COLUMBUS, Ohio -- Automakers may shape aluminum parts more easily in the future because of a new technique developed at Ohio State University that uses electromagnetic pulses to shape metal.
Manufacturers have known for years that they could make cars lighter and more fuel efficient by incorporating aluminum parts, but the metal often tore when they tried to stamp it into shape.
“Manufacturers could take about half the weight out of an auto body if they could translate a steel design into aluminum,” said Glenn S. Daehn, professor of materials science and engineering. “But until now aluminum has been hard to form.”
To address the problem, Daehn and his colleagues at Ohio State and the Big Three auto makers developed a new process that combines traditional metal stamping with electromagnetic forming. In the new hybrid technique, a tool stamps out the general shape of a part, and electromagnetic pulses help form fine details.
Daehn and Vincent J. Vohnout, a postdoctoral researcher in materials science and engineering, conducted this most recent work in conjunction with researchers at General Motors Corp. Vohnout presented their most recent results at the International Conference on Technology of Plasticity in Nuremberg. Daehn posted related material to his Web site. [see http://www.osu.edu/hyperplasticity]
Commercial aircraft bodies are largely aluminum, Daehn explained, including the fuselage, wing structure, and door panels -- parts with gradual, sloping curves and few sharp corners. Automakers may make hoods or trunk lids out of aluminum, but not much more. Parts with complex shapes are too difficult to form, he said.
“If you bring a magnet to an auto show, you can figure out how much aluminum is actually in the cars,” Daehn said. “You’ll find that there’s not very much.”
The researchers used the hybrid process to form an automobile door inner panel, that of GM’s Chevy Cavalier. Daehn said an aluminum panel would be impossible to make the same way steel panels are made -- with a single stamp of a tool and die -- because they are full of sharp corners and pockets.
To keep the aluminum sheet from tearing, they softened the shape of the tool, replacing sharp corners with gradual curves, and stamped the general shape of the part.
Then they turned to electromagnetic forming, a technique in which electric current creates a magnetic field around a metal, and like-charged metal coils then repel the metal into a mold. The researchers placed coils behind only the unfinished spots of the panel, and used electromagnetic force to push the panel all the way into the sharp corners of the original mold.
In tests, the researchers were able to form aluminum door panels that closely matched the shape of their steel counterparts without tears or wrinkles. They also performed formability tests on both age-hardened and non-hardenable aluminum -- two types of the metal used commercially -- and found both exhibited tremendous gains with this process.
While traditional stamping can stretch most aluminum alloys to a maximum of 30 percent of their original length before tearing, Daehn and colleagues have stretched parts a full 100 percent without tearing. Also, tests have shown this process does not degrade the material in any way.
“That extra elongation enables us to form many complicated parts that are otherwise difficult to impossible,” Daehn said.
These tests were performed with two steps, first the stamping and then the electromagnetic forming. But Daehn envisions that manufacturers could install electromagnet coils within a die and perform both steps at the same time.
According to this scenario, when the mold closes, the aluminum will first conform to the softer shape of the tool. Then electromagnetic force from the coils will push the metal the rest of the way into the die. As Daehn describes it, the part would “pop into shape.”
Daehn said manufacturers already use electromagnetics for assembly, but not for sheet metal forming. “What we’re trying to do is develop methods of aggressive sheet metal forming based on electromagnetic forming -- take it in a new direction,” he said.
“In principle, this is fairly simple to do,” Daehn continued. “It’s just that nobody thought of it before.”
Manufacturers wouldn’t need to buy new forming tools to use the hybrid process, Daehn said, because they could retrofit their existing equipment. He estimated that adding electromagnetic coils and connections would cost less than 25 percent of the price of the original equipment.
“That’s one of the beauties of this process. The original equipment probably cost millions of dollars, but for a few percent more, manufacturers can have much more capability,” he said.
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