The thunka-thunka of massive stamping presses for aluminum in sheet-metal forming plants may someday be replaced by the buzz of giant electromagnetic coils.
A technology being tested by Ohio State University and automakers in the industry-government U.S. Council for Automotive Research uses powerful magnetic fields to form aluminum panels quickly. Compared with conventional stamping, electromagnetic metal forming could offer higher precision and greater latitude for designers working in aluminum, although it may be more expensive.
Aluminum is being used more and more in vehicles as a lightweight alternative to steel. But it presents problems: Aluminum is more expensive than steel, and its unique properties make it tricky to form with conventional stamping presses.
Springback, or the tendency of a stamped part to return to its original shape after the press opens, is three times greater in aluminum than in steel. Also, aluminum wrinkles and tears more easily in corners and creases.
LIKE ELECTRIC MOTORS
'It would be nice to have another way of forming aluminum,' says Andrew Sherman, senior technical specialist with Ford Motor Co. research and leader of the team developing electromagnetic metal forming for the auto industry.
The technology is currently used to put yokes onto driveshafts and in some aerospace applications, but 'the use of large coils to form metal is untried,' says Sherman.
It works on some of the principles that drive electric motors. Large electric coils behind a sheet of aluminum are charged with a short but high-current pulse of electricity. The coils thus generate a magnetic field which automatically induces an oppositely charged field in the metal. The sheet is then repelled from the coil and into a die.
The technique is also called high-velocity forming because the charged aluminum sheet rockets into the die at more than 600 feet per second.
WRITING THE BOOK
In early tests, the process reduced wrinkling and springback in door and hood pieces with tight corners and creases.
Cost and tooling durability are issues that remain unsettled. Also, there is little experience with arranging and powering the coils to achieve the desired pressure on the part without cumbersome trial-and-error. Engineers will need time to 'write the book' on electromagnetic metal forming.
Meanwhile, they are exploring alternatives such as improved stamping technology, hydroforming, so-called warm forming with heated metal and super plastic metal forming, which uses gas pressure to form the aluminum.
The consortium is about to embark on a second, two-year phase of the project to address the unknowns in electromagnetic forming. The project is expected to cost $1 million to $2 million, which will be shared by the government and the auto and aluminum industries.
'We have demonstrated that the technology can do something we are interested in,' says Sherman. 'Now we have to figure out if it is useful, if it is a repeatable process in an industrial environment, and whether it is economical.'