Design of an Electrically Assisted Manufacturing Process - Electrically Assisted Forming - page 246

E EAF = E EAF,mech + E EAF,elec

ε f

VI d t
η e

E EAF = σ EAF d ε +

(10.12)

0

The model of Eq. ( 4.9 ) is used to predict the stress state:

VI d t
η e

K ′ ε n exp −(ε − c ) B Φ a E EAF = d ε +

(10.13)

Using an efficiency of 90 %, resistivity of 9.8 × 10 − 8 Ohm-m, constants of
a = 3.38, B = 0.00009, c = 0.018, and applying 40 A/mm 2 ; this is evaluated with
the result:

E EAF,mech = 1552 J
E EAF,heat = 83 J
E EAF = 1635 J

(10.14)

10.1.4 Energy Comparison

The summary of energy use for each of the test cases is given in Fig. 10.5 .
We see that energy-assisted forming (thermal or electrical) can reduce the
required mechanical work significantly. However, there is a considerable differ-
ence between thermal softening (at the bulk material level) and electrical softening
(at specific locations in the lattice structure). For thermal softening, the bulk work-
piece must be brought to temperature as a whole. However in EAF, the electric-
ity works to soften the material directly in the zones of deformation. In the given
example, the total mass of the part was relatively insignificant to thermal softening
energy. However, in larger mass parts such as vehicle body panels, the difference
between thermal and electrical energy to achieve the same reduction in flow stress
should be more significant.
Electrically assisted softening significantly reduces the amount of deformation
energy required at a quite low augmentation energy cost. Though current is very

Fig. 10.5 Energy use in
forming Mg-AZ31B-O
sample using various
methods