With the desire to lighten the frame while keeping or increasing the strength, Advanced High-Strength Steels (AHSS) have been developed for use in the automotive industry. AHSS meet many vehicle functional requirements because of their excellent strength and acceptable ductility. But joining AHSS is a challenge, because weldability is lower than that of mild steels. Friction stir spot welding (FSSW) is a solid state joining process that can provide a solution to the weldability issues in AHSS, but FSSW has not been studied in great detail for this application. In this work, Si3N4 tools were used for FSSW experiments on DP 980 steel with 1.2mm thickness. Joint strength was measured by lap shear tension testing, while thermocouples were used for the temperature measurements. A finite element model was developed in order to predict material flow and temperatures associated with FSSW. Since a 3D model of the process is very time consuming, a novel 2D model was developed for this study. An updated Lagrangian scheme was employed to predict the flow of sheet material, subjected to the boundary conditions of the fixed backing plate and descending rotating tool. Heat generation by friction was computed by including the rotational velocity component from the tool in the thermal boundary conditions. Material flow was calculated from a velocity field while an isotropic, viscoplastic Norton-Hoff law was used to compute the material flow stress as a function of temperature, strain and strain rate. Shear stress at the tool/sheet interface was computed using the viscoplastic friction law. The model predicted welding temperatures to within 4% of the experiments. The welding loads were significantly over predicted. Comparison with a 3D model of FSSW showed that frictional heating and the proportion of total heat generated by friction were similar. The position of the joint interface was reasonably well predicted compared to experiment.

In this study tools consisting of a 5mm cylindrical pin and a 12mm shoulder held by a simple tool holder were used to compare the wear of 11 tooling materials. The objective was to determine if using these tools in a spot welding configuration to simulate friction stir welding could differentiate the potential performance of tooling materials. All tools were made of varying percentages of polycrystalline cubic boron nitride (PCBN), tungsten (W) and rhenium (Re). The materials are referred to herein as GV1, GV2, G1, G2, G3, G4, G5, G6, G7, G8 and G9.The tools were run to 205 welds if they did not fracture first. The grades averaged the following quantities of welds before fracture failure GV-1:0; GV-2:200; G1:82; G2:204; G3:205; G4:205; G5:96; G7:102.73; G8:21.2; G9:38.5. Of the tools that ran the full 205 welds without chipping, the average calculated volume loss, which was the best indication of wear, was as follows G2:1.83%; G3:2.53%; G4:2.41%; G5:1.93%; and G7:2.30%.The study showed that G2 had the least wear and G6 had the most wear, of those tools that completed all 205 spot welds. Fracture was the failure mode of all grades with over 70% CBN content. It was found that small CBN grain size was not correlated to better wear performance, as has been seen in a prior study.

Friction bit joining (FBJ) is a new solid-state spot joining technology developed in cooperation between Brigham Young University of Provo Utah, and MegaStir Technologies of West Bountiful Utah. Although capable of joining several different material combinations, this research focuses on the application of FBJ to joining 5754 aluminum to DP 980 steel, two alloys commonly used in automotive applications. The thicknesses of the materials used were 0.070 inches (1.78 mm) and 0.065 inches (1.65 mm), respectively. The FBJ process employs a consumable 4140 steel bit and is carried out on a purpose built research machine. In the first stage of the weld cycle the bit is used to drill through the aluminum top sheet to be joined. After this, spindle speed is increased so that the bit tip effectively forms a friction weld to the steel bottom sheet. Momentary stoppage of the spindle facilitates weld cooling before the spindle is restarted, shearing the bit tip from the bit shank, and retracted. Incorporated into the bit tip geometry is a flange that securely holds the aluminum in place after joint formation is complete. This research consists of several developmental steps since the technology only recently began to be formally studied. Initial joint strengths observed in lapshear tensile testing averaged only 978.5 pounds (4.35 kN), with a relatively high standard deviation for the data set. Final lapshear tensile test results were improved to an average of 1421.8 pounds (6.32 kN), with a significantly lower, and acceptable, standard deviation for the data set. Similar improvements were realized during the development work in cross tension tensile test results, as average strengths increased from 255.8 pounds (1.14 kN) to 566.3 pounds (2.52 kN). Improvements were also observed in the standard deviation values of cross tension data sets from initial evaluation to the final data set presented in this work.

With the desire to improve passenger safety and fuel efficiency, Ultra High Strength Steels (UHSS) have been developed for use in the automotive industry. UHSS are high strength steels with high ductility and strength. DP 980 is one of these UHSS being applied in automobile manufacturing. DP 980 is difficult to join with Resistance Spot Welding (RSW) because of the high carbon content and alloying in this material. The weld becomes brittle when it solidifies during the welding process. With the desire and motivation of widely using UHSS, new welding processes are needed to be developed in order to effectively join DP 980. Friction Stir Spot Welding (FSSW) is a developing welding process aimed to replace RSW in the automotive industry because of its ability to join materials at a lower temperature. Currently the welding loads of the tools are higher than 2000 pounds, ranging from 3,000 to 5,000 pounds, which exceeds the limit of the welding robots in the automotive factories. It is proposed that the welding loads can be reduced by increasing the spindle speed of the FSSW tool. Other focuses in the research include increasing the life of the tool and developing acceptable welding parameters for High Speed FSSW. The experimental work done for this thesis provided support that weld strength can be obtained at levels above the acceptable standard for DP 980 material (greater than 2400 pound lap shear fracture load for 1.2 mm material) while keeping the vertical load on the welding machine spindle below 2000 lbs.

The amount of aluminium sheets in future body-in-white concepts is still on the rise. There is a need for optimizing the joining techniques, caused by the different characteristics compared to the established steel components. Especially the electrode life for resistance spot welding as a reliable and established process needs to be improved. One reason for the short electrode life when welding aluminium is the insulating effect of the aluminium oxide layer. One possibility to reduce the electrode wear is the mechanical destruction of the oxide layer before the welding. This paper describes the influence of a translational and rotational electrode movement on the electrode wear. The oxide layer destruction is detected by resistance measurement. It could be shown that the destruction of the oxide layer already occurs at low movements. However, a homogeneous, large-area destruction is necessary for a wear reduction.

The demand for high energy battery assemblies is growing in sectors such as transportation. Alongwith it is the need for reliable, efficient and cost-effective ways to electrically connect the batteries toensure their performance. Battery cells are most often put into modules or packs when produced forelectrically driven vehicles. The variable of greatest influence when welding battery packs is thecontact resistance between the cell and the connection tab. It is crucial to minimize this variable asmuch as possible to prevent energy loss in the form of heat generation. The purpose of this project is to conduct a comparative literature study of different weldingtechniques for welding batteries. The compared techniques are resistance spot welding, laser beamwelding and ultrasonic welding. The performance was evaluated in terms of numerous factors such asproduction cost, degree of automation and weld quality. All three methods are tried and proven to function in the production of battery applications. Eachmethod has separate strengths and limitations which makes them complement each other. Thus, it isimportant to look at several factors when deciding which welding technique is the most suitable forthe desired application. The scale of production, economical aspects as well as battery cell geometrywere concluded to be the most important in making this decision.

Este trabalho teve como principal objetivo a determinação dos parâmetros de soldagem a ponto pelo processo de fricção-mistura (FSSW) em uma liga de alumínio AA2024-T3, pela comparação de resultados obtidos em ensaios de cisalhamento e arrancamento em tração e ensaios de fadiga em juntas sobrepostas. Juntas rebitadas da mesma liga também foram ensaiadas, nas mesmas condições, para comparação de propriedades mecânicas. Os principais parâmetros do processo FSSW são: velocidades de avanço e de rotação da ferramenta, profundidade de penetração e tempo de patamar. Foram explorados principalmente os parâmetros: profundidade de penetração e rotação da ferramenta. Os resultados dos ensaios de cisalhamento em tração possibilitaram a determinação da resistência ao cisalhamento das juntas soldadas a ponto, que apresentaram valores inferiores, mas próximos aos obtidos nas juntas rebitadas. Análises microestruturais e de microdureza foram realizadas para elucidar alguns resultados dos ensaios executados. Os ensaios de fadiga foram executados sob controle de carga, com razão de carga R=0,1, em corpos de prova confeccionados com os parâmetros que geraram os melhores resultados em ensaios de cisalhamento em tração. Para as juntas soldadas, uma técnica de monitoramento de defeitos (MCV monitoramento comparativo de vácuo), baseada na diferença de pressão de vácuo, foi utilizada apresentando bons resultados. Apesar de resultados similares em ensaios de cisalhamento em tração, as juntas soldadas apresentaram vida bastante inferior nos ensaios de vida à fadiga, quando comparadas com as juntas rebitadas. / The main aim of this work was the determination of the parameters governing the Friction Stir Spot Welding (FSSW) of a AA2024-T3 aluminum alloy, by the obtained results comparison in pull-out and shear tensile tests and fatigue tests in lap-joints. Riveted joints of the same alloy were also tested in the same conditions for mechanical properties comparison. The main FSSW process parameters were: plunge rate, dwell time, tool penetration and tool rotational speed. The tool penetration and the tool rotational speed parameters were focused. The shear tensile tests results allowed the lap-joint shear resistance determination, that was lower, but close, of those obtained with riveted lap-joints. Microstructure and micro-hardness analysis was carried out to elucidate some tests perfomed results. The fatigue tests was performed in load control, with load ratio R of 0,1, in a lap joint produced with the same parameters of the specimen which presented the best tensile results. For the welded joints, a monitoring defect technique (CVM comparative vacuum monitoring), difference vacuum pressure based, was used showing good results. Although similar results in shear tensile tests, the welded joints showed so lower life in the fatigue tests, when compared with riveted joints.

A soldagem a ponto por resistência é o processo mais usado na montagem de estruturas, tais como: automóveis, caminhões, aviões, vagões de trem, etc. Como exemplo, na montagem das carrocerias de automóveis são necessários em média 5.000 pontos de solda. Segundo a ANFAVEA a produção em 2010 no Brasil ultrapassou 3,5 milhões de automóveis, ou seja, aproximadamente 17,5 bilhões de pontos de solda por ano. Estes fatos evidenciam a importância deste processo de soldagem na montagem de carroceria devido a sua eficiência, rapidez e facilidade na automação. Além disso, o comportamento da soldagem a ponto por resistência é extremamente importante para a qualidade de toda a estrutura soldada. O presente trabalho será voltado para a avaliação e estudo da soldabilidade de chapas de aço de 0,8 mm, revestidas e não revestidas com zinco, na indústria automotiva, comparando-se dois equipamentos de soldagem com dois tipos de corrente de soldagem: corrente alternada (CA) e corrente contínua de média freqüência (CC). Foram feitos diagramas de soldabilidade: corrente (kA) x tempo (ms) com força constante e corrente (kA) x força (kgf) com tempo (s) de soldagem constante e localizada suas respectivas áreas comuns. Em seguida foram feitos diagramas em terceira dimensão (3D) com os três principais parâmetros (força, corrente e tempo) e localizado um ponto otimizado. Posteriormente foram analisadas, nos pontos otimizados, as dimensões geométricas do ponto através da macrografia, a resistência mecânica com ensaio de tração e, durante a soldagem, a resistência dinâmica e a energia elétrica dinâmica. Foram seguidos como requisitos técnicos para qualificação de soldagem conforme norma. Os resultados mostraram que, a soldagem em CC apresentou-se melhor em chapas sem revestimento se comparada com a soldagem em CA. E a soldagem em CA apresentou-se melhor em chapas com revestimento de zinco se comparada com a soldagem em CC. A queima do revestimento de zinco e a rugosidade superficial das chapas não afetaram a formação do ponto de solda. As durezas nas regiões da ZAC e no ponto de solda apresentaram-se maiores em chapas sem revestimento. Todos os pontos de solda com os parâmetros otimizados, encontrados pelo método apresentado neste trabalho, foram aprovados conforme norma. / Resistance spot welding is highly used in the structures assembly, such as: cars, trucks, planes, trains, etc. For example, 5.000 weld spots are necessary in an auto-body assembly. According to ANFAVEA, Brazilian production in 2010 overtook 3.5 millions of cars, in order words, around 17,5 billions weld spot per year. This fact evidences the importance of this welding process due to its efficiency, rapidity and easiness in the automation. Moreover, the resistance spot welding behavior is highly important for all the welded structure quality. This work aimed to study the weldability of zinc non-coated and zinc coated steel sheets of 0,8 mm thickness for automotive industry, comparing two welding equipments with two kinds of current: alternating current (AC) and medium frequency direct current (DC). The weld lobes are presented: current (kA) x time (s) with constant force (kgf) and current (kA) x force (kgf) with constant welding time. After, lobes in third dimension (3D) with the three main parameters were done (force, current and time) and located the great point. Afterwards, the great points were characterized using, optic metallografly, mechanical resistance with tensile-shear test and, during welding, the dynamic resistance and dynamic energy. The describe techniques were followed as technical requisites according to the standard. The results showed that the welding in DC presented better performance in uncoated sheets when compared to the AC welding. And the AC welding presented better performance in zinc coated sheets when compared to DC welding. Zinc coating burning and sheets surface roughness did not affect the spot weld formation. The hardness in the HAZ regions and in the spot weld was higher in uncoated sheets. All spot welds with the optimized parameters, found by the method presented in this work, were approved according to the standard.

A soldagem a ponto por resistência é o processo de união de partes mais comum utilizado na indústria automobilística. Vários métodos de representação de pontos de solda estão disponíveis, e este trabalho se propõe comparar dois métodos de modelagem de pontos de solda através de um estudo de correlação, em termos da força máxima suportada pela junta soldada, entre os resultados de testes virtuais e de laboratório. Estes métodos de representação dos pontos de solda são os elementos de viga e os elementos sólidos. Os testes utilizados neste estudo de correlação carregam o corpo de provas sob ação de forças de cisalhamento e normal aplicadas diretamente no ponto de solda. E para completar este estudo de correlação, o entendimento dos modos e critérios de falha de juntas soldadas também é necessário. Os modelos de elementos finitos dos corpos de prova gerados para serem testados sob condições de cisalhamento e de força normal são detalhados pela apresentação dos tipos de materiais, elementos, formulações de contato e carregamento utilizados. Estes modelos foram analisados pelo LS-DYNA, que é um código de elementos finitos de propósito geral para análise de respostas dinâmicas provenientes de grandes deformações de estruturas. Da mesma forma, os testes físicos e os corpos de prova utilizados são detalhados, e os resultados provenientes dos testes são comparados aos obtidos nas simulações. Dos resultados obtidos, a melhor correlação se deu com a utilização do elemento sólido para representar o ponto de solda, com diferenças entre os resultados físicos e virtuais em torno de 4%. Uma representação simples do ponto de solda é indicada no caso de modelos completos e para aplicações na indústria, alguns fatores, tais como a modelagem da ZTA, podem ser suprimidos. Uma breve descrição do processo de soldagem a ponto, alguns tópicos da análise de elementos finitos não-linear e algumas características do LS-DYNA, além das conclusões e recomendações para trabalhos posteriores, completam este estudo. / Resistance spot welding is the most common jointing process of parts used in automotive industry. Several methods to represent spot welds are available, and the purpose of this work is to compare two different methods of spot weld modeling through a correlation study, taking into consideration the maximum force withstood by the welded joint, between virtual and lab test results. These spot weld representation methods are beam and solid elements. The tests used in this correlation study load the specimens under pure shear and pure normal forces. And in order to complete this correlation study, the understanding of the failure modes and criteria is also necessary. The specimens finite element models generated to be tested under purê shear and normal conditions are detailed by the presentation of materials, elements contact formulations and loading types used. These models were analyzed by the LS-DYNA, which is general purpose finite element code for analyzing the large deformation dynamic response of structures. As well, the physical tests and used specimens are detailed, and the results from the tests are compared to the results obtained in the simulations. Taking the obtained results, the best correlation was found using solid elements to represent the spot weld, due to differences between the physical and the virtual results about 4%. A simple representation of the spot weld is indicated in case of a complete model, and for the industry application, some factors such as the HAZ, may be suppressed. A brief description of the spot welding process, some topics of the non-liner finite element analysis and some features of the LS-DYNA, and also the conclusions and recommendations for future works, complete this study.

A crescente exigência do setor automotivo por maior produtividade com redução de custos, aliada aos novos materiais que compõe as carrocerias e seus revestimentos, levou ao estudo da correlação da resistência dinâmica, força de expansão térmica e indentação, com a formação do ponto de solda, a fim de qualificar e controlar a soldagem por resistência a ponto. Para o estudo ter validade prática a qualificação da solda, os parâmetros de soldagem e corpos de prova foram definidos conforme norma AWS-SAE D8-9M 2002. Os corpos de prova para os ensaios foram retirados das chapas que compõe uma carroceria veicular. O cabeçote de soldagem foi projetado e construído seguindo os padrões de máquinas industriais. Os instrumentos de medição foram desenvolvidos especificamente para atender as condições industriais da soldagem por resistência. Os ensaios simularam as variações de parâmetros e produção dos pontos de solda conforme ocorre na indústria automobilística. As análises foram realizadas através da comparação gráfica e matemática do comportamento das grandezas medidas com a qualificação dimensional do ponto. A correlação, apresentada, distingue chapas de espessuras diferentes, materiais de revestimento, variação de parâmetros, erros de posicionamento (ponto torto), expulsão de material (flash), variações na formação do ponto (undersize) e o mais importante, desgaste dos eletrodos. Esta correlação permite criar um sistema de qualificação e controle do ponto de solda. / The growing demand from the automotive sector for greater productivity, reduced costs, combined with new materials that make up their bodies and coats, led to the study of the correlation of the dynamic resistance, thermal force expansion and indentation, with the formation of the spot weld, in order to qualify and control the resistance spot welding. For the study to be valid practicing the qualification of spot weld, welding parameters and specimens were define according AWS - 9M SAE D8 2002 standard. The specimens for testing were removed from the sheets that make up a vehicle body. The welding head was designed and built according the standards of industrial machinery. Measuring instruments were developed specifically to meet the conditions of industrial resistance welding. The tests simulated the variations of parameters and production of welding spots as occurs in automotive industry. The analyzes were performed through the graphical comparison and mathematical behavior of measured quantities with dimensional spot qualification. The correlation presented distinguishes sheets of different thicknesses, coating materials, variation of parameters, positioning errors (crooked point), expulsion of material (flash), variations in spot formation (undersize) and most important, wear of the electrodes. This correlation allows to create a system of qualification and control of the spot welding.