Asymmetrical roll bending process study : dynamic finite element modeling and experiments

Roll bending is an efficient metal forming technique, where plates are bent to a desired curvature using forming rolls. This type of sheet forming process is one of the most widely used techniques for manufacturing axisymmetric hollow shapes. Moreover, this process is beginning to be taken into serious consideration by industries for producing large, thick parts such as the conically shaped crown of a Francis turbine runner or of a wind turbine tower.
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\nBecause of the numerous processing parameters, reducing the bending force and improving the accuracy of the final shape are significant challenges in the roll bending process. Therefore, the primary aim of this research is to find the strategies for reducing forming forces and improving final part quality by employing numerical and experimental methods. In this thesis, a 3D dynamic Finite Element (FE) model of an asymmetrical roll bending process is developed using the Ansys/LS-Dyna software. The simulation results are then compared with experiments performed with instrumented parts and roll bending machine. The parameters that affect the accuracy of the final shape, the bending forces and the residual strain left in the formed plate have been investigated. Applying this 3D dynamic FE model in an industrial context may predict the forming forces or the accuracy of the final shape’s radius and thus will decrease the setup time before manufacturing.
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\nThe forming forces can be reduced by heating the plate. In this research, the relationships between the heating plate temperature and the output parameters of roll bending process such as applied forces and final shape quality have been studied by performing FE simulation and analytical computations. These results yield to a better understanding of the mechanism of the process and provide an opportunity for the design of an efficient heating system to control the heat energy to be input in the plate during the roll bending process.
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\nThis research also proposes a new, simple approach for reducing flat areas and forming forces. This approach includes moving the bottom roll slightly along the feeding direction and adjusting the bottom roll location. The FE results indicate that this new approach effectively minimizes the flat area extents and reduces also the forming forces.

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