27 July 2012 00:00 [Source: ICB]
Despite the chemical industry's best efforts, cars have recently been getting heavier, thanks in part to our affinity for gadgetry and luxury, as well as the need for improved safety measures. According to statistics published in December by the American Chemistry Council (ACC) in its Chemistry & Light Vehicles report, the average US vehicle weight in 2010 rose by 3.8% to 4,039lb (1.83 tonnes), breaking a downtrend seen since the onset of the global economic downturn in 2008.
Although rising gasoline prices had temporarily stalled consumers' appetite for so-called gas-guzzling sports utility vehicles, the ACC said signs of economic recovery and renewed demand for larger vehicles fueled the 2010 weight gains.
Steel still represents more than half a vehicle's overall weight (around 52%) but plastics content is climbing and can clearly help to stymie that tradition. Producers are now looking to achieve greater savings not only through metal-to-plastic substitution but also by shaving pounds off existing plastic parts through the use of nanotechnology and additives.
Bert Havenith, Netherlands-based DSM Engineering Plastics' automotive business and innovation manager, says: "Plastics have contributed greatly to the weight reductions achieved in recent years and still pose the greatest opportunities. We are continuously looking at ways in which we can substitute heavy metals and integrate different parts for easier assembly and to remove weight."
He adds: "The basic drivers for weight reduction are the penalties on carbon-dioxide emissions and the improvement of fuel efficiency. The automotive OEMs have different choices; they work hard on improving the efficiency of the engine and transmission - downsizing the engine, for instance - and are also looking at the electrification of parts and components, getting smaller cars in their portfolio, smarter design and making parts lighter by switching metal to plastic."
The European Commission has set 2012-2015 targets for emissions from passenger cars of 120g/km of carbon dioxide (CO2), down from the current levels of 130-160g/km, depending on the specific OEM, and has opted for a new long-term target of 95g/km for 2020 - ambitious targets that will require a lot of hybrid and electrical cars in the OEMs' portfolios.
Hartwig Meier, global head of product and application development at Germany's LANXESS, says such environmental demands and legislation are certainly spurring the chemical industry to find solutions.
COMFORT AND SAFETY
"Lightweighting will always be on the agenda in the next decade," he says. "There's an increasing demand for comfort and better safety demands, while CO2 discussions are still ongoing and targets are in place, putting pressure on lightweight solutions. Ten years ago, we were talking about one airbag system; now there are cars on the road with 10 different airbags - that means the housings and explosion systems all add extra weight to the car. We have to find a solution to take this extra weight out."
The ACC statistics state that each pound of plastic and composites used in car construction replaces two to three pounds of heavier materials. It also offers other benefits, such as improved strength, design flexibility and cheaper tooling. With the average light vehicle now containing 378lb of plastics and composites - 9.4% of its weight - rather than the meager 20lb used on average in 1960, there has been significant progress in a fairly short period of time. Polymers such as polypropylene (PP), polyurethane (PU), polyamide, polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC) and polyethylene (PE) are now common throughout vehicles in seating, paneling, glazing and under the hood.
NEGATIVE WEIGHT SPIRAL
Manfred Rink, head of new business at German major Bayer MaterialScience, says: "Without all the efforts in weight reduction and plastics, I would say cars would weigh hundreds of kilos more than they do now and this would lead to a negative weight spiral."
To reinforce his point, Rink points to his own company's three business units - PU, PC and coatings, adhesives and sealants - and the way in which all three can contribute to weight saving. "It's an important material mix for the automotive industry," he says. "It's about how you fix and assemble various materials. There is a trend towards a multi-material mix in cars and getting the best balance for all their attributes.
"The question is what the OEM is willing to pay for an additional kilo weight reduction. It's important to balance the performance, weight and cost of car parts. the most important thing is that they fulfil the performance requirements. The next challenge is how to achieve the lowest cost and weight."
MAKING COMPONENTS LIGHTER
Besides substituting for heavier materials, removing weight from existing plastic components is also integral to meeting these challenges. LANXESS, for example, has been working with Japanese firm Takata to develop a lighter passenger airbag system. Using polyamide 6 (40-60% glass-fiber reinforced) injection molding grade, the thickness of the airbag housing has been reduced to only 1mm from 3mm when using conventional materials. Meier says: "Altogether, this gave us weight savings of around 30%. I'm very bullish that you'll find this in a lot of cars in two to three years."
Similarly, he adds, substituting brake pedals with plastic alternatives helps to shed the pounds. Together with German auto supplier ZF, the chemical company has developed a full plastic version using polymer sheet molded 60% injection grade polyamide 6 that is 40% lighter and meets all safety requirements. Production is starting for premium cars at the end of next year after a development cycle that has taken two to three years.
Meier also points to a trend towards the use of carbon fiber, a strong but light material that could provide plenty of automotive weight-reduction opportunities in the longer term as its usage increases and its costs ease.
Fredric Petit, DSM Engineering Plastics' sustainability director and global communications and branding director, adds: "One intrinsic advantage of metal over plastic is the heat resistance. On the other hand, the automotive industry wants to replace these metals with plastics, so there is a need for high-temperature performance plastics - and polyamides have this combination of properties."
He says polyamides are increasingly replacing metals and gaining a greater share in modern vehicles because their properties give them heat resistance while retaining stiffness and strength.
Looking ahead, there is also an increased impetus to harness electric mobility to drive down CO2 emissions. However, with this emphasis on electric vehicles, the chemical industry and OEMs have to find ways to compensate for the additional weight of the batteries they require. Polymers are central to this strategy and, besides being lighter, have other benefits too.
"It is not just about reducing the weight of a part but the effect that part and material has on the rest of the car," Rink says. "With electric cars, there is a problem in the winter months with thermal management; the normal combustion engine delivers a lot of heat that can be used to heat the car. In an electric vehicle, the energy needed to heat it comes from the battery, which adds weight. Therefore, if you have a better-insulated cabin with PC glazing, you can reduce the size of the battery and thus the weight.
Arguably, any recent weight gains seen in motor vehicles should be relatively short lived with the mega trends of mobility and urbanization driving industry's efforts to enhance fuel efficiency and contribute to fewer CO2 emissions. Plastics use, therefore, will remain central to these efforts and looks likely to dominate an already well-populated product pipeline in the years ahead.
Materials matter in the modern vehicle
Average US vehicle weight in 2010 was 4,039lb - 1.83 tonnes - up from 3,919lb (2000) and 3,425lb (1990).
Iron and steel account for nearly 61% of average US vehicle weight, down from 65% in 2000 and 70% in 1990.
Plastics and composite use in US cars is now 378lb - up from 286lb (2000) and 194lb (1990)
Composites are typically up to 40% lighter than steel parts of equal strength.
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