1. Anne
Bowers
ECE/MAE
535
July
14,
2014
Helion
Dhrimaj
Summer
2014
NORTH
CAROLINA
STATE
UNIVERSITY
Design
of
Electromechanical
Systems
Semester
Design
Project
Electro-­‐Permanent
Magnet
Clamp
ABSTRACT
Manufacturing
processes
that
involve
‘material
removal’
(such
as
milling,
drilling,
etc.)
depend
upon
a
secure
attachment
of
the
work
piece
to
the
machine
table
in
order
for
the
work
to
be
completed
safely
and
with
the
desired
precision.
Traditionally
a
mechanical
clamp
would
be
used
to
secure
the
work
piece,
but
this
process
can
become
tedious
and
time
consuming.
In
an
effort
to
improve
upon
these
two
issues,
an
electro-­‐magnetic
solution
was
developed.
An
electromagnet
would
be
turned
on
to
secure
the
work
piece
to
the
table,
due
to
reluctance
forces,
and
then
would
be
switched
off
when
the
process
was
finished.
This
solution
was
able
to
provide
the
desired
faster
and
easier
set
up,
but
now
had
the
additional
risk
of
catastrophic
failure
during
a
power
interruption,
and
was
expensive
to
operate
due
to
high
power
consumption.
The
electro-­‐permanent
magnet
clamp
is
a
new
design
that
strives
to
maintain
the
fast
and
easy
setup
provided
by
the
electromagnetic
clamp,
while
making
use
of
rare
earth
magnets
to
minimize
power
consumption.
INTRODUCTION
This
project
will
focus
on
the
development
of
an
optimized
design
for
an
electro-­‐
permanent
magnet
clamp.
The
basic
design
for
the
electro-­‐permanent
magnet
clamp
is
to
have
two
different
kinds
of
rare
earth
magnets
distributed
within
the
workbench.
NdFeB
magnets
are
used
to
provide
a
strong
flux
density
that
is
undisturbed
regardless
of
being
in
the
on
or
off
state.
AlNiCo
magnets,
which
have
a
lower
coercivity,
are
then
used
to
direct
the
flux
to
either
stay
within
the
workbench,
or
through
the
work
piece.
The
different
states
of
the
clamp,
‘on’
or
‘off’,
are
manipulated
by
placing
the
AlNiCo
magnets
within
a
wire
coil
that
can
reverse
the
polarity
of
the
AlNiCo
by
pulsing
current
through
the
coil
in
either
direction.
This
results
in
a
clamp
that
is
either
‘on’
or
‘off’
without
the
need
to
constantly
run
electricity
to
sustain
an
electro-­‐magnet.
Figure
1
shows
the
arrangement
and
polarity
of
the
permanent
magnets
within
the
workbench
when
the
clamp
is
in
the
‘off’
state.
There
are
three
NdFeB
magnets
that
are
arranged
so
that
their
polarities
are
oriented
horizontally.
There
are
two
AlNiCo
magnets
placed
within
coils
of
wire
with
their
polarities
oriented
vertically.
The
arrows
in
the
figure
indicate
the
path
of
magnetic
flux,
and
show
how
all
flux
is
ideally
contained
within
the
workbench.
This
leaves
the
work
piece
free
to
move
around
for
easy
adjustment.
Figure
2
shows
that
when
the
AlNiCo
magnets
are
pulsed
with
sufficient
current
through
their
surrounding
coils,
a
strong
enough
magnetic
field
can
be
generated
to
reverse
their
polarity.
This
reversal
in
polarity
now
directs
flux
through
the
work
piece,
creating
a
reluctance
force
that
holds
the
work
piece
in
place
for
processing.
This
is
the

2. Anne
Bowers
ECE/MAE
535
July
14,
2014
Helion
Dhrimaj
Summer
2014
clamp
‘on’
state,
and
it
does
not
require
sustained
electrical
power
to
maintain
the
clamping
force,
making
it
both
safer
and
more
efficient
than
the
electromagnet
clamp.
Figure
1.
Cutaway
of
Electro-­‐Permanent
Magnet
Clamp
in
the
‘Off”
State
Figure
2.
Cutaway
of
Electro-­‐Permanent
Magnet
Clamp
in
the
‘On’
State
The
design
optimizations
for
this
clamp
will
focus
on
minimization
of
the
overall
size
and
weight
of
the
electro-­‐permanent
magnet
clamp
(EMPC)
and
required
permanent
magnetic
materials,
NdFeB
and
AlNiCo,
while
still
maintaining
a
minimum
of
500lbs
of
vertical
reluctance
force
while
in
the
‘on’
state.
Minimization
of
these
two
parameters
will
reduce
the
overall
cost
to
produce
the
clamps.
The
design
will
also
seek
to
maximize
the
vertical
reluctance
force
as
a
secondary
goal
to
minimizing
the
material
costs.
METHODS
AND
MATERIALS
The
materials
that
will
be
used
for
this
clamp
are
AlNiCo
permanent
magnets,
NdFeB
permanent
magnets,
1025
steel,
magnet
wire,
and
a
230V
source.
The
grades
and
volume
of
the
permanent
magnets
will
be
part
of
the
design
optimization.
The
size
of
magnet
wire
to
be
used
will
need
to
be
determined
based
on
the
number
of
turns
required
to
generate
the
magnetic
pulse
that
flips
the
AlNiCo
polarization,
and
the
amount
of
current

3. Anne
Bowers
ECE/MAE
535
July
14,
2014
Helion
Dhrimaj
Summer
2014
that
can
be
sustained
within
the
wire.
Tables
1-­‐3
summarize
the
material
properties
for
the
available
permanent
magnet
materials
and
1020
Steel.
1020
steel
is
being
considered
because
it
is
the
closest
grade
to
1025
that
is
available
for
simulation.
Table
1.
Summary
of
Properties
of
Available
NdFeB
Materials
Available
NdFeB
Materials
Grade
Remanence
Flux
Density
Coercive
Max.
Energy
Density
Br
HcB
HcJ
(BH)max
mT
G
kA/m
Oe
kA/m
mT
G
kA/m
N10[3]
690
6,900
424
5,300
760
9,500
90-­‐100
7.3-­‐8.1
N38[1]
1,220
12,200
899
11,300
955
12,000
287
36
N40[1]
1,250
12,500
907
11,400
955
12,000
302
38
N42[1]
1,280
12,800
915
11,500
955
12,000
318
40
N52[1]
1,430
14,300
796
10,000
876
11,000
398
50
Table
2.
Summary
of
Properties
of
Available
AlNiCo
Materials
Available
AlNiCo
Materials[4]
Grade
Remanence
Flux
Density
Coercive
Max.
Energy
Density
Operating
Temp
MMPA
Br
HcB
HcJ
(BH)max
Tw
Max
kGs
mT
kOe
kA/m
kOe
kA/m
MGOe
kJ/m3
C
LNG34
11
1100
0.63
50
0.65
52
4.25
34
525
AlNiCo5
LNG37
11.8
1180
0.61
49
0.64
51
4.63
37
525
AlNiCo5
LNG40
12
1200
0.63
50
0.65
52
5
40
525
AlNiCo5
LNG44
12.5
1250
0.65
52
0.68
54
5.5
44
525
AlNiCo5
LNG52
13
1300
0.7
56
0.73
58
6.5
52
525
AlNiCo
5DG
LNG60
13.5
1350
0.73
58
0.75
60
7.5
60
525
AlNiCo
5-­‐7
Table
3.
Summary
of
Properties
of
1020
Steel
AISI
1020
Steel
Characteristics
Density
0.2839
lb/in3
Tensile
Strength
63800
psi
Relative
Permeability
(0.3440
T)[2]
1496
Relative
Permeability
(0.9600
T)[2]
444
Relative
Permeability
(1.4700
T)[2]
97
Relative
Permeability
(1.6150
T)[2]
55
The
data
in
Table
1
shows
that
the
increase
in
grade
for
NdFeB
corresponds
to
an
increase
in
BHmax,
the
maximum
energy
product.
It
is
expected
that
higher
grades
of
NdFeB
will
require
less
material
to
make
a
clamp
with
sufficient
holding
force,
but
depending
on

4. Anne
Bowers
ECE/MAE
535
July
14,
2014
Helion
Dhrimaj
Summer
2014
the
market
value
for
different
grades,
the
highest
and
lowest
grade
may
not
prove
to
be
the
most
economical
choice.
The
data
in
Table
2
indicates
that
the
lower
grades
of
AlNiCo
have
a
lower
coercivity,
and
so
it
should
take
less
current
in
the
coils
to
flip
the
magnet
poles
making
it
a
more
efficient
clamp
to
operate.
The
lower
grades
will
also
require
more
material
because
their
maximum
energy
density
is
lower.
The
magnetic
flux
that
is
responsible
for
generating
the
holding
force
while
the
clamp
is
in
the
‘on’
state
must
also
be
fully
contained
in
the
clamp
during
the
‘off’
state
in
order
to
make
it
easy
to
position
and
adjust
the
work
piece
before
clamping
it
down
for
work.
In
order
to
prevent
any
flux
from
travelling
through
the
work
piece
while
the
clamp
is
in
the
‘off’
state,
the
flux
supplied
by
the
AlNiCos
must
equal
the
flux
supplied
by
NdFeBs.
This
can
be
calculated
using
equation
1,
and
confirmed
by
simulation
using
FEMM.
𝐵!"#$%& ∗ 𝐴!"#$%& = 𝐵!"#$% ∗ 𝐴!"#$%
Eq.
(1)
The
data
in
Table
3
includes
the
relative
permittivity
values
for
steel
at
different
flux
density
values.
This
is
important
because
it
indicates
when
the
steel
in
the
clamp
and
work
piece
are
reaching
their
saturation
point.
If
the
steel
becomes
saturated
then
energy
is
being
wasted,
and
a
lower
grade
of
magnet
that
supplies
less
flux
density
will
be
able
to
achieve
the
same
holding
force,
presumably
for
less
cost.
Table
3
shows
that
steel
becomes
saturated
between
1.4
T
and
1.6
T.
Any
designs
that
result
in
points
of
flux
density
greater
than
this
range
should
not
be
considered.
The
last
parameter
is
the
ability
to
switch
the
clamp
‘on’
and
‘off’
using
the
coil
bobbins.
The
minimum
current
pulse
required
in
the
coil
bobbins
can
be
predicted
using
Ampere’s
Law.
Ampere’s
Law
relates
the
current
enclosed
by
a
closed
contour
integral
to
the
magnetic
field.
Equations
2,
3,
and
4
show
Ampere’s
Law
and
how
it
will
be
used
to
determine
the
minimum
current
for
turning
the
clamp
on
and
off.
𝐻Ÿ 𝑑𝑙
!
!
= 𝐼!"#!
Eq.
(2)
𝐻 ∗ 𝐿 = 𝑁 ∗ 𝐼
Eq.
(3)
!∗!
!
= 𝑁𝐼 → 𝐼 =
!∗!
!∗!
Eq.
(4)
Given
Equation
4
we
can
determine
the
necessary
current
to
turn
the
clamp
on
and
off.
This
relationship
shows
that
the
necessary
current
is
directly
related
to
the
strength
of
the
magnetic
flux
of
the
AlNiCo
magnets,
and
inversely
proportional
to
the
number
of
turns
wire.
The
length
of
wire
will
be
limited
by
the
coil
bobbin
dimensions
and
available
space,
and
the
permeability
will
be
determined
by
the
grade
of
AlNiCo
chosen
in
the
final
design.
The
resistance
of
the
wire
is
also
a
factor
in
determining
how
much
current
can
be
pulsed
with
a
230V
source.
The
physical
properties
of
several
common
gauges
of
magnet
wire
are
summarized
in
Table
4.

5. Anne
Bowers
ECE/MAE
535
July
14,
2014
Helion
Dhrimaj
Summer
2014
Table
4.
Physical
Properties
of
Different
Magnet
Wire
Sizes
Magnet
Wire
Specifications
Wire
Gauge
(AWG)
Resistance
(Ω/1000ft)
Total
Resistance
for
97
Turns
(Ω)
Maximum
Current
w/
230
V
Source
Cross-­‐sectional
Area
for
97
Turns
(in2
)
24
25.67
2.27
101.3
0.031
22
16.14
1.43
160.8
0.049
20
10.15
0.897
256.4
0.078
18
6.385
0.565
407.1
0.124
16
4.016
0.355
647.9
0.197
Using
the
FEMM
software
introduced
in
the
course,
and
the
provided
general
layout,
a
model
was
constructed.
Figure
3
shows
this
layout,
including
the
materials
that
were
used
in
the
simulation.
1020
steel
was
used
for
the
simulation
because
it
was
the
closest
available
material
in
the
material
library.
The
air
gap
is
0.1
mm
wide,
and
the
model
shown
has
a
depth
of
2.6cm,
which
is
midway
through
the
clamp.
All
forces
calculated
by
FEMM
will
need
to
be
doubled
to
account
for
the
other
half
of
the
clamp.
Figure
3.
Cross-­‐sectional
layout
of
Electro-­‐Permanent
Magnet
Clamp
RESULTS
The
initial
magnetics
simulation
results,
using
NdFeB
37
and
AlNiCo
5
were
able
to
achieve
an
attractive
force
between
the
work
piece
and
the
body
of
6034
N,
which
is
roughly
1356
lbs.
This
design
meets
the
minimum
force
specifications,
but
can
be
improved.
The
magnetic
flux
was
concentrated
in
the
two
poles
of
the
workbench
at
nearly
2
Tesla.
Given
that
steel
reaches
saturation
between
1.4
and
1.6
Tesla[2],
energy
was
being
wasted
in
this
saturated
condition.
The
clamp
was
redesigned
to
help
minimize
this
inefficiency
in
each
different
magnet
grade
combination,
which
is
summarized
in
Table
6.
The
minimum
clamp
dimensions
that
were
found
to
ensure
a
reasonable
path
for
flux
without
unnecessary
bulk
are
summarized
in
Table
5.
While
the
overall
size
of
the
clamp
is
not
large
in
dimensions,
it
is
ultimately
a
heavy
piece
of
equipment,
totaling
around
62
pounds.
The
varying
height
of
the
AlNiCo
magnets
for
each
design
made
it
difficult
to
predict
exactly
how
much
steel
would
be
in
the
pole
without
knowing
the
final
client
design
choice,
so
the
total
weight
is
a
conservative
maximum
based
on
the
presence
of
no
AlNiCo.
Any
final
clamp
will
have
slightly
less
steel.

6. Anne
Bowers
ECE/MAE
535
July
14,
2014
Helion
Dhrimaj
Summer
2014
Table
5.
Clamp
Steel
Weight
Clamp
Steel
Weight
Based
1025
Steel
Density
Clamp
Piece
Volume
(mm3)
Volume
(in3)
Density
(lb/in3)
Weight
(lb)
Pole*
245000
14.951
0.2839
4.24
Base
1485000
90.620
0.2839
25.73
Sides
1862000
113.63
0.2839
32.26
Total
3592000
219.201
-­‐
62.23
Table
6.
Summary
of
Minimum
Required
Dimensions
and
Cost
for
Different
Magnet
Grade
Combinations
Magnet
Combination
Force
in
ON
(N)/(lbs)
Force
in
OFF
(N)/(lbs)
Max.
Satu-­‐
ration
(T)
NdFeB
Dimensi
ons
(mm)
AlNiCo
Dimension
s
(mm)
NdFeB
Price
($)
AlNiCo
Price
($)
I
(A)
NdFeB10[8-­‐
11]
/
AlNiCo
5[6]
4552.99/
1023
~0/0
1.41
(60
x
50
x
36)
(47
x
46
x
17)
324
103.21
66.6
NdFeB10[8-­‐
11]
/
AlNiCo
5[6]
6432.22/
1446
~0/0
1.71
(60
x
50
x
44)
(47
x
46
x
45)
396
274.99
188.
9
NdFeB37[8]
/
AlNiCo6[5][6][7]
2422.7/
544
34/7.6
1.293
(60
x
50
x
17)
(47
x
46
x
10)
699.50
80.57
10
NdFeB37[8]
/
AlNiCo6[5][6][7]
6773.06/
1522
34/7.6
1.747
(60
x
50
x
17)
(47
x
46
x
30)
699.50
241.72
100
NdFeB40[9]
/
AlNiCo6[5][6][7]
2676.94/
601
36.38/
8.1
1.36
(60
x
50
x
17)
(47
x
46
x
10)
141.984
80.57
10
NdFeB40[9]
/
AlNiCo6[5][6][7]
6853.24/
1540
36.37/
8.1
1.814
(60
x
50
x
17)
(47
x
46
x
30)
141.98
241.72
100
NdFeB52[10]
/
AlNiCo6[5][6][7]
2488.2/
559
32.157/
7.2
1.374
(60
x
50
x
17)
(47
x
46
x
10)
199.18
80.57
10
NdFeB52[10]
/
AlNiCo6[5][6][7]
6712/
1508
36.637/
8.2
1.84
(60
x
50
x
17)
(47
x
46
x
30)
199.18
241.72
100
NdFeB37[8]
/
AlNiCo8[5]
2378.9/
535
47.178/
10.6
1.351
(60
x
50
x
17)
(47
x
46
x
12.5)
690.50
75.72
24
NdFeB37[8]
/
AlNiCo8[5]
6669.97/
1500
44.62/
10.0
1.813
(60
x
50
x
17)
(47
x
46
x
32.5)
690.50
196.89
150
NdFeB40[9]
/
AlNiCo8[5]
2463.62/
554
57.72/
13.0
1.366
(60
x
50
x
17)
(47
x
46
x
12.5)
141.984
75.72
24
NdFeB40[9]
/
AlNiCo8[5]
6756.47/
1519
54.659/
12.3
1.837
(60
x
50
x
17)
(47
x
46
x
32.5)
141.984
196.89
150
NdFeB52[10]
/
AlNiCo8[5]
2565.4/
577
127/
28.6
1.307
(60
x
50
x
17)
(47
x
46
x
12.5)
199.18
75.72
22
NdFeB52[10]
/
AlNiCo8[5]
6794.49/
1527
124.4/2
8.0
1.839
(60
x
50
x
17)
(47
x
46
x
35)
199.18
212.04
150

7. Anne
Bowers
ECE/MAE
535
July
14,
2014
Helion
Dhrimaj
Summer
2014
Figures
4-­‐6
show
results
of
simulations
made
with
NdFeB
10
and
AlNiCo
5
magnets.
Simulations
of
all
other
magnet
combinations
yielded
similar
results.
Figure
4
shows
the
clamp
in
the
‘on’
position.
The
maximum
flux
density
is
concentrated
in
the
poles
and
the
work
piece
but
does
not
exceed
1.41T
so
minimal
amounts
of
energy
are
being
wasted.
Figure
5
shows
the
same
clamp
in
the
off
state
with
a
measured
0.05lbs
of
off
force.
That
amount
of
force
should
be
unnoticeable
to
anyone
responsible
for
positioning
the
work
piece.
The
last
figure,
figure
6,
shows
the
clamp
in
the
midst
of
switching.
The
lack
of
flux
lines
through
the
AlNiCo
magnets
and
coils
shows
that
the
current
in
the
coil
is
at
least
strong
enough
to
balance
the
AlNiCo
flux.
Any
current
increase
past
that
point
will
cause
the
AlNiCo
magnet
poles
to
flip.
Figure
4.
Clamp
with
Minimum
PM
Materials
N10
and
AlNiCo
5
in
On
Position
with
2046lbs
of
holding
force
Figure
5.
Clamp
with
Minimum
PM
Materials
N10
and
AlNiCo
5
in
Off
Position
with
-­‐0.05lbs
of
Holding
Force

8. Anne
Bowers
ECE/MAE
535
July
14,
2014
Helion
Dhrimaj
Summer
2014
Figure
6.
Clamp
with
66.6
A
of
Current
During
Switching
from
On
to
Off
CONCLUSIONS
The
NdFeb10/AlNiCo5
combination
achieved
the
required
force
with
a
force
of
nearly
zero
in
the
“OFF”
state.
For
our
clamp
design,
this
proved
unobtainable
with
the
higher-­‐grade
magnets.
As
evident
in
the
table
above,
all
of
the
higher
grade
magnetic
combinations
experienced
some
force
in
the
air
gap
during
the
“OFF”
state.
With
the
NdFeB37,
40,
and
50,
the
ideal
dimensions
ranged
from
(60
mm
x
50mm
x
15mm)
to
(60
mm
x
50mm
x
22.5
mm).
This
NdFeB37/40/50
dimensional
range
supplied
enough
magnetic
flux
density
to
achieve
500
lbs.
and
1500
lbs.
of
force.
At
the
same
time
it
minimized
the
magnetic
saturation
as
well
as
the
force
in
the
OFF
state.
For
the
sake
of
time,
we
chose
to
leave
the
NdFeB
magnets
at
a
constant
(60mm
x
50mm
x
17mm).
The
only
variable
left
to
modify
was
the
AlNiCo
dimension.
According
to
the
reluctance
force
in
the
“ON”
state,
the
AlNiCo5
length
ranged
from
(17
mm
-­‐
45
mm),
the
AlNiCo6
length
ranged
from
(10
mm-­‐
30
mm),
and
the
AlNiCo8
length
ranged
from
(12.5mm
to
35
mm).
Combinations
of
higher
magnetic
grades,
NdFeB37
and
above,
as
well
as
AlNiCo6
and
above,
provided
sufficient
force
for
the
clamp.
On
the
negative
side,
these
aforementioned
magnets
experienced
high
levels
of
saturation
when
designed
for
the
1500
lbs.
of
force.
Furthermore,
an
air
gap
force
was
measured
in
the
FEMM
analysis
even
in
the
OFF
state.
This
is
more
substantial
in
the
NdFeB52/AlNiCo8
combination,
where
we
measured
a
force
close
to
130
N
in
“OFF”
state.
The
maximum
cross-­‐sectional
area
that
is
available
for
the
coil
is
0.558in2
so
the
clamp
dimensions
would
accommodate
any
of
the
wire
sizes
in
table
4.
The
larger
size
wire
would
be
more
desirable
for
the
final
product
because
it
is
better
able
to
handle
the
higher
current
pulses
and
the
heat
that
is
generated
during
the
pulse.
Overall
it
would
be
difficult
to
choose
an
ideal
magnet
design.
The
NdFeB10/AlNiCo5
combination
has
a
high
price
due
to
the
amount
of
material
being
used.
At
the
same
time
it
experiences
almost
no
force
in
the
“Off”
state
and
relatively
low
saturation
levels,
even
for
the
1500
lbs.
force
requirement.
Alternatively,
the
higher
grades
of
magnet
tend
to
require
less
overall
material.
This
equates
to
slightly
lower
costs
but
at
the
same
time
higher
levels
of
saturation
result,
and
a
force
is
present
in
the
“Off”
state.
Considering
the
alternatives
we
were
able
to
develop,
and
our
ability
to
apply
FEMM
as
a
tool
in
the
design
process,
this
project
has
been
a
good
opportunity
to
demonstrate
the
material
we
have
learned
throughout
the
semester.

9. Anne
Bowers
ECE/MAE
535
July
14,
2014
Helion
Dhrimaj
Summer
2014
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Herdforshire,
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Iron
Boron
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2014
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