When Plymouth Prowlers started rolling into new-car showrooms late this month, the roadsters turned heads not only because of their sporty design but also because of their materials application.
More than 900 pounds of the 2,780-pound vehicle is aluminum, including the body, frame and suspension parts.
The Prowler, though not your average car, is typical of how automakers have been embracing aluminum along with plastic as components.
“There’s been a continuing growth for both materials in the auto industry for the past 15 to 20 years,” says Dave Cole, director of the Office for the Study of Automotive Transportation at the University of Michigan in Ann Arbor.
Automakers in recent years have been striving to make cars lighter to meet current and potentially tighter future Corporate Average Fuel Economy standards mandated by the federal government.
For every 10 percent drop in weight, a car’s fuel efficiency increases about 7 percent. That also translates into reduced carbon dioxide emissions.
“The industry has been moving in the direction of using less dense materials that don’t compromise safety or performance but do increase fuel efficiency by reducing curb weight. This is where aluminum and plastic come in,” says James Conley, an associate professor of mechanical engineering at Northwestern University in Evanston.
“As a result, the engine doesn’t have to do as much work to move a lighter car, and you get much better fuel efficiency,” he adds.
“Depending on the component, there can also be a cost-savings benefit by going to aluminum or plastic,” says Cole.
Though steel still makes up about 55 percent of a vehicle’s overall weight, aluminum and plastics have been gaining ground.
Aluminum industry officials say aluminum accounts for about 7 percent of a car’s weight–about 250 pounds per average vehicle–twice what it did in 1980. Cole says an aluminum engine block weighs 40 to 50 pounds compared with 80 to 100 pounds for a cast-iron block.
American Plastic Council members are quick to point out that since 1970, plastic parts in cars have grown by more than 500 percent, from an average of about 60 pounds per car to 365 pounds, or about 8 percent of an average passenger car’s weight.
Its lighter weight, durability and ability to resist corrosion, tarnish and rust have helped the use of aluminum, a trivalent metallic element, to increase in the auto industry, though it is up to four times more expensive than steel.
Aluminum has been a longtime choice of the auto industry. Since the beginning of the automotive era, it has been used in the body of some models and occasionally in the engine.
“The giant growth has been in the last 10 years, and it’s been in the powertrain of the car because that’s where you save the most weight,” says Conley.
Typically, aluminum is now found in such car parts as the engine, chassis and suspension, transmission, wheels and brakes. The use of aluminum body panels is slowly increasing.
Manufacturers have created aluminum composites that can cut the weight of parts by 50 percent and increase durability.
The two-seat Acura NSX, introduced in 1991, contains about 900 pounds of aluminum for 1997 out of a total weight of 3,200 pounds.
In 1995, Audi introduced the all-aluminum body A8 in Europe. Thanks to more energy-absorbing abilities, the A8 was deemed as crash-worthy as steel cars.
It was also 300 pounds, or about 400 percent, lighter than a similar car made from steel.
Last year, Chrysler unveiled the Prowler, which took the technology used to shape aluminum–a commercialized joining process–to a new level. So, Prowler has the same body stiffness of steel cars.
Instead of welding, Chrysler engineers decided to use rivet bonding, in which two sheets of aluminum are held together with a shank of metal and epoxy.
Plastic began appearing in autos as early as the 1920s, when lacquers replaced varnish as a exterior finish and vinyl seats replaced leather.
The growth has been nonstop. “Most of the decorative trim on an automobile is now all plastic,” says Conley. “Plus, the interior of a car is mostly plastic. That has resulted in a substantial increase in the volume of plastics.”
Typically, seat belts, air bags, instrument panels, safety glass and rust-free body panels on certain cars are made of plastic.
More important, plastics such as nylon, polyesters, polyvinyl chloride and polyurethanes have made significant inroads since the 1980s, when they were first accepted for integral structural parts, such as bumpers, says William Windscheif, marketing manager for the Montell Automotive Business Group in Troy, Mich.
“The movement away from chrome on the outside of the car to different types of plastic for the grille and bumpers was a big step,” says Windscheif.
“The damageability improvement you’ve got to the front and rear ends on cars is phenomenal,” says Allen Maten, director of automotive programs for the Automotive Committee of the American Plastics Council. Maten cites plastic car bumpers, which can withstand a 5-mile-per-hour impact and flex back to shape, while a chrome bumper will dent.
“Plastics have now made a big inroad in the fuel-tank area,” says Maten. “They provide lighter-weight and safer fuel tanks, and engineers are able to package the design and shape of the fuel container in such a way that they can easily fit into the smaller confines on new cars.”
Plastics manufacturers are trying to persuade automakers to use plastic for intake-manifolds and rocker-arm covers.
“Eventually, I can see plastic making inroads into frames, chassis and engines, but how soon that’s going to happen I don’t know,” says Maten. “Weight and durability will drive this. Plus the corrosion resistance that we have is phenomenal.”
Auto industry officials believe the use of plastic and aluminum will continue to increase, especially if Corporate Average Fuel Economy requirements for cars are raised from 27.5 to 35 m.p.g. One industry study shows the use of aluminum increasing 20 percent if that happens.
In addition, Maten and Windscheif see recycling as a key issue to growth.
“Automakers are very interested in that because they want to appear green,” says Maten.
Maten said plastics can be recycled several ways: A part such as the fascia can be taken off a car damaged in an accident and used on another car; the old seat foam from one car can be reprocessed into carpet underlayment; and plastic items such as pop bottles provide material for headliners.
Steel companies, however, aren’t “standing still,” says Cole. “The steel industry has made some outstanding strides in the last couple of years” in producing a lighter but strong steel.
“Of all the competition in the automotive industry, one of the most interesting is the one regarding materials,” adds Cole. “The stakes are high, and it’s too early to determine a winner.”
