Theoretical Prediction of Sheet Metal Wrinkling Based on the Potential Function Analysis

The wrinkling research in sheet metal forming process has always been one of the most common hot topics. There are many methods to predict the sheet metal wrinkling while it is still difficult to accurately predict the initiation of wrinkling. The variational study of the potential function can be used to analyze the sheet metal wrinkling and acquire the stable energy criterion. In this paper, the sheet metal wrinkling mechanisms are explained in detail, and a wrinkling prediction model is proposed based on derivation and the potential function analysis during sheet metal forming processes. Meanwhile, the finite element (FE) simulation and experimental results of Yoshida buckling test (YBT) are used to verify the accuracy of the theoretical wrinkling prediction model. And the wrinkling prediction model has also applied to analyze the conventional spinning forming process, and the critical moment of flange wrinkling had been accurately predicted.

Springback optimization in automotive Shock Absorber Cup with Genetic Algorithm

Drawing or forming is a process normally used to achieve a required component form from a metal blank by applying a punch which radially draws the blank into the die by a mechanical or hydraulic action or combining both. When the component is drawn for more depth than the diameter, it is usually seen as deep drawing, which involves complicated states of material deformation. Due to the radial drawing of the material as it enters the die, radial drawing stress occurs in the flange with existence of the tangential compressive stress. This compression generates wrinkles in the flange. Wrinkling is unwanted phenomenon and can be controlled by application of a blank-holding force. Tensile stresses cause thinning in the wall region of the cup. Three main types of the errors occur in such a process are wrinkling, fracturing and springback. This paper reports a work focused on the springback and control. Due to complexity of the process, tool try-outs and experimentation may be costly, bulky and time consuming. Numerical simulation proves to be a good option for studying the process and developing a control strategy for reducing the springback. Finite-element based simulations have been used popularly for such purposes. In this study, the springback in deep drawing of an automotive Shock Absorber Cup is simulated with finite element method. Taguchi design of experiments and analysis of variance are used to analyze the influencing process parameters on the springback. Mathematical relations are developed to relate the process parameters and the resulting springback. The optimization problem is formulated for the springback, referring to the displacement magnitude in the selected sections. Genetic Algorithm is then applied for process optimization with an objective to minimize the springback. The results indicate that a better prediction of the springback and process optimization could be achieved with a combined use of these methods and tools.

An Analytical and Numerical Investigation on Flange Wrinkling Behavior in Warm Forming Process of AA5754 Using Macro-Textured Tool Design

In this paper, an analytical buckling model is established to predict the flange wrinkling behavior of deep drawn cylindrical cups of aluminium alloy sheet in warm forming conditions using macro-textured blankholders for the first time. A continuum damage mechanism (CDM) based material model was utilized to reflect the visco-plastic feature of material at elevated temperatures. Forming speed and temperature effects were investigated, and texture ratio and draw ratio effects were also discussed. The developed analytical buckling model was validated by finite element simulations. The increase of forming temperature and forming speed is prone to cause wrinkling for AA5754, but the effects are not as significant as the texture geometry and draw ratio. The analytical model presented in this paper can be used as a design guide to determine tool texture geometry necessary to avoid wrinkling defects in the warm forming processes of aluminium alloy.