EDM cuts cleaner, smoother
Coordinates for the shape to the cut are entered on a keypad of the EDM (in this case a cutting tool as shown on the monitor). The actual cutting is done by an electric arc in the water-tight chamber on the left.
The Charmilles Technologies Robofil 290 Wire Electrical
Discharge Machine, or EDM for short, uses an electrical spark
delivered by a fine wire to cut through any material that conducts
electricity. Mike Harper, design engineer and the technical
support for the EDM, says that this type of cutting procedure
works cleaner and smoother than any conventional rotary cutting
Looking at the electrical discharge machine in action, one might
think that the material is being cut by the wire in somewhat the
same way a band saw operates. However, the 0.01-inch diameter
wire is actually one of two electrodes, the second being the
soon-to-be-cut material, itself. The EDM can carve anything that conducts electric current, including hardened steel and
silicon carbide, a ceramic. A spool of half-hard brass wire feeds continuously downward, maintaining a spark gap as small
as 0.0002 of an inch, depending on the type and thickness of the material being cut.
Cutting is achieved by spark implosion. As the spark discharges, the workpiece melts locally and disintegrates, throwing off
small particles. This waste material is then flushed away by a powerful jet of deionized water, and the wire advances to
repeat the procedure until the piece is sliced to the desired shape.
Virtually any shape and dimension can be programmed into the computer that guides the wire. For instance, Harper and
Steve Lee, senior lead machinist, fabricated an artificial elbow joint for a dog to specifications from the ISU College of
Veterinary Medicine. The largest workpiece the machine can accommodate in centimeters is 80 cm long, 50 cm wide and 25
cm high, or roughly the size of a half-filled duffel bag.
Since the whole process is computer-controlled, it is highly accurate and allows for creation of precise molds and dies.
"The capabilities of the EDM are amazing," Harper sums up, after expounding the machine's abilities. "You can actually cut
an hourglass shape through a part," by feeding the wire through a starter hole, then rotating it in an offset from the center
point. The five axes of translation allow the upper head to offset the lower head, enabling an angle cut, such as a taper or an
by Courty Arney, student intern