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.

No abstract

Modern car-body design entails increasing requirements for the dimensional accuracy of outer car-body panels. However, tolerance limits to be met in this regard are based on specifications from component engineering aimed at ensuring dimensional accuracy of the product, less on real structural springback behaviour of outer car-body panels. Process-reliable tolerance limits for outer car-body panels can be characterized by a bandwidth in springback variation caused by fluctuations in material characteristics and process parameters during production. Differences between assumptions from component engineering and real structural springback behaviour of outer car-body panels thus leads to avoidable iterative corrections in die manufacturing and following processes. Therefore, the goal of this research work presented in this paper is to predict springback variation potentially occurring during production already in the virtual design stage of a car-body and hence set process-reliable tolerance limits. Stochastic sheet metal forming simulation is used for prediction of springback variation. Here, deterministic multi-stage springback simulation of a sidewall panel is extended by stochastic variation of material properties and process parameters. Simulation results are validated by measurement reports from series production. Results presented show strong fit in characteristics of springback variation between stochastic simulation and series measurement reports. In future, stochastic simulation results can be fed back into component engineering, making die manufacturing and following joining and assembly processes more effective.

Effizienzsteigerungen in Presswerken aufgrund erhöhter Hubzahlen stellen Werkzeugkonstrukteure vor Herausforderungen. Die Beschleunigungsvorgänge bewegter Massen werden für servo-mechanische Pressen zu kritischen Belastungen. In Folgeoperationen resultieren durch Niederhalter stoßartige Belastungen der Werkzeugstruktur. Der Beitrag stellt einen Versuchsaufbau vor, der zur Validierung von Modellen der Stoßbelastungen entwickelt wurde. Dieser erlaubt die Untersuchung bei Variation der Betriebsparameter.   With increased efficiency in press shops due to higher stroke rates of series presses, die designers are facing a challenge. Limiting factors are acceleration effects of heavy weighing moving structures in servo-mechanical presses. In trimming and restriking operations the part holder results in impact loads applied onto the structure. This paper presents a tool setup for investigating part holder impacts. By varying process parameters, the tool allows for analyzing occurring impact loads.

In recent decades, numerical simulation methods have become increasingly important in car body engineering to achieve the high dimensional quality requirements for closure assemblies like bonnets, doors and tailgates. In order to model the entire manufacturing process, latest research works have been focusing on combining the finite element-based simulation models. These complete process chain simulations are able to predict the springback behaviour of the assembly before the physical realization of the tools and processes. The purpose of this study is to introduce a method to use finite element process chain simulations to analyse the structural springback behaviour of car body closure assemblies. Therefore, the numerical process chain simulations are combined with statistical and stochastic tools in order to develop a meta-model, which represents the dimensional accuracy of the investigated assembly. The presented method will then be schematically advanced to be ultimately used in different application areas like robustness and tolerance analyses.