Page 136 - Module DMV20173

7.0 NON CONVENTIONAL PROCESSES

i. DIELECTRIC FLUIDS

The main functions of the dielectric fluid are to:
 act as an insulator until the potential differences is sufficiently high;
 act as a flushing medium and carry away the debris in the gap;

 act as a cooling medium;
1. The most popular dielectric fluids are hydrocarbon fluids, silicone-based oils and
de-ionised water.
2. Kerosene and water with Glysol are generally used. The requirements of a

dielectric fluid are:
i) It should have sufficient and stable dielectric strength to serve as an
insulation between tool and work till the breakdown voltage is reached.
ii) It should de-ionise rapidly after the spark discharge has taken place.
iii) It should have low viscosity and a good wetting capacity to provide an

effective cooling mechanism and remove the chip particles from the
machining gap.
iv) It should be chemically neutral so as not to attack the electrode, the
workpiece, the table or the tank.

v) Its flash point should be high so that there are no fire hazards.

ii. ELECTRODES

1. In the EDM process the shape of the electrode is impressed on the workpiece in
its complimentary form and as such the shape and accuracy of the electrode

plays a major role in the final accuracy of the workpiece machined.
2. The electrode material should have the following characteristics to serve as a
good tool:
i) It should be a good electrical and heat conductor.
ii) It should exhibit low electrode wear rates.

iii) It should be easily machinable to any shape at a reasonable cost.
3. Electrodes are made of graphite, copper, copper graphite, zinc alloy, brass,
copper tungsten, silver tungsten, and other materials.

4. The selection of electrode material depends on the type of power supply circuit
available, the type of the workpiece, and whether roughing or finishing is to be
done. Graphite is preferred for many applications because of its melting
characteristics.

BPLK 168 DMV 20173