A Visual Technique to Determine the Forming Limit for Sheet Materials 2002-01-1062
The forming limit diagram of sheet materials has been used as an effective quality assurance tool in the stamping industry for almost forty years. Empirical relations have been established to predict the position of the Forming Limit Curve (FLC) in strain space for many grades of automotive sheet steel. Nevertheless, experimental FLC determination continues to be required not only for new materials (new generation high strength steels, aluminum alloys, etc.) but also to evaluate manufacturing processes where a prestrain is applied prior to the final forming operation.
A variety of testing methods has been used to determine limiting strains in sheet metal samples for a range of forming modes. Also, various techniques have been developed to determine the onset of necking in the formed samples. The purpose of this paper is to present the details of a visual method for determining the occurrence of incipient necking. By using this technique in conjunction with an accurate strain measuring system, limiting strains can be obtained and the FLC established.
This experimental technique has been used to determine the FLC for several automotive sheet steels and has been shown to provide consistent and reliable data, albeit slightly more conservative than the FLC obtained with other techniques.