Meeting the tough CAFÉ standards for 2025 (54.5 mpg) is quite possibly the most daunting challenge for automotive manufacturers across the globe, especially with the ever growing consumer demand for safe, low-priced highly-equipped vehicles. Among the different research and development strategies to tackle this issue, “lightweighting” remains one of the most effective means to reduce fuel consumption levels. However, all previous efforts in this area have been somewhat incremental; current models are slightly lighter than previous models, utilising similar materials in components produced by the same manufacturing processes. It is therefore not surprising to note that the increase in fuel economy figures for any particular make/model over the past few decades has been also incremental (for instance, the combined mileage of Toyota Camry increased from 22 in 2003 to 28 in 2013 – US Department of Energy). So, based on this history, are we ready to meet the 54.5mpg by 2025?
What the automotive sector needs is radical lightweighting solutions that could bring down the weight of entire sections or modules, and this is the main target of the proposed technology, which we refer to as “pressurised foils for ultra-lightweight automotive panels.” Conventionally, outer body panels in a car are stamped out of steel sheets, the thickness of which is ~1mm. These panels do not carry any major loads; they carry their own weight, and serve an aesthetic function. The proposed technology is based on replacing these outer sheet panels with thin foils (~0.05mm in thickness), thus reflecting significant weight savings. Naturally, the simple replacement of sheets with foils does not work, since foils cannot hold a shape and can easily rip, dent and wrinkle. So, we propose constructing a panel out of two foils with a seal around the perimeter, and pressurising the gap between the two foils. This pressurization (very small pressure is needed) should be more than sufficient for the foil panel to hold a shape, and have sufficient dent and deformation resistance (think of an inflated rubber balloon …. Now imagine that balloon is made of a metallic foil instead!). With this replacement, a pressurised foil component (total thickness of ~0.1mm) is expected to provide mass savings of ~90% compared to a conventional sheet counterpart (based on ~1.0mm thickness).
We propose using materials such as stainless steel and aluminium for these foil structures, simply because of their suitability and wide availability. Using these materials brings other possible benefits, including high corrosion resistance and a great lustrous appearance! This also implies the possible elimination of paint (which means additional mass savings and positive environmental impact).
Other factors …
High speed driving: pressurisation should provide rippling resistance at high speeds.
Ability to produce complex design features and contours: can be easily done by line/contour “creasing” in the foil before pressurisation, and strategically bonding the inner and outer foils at selected locations.
Manufacturability: this is a major benefit that comes with this technology …. Foils require “creasing,” which will replace the costly and energy demanding “sheet stamping” operations.