PROWLER PUTS ALUMINUM ON THE STREET

The Plymouth Prowler turns heads everywhere it goes, but it's biggest impression may yet be on the future of aluminum production.

Purple cat passion runs deep among metallurgists too, but for slightly different reasons. Nearly 900 pounds of the 2,838-pound roadster is aluminum - including body, frame and suspension parts. It may be the most significant production effort with aluminum to date and marks a watershed moment in the history of automotive material application, according to Saad Abouzahr, materials executive for Team Prowler.

The aluminum-intensive Prowler is 21 percent lighter - roughly 600 pounds - than it would be had it been made of conventional steel.

"The most important lesson we learn through Prowler may be how to make aluminum cars in mass production," said Abouzahr. "If we can take 25 percent of the weight out of tomorrow's cars and trucks, we can expect dramatic gains in performance and fuel efficiency.

"It's a test bed for new material technology. From the welded aluminum extrusions and castings used in the vehicle frame to the metal matrix composite brake rotors, Prowler will accelerate the pace at which these materials and processes move forward."

Prowler is the latest and most visible effort in a series of Chrysler's advanced material projects. Many lessons were learned from an aluminum-intensive Neon project two years ago and a composite car project from the late 1980s, according to Abouzahr.

"The Neon Lite project in 1994 took 25 percent of the weight out of a production Neon, 50 percent out of the body itself, but at a major cost penalty," said Abouzahr. "The Prowler would be 21 percent heavier had we used conventional methods."

Some engineers argue the technical stumbling blocks are still daunting.  Conventional wisdom says aluminum cars should be noisier, less able to hold up in a crash, and rust more easily.  Abouzahr says that's old thinking.

"I still get people coming up to me saying, 'You're seriously going to make this car out of aluminum?'," Abouzahr said. "I tell them these are high, strength aluminum alloys, the kind they use for airplanes, boats and sporting equipment."

Using a recently commercialized joining process, aluminum cars have the same body stiffness of steel cars. That gives the Prowler very good noise, vibration and harshness characteristics.

The alloys used on the Prowler are as strong as any steel, so durability is not an issue. When aluminum parts touch steel parts, corrosion is an issue, but painting or coating the steel parts eliminates that problem.

The Prowler was designed to absorb energy in stages during a crash, protecting the occupant just as if the vehicle were made of steel.

Cost is still a significant barrier but interest in aluminum remains high. Pound for pound, aluminum is about four times as expensive as steel. The aluminum industry contends there is little it can do to change the raw costs of aluminum because it's traded as a commodity on the London Stock Exchange. What aluminum producers can address, however, is processing costs and progress is being made, according to Dennis Peters, manager, body-in-white and exterior systems.

"Steel has been the material of choice for a couple of thousand years, ever since armies started forging weapons," said Peters. "However, some of the metallurgical knowledge accumulated over the last several centuries can be transferred to aluminum, and that's an advantage over composites. For example, sheet aluminum can be stamped using the same techniques developed for sheet steel, drawing from an existing infrastructure and a skilled workforce."

ARMS, KNUCKLES AND OTHER BODY PARTS

The front and rear suspensions are multi-link systems, which enhance performance, according to Joe Crowley, steering and suspension engineer.  The front is a double wishbone suspension with upper and lower control arms, giving the driver better control. The front spring and shock assemblies are set up similar to Indy and Formula cars, using a pushrod rocker. The rear suspension uses a lower control arm and a three-bar-link upper configuration.

SECRET INGREDIENTS

The hood, decklid, doors and hood side panels are stamped from aluminum alloy 6022-T6. Body tub components are nearly all made of aluminum alloy 5454-0. High strength alloys, 6061 and 6063 (both in T6 temper), were used in the frame. All castings were A-356 T6.

Cold rolled low carbon steel is used to reinforce the front hinge pillar and the tapping plates. The front and rear quarter panels, rear valance panel and "motorcycle" fenders are made of sheet molding compound (SMC). A type of polymer, called acrylonitryle-butadiene-styrene, was used to mold the grille. The front fascia, front and rear bumper covers are made of reaction injection molding (RIM) urethane. Magnesium was used as a frame for the instrument panel.

The magnesium instrument panel, which combines more than 20 stamping and plastic components into a single casting, is eight pounds lighter than a conventional instrument panel construction. An all-aluminum seat saves another seven pounds. Composite rear brake rotors take out another 15 pounds of weight. Several aluminum drive line components not only reduce weight but also vibration.

No single material will ever be the best answer for all situations.

"Cars of the future will continue to be a mix of materials," said Peters. "As promising as aluminum is, no one material is the exclusive choice for all parts.

"In addition to Prowler's stunningly attractive looks, this vehicle has a chance to start a paradigm shift in material processing. At Chrysler, we knew a lot of questions wouldn't be answered until we committed to production. I submit this is just the start of something very big."