Predicting dimensional accuracy of mechanical joined car body assemblies
Mechanical joining of complex car body components is an essential part of the lightweight construction concepts in the field of car body manufacturing. Besides the mechanical behavior of the joints the influence on the dimensional accuracy is of particular interest as joining techniques like clinching or self-piercing riveting cause distortion comparable to spot welding. In recent years, a lot of simplified models using the finite element method (FEM) to predict the distortion of assemblies caused by welding (weld seams, spot welds) were presented and commercialized. In contrast to thermal joining technologies, there are no such simplified models with practical relevance existing in the mechanical joining technology sector. Simulating mechanical joining techniques was basically feasible by models consisting of small volume elements and is more and more used to optimize process parameters. The use of volume elements implicates high calculation time and is not applicable to predict the distortion of large sheet metal assemblies. Along the process chain of car body assemblies quick as well as accurate FE-methods are required. This paper indicates that a transmission of calculation methods from thermal to mechanical joining technologies is not directly possible due to technological differences. Furthermore a new method to predict distortion caused by different mechanical joining technologies including effects from previous forming processes and clamping conditions is presented. The validation of the simplified model takes place due to an extensive design of experiments. In the course of experiments of the simplified model approach, it can be proved that the distortion of simple as well as of complex samples can be reliably predicted. The agreement between reality and simulation comes to more than a ninety percent average. In addition, a method to validate simulation methods with varying designs of the assembled parts along the entire process chain of car body assemblies is presented.