The generic term EDM (Electrical Discharge Machining) can be applied to
any machining process that uses an electrode to remove metal, or any other conductive
material, from a workpiece by generating sparks between conducting surfaces. During this
process, energy from the sparks created between the electrode and the workpiece is
dissipated by the melting and vaporizing of the workpiece material. All this being
performed in a dielectric fluid to prevent premature spark discharge.
Wire EDM is a method to cut conductive materials with a thin electrode
that follows a programmed path. The electrode is a thin wire. As the
wire feeds from reel to reel, it uses sparks of electrical energy to progressively erode
an electrically conductive work-piece along a path determined by the relative motion of
the machine's axis. Typical wire diameters range from
.004" - .012" although smaller and larger diameters are available. The
hardness of the work piece material has no detrimental effect on the cutting speed.
There is no physical contact between the wire and the part being machined. Rather,
the wire is charged to a voltage very rapidly. This wire is surrounded by de-ionized
water. When the voltage reaches the correct level, a spark jumps the gap and melts a small
portion of the work piece. The de-ionized water cools and flushes away the small particles
from the gap.
Wire EDM can be accurate to +/-.0001". No burrs are generated.
Since no cutting forces are present, wire EDM is ideal for delicate parts. No
tooling is required so delivery times are short. Pieces over 16" thick can be
machined. Tools and parts are machined after heat treatment so dimensional accuracy is
held and not affected by heat treat distortion.
Today, wire EDM is considered a mainstream metalworking process and it is
not unusual to find a wire machine in the average job shop or typical toolroom.
Although the basic principle of wire EDM has not changed, the process has
advanced dramatically in the size, complexity, speed and accuracy of the metal-cutting it
can perform even as the equipment has become more affordable, more reliable, and easier to
operate.
The EDM scene has changed dramatically since the Swiss firm Agie
introduced the world's first industrial NC controlled EDM machine in 1969. In the
early days of EDM a typical machine would cut under two square inches per hour.
Today's machines cut well over twenty square inches per hour. Speed, finish, and
techniques have all improved at a dramatic rate, making EDM a contender for production
machining where accuracy and finish are primordial.
