Note: This is the third of a three-part article series covering automotive lightweighting (1) trends, (2) material/process advances and (3) applications.
Every car model that is launched over the coming years is expected to include lightweighting measures. Innovative materials together with new production methods and reinforcing structures will play an important role in reducing vehicle weight. Lower vehicle weight not only improves fuel efficiency but also reduces the load on the brakes and suspension systems.
Currently, 15 percent of the average car's total weight (or 360 pounds) is plastic material, with its use accelerating. Experts predict this use will more than double over the next five years as the auto industry gears up to meet new emissions regulations.
The trend to replace metal with plastics is also allowing integration of functionality often not possible in metal versions. Double-curved glazing, incorporating integrated spoilers and merged taillights into tailgates are emerging key design trends.
Metal is also increasingly replaced by plastics under the hood. The industry move toward alternative fuels such as diesels, hybrid vehicles, turbo systems and electric-only cars is similarly increasing plastics opportunities.
Progress is being made as well in lightweight metal development to reduce car weight, including aluminum, magnesium and high-strength steel. On a worldwide basis, aluminum use is expected to increase from the current average of 248 pounds per light vehicle to 300 pounds by 2020.
Carbon fiber continues to have great appeal to designers and manufacturers. Various efforts are underway to reduce carbon fiber cost and make carbon-fiber composites available for mass production. Ford is partnering with Dow to research use of advanced carbon fiber composites in high volume vehicles. All major carbon-fiber producers are boosting carbon fiber production capacity.
Let's start in automotive lightweighting by looking at Nylon 6 (Polyamide, PA), replacing metal in an oil sumps application. Oil sumps offer considerable challenge for developers as their exposed position under the engine means they have to withstand considerable mechanical stress caused by flying stones and curb impacts.
DSM Akulon Ultraflow PA 6 is being used to replace metal oil sumps in the new Mercedes-Benz S Class and Peugeot 508. Both use Akulon Ultraflow K-FHG7 from DSM.
The heat-stabilized PA 6 used is 35 percent glass, reinforced with high resistance to engine oil and very good flow properties. The injection-molded parts are not only lighter, but also less expensive to produce. The Mercedes oil sump developed by BBP in Germany is roughly 50 percent lighter than the metal version it replaces. French Tier One supplier Steep Plastique developed the Peugeot oil sump, which is 60 percent lighter than the metal one.
The parts were subjected to demanding application tests including vibration, stone impact, curb impact and engine drop tests. The good flow properties of Akulon Ultraflow K-FHG7 offer significant processing advantages compared to standard PA 6 while maintaining required mechanical properties.
Elsewhere in this application space, DuPont Performance Polymers and ElringKlinger AG of Germany have developed a lightweight, injection-molded truck oil sump of DuPont Zytel PA resin. The oil pan is up to 50 percent (6 kg) lighter than aluminum and can resist stone and gravel chip impact during the typical 1.5 million kilometer lifetime of a truck or bus engine. There also is a 2 decibel reduction in noise level compared with metal.
The use of nylon resin also enables the integration of functions that are not possible with metal, such as oil pickup pipes and fluid level sensors.
Next, let's examine a composite vehicle floor that is one-third lighter than steel.
Faurecia engineers have developed an integral structural floor comprising a front and rear passenger floor and a trunk floor made of composite thermoplastic material reinforced with glass fiber. The floor is 16.5 kilograms lighter (11.5 kilograms in front and 5 kilograms in the rear) than a conventional steel floor.
The product achieves the goal of a 33 percent weight saving set by Renault for its EOLAB concept, reducing carbon dioxide emissions by 1.65 grams per kilometer. Made using "thermostamping" techniques, Faurecia has also improved the floor design by incorporating acoustic components into the empty space between the upper and lower layers of the thermoplastic structure.
Faurecia/Automotive World
Lightweight floor incorporates acoustic elements to muffle noise resulting from density drop.
In addition to offering outstanding mechanical performance to meet crash-test requirements and ensure recyclability, the PA 66 composite thermoplastic with glass-fiber reinforcement also makes it possible to weld and overmold parts. The technology is said to reduce both weight and costs compared with bonding, while producing a material able to withstand the high temperatures created during painting processes that employ cataphoresis (cathodic electrodeposition).
Finally let's review lightweight bodyshells and door panels.
The Mercedes SL model got lighter with an all-aluminum bodyshell that started in 2013 and has continued through to the upcoming 2017 model. The new SL's bodyshell weighs 242 pounds less than its steel predecessor. The aluminum structure is also superior to steel in regard to its rigidity, safety and comfort.
The parts are variously manufactured by chill casting or vacuum die casting and worked into extruded aluminum sections or into aluminum panels of varying thickness. The end result is high rigidity and excellent safety combined with low resonance and vibration.
Elsewhere, BMW is specifying Novelis Fusion technology for its new-generation BMW 5 Series Sedan to produce lightweight inner door panels. Novelis Fusion technology first used in mass production in the BMW 7 series and also currently featured in the BMW 5 Series Grand Turismo is being integrated into the high volume 5 Series sedan.
Doors represent approximately 20 percent of the total weight of the body-in-white (BIW) sedan weight and offer a significant opportunity for weight saving. The multilayer aluminum alloy sheet allows BMW to manufacture one-piece door "inners" with integral window frames, a design not achievable with conventional aluminum sheet. The alloy combination used in this application delivers both high formability and superior corrosion resistance, a combination of properties not previously available.
The BMW 7 Series also features extensive use of aluminum in conventional form for the roof (15.4 pounds lighter than the conventional steel roof), hood, outer door and side panels and some structural reinforcement. Overall, aluminum use in the BMW cuts 48.4 pounds from the vehicle's BIW weight. Now the BMW model 5 Series sedan will include conventional lightweight aluminum sheet in the hood, front fenders and reinforcement parts in addition to Novelis Fusion Aluminum for the door structure.
With its lightweight vehicle strategy, Jaguar's XJ sedan is also advancing the use of aluminum in its design. The Jaguar XJ will employ Fusion technology to reduce vehicle weight and improve handling performance. Jaguar is the second automaker to employ aluminum sheet fabricated via the Fusion process.
