New process improves ‘bump forming’

A process developed at Ohio State University for shaping metal parts using magnetism may cut manufacturing costs and help preserve the environment.The process could also expand manufacturers’ choice of available metals, and enable the use of aluminium 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’ car manufacturers.

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.

In tests, they were able to create an aluminium 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 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 is said to work well in electrically conductive metals, including aluminium. 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 aluminium 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, manufactures 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 aluminium, the engineers stamped out a shape similar to a baking pan. Because aluminium 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 aluminium was 1.7 inches. After placing electromagnetic actuators in the same equipment and using the bump forming procedure, they were able to stamp a pan 2.5 inches deep.

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

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.