Validation of the stoning method by numerical and experimental investigation of outer panels with and without surface deflections

Abstract

Surface deflections have a negative effect on the appearance of exterior body panels in the automotive industry. They occur during springback and depend on part geometry and stress states. To detect whether a produced part has surface deflections, inspection methods, such as stoning, are applied. If the part has surface deflections, the tool geometry is modified in an iterative process until no more surface deflections are detected on the produced part. Besides stoning of physical parts, surface deflections can also be detected in post-processing of a finite element simulation by use of a numerical stoning method. The advantage is that the design of the tool can be modified before it is manufactured. However, the appearance of detected surface deflections depends on the software used and its settings. Therefore, the accuracy of surface deflections detected in simulations is worth investigating. This paper describes surface deflections detected by stoning method in experiments and compares them with the numerical results from AutoForm. In doing so, the influence of the numerical settings on the appearance of the surface deflections is analyzed. For this study, various parts with door handle pockets are produced. By changing the shape of the blank, and as a consequence, also the stress state, it is possible to generate parts with surface deflections of different sizes or parts without surface deflections. A blank of AA6016 with a sheet thickness of 1.0 mm is used. The results show that it is possible to detect surface deflections in simulations accurately if suitable settings are chosen. The meshing has a significant influence on the detected surface deflection whereas the draw bead model has less of an effect.