Many applications of conical roll bending can be found in manufacturing industry, such as rolling a conical segment of a wind turbine tower or an alternative process of molding a large crown for a Francis turbine. This molding process could be achieved by assembling several conical segments. For the purpose of using cylindrical rolls or reusing the existing conical rolls of the kinematical conical roll bending process for non-kinematical conical roll bending process, attachments were proposed in order to reduce the velocity at the top edge of the plate. In contrast with a kinematical conical roll bending machine where no sliding exists between the plate and the rolls, the contact surface near the top edge of the plate of the three driving rolls of a non-kinematical conical roll bending machine slides on the plate due to the friction between the attachments and the plate. Therefore, the appropriate velocity at the top edge of the plate corresponding to that of the kinematical conical roll bending process can be obtained. This paper deals with the simulation analyses of the non-kinematical multi-pass conical roll bending process based on the finite element method, for example, the analyses of the applied force on the pressing roll. The components of the roll bending machine, such as the rolls and the attachments, etc. were assumed to be rigid bodies and the 4-node shell elements were used in the modeling. Bilinear material properties were used for the elasto-plasticity of the plate. Automatic node-surface contacts were chosen on the interfaces between the plate and the rigid bodies. The nonlinear equations which represent the structural dynamics with large displacement were resolved using explicit time integration. The simulations were performed under the well-known ANSYS/LS-DYNA environment. A well bent cone was obtained and compared very well with the ideal cone. The numerical simulation results show that the bent cone depends on the static and dynamic friction coefficients for a geometrical configuration with an appropriate span of the outer rolls.
Explicit dynamics finite element analyses of asymmetrical roll bending process
