Thesis (Ph. D.)--University of Rhode Island, 2006. / Includes bibliographical references (leaves 213-220).

Made available in DSpace on 2014-06-11T19:27:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-01-29Bitstream added on 2014-06-13T20:55:47Z : No. of bitstreams: 1 000756231.pdf: 3428054 bytes, checksum: d0cdfa43da88169d40275d58b3369674 (MD5) / O presente trabalho apresenta um modelo matemático para a análise da conformação de chapas metálicas por dobramento considerando o atrito entre a ferramenta e a peça, com o objetivo de obter uma estimativa para a carga de conformação e do valor do coeficiente de atrito no processo de conformação por dobramento . O modelo foi desenvolvido com base nas teorias plásticas pelo método da energia de conformação utilizando o critério de escoamento de von-Mises, conforme apresentado por Chakrabarty, Mellor e Al-Qureshi. Para a análise dos resultados, foram consideradas as propriedades geométricas que definem a peça e a matriz de conformação, bem como as propriedades do material. Os resultados teóricos para a tensão residual para o trabalho total de conformação, para a força de conformação e para o raio final de conformação são obtidos em função das propriedades geométricas do processo e das propriedades do material / The present work presents, a mathematical model for analysis the conformation of sheet metal folding considering the friction between the tool and workpiece to obtain an estimate for the conformation load and the value to coefficient friction. The model was developed based on the theories the energy method of the plastic deformation using the yield criterion of von Mises as presented by Chakrabarty, Mellor e Al-Qureshi. For the analyze the results, were considered the geometric properties that define the workpiece, the conformation tool and the material properties. The theoretical background for the residual strain the total work of conformation, force of conformation and the forming results, are obtained according the process, the geometrical properties and material properties

Orientador: Ângelo Caporalli Filho / Co-orientador: Anselmo Monteiro Ilkiu / Banca: Peterson Luiz Ferrandini / Banca: Miriam de Lourdes Noronha Motta Melo / Resumo : O presente trabalho apresenta um modelo matemático para a análise da conformação de chapas metálicas por dobramento considerando o atrito entre a ferramenta e a peça, com o objetivo de obter uma estimativa para a carga de conformação e do valor do coeficiente de atrito no processo de conformação por dobramento . O modelo foi desenvolvido com base nas teorias plásticas pelo método da energia de conformação utilizando o critério de escoamento de von-Mises, conforme apresentado por Chakrabarty, Mellor e Al-Qureshi. Para a análise dos resultados, foram consideradas as propriedades geométricas que definem a peça e a matriz de conformação, bem como as propriedades do material. Os resultados teóricos para a tensão residual para o trabalho total de conformação, para a força de conformação e para o raio final de conformação são obtidos em função das propriedades geométricas do processo e das propriedades do material / Abstract: The present work presents, a mathematical model for analysis the conformation of sheet metal folding considering the friction between the tool and workpiece to obtain an estimate for the conformation load and the value to coefficient friction. The model was developed based on the theories the energy method of the plastic deformation using the yield criterion of von Mises as presented by Chakrabarty, Mellor e Al-Qureshi. For the analyze the results, were considered the geometric properties that define the workpiece, the conformation tool and the material properties. The theoretical background for the residual strain the total work of conformation, force of conformation and the forming results, are obtained according the process, the geometrical properties and material properties / Mestre

Les procédés de mise en forme des tôles minces sont largement utilisés dans l'industrie. L’utilisation optimale des alliages légers ou des aciers à haute résistance, propices à des économies d’énergie dans le domaine des transports, nécessite une connaissance approfondie de leurs limites de formabilité. Classiquement, la formabilité d’une tôle est caractérisée par l’apparition d’une striction localisée. Cependant, pour des chargements spécifiques (chemins de déformation complexes ...), la rupture caractérise la formabilité du matériau, la courbe limite de formage à rupture (CLFR) plutôt que celle à striction (CLFS) doit alors être considérée. Pour identifier la CLFS et la CLFR pour des chemins de déformation linéaires et non-linéaires, les méthodes conventionnelles requièrent différents dispositifs expérimentaux et différentes formes d'éprouvette pour atteindre une large gamme de chemins de déformation. L'essai de traction biaxiale, associé à une éprouvette cruciforme, est possible pour la réaliser. De plus, le changement de chemin est activé au cours de l’essai, sans déchargement. Le premier objectif de cette étude est de montrer que l'essai de traction biaxiale, associé à une forme unique d'éprouvette cruciforme, permet de tracer la CLFS et la CLFR pour plusieurs chemins de déformation, qu’ils soient linéaires ou non-linéaires. En premier lieu, des essais ont été réalisés sur des tôles d’alliage d’aluminium 5086 (épaisseur initiale de 4 mm) à partir d’une forme d’éprouvette déjà proposée au laboratoire. Une nouvelle forme d'éprouvette cruciforme a été proposée pour des tôles moins épaisses (2 mm), plus répandues. Cet éprouvette a été validée pour étudier la formabilité d’un acier dual phase DP600 pour plusieurs chemins de déformation. Le deuxième objectif est de discuter la validité de critères classiques de rupture ductile. Pour les deux matériaux, un critère a finalement été identifié pour prédire assez précisément les résultats expérimentaux. / Sheet metal forming is very common in industry for producing various components. The optimal use of light alloys or high strength steels in transportation for energy economy, requires in-depth analysis of their formability. Usually, the formability of sheet metal is controlled by the onset of localized necking. However, under specific loadings (complex strain paths...), fracture characterizes the formability and the forming limit curve at fracture (FLCF) instead of the forming limit curve at necking (FLCN) should be considered. For identifying FLCN and FLCF under linear and non-linear strain paths, conventional methods require different experimental devices and geometrical specifications of specimen to cover a wide range of strain paths. However, using the in-plane biaxial tensile test with just one shape of cruciform is sufficient for that, even changes of strain path without unloading can be made during the test. The first objective of this study is to show that the in-plane biaxial tensile test with a single type of cruciform specimen permits to investigate the FLCN and FLCF of sheet metals under different linear and non-linear strain paths. Firstly, the forming limit strains at fracture of AA5086 sheet (t=4 mm) under linear and non-linear strain paths have been characterized, by testing an existed dedicated cruciform specimen. Thinner sheet metals are often used in industry, so a new shape of cruciform specimen with an original thickness of 2 mm was proposed. This specimen is successfully used to investigate the formability of DP600 sheet under linear and two types of non-linear strain paths. The second objective is to discuss the validity of commonly used ductile fracture criteria to predict the onset of fracture. Some ductile fracture criteria were used to produce numerical FLCFs for AA5086 and DP600 sheet. Finally, for the two tested materials, it is possible to find a criterion to predict the experimental FLCFs for either linear or non-linear strain paths.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2016. / The purpose of this study is the optimisation of the stamping analysis process in order to investigate the possible reasons for the part failure. (Altan & Vasquez, 2000) have conducted similar research to optimise a forming process. However, they focussed on dies for a forging process and in this study, we are looking at cold forming and this study is also different in that we are trying to reduce the number of stages while maintaining the formability. Formability is based on the dimensional conformance of the final part with additional criteria being the thinning, appearance of wrinkling, dynamic effects leading to the localisation of strain, cracking and residual stress. A numerical modelling procedure that is close enough to the real process is used to investigate the effects of changes in the frictional contact that would correspond to lubrication and also the effect of adding draw beads to the forming tools to change the frictional contact. We also investigated the effect of using a different material in terms of meeting the design requirements. Experimental results for comparison are available for certain of the stamping processes investigated that were tested in pre-production. The finite element simulation is used to account for all residual thinning, stress and strain of the multi-stage forming process to ensure optimum thickness changes of the sheet at each stage. The variations of material and manufacturing parameters are established to accurately predict the behaviour of this specific forming process. The material model required to meet physical experiments is deduced from the results of standard tensile tests and fitted to the Hill’s 48 Law for Work Hardening. The commercial packages Ls-Dyna with Dynaform and Pam-Stamp software are used for the simulation to produce 2 results for comparison.

HUDOUSEK Jiří: Drawing of a tin-coated metal sheet. The project elaborated in frame of master studies is submitting design of the given part production - business card case from tin-coated metal sheet by deep drawing technology. From a variations of the design of the product has been chosen option, when the case is assembled from two identical drawn parts which form the bottom and the lid of the component, the connection of these two parts is arranged by a spacer in form of a plastic insert on which the metal parts are attached. Based on the literary survey and calculations drawing in die with blankholder was designed for metal parts production, according to the force needed and tool size a hydraulic press ZH 100 was selected. Part of the work is the process parameters determination, technical and economic evaluation and drawing documentation.

Master thesis reports questions about purchasing supplies for stamping shop. It solves task, that is cheaper buy blanks, or buy coils and cut them in free time of Raster 250 press. Thesis contains a design of cutting tools for production rectangular and trapeze shaped blanks. Tool for cutting of rectangular blanks is documented with drawings of assembly and main parts. The project was verified in techno-economic summary including repayment time calculation.

Master’s thesis deals with application of lasers in manufacturing, mainly with the technology of cutting material. This technology is compared with the technology of punching and cutting sheet metal, with the aid of control specimens. The parameters of surface structure, dimension accuracy and appearance of cut-ting surfaces are compared. By consensus of results the recommendation for practical realization was created.

Strain path changes are common in complex automotive stampings, where sheet materials undergo a combination of drawing, stretching, and bending to achieve a desired part shape. Aluminum sheet alloys are increasingly used in vehicle structure light-weighting efforts, but limited formability and high levels of springback present challenges to the manufacturing and assembly processes. The current work explores springback levels in AA6016-T4 sheet after various pure bending operations, where sheets were first pre-strained in uniaxial, plane-strain, and biaxial tension. Finite element modeling of the pre-straining and subsequent bending operations will be performed using both isotropic and elasto-plastic self-consistent (EPSC) crystal plasticity approaches. Because the EPSC model incorporates backstresses informed by GND content, as measured via high-resolution EBSD, the predictions are more accurate than those of the isotropic model. The benefits and limitations of the current EPSC model, regarding accuracy of the predictions for the proposed strain path changes, are discussed.

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