Prediction And Control Of Distortional Springback Induced By Non-Uniform Local Deformation During Large Flat Panel Stamping

Large flat stamped parts are used widely as bottom panel and basal body in household appliance industry. These stamped parts often contain a lot of non-uniform local deformation. For large complex flat stamped parts, due to non-uniform local deformation, distortional springback phenomenon is a big problem, affecting the quality and appearance of the product. Although a lot of research work has been done to improve the springback prediction accuracy, these improvements are still unsatisfactory. Besides, there are no mature evaluating indicators to describe the distortional springback, and the effects of processing parameters on distortional springback are less investigated.Based on the stamped parts of LCD TV black-light, two similar models are established which reflect distortional springback phenomenon induced by the non-uniform local deformation. Then the mechanical mechanisms of distortional springback are investigated. In software LS-DYNA, the springback of actual parts are predictions by similar model and vertical suspension constraints. It is shown that the numerical springback value is a little higher than the practical measurement results. But the overall distribution and variation trend of distortional springback demonstrate good agreement with experiments.In order to study the distortional springback, a new method to evaluate it is proposed. The impacts of blank holder force, frictional coefficient and die clearance on distortional springback are investigated. The simulation results indicate, as the blank holder force and friction coefficient increase, the distortional springback will decrease, and the die clearances have no obvious infection with distortional springback. The results are helpful to control the distortional springback. Based on the similar model of distortional springback, the technique of variable blank holder force (VBHF) is investigated. Using ten VBHF loading curves and local VBHF, the distortional springback is simulated. The best of blank holder force curve loading mode and block blank-holder mode are obtained under these VBHF modes, and the springback value obviously decreases. The results show: that the incremental model, peak shape model and increasing the blank holder force in the final stage of forming can decrease the springback. The springback can be reduced by optimizing the key parameters in the curves. Dividing the blank holder and increasing the holder force at the feature area can reduce springback effectively. The results show a new approach for springback control research in the future.Meanwhile, the distortional springback control technique based on feature-reverse-pressing is investigated. Three feature-reverse-pressing types are summarized, and the impacts of reverse-pressing types and reverse-pressing dimensions on distortional springback are investigated. A set of optimal reverse -pressing type and dimension is obtained. The impacts of bending radius and bending height to distortional springback are also analyzed by numerical simulation. The simulation results indicate, as the bending radius increase, the distortional springback decrease. The bending height should be determined according to the distribution of features. Increasing the bending height where there are more forming features can reduce distortional springback effectively. The results can provide technical support for actual distortional springback control in the industry.