Lightweight garage #11 Curved sheet metal in the Mercedes SLK

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Lightweight garage, News

The vehicle

Behind this garage door is a vehicle that everyone has probably seen before. It is the Mercedes-Benz SLK, a roadster introduced by Mercedes-Benz in 1996. The vehicle is related to the C-Class and is known for its folding steel roof. But there is also an innovative solution hidden away, which is presented here. This is the rear wall, which has a special curved structure and has been reducing the weight of the SLK since 2004.

©Steve Coulter, Mercedes Benz SLK, CC BY-NC-ND 2.0

The technology

Curvature structuring is a forming technology process used to create square or honeycomb structures in sheet metal. For production, the sheet metal is supported at certain points and subjected to pressure from the outside. This creates a self-organized 3D structure. It differs from conventional sheet metal forming processes (e.g. embossing, beading, hydroforming) due to its energy-minimized self-organization process. As the material automatically takes on a shape with minimal energy, the energy required to create the camber structure is low and the surface quality is fully maintained.

The incorporated structures represent a form of instability failure, which is why such a sheet is automatically in the post-buckling area when in use. The reason for the improved properties lies in the work hardening that occurs during buckling. Compressive and bending stresses with slight plastic deformation occur in the indentations and tensile stresses occur in the folds, which stabilize the structure.

©Dr. Mirtsch GmbH Germany, Sheets with arched structure, CC BY-SA 3.0

Arched structures are originally known from nature and are therefore a good example of a bionic application. The honeycomb-like patterns are found in turtle shells, for example. They have been evolutionarily optimized by nature for many millions of years and thus form a perfect shell for the animals. Technical applications cleverly imitate this structure in order to benefit from its positive properties.

©Punch, Turtle with domed shell, CC BY-SA 2.0

The lightweight aspect

The weight advantage of the arch-structured rear wall of the SLK results from the increase in form rigidity, which makes it possible to reduce the wall thickness. Similar to the introduction of beads in sheet metal, the surface moment of inertia is increased by a distance to the neutral fiber and the load is thus reduced. This results in high rigidity with low weight, reduced installation space and good acoustic properties. Due to the special manufacturing process, arched structures also have other positive properties. They are more resistant, more thermally stable, more streamlined and have less glare than corrugated sheets.

All these positive properties mean that arch-structured components can be made up to 30% lighter than conventional sheet metal parts.

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