Analysis of the Pulses used in the EDM Process | filter cartridge manufacturers
Performance measures such as MRR, tool wear, and surface finish for the same energy depend on the shape of the current pulses. Depending upon the situation in the gap which separates both electrodes, principally four different electrical pulses may be distinguished:
a) Open circuit or open voltage
b) Effective discharges or real Sparks
c) Arcs and
d) Short circuits
They are usually defined on the basis of time evolution of discharge voltage and (or) discharge current (Fig). Their effect upon material removal and tool wear may differ quite significantly. Open voltages, occurring when the distance between both electrodes is too large, obviously do not contribute to any material removal or electrode wear.
When contact between tool and workpiece takes place, a short circuit occurs which also does not contribute to material removal.The range of the electrode distances in between these two extreme cases can be considered to be a practical working gap yielding actual discharges, i.e., sparks and arcs. Both pulse types do show a characteristic voltage drop across the gap during a pulse. The difference between sparks and arcs is quite difficult to establish. It is believed that arcs occur in the same spot, or on the electrode surface and may therefore severely damage tool and workpiece.It is assumed that arcs occur when the plasma channel of the previous pulse is not fully deionized; the current during the following pulse will flow by preference along the same current path. Therefore, in such a case, no time is required to form a new gaseous current path. The formation of the gaseous channel is normally considered to be necessary to initiate a new spark breakdown. This peculiarity of EDM arcs is often proposed as a discrimination characteristic with respect to effective discharges or real sparks.It is believed that only “sparks” really contribute to material removal in a desired mode. Until now it remains an open question how much arcs contribute in terms of material removal and tool wear. filter cartridge manufacturers
