Deep drawing operations are crucial for metal forming operations and manufacturing. Obtaining a defect free final product with the desired mechanical properties is very important for fulfilling the customer expectations and market competitions. Wrinkling is one of the fatal and most frequent defects that must be prevented. This study focuses on understanding the phenomenon of wrinkling and probable precautions that can be applied. In this study, dynamic &ndash / explicit commercial finite element code is used to simulate deep drawing process. The numerical experiments are compared with NUMISHEET benchmarks in order to verify the reliability of the finite element code and analysis parameters. In order to understand plastic wrinkling, the effect of blank holder force is investigated. Axisymmetrical numerical models of a cup are investigated with different blank holder forces. Wrinkling instability is illustrated in energy diagrams of the process. Effect of anisotropy on wrinkling is also discussed by comparing isotropic and anisotropic numerical experiments with the material as steel. Different drawbead models, both equivalent and physical, are implied to the problem and results are discussed. Besides numerical analysis, experimental verification is also conducted as conventional deep drawing operation by a hydraulic press. This yields to the ability to understand the effect of blank thickness on wrinkling formation through numerical and experimental analyses. The wave formations of different sized blanks with four different thicknesses are illustrated.

The sheet metal forming process basically involves the shaping of sheet metal of various thickness and material properties into the desired contours. This metal forming process has been extensively used by the automotive industry to manufacture both car panels and parts. Over the years numerous investigations have been conducted on various aspects of the manufacturing process with varied success. In recent years the requirements on the sheet metal forming industry have headed towards improved stability in the forming process while lowering environmental burdens. Therefore the overall aim of this research was to identify a technique for developing lubricant formulations that are insensitive to the sheet metal forming process. Due to the expense of running experiments on production presses and to improve time efficiency of the process the evaluation procedure was required to be performed in a laboratory. Preliminary investigations in the friction/lubricant system identified several laboratory tests capable of measuring lubricant performance and their interaction with process variables. However, little was found on the correlation between laboratory tests and production performance of lubricants. Therefore the focus of the research switched to identifying links between the performance of lubricants in a production environment and laboratory tests. To reduce the influence of external parameters all significant process variables were identified and included in the correlation study to ensure that lubricant formulations could be desensitised to all significant variables. The significant process variables were found to be sensitive to die position, for instance: contact pressure, blank coating of the strips and surface roughness of the dies were found significant for the flat areas of the die while no variables affected friction when polished drawbeads were used. The next phase was to identify the interaction between the significant variables and the main lubricant ingredient groups. Only the fatty material ingredient group (responsible for the formation of boundary lubricant regimes) was found to significantly influence friction with no interaction between the ingredient groups. The influence of varying this ingredient group was then investigated in a production part and compared to laboratory results. The correlation between production performance and laboratory tests was found to be test dependant. With both the Flat Face Friction test and the Drawbead Simulator unaffected by changes in the lubricant formulation, while the Flat Bottom Cup test showing similar results as the production trial. It is believed that the lack of correlation between the friction tests and the production performance of the lubricant is due to the absence of bulk plastic deformation of the strip. For this reason the Ohio State University (OSU) friction test was incorporated in the lubricant evaluation procedure along with a Flat Bottom Cup test. Finally, it is strongly believed that if the lubricant evaluation procedure highlighted in this research is followed then lubricant formulations can be developed confidently in the laboratory.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In order to get a better part quality in sheet metal forming, the rate of the material flow into the die cavity must be efficiently controlled. This control is made by a restraining force supplied either by the blankholder, the drawbeads or both. When the restraining force required is too high, the use of drawbeads is necessary, although excessive deformations may be produced. Some others disadvantages, such as difficulties of adjustment during die try-outs in order to determine the actual Drawbead Restraining Force (DBRF), may also be emphasized. To solve these problems and to reduce the number of die try-outs, which are very time consuming, accurate enough drawbeads concepts are necessary. Aiming to understand the influence of the most important parameters on the DBRF and to establish a pre-estimate DBRF theory, in this study a methodology has been developed using similitude. The data bases were achieved by Finite Element (FE) simulations done with an explicit code. Two different materials were used: A-K Steel and 2036-T4 Aluminum. The results have been compared with experimental databases of Nine(1978, 1982) and with the analytical model of Stoughton(1988). The average of absolute error with respect to experimental data bases was about 6 % and, for those cases studied, the maximum discrepancy was found to be less than 11%. For analytical ones, the average of absolute error was about 5 % and, for the cases studied, the maximum error was about 7%. Predictions made with this approach have a very good precision when compared with analytical and experimental results. For this reason, it was used as a contribution for STAMPACK®, an explicit finit element code used to simulate forming process. / Para se obter peças com a melhor qualidade possível em um processo de estampagem de chapas metálicas, a taxa de fluxo de material para dentro da matriz deve ser eficientemente controlada. Este controle é feito por uma força de retenção (FR) originada no prensachapas, nos freios de estampagem ou em ambos. Quando a FR requerida é muito alta, o uso dos freios se torna ainda mais necessário, embora excessivas deformações possam ocorrer na peça estampada por causa do contato com os freios. Outros tipos de efeitos indesejáveis decorrentes do uso deste tipo de dispositivos ainda podem ocorrer, tais como dificuldades para se determinar o valor adequado da FR, o que pode consumir muito tempo. Para se resolver estes problemas e reduzir o número das tentativas de ajustes, são necessários conceitos mais precisos sobre os freios de estampagem. Com a finalidade de se avaliar a influência dos parâmetros mais importantes na FR e de se estabelecer uma teoria para se fazer a predição da FR, desenvolveu-se neste estudo uma metodologia híbrida, empregando-se a teoria da similitude com bases de dados gerados através de simulações numéricas pelo Método dos Elementos Finitos (MEF). Os resultados foram comparados com os experimentos de Nine (1978, 1982) e com o modelo analítico de Stoughton (1988). A média dos desvios absolutos com respeito aos dados experimentais foi de 6% e, para os casos estudados, a discrepância máxima foi sempre menor ou igual a 11%. Em relação ao modelo analítico, a média dos desvios absolutos foi de 5% e, para os casos estudados, o desvio máximo nunca foi superior a 7%. Predições feitas com esta abordagem tiveram, portanto, uma boa precisão, quando comparadas com o modelo analítico e com os dados experimentais. Por este motivo, esta teoria foi aceita como contribuição para o programa STAMPACK®, um código de solução explícita utilizado na simulação de processos de estampagem de chapas metálicas. / Doutor em Engenharia Mecânica