Apostolos Pavlos Karafillis

Prediction of flange wrinkles in deep drawing

A numerical method for predicting the onset of flange wrinkles of small wavelength during deep drawing process is presented. The method is based on the approach developed by Cao and Boyce (1997) for predicting the buckling behavior of sheet metal under lateral constraint using a combination of energy conservation and finite element method. Continuum elements are used in a simple Finite Element Analysis model to study wrinkles with a maximum wavelength of ten times the sheet thickness. The analysis provides the critical buckling stress and the resulting buckling wavelength as functions of normal pressure. Such relationships are then implemented in a Finite Element Method (FEM) package that uses membrane elements to simulate the workpiece deformation during a forming process. The use of membrane elements significantly reduces the amount of computation time required in comparison to using structural shell elements with multiple integration points through the thickness. The stress histories calculated from the FEM membrane analysis are used to predict the onset of buckling during the forming process. The application of the forming of a rectangular pan is examined. The comparison between numerical simulation and the experimental results is presented. Our approach predicts the onset of buckling in excellent agreement with the experimental observations.