Solving a pressing problem

The ever-growing emphasis on safety in the design of today’s cars presents some significant challenges for manufacturers, and not just in the integration and development of advanced safety technologies.

One challenge is that the stronger materials designed to offer maximum passenger protection in a collision are increasingly hard to cut and modify. This is problematic when manufacturers have to punch holes in hard steel for cable routing — a process that can place considerable stress on traditional mechanical cutting tools. As these tools also leave unwanted material, or burr, on the underside of the steel, extra time has to be spent on a finishing process.

One possible alternative is to use lasers as cutters. However, although the auto industry has used high-power lasers since the early 1980s for a variety of cutting, welding and marking applications, their high-energy demands make the entire process time consuming and costly for this application.

However, researchers at Germany’s Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz believe they may have come up with an alternative.

Working with engineers at Volkswagen, the team, headed by Dr Verena Kräusel, is developing an innovative and potentially lower-cost method of making holes in press-hardened steel bodywork that uses high-pressure electromagnetic pulses.

“Electromagnetic pulse technology was previously used primarily to expand or neck aluminium tubes”

‘The new method is based on electromagnetic pulse technology [EMPT], which was previously used primarily to expand or neck aluminium tubes,’ said Kräusel. ‘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.’

She claims an additional advantage of the technique is that it does not produce any burr and therefore dispenses with the need for a time-consuming and expensive finishing process. What’s more, as the technique has few moving parts, it requires potentially less maintenance than traditional stamping-press-based approaches, which often require the replacement of worn parts.

The pulse generators used consist of a coil, a capacitor battery, a charging device and high-current switches. When the switch closes, the capacitors discharge via the coil within 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 team modified the coil to ensure that resulting electromagnetic field was 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 3,500bar, which equates to the weight of three small cars on a single fingernail,’ said Kräusel.
The original EMPT system was provided by PST Products, but the team is now modifying it for different cutting geometries.