Springback measuring and curvature evaluation for sheet metal forming

Trial and error is still an important method to control the springback of complicate-shaped stampings. According to the theory of plastic bending, the springback caused by membrane force and bending moment is related to Gaussian curvature and mean curvature respectively. A method for calculating the curvatures of measured data is proposed in this paper. Firstly, the measured points near to the target points are fitted to a quadric surface; then the Gaussian curvature and mean curvature are calculated and their change is used to indicate springback. This method can be used for any complicate shapes and is helpful for analyzing the cause and trend of springback. The results showed that this method more precisely reflects the curvature change of local area than global fitting methods and hence can indicate more accurately the curvature change caused by springback.