Conselho Nacional de Desenvolvimento Científico e Tecnológico / The use of active flux in TIG process can be an alternative to increase the productivity since this technique increases the depth of penetration of weld bead maintaining the same parameters of conventional TIG welding. The results obtained indicate that the use of the traditional way of flux application tend to produce slag, which is hard to remove. In order to avoid this problem, are approach is by applying two flux strips alongside the joint, separated by a predetermined distance, defined as parameter \"a\". This technique is called Contraction Controlled Technique (CCT). The result with this methodology was satisfactory, allowing increasing the depth of penetration and ensuring a good weld bead surface finish. The objective of this research is to verify and analyze the influence of the use of Contraction Controlled Technique with the A-TIG process in the welding of ferritic stainless steel. It also aims to identify and quantify the main phenomena involved such as increase of the penetration, the changes in the arc, and changes in mechanical and metallurgical properties of the ferritic steel. For this purpose, it were done welding of ferritic stainless steels surfaces using the Contraction Controlled Technique, varying the width of the parameter \"a\", the distance between the piece and the electrode, the electrical current and welding speed. It was observed that the geometry of the weld beads has suffered modifications such as reduction in width and increased of the penetration of the weld beads for all cases where the active flux was used. The use of the active flux in TIG welding process is a technique that allows the increased of penetration depth of weld maintain keeping the same parameters used in the conventional TIG. However, it was not possible to increase the speed of the welding within the parameters used. When it was employed the technique of controlled contraction in a disalignment joint, the data showed that it is possible to improve results of arc direction, direct it to the edge of the board, using active flux and modifing both the parameter \"a\" and the deviation of the torch (dt). The application of this technique did not cause changes in the toughness or in the microstructure of the fusion zone the ferritic stainless steel. / O uso de fluxo ativo no processo de soldagem TIG pode ser uma alternativa para aumentar a velocidade de soldagem do processo, pois esta técnica permite o aumento da profundidade de penetração do cordão de solda mantendo os mesmo parâmetros empregados no TIG convencional. A principal desvantagem desta técnica reside principalmente na propensão à formação de uma camada oxidada sobre o cordão de solda o que pode também acarretar num acabamento superficial ruim. Uma forma de tirar proveito desta técnica garantindo um bom acabamento do cordão é aplicar o fluxo de tal maneira que, ao invés de uma camada que cubra toda a superfície da chapa, sejam feitas duas faixas de fluxo, separadas por uma distância predeterminada, definida como parâmetro a . Esta técnica é chamada neste trabalho de Técnica da Constrição Controlada (TCC). Desta forma, a camada de fluxo isola eletricamente certas regiões da superfície da peça direcionando a região de incidência do arco e, como a diluição do fluxo na poça de solda é menor, alia-se a vantagem do aumento de penetração com o bom acabamento do cordão de solda. O objetivo desta pesquisa é verificar e analisar a influência do uso da Técnica da Constrição Controlada com o processo A-TIG na soldagem do aço inoxidável ferrítico; identificar e quantificar os principais fenômenos envolvidos como, aumento da penetração, alterações no arco voltaico e as possíveis modificações nas propriedades mecânicas e metalúrgicas do aço ferrítico. Para isso, realizou-se a soldagem do aço inoxidável ferrítico empregando a técnica da constrição controlada variando-se a largura do parâmetro a , a distância eletrodo-peça, a corrente de soldagem e a velocidade de soldagem. Foi possível observar que a geometria do cordão de solda sofre modificações como redução na largura e aumento da penetração do cordão de solda para todos os casos em que se empregou o fluxo ativo. Porém, não foi possível um aumento da velocidade de soldagem com os parâmetros empregados. Quando empregada a Técnica da Constrição Controlada em uma junta desalinhada, os dados comprovaram que é possível conseguir resultados de desvios satisfatórios no arco, ou seja, direcioná-lo para a borda da junta, com a utilização de fluxo ativo e a modificação tanto do parâmetro a quanto do desalinhamento na tocha (dt). A aplicação desta técnica não provocou alterações nem na tenacidade nem na microestrutura da zona fundida. / Doutor em Engenharia Mecânica

A microestrutura e a composição química dos aços inoxidáveis duplex são responsáveis pela sua resistência mecânica e sua resistência à corrosão que, geralmente, é superior aos aços inoxidáveis ferríticos e austeníticos convencionais. A soldagem destes materiais causa tanto alteração de microestrutura como de composição química, que podem ser alteradas dependendo dos processos de soldagem, dos parâmetros de soldagem, da utilização ou não de metal de adição e da composição química do gás de proteção, nos processos que utilizam proteção gasosa. No caso dos aços inoxidáveis duplex baixa liga, a solidificação é completamente ferrítica, podendo produzir tamanho de grão exagerado no metal de solda e na ZAC. O objetivo deste trabalho é de avaliar o efeito da freqüência de pulsação do processo TIG autógeno na soldagem de aços inoxidáveis duplex baixa liga. Foram soldadas chapas de aços inoxidáveis duplex baixa liga UNS S32304 e UNS S32101 (lean duplex), sem metal de adição e empregando-se argônio como gás de proteção. A soldagem foi executada com o processo TIG, mantendo-se a energia de soldagem constante, de 340 J/mm, e variando-se a freqüência de pulsação entre 1, 5, 10 e 20 Hz. As microestruturas resultantes tanto no metal de solda, região central e região sem mistura, bem como na zona afetada pelo calor foram caracterizadas através de microscopia ótica. Os resultados mostraram que, na soldagem autógena, independente de ter ou não a pulsação da corrente, ocorre um aumento no tamanho do grão da zona fundida devido a solidificação ferrítica deste aço. Comparando-se os resultados do tamanho do grão e da fração volumétrica de ferrita no metal de solda, notouse um aumento no tamanho de grão e na fração volumétrica da ferrita com o aumento da freqüência de pulsação. / The microstructure and chemical composition of duplex stainless steel are responsible for their mechanical strength and corrosion resistance. The welding of these materials produces a change in the microstructure and chemical composition. These changes depend on: welding processes, welding parameters, the use or absence of filler metal and composition of shielding gas in processes that use shielding gas. In the case of lean duplex stainless steel the solidification is fully ferritic, which may produce an excessive grain size in the weld metal and in the heat affected zone (HAZ). The main goal of this paper is to evaluate the effect of pulse frequency in autogenous TIG welding process of lean duplex stainless steel. In this sense, plates of UNS S32304 and UNS S32101 lean duplex were welded without filler metal and using argon as shielding gas. The welds were made using the GTAW process, keeping the heat input constant at 340 J/mm and varying the pulse frequency between 1,5,10 and 20 Hz. The results showed that, independent of pulse frequency, grain growth in the fusion zone took place since this duplex stainless steel type has a ferritic solidification mode. Comparing the grain size and ferrite volumetric fraction in the weld bead, an increase in the mean value of grain size in the central region and unmixed region of weld beads was related to an increase of pulse frequency.

This master's thesis deals with the selection and evaluation of the appropriate welding technology for stainless steel and titanium alloys. Describes advantages and disadvantages of selected technologies. The experiment compares the mechanical properties, the heat input and the resulting surface structure of the welded samples. In conclusion, the thesis deals with the technical - economic evaluation of selected welding technologies.

Theoretical part of this thesis includes overview of laser welding technology and possible combinations with arc welding methods for meeting desired properties of the weld. It also explains mechanical testing and metallographic examination on welds. The experimental part deals with optimisation of process parameters during welding of martensitic stainless steel, used in energetic industry using hybrid laser - TIG technology in regard of mechanical properties of the weld, its structure and proposal of technological parameters.

The project aimed at the selection of the optimal welding method for a „fuel cell“ component in terms of the VN-Ú Ltd engineering company. The goal is to compare the methods available in VN-Ú, that is: TIG, MIG/MAG and CMT. It is necessary to analyze the specifics of each of the technologies and the operation conditions which the component will be exposed to. For the comparison of the methods, non-destructive testing of the components, as well as destructive tests of the produced samples have been used. The economic evaluation has been used to compare the costs of different welding methods of the components and to assess the potential investments in CMT device that has only been leased by VN-U so far.

Master's thesis deals with consideration possibility of conventional and unconvetional welding methods of wrought magnesium alloys. Methods of Friction Stir Welding, Pulsed Nd:YAG laser and Continuous Fiber laser was used to join magnesium alloy sheets AZ31, AZ61, ZE10 and ZE41. For studying influence of processing parameters on microstructure and mechanical properties were used methods of light microscopy, scanning electron microscopy, tensile tests and microhardness measurements. The results of tensile tests show that from the point of view of keeping ultimate tensile strength is the best methods for welding magnesium alloys Friction Stir Welding. Compared with Nd:YAG laser, fiber laser give better properties of welds. From comparing microstructure and mechanical properties . It wasn't found publications about Friction Stir Welding of magnesium ZE alloys or about FSW sheets with thickness only 0,8 mm and 1,6 mm.

In this thesis, new methods for shear strength are proposed and backed up through extensive experimentation, ABAQUS models and data analysis of Titanium welds of three different alloys. The results are compared with those obtained by using the procedure outlined by AWS B4 for calculating Shear Strength in the transverse and longitudinal directions; this equation is widely used by the American Welding Society (AWS) and all those in search of more efficient designs involving welding. It is a well-documented issue that the equation provided by AWS yields a large discrepancy between the values for shear strength of longitudinal and transverse welds.

Tungsten Inert Gas (TIG) welding is extensively used in aerospace applications, due to its unique ability to produce higher quality welds compared to other shielded arc welding types. However, most TIG welding is performed manually and has not achieved the levels of automation that other welding techniques have. This is mostly attributed to the lack of process knowledge and adaptability to complexities, such as mismatches due to part fit-up. Recent advances in automation have enabled the use of industrial robots for complex tasks that require intelligent decision making, predominantly through sensors. Applications such as TIG welding of aerospace components require tight tolerances and need intelligent decision making capability to accommodate any unexpected variation and to carry out welding of complex geometries. Such decision making procedures must be based on the feedback about the weld profile geometry. In this thesis, a real-time position based closed loop system was developed with a six axis industrial robot (KUKA KR 16) and a laser triangulation based sensor (Micro-Epsilon Scan control 2900-25).

En raison de sa stabilité microstructurale l'acier martensitique 'X10CrMoVNb9-1' est considéré comme un des candidats pour plusieurs futurs composants des réacteurs à hautes températures 'Very High Temperature Reactor' (VHTR). Ces épais composants (200 mm) sont assemblés par soudage TIG multi-passe. Ce procédé de soudage génère des cycles thermiques et thermomécaniques complexes au niveau de la Zone Affectée Thermiquement (ZAT). Cette thèse est la suite de celle de G.-M. Roux. Ce travail de six ans a pour but de prédire l'état microstructural après soudage dans la ZAT. G.-M. Roux a déjà développé une première version d'un modèle Thermo-Métallurgico-Mécanique (TMM) et a été validée en termes de contraintes résiduelles sur des essais de soudage simples mono-passe. Dans cette thèse une nouvelle version du modèle TMM est proposée, permettant d'améliorer les prévisions en termes de l'état microstructural post soudage dans la ZAT, et les contraintes résiduelles engendrées par l'opération de soudage.Cette thèse s¿appuie sur une approche de modélisation fine des transformations de phases, à savoir la modélisation de la transformation matériau de base - austénite lors d'un chargement anisotherme complexe, la modélisation de la transformation austénite - martensite et finalement la modélisation du revenu de la martensite. Sans oublier la caractérisation du comportement mécanique de chaque phase et l'étude du comportement multi-phasique. La simulation numérique avec le code éléments finis Cast3M de plusieurs procédés de soudage permet de comparer les modèles aux résultats expérimentaux. / Due to its microstructural stability, the martensitic steel 'X10CrMoVNb9-1 is considered a candidate for several future high temperatures reactor components. These thick components (200 mm) are assembled by GTA multi-pass welding. This welding process generates complex thermal and thermomechanical cycles in the Heat Affected Zone (HAZ). This thesis is following that of G.-M. Roux. This work of 6 years aims to predict the microstructural state after welding in the HAZ. A first version of a Thermo-Metallurgical-Mechanical model (TMM) has been developed and validated in terms of residual stresses on single-pass welding simple tests. In this thesis a new version of the TMM model is proposed to improve the forecasts in terms of the microstructural state and residual stresses post welding in the HAZ. The main improvements of this model TMM its capabilities to take into account the successive heating and cooling cycles, characterizing the multi-pass welding process. This thesis is based on a detailed modeling approach for phase transformations, namely modeling the transformation base material - austenite during anisothermal complex loadings, modeling transformation austenite - martensite and finally the martensite tempering modeling. Not to mention the characterization of the mechanical behavior of each phase and the study of multiphase behavior. Numerical simulation with the finite element code Cast3M of several welding processes was used to compare models with experimental results.

Im Anlagenbau und der Energietechnik werden Rohrleitunen vornehmlich aus nichtrostenden Stählen hergestellt Hierbei hat sich das WIG-Orbitalschweißen als standardmäßiges Fügeverfahren etabliert. Es bietet hohe erreichbare Gütewerte der Fügestelle und eine gute Reproduzierbarkeit der Schweißergebnisse. Aufgrund der positiven Eigenschaften von Kupfer, besteht in einigen Anwendungsbereichen ein gesteigertes Interesse an der Substitution von Rohren aus nichtrostendem Stahl durch Kupferleitungen. Gegenwärtig werden dünnwandige Kupferrohre meist durch Pressfittings, Klemm- sowie Schneidringverschraubungen oder Löten gefügt. Wegen der hohen erreichbaren Gütewerte der Fügeverbindung, ist eine Anwendung des WIG-Orbitalschweißverfahrens auch für Kupferrohre wünschenswert. Ziel dieser Arbeit ist die Bewertung der Schweißversuche zur Etablierung des WIG-Orbitalschweißverfahrens für dünnwandige Kupferrohre. Dazu werden zunächst grundlegende Aussagen über den Rohrleitungswerkstoff Kupfer und das WIG-Orbitalschweißverfahren zusammengetragen. Anschließend werden der Aufbau und die Durchführung der Experimente beschrieben sowie eine Auswertung der Versuchsergebnisse vorgenommen. Die Prüfung der Schweißergebnisse erfolgt durch zerstörungsfreie und zerstörende Prüfverfahren. Soweit vorhanden, wird sich dabei an gebräuchlichen Normenwerken orientiert. Als Ergebnis der Versuche zeigt sich, dass eine sichere Durchschweißung mit einer guten Wurzelausbildung realisierbar ist. Jedoch sind die Schweißnähte sowohl innerlich, wie auch oberflächlich, anfällig für Hohlraumbildung. Innerlich ist eine gleichmäßige Verteilung von Poren, über den gesamten Rohrquerschnitt, zu beobachten. Oberflächlich konzentrieren sich die Unregelmäßigkeiten hauptsächlich auf das oberste Viertel der Schweißnaht, welches in der Rohrposition für Fallendschweißen gefügt wurde. Trotz der detektierten Unregelmäßigkeiten stellt das WIG-Orbitalschweißen ein vielversprechendes Fügeverfahren zum Verbinden dünnwandiger Kupferrohre dar. Bereits denkbare Anwendungen wären Rohre im Niederdruckbereich, welche permanent vom selben Medium durchströmt werden sowie Abgas- und Abwasserleitungen. Aus Korrosionsschutz- und Sicherheitsgründen wird jedoch von einer Durchströmung der Leitungen mit sauren oder toxischen Fluiden abgeraten.