Study on the wrinkling behavior of cylindrical deep-drawn cups

This study presents theoretical methods and experimental investigations for prediction on the flange wrinkling of deep drawn cylindrical cups. The prevention of wrinkling in the flange area is most commonly solved by a blank holder. The appropriate suppress of wrinkling is only possible with optimal process parameters, since inadequate blank holder pressure leads to wrinkling, while too much blank holder force can increase the risk of splits. Although some theoretical and semi-empirical aspects as well as experimental process windows on optimal blank holder pressure are known (the most popular optimal blank holder pressure estimation is originated from Siebel), even the exact criterion what we consider to wrinkling is not always trivial. To make the comparison of the applied wrinkling criterion theories, different approaches are collected from the literature. The closed form solutions of the bifurcation method - from Hutchinson and Neale - and the energy-based theory - from Yu and Johnson - are discussed primarily. Besides, critical wrinkling stress analysis is also studied. The results of the investigated wrinkling criteria were resembled to experimental observations and to finite element calculations done by the AutoForm R7 software. Our results show, that some of the closed form solutions do not make direct connection between the theoretical results and the industrial practice. Even if, both the results from the bifurcation and the energy based methods seem to be realistic. However, the finite element calculations provide the most widespread and most precise wrinkling evaluation, at a workpiece, which flange is finally drawn into the die cavity, the interpretation of the numerical results is also not obviously self-evident.