Electromagnetic pulses to punch holes in steel

German researchers discovered something very interesting.
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It's a knockout
Jan 14th 2010
From The Economist print edition
Engineers find a new way to punch holes through steel
ELECTROMAGNETIC pulses (EMPs) are usually associated with warfare. The
idea is to use a blast of energy to fry the enemy?s computers and
telecommunications gear. One common way proposed to do this is with an
atomic bomb. In a less extreme fashion, however, EMPs have peaceful
uses. They are already employed industrially to shape soft and light
metals, such as aluminium and copper. Now a group of researchers at
the Fraunhofer Institute for Machine Tools and Forming Technology in
Chemnitz, Germany, has found a way to use an EMP device to shape and
punch holes through industry?s metallic heavyweight?steel. This
could transform manufacturing by doing away with the need to use
large, heavy presses to make goods ranging from cars to washing
Verena Kräusel and her colleagues performed their trick by beefing up
an existing electromagnetic-forming machine. Such machines use a bank
of capacitors to discharge a current rapidly through a coil. The coil
converts the current into a powerful magnetic field. When the
component to be worked is placed next to such a machine, the coil
induces in it a corresponding field. Like poles repel, and the
repulsion between the two fields is strong enough to make the metal
Dr Kräusel and her colleagues boosted the power of their machine by
strengthening its coil and speeding up the rate at which the
capacitors dump their charge. The result is an extremely strong
field?one that delivers enough pressure when it hits the steel to
punch out the material next to it, leaving a hole behind. The impact
pressure on the steel is about 3,500 atmospheres. That is the weight
of three small cars pressing on an area only a centimetre or so
The result is that the machine is able to punch holes 30mm in diameter
through the type of sheet steel used to build car bodies, which is
usually around 1mm thick. The group have also used their machine to
punch holes in hardened steel, including stainless steel. And, besides
punching holes in steel, such a machine could also be used to form
shapes out of the metal without the need to use a mould or a die.
Firms such as Germany?s giant carmaker Volkswagen are sponsoring the
project because forming steel components with an EMP device provides a
number of advantages. Although using a heavy press to bend metal and
cut holes in it is fast, the tearing action at the edges of the holes
leaves ragged, sharp tailings, known as burrs. This means that parts
stamped out this way have to be cleaned up, usually by hand, which
increases production costs. The need to keep replacing the stamps and
dies used by the press, as they become blunt, also adds to the
Lasers are one alternative. They can cut cleaner holes in steel, but
they are slower than stamping because they need to burn their way
around the part. They are also expensive to operate. An
electromagnetic punch, however, stamps its hole without tearing the
metal, which means no burrs are left behind, and it never gets
blunt. In fact, says Dr Kräusel, her machine can punch a hole clean
through a sheet of steel in a fifth of second?compared with the 1.4
seconds needed by a laser.
The team members are now carrying out further development work on the
coil. They expect factories to take up the idea quickly, because it is
a modification of equipment that is already familiar. The size of
holes that can be cut depends on the size of the coil, so specific
coils will be needed for each application. Specific punches, however,
are needed for traditional presses, so this would not seem to be a
deterrent?especially as an EMP device should be able to deliver
consistently accurate blows without wearing itself out. A hole, new
technology, as it were.
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