Fraunhofer Institute creates electromagnetic “drill”
By DE StaffGeneral Automotive Metal Fabrication metalworking R&D
EM field provides superior hole-cutting in press-hardened steel for automotive applications.
Working together with a number of partners including Volkswagen, researchers at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz have come up with another way to make holes in press-hardened steel bodywork.
"The new method is based on electromagnetic pulse technology (EMPT), which was previously used primarily to expand or neck aluminum tubes," explains Dr. Verena Kräusel, head of department at the IWU. "We’ve modified it to cut even hard steels. Whereas a laser takes around 1.4 seconds to cut a hole, EMPT can do the job in approximately 200 milliseconds – our method is up to seven times faster."
Another advantage is that it produces no burr, thus doing away with the need for a finishing process. Stamping presses become superfluous, and no costs arise from the need to replace worn-out parts.
The pulse generators comprise a coil, a capacitor battery, a charging device and high-current switches. When the switch closes, the capacitors discharge via the coil within a matter of microseconds, producing a high pulsed current. The coil converts the energy stored in the capacitors into magnetic energy. To be able to use this process to cut steel, the researchers had to modify the coil to ensure the resulting electromagnetic field is strong enough: the pressure with which the field hits the steel must be so high that it forcibly expels the material from the sheet.
"The impact pressure on the steel is approximately 3,500 bar, which equates to the weight of three small cars on a single fingernail," says Kräusel. PSTproducts GmbH in Alzenau provided the original EMPT system. Presently, researchers are developing coils for various cutting geometries.