
390 Fundamentals of Machining Processes
The discharging current I
d
becomes
I
V
d
d
=
The volumetric removal rate VRR (mm
3
/min) is given by
VRRC
C
ap
sp
cap
dsp
=
−
K
V
R
VV
1
2
1
1
ln
(/ )
The average surface roughness (R
a
) is given by the following empirical
formula:
RK
a
=
−
2
05
p
0.5
.
where
V
sp
is the supply voltage in V
V
d
is the discharge voltage in V
R
c
is the resistance in Ω
C
ap
is the capacitance in f
t
1
is time in s
K
1
and K
2
are constants
VRR is the volumetric removal rate in mm
3
/min
R
a
is the average surface roughness in μm
c
sp
V
d
I
d
I
c
C
FIGURE 12.7
Various parts of an RC.