Tribological and Contact Area Effects - Electrically Assisted Forming - page 220

Fig. 9.17 Voltage versus
static load stationary
electrical tests (Large
CA and surface ground
4.76-mm-diameter
specimens) [ 6 ]. There is more
of a change in the voltage
of the Large CA specimens
at the lower static loads in
comparison with the surface
ground specimens

450

400

350

300

250

200

150

100

Surface ground (4.76mm)
Large CA (4.76mm)

50

0

1000 1500 2000 2500 3000 500 000 500

Static Load (N)

Fig. 9.18 Voltage versus
stationary electrical
tests (surface ground
6.35-mm-diameter
specimens) [ 6 ]. The voltage
in the 6.35-mm-diameter
surface ground specimens
shows a decreasing linear
trend with the increase in
static load

360

340

All loads in the
elastic region.

320

300

280

260

240

220

220

Surface ground (6.35mm)

200

1500 2500 3500 4500 5500 6500 7500

Static Load (N)

be expected since there is less contact area (because the EDM profiled it out) and
there is the same electrical current running through these parts as is with the sur-
face ground parts.
Figure 9.18 displays the voltage versus static load relationship for the
6.35-mm-diameter specimens. There is a very steep decrease in the voltage as the
static load is increased, which correlates to the same decrease in specimen tem-
perature as the static load was increased, in Fig. 9.16 above.
Now, utilizing the voltage measurements, the actual contact area can be pre-
dicted. The basic relation for electrical power can be described as Eq. ( 9.2 ):

P = IV = I 2 R

(9.2)

where P is electrical power, I is current, V is voltage, and R is the resistance. Then,
the voltage can be written as Eq. ( 9.3 ):

V = IR = I · R · L part
A contact

(9.3)