Springback Simulation of the Process Chain Press Line Forming and Roller Hemming Processes

Abstract

In recent years the process simulation of entire manufacturing chains in sheet metal forming has gained more ground on its way to be established in the validation of feasibility and the meeting of quality targets. Nowadays, especially the simulation of manufacturing automotive sheet metal components such as doors, hoods roofs etc., using the finite element analysis, belongs to state of the art in the development process of sheet metal components. The different joining technologies in the bodyshell work, such as riveting, welding etc., can be simulated by numerical methods. Rarely are any of these methods linked to the forming simulations of the previous process step. Further developments in this field should deal with new strategies, linking both the forming simulation and the joining simulation. Regarding the process chain press line forming and bodyshell work, the prediction of springback of closure assemblies is of special interest, and thereby new strategies for springback compensation have to be developed in an early stage of product development. Until now, only few experiences have been gained concerning application of method to calculate springback of an assembly, so far a reliable comparison between simulation and reality is required. For this reason in this paper a closer examination of an automotive hood assembly was carried out to develop and to validate a corresponding simulation model. Based on close-to-production experiments and optical surface measurements of outer skin components (doors, bonnets, trunk lids etc.) and their assembly prior start of series production, a new simulation strategy was developed for a consistent process chain for the press plant and bodyshell work. The assembly in this example was comprised of an inner and outer panel. For forming objectives of both parts, finite element simulations were conducted, including secondary forming operations, as for instance trimming and flanging including individual unloading sequences. In a following simulation step both parts were joined together by roller hemming. Finally, a springback analysis of the assembly was also conducted. The simulation method illustrates the possibility of predicting springback of assemblies. Furthermore, the experiments and simulations show, that the springback of the assembly leads to different final shapes than those obtained from individual components. With this method it is possible to predict the final shape and the influence of the individual components on shape and dimensional accuracy, aiding the optimization of the assembly process.