mirror together with computer vision methods and also to increase knowledge about the benefits and limitations with this approach.Beam shaping in this work was realized by a novel deformable mirror system integrated into an industrial processing optics. Together with a wave front sensor, a controlled adaptive beam shaping system was formed with a response time of 10 ms. The processes were monitored by a coaxial camera with selected filters and passive or active illumination. Conduction mode autogenous bead-on-plate welding and butt joint welding experiments have been used to understand the effect of beam shaping on the melt pool geometry. Circular Gaussian, and elliptical Gaussian shapes elongated transverse to and along the welding direction were studied. In-process melt pool images and cross section micrographs of the weld seams/beads were analyzed. The results showed that the melt pool geometry can be significantly modified by beam shaping using the deformable mirror. T-joint welding with different beam offset deviations relative to the center of the joint line was conducted to study the potential of using machine learning to track the process state. The results showed that machine learning can reach sufficient detection and estimation performance, which could also be used for on-line control. In addition, in-process and multidimensional data were accurately acquired using computer vision methods. These data reveal weaknesses of current thermo-fluid simulation model, which in turn can help to better understand and control laser beam welding. The obtained results in this work shows a huge potential in using the proposed methods to solve relevant challenges in laser beam welding.
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| 49. |
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| 50. |
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