Predicting the wrinkling in AA5052 seamless tubes manufactured by free bending forming technology

Abstract

Wrinkling is a significant defect during forming of thin-walled metallic tubes via free-bending forming (FBF) technology. Thus, it's quite important to predict the wrinkling in the tubes to improve the quality of the final products. Accordingly, new theoretical and numerical frameworks were proposed for predicting the wrinkling of the tubes manufactured via FBF technology. The theoretical wrinkling prediction model is based on the energy criteria and the thin shell theory. The numerical prediction model was constructed on the ABAQUS/Implicit FE code. Besides, The Knoop microhardness test characterized the anisotropy of the tube. The tube's imperfection was introduced to the numerical model through pure bending buckling analysis. The bending experiments were conducted to verify the results obtained from the proposed theoretical and numerical frameworks and showed good agreement with them. Furthermore, it was noticed that the additional axial force in the FBF process reduces the tube's ability to resist wrinkles. The larger additional axial force makes tubes more sensitive to imperfection in free bending than in other bending technologies. The numerical prediction model with the perfect tube exhibits good accuracy in predicting the initiation of the tube wrinkling in free bending but not in terms of the wrinkling shape. The model considering the imperfection can predict the onset and development of wrinkling properly.