Making fair comparisons

Recently an article from The Register popped up in my e-mail with a report on work done for Volkswagen using electromagnetic pulses (EMP) to cut holes in press hardened steel.

Recently an article from The Register popped up in my e-mail with a report on work done for Volkswagen using electromagnetic pulses (EMP) to cut holes in press hardened steel. The developers, Fraunhofer Institut für Werkzeugmaschinen und Umfomtechnik claim their EMP process is seven times faster than laser. The author of the article, Lewis Page, sums up the Fraunhofer work saying, "The laser is, quite literally, no longer on the cutting edge."

Normally I would have ignored this except that Page's article headline is "German electropulse energy drill bitchslaps lasers." Now that gets my attention. So I contacted knowledgeable people within the laser community and asked for their comments. The following summarizes what they had to say in regard to the Page article.

The EMP technology has been around for many years, for example, a 1975 UK patent, 1388444 for Magnetic Pulse Welding and Apparatus, describes the technology, in this case by Thermatool Corporation in the U.S. This process, and others including the Volkswagen application, requires a coil to be positioned above the workpiece, replacing one side of the die. The coil requires accessibility to the processing area and a die is still needed to punch the hole, the latter raising the issue of tool wear. Both of these process concerns are exactly what the non-contact laser beam with its remote laser location potential offer as advantages in stamping processes.

While the fast cutting time (200 ms) is an EMP advantage, the total time to make a hole (the total processing cycle) should include the time to position and remove the die and coil and the time, needed to recharge the power supply capacitor bank. In fairness the laser's time may not be seven times slower than EMP.

The laser has the ability to rapidly change the beam's cutting path, whereas the EMP process typically requires a coil adaption to the hole size and shape and a complementary die change, cycle time extenders compared to the laser. So a direct comparison of the two processes should account for all of the above.

A comment expressed to me concerned tool wear. While one die is eliminated by the electromagnetic field, the remaining one still needs maintenance, as does the coil because of the required field's resulting high Lorentz forces within the coil. As field pulse strength increases with decreasing material conductivity and increasing material strength, coil lifetime may be a critical issue when processing material like steel. This should also be a factor in a cycle time analysis.

Further opinion is the laser's inherent flexibility as a non-contact processing tool, except when the process is one in which hole shapes and sizes do not vary within a given cycle time, is an advantage. And if the process requires a large number of holes to be made in a part, the power supply recharge time between pulses may be an issue.

So, as is the case in many applications, the laser's competitiveness should be fairly judged taking into account all factors of the process cycle. Over the years the laser has found its niche as an economical processing tool, even in certain conditions where its flexibility is not an issue. I would have ignored the EMP application if the article author had not used the particularly irritating action verb, "bitchslaps."--DAB

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