Recent developments in materials and material joining [specifically Aluminum and Pulse Gas Metal Arc Welding (GMAW-P) technology] have increased the scope and extent of their areas of application. However, stern market demand for the improved weld quality necessitates the need for automation of the welding processes. As a result, improvements in the process parameter feedback, sensing and control, are necessary to successfully develop the automated control technology for the welding processes. Hence, several aspects of the GMAW-P process have been investigated in this study in order to improve its control techniques. Welding was conducted on 6XXX aluminium, using 1.2 mm diameter 4047 aluminum electrode and argon shielding gas. An extensive collection of high speed camera pictures were taken over a wide range of pulse parameters and wire feed rates using a xenon shadowgraph setup to improve understanding of the physics of GMAW-P process. Current and voltage signals were recorded concurrently too. This investigation explores the effects of different process parameters namely pulsing parameters (Peak current (IP), Base Current (IB), Peak time (TP), Base Time (TB)) and wire feed rate on metal transfer phenomena in GMAW-P. Number of drops per pulse, arc length and droplet diameter were measured for aluminium electrodes by high speed videography. The pulsing parameters and wire feed rate were varied to investigate their effect on the metal transfer behaviour. Analysis showed that transition between the different metal transfer modes is strongly influenced by the electrode extension. Lower electrode extension reduced the number of droplets detached per pulse, while at higher electrode extension, spray mode is observed due to increased influence of the resistance heating. Analysis of the current and voltage signals were correlated with the high speed films. A simple derivative filter was used to detect the sudden changes in voltage difference associated with metal transfer during GMAW-P. The chosen feature for detection is the mean value of the weld current and voltage. A new algorithm for the real time monitoring and classification of different metal transfer modes in GMAW-P has been developed using voltage and current signals. The performance of the algorithm is assessed using experimental data. The results obtained from the algorithm show that it is possible to detect changes in metal transfer modes automatically and on-line. Arc stability in the GMAW-P has a close relationship with the regularity of metal transfer, which depends on several physical quantities (like voltage, current, materials, etc.) related to the growth and transfer of the metal droplet. Arc state in GMAW-P can be assessed quantitatively in terms of number of drops per pulse, droplet diameter and arc length. In order to assess the arc state in GMAW-P quantitatively, statistical and neural network models for number of drops/pulse, droplet diameter and arc length were developed using different waveform factors extracted from the current waveform of GMAW-P. To validate the models, estimated results were compared to the actual values of the number of drops per pulse, droplet diameter and arc length, observed during several welding conditions. Determination of stable one drop per pulse (ODPP) parametric zone containing all the combinations of peak current (IP), base current (IB), peak time (TP), and base time (TB) that results in stable operation of GMAW-P, is one of the biggest challenges in GMAW-P. A new parametric model to identify the stable ODPP condition in aluminium which also considers the influence of the background conditions and wire feed has been proposed. Finally, a synergic control algorithm for GMAW-P process has been proposed. Synergic algorithm proposed in this work uses the sensing and prediction techniques to analyse state of the arc and correct the pulsing parameters for achieving the stable ODPP. First arc state is estimated using the signal processing techniques and statistical methods to detect the occurrence of short circuit, unstable ODPP or multiple drops per pulse (MDPP) in GMAW-P system. If the arc state is not stable ODPP, then parametric model and genetic algorithm (GA) is used to assess the deviation of the existing pulsing parameters from the stable operation of GMAW-P process and automatically adjust pulsing parameters to achieve stable ODPP.

Os aços inoxidáveis duplex são ligas Fe-Cr-Ni-Mo, apresentando em sua maioria também o N, como elemento de liga, substituindo parcialmente o níquel. Possuem uma microestrutura balanceada, composta de 50% de ferrita (?) e 50% de austenita (?), aproximadamente. Combinam elevadas propriedades mecânicas associadas a excelente resistência à corrosão. Estes aços são classificados conforme a sua composição química. Uma classe recente são os aços duplex baixa liga (lean duplex), que possuem teores de Ni e Mo reduzidos. A soldabilidade dos aços duplex baixa liga, como o UNS S82441, é pior que a dos austeníticos e que alguns aços duplex de outras classes. O presente trabalho tem como objetivo estudar a influência da variação da energia de soldagem na soldabilidade do aço inoxidável duplex UNS S82441, variando-se a energia de soldagem. Foi utilizado o processo MIG/MAG (Metal inerte gás / metal ativo gás) na realização de cordões de solda em chapas com 100 x 300 x 6,1 mm. O metal de adição empregado foi o ER2209 segundo a norma AWS A5.9 e gás de proteção com 98%Ar + 2%O2, com energias de soldagem de 0,85; 1,07 e 1,34 kJ/mm. As juntas soldadas e o metal de base foram caracterizados microestruturalmente utilizando técnicas como: Microscopia Óptica (MO), Microscopia Eletrônica de Varredura (MEV), Metalografia Quantitativa, Difração de Raios-X, Análise por Difração de Elétrons Retroespalhados (EBSD), Análise por Calorimetria Diferencial e Análise por Dilatometria. As juntas e o metal de base foram caracterizados com relação as suas propriedades mecânicas e de resistência a corrosão com os seguintes ensaios: Ensaio de Microdureza, Ensaio de impacto Charpy V e Ensaio de Corrosão pela técnica de varredura de eletrodo em vibração (Scanning Vibrating Electrode Technique - SVET). Através da análise de imagens com o Microscópio Óptico notou-se a precipitação de austenita de diferentes tipos: alotriomorfa, de Widmanstatten e intragranular e um desbalanceamento da microestrutura para todas as energias de soldagem. O MEV comprovou a existência de fases secundárias, previstas pelo programa do Thermo-calc®. Foram observados maiores valores de microdureza da ferrita e da austenita na zona afetada pelo calor e na zona fundida para o caso em que foi empregado baixa energia de soldagem. A resistência à corrosão destes corpos de prova foi analisada utilizando-se a técnica local de Varredura com Eletrodo Vibratório (SVET). Foi observado que a variação da energia de soldagem influencia de maneira distinta, ao longo do tempo de exposição dos corpos de prova, a corrosão nas diferentes zonas em torno dos cordões de solda. Inicialmente, o cordão de solda com energia de soldagem menor, foi o que sofreu maior intensidade de corrosão e o de maior energia de soldagem, a menor intensidade de corrosão. O cordão de solda de energia intermediária, após 10 horas, foi o que sofreu maior intensidade de corrosão. / Duplex stainless steels are Fe-Cr-Ni-Mo-C alloys, which have a balanced microstructure composed of 50% of ferrite and 50% of austenite, approximately. They combine good mechanical properties and excellent corrosion resistance. These steels are classified according to their chemical composition. A recent class is the lean duplex stainless steels having lower content of Ni and Mo. The weldability of lean duplex steels, like UNS S82441, is worse than that of austenitic and duplex steels of different types. The objective of this work is to study the influence of the variation in welding heat input on lean duplex stainless steel UNS S82441 weldability. GMAW (Gas Metal Arc Welding) was used to weld plates with 100 x 300 x 6.1 mm. The filler metal was ER2209 according to AWS standard A5.9; and shielding gas with 98% Ar + 2% O2 using welding heat inputs of 0.71; 0.98 and 1.42 kJ/mm. Welded joints and base metal were microstructurally characterized using techniques such as optical microscopy, scanning electron microscopy (SEM), quantitative metallography, X-rays diffraction of, analysis by backscattered electrons diffraction (EBSD), analysis by differential calorimetry s and dilatometry . The joints and the base metal were characterized with respect to their mechanical properties and corrosion resistance using the following tests: Microhardness test, Charpy V Impact test and corrosion test by Scanning Vibrating Electrode Technique (SVET). Through image analysis with an Optical Microscope it was observed that there was an unbalanced microstructure for all welding heat inputs. The SEM showed the existence of secondary phases, confirmed by X-rays diffraction and by the Thermo-calc® program. Higher values of ferrite and austenite microhardness were observed in the heat affected zone and in the fusion zone in the case where low welding energy was used. The corrosion resistance of these specimens was analyzed using the local Vibratory Electrode Scanning Technique (SVET). It was observed that the variation of the welding heat input influences the corrosion in the different zones around the weld beads, during the time of exposure of the specimens. The weld bead with the lowest welding heat input was the one that suffered the highest corrosion intensity and the sample welded with the highest welding energy presented the lowest corrosion intensity.

abstract: This report presents the effects and analysis of the effects of Pulsed-Gas Metal Arc Welding's (P-GMAW) on Lean Duplex stainless steel. Although the welding of Duplex and Super Duplex Stainless steels have been well documented in both the laboratory and construction industry, the use of Lean Duplex has not. The purpose for conducting this research is to ensure that the correct Ferrite-Austenite phase balance along with the correct welding procedures are used in the creation of reactor cores for new construction nuclear power generation stations. In this project the effects of Lincoln Electrics ER-2209 GMAW wire are studied. Suggestions and improvements to the welding process are then proposed in order to increase the weldability, strength, gas selection, and ferrite count. The weldability will be measured using X-Ray photography in order to determine if any inclusions, lack of fusion, or voids are found post welding, along with welder feedback. The ferritic point count method in accordance with ASTM A562-08, is employed so that the amount of ferrite and austenite can be calculated in the same manor that is currently being used in industry. These will then be correlated to the tensile strength and impact toughness in the heat-affected zone (HAZ) of the weld based on the ASTM A923 testing method. / Dissertation/Thesis / M.S.Tech Technology 2012

Os aços inoxidáveis duplex são ligas Fe-Cr-Ni-Mo, apresentando em sua maioria também o N, como elemento de liga, substituindo parcialmente o níquel. Possuem uma microestrutura balanceada, composta de 50% de ferrita (?) e 50% de austenita (?), aproximadamente. Combinam elevadas propriedades mecânicas associadas a excelente resistência à corrosão. Estes aços são classificados conforme a sua composição química. Uma classe recente são os aços duplex baixa liga (lean duplex), que possuem teores de Ni e Mo reduzidos. A soldabilidade dos aços duplex baixa liga, como o UNS S82441, é pior que a dos austeníticos e que alguns aços duplex de outras classes. O presente trabalho tem como objetivo estudar a influência da variação da energia de soldagem na soldabilidade do aço inoxidável duplex UNS S82441, variando-se a energia de soldagem. Foi utilizado o processo MIG/MAG (Metal inerte gás / metal ativo gás) na realização de cordões de solda em chapas com 100 x 300 x 6,1 mm. O metal de adição empregado foi o ER2209 segundo a norma AWS A5.9 e gás de proteção com 98%Ar + 2%O2, com energias de soldagem de 0,85; 1,07 e 1,34 kJ/mm. As juntas soldadas e o metal de base foram caracterizados microestruturalmente utilizando técnicas como: Microscopia Óptica (MO), Microscopia Eletrônica de Varredura (MEV), Metalografia Quantitativa, Difração de Raios-X, Análise por Difração de Elétrons Retroespalhados (EBSD), Análise por Calorimetria Diferencial e Análise por Dilatometria. As juntas e o metal de base foram caracterizados com relação as suas propriedades mecânicas e de resistência a corrosão com os seguintes ensaios: Ensaio de Microdureza, Ensaio de impacto Charpy V e Ensaio de Corrosão pela técnica de varredura de eletrodo em vibração (Scanning Vibrating Electrode Technique - SVET). Através da análise de imagens com o Microscópio Óptico notou-se a precipitação de austenita de diferentes tipos: alotriomorfa, de Widmanstatten e intragranular e um desbalanceamento da microestrutura para todas as energias de soldagem. O MEV comprovou a existência de fases secundárias, previstas pelo programa do Thermo-calc®. Foram observados maiores valores de microdureza da ferrita e da austenita na zona afetada pelo calor e na zona fundida para o caso em que foi empregado baixa energia de soldagem. A resistência à corrosão destes corpos de prova foi analisada utilizando-se a técnica local de Varredura com Eletrodo Vibratório (SVET). Foi observado que a variação da energia de soldagem influencia de maneira distinta, ao longo do tempo de exposição dos corpos de prova, a corrosão nas diferentes zonas em torno dos cordões de solda. Inicialmente, o cordão de solda com energia de soldagem menor, foi o que sofreu maior intensidade de corrosão e o de maior energia de soldagem, a menor intensidade de corrosão. O cordão de solda de energia intermediária, após 10 horas, foi o que sofreu maior intensidade de corrosão. / Duplex stainless steels are Fe-Cr-Ni-Mo-C alloys, which have a balanced microstructure composed of 50% of ferrite and 50% of austenite, approximately. They combine good mechanical properties and excellent corrosion resistance. These steels are classified according to their chemical composition. A recent class is the lean duplex stainless steels having lower content of Ni and Mo. The weldability of lean duplex steels, like UNS S82441, is worse than that of austenitic and duplex steels of different types. The objective of this work is to study the influence of the variation in welding heat input on lean duplex stainless steel UNS S82441 weldability. GMAW (Gas Metal Arc Welding) was used to weld plates with 100 x 300 x 6.1 mm. The filler metal was ER2209 according to AWS standard A5.9; and shielding gas with 98% Ar + 2% O2 using welding heat inputs of 0.71; 0.98 and 1.42 kJ/mm. Welded joints and base metal were microstructurally characterized using techniques such as optical microscopy, scanning electron microscopy (SEM), quantitative metallography, X-rays diffraction of, analysis by backscattered electrons diffraction (EBSD), analysis by differential calorimetry s and dilatometry . The joints and the base metal were characterized with respect to their mechanical properties and corrosion resistance using the following tests: Microhardness test, Charpy V Impact test and corrosion test by Scanning Vibrating Electrode Technique (SVET). Through image analysis with an Optical Microscope it was observed that there was an unbalanced microstructure for all welding heat inputs. The SEM showed the existence of secondary phases, confirmed by X-rays diffraction and by the Thermo-calc® program. Higher values of ferrite and austenite microhardness were observed in the heat affected zone and in the fusion zone in the case where low welding energy was used. The corrosion resistance of these specimens was analyzed using the local Vibratory Electrode Scanning Technique (SVET). It was observed that the variation of the welding heat input influences the corrosion in the different zones around the weld beads, during the time of exposure of the specimens. The weld bead with the lowest welding heat input was the one that suffered the highest corrosion intensity and the sample welded with the highest welding energy presented the lowest corrosion intensity.

With the growth in pipeline installations all over the world, there is a great demand for highly productive and robust welding systems. Mechanised pipe welding has been developed over the last 50 years and the present focus is towards development of automated pipeline welding systems. Pipeline welding automation is aimed at reducing costs and improving the installation quality. To attain fully automated pipe welding systems there is a need to rely on sensors and controls systems to mimic human like capabilities, such as visual inspection, in real time. The key aim of this work is to develop and evaluate methods of automatic assessment of weld bead shape and quality during narrow gap GMAW of transmission pipelines. This implies that the measured bead profile will be assessed to determine whether the bead shape will cause defects when the subsequent pass is deposited. Different approaches have been used to conquer the challenge that is emulating human reasoning, all with different objectives in mind. In spite of extensive literature research performed, very little information was found concerning the real time determination and assessment of bead shape quality and none of it was reported to be applied successfully to the pipeline industry. Despite the continuous development of laboratory laser vision systems commercial ones have been on the market for decades, some specifically developed for the welding application. Laser vision sensor systems provide surface profile information, and are the only sensors which can satisfactorily measure bead profile on a narrow groove. In order to be able to use them to automatically assess weld bead shape and quality, a deep understanding of their characteristics and limitations needs to be achieved. Once that knowledge was attained it was then applied to determine the best sensor configuration for this purpose. After that the development of human like judgment algorithms were developed to accomplish the aim that was set. Empirical rules were obtained from an experienced welder regarding the acceptability of bead shapes and were then applied in the developed system with good results. To scientifically evaluate and determine the rules to use in this system, further experiments would be required. The output of the system developed showed very accurate, reliable and consistent results that were true to the external measurements and comparisons performed. The developed system has numerous applications in the pipeline industry and it could easily be implemented on commercial systems.

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