**1. Introduction**

84 Metal Forming – Process, Tools, Design

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## **1.1. Sandwich sheets**

For many applications there are claims concerning the metal sheet, which cannot be reached with a single sheet. Composite materials, which can be classified in fiber-composites, sandwich materials and particle-composites are increasing year by year [1]. Sandwich respectively laminates with various thicknesses and materials of the different layers offer highly useful properties. As seen in Figure 1 every material has different mechanical, acoustical, tribological, thermal, electrical, chemical as well as environmental and technological properties.

**Figure 1.** Classification of composites; preparing of sandwich sheets

Figure 1 illustrates an example of a fictive constellation of a composite. The price of the raw material itself has to be lower than the price of stainless steel. The nearly symmetrical sandwich should be resistant against corrosion and appear like stainless steel. For application in the automotive industry, it should be highly formable and reduce vibrations.

© 2012 Engel and Buhl, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Engel and Buhl, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

So the thin outer sheets are chosen of 1.4301, the supporting layer of DC06 and the vibration damping layer of a viscoelastic adhesive. At first, the metal layers of both sides are cladded 1. In step no. 2 they are bonded with a very thin adhesive layer (see chapter 5.4). To achieve advantages concerning the forming process (see chapter 4.1), a metal interlayer is included.

Forming of Sandwich Sheets Considering Changing Damping Properties 87

stiffnesses with thick synthetic cores. [10] As well as by shear weak connection, the cover layer of shear transmitting sandwiches usually does not crack. Now, additive failures like core-failure, local dents and wrinkling of cover sheets limit the forming capabilities. [11]

The joining process of several layers has a great influence of the formability and the damping behavior of the sandwich. Layers can be connected viscoelasticly by using an adhesive film. The cover sheets are allowed to slide on each other. For that displacement only a negligible shear force is necessary. This viscoelastic bond is weak. Shear transmitting bond lines like 1 or 2 component-adhesives are ductile. Parameters of the roll bonding process and surface treatments are shown in [10]. Layers which are connected shear fixed (cladded) can´t slide on each other. [15] In a forming process the sheet behaves like a single sheet, but after

Typically, laminates which are jointed shear fixed crack on the brittle side. [12]

forming, astonishing effects due to different Young's moduli and hardness occur.

**Figure 3.** Classification of joining with respect to transmitting shear force

**Figure 4.** Tensile shear test of sandwich sheets; Strip production line similar to [3]

**1.3. Classification of sandwich sheets** 
