Metal Information Center

Aluminium takes starring role in GM car

October 29, 2007 – 5:33 am

LIVONIA, Mich. - General Motors Corp. has put two-and-a-half times as much aluminum as steel into the Precept, its first high-mileage supercar concept model which foreshadows the prototype auto GM is expected to unvell before 2004 to meet its commitment to the government-industry Partnership for a New Generation of Vehicles (PNGV).

Equipped with more than half a ton of lightweight aluminum components, including several parts of the hybrid electric propulsion system, the Precept is a 5-passenger car capable of providing approximately 90 miles per gallon with diesel fuel, equivalent to about 80 mpg with gasoline.

The first detailed account of the body structure (spaceframe) and body shell applications for metals in the Precept, which was introduced early this year, was given by Thomas L. Lobkovich, manager of advanced body engineering for GM, at the 21st annual Automotive Design and Fabrication Seminar here sponsored by the Automotive and Light Truck Group of the Aluminum Assocaiton.

Lobkovich said that the aluminum body structure of the Precept weighted 152 kilograms (335 pounds). The structure is made up of 192 parts joined by 600 rivets, 1,600 spot welds and 15 meters of metal inert gas (MIG) welds but no adhesive bonds.

The Precept’s body shell employs approximately 163 pounds of aluminum in such applications as the doors, hood, fenders and roof, he said. About 60 percent of the chassis, which weights a little over 440 pounds, is aluminum, used in components of the suspension, steering, braking and other systems. Altogether, the Precept contains more than 1,100 pounds of aluminum vs. less than 440 pounds of steel, Lobkovich said.

Stampings, or sheet parts, account for the biggest share of the aluminum applications in the body structure of the Precept, the GM executive said, followed by extrusions and castings. The stamped spaceframe components are believed to account for around 140 pounds while the extrusions and castings make up 108 pounds and 71 pounds, respectively.

Lobkovich said that some aluminum matrix composites were used in the demonstration car in such applications as brake rotors and engine mounting brackets.

Although the Precept is the big automaker’s proof-of-concept vehicle for the PNGV program (AMM, Jan. 12), Lobkovich said that GM engineers also viewed the car as a test bed for advanced technology. In addition to aluminum and steel, the vehicle contains carbon fiber composites, magnesium, powder metals, copper and other materials. Applications for the carbon fiber-reinforced plastics include the front and rear bumper beams.

Other aluminum components in the unusual car include the front and rear cradles, engine block and head, electric motor housing, differential housing, steering column support (including the cross-car instrument panel beam), all four road wheels and some parts of the seat frames.

Excluding the powertrain, Lobkovich said that GM’s extensive use of aluminum provided a mass reduction of more than 250 kilograms (551 pounds) compared with a conventional steel-intensive vehicle. “For the future, we think aluminum has the potential to provide mass reductions of 30 to 55 percent compared with conventional materials, depending on the applications.” The fact that aluminum parts can be made in a wide variety of product forms, such as castings, extrusions, stampings and forgings, was a factor in its favor, he said.