Wire EDM Machine Operation Chapter 1
Copyright November, 98 Page 1-5 Sodick Inc.
install another DI bottle on the incoming water line being used by the wire EDM dept.
These bottles are available from a water service company like Culligan. High water
resistivity allows a focused discharge, which allows the machine to cut fast, stable and
reduces rusting of the workpiece. Low water resistivity allows the discharge to leak out
of the cutting area, which slows down the cut, the EDM process becomes unstable and
parts rust easier. Water additives available from after market suppliers that reduce rusting
may decrease the cutting speed and the life of the DI resin. Normal setting for water
resistivity is 50,000 ohms to 100,000 ohms per centimeter (5 to 10 on the resistivity
meter). Use a setting of 20 when cutting carbide or aluminum. This allows a more
focused discharge for carbide and prevents oxidation on aluminum. When the DI bottle
cannot maintain a resistivity higher than 3 it must be refilled with new medium. Some
water service companies also offer this service. NOTE: If you are cutting using EFII
circuitry, the resistivity should be between 5 and 7 for all materials. Clean the probe in
the dielectric tank on a regular basis to maintain a valid reading on the meter (see page
12-3).
WORKPIECE MATERIAL AND HARDNESS
Another factor that contributes to the EDM process is the material to be machined. Any
material that will conduct electricity can be machined on an EDM machine. However,
some materials will cut more easily than others will. A hardened piece of tool steel will
cut better than in its soft state. With soft material, the particles formed will usually be
larger, and harder to flush.
Conductivity and melting point of a material are the two biggest factors that contribute to
how the material cuts. Carbide is considered one of the more difficult materials to EDM
because it doesn’t conduct electricity very well and it has a very high melting point.
You may want to make a test cut if you are going to be machining a new material that
you have never cut before. Sodick application engineers will be able to help you with the
specifics of cutting many kinds of materials if you need assistance.
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Many factors called parameters control the way the EDM process occurs. What follows is
an attempt to explain each of the parameters. For the beginner, remember that we are just
introducing each one. Try not to become bogged down by attempting to memorize each
one now. Cutting conditions developed by Sodick will usually generate the desired
cutting without you having to adjust them. However, as time goes on you will want to get
more familiar with each of the parameters so you can easily fine tune for desired results
and even create your own cutting conditions.
Each factor directly contributes to machining speed, part finish, and accuracy. Keep in
mind that as you modify the parameters that make up a cutting condition to improve one
of these objectives, the other two may suffer.
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