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A blankholder is used to hold the edges of metal sheet while it is being formed by a matrix and a punch. An efficient way to design a stamping die is to integrate the blankholder plate into the die structure. This would eliminate the time and cost to manufacture blankholder plates. The integrated structure is called integrated blankholder. The main focus of this thesis is structural analysis and optimization of the integrated blankholder. The structural analysis of the integrated blankholder model (used for the production of doors of Volvo car model V70) is performed using Hypermesh and Abaqus. The FE-results were compared with the analytical calculations of the fatigue limit. To increase the stiffness and reduce the stress levels in the integrated blankholder, topology and shape optimization is performed with Optistruct. Thereafter, a CAD model is set up in Catia based on the results of optimization. Finally, structural analysis of this CAD model is performed and the results are compared with the original results. The results show reduction in stress levels by 70% and a more homogeneous stress distribution is obtained. The mass of the die is increased by 17 % and in overall, a stiffer die is obtained. Based on the simulations and results, discussion and conclusions are formulated.

Electromagnetic (EM) forming is a high-speed forming process that uses the forces induced on a conductive workpiece by a transient high frequency current to form the workpiece into a desired shape. This thesis presents the results of an experimental and numerical study carried out to determine whether an EM forming process could be used to sharpen the radius of part pre-formed using a stamping process. Two processes were studied; a single step EM forming operation and a “hybrid forming” operation consisting of a conventional pre-forming step and an EM corner fill, both considering aluminum alloy AA 5754. The single step EM process proved unable to form acceptable samples due to excessive sample distortion, but was used to gain insight into the EM forming process. The hybrid operation consisted of pre-forming 1 mm AA 5754 sheet into a v-shape with a 20 mm outer radius using a conventional stamping operation and then reducing or “sharpening” the radius to 5 mm using EM forming. Sharpening the radius to 5 mm using conventional stamping was not achievable. The hybrid operation proved successful in forming the 5 mm radius, thus demonstrating that the material could be formed beyond its conventional formability limit using the hybrid operation. Numerical models were used to gain insight into the processes and the challenges involved in their numerical simulation. The numerical simulations showed that EM corner fill operation produces very high strain rates (10,000- 100,000 s-1) and complex three dimensional stress and strain states. The effect of the high strain rates could not be properly assessed, since no constitutive data was available for such high strain rates. The predicted stress states show that the process was not plane stress and that large through-thickness compressive stresses are produced that are favorable to damage suppression and through-thickness shear strains that increase ductility. The high strain rates and the complex stress and strain states are considered the likely causes for the observed increase in formability. The models provided valuable insight, but did not predict the final shape exactly and the possible reasons behind this are analyzed. The research indicates that features that are not achievable using traditional stamping techniques can be obtained with the hybrid EM forming process.

The design of new forming tools get more problemtic as the geometries get more complicated and the materials less formable. The idea with this project is to evaluate if an implementation of a simulation software in the designing process, to simulate the forming process before actually building the tools, could help Duroc Tooling avoid expensive mistakes. To evaluate this, the commercial FEM simulation software LS-DYNA was used in a complicated project, where the design of the forming tools for forming a girder was considered. The main objective was to avoid cracking and severe wrinkling which may result in the forming process. With help of simulations a stable forming process which did not yield cracks or severe wrinkling, was eventually found. The girder was almost impossible to form without cracking, but the breakthrough came when we tried to simulate a preforming step which solved the problem. Without a simulation software this would never have been tested since it would be to risky and expensive to try an idea which could turn out to be of no use. The simulations also showed that the springback - shape deformation occuring after pressing - was large and hard to predict without simulations. Therefore, the tools were also finally springback compensated. We concluded that simulations are very effective to quickly test new ideas which may be necessary when designing the tools for forming complicated parts. Simulation also provided detailed quantitative information about the expected cracks, wrinkles, and weaknesses of the resulting pieces. Even though there is cost associated with simulations, it is obvious from this project that a simulation software is a must if Duroc Tooling wants to be a leading company in sheet metal forming tools, and stand ready for the higher demands on the products in the future.

Electromagnetic (EM) forming is a high-speed forming process that uses the forces induced on a conductive workpiece by a transient high frequency current to form the workpiece into a desired shape. This thesis presents the results of an experimental and numerical study carried out to determine whether an EM forming process could be used to sharpen the radius of part pre-formed using a stamping process. Two processes were studied; a single step EM forming operation and a “hybrid forming” operation consisting of a conventional pre-forming step and an EM corner fill, both considering aluminum alloy AA 5754. The single step EM process proved unable to form acceptable samples due to excessive sample distortion, but was used to gain insight into the EM forming process. The hybrid operation consisted of pre-forming 1 mm AA 5754 sheet into a v-shape with a 20 mm outer radius using a conventional stamping operation and then reducing or “sharpening” the radius to 5 mm using EM forming. Sharpening the radius to 5 mm using conventional stamping was not achievable. The hybrid operation proved successful in forming the 5 mm radius, thus demonstrating that the material could be formed beyond its conventional formability limit using the hybrid operation. Numerical models were used to gain insight into the processes and the challenges involved in their numerical simulation. The numerical simulations showed that EM corner fill operation produces very high strain rates (10,000- 100,000 s-1) and complex three dimensional stress and strain states. The effect of the high strain rates could not be properly assessed, since no constitutive data was available for such high strain rates. The predicted stress states show that the process was not plane stress and that large through-thickness compressive stresses are produced that are favorable to damage suppression and through-thickness shear strains that increase ductility. The high strain rates and the complex stress and strain states are considered the likely causes for the observed increase in formability. The models provided valuable insight, but did not predict the final shape exactly and the possible reasons behind this are analyzed. The research indicates that features that are not achievable using traditional stamping techniques can be obtained with the hybrid EM forming process.

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This thesis explores opportunities in the mathematical modelling of metal rolling processes, specifically asymmetrical sheet rolling. With the application of control systems in mind, desired mathematical models must make adequate predictions with short computational times. This renders generic numerical approaches inappropriate. Previous analytical models of symmetrical sheet rolling have relied on ad hoc assumptions about the form of the solution. The work within this thesis begins by generalising symmetric asymptotic rolling models: models that make systematic assumptions about the rolling configuration. Using assumptions that apply to cold rolling, these models are generalised to include asymmetries in roll size, roll speed and roll-workpiece friction conditions. The systematic procedure of asymptotic analysis makes this approach flexible to incorporating alternative friction and material models. A further generalisation of a clad-sheet workpiece is presented to illustrate this. Whilst this model was formulated and solved successfully, deterioration of the results for any workpiece inhomogeneity demonstrates the limitations of some of the assumptions used in these two models. Attention is then turned to curvature prediction. A review of workpiece curvature studies shows that contradictions exist in the literature; and complex non-linear relationships are seen to exist between asymmetries, roll geometry and induced curvature. The collated data from the studies reviewed were insufficient to determine these relationships empirically; and neither analytical models, including those developed thus far, nor linear regressions are able to predict these data. Another asymmetric rolling model is developed with alternative asymptotic assumptions, which shows non-linear behaviour over ranges of asymmetries and geometric parameters. While quantitative curvature predictions are not achieved, metrics of mechanisms hypothesised to drive curvature indicate these non-linear curvature trends may be captured with further refinement. Finally, coupling a curved beam model with a curvature predicting rolling model is proposed to model the ring rolling process. Both of these parts are implemented but convergence between them is not yet achieved. By analogy this could be extended with shell theory and a three-dimensional rolling model to model the wheeling process.

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