Goodbye to the sheet metal

Steel, plastics, carbon and hemp – modern vehicles contain a huge amount of materials. Innovations in materials are the basis for implementing new vehicle concepts. New approaches and manufacturing methods are a main topic at the IAA MOBILITY.

During the past 130 years automotive engineers have tested and used a number of very different materials: automotive pioneer Gottlieb Daimler built his motorized carriage from wood, a time-tested building material. Ridiculed as a "cardboard racing car," the Trabant made in East Germany was manufactured, for lack of alternatives, entirely of plastic. Today mainly steel, aluminum, carbon, alloys and hybrid materials are used for bodywork and frames while natural fibers (such as linen and hemp) or plastics add value to the interior. Teflon, a “jack of all trades,” is used to seal paint and coat gaskets. Manufacturers, suppliers and scientists are also working on increasingly intelligent solutions. To achieve this, they furnish materials with conductors and network components. When equipped with control electronics, materials can serve as sensors or adapters.

With the discovery of piezo crystals, which first coaxed music out of record players, the Curie brothers laid the physical foundations for adaptronic – short for "adaptive structure technology.”  Material combinations which react and change their form as a result of external factors – but without software and electrical circuits – are similar to piezo materials. The trick is that the materials change shape repeatedly on their own when exposed to electrical power, magnetic forces, heat and light, compressed air or chemical reactions. Shape memory materials, for example, take on a different form at low temperatures and then return to their original form. The automobile interior, in particular, is an ideal environment for such materials.

Take automobile seats. In the latest models, they are pieces of sophisticated wellness furniture. However, underneath the upholstery is a vast array of electronics. Shape memory alloys adapt to individual body contours without the use of manual adjustment buttons or expensive biometric automatic devices such as Nissan’s butt identification sensor. Passengers cars no longer need extensive electronics and complicated wiring. In contrast, electroactive plastics generate electrical power when subjected to mechanical forces and vice versa – literally an engine and hydraulics system all in one.  Moreover, using a shoe sole as an example, a Fraunhofer project has demonstrated how the material can become a mini-power plant: when running, the wearer generates enough electrical power to operate portable devices such as smartphones or wearables. In the future it may be possible to integrate such materials into automotive wheels, thus enabling them to charge the automobile’s battery during travel.

Wood, a material once banished from bodywork, is now making a comeback – if only in small series. This natural material from the forest is much more versatile than many realize. Extremely resistant to bending and as stable as aluminum, it is also several times lighter than its metallic and synthetic counterparts. Wood is thus suitable not only for veneer strips but also for load-bearing parts, panels in the car interior, or side impact protection for doors – advantages exploited by the British Morgan Motor Company since 1909. At Morgan exotic roadsters with ash frames are still rolling off the assembly line. Toyota’s Setsuna concept study is far more antiquated. The exterior paneling is made of cedar; birch and other materials are used in the frame. In determining the composition of the individual parts, the engineers followed the principles of okuri ari, a Japanese carpentry method in which perfectly fitting wooden elements are simply put together without screws.

Besides wood, other renewable raw materials such as hemp, cotton, linen and flax are used for automobile construction. Usually these natural materials are hidden in trunk floors, paneling or floor coverings. The automobile manufacturer Ford has experimented with sustainable materials for 20 years. Today various biomaterials – including soy, ricinus oil, wheat straw, kenaf, cellulose, wood, coconut and rice – are used in these models. The company has even embarked on a collaboration with the Mexican tequila producer Jose Cuervo to investigate the suitability of  agave for various components. Ford is also interested in the use of bamboo.

One of the top topics in the automotive industry is how to make cars – but especially electric cars – lighter and thus more efficient. The word “carbon” is used repeatedly in this context. Although this "super material" weighs only half as much as steel and about a third less than aluminum, it is expensive. Apart from the complicated production method, the material can splinter uncontrolledly in an accident and can then no longer be repaired. Carbon is thus of limited use in large-scale automobile manufacture. Improved aluminum alloys and sandwich steels are thus good alternatives for reducing weight. However, conventional manufacturing methods, in particular, often set tight limits on lightweight construction.

Now totally new approaches – such as additive manufacturing methods like selective laser melting and sintering, 3D printing, stereolithography and fused deposition modelling – have brought us a giant step closer to the use of natural building principles such as honeycomb or lattice structures, which require a far lower amount of materials and thus help to conserve resources. The vehicle studies "Light Cocoon" and "Soulmate" from EDAG, for example, consist totally of a skeleton-like bionically optimized vehicle structure. The sportscar is covered with a weather-resistant outer skin of three-layer polyester-jersey fabric developed by the outdoor clothing specialist Jack Wolfskin. Apart from its high potential for lightweight construction, this fabric can be used to cover movable parts such as the spoiler. It copies all movements, allowing the driver to change the car size or adapt to wind conditions by pressing a button.