High Performance Bonded Neo Magnets using High Density Compaction

1
High Performance Bonded Neo Magnets using High
Density Compaction

• J. Herchenroeder, D. Miller, N. K. Sheth,
• C. Foo, D. Brown and K. Nagarathnam

2
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.

3
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.

4
What is Combustion Driven Compaction (CDC)?
Gas Inlet

• 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, transferring energy into and
  compacting the powder
• CDC converts chemical energy directly to
  mechanical energy for high efficiency!
• The entire process is smooth and continuous,
  keeping constant pressure on the part at all times

-
Electric Ignition
US Patent 6,767,505
Natural Gas (CH4) Air at High Pressure
One moving part!
Powder
Die
5
The CDC Load Cycle can be tailored

• Fill gas creates pre-load pushing the piston or
  ram down, pre-compressing and removing entrapped
  air from the powder
• 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
Load
Significant pre-load from gas fill, 15 20 tsi
The process, although fast and powerful, is
smooth and continuous
Time
6
CDC Compact Properties
Powder metal part density increases with load
(without lubricant in powder).
Green density versus load for F-0000 powder
presses using CDC
7
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
8
Results of ?15 x 13mm cylindrical magnets
Pressure tonne/cm2 Density g/cm3 (BH)max MGOe Hci kOe
12 6.12 10.4 8.9
21 6.37 11.6 9.1

• Density 6.5 g/cm3
• Br 7.7 kG
• (BH)max 11.7 MGOe

9
Effect of Different Magnets on Seat Motor
Performance

• Ring magnets using CDC were made from MQLP-B
  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 CCM
Magnet produced using CDC
10
Effect of Different Magnets on Seat Motor
Performance - Measurement of Magnet Density

• Wet-Dry method is used,

Process Density g/cm3 (BH)max MGOe Br kG
CCM 5.88 9.5 6.8
CDC 6.22 10.6 7.2
Magnet produced using CDC has 5.8 higher
density.
11
Effect of Different Magnets on Seat Motor
Performance - Magnetization of the Isotropic
Bonded NdFeB Magnets
Magnet
Laminated back iron
Magnetic Fixture
Magnetization of the Magnets in presence of
laminated back iron
Closed Magnetic Circuit for Mid Airgap Flux
Measurement
12
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
13
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
  (un-operational) in an oven at 120? C for 24
  hours.
• Anisotropic Neo (Original magnet in the motor)
• Isotropic bonded neo made using CCM
• Isotropic bonded neo made using CDC

14
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
15
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
16
Effect of Different Magnets on Seat Motor
Performance - Back-emf Constant before/After
Thermal Aging at 120? C for 24 hrs.
Type of Magnet Type of Magnet Type of Magnet
Anisotropic Neo (Original Magnet in Motor) Isotropic Neo using CCM Isotropic Neo using CDC
kb (mV/rpm) before thermal aging kb (mV/rpm) before thermal aging kb (mV/rpm) before thermal aging
4.52 3.98 4.25
kb (mV/rpm) after thermal aging at 120? kb (mV/rpm) after thermal aging at 120? 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.

17
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.

18
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.
19
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.

20
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