Additive manufacturing (AM) is the name given to the technology of building 3D parts by adding layer-by-layer of materials, including metals, plastics, concrete, etc. Of the different types of AM techniques, electron beam melting (EBM), as a powder bed fusion technology, has been used in this study. EBM is used to build parts by melting metallic powders by using a highly intense electron beam as the energy source. Compared to a conventional process, EBM offers enhanced efficiency for the production of customized and specific parts in aerospace, space, and medical fields. In addition, the EBM process is used to produce complex parts for which other technologies would be either expensive or difficult to apply. This thesis has been divided into three sections, starting from a wider window and proceeding to a smaller one. The first section reveals how the position-related parameters (distance between samples, height from build plate, and sample location on build plate) can affect the microstructural characteristics. It has been found that the gap between the samples and the height from the build plate can have significant effects on the defect content and niobium-rich phase fraction. In the second section, through a deeper investigation, the behavior of Alloy 718 during the EBM process as a function of different geometry-related parameters is examined by building single tracks adjacent to each other (track-by-track) andsingle-wall samples (single tracks on top of each other). In this section, the main focus is to understand the effect of successive thermal cycling on microstructural evolution. In the final section, the correlations between the main machine-related parameters (scanning speed, beam current, and focus offset) and the geometrical (melt pool width, track height, re-melted depth, and contact angle) and microstructural (grain structure, niobium-rich phase fraction, and primary dendrite arm spacing) characteristics of a single track of Alloy 718 have been investigated. It has been found that the most influential machine-related parameters are scanning speed and beam current, which have significant effects on the geometry and the microstructure of the single-melted tracks.

Samhället efterfrågar idag i allt högre grad miljövänlig och hållbar byggnation. Ett sätt möta dessa nya krav på miljövänlig byggnation är att använda mer trä då detta minskar koldioxidutsläpp genom substitutionseffekten. Syftet att undersöka huruvida traditionella fogningstekniker som helt utförs i trä kan ersätta samtida fogar i framtida byggnation. Målet är att visa att detta är möjligt ur hållfasthetssynpunkt. Undersökningen kommer att begränsas till att undersöka en pelar-balk-anslutning där den traditionella fogen representeras av tre olika varianter tapp i tapphålsfog och den samtida av balksko. Fogarna undersöks beräkningsmässigt samt genom försök där belastningsfallet ämnar ge en hög tvärkraft. Resultaten pekar på att det är möjligt att introducera den undersökta traditionella träfogningstekniken vid samtida byggnation. / Societies demand for environmentally friendly and sustainable construction is ever increasing. One way to meet these new demands on environmentally friendly construction is to use more wood which decreases carbon emissions through the substitution effect. This report aims to research whether traditional joinery techniques entirely executed in wood can replace contemporary joinery techniques in future construction. The goal is to show whether this is possible from a strength standpoint. The research will be limited in that it will strictly seek to study a pillar-beamconnection where the traditional joint researched will be three varying mortise and tenon joints and the contemporary joint is a joist hanger. The joints will be analyzed with calculation and experimentation where the load case aims to produce mainly shear in the joint. The results point towards it being possible to introduce this traditional joint in contemporary construction.

Laser is an efficient and widely used heat source in metal processing suchas welding and additive manufacturing. It has some great advantages compared to the other conventional heat sources like electron beam and arc namely: ability of handling complicated joint geometries and producing large components. Laser beam welding encompasses many complex physical phenomena such asheat transfer, metal melting, flow and solidification, free surface deformation, evaporation and possibly vaporization. The aim of this research work istwo-fold: gain deeper process understanding and improve the model reliability. Deeper process understanding is sought on the effect of beam shaping on themelt pool. To achieve improved model reliability, a good support consists in using qualitative experimental data representing the process. Thus, 3D validation of the melt pool geometry is performed while it was usually 2D inprevious research works. Furthermore, a new calculation procedure for laser absorption is introduced. To conduct this research work, a Computational Fluid Dynamics approach is used. A solver, capable of tracking the deformation of the melt free surface, is developed in OpenFOAM. Concerning beam shaping, it is found that not only the melt pool size as previously known but also the melt flow pattern is modified through elongating the beam shape.This last result could not be revealed by former studies as the non-transparent media hinders optical observation. New in-process quantitative measurements performed by a project partner are used to test the model. Weaknesses of the former absorptivity models are highlighted, as well as the limitations of the proposed model. Finally, the results show that the proposed absorptivity model function of local surface conditions leads to much better agreement with experimental results compared to the former constant absorptivity model. The maximum discrepancy compared to the experimental measurement, which is observed for the melt pool depth, can indeed be reduced to about 10%. / Laser är en effektiv och allmänt använd värmekälla vid svetsning och additiv tillverkning. Den har några viktiga fördelar jämfört med andra konventionella värmekällor såsom elektronstråle och elektrisk ljusbåge, nämligen: den kan ofta användas till komplicerade svetsgeometrier, och den kan producera stora komponenter. Lasersvetsning involverar olika sammansatta fysikaliska fenomen såsom värmeöverföring, metallsmältning, flöde, stelning, ytdeformation, avdunstning och i vissa fall förångning. Syftet med mitt forskningsarbete är tvåfaldigt: att få en djupare processförståelse och att förbättra modellens tillförlitlighet. Fördjupad processförståelse eftersträvades för att förstå hur formen på laserstrålen påverkar svetssmältan. För att uppnå förbättrad modellsäkerhet behövs experimentella data av hög kvalitet som representerar processen. Således utfördes 3D-validering av smältgeometrin medan det vanligtvis var 2D i tidigare forskningsarbeten. Dessutom har en ny modell för laserabsorption föreslagits. I forskningen har numerisk strömningssimulering (Computational Fluid Dynamics) använts för att simulera processen och en numerisk lösare, som kan spåra deformationen av den rörliga smälta ytan, är utveckladi programvaran OpenFOAM. Beträffande laserstrålens utbredning visar resultaten att svetssmältans storlek och även svetssmältansflöde modifieras genom att laserstråleformen förlängs. Medan den förra är känd från tidigare experimentella studier upptäcktes den senare inte före denna studie eftersomdet icke-transparenta mediet hindrar optisk observation. Nya (in-process) kvantitativa mätningar utförda av en projektpartner har använts för att testa modellerna. Svagheter i den tidigare absorptionsmodellen framhävdes, liksom begränsningarna i den föreslagna modellen. Slutligen visade resultaten att den föreslagna modellen där laserabsorptionen är en funktion av lokala ytförhållanden ledde till en bättre overensstämmelse med mätningar jämfört med den tidigare modellen med konstant laserabsorbtion. Den maximala avvikelsen jämfört med experimentell mätning, som observerades med avseende på smältbassängsdjupet, kunde reduceras till cirka 10%. / <p>Till licentiatuppsats hör 2 inskickade artiklar, som inte visas nu.</p>

Nickel-based alloys are used in components such gas turbines within the aerospace industry and electric power generation due to its high tensile, rapture and creep strength. Increasing the efficiency of gas turbines are crucial to reduce emissions within the aerospace industry and increasing power gain for electric power generation. Innovation to increase the efficiency relies in part on the development of new nickel-based alloys with beneficial material properties. But also on stable and predictable material behavior during processing and post-processing of the components in the gas turbine. In two prominent material processing fields of precipitation hardened nickel-based alloys, additive manufacturing and welding, strain-age cracking (SAC) is a common phenomenon. SAC is a solid state phenomenon that generally occurs in alloys strengthened with 𝛾′, L12(Pm3m), or 𝛾′′, D022(I4/mmm), phase precipitates during post weld heat treatment or reheating where it manifests as intergranular cracking. Even though the existence of SAC has been known for several decades, its dominant mechanisms are still under considerable debate and the undertaken modeling efforts to gain insight on the phenomenon are virtually non-existent. This study aims to clarify the dominant mechanisms behind strain-age cracking. Breaching this gap would allow for new development for nickel-based alloys within both additive manufacturing and welding. To that extent the goal of this study is to provide tools to aid in clarifying the dominant mechanisms behind strain-age cracking. This is done by implementing the recently developed structural phase-field crystal (XPFC) model and examining the capabilities to model a precipitation event during reheating for a reference binary alloy in two dimensions. To evaluate the strain because of precipitation, a simple method based on the principles of neutron and synchrotron strain scanning is outlined and tested on the limited precipitation event achieved within the study. The XPFC model is capable of modeling precipitation with some restrictions that need further development with extended computational recourses. Lastly, the possibilities to extend the implemented XPFC model to cover nickel-based alloys is discussed.

Additive manufacturing (AM) is a quickly rising method of manufacturing due to its ability to increase design freedom. This allows the manufacturing of components not possible by traditional subtractive manufacturing. AM can greatly reduce lead time and material waste, therefore decreasing the cost and environmental impact. The adoption of AM in the aerospace industry requires strict control and predictability of the material deposition to ensure safe flights.  The method of AM for this thesis is Laser Metal Deposition with wire (LMD-w). Using wire as a feedstock introduces a potential problem, the material transfer from the wire to the substrate. This requires all process parameters to be in balance to produce a stable deposition. The first sign of unbalanced process parameters are the material transfer stabilities; stubbing and dripping. Stubbing occurs when the energy to melt the wire is too low and the wire melts slower than required. Dripping occurs when too much energy is applied and the wire melts earlier than required.  These two reduce the predictability and stability that is required for robust manufacturing.  Therefore, the use of thermal simulations to predict the material transfer stability for LMD-w using Waspaloy as the deposition material has been studied.  It has been shown that it is possible to predict the material transfer stability using thermal simulations and criterions based on preexisting experimental data. The criterion for stubbing checks if the completed simulation result produces a wire that ends below the melt pool. For dripping two criterions shows good results, the dilution ratio is a good predictor if the tool elevation remains constant. If there is a change in tool elevation the dimensionless slenderness number is a better predictor.  Using these predictive criterions it is possible to qualitatively map the process window and better understand the influence of tool elevation and the cross-section of the deposited material. / Additiv tillverkning (AT) är en kraftigt växande tillverkningsmetod på grund av sin flexibilitet kring design och möjligheten att skapa komponenter som inte är tillverkningsbara med traditionell avverkande bearbetning.  AT kan kraftigt minska tid- och materialåtgång och på så sett minskas kostnader och miljöpåverkan. Införandet av AT i flyg- och rymdindustrin kräver strikt kontroll och förutsägbarhet av processen för att försäkra sig om säkra flygningar.  Lasermetalldeponering av tråd är den AT metod som hanteras i denna uppsats. Användandet av tråd som tillsatsmaterial skapar ett potentiellt problem, materialöverföringen från tråden till substratet. Detta kräver att alla processparametrar är i balans för att få en jämn materialöverföring. Är processen inte balanserad syns detta genom materialöverföringsstabiliteterna stubbning och droppning. Stubbning uppkommer då energin som tillförs på tråden är för låg och droppning uppkommer då energin som tillförs är för hög jämfört med vad som krävs för en stabil process. Dessa två fenomen minskar möjligheterna för en kontrollerbar och stabil tillverkning.  På grund av detta har användandet utav termiska simuleringar för att prediktera materialöverföringsstabiliteten för lasermetalldeponering av tråd med Waspaloy som deponeringsmaterial undersökts. Det har visat sig vara möjligt att prediktera materialöverföringsstabiliteten med användning av termiska simuleringar och kriterier baserat på tidigare experimentell data. Kriteriet för stubbning kontrolleras om en slutförd simulering resulterar i en tråd som når under smältan.  För droppning finns två fungerande kriterier, förhållandet mellan svetshöjd och penetrationsdjup om verktygshöjden är konstant, sker förändringar i verktygshöjden är det dimensionslös ”slenderness” talet ett bättre kriterium.  Genom att använda dessa kriterier är det möjligt att kvalitativt kartlägga processfönstret och skapa en bättre förståelse för förhållandet mellan verktygshöjden och den deponerade tvärsnittsarean.

Thermal barrier coating (TBC) systems are widely used on gas turbine components to provide thermal insulation and oxidation protection. TBCs, incombination with advanced cooling, can enable the gas turbine to operate at significantly higher temperatures even above the melting temperature of the metallic materials. There is a permanent need mainly of environmental reasons to increase the combustion turbine temperature, hence new TBC solutions are needed.By using a liquid feedstock in thermal spraying, new types of TBCs can be produced. Suspension plasma/flame or solution precursor plasma spraying are examples of techniques that can be utilized for liquid feedstock thermal spraying.This approach of using suspension and solution feedstock, which is an alternative to the conventional solid powder feed stock spraying, is gaining increasing research interest, since it has been shown to be capable of producing coatings with superior coating performance.The objective of this research work was to explore relationships between process parameters, coating microstructure, thermal diffusivity and thermal conductivity in liquid feedstock thermal sprayed TBCs. A further aim was to utilize this knowledge to produce a TBC with lower thermal diffusivity and lower thermal conductivity compared to state-of-the-art in industry today, i.e. solid feed stock plasma spraying. Different spraying techniques, suspension high velocity oxy fuel,solution precursor plasma and suspension plasma spraying (with axial and radialfeeding) were explored and compared with solid feedstock plasma spraying.A variety of microstructures, such as highly porous, vertically cracked and columnar, were obtained. It was shown that there are strong relationships between the microstructures and the thermal properties of the coatings.Specifically axial suspension plasma spraying was shown as a very promising technique to produce various microstructures as well as low thermal diffusivity and low thermal conductivity coatings.

Ti-6Al-4V manufactured by electron beam melting Keywords: Additive manufacturing, high-temperature tensile properties, low cycle fatigue, neutron diffraction, fatigue crack growth ISBN: 978-91-89325-27-2 (Printed) 978-91-89325-26-5 (Electronic) Ti-6Al-4V is the most widely used α+β titanium alloy in aerospace engine applications due to its high specific strength. Typically, the alloy is manufactured as castings or forgings and then machined to final geometry. These conventional manufacturing processes do however generate a lot of waste material, whereas additive manufacturing (AM) can potentially produce a near-net-shape geometry directly from the feedstock. In the past decade, electron beam melting (EBM), one of the powder bed fusion techniques, has been widely researched to build Ti[1]6Al-4V components. Still, the as-built material can contain defects such as gas pores that require post-processing, such as hot isostatic pressing (HIP) to produce nearly fully dense components. HIP treatment of conventionally cast Ti-6Al-4V is normally performed at 920 ˚C, 100 MPa for 2 hours. This same HIP treatment has then been adapted also for EBM-manufactured Ti-6Al-4V, which however results in coarsening of α laths and reduction of yield strength. Therefore, finding a more appropriate HIP treatment for this new type of Ti-6Al-4V material, i.e. EBM manufactured, would be of great benefit for the industry. Lowering the HIP treatment temperature to 800 ˚C and increasing the pressure to 200 MPa has recently been proven to close the porosity to a high degree while sustaining the high yield strength. In this thesis, the high-temperature tensile properties of EBM-manufactured Ti[1]6Al-4V subjected to a low-temperature (800 ˚C) HIP treatment were evaluated and compared with standard HIP-treated (920 ˚C) materials. Metallurgical characterization of the as-built, HIP-treated materials have been carried out to understand the effect of temperature on the microstructures. The standard HIP[1]treated material measured about 1.4x - 1.7x wider α laths than those in the low[1]temperature HIP treated and as-built samples, respectively. The standard HIP[1]treated material showed about 10 - 14% lower yield strength than other HIP treated materials. At 350 ˚C the yield strength decreases to about 65% compared to the room temperature strength for all tested materials. An increase in ductility vi programvaran NASGRO där livsförutsägelserna visade god överensstämmelse med experimentella livscykler i de flesta fall. vii Abstract Title: Microstructure and mechanical properties of low-temperature hot isostatic pressed Ti-6Al-4V manufactured by electron beam melting Keywords: Additive manufacturing, high-temperature tensile properties, low cycle fatigue, neutron diffraction, fatigue crack growth ISBN: 978-91-89325-27-2 (Printed) 978-91-89325-26-5 (Electronic) Ti-6Al-4V is the most widely used α+β titanium alloy in aerospace engine applications due to its high specific strength. Typically, the alloy is manufactured as castings or forgings and then machined to final geometry. These conventional manufacturing processes do however generate a lot of waste material, whereas additive manufacturing (AM) can potentially produce a near-net-shape geometry directly from the feedstock. In the past decade, electron beam melting (EBM), one of the powder bed fusion techniques, has been widely researched to build Ti[1]6Al-4V components. Still, the as-built material can contain defects such as gas pores that require post-processing, such as hot isostatic pressing (HIP) to produce nearly fully dense components. HIP treatment of conventionally cast Ti-6Al-4V is normally performed at 920 ˚C, 100 MPa for 2 hours. This same HIP treatment has then been adapted also for EBM-manufactured Ti-6Al-4V, which however results in coarsening of α laths and reduction of yield strength. Therefore, finding a more appropriate HIP treatment for this new type of Ti-6Al-4V material, i.e. EBM manufactured, would be of great benefit for the industry. Lowering the HIP treatment temperature to 800 ˚C and increasing the pressure to 200 MPa has recently been proven to close the porosity to a high degree while sustaining the high yield strength. In this thesis, the high-temperature tensile properties of EBM-manufactured Ti[1]6Al-4V subjected to a low-temperature (800 ˚C) HIP treatment were evaluated and compared with standard HIP-treated (920 ˚C) materials. Metallurgical characterization of the as-built, HIP-treated materials have been carried out to understand the effect of temperature on the microstructures. The standard HIP[1]treated material measured about 1.4x - 1.7x wider α laths than those in the low[1]temperature HIP treated and as-built samples, respectively. The standard HIP[1]treated material showed about 10 - 14% lower yield strength than other HIP treated materials. At 350 ˚C the yield strength decreases to about 65% compared to the room temperature strength for all tested materials. An increase in ductility viii was observed at 150 ˚C compared to that at room temperature, but the ductility decreased between 150 - 350 ˚C because of activation of different slip systems. The low cycle fatigue (LCF) behavior of such a modified HIP (low-temperature HIP) material is assessed at two different strain levels and compared with the corresponding LCF properties for the standard HIP material. Even though the modified HIP material had lowest minimum life cycles to failure, the overall fatigue performance is comparable with that of the standard HIP material. Also, fatigue life predictions were made from the measured defect size at the crack initiation site using NASGRO. The calculated life predictions showed good agreement with the experimental values in most cases. In-situ neutron diffraction measurements on tensile test specimens were conducted, at both room temperature and at 350˚ C, for the standard and modified HIP-treated materials. The objective was to gain essential insights on how the crystal lattice strains relate to the macroscopic strengths in these specific microstructures. This investigation helped to understand the load partitioning between different slip planes and constituent phases in the microstructure at different temperatures. / Ti-6Al-4V är den mest använda α+β titanlegeringen i flygmotortillämpningar på grund av sin höga specifika hållfasthet. Vanligtvis tillverkas legeringen som gjutgods eller smide och bearbetas sedan till slutlig geometri. Dessa konventionella tillverkningsprocesser genererar dock en hel del avfallsmaterial, medan additiv tillverkning (AM) potentiellt kan producera en nästan slutgiltlig geometri direkt från råvaran. Under det senaste decenniet har elektronstrålesmältning (EBM), en av pulverbäddsfusionsteknikerna, undersökts mycket för att bygga Ti-6Al-4V-komponenter. Ändå kan det byggda materialet innehålla defekter såsom gasporer som kräver efterbearbetning, såsom varm isostatisk pressning (HIP) för att producera nästan helt täta komponenter. HIP[1]behandling av konventionellt gjutet Ti-6Al-4V utförs normalt vid 920 ˚C, 100 MPa under 2 timmar. Samma HIP-behandling har sedan anpassats även för EBM[1]tillverkat Ti-6Al-4V, vilket dock resulterar i förgrovning av α-lameller och minskning av sträckgränsen. Att hitta en mer lämplig HIP-behandling för denna nya typ av Ti-6Al-4V-material, dvs EBM-tillverkat, skulle därför vara till stor fördel för industrin. Att sänka HIP-behandlingstemperaturen till 800 ˚C och öka trycket till 200 MPa har nyligen visat sig stänga porositeten i hög grad samtidigt som den höga sträckgränsen bibehålls. Ti-6Al-4V används huvudsakligen i applikationer för flygmotorer upp till en maximal driftstemperatur på 300 ˚C. Därför studerades högtemperaturdragegenskaperna hos de olika HIP-behandlade EBM[1]byggmaterialen i detta forskningsarbete. Denna studie visade att duktiliteten påverkas av aktiveringen av olika glidsystem baserat på temperatur. Ytterligare neutrondiffraktionsexperiment utfördes tillsammans med in-situ dragprovning för att bestämma det aktiva glidsystemet vid en specifik temperatur. Utmattningsbeteendet hos det lågtemperaturbehandlade HIP-materialet utvärderas också genom lågcykelutmattningstestning och utmattningsspricktillväxttest. Utmattningsprestandan för det modifierade HIP[1]materialet utvärderades mot standard HIP- material och visade sig ha jämförbara utmattningsegenskaper. Förutsägelser om utmattningsliv utfördes med hjälp av vi programvaran NASGRO där livsförutsägelserna visade god överensstämmelse med experimentella livscykler i de flesta fall. / <p>Submitted papers or manuscripts have been excluded from the fulltext file.</p>

Sammanfattning Syfte – Syftet med studien är att ta fram en metod för att bevara ett stort antal verktyg för enstörre bearbetningsmaskin med en lösning för verktygsbyte. Frågeställningar sammanställdesgenom personlig kommunikation och kravspecifikationer som MFAB begärt. Metod – För att ta fram och producera koncept användes flera metoder som beskrivs i Produktutveckling – Effektiva metoder för konstruktion och design av Johannesson, Perssonoch Pettersson. Koncepten som skapats värderas mot krav i form av en Pughs matris. Resultat – I en informationssamling som utförs i förstudien samlas information om dagensvanligaste magasinlösning för fräs- och svarvmaskiner. Trum- och linjärmagasinet är devanligaste lösningarna för dagens bearbetningsmaskiner. Ett visuellt koncept beskrivs med hjälp CAD-programmet det är designat i samt en beskrivandetext för varje del. Det färdiga konceptet inkluderar:• En inhägnad för att hålla alla delar inom den förbestämda arbetsytan.• En serviceport för smidigt byte av verktyg utanför användning av magasinet.• Lösning för underhåll så att en person kan komma åt inuti magasinet.• Hyllor som agerar magasin då de håller verktygen som maskinen inte använder förtillfället.• En kedja som hyllorna är fästa på som roterar så att hyllorna kan nå dit de är behövda.• En linjärenhet som hämtar verktygen från hyllorna och lämnar vidare dem tillbufferten.• Bufferten som håller ett visst antal verktyg som maskinen är i behov av snart.• Restupplockning som tar hand om eventuellt skräp som kan förekomma på verktygen.Med dessa delar kan frågeställningarna besvaras. Begränsningar – Två begränsningar i studien har påträffats. Den första begränsningen varatt i konstruktionen gick mer plats åt till magasinet än vad som ursprungligen hade beräknatsför. Nästa begränsning var att storleken av studien över den givna tiden som projektet varadebegränsade möjligheten att fullt utveckla det slutgiltiga konceptet. Nyckelord – Bearbetningsmaskin, Automation, Magasin, Verktygshantering, Konstruktion, Skyddsinhägnad, Produktutveckling / Abstract Purpose – The purpose of the study is to create a method to store a large number of tools fora big processing machine with a solution for tool-changing. The main issues were compiledthrough personal communication and with the product requirements requested from MFAB. Method – To create and produce concepts different methods were used as described in Produktutveckling - Effektiva metoder för konstruktion och design by Johannesson, Perssonand Pettersson. The concepts that were created are valued against the product requirementswith a Pughs matrix. Result – Information is gathered about the most commonly used solutions for tool-magazinesfor milling- and lathing-machines. Drum-magazines and linear magazines are the mostcommonly used magazines for these kinds of machines.A visual concept is described with the help of the CAD-program it was designed in and adescribing text for each part. The finished concept includes:• An enclosure to hold all the part of the magazine within the decided area.• A service-port for easy changing of tools when the magazine is not in use.• A solution for maintenance where a person can get into the magazine.• Shelves that act as a magazine, holding the tools that the machine is not using currently.• A chain that the shelves are attached to which rotates so that the shelves can reach towhere they are needed.• A linear unit that retrieves the tools from the shelves and places them into a buffer.• The buffer that holds a few tools that the machine will be using soon.• Waste disposal that takes care of any residue or scraps that might get stuck on the tools.With these parts the main issues can be answered. Limitations – Two limitations in this study were discovered. The first was the fact that theconstruction used more space for the magazine than it was originally calculated for. Nextlimitation was that the scope of the study over the given time limited the development for thefinal concept. Key words – Processing machine, Automation, Magazine, Tool handling, Construction, Safetyenclosure, Product development.

Gas metal arc is a high-efficiency and widely used heat source for metal processing applied predominantly in welding and additive manufacturing. In this study, it was applied to welding. It offers high productivity, low production and investment cost, as well as suffers from some drawbacks such as humping or undercut when welding large parts that are curved and impose changing the orientation of the welding torch along the joint path. Deeper process understanding was therefore sought to mitigate these drawbacks. The difficulty is then the non-lineardependence of the process to the welding parameters and material properties. Besides, visual observation of this process is also difficult. For instance, the elevated temperature and the intense radiative emission from the electric arc, smoke, spatter, as well as the non-transparency of the processed alloy can hinder in-process observation or limit it. Process simulation provides a complementary means to reach process knowledge. It was thus the approach used in this study. For this, a thermo-fluid melt pool model that can predict melting and solidification, track free surface deformation, metal transfer, and coalescence with the melt pool was developed. Two main research questions were identified and addressed.The first one led to studying the effect of the substrate orientation during multilayer welding of a V-groove joint with INVAR and gas metal arc. It was foundthat the force balance in the melt pool changes significantly when the workpieceorientation is changed, resulting in distinct melt flow patterns, melt pool and bead geometries, and in some conditions defect initiation such as humping, undercut, and lack of fusion. As a result, multi-layer welding with flat substrate and downhill welding of a 20◦ inclined substrate are recommended with these process conditions. On the contrary, welding of a side inclined substrate and uphill welding of a 20◦ inclined substrate are not recommended. The second question gave rise to the comparative investigation of the three electromagnetic force models commonly used when modelling a melt pool produced by an electric arc. The underlying modelling assumptions were retrieved and investigated. It was found that each of these three models predicts a different melt flow pattern, different heat convection, melt pool shape, free surface oscillation, and interaction with the transferred metal drops, and thus result in different bead geometry. All these models can be adjusted to predict the penetration depth, however, only the most complete of them is recommended for developing a predictive melt pool model. For this, it is proposed as a future work to improve this model through predicting an electromagnetic force that takes also into account the local deformation of the free surface. / Gasmetallbåge är en effektiv och allmänt använd värmekälla vid svetsning och additiv tillverkning. I denna studie tillämpas den på svetsning. Den erbjuder hög produktivitet, låg kostnad vid inköp och användning, såväl som vissa nackdelarsom ojämn "bucklig" svetssträng och smältdiken vid svetsning av stora komponenter som är krökta och medför att svetsbrännarens orientering ändras utmed fogen. Bättre processförståelse eftersträvas därför för att mildra dessa nackdelar. En utmaning är processens icke-linjära beroende av svetsparametrarna och materialegenskaperna. Dessutom är experimentell optisk övervakning svår. Till exempel kan den höga temperaturen och den intensiva elektromagnetiska strålningen från ljusbågen, rök, sprut, såväl som legeringens ogenomskinlighet, förhindra observation under processen eller begränsa den. Processimulering erbjuder en komplementär metod för att nå processkunskap. Det är alltså detta tillvägagångssätt som används i denna studie. För detta har en modell av värme och materialflödena i smältan utvecklats som kan prediktera smältning och stelning, spåra smältytans deformation, metallflöde och koalescens med smältan.Två huvudsakliga forskningsfrågor har identifierats och adresserats. Den första studerade gravitationens påverkan vid flersträngs-, gasmetallbågsvetsning av V-fogar i INVAR. Olika svetslägen har visat sig ha en betydande påverkan på kraftbalanserna i svetssmältan vilket resulterar i distinkta smältflöden, smält- och svetsförbandgeometrier, och under vissa förhållanden svetsdefekter såsom ojämn "bucklig" svetssträng, smältdiken och bindfel. Som ett resultat rekommenderas horisontellt och 20◦ fallande läge vid flersträngssvetsning, medan 20◦ stigande och sidolutande inte rekommenderas. Den andra frågan undersökte inverkan av de tre huvudsakliga modellerna för den elektromagnetiska kraften som idag används vid svetssimuleringar. För modelleringen har antaganden lagts fram och undersökts. Det visade sig att de tre modellerna predikterar olika flödesmönster i smältan, olika värmekonvektion, smältgeometri, ytvågor och interaktion med de överförda metalldropparna, och därmed också predikterar olika svetsstränggeometrier. Alla tre modeller kan justeras för att prediktera svetspenetrationen, men endast den mest kompletta av dessa rekommenderas för sant prediktiv modellering. Det föreslås också att ytterligare förbättra den mest kompletta modellen så att det elektromagnetiska kraftfältet följer deformationen av den fria smältytan. / <p>Submitted papers or manuscripts have been excluded from the fulltext file. </p>

PureFize Technologies AB develops and manufactures a broadband ultraviolet (UVC) light technology device that is mercury-free and based on nanotechnology, using the principle of field emission. The light source is made of Ti and glass, which are hermetically bonded, using a low-temperature glass frit, at elevated temperatures. The bonding procedure will induce stresses in the device originating from the mismatch of the coefficient of thermal expansion (CTE) between the materials. Brittle materials, as glass, withstands tensile stresses poorly. Therefore, the stress magnitude and distribution needs to be understood.  This work develops a quality inspection method for the glass bond and internal stresses, as well as stress simulations of the device, to be used in production at the company. The glass bond width and the internal stresses in the device were classified and analyzed by light optical microscopy and by polarised light optical microscopy. The optical analysis was followed by pressure tests of the devices using a chamber that allowed for pressurized air up to 7 bar. In parallell with the experimental work, stress and deformation simulations of the device using the finite element method (FEM) was made. Data collected from the inspections and pressure tests were compiled and analyzed, showing clear connections between the glass bond quality and the device's ability to withstand external pressure. A narrow glass bond could withstand external pressure poorly, whereas a wide glass bond could withstand external pressure well. Correlations could be made both between the glass bond appearance and the stress patterns, as well as between the FEM simulations and the stress patterns in the device. It is clear that the stresses induced in the device after bonding originates from the CTE mismatch of the bonded components when cooling it from the bonding temperature to room temperature. The pressure testing method proved to be an efficient way of verifying the maximum pressure capacity of the devices.  The knowledge from this thesis can be used when further investigating induced stresses from glas frit bonding.