Thèse de doctorat : Automatique, Traitement du Signal et Génie Informatique : Nancy 1 : 2008. / Titre provenant de l'écran-titre.

In the novel Double Electrode Gas Metal Arc Welding (DE-GMAW), the transfer of the liquid metal from the wire to the work-piece determines the weld quality and for applications where the precision is critical, the metal transfer process needs to be monitored and controlled to control the diameter, trajectory, and transfer rate of the droplet of liquid metal. In this doctoral research work, the traditional methods of tracking, Correlation, Least Square Matching (LSM) and Kalman Filtering (KF), are tried first. All of them failed due to the poor quality of the metal transfer image and the variety of the droplet. Then several novel image processing algorithms, Brightness Based Separation Algorithm (BBSA), Brightness and Subtraction Based Separation Algorithm (BSBSA) and Brightness Based Selection and Edge Detection Based Enhancement Separation Algorithm (BBSEDBESA), are proposed to compute the size and locate the position of the droplet. Experimental results verified that the proposed algorithms can automatically locate the droplets and compute the droplet size with an adequate accuracy. Since the final objective is to automatically process the metal transfer in real time, a real time processing system is implemented and the details are described. In traditional Gas Metal Arc Welding (GMAW), the famous laser back-lighting technique has been widely used to image the metal transfer process. Due to laser imaging systems complexity, it is too inconvenient for practical applications. In this doctoral research work, a simplified laser imaging system is proposed and two effective image algorithms, Probability Based Double Thresholds Separation Algorithm and Edge Based Separation Algorithm, are proposed to process the corresponding captured metal transfer images. Experimental results verified that the proposed simplified laser back-light imaging system and image processing algorithms can be used for real time processing of metal transfer images.

Approved for public release; distribution is unlimited / HY-130 is a high-strength, low-carbon steel used in the quenched and tempered condition . It is designed for high performance and marine applications where good weldability is a requirement. Optimum welding parameters are currently under investigation. In this study, 1/2 inch (12.7 mm) HY-130 steel weldments produced by submerged arc welding (SAW) and gas metal arc welding (GMAW) processes are compared by means of a systematic microstructural characterization of the base metal, weld metal, and heat affected zone (HAZ). The microstructures are characterized by optical and electron micro­scopy and microhardness measurements are performed in the weld metal and across the HAZ to relate the microstructure with the microhardness profiles. The weld metal microstructure of both weldments showed a predominantly martensitic structure. The GMAW weld metal had a finer lath martensite structure and contained more retained austenite and twinned martensite. The SAW weld metal had a less defined lath structure which was more bainitic. The microhardness values were higher in the GMAW weld metal. No significant differences in microstructure and hardness were observed in the HAZ of the two weldments. / http://archive.org/details/effectofweldingp00mcnu / Captain, Canadian Forces

Made available in DSpace on 2014-06-12T17:37:54Z (GMT). No. of bitstreams: 2 arquivo3813_1.pdf: 4917283 bytes, checksum: adb1b09d841ae714682b1d0cad90ae76 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A influência do gás de proteção no modo de transferência do metal de adição e nas propriedades mecânicas associadas foram estudadas neste trabalho. Considerando-se que o tema é pouco explorado no meio científico, a correlação microestrutura / propriedades mecânicas foi realizada para os diferentes processos GMAW. Para a realização deste estudo, foram utilizados gases de proteção disponíveis no mercado: Argônio Puro (Ar), Mistura Stargold Plus (75% Ar / 25% CO2) e o Dióxido de Carbono Puro (CO2). O metal de base utilizado foi o açocarbono de classificação ASTM A36 e o metal de adição utilizado foi o arame de classificação ER70-S6. Os resultados deste estudo mostraram que o modo de transferência do metal de adição passa de globular, quando soldado com o Dióxido de Carbono Puro (CO2), para spray (aerosol) na soldagem com a Mistura Stargold Plus (75% Ar / 25% CO2) ou com o Argônio Puro (Ar). As microestruturas associadas a estes diferentes processos foram caracterizadas macro e microestruturalmente por microscopia ótica (MO) e microscopia eletrônica de varredura (MEV). A microestrutura da junta soldada com o Argônio Puro (Ar) revelou falta de penetração e uma grande densidade de poros. A microestrutura da junta soldada com a Mistura Stargold Plus (75% Ar / 25% CO2) revelou uma pequena densidade de poros e uma completa fusão na raiz. A microestrutura da junta soldada com o Dióxido de Carbono Puro (CO2) revelou uma densidade de poros intermediária em relação às juntas soldadas com os outros gases de proteção. As propriedades mecânicas levantadas foram microdureza e resistência à tração. Os resultados das propriedades mecânicas ratificaram os resultados obtidos com a caracterização microestrutural. As melhores propriedades foram obtidas com a Mistura Stargold Plus (75% Ar / 25% CO2)

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.

Dissimilar welding has been subject of several investigations due to its potential importance in various industrial fields such as transportation, energy generation and management. Dissimilar welding can increase the design efficiency, by the use of complementary alloys with different properties, cost cutting and light weighting structures. The use of different materials within a component or structure to best suit a particular task, requirement or increase its life and performance has always been an ambition of several designers and engineers. This project investigated the joining steel and aluminium for the automotive industry and also stainless steel and titanium to be applied in the civil nuclear energy generation industry. These dissimilar metallic combinations are metallurgically incompatible and the formation of brittle intermetallic phases (IMC) need to be controlled or eliminated. To join steel to Al, laser spot welding process was selected, to avoid the bulk melting of steel and Al at the joint interface that enhance the formation of brittle IMC. This part of the work was focused in controlling the joining process to control the IMC formation of galvanized and uncoated steel to Al and verify if it was possible to have a sound and reliable joint in the presence of an IMC layer. In the second part of this study, stainless steel to titanium joining, a different approach was taken with the application of weld metal engineering to modify or eliminate the IMC formation. Several metals were evaluated as potential interlayers to use and laser welding with a Ni interlayer was evaluated with moderate success, due to the modified IMC with improved mechanical properties and the good compatibility between Ni and the stainless steel. A further improvement was achieved when Cu was brazed between stainless steel and Ti using CMT (Cold Metal Transfer) a low heat input MIG process. The final attempt was to use a different interlayer that was 3D printed and deposited in several layers. This interlayer was composed Cu and Nb that were selected as candidates to avoid the IMC formation between the stainless steel and Ti. With this approach it was possible to build an IMC free component and possibly improve and avoid IMC formation in several other dissimilar metallic combinations.

The effects of mastering 1F (flat position-fillet) welds on carbon steel using a sequenced pattern of welding was examined. Participants (N = 71) were randomly assigned a specific sequence of welding between Gas Metal Arc Welding (GMAW) and Shielded Metal Arc Welding (SMAW). The hypothesis of teaching beginning welders the GMAW process before the SMAW process to improve the ability to master American Welding Society (AWS) welds was tested. A welding pretest was administered to determine any prior welding knowledge. Sixty minutes of welding instruction taught proper welding safety, machine set-up, arc length, travel speed, work angle, and correct bead formation. Two practice sessions of 60 minutes were given for participants to become familiar with each welding process, followed by two testing sessions of ten minutes. During the testing period, individuals were assessed on their ability to produce an AWS 1F (flat position- fillet) lap weld in a given sequence. Welds were graded according to the AWS rubric for fillets with a total of four criteria categories based on the following criteria: a) presence of cracks or porosity, b) complete fusion, c) fillet leg size is specified minimum, and d) undercut - not to exceed 1/32 inches. The study indicate that students perform welds that meet AWS quality standards when using the GMAW process, however, the results were not statistically significant.

Simulations of the welding process for butt and tee joints using finite element analyses are presented. The base metal is aluminum alloy 2519-T87 and the filler material is alloy 2319. The simulations are performed with the commercial software SYSWELD+®, which includes moving heat sources, material deposit, metallurgy of binary aluminum, temperature dependent material properties, metal plasticity and elasticity, transient heat transfer and mechanical analyses. One-way thermo-mechanical coupling is assumed, which means that the thermal analysis is completed first, followed by a separate mechanical analysis based on the thermal history. The residual stress state from a three-dimensional analysis of the butt joint is compared to previously published results. For the quasi-steady state analysis the maximum residual longitudinal normal stress was within 3.6% of published data, and for a fully transient analysis this maximum stress was within 13% of the published result. The tee section requires two weld passes, and both a fully three-dimensional (3-D) and a 3-D to 2-D solid-shell finite elements model were employed. Using the quasi-steady state procedure for the tee, the maximum residual stresses were found to be 90-100% of the room-temperature yield strength. However, the longitudinal normal stress in the first weld bead was compressive, while the stress component was tensile in the second weld bead. To investigate this effect a fully transient analysis of the tee joint was attempted, but the excessive computer times prevented a resolution of the longitudinal residual stress discrepancy found in the quasi-steady state analysis. To reduce computer times for the tee, a model containing both solid and shell elements was attempted. Unfortunately, the mechanical analysis did not converge, which appears to be due to the transition elements used in this coupled solid-shell model. Welding simulations to predict residual stress states require three-dimensional analysis in the vicinity of the joint and these analyses are computationally intensive and difficult. Although the state of the art in welding simulations using finite elements has advanced, it does not appear at this time that such simulations are effective for parametric studies, much less to include in an optimization algorithm. / Master of Science

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

O objetivo deste trabalho é analisar a influência dos parâmetros de um sistema mecanizado de soldagem, composto por uma tocha TIG e outra MAG em tandem, sobre a geometria do cordão de solda resultante. Os resultados obtidos foram comparados com soldas realizadas pelos processos TIG e MAG operando isoladamente. Os testes foram executados por meio de simples deposição de cordões sobre chapas de aço ao carbono AISI 1010 com espessura de 6,3 mm. Os parâmetros analisados foram: corrente de soldagem e distância da ponta do eletrodo até a peça no processo TIG, velocidade de alimentação de arame e tensão do arco no processo MAG, além de velocidade de soldagem e distância entre as tochas. Os cordões de solda foram executados em um dispositivo de soldagem mecanizado, que permite a variação da velocidade de soldagem, distância da ponta do eletrodo TIG e a distância entre as tochas. Os ajustes de corrente e tensão de soldagem foram feitos em duas fontes de potência separadas, ambas do tipo transformador-retificador, uma para cada tocha, devido às diferentes curvas características de cada processo. Através do projeto de experimento fatorial fracionado, foram avaliados os efeitos de dois níveis, um mínimo e outro máximo, mais quatro réplicas dos seus níveis intermediários, resultando em 20 experimentos para cada processo de soldagem. Os valores dos resultados finais indicam uma diferença ao utilizar uma tocha TIG para pré-aquecer o material base, porém, estatisticamente, essa diferença não é significativa entre os processos TIG e MAG em tandem e MAG convencional para a faixa de parâmetros de soldagem adotada. / This study aims to investigate the influence of process parameters of a mechanized welding system, comprising a GTAW torch and a GMAW torch in tandem configuration, on the geometry of the resulting weld bead, performed using GTAW and GMAW welding processes in tandem. The results were compared with weld beads performed by conventional GTAW and GMAW welding processes. The tests were conducted performing bead-on-plate deposits over AISI 1010 6,3 mm thick carbon steel plates. GTAW current, GMAW wire feed speed, GTAW arc length, GMAW voltage, welding speed and the distance between GTAW and GMAW torches were the analyzed parameters. The weld beads were performed in a mechanized welding bench, which allows the variation of speed, distance between torches and arc length of the GTAW torch. Current and voltage adjustments were made in two separate transformer-rectifier power sources, one for each welding torch, due to their different characteristic curves of each process. Through the fractional factorial design of experiment, the effects of two different levels for each parameter were analyzed, plus four replicates of the average values of these levels, resulting in 20 experiments for each welding process. The results show a difference on the weld bead geometry using a GTAW torch to preheat the base metal, however, this difference is not statistically significant between GTAW and GMAW welding process in tandem and GMAW welding process for the adopted range of welding parameters.