Calculating the gravity-free shape of sheet metal parts

This paper presents an iterative finite element (FE)–based method to calculate the gravity-free shape of nonrigid parts from an optical measurement performed on a non-over-constrained fixture. Measuring these kinds of parts in a stress-free state is almost impossible because deflections caused by their weight occur. To solve this problem, a simulation model of the measurement is created using available methods of reverse engineering. Then, an iterative algorithm calculates the gravity-free shape. The approach does not require a CAD model of the measured part, implying the whole part can be fully scanned. The application of this method mainly addresses thin, unstable sheet metal parts, like those commonly used in the automotive or aerospace industry. To show the performance of the proposed method, validations with simulation and experimental data are presented. The shown results meet the predefined quality goal to predict shapes within a tolerance of ± 0.05 mm measured in surface normal direction.