Subtle cosmetic defects in automotive skin panels

Cosmetic defects such as 'hollows' are the result of deviations in a skin panel. These deviations are usually too small and local to be detected by discrete measurements of the panel but become visually apparent after the application of paint. As a result, the perceived quality of a panel may become unacceptable and considerable time may be dedicated to minimizing their occurrence through tool modifications. This paper proposes that there are three aspects to the problem: the springback or buckling of the panel, the optics of the painted panel and the ability of an observer to perceive the defect. In particular, it will be argued that hollows cause optical distortions that inform the human eye of the presence of a defect. The paper then suggests that signal processing techniques, in particular the wavelet transform, provide a simple way of locating and quantifying the severity of these defects. The transform was applied to two physical parts and a simulation model