Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Young Shin, Ilbae Ham. Includes bibliographical references (p. 63). Also available online.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / O objetivo deste trabalho foi realizar um estudo sistemÃtico de parÃmetros de soldagem TIG com alimentaÃÃo de arame frio para aplicaÃÃo de revestimento de ligas de nÃquel (UNS N06625, UNS N06686 e UNS N10276) em substratos de aÃo C-Mn considerando a anÃlise das caracterÃsticas geomÃtricas, econÃmicas e operacionais dos depÃsitos, de forma a adequar estes revestimentos para as indÃstrias do Setor de PetrÃleo e GÃs Natural. As soldagens foram realizadas utilizando um robà industrial e um alimentador automÃtico de arame frio. Foi realizado um estudo preliminar para determinar as condiÃÃes iniciais para exploraÃÃo dos parÃmetros, em seguida realizado a soldagem de um fatorial completo. Em uma Ãltima exploraÃÃo dos parÃmetros de soldagem foi aplicado o MÃtodo Taguchi para realizar a anÃlise de diversos fatores de controle com um nÃmero reduzido de experimentos. O perfil geomÃtrico do cordÃo de solda foi levantado na seÃÃo transversal dos corpos de prova. ApÃs obtenÃÃo dos resultados, foram feitos alguns ajustes de modo a realizar soldagens dos revestimentos. Os resultados mostraram que, o correto ajuste da DistÃncia da Ponta do Arame a PeÃa (DPAP) influenciou na geometria e diluiÃÃo do cordÃo de solda e na estabilidade do arco. Foi visto tambÃm que para obter menores nÃveis de diluiÃÃo, a DistÃncia da Ponta do Eletrodo a PeÃa (DPEP) depende do nÃvel de energia utilizado, para menores energias utiliza-se menores DPEPs e, para maiores energias, maiores DPEPs devem ser utilizadas. Os nÃveis de diluiÃÃo e reforÃo foram reduzidos com o uso do tecimento. A tÃcnica da energia influenciou de forma significativa na geometria e diluiÃÃo do cordÃo de solda. Para uma mesma energia de soldagem e, consequentemente velocidade de resfriamento e aporte tÃrmico semelhantes, podem haver nÃveis distintos de diluiÃÃo sem alteraÃÃes metalÃrgicas. O gÃs de proteÃÃo influenciou na diluiÃÃo e no Ãndice de convexidade (R/L) do cordÃo de solda, de uma maneira geral, a mistura de argÃnio e Ãxido nitroso apresentou a melhor condiÃÃo para soldagem dos revestimentos. O ajuste da energia pela corrente de soldagem (Tipo I) apresentou melhor eficiÃncia de deposiÃÃo para baixa energia, jà para alta energia, o melhor ajuste se dà pela velocidade de soldagem (Tipo V). Para baixos nÃveis de diluiÃÃo, o uso do tecimento reduz de maneira significativa os tempos e custos associados a realizaÃÃo dos revestimentos. Com os resultados obtidos foi possÃvel realizar revestimentos de qualidade com baixos nÃveis de diluiÃÃo (<10 %) atravÃs do processo TIG com alimentaÃÃo de arame frio. / The aim of this work was to carry out a systematic study of GTAW welding parameters with feeding of cold wire for covering application of nickel alloys (UNS N06625, UNS N06686 and UNS N10276) in substract of steel C-Mn considering the analysis of geometric, economic and operational characteristics of layers, form to adjust these coverings for the industries of the Sector of Oil and Natural Gas. The weldings were carried out employing an industrial robot and an automatic feeder of cold covered. A preliminary study was carried out to determine the initial conditions to exploration of the parameters, after that it was carried through the welding of a complete factorial. In a last exploration of welding parameters was applied the Taguchi Method to carry out to the analysis of diverse factories of control with a reduced number of experiments. The geometric profile of weld filet was raised in the transversal section of the test specimen. After it obtained the results, some adjustments were made to carry out weldings of coverings. The results showed that the correct adjustments of the Distance of the Tip of the Wire Workpiece (DTWW) influenced in the geometry and diluition weld filet and in the arc stability. It was also seen that to obtain minors levels of dilution, a Distance of the Tip of the Electrode Workpiece (DTEW) depends of the level of energy employed, for lesser energies use lesser DTEWs and, for higher energies, higher DTEWs must be used. The levels of dilution and reinforcement were reduced with the use of the weaving technique. The technique of the energy influenced of significant way in the geometry and dilution of the weld filet. For the same energy welding and, consequently nearly equal cooling rate and heat in the sample, it can have diverse levels of the dilution without metallurgical alterations. The protection gas influenced in the dilution and the convexity index (R/L) of the weld metal, in a general way, the mixture of argon and nitrous oxide presented the best condition for welding of coverings. The adjustment of the energy for current welding (Type I) presented the best efficiency of for low energy, already for high energy, the best adjustment is for welding speed (Type V). For low levels of dilution, the use of weaving technique reduced of significant way the times and associates costs accomplishment of coverings. With the results obtained it was possible to carry out coverings of quality with low levels of dilution (<10 %) trough of GTAW process with feeding of cold wire.

In der vorliegenden Arbeit wurde die Energiebilanz von der Schweißenergiequelle bis zur Schmelzebildung im Bauteil eingehend analysiert. Hierfür wurden geeignete Messsysteme auf Basis der Kalorimetrie entwickelt und validiert. Neben dem Energieverbrauch der Anlage wird der Wärmeeintrag in das Bauteil kalorimetrisch analysiert. Zur umfassenden Analyse des Energieflusses werden zudem die Verlustgrößen, wie die Wärmeleitung, Wärmestrahlung und der Wärmedurchgang des Lichtbogens als auch der externe Brennerkühlkreislauf der Schweißenergiequelle untersucht. Neueste Untersuchungsmethoden ermöglichen zudem die Tropfentemperatur und die Lichtbogenleistung zu bestimmen. In Abhängigkeit definiert gewählter Prozessparameter wurde der Energiefluss für Schutzgasschweißverfahren mit abschmelzender und nicht abschmelzender Elektrode, sowie für das Unterpulverschweißen erstellt. Die einzelnen Wirkmechanismen der Prozesse wurden analysiert und bewertet sowie Zusammenhänge herausgestellt. Neben der Empfehlung für die Überarbeitung gültiger Normen, wie DIN EN 1011-1 kann mit der Kenntnis das Fügen temperatursensibler Werkstoffe verbessert werden. Gleichzeitig wird die Genauigkeit von Prozess- und Werkstoffsimulationen erhöht und Berechnung von Bauteildeformationen vereinfacht. Es wurden mittlere Tropfentemperaturen in einem Bereich zwischen TTr = 2.350…2.700°C ermittelt. Die Untersuchungen zeigen zudem, dass eine ausschließlich gezielte Änderung der Tropfentemperatur im Schweißprozess nicht möglich ist. Weiterhin konnte nachgewiesen werden, dass der Lichtbogen und dessen Intensität den entscheidenden Einfluss auf die Entstehung des Einbandes in den Grundwerkstoff besitzt. / Welding performance is not the same as the energy input in the component. The efficiency is the ratio of usable to required energy. The aim of any process is to achieve a high efficiency, and thus to keep the share of losses as small as possible. Recent process developments in arc welding with consumable electrode have the aim to regulate the energy input in the component to achieve the target of an optimum welding result. This is based on a fundamental understanding of the operations during the welding process. For this purpose, the knowledge of the individual operations of the energy transport from the electrode contact to the heating behaviour of the component is necessary. Different measurement methods and results for the separate determination of the energy content of droplet and welding arc as well as energy input into the component are presented. For instance the question is analysed and discussed - whether the arc, or the overheated droplet is responsible for the weld penetration? In addition, the situation between relative and absolute efficiency of the welding process is discussed. In welding standards often global efficiencies for different welding processes are indicated. These standards provide this efficiency in relation to the as 100 % set submerged arc welding. This leads to errors in the use of the values for calculations or simulations. With the methods presented a sophisticated analysis of the influence of different parameter settings of the shielding gas welding process on the energy efficiency is possible.