A Study of Accuracy in an Intelligent V-Bending Process for Sheet Metals-Change in Young's Modulus due to Plastic Deformation and Its Effect on Springback-

An intelligent V-bending process developed by the authors is briefly described and the importance of change in Young's modulus due to plastic deformation, which influences the amount of springback and therefore the accuracy, is emphasized. The change in Young's modulus in simple tension of a cold rolled steel sheet is experimentally investigated by affixing strain gauges on the specimen. It is shown that the Young's modulus changes drastically with plastic deformation and that this is much larger than that estimated from the change in apparent density. A model that explains this phenomenon is presented. By using the experimentally derived Young's modulus, V-bending process of the same metal is simulated by the finite element method in plane strain; the amount of springback is calculated and compared with the experimental results. It is shown that the springback calculated with the commonly used value of Young's modulus is far less than the experimentally derived one and that the calculation with varying modulus provides the better results. It is thus concluded that, for a better accuracy in sheet bending, the change in Young's modulus due to plastic deformation should be taken into consideration.