The numerical forecasting of car body construction processes is already being used in industry to provide support in the ramp-up process. However, long calculation times are stretching the finite element method (FEM) to the limit, in particular when analyzing the effect of the variation of an input variable on one or more dependent variables. Moreover, there is still a need for experienced users to separate relevant from irrelevant parameters and to determine their variation. This paper presents a method that makes it possible, based on stochastic experimental design (DOE) in combination with both principle component analysis (PCA) and singular value decomposition (SVD), to create mathematical models that separate relevant from irrelevant input variables and that represent the effect of individual variables on all part or assembly areas by means of a variance-based sensitivity analysis. The method is verified in a case study based on realistic front hood geometry. The study examines the deep-drawing process steps as well as the geometrical accuracy in a measuring device. It is shown that it is possible to represent the effects of the most important variables from these processes on the strain and geometry parameters of the car body part and to vary these, based on a model function, interactively
The use of FEM (finite element method) to assistant in ramp-up processes of car body construction lines is increasing, thanks to developments in recent years [1-3]. Car body manufacturing begins with sheet metal forming, while in subsequent steps the inner structures of the vehicle are assembled and connected to the outer skin by hemming. With reference to the current state of the art, there is no methodology which can reliably predict the dimensional accuracy of body parts through metal forming [4].Additionally, several methods to predict the distortion of joining and the dimensional effect of clamping during the assembly process were presented and validated [4-11]. Dimensional effects of the clamping process are basically the result of a deliberate alignment, other than the given values of construction to compensate dimensional inaccuracy of single parts from the body shop. These deliberate alignments are generally effected through a translation of clamps and pins in the clamping device. Until now, most of the methods of clamping and joining simulation presented have been verified using academic samples.In this report, the quality of forecasting in real problems during a ramp-up process will be verified and expanded. As part of a national project, co-funded by Sächsische Aufbaubank (SAB), the potential of FEM to assist in the ramp-up process were reviewed in a cooperative effort between Porsche Leipzig GmbH and Fraunhofer Institute for Machine Tools and Forming Technology (IWU). Furthermore, it will be shown that developed methods are able to represent the influence of deliberate positioning of clamps in complex samples. For the first time the quality of forecasting through the translation of locating pins is numerically and experimentally qualified.
The manufacturing process of body parts starts with the step of sheet metal forming. The single parts, produced at the press shop, are put into clamping devices in order to align and to fix them. The fixation takes part before further operations like joining can be carried out. In order to simulate the process chain of add-on body parts realistically, the clamping process (closing the clamping device) has to be taken into account. The stationary surfaces of a clamping device are called passive and the moveable surfaces are called active surfaces. If the clamping process is calculated by means of active surfaces, their positions need to be measured in the state of a closed clamping device. While the passive surfaces of a body construction device can be measured with high reproducibility, the measurement of active surfaces in the state of a closed device is impracticable because of the loss of accessibility. Furthermore, if the parts to be clamped or the position of the clamping device differ from their designed position, the assembly works like a flat spring against the clamping device force in all spatial directions. The active surface does not reach the position which was measured before. In order to take these facts in clamping simulations into account, the end position of the active surfaces should be known. A clamping device concept on the basis of a measuring probe for optical measurement systems was developed. It is possible to determine the position of active surfaces with high reproducibility while the parts are clamped. It can be shown, that the presented clamping device concept contributes to significantly better results of clamping simulations. Thus a better starting basis for further simulations along the process chain is offered.
This paper presents a method with whose help it is possible, to quickly and precisely predict the influence that thermal spot-shaped joining processes has on the dimensional stability of complex component structures even in early planning phase. The welding distortion is calculated in the context of reduced computing time, based upon an experimentally calibrated mechanical substitute model. This expands existing approaches of substitute models and defines both an experimental and numerical procedure for creating adequate calibration samples. In turn, this makes use of the potential obt ained for standardizing the experimental basis for calculating and modelling the distortion to automatically carry out painstaking calibration processes in simulations and experiments in future based upon mathematical model functions. Finally, the limits to applying the substitute spot welding model are verified with reference to its predictability using a complex joining situation of a car body construction.
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