The welding of austenite stainless steel often results in large amount of welding distortion due to its high thermal expansion coefficient and low thermal conductivity. This has created great difficulty in the dimensional control of the welded stainless steel structure, ending up with high manufacturing cost. Researches on the welding distortion of stainless steels were very limited, especially for large weld structures with complex component shapes. The studies of this thesis were initiated with focus on the stainless steel nozzle-to-shell-can weld structures, a very typical structural configuration for pressure vessels used in petrochemical and nuclear power generation industries. Both the experimental and the FEA (finite element analysis), i.e. computational simulation, approaches were taken in the studies which addressed the influences of the welding fixture, the welding sequence, and the welding process on the distortion caused by stainless steel nozzle-to-shell welding. The investigations employed single and multi-nozzle weld test models (called mockups in the thesis) or FEA models. Manual GTAW (gas tungsten arc welding) and SMAW (shielded metal arc welding) processes were selected to represent the most common practice for stainless steel nozzle welding. The FEA simulations were conducted with ABAQUS program using sequentially coupled transient analysis method with lumped weld passes to achieve high computing efficiency. The investigations on the effect of the welding fixture concluded that the contour fixtures introduced in the thesis be effective for reducing the welding distortion for both the single and the multi-nozzle welding. The contour fixtures tend to localize the welding distortion, hence yield less impact on the global distortion of the whole weld structure. The rib-bar fixture, a more common fixture type for multi-nozzle welding, was found resulting in a big jump in the shell plate distortion when the fixture was removed. The studies on the influence of the welding sequence revealed that a progressive approach was more favorable for distortion control under the given nozzle-to-shell weld structure configurations. The best sequence suggested is to start welding at one nozzle, firstly on shell OD (outside diameter) side then on ID (inside diameter) side, then proceed to next neighboring nozzle. The effect of the welding direction of each weld pass was found affecting only the nozzle angular distortion. The experimental data showed that the manual GTAW process developed much higher shell plate distortion than the SMAW process. The reason would be that a higher percentage of the welding heat had been consumed on the base metal. The influence of the weld bead size didn???t appear to be significant. In the FEA study on the effect of the size of the lumped weld pass, the increase in weld bead size even resulted in a decrease in weld distortion. From the FEA simulation point of view, using large lumped pass would be a highly efficient choice without compromising too much in the precision of the distortion prediction. The FEA study confirmed that a decrease in cooling time after welding would result in more welding distortion. The large scale multi-nozzle mockup with rib-bar fixture demonstrated a maximum out-of-plane shell distortion of 16.4mm after the welding of 10 nozzles with GTAW+SMAW process, which suggests that additional measures should be developed to further control the welding distortion.

O elevado fluxo de calor envolvido no processo de soldagem de componentes favorece o aparecimento de tensões residuais, cujo alívio propicia o surgimento das distorções. Uma vez que essas distorções podem comprometer a utilização dos componentes, tornam-se relevantes pesquisas a respeito dos parâmetros, mensuração e previsão das distorções. Este trabalho tem como objetivo analisar as distorções na soldagem GMAW de uma junta tipo T, através do estudo termoestrutural em um modelo numérico pelo método dos elementos finitos com validação experimental. Para isso, o trabalho foi dividido em duas etapas sequenciais, sendo a primeira destinada à validação do modelo numérico e a segunda à elaboração de casos numéricos para análise. O modelo numérico utiliza elementos finitos tridimensionais para a obtenção do campo de temperaturas e distorções. Para a aplicação do fluxo de calor à peça utilizou-se a equação de Goldak como modelo de aporte de calor na análise térmica transiente. A dependência da temperatura na variação das propriedades físicas e mecânicas dos materiais foi considerada. A parte experimental da primeira etapa permitiu definir duas velocidades de soldagem mantendo a mesma energia do processo, originando dois conjuntos de parâmetros denominados como principais e alternativos. Na segunda etapa foram analisados oito casos, definidos através da combinação de três variáveis: variação da velocidade, sequência de soldagem e tempo de resfriamento entre filetes. O campo de temperaturas transiente é verificado pela medição de temperaturas em oito pontos, enquanto o campo de distorções é verificado utilizando um sistema de medição por coordenadas. Dentre os casos analisados, a menor distorção foi observada no caso 6 (velocidade mais rápida, sequência “vai-volta” e com intervalo de resfriamento) onde a distorção máxima foi de 4,31 mm, enquanto a maior distorção foi apresentada pelo caso 4 (velocidade mais lenta, sequência “vai-vai” e com intervalo de resfriamento) com distorção máxima de 6,41 mm. / The high heat flow involved in the component’s welding process favors the appearance of residual stress, which alleviation provides the appearance of distortions. Once these distortions can impair the use of the components, become relevant searches about the parameters, measurement and prediction of distortions. This work aims to analyze the distortions in GMAW welding of a T-type joint, through thermo-structural study in a numerical model by finite element method with experimental validation. For this, the work was divided in two sequential stages, the first aimed to the numerical model’s validation and the second to the development of numerical cases to analysis. The numerical model uses three-dimensional finite elements for obtainment the temperature field and distortions. For the application of heat flow to the part was used the Goldak’s equation as a model of heat input in transient thermal analysis. The temperature dependence in the variation of physical and mechanical properties of the materials was considered. The experimental part of the first stage allowed to define two welding speeds while keeping the same process energy, originating two sets of parameters called principal and alternative. In the second stage, eight cases were analyzed, defined by the combination of three variables: speed variation, sequence of welding and cooling time between fillets. The transient temperature field is checked by measuring temperatures in eight points, while the distortion field is checked using a coordinate measuring system. Among all cases analyzed, the lowest distortion was observed in case 6 (fastest speed, "going-back" sequence and cooling interval) in which the maximum distortion was 4.31 mm, while the largest distortion was presented by the case 4 (slower speed, "go-go" sequence and cooling interval) with maximum distortion of 6.41 mm.

O elevado fluxo de calor envolvido no processo de soldagem de componentes favorece o aparecimento de tensões residuais, cujo alívio propicia o surgimento das distorções. Uma vez que essas distorções podem comprometer a utilização dos componentes, tornam-se relevantes pesquisas a respeito dos parâmetros, mensuração e previsão das distorções. Este trabalho tem como objetivo analisar as distorções na soldagem GMAW de uma junta tipo T, através do estudo termoestrutural em um modelo numérico pelo método dos elementos finitos com validação experimental. Para isso, o trabalho foi dividido em duas etapas sequenciais, sendo a primeira destinada à validação do modelo numérico e a segunda à elaboração de casos numéricos para análise. O modelo numérico utiliza elementos finitos tridimensionais para a obtenção do campo de temperaturas e distorções. Para a aplicação do fluxo de calor à peça utilizou-se a equação de Goldak como modelo de aporte de calor na análise térmica transiente. A dependência da temperatura na variação das propriedades físicas e mecânicas dos materiais foi considerada. A parte experimental da primeira etapa permitiu definir duas velocidades de soldagem mantendo a mesma energia do processo, originando dois conjuntos de parâmetros denominados como principais e alternativos. Na segunda etapa foram analisados oito casos, definidos através da combinação de três variáveis: variação da velocidade, sequência de soldagem e tempo de resfriamento entre filetes. O campo de temperaturas transiente é verificado pela medição de temperaturas em oito pontos, enquanto o campo de distorções é verificado utilizando um sistema de medição por coordenadas. Dentre os casos analisados, a menor distorção foi observada no caso 6 (velocidade mais rápida, sequência “vai-volta” e com intervalo de resfriamento) onde a distorção máxima foi de 4,31 mm, enquanto a maior distorção foi apresentada pelo caso 4 (velocidade mais lenta, sequência “vai-vai” e com intervalo de resfriamento) com distorção máxima de 6,41 mm. / The high heat flow involved in the component’s welding process favors the appearance of residual stress, which alleviation provides the appearance of distortions. Once these distortions can impair the use of the components, become relevant searches about the parameters, measurement and prediction of distortions. This work aims to analyze the distortions in GMAW welding of a T-type joint, through thermo-structural study in a numerical model by finite element method with experimental validation. For this, the work was divided in two sequential stages, the first aimed to the numerical model’s validation and the second to the development of numerical cases to analysis. The numerical model uses three-dimensional finite elements for obtainment the temperature field and distortions. For the application of heat flow to the part was used the Goldak’s equation as a model of heat input in transient thermal analysis. The temperature dependence in the variation of physical and mechanical properties of the materials was considered. The experimental part of the first stage allowed to define two welding speeds while keeping the same process energy, originating two sets of parameters called principal and alternative. In the second stage, eight cases were analyzed, defined by the combination of three variables: speed variation, sequence of welding and cooling time between fillets. The transient temperature field is checked by measuring temperatures in eight points, while the distortion field is checked using a coordinate measuring system. Among all cases analyzed, the lowest distortion was observed in case 6 (fastest speed, "going-back" sequence and cooling interval) in which the maximum distortion was 4.31 mm, while the largest distortion was presented by the case 4 (slower speed, "go-go" sequence and cooling interval) with maximum distortion of 6.41 mm.

O elevado fluxo de calor envolvido no processo de soldagem de componentes favorece o aparecimento de tensões residuais, cujo alívio propicia o surgimento das distorções. Uma vez que essas distorções podem comprometer a utilização dos componentes, tornam-se relevantes pesquisas a respeito dos parâmetros, mensuração e previsão das distorções. Este trabalho tem como objetivo analisar as distorções na soldagem GMAW de uma junta tipo T, através do estudo termoestrutural em um modelo numérico pelo método dos elementos finitos com validação experimental. Para isso, o trabalho foi dividido em duas etapas sequenciais, sendo a primeira destinada à validação do modelo numérico e a segunda à elaboração de casos numéricos para análise. O modelo numérico utiliza elementos finitos tridimensionais para a obtenção do campo de temperaturas e distorções. Para a aplicação do fluxo de calor à peça utilizou-se a equação de Goldak como modelo de aporte de calor na análise térmica transiente. A dependência da temperatura na variação das propriedades físicas e mecânicas dos materiais foi considerada. A parte experimental da primeira etapa permitiu definir duas velocidades de soldagem mantendo a mesma energia do processo, originando dois conjuntos de parâmetros denominados como principais e alternativos. Na segunda etapa foram analisados oito casos, definidos através da combinação de três variáveis: variação da velocidade, sequência de soldagem e tempo de resfriamento entre filetes. O campo de temperaturas transiente é verificado pela medição de temperaturas em oito pontos, enquanto o campo de distorções é verificado utilizando um sistema de medição por coordenadas. Dentre os casos analisados, a menor distorção foi observada no caso 6 (velocidade mais rápida, sequência “vai-volta” e com intervalo de resfriamento) onde a distorção máxima foi de 4,31 mm, enquanto a maior distorção foi apresentada pelo caso 4 (velocidade mais lenta, sequência “vai-vai” e com intervalo de resfriamento) com distorção máxima de 6,41 mm. / The high heat flow involved in the component’s welding process favors the appearance of residual stress, which alleviation provides the appearance of distortions. Once these distortions can impair the use of the components, become relevant searches about the parameters, measurement and prediction of distortions. This work aims to analyze the distortions in GMAW welding of a T-type joint, through thermo-structural study in a numerical model by finite element method with experimental validation. For this, the work was divided in two sequential stages, the first aimed to the numerical model’s validation and the second to the development of numerical cases to analysis. The numerical model uses three-dimensional finite elements for obtainment the temperature field and distortions. For the application of heat flow to the part was used the Goldak’s equation as a model of heat input in transient thermal analysis. The temperature dependence in the variation of physical and mechanical properties of the materials was considered. The experimental part of the first stage allowed to define two welding speeds while keeping the same process energy, originating two sets of parameters called principal and alternative. In the second stage, eight cases were analyzed, defined by the combination of three variables: speed variation, sequence of welding and cooling time between fillets. The transient temperature field is checked by measuring temperatures in eight points, while the distortion field is checked using a coordinate measuring system. Among all cases analyzed, the lowest distortion was observed in case 6 (fastest speed, "going-back" sequence and cooling interval) in which the maximum distortion was 4.31 mm, while the largest distortion was presented by the case 4 (slower speed, "go-go" sequence and cooling interval) with maximum distortion of 6.41 mm.

In this master’s thesis there are set down dependencies of distortion of T-joints on the size of heat input and welding speed. Dependencies were found for single- and double-fillet welds, for single- and multiple-pass welding. The computer simulations were carried out in programs Visual-Weld and SYSWELD. The size of the melted zones, stress fields, material structure and hardness of the weld specimens were specified. Simulation results were compared with experimentally detected values.

An effective approach to determine optimum welding process parameters is implementation of advanced computer aided engineering (CAE) tool that integrates efficient optimization techniques and numerical welding simulation. In this thesis, an automated computational methodology to determine optimum arc welding process parameters is proposed. It is a coupled Genetic Algorithms (GA) and Finite Element (FE) based optimization method where GA directly utilizes output responses of FE based welding simulations for iterative optimization. Effectiveness of the method has been demonstrated by predicting optimum parameters of a lap joint specimen of two thin steel plates and automotive structure of nonlinear welding path for minimum distortion. Three dimensional FE models have been developed to simulate the arc welding process and subsequently, the models have been used by GA as the evaluation model for optimization. The optimization results show that such a CAE based methodology can contribute to facilitate the product design and development.

Friction Stir Welding (FSW) was used to perform Bead on Plate (BOP) welds on 6061-T6511 aluminum extrusions. Using a DOE approach, tool rotation speed, clamp spacing, and clamping force were altered to ascertain their effects on distortion in the welded panels. Mechanical forces were monitored during the weld process. Both linear and out of plane distortion were measured on the welded extrusions. The Vickers hardness of the weld nugget was measured. The effect of each parameter on weld distortion was discovered and the mechanism of this link was suggested.

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