Straight hemming of aluminum sheet panels using the electromagnetic forming technology: First approach

Hemming is the last or one of the latest stage operations for the stamped parts. For this reason it has a critical importance on the performance and perceived quality of assembled vehicles. It is used to attach two sheet metal parts together or to improve appearance creating a smooth edge rather than a razor edge with burrs. However, designing the hemmed union is not always easy and is deeply influenced by the 9 mechanical properties of the material of the bended part. Main problems for the automotive industry arise when bending aluminum alloys. Aluminum sheet is more difficult to hem due to its susceptibility to strain localization during the hemming process. This phenomenon produces cracking on the hemmed edge [1]. In order to avoid this problem and due to the limitations of conventional flanging and hemming technologies, the flange radii must be increased and a rope hem used (instead of the flat hem used with steels) when working with aluminum alloys. These changes on the design of the hem union give as a result a lower quality final product [2]. Dies and tools used for the hemming process are designed based on experience and on lengthy and costly die tryouts. Continuing with the development of new applications for the Electromagnetic Forming (EMF) technology. LABEIN-Tecnalia and Professor Glenn Daehn's group from The Ohio State University carried out some first straight flat hemming experiments using the AA 6016 T4 aluminum alloy. The results obtained from these first trials are presented in this paper giving a first sight of the possibilities, advantages and disadvantages of using the Electromagnetic Forming technology for the hemming of aluminum sheet panels. Using a non-clouped FEM simulation method, the experimental results are compared to the ones obtained with the simulations. The future working line in developing this new application for the Electromagnetic Forming technology will be based on the results obtained by this study.