An interesting report shows how plastics can contribute to improving vehicle efficiency.
By one estimate, 10% of the average weight of a vehicle needs to be removed to reach future EPA fuel economy standards. One way to do this is to make increased use of plastic. These can improve aerodynamics and also make the cars easier to produce and more durable. The use of fibre-reinforced composites means that less metal can be used for the body-in-white. Plastics can also be used in the drivetrain and electrical system.
Carbon fiber-reinforced polymer composites (CFRP) are 50% lighter than conventional steel and 30% lighter than aluminum which is encouraging more and more parts suppliers and automakers to take notice. BMW now uses the material as the body structure of its electric vehicle, the i3.
Further advantages can be found in the area of crash performance. Plastics have good energy-absorption characteristics. “Energy-absorbing, injection-mouldable materials such as polypropylene or polycarbonate blended with polybutylene terephthalate (PC+PBT) as well as low-density foam polymer materials are already being incorporated into vehicle bumpers in Europe to meet new pedestrian protection guidelines set forth by the European Commission,” says the report. I decided not to try and paraphrase that as it was such a lovely sentence to begin with.
Cars feature a lot of parts joined together in subsystems. Each join takes time and material-to-material junctions are a potential source of failure. By using plastics to make consolidated parts these potential areas of failure can be eliminated. This also has savings in reducing the number of processes, the amount of tooling and the need for assembly: “The 2013 Ford Escape features a two-shot window lift carrier plate that replaces a metal-intensive assembly comprising 21 components produced with 16+ processing and assembly steps with a plastics-intensive, 10-component.”
Spot welds, rivets and fasteners are being replaced polymer-based structural adhesives. These weigh less than rivets and are faster to apply than using welds. All of these also save time and improve performance. The catch is that perhaps some of these materials are not be as durable in the long-term. Whereas steel can be welded and rivets replaced, failed adhesives are hard to repair and may require the complete replacement of an assembly. If the replacement assemblies are sourced from used-vehicles they may also be deteriorating at a similar pace, regardless of whether the vehicle is used. What we may see are vehicles that perform well during the design life and not much beyond it. The dream of Renault to have no car lasting more than 7 years or three owners is being designed in to the cars across the industry although the trade-off is lower energy consumption and reduced resource-use for each vehicle.