EM pulses to cut holes in steel

Looking for a way to drill holes in the steel chassis of vehicles without weakening the surrounding structure, researchers from the Fraunhofer Institute for Machine Tools and Forming Technology in Germany have started to use pulses of electromagnetic energy.

Automobile manufacturers often have to punch holes in the steel frames for cable routing. Struggling to pierce the hard steel, mechanical cutting tools rapidly wear out. And because they also leave some unwanted material, or burrs, on the underside of the steel additional time has to be spent on a finishing process. One possible alternative is to use lasers as cutters, but they require a great deal of energy, which makes the entire process time-consuming and costly.

Working together with a number of partners including Volkswagen, researchers at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz came up with another way to make holes in press-hardened steel bodywork.

Verena Kräusel, head of department at the IWU, explained: “The new method is based on electromagnetic pulse technology (EMPT), which was previously used primarily to expand or neck aluminum tubes. 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. The pulse generators comprise a coil, a capacitor – to provide a rapid pulse of electricity –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 electrical energy into a magnetic field. To be able to use this process to cut steel, the researchers =had to modify the coil to increase the peak strength of the electromagnetic field: 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,” claimed Kräusel.

PSTproducts in Alzenau provided the original EMPT system and the researchers are now altering the coils for various cutting geometries.

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