Dissertations / Theses on the topic 'Polymers welding'

Due to the wide range of properties of plastics (e.g. low density), more and more conventional materials are substituted by polymer materials. Complex requirement profiles on technical parts increase the demand for joining processes that enable the reliable joining of otherwise incompatible thermoplastics. In this case, material bonded connections are approaching their limits. In the following study two incompatible thermoplastic polymers were welded by using polymer blends that are compatible to both components. Industrially relevant thermoplastics polyethylene (PE) and polyamide 12 (PA12) were chosen to demonstrate the potential of an innovative joining technology.

Due to the wide range of properties of plastics (e.g. low density, low electrical and thermal conductivity), conventional materials will be increasingly substituted by polymers. Multifarious requirements on technical parts intensify the demand for joining processes, which ensure the reliable joining of incompatible thermoplastics. In this case, material bonded joints are approaching their limits. The present study focusses on the welding of two incompatible thermoplastic polymers (polyamide and polyethylene) by using adapted blend materials, which are compatible to both joining components. The results prove the feasibility of this method and indicate the high potential regarding the reachable joint strength. Furthermore, the study demonstrates the challenges regarding the suitable application of blend materials and deals with open scientific questions concerning their industrial usage.

Diploma thesis is focused on injection molding and welding technology of plastic materials. First, in theoretical part, are commonly described polymer materials, following by description of welding, and multi-injection molding. There are closely described different methods for chosen part. Practical part is about comparison of method according differ criteria and application suitability. At the end of the thesis there is economic estimation of methods.

Combinations of different materials are increasingly used in the modern engineering structures. The driving forces of this trend are rising fuel costs, global warming, customer demands and strict emission standards. Engineers and industries are forced to improve fuel economy and cut emissions by introducing newly design engines and lightweighting of structural components. The use of lightweight materials in the structures has proved successful to solve these problems in many industries especially automobile and aerospace. However, industry still lacks knowledge how to manufacture components from polymeric materials in combination with metals where significant differences exist in properties. This thesis aims to demonstrate and generate the methodology and guidelines for hybrid joining of aluminium alloys to thermoplastics using friction stir welding. The developed technique was identified, optimized and evaluated from experimental data, metallography and mechanical characterization. The success of the technique is assessed by benchmarking with recent literatures. In this work, lap joints between aluminium alloys (AA5754, AA6111) and thermoplastics (PP, PPS) were produced by the friction stir welding technique. The specimens were joined with the friction stir welding tools under as-received conditions. Metallic chips were generated and merged with the molten thermoplastic to form a joint under the influence of the rotating and translating tool. The effects of process parameters such as rotational speed, translational speed and distance to backing were analyzed and discussed. The investigation found joint strength was dominated by mechanical interlocking between the stir zone and the aluminium sheet. The results also show that the joint strength is of the same order of magnitude as for other alternative joining techniques in the literature.

QC 20150908

Due to the rising demand of light-weight constructions as well as the conservation of resources, the density and weight of thermoplastic parts could be influenced significantly by using the thermoplastic foam injection molding process. The structure of the foam injection molded part, which typically means solid surface layers and a cellular core, usually results in a weight saving. Furthermore the materials structure leads to an increasing of the specific bending stiffness with a simultaneous low tendency to warp. The present study was aimed to analyze the interactions between microcellular structure, joining process and the resulting mechanical properties of the molded part. Therefore, the microcellular injection molding process (MuCell®) as well as the vibration welding were used. Whereas the established welding processes for solid injection molded parts have already achieved a high degree of perfection within the last decades, the joining of microcellular thermoplastics entails several specific characteristics, because the injection foaming process highly influences the basic material properties. In contrast to solid materials, the weld seam properties after joining are mainly affected by the design constraints of the microcellular structure.

Les matériaux thermoplastiques gagnent en popularité dans l'industrie aérospatiale en tant qu'alternatives aux métaux et aux thermodurcissables, offrant des avantages tels que la rapidité de fabrication, la réparabilité et la recyclabilité. Leur capacité à ramollir et à fondre sous l’effet de la chaleur leur permet d’être soudés sans avoir besoin d'incorporer de composants. De plus, certains thermoplastiques présentent une résistance aux environnements extrêmes, tels que des températures élevées et divers produits chimiques, ce qui les rend idéaux pour des applications exigeantes. Ces caractéristiques font des thermoplastiques des matériaux adaptés aux applications où la réduction du poids, les performances et la durabilité sont des critères essentiels. Dans ce contexte, le soudage par transmission laser (LTW) se révèle être une technique efficace pour le soudage des thermoplastiques en raison de sa simplicité, de sa précision et de sa capacité à produire des joints de haute qualité. Dans cette technique, un faisceau laser traverse une partie supérieure semi-transparente et est absorbé par une pièce inférieure absorbante, ce qui génère de la chaleur à l’interface pour faire fondre et fusionner les pièces. Le procédé LTW repose sur les propriétés thermochimiques et optiques des matériaux à souder. Le soudage laser de thermoplastiques semi-cristallins, tels que les polyaryléthercétone (PAEK), nécessite une attention particulière. Le polyéthercétonecétone (PEKK) a reçu moins d'attention que le PEEK en soudage laser. Cependant, le PEKK est un matériau encore plus prometteur pour le soudage laser par transmission en raison de sa cinétique de cristallisation modifiable par rapport au PEEK. Cette thèse doctorale étudie le procédé de soudage laser par transmission du PEKK, en se concentrant sur l'influence des propriétés du matériau et des paramètres de soudage sur la morphologie et les propriétés mécaniques du joint de soudure. La configuration d’assemblage consiste en un échantillon de PEKK quasi-amorphe sur une pièce de PEKK fortement cristallisée (PEKK-A/SC). Les propriétés thermophysiques et optiques des matériaux sont caractérisées afin de s’assurer qu'ils sont adaptés au LTW. Ensuite, les paramètres du procédé, tels que la puissance du laser et l’épaisseur de la pièce semi-transparente, sont systématiquement étudiés pour comprendre leur impact sur les propriétés du joint. Certains assemblages sont recuits à la température de cristallisation à froid du PEKK pour améliorer la qualité des joints soudés. La qualité des assemblages soudés et recuits est évaluée à l'aide d'essais mécaniques de cisaillement à simple recouvrement et de la microscopie. Le procédé LTW est modélisé à l'aide de la méthode des différences finies sous environnement MatLab, en incorporant le transfert de chaleur et la cinétique de cristallisation du PEKK. Cette modélisation a permis de comprendre l'histoire thermique des échantillons pendant le soudage et de prédire l'évolution de la cristallinité du joint de soudure en fonction des paramètres de soudage. Après avoir étudié et validé le procédé LTW pour le PEKK, la thèse étend l’étude LTW aux composites PEKK renforcés par des fibres courtes de carbone (PEKK-CF). Pour permettre le LTW des échantillons PEKK-CF, le PEKK quasi-amorphe est utilisé comme pièce supérieure pour l’assemblage. Cela représente un nouveau domaine de recherche, car aucune étude antérieure n'a été trouvée sur le soudage laser par transmission des composites PEKK-CF. Le soudage des échantillons de PEKK-CF est optimisé par des essais expérimentaux, et la qualité du joint de soudure est évaluée en faisant varier l’intensité de laser. Les résultats de cette thèse contribuent à une meilleure compréhension du procédé de soudage laser par transmission du PEKK et de ses composites, et fournissent des lignes directrices pour optimiser les paramètres de soudage et améliorer la résistance des joints dans les applications industrielles
Thermoplastic materials are gaining popularity in the aerospace industry as alternatives to metals and thermosets, providing benefits such as fast manufacturing, repairability, and recyclability. Their ability to soften and melt allows them to be welded without needing to incorporate external components. Additionally, high-performance thermoplastics exhibit resistance to harsh environments, such as high temperatures and various chemicals, making them ideal for high-demanding applications. These features make thermoplastics suitable for applications in which weight reduction, performance, and durability are essential. Laser transmission welding (LTW) has emerged as an effective technique for welding thermoplastics due to its simplicity, precision, and ability to produce high-quality joints. In LTW, a laser beam passes through a semi-transparent upper part and is absorbed by a lower absorbent sample, generating heat at the interface to assemble the parts. The LTW process relies on the thermo-chemical and optical properties of the materials to be welded. Careful consideration is needed when laser welding semi-crystalline thermoplastics, like polyaryletherketones (PAEK). Polyetherketoneketone (PEKK) has received less attention than PEEK in laser welding. However, PEKK is a more promising material for LTW due to its unique crystallization properties compared to PEEK. The crystallization kinetics of PEKK can be modified, which provides better control of its crystallinity by manipulating processing parameters. This PhD thesis investigates the laser transmission welding process of PEKK, focusing on the influence of material properties and process parameters on the weld joint morphology and mechanical properties. The overlapping configuration consists of a quasi-amorphous semi-transparent PEKK sample over a highly crystallized opaque PEKK one (PEKK-A/SC). Thermo-physical and optical properties of the PEKK samples are characterized to ensure their suitability for LTW. Then, process parameters for LTW, such as laser power and thickness of the upper part, are systematically studied to understand their impact on weld joint properties. After welding, some assemblies are annealed at the cold crystallization temperature of PEKK to enhance joint quality. The quality of the weld joints is assessed by mechanical tests and microscopic observations. Single lap-shear tests are employed to identify the failure type and mechanical strength of assemblies. Microscopy is used to analyze failure zones and the weld joint morphology on the cross-section along the welding path. A numerical simulation of the LTW process of PEKK parts was developed in MatLab using the finite differences method, incorporating heat transfer and the crystallization kinetics of PEKK. This model provided insights into the thermal history of the samples during welding and predicted the evolution of weld joint crystallinity as a function of welding parameters. The developed simulations offer insights into the complex thermal and crystallization behaviors observed during LTW of PEKK parts. Furthermore, after studying and validating the LTW process for PEKK polymer, this thesis extends the LTW study to PEKK composites reinforced with short carbon fibers (PEKK-CF). To enable LTW of PEKK-CF samples, the quasi-amorphous PEKK is used as the upper part for the overlapping configuration. That represents a novel area of research, with no prior studies found on LTW of PEKK-CF composites. The welding of PEKK-CF samples is optimized through experimental trials, and the weld joint quality is evaluated under varying laser intensities and the thickness of the upper part. The findings from this thesis contribute to a deeper understanding of the LTW process for PEKK and its composites, providing valuable guidelines for optimizing welding parameters and improving joint strength in industrial applications

Das Forschungsvorhaben liefert einen Beitrag zum Schweißen von Gleich- und Mischmaterialverbindungen aus Naturfaserverstärkten Kunststoffen (NFK) sowie deren Verarbeitung im Compoundieren und Spritzguss. Es wurde holzfasergefülltes (WPC) und flachsfasergefülltes (FFC) Polypropylen (PP) mit unterschiedlichen Füllgraden verwendet. Der Einsatz synthetisch-organsicher Fasern (PET-Fasern) im Compound zielte darauf ab, besonders die Schlagzähigkeit zu verbessern. Im Bereich des Urformens wurden Aussagen zur Verarbeitbarkeit, zu rezepturabhängigen Kurz- und Langzeiteigenschaften sowie Aussagen zur Dauergebrauchsfähigkeit erarbeitet. Die Anwendbarkeit der Fügeverfahren Heizelement- (HE-Schweißen) und Vibrationsschweißen (VIB-Schweißen) konnte für Gleich- und Mischmaterialverbindungen sowohl ohne als auch mit angepasster Energieeinbringung nachgewiesen werden. In diesem Zusammenhang können Aussagen zur Rezepturabhängigkeit, Verfahrensführung, Parameterauswahl, Prüfkriterien sowie den technischen Grenzen der Schweißverbindung unter kurzzeitmechanischer Beanspruchung getroffen werden. Weiterhin wird ein Beitrag zur Dauergebrauchsfähigkeit unter UV-Globalbewitterung und thermischer Alterung sowie zu langzeitmechanischen Eigenschaften von NFK-Schweißverbindungen geliefert.

Understanding how different processing variables influence wood welded bonds is vital if the technique will ever be used to create engineered lumber without using adhesives. A variation of vibration welding, wood welding uses pressure and friction to bond materials together. During welding, heat causes a softening in the wood, a naturally occurring composite material. This softening leads to fiber entanglement and a bond forms upon cooling. The goal of this research was to investigate several processing aspects of the wood welding procedure. A prototype wood welding machine, designed and fabricated from the ground up, was used to investigate the effects of various welding parameters using birch wood. Wood welds were evaluated on the basis of bond coverage and ultimate shear strength. Four experiments were performed: welding frequency and duration interaction, grain orientation effects, alternative welding completion metrics, and strength development over time. During the wood welding process, three distinct phenomena were repeatedly observed: smoke creation, welding residue formation, and an audible pitch change. The presence of each was recorded for every wood welded specimen and used later in additional data analysis. Investigating each of the welding phenomena was done in an attempt to better characterize when fusion was achieved at the weld interface. ImageTool, an image analysis software package, was used to investigate and quantify the often irregular bonds exposed after shear fracture. The results of the various welding variables were analyzed on the basis of shear strength and bond uniformity. From the birch samples, it was shown that better bonds result from lower welding frequencies and longer welding durations. The grain orientation analysis demonstrated that welding orientation marginally affects the average shear strength of the wood weld. The data from the alternative welding metrics suggests that welding time is not a quality indicator of welding completion (bond coverage). The strength development trials confirmed previous research; wood welds obtain most of their strength in a relatively short period of time. Douglas fir and poplar both proved to be weldable for the first time, but they were sufficiently weaker than birch. When welding was attempted with Douglas fir under similar pressures used for birch, Douglas fir samples would commonly “washboard.” With reduced welding pressure, Douglas fir formed wood welds more easily.

Nesta pesquisa estudou-se a soldagem de materiais poliméricos por ultra-som, sendo estes, policarbonato (PC) e poli(metacrilato de metila, PMMA. As soldagens foram obtidas através do equipamento especifico para soldagem Soldadoras Integradas, série 900IW, empresa BRANSON Ultrasonics Corporation. Onde detalhamos alguns aspectos do equipamento: mecanismo de soldagem, conversores, transformador e sonotrodo. Para o sonotrodo especificamos a relação de área em função da geometria do mesmo. Ressaltamos também os tipos de métodos de soldagem: direto e indireto, de forma que concluímos que os materiais semicristalinos devem ser soldados apenas pelo método direto em conseqüência destes apresentarem grande perda de amplitude durante a soldagem. Em função destes possuírem uma acentuada queda do módulo de cisalhamento (G) e um aumento no fator de perda mecânica Tang δ acima da temperatura de transição vítrea (Tg), o que prejudica a soldagem. Foram analisados outros fatores que influem no processo de soldagem da junta como: tipos de juntas para uma melhor transmissão de energia, onde verificamos que juntas que possuem um D.R (diretor de energia) apresentam uma boa soldagem, diferente o que acontece com superfícies planas que apresentaram uma soldagem inadequada. Pesquisou-se também a propagação da onda no diretor de energia onde verificamos variações da amplitude através do mesmo. Estudou-se o método para estimar a capacidade de soldagem por ultra-som dos matérias através de fórmulas, onde verificou-se resultados coerentes com os valores reais. Experimentalmente variou-se os parâmetros de soldagem tais como: tempo de soldagem, pressão, e o tempo de recalque, com o intuito de obter-se variações na área soldada e na resistência ao cisalhamento das juntas. Os resultados apresentados pela variação dos parâmetros foram significativos, de modo, que o aumento do tempo de soldagem influenciou em um aumento da área das amostras em 90% das soldagens realizadas, tanto para soldagens similar (de mesmo material) e dissimilar (de materiais diferentes). Com aumento da pressão de soldagem obtivemos resultados menos significativos, ou seja, verificamos que 86,52% das amostras com junção similar, aumentaram a área em função do aumento da pressão. Os outros 13,48% diminuíram a área soldada em função do aumento da pressão, fenômeno causado pela diferença de rechupe encontrado nas amostras injetadas. O aumento do tempo de recalque não apresentou variações de área e de resistência ao cisalhamento significativas. As amostras soldadas apresentam o fenômeno de esbranqueceamento da região unida, onde concluímos que a umidade presente no material e as microrugosidades presentes na superfície do mesmo, causam este fenômeno. O qual pode ser minimizado através de secagem do material antes da injeção. Mediu-se a área soldada, e a resistência ao cisalhamento de todos os tipos de juntas, de forma que obtivemos diferentes valores para cada tipo de material analisado (PMMA e PC) com junções similares (PMMA/PMMA e PC/PC), dissimilares (PMMA/PC) e com direções de injeção similares (HH, VV) e direção de injeção dissimilar (HV). Com estes resultados podemos aplicar o método estatístico de análise de variância em função da variação de área e da variação de resistência. Os resultados da análise de variância foram mais coerentes com os resultados experimentais em função do parâmetro tempo de soldagem. A análise de variância em função da pressão apresentou resultados menos significativos, comparado aos resultados experimentais. As juntas soldadas foram adaptadas da norma ASTM D638M, e para realização do teste de cisalhamento projetou-se um dispositivo especial para esta aplicação.
In this research it was studied welding of polymerics materials by ultrasound, being these, polycarbonate (PC) and poli(metacrilate of metila, PMMA). The weldings had been gotten through the equipment specify for welding (Integrated Soldering, series 900IW, company BRANSON Ultrasonics Corporation). Detail some aspects of the equipment: mechanism of welding, converters, transforming and sonotrode. For sonotrode we specify the relation of area in function of the geometry. Empathized also two types of welding methods: direct and indirect, then we conclude that the semi crystalline materials must be welded only by the direct method, in consequence of these materials to present great loss of amplitude during the welding. In function of these to possess one accented fall of the module of shear (G) and an increase in the mechanics loss factor (Tang δ), above of the glass transition temperature (Tg), these factors it harms the welding. Other factors had been analyzed that influence in the process of welding of the joining, as: geometric of joining for one better transmission of energy, where we verify that joining that possess a D.R (director of energy) these present a good welding, different of others joining with plain surfaces that had presented an inadequate welding. The propagation of the wave in the energy director was also searched where we verify variations of the amplitude through D.R. The method was studied for estimate of the capacity of welding for ultrasound of the materials through formulas, where it was verified coherent resulted with the real results. Experimentally varied the welding parameters such as: welding time, pressure, and the time pressure after welding, with intention to get variations in the welded area and the shear strength of the joining. The results presented for the variation of the parameters had significant, in way, that the increase of the welding time influenced in an increase of the area of the samples in 90% of the carried through weldings, as much for weldings similar (of same material) and dissimilar (of different materials). With increase of the welding pressure we got resulted less significant, or either, we verify that 86.52% of the samples with similar junction, had increased the area in function of the increase of the pressure. The others 13.48% had diminished the area welded in function of the increase of the pressure, phenomenon caused for the difference of contraction found in the injected samples. The increase of the time of the time pressure after welding did not present variations of area and significant shear strength. The welded samples present the phenomenon of change of color of the joined region, where we conclude that the present humidity in the material and the microrugosidades of the surface causes this phenomenon. The change color can be minimized through drying of the material before the injection. It measured welded area, and the shear strength of all the types of joining, and this form we got different values of area and of shear strength for each type of material analyzed (PMMA and PC) with similar junctions (PMMA/PMMA and PC/PC) and dissimilar (PMMA/PC) with similar directions of injection (HH, VV) and direction of dissimilar injection (HV). With these results we can apply the statistical method of analysis of variance in function of the variation of area and in function of the variation of resistance. The results of the variance analysis had been more coherent with the experimental results in function of the parameter welding time. The analysis of variance in function of the pressure presented resulted less significant, comparative to the experimental results. The welded joining had been adapted according to norm ASTM D638M, and for development of the shear test a special device for this application was projected.

This thesis presents a theoretical and experimental investigation into the modelling of the electro-fusion process, applied to welding polymer pipes. The theoretical background of the transient heat transfer between the fitting and pipe, including variable interface thermal resistance and involving consecutive changes of phase (melting and re-solidification) and the problem of the thermo-mechanical induced stresses in the joint, are fully discussed. Three 2D axisymmetric models of the EFW process, with different degrees of complexity, have been developed, refined and validated by comparison with experimental data: a finite element coupled model, with both temperature and displacement degrees of freedom, and two sequential heat transfer models, finite element and finite difference based. The effect of the melt movement into the fitting-pipe initial clearance is discussed and has been modelled by a 'virtual material movement' method. For the sequential models a 'gap evolution model' has been developed to describe the closure of the initial fitting-pipe gap through the process. Results from the simulations of the electro-fusion welding process performed using all three models, which give an exceptionally good insight into the temperature, displacement and stress fields within the joint, are fully discussed and validated through comparison with experimental data.

On assemble par fusion (electrosoudage) et reticulation (soudage chimique) a l'interface grace a la diffusion et la reaction d'un agent reticulant present unitialement dans l'une des deux pieces. Simulation du processus

Le soudage par vibration est un procédé largement utilisé dans l’industrie automobile pour assembler des pièces en polymère. Lorsque la matière à souder ne contient pas de renforts, le coefficient de soudage, défini comme le rapport entre la contrainte à la rupture du matériau soudé et celle du matériau non soudé est proche de 1. En revanche, il devient difficile d’obtenir des coefficients de soudage dépassant 0,6 lorsque le matériau contient des fibres de verre. Afin de mieux comprendre pourquoi, différents grades de polyamide (PA) 6 et 66 renforcés à 30% de fibres ainsi que du polypropylène (PP) à 0, 20, 35 et 50% de fibres ont été injectés en plaques et soudées par vibration. Pour les échantillons en PA, des corrélations sont obtenues entre la contrainte à la rupture des assemblages soudés et l’orientation des fibres mais aussi avec l’épaisseur de la zone soudée déterminée par tomographie RX. L’étude sur les échantillons en PP indique que des cavités, probablement nocives, sont présentes uniquement dans la zone soudée des polymères renforcés. Leur présence est alors principalement attribuée à la réorientation des fibres pendant l’opération de soudage. Enfin, une simulation par éléments finis du comportement mécanique jusqu’à la rupture a été réalisée sur une éprouvette maillée comprenant une zone soudée. Les résultats obtenus mettent en exergue un phénomène d’amplification et de redistribution des contraintes dans la zone soudée en raison du confinement. Cette triaxialité générée favorise la croissance et la coalescence des cavités dans la zone soudée expliquant ainsi l’affaiblissement de la contrainte macroscopique uniaxiale à la rupture
Vibration welding is a common process used in automotive industry to assembly polymer parts. For pristine polymers, welding ratio, defined as the ratio between weld strength and tensile strength of non-welded material, is close to 1. However, for glass-fiber reinforced polymers, welding ratios are around 0.6 at best. In order to understand this discrepancy, several grades of polyamide (PA) 6 and 66 reinforced with 30% glass fibers as well as polypropylene (PP) with 0, 20, 35 and 50 % glass fibers have been injected in plates and vibration welded. A linear relationship was obtained between tensile strength of welded and non-welded PA specimens and their glass fiber orientation. Correlations were also found when plotting weld strength of samples regarding their welded zone thickness. In addition, voids are present only in the welded zone of glass fiber reinforced specimens, indicating that these voids are due to reorientation of fibers during the welding process. Finally, finite element modeling of mechanical behavior up to failure has been applied on a meshed specimen with a welded zone. Results show an amplification and distribution of stresses in the three directions inside the welded zone due to geometrical confinement. This generated triaxiality promotes growth and coalescence of cavities in the welded zone, explaining the weakening of the macroscopic uniaxial stress at failure

L'arrivée des aéronefs bas carbone à l'horizon 2035 s'annonce être un bouleversement pour la motorisation, et un véritable défi d'un point de vue des matériaux à mettre en œuvre. Le développement des technologies de soudage va de pair avec l'incorporation progressive de composites thermoplastiques. Parmi elles, le soudage par ultrasons nécessite encore une montée en maturité pour prendre une dimension industrielle, ce qui commence par la maîtrise du soudage statique. Cette technique d'assemblage implique l'emploi d'un équipement spécifique capable de délivrer des vibrations ultrasoniques à travers un mode de contrôle défini, tout en appliquant une pression. Elle nécessite également l'incorporation d'un film de polymères entre les surfaces à souder : le directeur d'énergie. Des éprouvettes en composite CF/PEEK, calibrées en épaisseur, ont été fabriquées par thermocompression. La matrice PEEK a été choisie pour ses performances mécaniques et sa capacité de cristallisation rapide, tandis que deux matériaux différents ont été utilisés comme directeurs d'énergie : le PEI et le PEEK. Une nouvelle méthodologie d'optimisation du soudage par ultrasons a été mise au point, en donnant aux courbes de soudage la forme désirée. Cette méthode se base sur l'emploi de phases multiples de soudage : le multimode. Elle garantit des résistances d'assemblage des composites CF/PEEK > 40 MPa et promet une optimisation rapide de tout assemblage comprenant des matériaux compatibles. L'importance de la nature et de la surface du directeur d'énergie a été démontrée. L'étude de mélanges modèles de PEEK et de PEI a permis d'écarter des hypothèses sur l'origine de la rupture des assemblages. Les températures ont été mesurées de façon peu intrusive pendant le soudage au moyen de réseaux de Bragg, apportant la preuve de l'hétérogénéité thermique dans l'interphase. Cette zone qui entre en fusion pendant l'activation des ultrasons atteint des températures comprises entre 500 et 700°C. La cinétique rapide du procédé permet des temps d'assemblage de l'ordre de quelques secondes. Les interphases soudées ont été visualisées à l'aide d'un microscope numérique, permettant de valider une méthode de contrôle manuelle
Low-carbon aircraft by 2035 are expected to be a major change in motorization, and a real challenge in terms of new materials. The development of welding technologies is closely linked to the growing use of thermoplastic composites. However, ultrasonic welding still needs significant advancements to reach an industrial scale, starting with the mastery of static welding. This assembly technique involves specific equipment designed to deliver ultrasonic vibrations through a defined control mode, while applying pressure. It also requires a polymer film to be incorporated between the surfaces to be welded: the energy director. Thickness-calibrated specimens of CF/PEEK composite were manufactured by thermocompression. The PEEK matrix was chosen for its mechanical performance and rapid crystallization capacity, while two different materials were used as energy directors: PEI and PEEK. A new methodology was developed to optimize ultrasonic welding, by giving the welding curves the desired shape. This method is based on using multiple welding phases: multimode. It ensures CF/PEEK composite joining strengths > 40 MPa and promises rapid optimization of any assembly using compatible materials. The significance of nature and surface of the energy director was demonstrated. Hypotheses concerning the origin of joint failure were discarded by studying model blends of PEEK and PEI. Temperatures during welding were measured with minimal intrusion using Fiber Bragg gratings, providing evidence of heterogeneous heating in the interphase. This region, which melts during ultrasound activation, reaches temperatures of between 500 and 700°C. The rapid kinetics of the process enable assembly times on the order of a few seconds. The welded interphases were visualized using a digital microscope, validating a manual inspection method

Les technologies de placement de plis ou d’enroulement filamentaire de composite à matrice thermoplastique avec consolidation en continu ont fait l’objet de nombreux travaux ces dernières années. Ces études ont porté principalement sur des composites à base de matrice thermoplastique semi-cristalline comme le poly(éther éther cétone) (PEEK) renforcée de fibres de carbone. L’objectif de la thèse est de déterminer les lois de comportement du composite fibres de carbone/matrice thermoplastique lors de la mise en œuvre afin de déduire quelle étape gouverne le processus de soudage et quels sont les paramètres procédés et matériaux influençant sa durée. Dans ce but, les principales propriétés de la matrice utiles à l’étude ont, dans un premier temps, été déterminées. Une attention particulière a été portée sur la dégradation thermique. Les analyses en thermogravimétrie ont ainsi permis d’évaluer sa cinétique de dégradation. Dans un deuxième temps, les mécanismes de contact intime et d’autohésion, responsables du soudage, ont été étudiés à partir de modèles. Pour cela, les mesures de rugosité de surface et de viscosité ont été intégrées au modèle de contact intime. Le temps de diffusion de la matrice a été déterminé par rhéologie puis intégré au modèle d’autohésion. Enfin, l’influence des paramètres procédé (temps, température et pression) et matériau (masses molaires et rugosité) sur les mécanismes de formation de l’interface et ses performances mécaniques a été évaluée expérimentalement par des tests d’adhérence (clivage et pelage) et comparée aux modèles
The automated tow placement or filament winding processes of thermoplastic-based composites have been intensively studied in recent years. These studies concerned mainly composites with thermoplastic semi-crystalline matrices as carbon fiber reinforced poly(ether ether ketone) (PEEK). The thesis objective is to understand the physical mechanisms taking place in a thermoplastic-based composite during the welding in order to deduce which step governs the welding process and what are the parameters influencing its duration. First, the main properties of matrix of interest for this study were determined, in particular its thermal degradation. The thermal gravimetric analysis thus allowed to evaluate the kinetics of degradation. Secondly, the mechanisms of intimate contact and self-adhesion responsible for welding were studied using models. For this, surface roughness and viscosity measurements were included in the model of intimate contact. The diffusion time of matrix was determined by rheology and integrated into the self-adhesion model. Eventually, the influence of process (time, temperature and pressure) and material (molecular weight and roughness) parameters on the mechanisms of interface formation and its mechanical performance was evaluated experimentally by adhesion tests (wedge test and peeling ) and compared with models

Cette étude porte sur la caractérisation des matériaux constituant le revêtement isolant de pipeline offshore ainsi que la soudure réalisée entre les deux polymères semi-cristallins du revêtement au niveau de la jonction entre deux tubes successifs.L’épaisseur très importante du revêtement induit, au cours du procédé de soudage, des vitesses hétérogènes de chauffe et de refroidissement des matériaux. Ces dernières ont été caractérisées grâce à une instrumentation du procédé en site industriel. Une modélisation numérique intégrant les phases successives du procédé est en bon accord avec les résultats expérimentaux. Cette modélisation permet de dresser une cartographie complète des champs de température dans l’ensemble du pipeline et plus précisément dans la zone de soudage.Cette étude nous a amené à réaliser une caractérisation des deux matériaux soudés au cours de leurs fusions et cristallisations qui représentent deux étapes cruciales lors du soudage. Une attention particulière a été portée au comportement rhéologique dans la zone de transition entre l’état fondu et l’état solide et inversement. Les données en refroidissement à différentes vitesses ont été corrélées avec le taux de transformation des matériaux.Les propriétés mécaniques des isolants ont été testées ainsi que celles des soudures en prélevant des éprouvettes sur les essais effectués en site industriel. Le peu de flexibilité du procédé industriel rend difficile une investigation de l’influence des paramètres de soudage. Une expérience « image », représentative des grandeurs industrielles, a donc été développée à l’échelle du laboratoire permettant de faire varier les paramètres de soudage. Il a été montré que le point de faiblesse de l’assemblage ne se situe pas au niveau de la soudure mais dans l’un des matériaux du revêtement
This PhD focuses on the characterization of the materials of the insulating coating of offshore pipelines as well as the welding made between the two semi-crystalline polymers of the coating at the junction of two consecutives pipes.The important thickness of the coating induces heterogeneous heating and cooling rates during the welding process. Those rates have been characterized through the implementation of thermal sensors during the industrial process. A simulation model of the different steps of the welding process is consistent with the experimental results. This simulation gives access to the thermal fields in the entire pipe and especially in the welding zone.This study allows us to characterize the two welded materials during their melting and crystallization which represent the two crucial steps during the welding. A particular attention has been drawn to their rheological behavior in the transition zone from the molten to the solid state and vice versa. The cooling data at different rates have been correlated with the transformation fraction of the materials.The mechanical properties of the insulating materials have been tested especially in the welding zone via the industrial process. However, the imposing infrastructure of the industrial process does not allow the study of the influence of welding parameters. To do so, a “mirror” experiment, representative of the industrial one, has been developed at a laboratory scale. Both the welding made via the industrial process and the “mirror” experiment have shown that the weak point of the structure is not the welding itself but one of the materials of the coating

Este trabalho objetivou a caracterização mecânica e a análise de falha de dois tipos de juntas compósitas através de ensaios mecânicos, em que uma das juntas era composta por dois laminados de fibras de carbono recoberto em ambas as faces por tecido de fibra de vidro reforçando uma matriz termoplástica (PPS-C) unidos via soldagem por resistência elétrica, e a outra confeccionada com dois laminados de fibras de carbono reforçando uma matriz de resina epóxi (EPX-C) unidos via colagem por filme de resina epoxídica. Os dois tipos de juntas foram submetidos a impacto único transversal de 10 J, condicionamento higrotérmico, além de carregamento em fadiga compressiva no plano nas mais diversas combinações destes processos degradativos de suas propriedades mecânicas. Observou-se, que a junta termorrígida colada de EPX-C apresentou a maior resistência mecânica em flexão em quatro pontos (F4P) na condição original (como-manufaturada), assim como os maiores valores de resistência residual para as várias condições de degradação mecânica e higrotérmica a que foi submetida. Por sua vez, a junta termoplástica soldada de PPS-C exibiu, em termos percentuais, menores reduções dos valores de resistência à flexão sob as condições avaliadas, relativamente às perdas apresentadas pela junta EPX-C em idênticas circunstâncias. A análise macroscópica da superfície de fratura de ambas as juntas indicou que o modo de falha predominante da junta termorrígida foi interfacial enquanto que, para a junta PPS-C, o modo de falha predominante foi o intralaminar. Análises fratográficas através da microscopia eletrônica de varredura (MEV) evidenciaram para a junta termorrígida EPX-C, uma alta adesão entre fibra/matriz, porém uma relativamente fraca interação entre os aderentes (laminado) e o filme adesivo de colagem, enquanto que, para a junta termoplástica PPS-C, reduzidas interações fibra/matriz forem inferidas na camada externa de PPS-V do aderente assim como entre a malha metálica resistiva e os filmes puros de PPS que a revestiam. Em ensaios de resistência ao cisalhamento interlaminar (ILSS), os espécimes retirados da junta EPX-C na condição virgem evidenciaram uma colagem uniforme/homogênea, enquanto que, para a junta PPS-C, os espécimes de ensaio usinados a partir da junta virgem indicaram a ocorrência de efeitos de degradação térmica altamente localizada nas bordas soldadas.
This study aimed to mechanical characterization and failure analysis of two kinds of composite single-lap joints by mechanical tests, in which a single-lap joint was made of two adherents of carbon fibers coated on both sides with glass fiber fabric reinforcing a thermoplastic matrix (PPS-C) welded via resistance welding, and the another type made of two adherents of carbon fibers reinforcing an epoxy matrix (EPX-C) bonded by epoxy adhesive film. The two types of single-lap joints were subjected to single transverse impact of 10 J, hygrothermal conditioning, and compressive fatigue loading in the plane in various combinations of these degradative processes of mechanical properties. It was observed that the thermosetting bonded joint EPX-C showed the highest strength in four point-flexure test in the original condition (as-manufactured), as well as greater residual strength values for the various conditions of mechanical and hygrothermal degradation which was subjected. In turn, the welded thermoplastic joint PPS-C exhibited, in percentage terms, smaller reductions in flexural strength values under the tested conditions, in respect of losses showed by EPX-C in similar circumstances. Macroscopic analysis of the fracture surfaces from both joints indicated that the predominant failure mode was interfacial to thermosetting while for PPS-C joint, the predominant failure mode was intralaminar. Analysis of fracture surfaces by scanning electron microscopy (SEM) showed, for thermosetting joints EPX-C, a high adhesion between fiber/matrix, but a relatively weak interaction between adherents and the bonding adhesive film, whereas for thermoplastic joint PPS-C, reduced interactions fiber/matrix are inferred in the outer layers of PPS-V and between metal mesh and the pure PPS films that coated it. In the interlaminar shear strength tests (ILSS), the specimens removed from the EPX-C joint in the pristine condition showed a uniform/homogeneous bonding along the joint area, while for PPS-C joint, coupons extracted from pristine condition joint indicated the occurrence of degradation caused by thermal effects localized in the welded edges.

Tese de doutoramento em Engenharia Mecânica, na especialidade de Controlo e Gestão, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
In the last few years, there has been a tendency in the way factories have evolved. Increasingly, manufacturing companies are changing and reinventing their production systems. The automation of some technological processes is today a major factor for the success of a manufacturing company. Owing to its flexibility, programmability and efficiency, industrial robots are a fundamental element of modern flexible manufacturing systems, promoting productivity when successfully implemented. In addition, automation can open the door of such processes to more companies, especially small and medium sized companies (SMEs). This thesis is dedicated to study methods that will conduct to the definition of a robotic platform for a relatively new joining process, friction stir welding (FSW). There is a lot of room for improvements concerning the robotization of the FSW process. In fact, this is an important topic due to the enormous advantages that a robot can bring to the FSW process when compared with conventional FSW machines. In this scenario, the advantages of robots over conventional FSW machines are multiple: flexibility, cost, faster setup and easier to programme. On the other hand, they present some relative disadvantages: the reduced stiffness of the robotic arm in the presence of the high forces involved into the process and the positional error associated to this kind of machine. The first axis of research focuses on the off-line definition of nominal robot trajectories with a high-level of abstraction from the robot specific language. This was achieved by directly interfacing with a common CAD package to extract nominal data. There follows a proposal for the discretization of the nominal robot trajectories in small sections. These small sections will then be on-line adjusted according to the inputs from sensory-feedback. Trajectory adjustments are required because the real robot operates in a dynamic environment involving contact between the FSW tool and the work pieces, a partially unknown environment (PUE). Thus, robotic systems must have autonomy to overcome this situation. It is proposed a method for robot self-recognition and self-adaptation through the analysis of the contact between the robot end-effector and its surrounding environment. The proposed force/motion control system has an external control loop based on forces and torques being exerted on the robot end-effector and an internal control loop based on robot motion. The external control loop is tested with a proportional integrative (PI) and a fuzzy-PI controller. Finally, connecting all the dots, it is defined a complete concept and design of a novel FSW robotic platform for welding polymeric materials. The platform is composed by three major groups of hardware: a robotic manipulator, a FSW tool and a system that links the manipulator wrist to the FSW tool (support of the FSW tool). Experimental tests proved the versatility and validity of the proposed solution. The produced welds on ABS plates were tested in order to study the influence of rotational speed, traverse speed and axial force on the quality of the welds. It is presented a comparison between welds produced in the robotic FSW system and in a dedicated FSW machine. Strength and strain properties of the welds are evaluated and correlated with the morphology of the welded zone. It was concluded that the welds produced in the robotic system present similar or better appearance and mechanical properties than the welds produced in the FSW machine.
Nos últimos anos tem-se verificado uma tendência na forma como as fábricas têm evoluído. Cada vez mais, as empresas de manufatura estão a mudar e reinventar os seus sistemas de produção. A automatização de alguns processos tecnológicos é hoje um fator muito importante para o sucesso de uma empresa de manufatura. Devido à sua flexibilidade e eficiência, os robôs industriais são hoje vistos por muitos como um elemento chave dos sistemas de manufatura modernos, promovendo a produtividade quando corretamente implementados. Estes aspetos podem facilitar a introdução de novos processos tecnológicos nas empresas, especialmente nas pequenas e médias empresas. Esta tese foca-se no estudo de metodologias que possam conduzir à definição de uma plataforma robótica para um processo tecnológico relativamente recente, a soldadura por fricção linear (SFL). Existe um enorme espaço para melhorias nos sistemas robóticos relativamente à sua aplicação no processo de SFL. De facto, este é um tópico bastante importante devido às vantagens que um robô pode trazer ao processo de SFL. Neste cenário, as vantagens dos robôs sobre as máquinas de SFL convencionais são diversas: flexibilidade, custo, instalação mais rápida e facilidade de programação. Por outro lado, os robôs apresentam algumas desvantagens: a baixa rigidez do manipulador quando sujeito a elevados esforços e o erro posicional associado aos robôs. O primeiro eixo de investigação foca-se na definição off-line das trajetórias nominais do robô de uma forma intuitiva para o utilizador, ou seja, com um elevado nível de abstração da linguagem do robô. Isto é conseguindo interagindo diretamente com um pacote de CAD comercial e extraindo dai os dados nominais necessários. Segue-se uma proposta para a discretização das trajetórias nominais em pequenas secções. Estas pequenas secções serão depois ajustadas on-line de acordo com os inputs recebidos do feedback sensorial. Os ajustamentos de trajetória são requeridos porque o robô irá operar num ambiente dinâmico que envolve contacto entre a ferramenta de SFL e as peças a soldar, um ambiente parcialmente desconhecido. Assim, o sistema robótico deverá apresentar autonomia para ultrapassar esta situação. É proposto um método para o auto reconhecimento e a auto adaptação do robô através da análise do contacto entre o robô e o ambiente envolvente. O método de controlo de força/movimento apresenta um ciclo de controlo externo baseado nas forças e momentos exercidos na ferramenta do robô e um anel de controlo interno baseado no movimento do robô. O anel externo é testado com um controlador proporcional integrativo (PI) e um fuzzy-PI. Finalmente, juntando o anterior referido, é definido o conceito de uma nova plataforma robótica para SFL de materiais poliémicos. A plataforma é composta por três grupos de hardware: um manipulador robótico, uma ferramenta de SFL e um sistema de suporte da ferramenta. Testes experimentais provaram a versatilidade e validade desta solução. As soldaduras realizadas foram testadas de modo a estudar a influência das velocidades rotacionais e transversais, e a força axial na qualidade das soldaduras levadas a cabo em placas de ABS. É apresentada a comparação entre as soldaduras produzidas pelo sistema robótico e as produzidas pela máquina convencional de SFL. As propriedades de tensão e deformação foram medidas, avaliadas e correlacionadas com a morfologia da zona soldada. Foi concluído que as soldaduras produzidas pelo sistema robótico apresentam aparência e propriedades mecânica similares ou melhores que as soldaduras produzidas pela máquina de SFL.
FCT - SFRD/BD/62485/2009

博士
國立清華大學
材料科學工程學系
95
Since the discovery of carbon nanotubes (CNTs) in 1991, there had been a huge number of investigations on its basic properties and applications. Superior properties have been found such as high electric and thermal conductivity, mechanical strength, low threshold voltage for field emission, among many others. Nowadays, CNT/polymer composite gains much attention due to its industrial development especially for flexible electronics. The general access to CNT/polymer composite has been studied such as melt-mixing, spinning, in-situ polymerization and adhesive. Among these, the unavoidable problem was that the poor adhesion between CNT/polymer or the thermal deformation of substrate. On the other hand, microwave is a kind of specific energy that could transfer energy directly to materials via molecular interactions. The unique characteristics of microwave heating such as remotely, quickly, volumetric and material-selective make it much suitable for solving the adhesion problem of CNT/polymer. In this study, we first successfully examined the microwave heating of multi-wall carbon nanotube (MWNT) while the maximum temperature could be higher than 900 oC and made clear the heating mechanism. By such characteristic, MWNT can be easily bonded onto polymer substrates under microwave irradiation within a few seconds which we developed and called it microwave welding process. It was shown that the MWNTs are good ‘solders’ of polymer parts with a strength two orders of magnitude higher than those bonded by adhesives. The other study was focused on the implication of microwave welding. The microwave welding is a new access to flexible electronic companying with the paste-printing technique. There is no more interlayer such epoxy necessary in MWNT/polymer composite and the MWNT welded on polymer’s surface could fully exhibit its superior properties such electron conduction, field-emission. The flexible device would exhibit better than traditional way due to the strong surface welding without crack or deformation within polymer substrates. Finally, for more rapidly, uniformly and selectively heating characteristics, microwave welding was demonstrated to be of great importance in flexible electronics, such as conductors, resistors and field emitters.

Laser transmission welding of polymers is a relatively new joining technique. It is based on the fact that the majority of thermoplastics are transparent to infrared radiation. A laser beam passes through the transparent part, and is then absorbed by a part rendered absorbent by additives such as carbon black. Absorbed laser energy is transformed into heat that melts the polymer at the interface between two parts, thus forming a weld. Many industrial applications have quite a complex geometry. This may often make it impossible to irradiate small elements of the joint interface directly. One of the possible solutions for this problem is to employ an oblique mirror to redirect a laser beam to the desired direction. In present work, transparent nylon tubes were welded to absorbing nylon plaques using a conical mirror inserted in the tube. The effects of the laser power, the angular motion speed, and the number of cycles on the joint shear strength were examined. Additionally, a two–dimensional axi-symmetric transient finite element heat transfer model was developed and evaluated. It simulated the temperature developed in the specimen during the welding cycle; the model was validated with the welding and mechanical testing results. The experimental results demonstrated good joint strength, confirming the feasibility of this technique. It was also found that welding at a lower laser beam power and a higher rotational speed allowed higher maximum weld strengths to be achieved at the expense of longer cycle time and higher energy consumption. Simulation of the temperature demonstrated that varying of the rotational speed at constant laser power does not change the overall temperature rise trend.
Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-08-14 23:12:18.491

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
O objetivo desta dissertação é estudar a influência dos parâmetros de Friction Stir Welding (FSW) na qualidade de soldaduras de topo em placas de Polietileno (PE) e Acrilonitrila Butadieno Estireno (ABS) com 6 mm de espessura. As soldaduras foram realizadas com uma ferramenta de base estacionária e pino cónico, sem aquecimento externo. Os parâmetros estudados foram a velocidade de rotação da ferramenta, com valores de 870, 1140 e 1500rpm, e a velocidade de soldadura, com 60 e 120mm/mim. Durante a soldadura foram registados os ciclos térmicos na vizinhança da soldadura. Depois de ser feita a inspeção visual, as soldaduras foram submetidas a microscopia ótica e a análise tomográfica, para caraterizar a morfologia das soldaduras, e a ensaios de microdureza, e a testes de tração, para caraterizar as propriedades mecânicas das soldaduras. Verificou-se que a morfologia das soldaduras, e em particular, a presença de defeitos, é muito influenciada pelo calor adicionado no processo. O aumento do rácio entre a velocidade de rotação e avanço da ferramenta (w/v) aumenta a temperatura na soldadura, principalmente nas soldaduras em ABS. O aumento de temperatura local facilita o fluxo de material e reduz a formação defeitos. O aumento do rácio w/v não alterou sensivelmente a dureza das soldaduras, mas aumentou a eficiência de soldadura. A resistência das soldaduras foi sempre inferior aos respetivos materiais de base, mas as soldaduras em PE apresentaram eficiência superior às realizadas em ABS. A eficiência de soldadura é muito condicionada pela presença de defeitos.
The aim of this dissertation is to study the influence of Friction stir Welding ( FSW ) parameters on the quality of butt welds in 6 mm thick Polyethylene ( PE ) and Acrylonitrile butadiene styrene ( ABS ) plates. The welds were carried out using a tool with a stationary shoulder and conical pin, without external heating. The parameters studied were the tool rotation speed, with values of 870, 1140 and 1500 rpm, and the welding speed, with 60 and 120 mm/min. During welding, thermal cycles in the vicinity of the weld were recorded. After visual inspection, the welds were submitted to optical microscopy and tomographic analysis, to characterize the morphology of the welds, and microhardness tests and tensile tests, to characterize the mechanical properties of the welds. It was found that the morphology of the welds, and in particular the presence of defects, is greatly influenced by the heat input in the process. Increasing the ratio between rotation speed and tool feed ( w/v ) increases the temperature in the weld, especially in ABS welds. On-site temperature rise facilitates material flow and reduces the formation of defects. Increasing the w/v ratio did not noticeably change the hardness of the welds, but it did increase the welding efficiency. The strength of the welds was always lower than the respective base materials, but the PE welds showed greater efficiency than those made in ABS. Welding efficiency is greatly affected by the presence of defects.

Thesis (M.S.)--University of Wisconsin--Madison, 2005.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 131a-134)

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
The work presented here corresponds to a bibliographic review on the union of polymeric materials by friction stir welding (FSW), with special focus on the analysis of the different parameters involved in this welding process.Due to the greater difficulty in obtaining strong joints with the conventional FSW method in polymeric materials, new tools and changes on the original process were developed, which were also presented and explained in this work.The main focus of this work was on the study of the influence of the different parameters on the quality of the welding, so that as much information as possible was gathered regarding the optimal values for each parameter and the way in which its variation affected the performance of the process.The studied parameters were the rotational speed, the welding speed, the axial force, the plunge depth, the tilt angle, the geometry and the size of the different components of the tool and also the heating and preheating temperatures of the tool and of the material.The comparison between the results obtained by the different researchers revealed that the optimal value for each parameter is dependent on too many factors and that, therefore, it is impossible to point to specific values. Based on the information collected in the literature on the joining of polymeric materials by FSW, the concentration of the optimum values was found for rotational speed between 300 and 3000 rpm, welding speed between 10 and 105 mm/min , axial force between 950 and 1500 N, plunge depth between 0.5 and 1.2 mm, tilt angle between 1º and 2º and heating temperature between 45 and 177ºC. It was also found that in most cases, the threaded pin tool led to better welds, as well as the use of stationary shoulder tools
O trabalho aqui apresentado corresponde a uma revisão bibliográfica sobre a união de materiais poliméricos recorrendo à soldadura por fricção linear (FSW), com especial foco na análise dos diferentes parâmetros envolvidos neste processo de soldadura.Pela maior dificuldade em obter ligações fortes com o método de FSW convencional em materiais poliméricos, foram desenvolvidas novas ferramentas e sugeridas alterações ao processo original, as quais também foram apresentadas e explicadas neste trabalho. O grande foco deste trabalho centrou-se no estudo da influência dos diferentes parâmetros na qualidade da soldadura, pelo que se tentou reunir o máximo de informação relativa aos valores ótimos para cada parâmetro e avaliar a forma de como a sua variação afetou o desempenho do processo. Os parâmetros estudados foram a velocidade de rotação, a velocidade de soldadura, a força axial, a profundidade de penetração, o ângulo de ataque, a geometria e o tamanho dos diferentes componentes da ferramenta e ainda a temperatura de aquecimento e pré-aquecimento da ferramenta e do material.A comparação entre os resultados obtidos pelos diferentes investigadores revelou que o valor ótimo para cada parâmetro está dependente de demasiados fatores e que por isso, é impossível apontar valores específicos. Com base na informação recolhida da literatura sobre a união de materiais poliméricos por FSW, verificou-se a concentração dos valores ótimos de velocidade de rotação entre 300 e 3000 rpm, de velocidades de soldadura entre 10 e 105 mm/min, de força axial entre 950 e 1500 N, de profundidades de penetração entre 0.5 e 1.2 mm, de ângulo de ataque entre 1º e 2º e de temperaturas de aquecimento entre 45 e 177ºC. Também se verificou que na maioria dos casos a ferramenta de pino roscado permitiu a obtenção de melhores soldaduras, assim como a utilização de bases estacionárias.

Laser Transmission Welding (LTW) involves localized heating at the interface of two pieces of plastic (a laser transparent plastic and laser absorbing plastic) to be joined. It produces strong, hermetically sealed welds with minimal thermal and mechanical stress, no particulates and very little flash. An ideal transparent polymer for LTW must have: a low laser absorbance to avoid energy loss, a low level of laser scattering so it can provide a maximum energy flux at the weld interface and also have a high resistance to thermal degradation. The objective of the project was to analyze the effect of blend ratios of polybutylene terephthalate and polyethylene terephthalate (PBT/PET) on these laser welding characteristics. The blends were manufactured by DSM (Netherlands). They were characterized using Differential Scanning Calorimetry (DSC) and Thermal Gravimetry Analysis (TGA). The latter technique was used to estimate the order (n), activation energy (ΔH) and frequency factor (A’) of the degradation reaction of the polymer blends. The normalized power profile of the laser after passing through the transparent polymer was measured using a novel non-contact technique and modeled using a semi-empirical model developed by Dr.Chen. Adding more PET ratio to the blend, did not change beam profile of the transmitted beam significantly. Laser welding experiments were conducted in which joints were made while varying laser power and scanning speed. Measuring the weld strength and width showed that the blends containing PET have higher strength in comparison to pure PBT. The temperature-time profile at the interface during welding was predicted using a commercial FEM code. This information was combined with the degradation rate data to estimate the relative amount of degraded material at the weld interface. It showed that increasing the ratio of PET in the blend makes it more resistant against thermal degradation which can be one of the reasons the PET containing blends reach higher weld strengths when compared to pure PBT.
Thesis (Master, Chemical Engineering) -- Queen's University, 2010-08-31 10:03:42.167

碩士
國立虎尾科技大學
機械與電腦輔助工程系碩士班
101
Ultrasonic plastic welding is a rapid and clean welding method that is characterized by short welding time, low energy consumption, and high welding strength. However, regarding research of welding quality control and the effect of the energy director on weldability, effective control methods have not been identified. In this study, two energy director geometries were designed and manufactured, employing ultrasonic frequency measurement devices to detect whether the horn achieves an appropriate amplitude. An experiment adopting an optic-fiber displacement sensor, thermal imager, and strain gauge was conducted to investigate the relationships among horn displacement, temperature, and the force received by the baseplate, to optimize the design of the energy director and improve welding quality. The results show that the range of output amplitude, horn oscillation heat, and strain data are connected and mutually influential. An optical microscope and ultrasonic tightness test were subsequently conducted to test the final welding quality. Three key factors were used in the welding quality control, enhancing the quality and improving numerous derived variables of plastic welding. This process also simplifies the solution of ultrasonic plastic welding problems in the industry.

Ceramic metal matrix composites (CMMCs) are materials generally created by mixing of hard ceramic particles in a metal matrix. They were expected to combine the ductility and toughness of the metal with the high strength and elastic modulus of the ceramic. MMCs have potential applications in automotive, aeronautical and aerospace industries. Hence, a simple and economical method for fabricating MMCs is an area of intense research. In MMCs, damage evolution starts preferentially at particle matrix interface or at particle clusters in the matrix. This is due to the different physical and mechanical properties of the particle and matrix. Higher local particle volume content leads to higher stress triaxiality making it a preferential site for damage nucleation. Problems with lowering of ductility, fatigue, fracture and impact resistance, agglomeration of ceramic phase and issues related to the predictability of properties of MMCs have been the major issues that have limited their use. In order to overcome some of these shortcomings, the use of nano particles has been attracting increasing attention. The reason is their capability in improving the mechanical and physical properties of traditional MMCs. The dispersion of a nanoscale ceramic phase is needed in order to overcome the problems related to fatigue, fracture toughness, and creep behaviour at high temperatures. However, manufacturing costs, preparation of nano composites and environmental concerns have to be addressed. Agglomeration of nano particles, when produced by the melt stir casting route, the primary route to produce MMCs, is a serious issue that limits the use of nano-particles to produce MMCs with good properties. To avoid agglomeration of the ceramic phase MMCs/nano MMCs have been produced through the powder metallurgy route. Agglomeration is avoided as this is a solid state process. Secondary processing, such as extrusion and rolling are often needed to fully consolidate materials produced in this manner. A high extrusion ratio is often required to get MMCs without porosity. A new method of making nano-ceramic MMC using a polymer derived ceramics (PDC) has been reported. A polymer derived ceramic is a material that converts itself into a ceramic when heated above a particular temperature. In the PDC method a polymer precursor is dispersed in the metal and then converted in-situ to a ceramic phase. A feature of this process is that all the constituents of the ceramic phase are built into the organic molecules of the precursor (e.g., polysilazanes contain silicon, carbon, and nitrogen); therefore, a reaction between the polymer and the host metal or air is not required to produce the ceramic phase. The polymer can be introduced through casting or powder metallurgy route. In the casting route, the polymer powder is directly added to molten metal and pyrolyzed in-situ to create castings of metal-matrix composites. These composites have shown better properties at elevated temperatures but the problem of agglomeration of particles due to Van der Waal's forces and porosity still remains. In the powder method, the organic precursor was milled with copper powder and then plasma sprayed to produce a metal matrix composite. It is reported that these composites retains its mechanical strength close to the melting point of the copper. However, getting a nano sized distribution is difficult through this route as the plasma spray route is a melting and solidification method. Solid state processing by powder metallurgy is possibly a better method to produce well dispersed nano-MMCs. However, powder metallurgy routes are much more expensive and only parts of limited sizes can be produced by this method. Another solid state process Friction Stir Processing (FSP) has successfully evolved as an alternative technique to fabricating metal matrix composites. FSP is based on the principles of Friction Stir Welding (FSW). In FSW, a rotating tool with a pin and a shoulder is inserted into the material to be joined, and traversed along the line of the joint. The friction between the tool and the work piece result in localized heating that softens and plasticizes the material. During production of MMCs using FSP method, the material undergoes intense plastic deformation resulting in mixing of ceramic particles and the metal. FSP also results in significant grain refinement of the metal and has also been used to homogenize the microstructure. FSP technology has also been used to fabricate surface/bulk composites of Al-SiC, friction stir surfacing of cast aluminum silicon alloy with boron carbide and molybdenum disulphide powders and to produce ultra-fine grained Cu-SiC composites. A major problem in the FSP of MMCs is severe tool wear that results from abrasion with hard ceramic particles. The progressive wear of the tool has been reported to increase the likelihood of void or defect development. This change in geometry has been reported in the friction stir welding of several MMCs. The problems concerning the tool life has become a serious issue in the application of FSP for producing MMCs. In the present work the advantages of the PDC method and FSP have been combined to produce polymer derived nano ceramic MMCs. This method mainly consists of three steps. In the first step, a polymer, which pyrolysis to form a PDC at temperatures lower than the melting point of the metal, is dispersed in the metal by FSP. This step is different from the melt route where the PDC forms at temperatures above the melting point of the metal. In the second step, external pyrolysis of the polymer dispersed material is carried out. Since this is a solid state process at stresses much higher than the shear or fracture of the polymer is expected to get evenly and finely distribution in the metal. This is done by heating the polymer dispersed material to a temperature above the pyrolysation temperature of the ceramic but lower than the melting point of the metal matrix. It should be mentioned that some pyrolysis of the polymer is possible during the FSP process itself. In the third step FSP is carried out on the pyrolised material for removing porosity that would form due to gas evolution during pyrolysis and to get a more uniform dispersion of polymer derived ceramic particles in the matrix. This method will produce nano-scale metal matrix composites with a relatively high volume fraction of the ceramic phase. This method can be extended to big sheets or a particular region in a sheet with no or low wear of tools. The material selected for the present study were pure Copper (99.9%) and Nickel Aluminum Bronze (NAB) copper alloy. The polymer precursor was poly (urea methyl vinyl) silazane, which is available commercially as CERASET. The polymer consists of silicon, carbon, nitrogen, oxygen and hydrogen atoms. The liquid precursor was thermally cross-linked into a rigid polymer, which was milled into a powder. This powder, having angular shaped particles of an average size of 10 µm, was used as the reinforcement. The polysilazanes convert into a highly refractory and amorphous ceramic upon pyrolysis and is known as polymer-derived silicon carbonitride which consists principally of silicon, carbon and nitrogen. The in-situ process is feasible because copper melts above the temperature at which the organic phase begins to pyrolise. The polysilazanes pyrolise in the temperature range of 973 to 1273 K, which lie below the melting temperature of copper, 1356K.The precursor has a density of approximately 1 gcm-3 in the organic phase and approximately 2 gcm-3 in the ceramic state. In the present work, we seek to introduce approximately 20 vol% of the ceramic phase into copper. The microstructure and mechanical properties of the developed copper-based in-situ polymer derived nano MMCs have been characterized in detail to understand the distribution of particles. The microstructure of the as received, processed as well as the FSP composite material was characterized using Optical Microscope (OM), Scanning Electron Microscope (SEM), Electron Probe Micro Analyzer (EPMA) and Transmission Electron Microscope (TEM). OM and SEM microstructural observations show that PDC particles are distributed uniformly with a bimodal (submicron+micron) distribution. In addition, TEM micrographs reveal the formation of very fine PDC particles of diameter 10-30 nm. X-ray diffraction and Thermo-gravimetric analysis confirms the presence of ceramic phase (Si3N4/SiC) in the matrix. Significant improvement in mechanical properties of the FSP PD-MMCs has been observed. This in-situ formed Cu/PDC composites show five times increase in micro-hardness (260Hv - 2.5GPa) compared to processed copper base metal and in-situ NAB/PDC composite shows two times increase in micro-hardness (325Hv- 3.2GPa) compared to NAB matrix. The Cu-PDC composites exhibited better tensile strength at room temperature. In-situ formed Cu-PDC composite’s yield strength increased from 110MPa to 235MPa as compared to processed base metal, where as ultimate tensile strength increases from 246MPa to 312MPa compared to processed base metal at room temperature. This strengthening could be attributed to the presence of in-situ formed hard phases and the concomitant changes in the microstructure of the matrix material such as reduction in grain size and contribution from Orowan strengthening. In the present work, we have observed tool wear by observing tool after each FSP pass and apart from producing a significantly harder material with higher elastic modulus, possibly for the first time, the issue of tool wear has been overcome. This is due to the fact that the composite is made by the polymer route and that the ceramic fractures easily till it reaches the nano-size. Wear studies of this composite was carried out in a pin-on-disc machine by sliding a pin made from the composite against an alumina disc. The wear rate of the FSP PD-MMC composites increased from 1.63×10-5 to 5.72×10-6 mm3/Nm. Improved wear resistance could be attributed to the presence of the in-situ formed hard nano-phase.

Ceramic metal matrix composites (CMMCs) are materials generally created by mixing of hard ceramic particles in a metal matrix. They were expected to combine the ductility and toughness of the metal with the high strength and elastic modulus of the ceramic. MMCs have potential applications in automotive, aeronautical and aerospace industries. Hence, a simple and economical method for fabricating MMCs is an area of intense research. In MMCs, damage evolution starts preferentially at particle matrix interface or at particle clusters in the matrix. This is due to the different physical and mechanical properties of the particle and matrix. Higher local particle volume content leads to higher stress triaxiality making it a preferential site for damage nucleation. Problems with lowering of ductility, fatigue, fracture and impact resistance, agglomeration of ceramic phase and issues related to the predictability of properties of MMCs have been the major issues that have limited their use. In order to overcome some of these shortcomings, the use of nano particles has been attracting increasing attention. The reason is their capability in improving the mechanical and physical properties of traditional MMCs. The dispersion of a nanoscale ceramic phase is needed in order to overcome the problems related to fatigue, fracture toughness, and creep behaviour at high temperatures. However, manufacturing costs, preparation of nano composites and environmental concerns have to be addressed. Agglomeration of nano particles, when produced by the melt stir casting route, the primary route to produce MMCs, is a serious issue that limits the use of nano-particles to produce MMCs with good properties. To avoid agglomeration of the ceramic phase MMCs/nano MMCs have been produced through the powder metallurgy route. Agglomeration is avoided as this is a solid state process. Secondary processing, such as extrusion and rolling are often needed to fully consolidate materials produced in this manner. A high extrusion ratio is often required to get MMCs without porosity. A new method of making nano-ceramic MMC using a polymer derived ceramics (PDC) has been reported. A polymer derived ceramic is a material that converts itself into a ceramic when heated above a particular temperature. In the PDC method a polymer precursor is dispersed in the metal and then converted in-situ to a ceramic phase. A feature of this process is that all the constituents of the ceramic phase are built into the organic molecules of the precursor (e.g., polysilazanes contain silicon, carbon, and nitrogen); therefore, a reaction between the polymer and the host metal or air is not required to produce the ceramic phase. The polymer can be introduced through casting or powder metallurgy route. In the casting route, the polymer powder is directly added to molten metal and pyrolyzed in-situ to create castings of metal-matrix composites. These composites have shown better properties at elevated temperatures but the problem of agglomeration of particles due to Van der Waal's forces and porosity still remains. In the powder method, the organic precursor was milled with copper powder and then plasma sprayed to produce a metal matrix composite. It is reported that these composites retains its mechanical strength close to the melting point of the copper. However, getting a nano sized distribution is difficult through this route as the plasma spray route is a melting and solidification method. Solid state processing by powder metallurgy is possibly a better method to produce well dispersed nano-MMCs. However, powder metallurgy routes are much more expensive and only parts of limited sizes can be produced by this method. Another solid state process Friction Stir Processing (FSP) has successfully evolved as an alternative technique to fabricating metal matrix composites. FSP is based on the principles of Friction Stir Welding (FSW). In FSW, a rotating tool with a pin and a shoulder is inserted into the material to be joined, and traversed along the line of the joint. The friction between the tool and the work piece result in localized heating that softens and plasticizes the material. During production of MMCs using FSP method, the material undergoes intense plastic deformation resulting in mixing of ceramic particles and the metal. FSP also results in significant grain refinement of the metal and has also been used to homogenize the microstructure. FSP technology has also been used to fabricate surface/bulk composites of Al-SiC, friction stir surfacing of cast aluminum silicon alloy with boron carbide and molybdenum disulphide powders and to produce ultra-fine grained Cu-SiC composites. A major problem in the FSP of MMCs is severe tool wear that results from abrasion with hard ceramic particles. The progressive wear of the tool has been reported to increase the likelihood of void or defect development. This change in geometry has been reported in the friction stir welding of several MMCs. The problems concerning the tool life has become a serious issue in the application of FSP for producing MMCs. In the present work the advantages of the PDC method and FSP have been combined to produce polymer derived nano ceramic MMCs. This method mainly consists of three steps. In the first step, a polymer, which pyrolysis to form a PDC at temperatures lower than the melting point of the metal, is dispersed in the metal by FSP. This step is different from the melt route where the PDC forms at temperatures above the melting point of the metal. In the second step, external pyrolysis of the polymer dispersed material is carried out. Since this is a solid state process at stresses much higher than the shear or fracture of the polymer is expected to get evenly and finely distribution in the metal. This is done by heating the polymer dispersed material to a temperature above the pyrolysation temperature of the ceramic but lower than the melting point of the metal matrix. It should be mentioned that some pyrolysis of the polymer is possible during the FSP process itself. In the third step FSP is carried out on the pyrolised material for removing porosity that would form due to gas evolution during pyrolysis and to get a more uniform dispersion of polymer derived ceramic particles in the matrix. This method will produce nano-scale metal matrix composites with a relatively high volume fraction of the ceramic phase. This method can be extended to big sheets or a particular region in a sheet with no or low wear of tools. The material selected for the present study were pure Copper (99.9%) and Nickel Aluminum Bronze (NAB) copper alloy. The polymer precursor was poly (urea methyl vinyl) silazane, which is available commercially as CERASET. The polymer consists of silicon, carbon, nitrogen, oxygen and hydrogen atoms. The liquid precursor was thermally cross-linked into a rigid polymer, which was milled into a powder. This powder, having angular shaped particles of an average size of 10 µm, was used as the reinforcement. The polysilazanes convert into a highly refractory and amorphous ceramic upon pyrolysis and is known as polymer-derived silicon carbonitride which consists principally of silicon, carbon and nitrogen. The in-situ process is feasible because copper melts above the temperature at which the organic phase begins to pyrolise. The polysilazanes pyrolise in the temperature range of 973 to 1273 K, which lie below the melting temperature of copper, 1356K.The precursor has a density of approximately 1 gcm-3 in the organic phase and approximately 2 gcm-3 in the ceramic state. In the present work, we seek to introduce approximately 20 vol% of the ceramic phase into copper. The microstructure and mechanical properties of the developed copper-based in-situ polymer derived nano MMCs have been characterized in detail to understand the distribution of particles. The microstructure of the as received, processed as well as the FSP composite material was characterized using Optical Microscope (OM), Scanning Electron Microscope (SEM), Electron Probe Micro Analyzer (EPMA) and Transmission Electron Microscope (TEM). OM and SEM microstructural observations show that PDC particles are distributed uniformly with a bimodal (submicron+micron) distribution. In addition, TEM micrographs reveal the formation of very fine PDC particles of diameter 10-30 nm. X-ray diffraction and Thermo-gravimetric analysis confirms the presence of ceramic phase (Si3N4/SiC) in the matrix. Significant improvement in mechanical properties of the FSP PD-MMCs has been observed. This in-situ formed Cu/PDC composites show five times increase in micro-hardness (260Hv - 2.5GPa) compared to processed copper base metal and in-situ NAB/PDC composite shows two times increase in micro-hardness (325Hv- 3.2GPa) compared to NAB matrix. The Cu-PDC composites exhibited better tensile strength at room temperature. In-situ formed Cu-PDC composite’s yield strength increased from 110MPa to 235MPa as compared to processed base metal, where as ultimate tensile strength increases from 246MPa to 312MPa compared to processed base metal at room temperature. This strengthening could be attributed to the presence of in-situ formed hard phases and the concomitant changes in the microstructure of the matrix material such as reduction in grain size and contribution from Orowan strengthening. In the present work, we have observed tool wear by observing tool after each FSP pass and apart from producing a significantly harder material with higher elastic modulus, possibly for the first time, the issue of tool wear has been overcome. This is due to the fact that the composite is made by the polymer route and that the ceramic fractures easily till it reaches the nano-size. Wear studies of this composite was carried out in a pin-on-disc machine by sliding a pin made from the composite against an alumina disc. The wear rate of the FSP PD-MMC composites increased from 1.63×10-5 to 5.72×10-6 mm3/Nm. Improved wear resistance could be attributed to the presence of the in-situ formed hard nano-phase.