Note: This is the first article of a four-part series covering automotive plastics lightweighting (1) trends, (2) material advances, (3) process technologies and (4) applications.
Auto-makers choose plastic parts for a multiplicity of performance features. Important characteristics include durability, chemical resistance, mechanical toughness, coloring and finishing ease, elasticity and light weight.
Plastics have appreciably reduced the weight of the average passenger car, saving millions of gallons of gas yearly. Plastics have penetrated automobile parts such as bumpers, fenders, doors, safety and rear-quarter windows, headlight housings, side-view mirrors, trunk lids, hoods, grilles and wheel covers.
Automobile designers also discovered that plastics solve one of their most complicated design problems, namely, what to do with the fuel tank. Plastics give engineering teams the freedom to fit tanks into the overall vehicle concept rather than designing around this unwieldy but essential part.
Advances in engine technology, fuel management and emissions requirements continue to drive up under-the-hood temperatures. Where certain high-temperature plastics were acceptable three to five years ago, today that is no longer the case.
These automotive advances are driving the use of higher-end plastics under the hood, as well as the development of new plastics and coatings to better perform in new under-the-hood environments. In automotive interiors, plastics used in flooring, seats, dashboards and paneling maintain their attractive appearance and are easy to clean.
Plastics clearly play a major role in today's vehicles. The automotive industry is the largest end user for many engineering plastics, such as nylons (PA), polycarbonate (PC), acetal (POM) or modified polyphenylene ether (PPE). It is also an important market for commodity polymers — i.e., polypropylene (PP), polyethylene (PE) and polyvinyl chloride (PVC).
On a volume basis, more plastics than steel are now used in today's cars for a wide range of components. With the end of an automobile's useful life, plastics parts are recycled, or via incineration there is energy recovery. Plastics' versatility assists the automotive industry in complying with more stringent requirements in terms of economic performance, safety, comfort and environmental factors.
Recent industry estimates expect the use of engineering thermoplastics in exterior automotive applications to grow by 4.8 percent annually through 2015, which currently equates to more than 1 billion pounds per year. By 2015, the figure is expected to climb to 1.3 billion pounds annually.
Overall, growth in automotive plastics use has progressed from a typical 60 pounds per vehicle in 1970 to more than 400 pounds today.
Industrial Environmental Association
Carbon dioxide emissions by end-use sectors.
Plastics/composites/alternative metals increasingly used to reduce vehicle weight
- Every pound of material used in a vehicle is under investigation, resulting in new materials, processes and assembly technologies
- Plastic and its composites offer enormous potential for weight reduction in auto applications
- Fiber-reinforced plastic composites are typically 25-35 percent lighter than steel parts of equal strength
- Advances in low/ultralow density sheet molding compound (SMC) are also facilitating weight reductions
- To reduce weight some of the more dramatic new material uses will be:
- PC as glazing material for car roofs and rear ends
- Increased use of molded plastic in car body panels
- More widespread use of thinner gauge high-performance steel
- Much higher use of aluminum and magnesium
Automotive contribution to CO2 emissions
- Reducing car weight would be a significant step in reducing CO2 emissions
- The transport sector accounts for 23 percent of all CO2 emissions across the globe
- 14 percent of auto CO2 emissions is accounted for by manufacturing materials and car, as well as transportation and maintenance (well to tank)
- The remaining 86 percent occurs during auto use (tank to wheels)
Facing growing concerns about the impact that automobiles have on the environment, OEMs are embracing the use of lighter weight materials in automotive components and parts, part optimization/consolidation and the use of innovative processes. As a result, plastics and composites, as well as lighter-weight metals, are increasingly being used to reduce vehicle weight.
The global market value for lightweight materials used in the transportation industry will grow to nearly $125.3 billion in 2015, up from an estimated $95.5 billion in 2010, for a five-year compound annual growth rate (CAGR) of 5.6 percent.
To meet the ambitious new U.S. government mileage targets they've agreed to, U.S. automakers are considering every avenue of part redesign and consolidation, including most recently a renewed interest in automotive under-the-hood metal to plastics conversions, as well as further plastics to plastics refinements.
Engineers are turning to advanced engineered-plastics technology to meet new design goals particularly weight reduction as a result of rising/fluctuating fuel prices. For example, U.S. automakers must achieve a corporate average fuel economy (CAFE) of 35 mpg by 2020 and 54.5 miles per gallon by 2025.
The first step increases CAFE standards for passenger vehicles and light trucks by 4.5 percent per year over the five years spanning 2011 to 2015. This in turn will increase passenger vehicle standards to 35.7 mpg and light trucks to 28.6 mpg. NHTSA (National Highway Traffic Safety Administration) estimates that these interim standards will save 55 billion gallons of gasoline and reduce CO2 emissions by 521 million metric tons.
Automakers will also be able to earn credits if they exceed to CAFE standards and can either bank them or sell them to other automakers at a cost below what the fine would be for not meeting the standards. A 10 percent reduction in vehicle mass yields a 6 percent increase in fuel economy.
Advanced plastic composites represent a good opportunity that offers enormous potential for weight reduction, as exterior body panels, and also in applications under the hood. Ford Motor Company has stated that it wants to lighten its cars by 200 to 700 pounds over the next 5-10 years.
For example, cam and engine covers, fuel screens, oil pans, grille opening reinforcements and even driveshafts are being weight-reduced. In addition to weight reduction, engineered-plastics systems offer many advantages in automotive applications over traditional steel and aluminum materials such as:
- Lower manufacturing complexity: Fewer parts are required for a finished assembly, cutting manufacturing costs and frequently accelerating the run-up to design completion and model introduction.
- Reduced tooling cost: Tooling cost is just 30 percent of the cost of steel stamping tooling, and can be up to 60 percent less than that of comparable metal parts.
- Improved design flexibility: Plastics molding permits more complex shapes, greater geometry details and a depth-of draw range unavailable with metal stamping; in some cases, a part just can't be manufactured out of other materials.
