There have generally been two major methods of electrode
clamping and feeding. These include the use of wire
(e.g. pure tungsten) on a spool which is fed through a system
of ceramic guides towards the workpiece, as shown in
Fig. 2 [6]. The electrode or clamping system does not rotate.
The other main method has been to use lengths of brittle,
more rigid electrodes (tungsten carbide). These electrodes
are fed prior to drilling to give a fixed protrusion of electrode.
The complete unit then rotates during drilling. Guu
and Hocheng [7] have stated that there are advantages in
rotating whilst drilling in EDM. Their experimental results
showed that better dielectric flow could be achieved. Higher
metal removal rates and better surface finish were all positive
aspects. However, in some cases, machining without
rotation is also carried out. Fig. 3 shows a schematic of the
system used for these experiments prior to the modifications
carried out.
The EDM process always requires a fluid that acts as an
insulator between the electrode and workpiece. There are
two main types of dielectric fluid used, de-ionised water
and oil. Water generally has the advantage that faster metal
removal rates can be realised. However the surface finish
of the material is generally poorer than that which can be
achieved when using oil [2]. Experience has also shown
that higher aspect ratios can be achieved when using oil as
a dielectric compared to water, e.g. (15–20):1 compared to
(10–14):1 with water. De-ionised water has a conductivity
value of ∼4 ×10
4
/cm and some EDM dielectric oils have
values of 2 × 10
−14
/cm, therefore it is possible to have a
much smaller gap when oil is used as a dielectric and less
electrode wear occurs which allows higher aspect ratios to
be achieved, this also allows finer machining as less energy
is transferred.
There have generally been two major methods of electrodeclamping and feeding. These include the use of wire(e.g. pure tungsten) on a spool which is fed through a systemof ceramic guides towards the workpiece, as shown inFig. 2 [6]. The electrode or clamping system does not rotate.The other main method has been to use lengths of brittle,more rigid electrodes (tungsten carbide). These electrodesare fed prior to drilling to give a fixed protrusion of electrode.The complete unit then rotates during drilling. Guuand Hocheng [7] have stated that there are advantages inrotating whilst drilling in EDM. Their experimental resultsshowed that better dielectric flow could be achieved. Highermetal removal rates and better surface finish were all positiveaspects. However, in some cases, machining withoutrotation is also carried out. Fig. 3 shows a schematic of thesystem used for these experiments prior to the modificationscarried out.The EDM process always requires a fluid that acts as aninsulator between the electrode and workpiece. There aretwo main types of dielectric fluid used, de-ionised waterand oil. Water generally has the advantage that faster metalremoval rates can be realised. However the surface finishof the material is generally poorer than that which can beachieved when using oil [2]. Experience has also shownthat higher aspect ratios can be achieved when using oil asa dielectric compared to water, e.g. (15–20):1 compared to(10–14):1 with water. De-ionised water has a conductivityvalue of ∼4 ×104/cm and some EDM dielectric oils havevalues of 2 × 10−14/cm, therefore it is possible to have amuch smaller gap when oil is used as a dielectric and lesselectrode wear occurs which allows higher aspect ratios tobe achieved, this also allows finer machining as less energyis transferred.
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