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Electrode Wear Process in Electrical Discharge
Machining
Annals of the CIRP
班級：碩研機械一甲
報告人： 黃柏慶
Introduction
In the resent development of EDM, the area of
application has been expanding rapidly such as
contour machining by scanning of an electrode,
drilling with a thin electrode, finish machining with
powder suspended working fluid, metal surface
modification with a composite electrode.
According to the new situation of EDM, it has been
necessary to change the old way of thinking on the
electrode wear phenomena.
The wear of specific portion of an electrode should be
focused on especially accurate machining.
Time Dependance of Electrode Wear at the
Transition State of Machining
It has been understood that the rate of electrode wear
depends on the considered portion of the electrode
and consequently it depends on the shape of the
electrode.
Some examples of measured shapes are shown in
Fig.1
A copper round bar with diameter of 10mm is used
as an electrode during the machining of carbon
steel plate.
The measured shape in Fig.1 shows the change of
the electrode at the edge portion at each machining
time which is displayed in a cross section
including the axis of symmetry.
Machining conditions are described in the upper part
of this figure.
It is confirmed that the radius of the edge portion
which is less than several μm enlarges up to
several hundred μ m at the machining time of 106
min.
The shape of edge portion in the cross section
changes from a sharp comer to a circular arc owing
to wear during the machining.
Fig.3 shows the change of the measured radius (R) of the
electrode edge portion against machining time and the
change of the electrode length (Δx) at bottom flat
portion.
The radius is about ten times the worn length in the
stationary state of the machining.
On the contrary, it can be confirmed that the radius is
several hundred times the worn length at the beginning
of machining.
Fig.4 tells us that the whole wear is very small at the
beginning of machining, and it gradually increases
in the progress of machining and tends to a certain
value which is determined by machining condition
and materials.
The wear ratio of the edge portion before about ten
minutes is greater than the whole wear ratio, and
then, it decreases to less than the whole wear ratio
in the progress of machining.
Black carbon layer is observed on the surface of the flat
portion through visual inspection and EPMA.
Therefore, it is imagined that the growth at the flat
portion is caused by the growth of attached carbon
from cracked carbon oil.
In the progress of machining, the growth at the flat
surface disappears and the adhesion of carbon gets in
equilibrium with wear consumption of the electrode.
Conclusions
The change of electrode wear against machining
time is examined by means of on- the- machinemeasurement for electrode shape.
Through the observation of electrode shape, it is
found that the edge portion of the electrode wears
remarkably at the beginning of machining.