‘Quick Forming’ Hits Fast Track
New Aluminum Forming Process Permits Easier Assembly, Greater Styling Flexibility for High-Volume Cars

An innovative aluminum forming process, expected to provide improved styling flexibility, simplify assembly, boost quality, and improve fuel economy, is getting its debut on the 2004 Chevy Malibu Maxx.

General Motors and Alcoa collaborated on the development of the aluminum forming process—referred to as quick plastic forming (QPF)—which enables the manufacture of more complex forms for production models. Previously, such shapes were limited to concept and low-volume niche vehicles.

The QPF process was adapted from a hot blow forming aluminum process used in the aerospace industry. The process, launched last year at GM's Metal Fabricating Center in New Hudson, Mich., is being used to create the panels for the Malibu Maxx liftgate.

"QPF provides GM greater flexibility to create body panels with eye-catching shapes and adds to our stable of technologies [to] improve fuel economy," said Larry Burns, GM vice president of Research and Development and Planning.

By using QPF, GM is able to make the entire outer panel for the liftgate as one piece instead of two pieces—one steel and one plastic part—which would later need to be joined together.

"We are able to make the entire outer and inner panels for the Malibu Maxx deck lid, without any compromises, exactly as the designer intended," said Greg Bellopatrick, vehicle chief engineer for mid-size vehicles. "Color and fit are not an issue because the panels are one piece instead of several pieces, and they are painted in the assembly plant. Quality is enhanced because the part is more stable, and the assembly process is simplified."

Total mass of the liftgate was also cut nearly in half—from 39 pounds to 20 pounds.

“Ultimately, the goal of both [Alcoa and GM] will be to reduce the cost of aluminum automotive products,” added Dr. Mohammad Zaidi, Alcoa’s chief technical officer. Alcoa has been collaborating with GM on QPF for the past three years through a joint development agreement focused on improving the alloy used for this process.

In the traditional stamping process, sheet metal is deformed between two dies in a heavy press, causing the metal to conform to the shape of the dies. Because aluminum is less rigid than steel, aluminum stampings have a tendency to spring back to their original shape.

With QPF, a heated aluminum sheet is subjected to high-pressure air that makes it conform to the shape of a hot tool. The high temperature improves the formability so that even complex shapes can be manufactured. Dimensionally correct panels are possible because "spring back" is nearly eliminated. The QPF process is math-based, with the dies created directly from design data. Simpler, one-sided tooling also reduces development time and aids in shortening the vehicle development process.

Evolution of an Idea
Before GM and the Department of Energy (DOE) sponsored research into QPF, "blow forming"—as the process is also known—was not a viable process for automakers. The prior blow-forming process, called superplastic forming (SPF), was not suited to the industry's high-production-rate demands, and the materials required for SPF were too expensive—three times the cost of standard, non-SPF, aluminum sheet metal. Bringing SPF to the automotive industry would require developing low-cost SPF alloys and faster forming cycles.

Reducing the cost of SPF alloys also required demonstrating the viability of SPF to both the automotive and aluminum industries. DOE initiated a program of joint-funded research between GM and Kaiser Aluminum, with the Pacific Northwest National Laboratory (PNL) providing encouragement to GM to develop aluminum blow-forming processes.

Based on early research, GM recognized the inherent limitations of superplastic forming and moved forward with the commercialization of an advanced blow forming process—which came to be QPF. The result is a cost-effective, higher-volume manufacturing technology that is producing lightweight components for today's automobiles.

Superplasticity in metals is characterized by very high tensile elongations ranging from 200 percent to several-thousand percent. Under controlled temperature and strain rates, the process dramatically increases the formability of certain aluminum alloys and allows production of highly integrated, net-shape components that often consolidate many parts into one. This reduces the number of parts, fasteners, and assembly operations required for complex automotive and aerospace applications—and enables the use of aluminum in place of steel at competitive costs. The drawback of conventional SPF, however, is that it can require cycle times of 20 minutes or more.

Following the close of the joint GM-PNL research program into SPF, GM's partnership with DOE tested new alloy compositions in an attempt to reduce forming time. In one test case, an apparent reduction in forming time was found for the modified alloys compared to one commercial, SPF-grade AA-5083.

The research results catalyzed thinking within GM to actively pursue hot blow forming of aluminum as a mainstream metal working technique. Following additional development work, GM successfully used hot blow forming to produce aluminum closure components.

GM's development of a cost-effective process and cost-effective sheet materials has made blow forming of aluminum viable for higher and higher volume vehicles, ensuring that future vehicles will be lighter, more fuel-efficient, and made from aluminum.