High Performance Bonded Neo
Magnets using High Density
Compaction
J. Herchenroeder, D. Miller, N. K. Sheth,
C. Foo, D. Brown and K. Nagarathnam
Introduction
 A compression bonded Neo magnet is comprised of NdFeB
powder, epoxy and additives conducive to magnet
manufacture such as curing agents, coupling agents and
lubricants.
 Typical magnet densities: 5.8-6.1 g/cm3
 Typical (BH)max of compression molded magnet 8-10 MGOe.
 The theoretical density of a compound of magnetic powder
and organic binders: 6.9 g/cm3  Higher (BH)max can be
obtained if density were increased during molding.
 To achieve compact, lighter and efficient products in
applications like pumps, power tools, BLDC motors and
consumer products a magnet with (BH)max of 11-12 MGOe
will help.
Introduction
 Magnet (BH)max of 11-12 MGOe  Compact, lighter and
efficient end products for applications like pumps, power
tools etc.
 How to increase density of magnet?
• Reduce the percentage of the epoxy binder.
• Binder is important to achieve good mechanical strength and
magnet integrity.
• Increase Compaction pressure.
• Frictional forces encountered during pressing put constrain on
the magnet geometries (Length of few mm).
 Innovative approach to powder compaction called
Combustion Driven Compaction (CDC).
• Magnet density of 6.5 g/cm3 can be achieved.
What is Combustion Driven Compaction (CDC)?
Gas
Inlet
+
Electric
Ignition
US Patent
6,767,505
One
moving
part!
Powder
•A pressurized mixture of natural
gas and air is introduced into the
combustion chamber
•The mixture is then ignited to
drive a piston (ram)
•A punch is driven downward by
the piston into the metal powder,
Natural Gas (CH4)
transferring energy into and
& Air at “High”
compacting the powder
Pressure
•CDC converts chemical energy
directly to mechanical energy for
high efficiency!
Die
•The entire process is smooth
and continuous, keeping
constant pressure on the part at
all times
The CDC Load Cycle can be tailored
• Fill gas creates pre-load
pushing the piston or
ram down, precompressing and
removing entrapped air
from the powder
The process, although
fast and powerful,
is smooth and
continuous
Load
• An ignition stimulus is
applied causing
combustion and rapid
pressure rise, further
compressing the metal
powder to its final net
shape.
Peak loads, 30 - 250 tsi
Significant pre-load
from gas fill, 15 –20 tsi
Time
CDC Compact
Properties
Applied Load (Tsi)
7.8
20
40
60
Green Density (g/cm3)
100
120
140
160
98.6 % dense
7.6
Powder
metal part
density
increases
with load
(without
lubricant in
powder).
80
7.4
7.2
Typical compaction load
with other presses
7.0
6.8
6.6
276
Single press at room temperature with die
wall lubricant (Zinc Stearate)
552
827
1103
1379
1655
Applied Load (MPa)
1931
2206
Green density versus load for F-0000 powder presses using CDC
CDC benefits
Improved green density
Waste heat can be used
for cogeneration heating or
cooling the work place.
Energy comes directly
from natural gas not from a
power plant.
The physical size of a CDC
press is only a fraction of a
conventional press – a 400 ton
press is the size of a phone
booth
When operating, CDC
makes little or no sound
80 inches tall
50 inches square
~12000 lbs
Results of 15 x 13mm cylindrical magnets
Pressure
tonne/cm2
12
21
Density
g/cm3
6.12
6.37
(BH)max
MGOe
10.4
11.6
Hci
kOe
8.9
9.1
6.60
 Density = 6.5 g/cm3
 Br = 7.7 kG
 (BH)max = 11.7 MGOe
7.80
6.6
12.0
6.4
11.5
6.2
11.0
Density
7.40
6.15
CDC Magnet Density (g/cm3)
6.30
7.20
Density
(BH)max
6.00
7.00
0.0
0.5
1.0
1.5
Epoxy (wt. %)
2.0
2.5
3.0
6.0
10.5
0.0
0.5
1.0
1.5
Epoxy (wt. %)
2.0
2.5
3.0
CDC Magnet (BH)max (MGOe)
7.60
Magnet Br (kG)
CDC Magnet Density (g/cm3)
Br
6.45
Effect of Different Magnets on Seat Motor
Performance
 Ring magnets using CDC were made from MQLPB+™ powder with 1% epoxy, compacted with an
average of 20 tonne/cm2 pressure and cured at
160C for 1 hour in argon gas.
 Ring magnet dimension
Outer Diameter Thickness
Length
33.72 mm
1.50 mm
25.30 mm
Magnet produced
using CDC
Magnet produced
using CCM
Effect of Different Magnets on Seat Motor
Performance - Measurement of Magnet
Density
 Wet-Dry method is used,
Density 
Process
CCM
CDC
Dry weight
 Dry
weight  Wet weight
Density
g/cm3
5.88
6.22
(BH)max
MGOe
9.5
10.6

Br
kG
6.8
7.2
Magnet produced using CDC
has 5.8% higher density.
Effect of Different Magnets on Seat Motor
Performance - Magnetization of the
Isotropic Bonded NdFeB Magnets
Magnetizing current pulse
Magnet
Laminated back
iron
Magnetic Fixture
Motor housing
Hall sensor or
probe
Center iron
piece
Magnet
Magnetization of the Magnets in
presence of laminated back iron
Closed Magnetic Circuit for Mid Airgap
Flux Measurement
Effect of Different Magnets on Seat Motor
Performance - Magnetization of the
Isotropic Bonded NdFeB Magnets
Magnet Saturation analysis
during magnetization
Mid airgap Flux Density for the
Closed Magnetic Circuit
Effect of Different Magnets on Seat Motor
Performance - Motor Testing
 Magnets were assembled in a seat motor.
 The motors with following three types of magnets
were tested to achieve the performance including
back-emf constant, and the performance was
compared at room temperature before and after
thermal aging in which motors were kept (unoperational) in an oven at 120 C for 24 hours.
1. Anisotropic Neo (Original magnet in the motor)
2. Isotropic bonded neo made using CCM
3. Isotropic bonded neo made using CDC
Effect of Different Magnets on Seat Motor
Performance - Test Setup for Motor
Testing
Measurement of back-emf constant
Dynamometer Test Setup for Motor
Characteristics Measurement
Effect of Different Magnets on Seat Motor
Performance - Motor Performance before
Thermal Aging
Motor efficiency and output
power at various load torques
before thermal aging of the
magnets
Motor current and speed at
various load torques before
thermal aging of the magnets
Effect of Different Magnets on Seat Motor
Performance - Back-emf Constant before/After
Thermal Aging at 120 C for 24 hrs.
Type of Magnet
Anisotropic Neo (Original
Isotropic Neo using Isotropic Neo
Magnet in Motor)
CCM
using CDC
kb (mV/rpm) before thermal aging
4.52
3.98
4.25
kb (mV/rpm) after thermal aging at 120
4.40
3.93
4.16
 The motor with anisotropic neo magnet has 11.9% higher
back-emf constant compared to the isotropic magnet
produced by CCM.
 The use of isotropic magnet produced by CDC reduces
the difference to 6.0%. This is due to the improved
magnet density for CDC compared to CCM.
Effect of Different Magnets on Seat Motor
Performance - Back-emf Constant before/After
Thermal Aging at 120 C for 24 hrs
 To study the effect of thermal aging on various
magnets and then on the motor performance, the test
motors were kept in an oven at 120 C for 24 hrs and
then again the Back-emf constant (kb) and motor
performance was evaluated.
 Reduction in Back-emf constant (kb) is the highest at
2.65% for the anisotropic Neo magnet compared to
1.26% and 2.12% for isotropic bonded Neo magnets
produced using CCM and CDC method respectively.
 Thermal aging reduces the difference in performance
for anisotropic Neo and isotropic bonded Neo from
CDC method.
Effect of Different Magnets on Seat Motor
Performance - Motor Performance after
Thermal Aging at 120 C for 24 hrs
Motor efficiency and output
power at various load torques
before thermal aging of the
magnets at 120 C for 24 hrs.
Motor current and speed at
various load torques after
thermal aging of the magnets
at 120 C for 24 hrs.
Conclusions
 The net shaped and thin walled ring magnet produced using
CDC technology has much higher density, 6.22 g/cm3,
compared to the isotropic bonded Neo magnets produced
commercially by CCM, 5.88 g/cm3, an increase of 5.8%.
 The airgap flux for the magnet produced by the proposed
method is 6% more compared to the commercial isotropic
bonded Neo magnet.
 At room temperature the performance of the motor with the
anisotropic magnet is comparable to the motor with the
isotropic bonded Neo magnet produced by proposed CDC
method, but after exposure to high temperature the
difference is further reduced.
Conclusions
 Bonded Neo magnets using CDC exhibits superior
thermal aging stability compared to anisotropic neo
magnets.
 Isotropic bonded Neo magnets produced by CDC will be
the ideal choice for applications where good thermal
stability is required and where slightly higher magnetic
property is needed compared to conventional bonded
Neo