M.Tech (Department of Electronic Engineering, Faculty of Engineering and Technology), Vaal University of Technology / In the world of research and development, the ability to rapidly manufacture a prototype or part has become a significant part of the manufacturing process. This requirement has given rise to some unique manufacturing technologies. One of these technologies is Additive Manufacturing (AM), or also more commonly known as 3D printing. There are several AM technologies available and can be divided into three major AM categories namely: liquid, powder and solid sheet based. For this research study, the primary focus will be on powder-based technologies. Powder-based technologies make use of materials in powder form and use different fusion techniques to fuse the powder particles together. All the powder bed fusion technologies consist of the same basic components, namely a powder chamber, build chamber, re-coater and a powder fusion system. For each layer of the build, the re-coater applies a new layer of powder from the powder chamber to the build chamber, and then the specific type of powder fusion system will fuse the powder particles together. This process will then be repeated until the entire build has completed. Currently, powder bed fusion AM platforms do not have re-coating quality feedback into the printing system. Thus, when errors or defects occur on the powder bed surface during the re-coating process, they can affect the structural integrity of the parts. Parts must then be reprinted, which becomes costly due to wasted raw materials, electricity and time. Raw material and sundry wastage was some of the key factors that reduces the overall efficiency of the identified AM technology. Due to the increased problem with wasted materials, the need arose to develop a re-coater monitoring system, which could be used to increase the overall efficiency of a powder-based system. For the development of a re-coater monitoring system, a review of three different types of monitoring technologies such as computer vision, laser scanning and a time-offlight camera was conducted. Based upon the relatively low cost, low computer resource requirements and high accuracy, computer vision was considered as the best suited technology for development of the monitoring system. To select the correct camera to capture images of the powder bed, the required specifications for the camera, lens and mounting position were determined mathematically. A software program was then developed to autonomously detect re-coating errors on the captured image after each re-coating cycle using image processing techniques. Each of the captured powder bed images were divided into 16 equal sized quadrants, where each quadrant was processed individually. Each of the quadrants was examined using an edge detection algorithm to detect any changes in contrast that would indicate a defect or re-coating error. The probability of a possible re-coating error or defect was calculated for each quadrant and displayed as a percentage value. The active re-coater monitoring system was also integrated into the Voxeljet VX500 to validate the system’s operation. The system was used to monitor a total of seven build jobs on the Voxeljet VX500. However, the first three build jobs could not be successfully monitored as some parameters of the system had to be re-adjusted to ensure proper operation. The last four build jobs were monitored successfully and recorded results that proved that the active re-coater monitoring system could indeed detect defects and re-coating errors when they occurred.

With the continued progression of Moore’s law into the sub-14nm technology nodes, interconnect RC and power dissipation scaling play an increasingly important role in overall product performance. As critical dimensions in the mainstream Cu/ULK interconnect system shrink below 30nm, corresponding increases in relative process variation and decreases in overall process window mandate increasingly complex integrated solutions. Traditional metallization processes, e.g. PVD barrier and seed layers, no longer scale for all layout configurations as they reach physical and geometric limitations. Interactions between design, OPC, and patterning also play more and more critical roles with respect to reliability and yield in volume manufacturing; stated simply, scaling is no longer “business as usual”. Restricted design layouts, prescriptive design rules, novel materials, and holistic integration solutions each therefore become necessary to maximize available process windows, thus enabling new generations of cost-competitive products in the marketplace.

Stark formbare Wabenkerne als Kernschicht geformter Sandwichbauteile finden in vorteilhafter Ausführung bisher lediglich Verwendung in kostenintensiven Anwendungen mit hoher Leistungsklasse. Für eine weite Verbreitung der kombinierten Leichtbauweise fehlen bisher kostengünstige Wabenkerne, die die Formung schadlos überstehen und so ihre Verbundeigenschaften auch im geformten Bauteil aufweisen. Die vorliegende Arbeit befasst sich zunächst mit der Entwicklung eines Verfahrens zur Herstellung eines formbaren Papierwabenkerns mit vorgegebener Zellstruktur. Nach dem Funktionsnachweis erfolgt ein Anforderungsabgleich, welcher zeigt, dass eine kostengünstige Herstellung nicht realisierbar ist. Nach Diskussion folgt der Entschluss, den größtmöglichen iterativen Schritt beim Konstruktiven Entwicklungsprozess zu gehen und das gesamte Verfahren als nicht anforderungsgerecht einzustufen. Zugleich wird die vorgegebene Zellstruktur hinterfragt. Darauf basierend erfolgt eine umfangreiche Recherche zu Wabenkernherstellungsverfahren und formbaren Wabenkernen. Aus Letzterem werden sieben Gestaltungselemente abgeleitet, die zur Formbarkeit führen. Mit dieser Kenntnis wird der Entwicklungsprozess erneut durchlaufen. Die Zellstruktur ist dabei nicht definiert, sondern lediglich die zu erzielenden Eigenschaften, wodurch eine möglichst geeignete Produkt-Verfahrenskombination ermittelt werden soll. U. a. resultiert ein Flexibilisierungsverfahren, bei dem gängige Hexagonalwabenkerne aus Papier in einem zusätzlichen Schritt umgeformt werden und so die geforderte Formbarkeit erlangen. Nach der Entwicklung und dem Funktionsnachweis mit einer Prototypenmaschine erfolgt die Weiterentwicklung des Verfahrens. Mit einer Laborversuchsmaschine werden wesentliche Steuergrößen ermittelt, das Wirkprinzip diskutiert, ein erstes Verarbeitungsspektrum erprobt sowie ein Verfahren zur optischen Erfassung von Wabenkernzellstrukturen entwickelt. Letzteres dient der Charakterisierung von Wabenkernen und, speziell beim flexibilisierten Wabenkern, der Vorhersage des Formänderungsvermögens. Abschließend werden wesentliche Verbundeigenschaften eines flexibilisierten Referenzwabenkerns seiner gängigen hexagonalen Form gegenübergestellt und exemplarisch erste Musterformteile gefertigt. Im Rahmen der Arbeit werden entwicklungsübergreifende Forschungsfragen aufgestellt, die anhand gewonnener Erkenntnisse diskutiert werden.:1Einleitung 2 Stand der Wissenschaft und Technik 2.1 Wabenbauweise 2.2 Schalenbauweise 2.3 Wabenformteile 2.4 Geschichte der Waben- und Schalenbauweise 2.5 Wabenkerne - Kategorisierung, Aufbau und Terminologie 2.6 Wabenwerkstoffe - insbesondere Papier 2.7 Ausgewählte Einflüsse auf Wabenkerneigenschaften 2.8 Herstellung von Wabenkernen 2.8.1 Wellprinzip 2.8.2 Reckprinzip 2.8.3 Zellgrundformen sowie Anwendbarkeit des Well- und Reckprinzips 2.9 Formbare Wabenkerne 2.9.1 Papierwabenkerne in Wabenformteilen 2.9.2 Gestaltung und Klassifizierung formbarer Wabenkerne 2.9.3 Herstellung zellstrukturbedingt formbarer Wabenkerne 2.10 Herstellungsaufwand, Leistungsfähigkeit und Kosten 3 Präzisierte Zielstellung und Vorgehensweise 4 Verfahrensentwicklung – Herstellung einer geometrisch definierten Zellstruktur 4.1 Ausgangssituation 4.2 Weiterentwicklung des Herstellungsverfahrens 4.2.1 Vervollständigung des Herstellungsverfahrens 4.2.2 Neuentwicklung Formvorrichtung 4.2.3 Entwicklung Formbaugruppe 4.2.3.1 Fertigung und Erprobung von Formschienen und -baugruppen 4.2.3.2 Entwicklung vorteilhafter Formschienenkonturen 4.2.3.3 Potentiell vorteilhafte Formbaugruppe 4.2.4 Entwicklung Trenn- und Fügemaschine 4.3 Bewertung der Entwicklung und Diskussion 5 Verfahrensentwicklung – Flexibilisierung zum formbaren Wabenkern 5.1 Angepasste Zielstellung und Vorgehensweise 5.2 Ermittlung eines Vorzugsprinzips 5.2.1 Ermittlung geeigneter Lösungsräume 5.2.2 Ermittlung geeigneter Verfahrensprinzipe 5.2.3 Bewertung der Verfahrensprinzipe 5.3 Entwicklung des FlexCore-Verfahrens 5.3.1 Entwicklung FlexCore-Prototyp 5.3.2 Funktionsnachweis 5.3.3 Weitergehende Erprobung 5.4 Bewertung des Flexibilisierungsverfahrens FlexCore 6 Ausarbeitung FlexCore-Verfahren 6.1 Identifizieren verbleibender Entwicklungsschwerpunkte 6.2 Entwicklung einer Methode zur Charakterisierung von Wabenkern-Zellstrukturen 6.2.1 Konkretisierung der Entwicklungsaufgabe 6.2.2 Ermittlung einer Methode zur Zellstrukturerfassung 6.2.3 Entwicklung eines mobilen Prüfstandes zur Zellstrukturerfassung 6.2.4 Erarbeitung und Erfassung potentiell charakteristischer Kenngrößen 6.3 Maschine für wissenschaftliche Untersuchungen 6.3.1 Maschinenentwicklung 6.3.2 Maschinenerprobung 6.4 Identifizierung charakteristischer Kenngrößen flexibilisierter Zellstrukturen sowie wesentlicher Verfahrenssteuergrößen 6.4.1 Versuchsplanung und -durchführung 6.4.2 Prüfung des Formänderungsvermögens formbarer Wabenkerne 6.4.3 Bestimmung charakteristischer Kenngrößen 6.4.4 Bestimmung wesentlicher Steuergrößen des FlexCore-Verfahrens 6.5 Rückschlüsse zur Funktionsweise des Wirkprinzips 6.6 Erste Erprobung des Verarbeitungsspektrums 6.7 Stützstoffeigenschaften flexibilisierter Wabenkerne 6.7.1 Geometrie- und Masseeigenschaften 6.7.2 Druckeigenschaften - unstabilisiert 6.7.3 Druckeigenschaften - stabilisiert 6.7.4 Schubeigenschaften 6.8 Exemplarische Musterfertigung von Wabenformteilen 7 Zusammenfassung und Ausblick Abbildungsverzeichnis Tabellenverzeichnis Quellen Anlagen

Manufacturing of aero engine components requires attention to residual stress and final shape of the product in order to meet high quality product standards.This sets very high demands on involved manufacturing steps to meet design requirements. Simulation of manufacturing processes can therefore be animportant tool to contribute to quality assurance.The focus in this work is on simulation of a manufacturing process chain comprising of sheet metal forming, welding and a stress relief heat treatment.Simulation of sheet metal forming can be used to design a forming tool design that accounts for the material behaviour, e.g. spring back, and avoid problems such as wrinkling, thinning and cracking. Moreover, the simulation can also show how the material is stretched and work hardened. The residual stresses after forming may be of local character or global depending on the shape that is formed. However, the heat affected zone due to welding is located near the weld.The weld also causes large residual stresses with the major component along the weld. It is found that the magnitude of the residual stresses after welding is affected by remaining stresses from the previous sheet metal forming. The final stress relieve treatment will relax these residual stresses caused by e.g. forming and welding. However, this causes additional deformations.The main focus of this study is on how a manufacturing process step affects the subsequent step when manufacturing a component of the nickel-based super alloy 718. The chosen route and geometry is a simplified leading edge of an exhaust case guide vane. The simulations were validated versus experiments. The computed deformations were compared with measurements after each manufacturing step. The overall agreement between experiments and measurement was good. However, not sufficiently accurate considering the required tolerance of the component. It was found from simulations that the residual stresses after each process affects the subsequent step. After a complete manufacturing process chain which ends with a stress relief heat treatment the residual stresses were not negligible. VIII Special experiments were performed for studying the stress relief in order to understand how the stresses evolve through the heat treatment cycle during relaxation. It was found that the stresses were reduced already during the beginning of the heating up sequence due to decreasing Young´s modulus and yield stress with increasing temperature. Relaxation due to creep starts when a certain temperature was reached which gave a permanent stress relief.

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La Fabrication Additive (FA) est un procédé de fabrication qui a commencé à se développer dans les années 80 et qui atteint actuellement une maturité qui lui permet d’être utilisé de manière rentable et fonctionnelle par les industriels. La fabrication additive est définie comme étant le procédé de mise en forme d’une pièce par ajout de matière, à l’opposé de la mise en forme traditionnelle par enlèvement de matière (usinage). Cette nouvelle technologie est une réelle révolution et permet de relever de nouveaux défis technologiques sans précédent. Que ce soit sur un axe matériau ou plus largement dans le cadre de l’usine du futur, la fabrication additive est un réel levier de croissance, mais de nombreux travaux de recherche sont encore à mener afin de perfectionner cette nouvelle technologie. C’est autour de cette problématique que les travaux de thèses se sont focalisés avec un accent sur l’intégration de matériaux électroactifs pour la réalisation de fonction mécatronique tirant profit des procédés de Fabrication Additive. Les actions de recherche montrent que la fabrication additive de matériaux électroactifs sera de plus en plus employée pour la réalisation de fonctions mécatroniques hybrides qui combineront à la fois la structure mécanique, des circuits intégrés en silicium, des pistes conductrices et des matériaux couplés imprimés, intégrant ainsi des fonctionnalités, telles que des capteurs, des affichages ou des sources d’énergie. Les travaux montrent le potentiel applicatif autour du contrôle de santé des structures en composites, mais aussi du contrôle de forme d’instrument pour la chirurgie. Pour arriver au développement de ces dispositifs, les points suivants ont été développés autour des matériaux électroactifs et de leurs règles d’intégrations et d’optimisation. / Additive Manufacturing (FA) is a manufacturing process that began to develop in the 1980s and is now mature enough to be used in a cost-effective and functional way by manufacturers. Additive manufacturing is defined as the process of shaping a part by adding material, as opposed to traditional shaping by material removal (machining). This new technology is a real revolution and enables us to meet new unprecedented technological challenges. Whether on a material axis or more widely as part of the plant of the future, additive manufacturing is a real growth driver, but many research work is yet to be conducted to perfect this new technology. It is around this issue that the work of theses focused with a focus on the integration of electroactive materials for the realization of mechatronics function taking advantage of Additive Manufacturing processes. Research shows that additive manufacturing of electroactive materials will be increasingly used for the realization of hybrid mechatronic functions that will combine both the mechanical structure, silicon integrated circuits, conductive tracks and printed coupled materials, integrating as well as features, such as sensors, displays or power sources. The work shows the potential application around the health control of composite structures, but also the instrument shape control for surgery. To arrive at the development of these devices, the following points have been developed around electroactive materials and their integration and optimization rules.

L'élaboration de céramiques polycristallines transparentes constitue un défi technologique important. Les matériaux transparents actuellement utilisés (verres ou monocristaux) possèdent des propriétés mécaniques (dureté, résistance à l'usure) et physico-chimiques (résistance à la corrosion) moins intéressantes que celles des céramiques polycristallines. Par ailleurs, le coût de production de ces dernières est inférieur à celui des monocristaux. Les deux principaux paramètres à contrôler afin d'augmenter les propriétés optiques de l'alumine alpha polycristalline sont sa porosité, comme pour tout matériau transparent, et sa taille de grains, du fait de sa biréfringence. Aussi on cherchera à obtenir après frittage un matériau possédant une très faible porosité (inférieure à 0,05%) avec une distribution fine en taille de pores centrée sur des porosités nanométriques, et une taille de grains très fine (plus grand que 0,5 µm). Actuellement, cette microstructure particulière est obtenue en ~ 15 heures en combinant un frittage naturel suivi d'un traitement par Hot Isostatic Pressing (HIP). La technique de Spark Plasma Sintering (SPS) utilisée dans cette étude permet d’obtenir des céramiques denses possédant une microstructure fine en des temps plus courts. Premièrement, un protocole d'élaboration d'une alumine pure transparente a été mis au point. Il repose sur la préparation de crus à microstructure contrôlée avant l'étape de frittage. Principalement, ils doivent présenter une distribution fine en taille de pores avec un empilement particulaire macroscopique homogène dépourvu d'agglomérats. Le cycle de frittage SPS a également été optimisé afin d'obtenir les meilleures transmissions optiques possibles. Ensuite, un protocole de dopage par des inhibiteurs de croissance de grains a été optimisé. La nature du sel dopant influe au second ordre sur les propriétés optiques des échantillons par rapport à une calcination préalable au frittage. La nature et/ou la quantité de dopant induisent un décalage plus ou moins important de la densification vers les hautes températures. Le cycle de frittage SPS doit donc être adapté en conséquence. Le taux de dopant doit être optimisé afin d'obtenir une microstructure fine après frittage sans présence de particules de seconde phase. Différents dopants ont été comparés (magnésium Mg, lanthane La et zirconium Zr) et l'échantillon possédant les meilleures propriétés optiques a été obtenu grâce à un dopage à 200 cat ppm de lanthane. Des optimisations au niveau de la morphologie des poudres (plus fines et plus sphériques) et de la préparation des suspensions d'alumine alpha dopées au lanthane (lavage par centrifugation) ont permis d'obtenir l'un des meilleurs échantillons d'alumine transparente reporté dans la littérature. Il possède une transmission optique de 68% et une taille de grains de l'ordre de 300 nm. Ses propriétés mécaniques (dureté, résistance à l'abrasion) sont supérieures à celles d'un monocristal de saphir. / Obtaining transparent polycrystalline ceramics became an important technological challenge over the last decade. Their high mechanical (hardness, wear resistance) and physico-chemical (corrosion resistance) properties combined with a high transparency and a reasonable price could lead them to replace glasses or monocrystals as sapphire in optical applications. The main parameters to control in order to obtain highly transparent polycrystalline alpha-alumina (PCA) are the porosity size and amount as for the other transparent materials. However, as PCA is a birefringent material, the grain size also needs to be controlled. That’s why PCA should possess after sintering grains as small as possible (bigger than 0.5 µm) and a porosity closed to 0.00% with nanometric pores. This particular microstructure is usually obtained in ~ 15 hours by combining natural sintering in air with a post Hot Isostatic Pressing (HIP) treatment. In our study, the Spark Plasma Sintering (SPS) technique was used as it enables to obtain fully dense ceramics in shorter times while limiting the grain growth. First, a protocol to obtain a pure transparent PCA was established. It consists on preparing green bodies with a controlled particle’s packing before sintering. Mainly, the particle’s packing has to be macroscopically homogeneous and without agglomerates. Moreover, the pore size distribution should be the narrowest. The SPS sintering cycle was also optimised to obtain the highest optical transmission. Then, a doping protocol with grain growth inhibitors was optimised. The nature of the doping salt has a secondary effect on optical properties compared to a thermal treatment applied before sintering. Depending on the doping agent nature and/or amount, the densification temperature changes. The SPS sintering cycle has thus to be adapted. The doping agent amount has to be optimised to obtain a fine microstructure after sintering without second phase particles. Different doping agents have been compared (magnesium Mg, lanthanum La and zirconium Zr). The sample having the highest optical properties was doped with 200 cat ppm of lanthanum. Finally, an optimisation of the powder’s morphology (finer and more spherical) was performed. Moreover, the lanthanum doped alpha-alumina slurry’s preparation was optimized using centrifugation. All these processes have enabled us to obtain one of the most transparent PCA sample ever reported in the literature. It possesses an optical transmission of 68% and a grain size around 300 nm. Its mechanical properties (hardness, wear resistance) are higher than the ones of a sapphire monocrystal.

Interest in accounting for environmental impacts of products, processes, and systems during the design phase is increasing. Numerous studies have undertaken investigations for reducing environmental impacts across the product life cycle. Efforts have also been launched to quantify such impacts more accurately. Life cycle energy consumption and carbon footprint are among the most frequently adopted and investigated environmental performance metrics. As efforts continue to incorporate environmental sustainability into product design, struggles persist in concurrent consideration of environmental impacts resulting from the manufacturing processes and supply chain network design. Thus, the objective of this research is to present a framework for reducing product cradle-to-gate energy consumption and carbon footprint through simultaneous consideration of manufacturing processes and supply chain activities. The framework developed in this thesis relies on unit process modeling, and is demonstrated for production of a bicycle pedal. It is shown that simultaneous consideration of manufacturing and supply chain processes can impact decision-making and improve product environmental sustainability at the design stage. The work presented contributes to the state of the science in sustainable design and manufacturing research. In addition, a point of departure is established for the research community to move current efforts forward for concurrent consideration of multiple stages of the product life cycle in pursuit of environmental, economic, and social sustainability. / Graduation date: 2012

During the design phase, it creates and transforms ideas into products. It needs to know the manufacturing aspects for ensuring success and calculating the product cost while developing of designs. However, the choice one or another way of manufacturing, it will get slightly different results to the proposed design. The design teams require knowing some manufacturing alternatives for evaluate. This thesis has been proposed a select manufacturing process chain tool. The system modeled the design and manufacturing process data by select attributes and the process relationship. Moreover, the system uses “transformation concept” that represents the capability of each manufacturing process to modify a determinate design attribute. Finally, the system is developed as algorithm and build as part of a CAD platform. / Al llarg de la fase de disseny és on es creen les idees i es transformen en productes. La incorporació d’aspectes de fabricació en el desenvolupament dels dissenys permetrà assegurar-ne l’èxit i calcular-ne el cost. Tanmateix, l’elecció d’un o un altre camí de fabricació farà obtenir resultats lleugerament diferents al del disseny proposat. Fent que els equips de disseny precisin obtenir alternatives de fabricació durant la fase de disseny per a valorar les possibilitats. S’ha proposat, amb aquest tesis, una eina que estableix cadenes de processos de fabricació per a cada disseny. Per a desenvolupar-la s’ha modelitzat per mitja dels atributs la informació de disseny i la dels processos de fabricació, enriquit amb les relacions entre processos. S’ha completat l’obtenció de les cadenes amb l’ús del “concepte de transformada” que indica com pot alterar un procés un determinat atribut. Finalment s’ha desenvolupat un algoritme que combina ambdós parts i s’ha implementat com a part d’una plataforma CAD.

År 2016 var världsproduktionen av textilfibrer mer än 100 miljoner ton. Mycket av textilierna hamnar till slut i hushållssoporna som i Sverige förbränns till energiåtervinning; textilier som egentligen hade kunnat återanvändas eller materialåtervinnas. Textilåtervinning delas vanligtvis upp i tre olika kategorier: mekanisk, kemisk och termisk återvinning. Mekanisk återvinning är en typ av down cycling, som idag endast sker i liten skala. Ett av problemen som gör att mekanisk återvinning inte tillämpas i större utsträckning är att fibrerna i processen deformeras och blir för korta för att kunna spinnas till garn. Detta leder till en försämrad fiberkvalité i jämförelse med jungfruliga fibrer, vilket gör att återvinningsprocessen idag inte är hållbar ur ett ekonomiskt perspektiv.   I projektet har textila tillverkningsmetoder i form av garnspinning och trikåtillverkning undersökts för att se hur val av metoder kan främja en återvinningsprocess. En jämförelse av spinnmetoder gjordes mellan ett egentillverkat ringspunnet garn av samma sorts bomullsfibrer som i ett färdigtillverkat rotorspunnet garn. Från resultat av dragprovning gick det att utläsa att ringspunnet garn var starkare än rotorspunnet garn gällande både brottlast, brottöjning och tenacitet. Emellertid kunde ingen signifikant skillnad beräknas i varken brottlast eller brottöjning i testet av trikåvaror som stickats av vardera garnsort. Däremot fick trikåvara av rotorspunnet garn en större fiberförlust än motsvarande trikå av ringspunnet i test av nötningshärdighet.   Vid mätning av fiberlängd upptäcktes det att ett rotorspunnet garn innehåller kortare fibrer än ett ringspunnet garn, vilket betyder att fibrerna har förkortats i rotorspinningsprocessen då de båda garnen tillverkats från samma förgarn. Visuell analys av fibrerna från de olika processtegen genomfördes genom mikroskopering för att undersöka eventuell fysisk deformation. I analysen gick det att urskilja formförändringar hos fibrerna från de båda garnsorterna men man har inte kunnat bekräfta att de formförändringarna har en direkt koppling till möjligheten för mekanisk återvinning.   Ur ett hållbarhetsperspektiv behövs mer forskning på tillverkningsmetoders påverkan på återvinning av textil och möjligheten för återspinning. Detta skulle kunna möjliggöra att det redan i tillverkningsprocessen kan göras smarta val för ett materials cirkulära kretslopp. Det bör tittas närmare på hur processer kan göras ekonomiskt hållbara, även skillnader i miljöpåverkan hos de olika tillverkningsprocesserna bör undersökas. / 2016 was the year the world market of textile fibers surpassed the volume of 100 million tonnes. In Sweden today, lots of textiles end up in the garbage bin, later used for energy recovery even though most of the material could be reused or recycled. Textile recycling is often categorized in mechanical, chemical and thermal recycling. Mechanical recycling is a type of down cycling, which today only takes place on a small scale. One of the reasons, is the deformation of the fiber in the recycling process. When the textile fibers are mechanically processed their length become too short for the following re-spinning of yarn. This results in a deteriorated fiber quality in comparison with virgin fibers and complicates the vision of an economically sustainable recycling process.   In this thesis an investigation of how textile manufacturing processes affect a possible recycling process was made. Cotton fibers were spun to yarn by a ring spinning machine and compared with a prefabricated rotor spun yarn made of same sort of cotton fiber and later knitted in a circular knitting machine. The manufacturing processes influence on the mechanical properties of the yarns and the knitted fabrics were tested using a tensile testing machine and a Martindale tester. From the result of tensile testing the yarn, it was found that the ring spun yarn was stronger than the rotor spun in breaking strength, elongation and tenacity. Meanwhile no statistically differences in breaking strength and elongation in the knitted fabrics could be calculated. In the abrasion resistant test the knitted fabric of rotor spun yarn showed a greater loss in fiber than the knitted fabric of the ring spun.   Moreover a visual analysis of the fibers from various process steps was made by microscopy to investigate any physical deformation of the fibers. The fibers from the ring spun yarn was more wave- formed compared with fibers from the roving, while the tip of the fibers were flattened and less natural twisted in the rotor spun yarn. In the knitted fabrics, the fibers from the rotor spun yarn showed similar shape like the ones from the spinning process but the ring spun fibers were tip shaped. In addition an investigation of fiber length of fibers from roving, ring spun yarn and rotor spun yarn was made. The result showed a lower mean value of fibers from rotor spun yarn, which could cause problem in a future recycling process.   In conclusion, from a sustainability perspective more research is required on the impact of manufacturing processes on recycling of textile fibers. This could enable the possibility to make better choices in manufacturing, which would prolong the life of the textile fiber and minimize the environmental footprints.