Development of formable all-metal sandwich sheets for automotive applications

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Development of formable all-metal sandwich sheets for automotive applications

Mohr, Dirk / Straza, George

In this study a formable all-metal sandwich sheet material for automotive applications has been developed. The starting point is a detailed discussion of the technical challenges related to the formability of sandwich sheets. Using leading sandwich manufacturing technology, a new formable sandwich sheet prototype was produced. The all-metal brazed sandwich sheet is composed of 0.2 mm thick stainless steel face sheets and a 2.1 mm thick hastelloy micro-cell honeycomb core. A draw-bending experiment is performed to demonstrate that thin sandwich sheets can be successfully formed if they are specifically designed for this type of application. The results of this pilot study demonstrate that all-metal sandwich sheets can be designed such as to withstand the mechanical loads in a draw bending experiment. Draw bending is seen as one of the most critical forming operations for sandwich sheets. Other membrane-dominated sheet metal forming techniques such as deep drawing are probably less critical as far as sandwich sheet design against failure is concerned. This is due to the fact that most sandwich-specific failure modes are activated by shear and bending loads. In the case of membrane loads on the other hand, the mechanical behavior of sandwich sheets is expected to be fairly similar to conventional solid-section sheets. Some conventional sheet metal forming failure modes such as sheet wrinkling are even anticipated to be less likely for sandwich sheets due to their superior bending stiffness. Thus, the successful draw bending of the 2.5 mm thick honeycomb sandwich sheet is seen as an important milestone in the development of thin formable sandwich sheets for automotive applications. Future research must consider the costs of the sandwich material in addition to technical requirements.