Better metal: Magnetic pulses bump metal into shape

By Pam Frost Gorder, Research Communications

A process developed at Ohio State for shaping metal parts using magnetism has reached a new milestone -- one that may cut manufacturing costs and help preserve the environment. The process could also expand manufacturers' choice of available metals, and enable the use of aluminum parts in lighter, fuel-efficient automobiles.

Glenn S. Daehn, professor of materials science and engineering, and his colleagues pioneered hybrid electromagnetic metal forming in 1999, while collaborating with the "Big Three" automakers. With this process, a traditional tool and die stamps the general shape of a part out of sheet metal. Afterward, a magnetic field pushes at specific locations of the sheet metal to form fine details or complex shapes.

Now the Ohio State engineers have discovered that they can improve the process if they use the magnetic field to stretch certain portions of the metal during the stamping operation.

Professor Glenn Daehn is heading a study of magnetic fields and metal.   By Kevin Fitzsimons

In tests, they were able to create an aluminum pan with a depth nearly 1.5 times greater than previously possible, and they did so without relying upon the potentially toxic industrial lubricants normally required for stamping.

Daehn described the improved process Oct. 9 in Columbus, at the annual meeting of the Minerals, Metals, and Materials Society, now known as TMS.

Daehn calls the process "bump forming," because the magnetic field bumps against the metal in many short pulses -- typically 5 to 20 times in less than one second -- while the metal moves into the die.

Normally, as a sheet of metal bends to fit inside a tool and die, some parts of the sheet stretch more than others. These are the parts that may tear if the metal stretches too much.

With Daehn's technique, electromagnetic fields work against the parts of the sheet that would not normally stretch, causing them to bow out. With this extra amount of "give" in the metal, other portions of the sheet will be less likely to tear.

The process works well in electrically conductive metals, including aluminum. When exposed to a strong electromagnetic field from a coil inside the punch portion of the stamping tool, a corresponding electrical current and electromagnetic field form inside the metal. The field in the coil and the field in the metal repel each other, pushing the aluminum away from the punch.

Bump forming could be very useful in mass production, Daehn said. From the auto industry to aerospace and electronics, large manufacturing operations often need to stamp as many as 10 million copies of their metal components per year.

"The process has to be reliable, and require as little human intervention as possible," Daehn said. "In automobile production especially, manufacturers need to make parts in as few steps as they possibly can. I think we can do a lot of good things for industry with this technique."

Daehn and Ohio State postdoctoral researcher Vincent J. Vohnout developed their bump forming technique with Ishikawajima-Harima Heavy Industries Co., Ltd., one of the largest manufacturing companies in Japan.

Using automotive-grade aluminum, the engineers stamped out a shape similar to a baking pan. Because aluminum tears easily, manufacturers typically need to coat the metal with lubricant in order to stamp it, Daehn explained. The potentially hazardous liquid is then washed from the metal and disposed of, at a significant cost.

With conventional stamping equipment and lubricant, the deepest pan they could create without tearing the aluminum was 1.7 inches (4.4 centimeters). After placing electromagnetic actuators in the same equipment and using the bump forming procedure, they were able to stamp a pan 2.5 inches (6.4 centimeters) deep -- a 47 percent increase.

Most significant to Daehn is that they were able to make a deeper impression using the same stamping pressure, and without using any lubricant.

Daehn counted off several potential benefits for industry.

"We can enable the use of higher strength materials and aluminum alloys in manufacturing. We can reduce the amount of equipment associated with metal forming. Parts that used to require multiple steps could be made with one set of tooling, which would mean a big cost savings. And we think we can eliminate reliance on these nasty lubricants," he said.

From start to finish, the bump forming process can be designed to take five seconds or less per part, which would fit in with typical manufacturing cycles.

Daehn and Vohnout patented their bump forming process, and are seeking further funding to develop it. The National Science Foundation has largely funded the work thus far.

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Increased CO levels are mixed blessing for agriculture

A new study suggests that rising levels of carbon dioxide in the atmosphere could be a boon for agricultural crops, as this greenhouse gas helps crop plants grow and reproduce more. But that boon comes with a price, said Peter Curtis, a professor of evolution, ecology and organismal biology. Greater growth and reproduction may hurt the nutritional value of crops.

"If you're looking for a positive spin on rising CO levels, it's that agricultural production in some areas is bound to increase," Curtis said. "Crops have higher yields when more CO is available, even if growing conditions aren't perfect. But there's a tradeoff between quantity and quality. While crops may be more productive, the resulting produce will be of lower nutritional quality."

Nutritional quality declines because while the plants produce more seeds under higher CO levels, the seeds contain less nitrogen. "The quality of the food produced by the plant decreases, so you've got to eat more of it to get the same benefits," Curtis said. "Nitrogen is a critical component for building protein in animals, and much of the grain grown in the United States is fed to livestock. "Under the rising CO scenario, livestock -- and humans -- would have to increase their intake of plants to compensate for the loss."