Advanced aluminum casting technologies increase critical component application possibilities for vehicle weight reduction.
Over the past two decades, spurred by government regulated corporate average fuel economy (CAFE) and clean air regulations, automotive designers have directed significant attention to reducing overall vehicle weight. Since fuel consumption of vehicles is directly linked to their weight -- a 10 percent decrease in weight results in an estimated 6 percent increase in fuel economy -- much of their effort has been directed toward conversions to lightweight, high-strength materials and improving engine efficiencies.
Starting in 1992, however, vehicle weight started to climb again. These increases have been traced to the adoption of dual air bag restraint systems, antilock brake systems, and added structural elements for improved ride and handling performance. Even customer luxury options like high-powered stereo systems have contributed to putting back weight.
Also adding weight are the increased crashworthiness requirements for front and side impact, as well as roll-over protection.
These new demands will further challenge automotive designers to strengthen structural components without significantly increasing vehicle weight.
Vehicle Aluminum Content
As designers struggle to meet these demanding requirements, they have turned to aluminum as an alternative material. With one-third the density of iron and steel, and a higher strength-to-weight ratio, aluminum has been used successfully to replace steel in load-bearing vehicle structures, with weight savings of up to almost 50 percent. Space frame and unibody chassis constructions have been developed and proven for lightweight vehicle structures, using aluminum sheet, castings and extrusions.
The use of aluminum in passenger cars and light trucks has been steadily increasing over the years, ranging from an average content of 90 kg to as much 160 kg for aluminum intensive models like the Chevrolet Corvette and Oldsmobile Aurora. The Audi A8, which incorporates aluminum in its structure and body, uses 384 kg of aluminum.
According to GM engineer Marv Miller, the combination of steadily rising fuel prices and more stringent CAFE requirements will lead automotive designers to consider aluminum an increasingly viable alternative to traditional materials. "I see the casting processes getting better and better in producing high-integrity components. This will allow the use of aluminum in safety critical areas where previously they have not been considered," he says.
Aluminum Casting Applications
A variety of automotive components have made successful transitions from cast iron and steel fabrication designs to aluminum. Performance-critical structural components include aluminum castings employed in the power train, transmission, steering system, brakes, suspension and wheels. Other parts like intake manifolds and cylinder heads, along with die-cast housings, represent a large share of components being converted to aluminum. Use of cast aluminum engine blocks is also on the rise.
Initially there has been some resistance from traditionally minded designers. But with recent advances in aluminum alloy development, in design, and in casting procedures, as well as with the success of early conversions, automotive engineers are becoming increasingly more confident and comfortable with the use of aluminum castings in performance-critical applications.
Design tools such as sophisticated stress analysis and process modeling techniques, along with modern high technology casting processes such as gravity permanent mold, low-pressure permanent mold, squeeze casting and others, are today producing high-integrity performance-critical components of premium quality.
Further vehicle weight reduction is still possible with aluminum. When body and structural elements are factored in, materials experts predict a doubling of aluminum content in light vehicles in the next decade.