General Motors Corp. engineers, working with researchers at Ohio State University, have developed a new "hybrid" method of manufacturing aluminum parts. The process combines conventional metal stamping with electromagnetic forming to create aluminum parts that would not be possible to manufacture in the traditional manner.
The new process may facilitate the increased use of aluminum for automotive applications.
Glenn Daehn, professor of materials science and engineering at OSU, says that aluminum parts often tear when attempting to simply stamp them into shape. Working with researchers at the Big Three, Mr. Daehn and Vincent J. Vohnout, a postdoc-toral researcher, developed the new technique in which a tool stamps out the general shape of a part, then electromagnetic pulses are used to form fine details.
James F. Quinn, an engineer with GM's materials group R&D and chairman of the U.S. Automotive Materials Partnership, a United States Council for Automotive Research (USCAR) subcommittee supervising the contract with OSU, says the research project is an enabling step for using more aluminum in vehicles.
The ultimate goal is to achieve cost neutrality with steel, but he admits further research is needed to perfect the hybrid process for making large aluminum body panels. The process is production-ready to manufacture smaller aluminum parts now, Mr. Quinn says.
Mr. Daehn and GM engineers used the hybrid method to form an inner door panel for a Chevrolet Cavalier; Mr. Daehn says it would be impossible to make the part with a single stamping of a tool and die because the part hasintricate corners and pockets.Conventional stamping can stretch most aluminum alloys to a maximum of 30% of their original sheet size before tearing. Mr. Daehn's research team has stretched parts 100% without tearing by using the hybrid process. Here's how it works:
The researchers soften the shape of the basic tool, replacing sharp corners with gradual curves to stamp the general shape of the part. In the second step, electromagnetic forming is used to complete the part; this involves creating a magnetic field around the aluminum and like-charged metal coils that repel the metal into a mold. The OSU researchers place coils only around the unfinished parts of the panel, then employ electromagnetic force to push the panel all the way into the more intricate areas of the mold.
Aluminum door panels that closely matched the shape of steel counterparts were produced without tears or wrinkles. Both age-hardened and non-hardenable aluminum showed tremendous improvement in formability tests. Aluminum parts produced with the new hybrid method did not degrade in any way.
The hybrid manufacturing process allows extra elongation to form complicated aluminum parts that are otherwise difficult with the traditional stamping process. Although the researchers achieved their results with a two-step process, Mr. Daehn says manufacturers could install electromagnetic coils within a die and pop the part into shape in a single-step process: when the mold closes, the aluminum will first conform to the softer shape of the tool, then the electromagnetic force from the coils would then push the metal the rest of the way into the die.
Mr. Quinn notes that the hybrid electromagnetic stamping process currently is used to manufacture small cylindrical parts such as shafts and tubes. The process also is used to crimp the housing of fuel sender units. Mr. Quinn says the OSU process promises to allow manufacturers to create aluminum panels with sharp lines - a feat now difficult to achieve with conventional metal stamping due to the springback characteristics of aluminum.
"What we're trying to do is develop methods of aggressive sheetmetal forming based on electromagnetic forming - take it in a new direction," Mr. Daehn says. "In principle, this is fairly simple to do, it's just that nobody thought of it before."
One of the advantages of the new process is that it would not require manufacturers to spend extra money on the forming tools because they could retrofit existing equipment. Mr. Daehn estimates that adding electromagnetic coils and connections would require an investment of 25% more than conventional tooling.
"That's one of the beauties of this process," Mr. Daehn says. "The original equipment probably cost millions of dollars, but for a few percent more, manufacturers can have much more capability."
