COLUMBUS, Ohio -- Researchers at Ohio State University have found a way to use light-emitting sensors to detect wrinkles as they begin forming in sheet metal during manufacturing processes.

The new sensing technique could help auto manufacturers prevent these wrinkles and build better quality car parts with higher productivity and fewer mistakes, said Yuan Zheng, a professor of electrical engineering at Ohio State.

Zheng and Pratap Pereira, a graduate student at Ohio State, successfully tested the new sensing technique using fiber optic and laser sensors.

Wrinkling is a common problem in a variety of processes where sheet metal is used, Zheng explained. When sheet metal is pushed into a die, the pressure on the metal has to be exactly correct. If the pressure is too strong, the metal will tear. If the pressure is too weak, the metal will wrinkle. Currently, manufacturers have to rely on trial and error to determine the correct pressure to use in a particular process. Even then, mistakes are routine.

"Our sensing process can monitor the status of sheet metal

while it is actually being pushed into the die," Zheng said. "The sensors can detect wrinkles being formed before they can be seen, and can adjust the pressure accordingly."

The researchers tested their technique using two different types of sensors. In one setup, two fiber optic sensors are used. The sensors each emit a beam of light which strikes the sheet metal as it is being pushed into the die and is reflected back to the sensor. If the length of one beam of light becomes longer or shorter than the other, that indicates a wrinkle is starting to form, Zheng said. That information can be fed into a computer that adjusts the pressure on the metal. This system can detect wrinkles being formed while they are still only a few microns high. (A micron is one-thousandth of a millimeter.)

A second setup uses a single laser sensor that measures changes on the metal surface by emitting a beam to the surface which is reflected back onto a third surface. This "triangulation" method is even more precise than the fiber optic system. However, it is bulkier and not practical for use during the manufacturing process.

"We think this laser process could be used off-line for quality control inspection of finished products," Zheng said.

Both types of sensors are already commercially available, according to Zheng. However, these sensors have never been used before to detect wrinkles in the manufacturing process.

Zheng emphasized that this sensing strategy has only been tested in the laboratory, and the results need to be replicated in a manufacturing environment. "But the auto industry is very interested in this process," he said.

With auto manufacturers introducing new models more frequently, new dies are constantly being designed. This sensing strategy will help manufacturers get new dies working properly more quickly, Zheng said.

While the auto industry is the most obvious beneficiary of this new process, he said companies using sheet metal to produce products ranging from house gutters to cake pans can use sensors to their advantage. "We think the sensing strategy will have a wide variety of uses in industry," he said.

The study was published in a recent issue of the journal IEEE Transactions on Instrumentation and Measurement. It was funded by the U.S. Office of Naval Research and Ohio State's Engineering Research Center for Net Shape Manufacturing.

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Contact: Yuan Zheng, (614) 292-2571

Written by Jeff Grabmeier, (614) 292-8457