Electromagnetic Self-Piercing Riveting (E-SPR) Process for Dissimilar Materials Joints

Abstract

Automobile manufacturers have recently focused their research on the concurrent improvement of fuel efficiency and stability. To implement lightweight body structures, the joining of dissimilar materials, such as advanced high-strength steel (AHSS) and carbon fiber-reinforced polymer (CFRP), is the most important, whereas fusion welding, which is the conventional welding process, is inapplicable owing to the difference in mechanical properties between materials. Thus, the development of an appropriate dissimilar material joining process is of utmost importance, considering productivity and safety. Self-piercing riveting (SPR), a representative lightweight material joining process, has no limitation in terms of applicable materials and has the advantage of improved joint strength. However, as the requirements on the mechanical properties of materials in the industry are continuously increasing, there is a need to further develop the process. Therefore, this study introduces the electromagnetic self-piercing riveting(E-SPR), a joining process that uses high electrical energy to discharge the high electrical energy charged in the capacitor to the working coil located in the head of the C-frame. In particular, this process enables high-quality joining parts to be secured by improving the formability of a material with poor formability under a high strain rate. Consequently, a simple piece of E-SPR equipment was manufactured, and an Al/Steel and Al/CFRP joint was further fabricated. The results of a preliminary test reported a quality equal to or higher than that of the previously reported SPR joint. Based on these research results, further studies on processes and equipment for commercialization will be conducted in the future.