
395Machining by Thermal Erosion
on the workpiece material but also on the material of the tool electrode and
the machining variables such as pulse conditions, electrode polarity, and the
machining medium. In this regard, a material of low melting point has a
high metal-removal rate and, therefore, a rougher machined surface. Typical
removal rates range from 0.1 to 10
3
mm
3
/min. Figures 12.13 and 12.14 explain
the effect of pulse energy (current) and duration on the crater size and, there-
fore, the removal rate. The material removal rate, VRR in mm
3
/min, is given
by Kalpakjian (1997):
=× ×
−
.
4
123
where
I
m
is the EDM current in A
T
w
is t ...