Determining Curvature of Air Bent Parts by Digital Image Processing

The dimensional accuracy of formed components is an important issue for stamping applications. The flexibility of the air bending process involve that for different bent angles, different final bent radius are obtained. For air bending parts, springback analysis and final angle measurement have usually been considered whereas final bent radius or curvature determination is pushed into the background. Even though this parameter is a non constant geometrical feature when punch bending radius is very small and there are few mechanical methods for measuring these non constant curvatures. This paper describes the measurement procedure of final bent radius through analysis and manipulation of scanned images of bent parts. The method fits different polynomial functions on bent profiles. Once the best adjustment is chosen, a zone curvature in an air bent part is defined and the radius on punch-sheet contact is quantified. For air bending conditions of small punch radius, this technique has given good results in order to determine the main geometrical features of an air bent part: final bent angle, final bent radius and curvature zone.