班級：碩研機械一甲報告人： 黃柏慶

Electrode Wear Process in Electrical Discharge Machining

Annals of the CIRP

IntroductionIn 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 theTransition State of MachiningIt 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.

ConclusionsThe change of electrode wear against machining

time is examined by means of on- the- machine-measurement 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.