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

Powder Die

One moving part!

Natural Gas (CH4)& Air at “High” Pressure

•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

US Patent 6,767,505

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.

The process, although fast and powerful, is smooth and continuous

Loa

d

Significant pre-loadfrom gas fill, 15 –20 tsi

Peak loads, 30 - 250 tsi

Time

CDC Compact Properties

Powder metal part density increases with load (without lubricant in powder).

Applied Load (MPa)

276 552 827 1103 1379 1655 1931 2206

Gre

en D

ensi

ty (

g/cm

3 )

6.6

6.8

7.2

7.4

7.6

7.8

7.0

Single press at room temperature with die wall lubricant (Zinc Stearate)

98.6 % dense

Typical compaction loadwith other presses

20 40 60 80 100 120 140 160

Applied Load (Tsi)

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 tall50 inches square~12000 lbs

Results of 15 x 13mm cylindrical magnets

Pressuretonne/cm2

Densityg/cm3

(BH)max

MGOeHci

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

7.00

7.20

7.40

7.60

7.80

6.00

6.15

6.30

6.45

6.60

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Magnet B

r(kG

)

CDC

Mag

net

Den

sity

(g/

cm3 )

Epoxy (wt. %)

Density

Br

10.5

11.0

11.5

12.0

6.0

6.2

6.4

6.6

0.0 0.5 1.0 1.5 2.0 2.5 3.0

CDC M

agnet (BH)m

ax (MG

Oe)CD

C M

agne

t D

ensi

ty (

g/cm

3 )

Epoxy (wt. %)

Density

(BH)max

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 160C for 1 hour in argon gas.

Ring magnet dimensionOuter 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,

ProcessDensityg/cm3

(BH)max

MGOeBr

kGCCM 5.88 9.5 6.8CDC 6.22 10.6 7.2

weightWetweightDry

weightDryDensity

Magnet produced using CDC has 5.8% higher density.

Effect of Different Magnets on Seat Motor Performance - Magnetization of the Isotropic Bonded NdFeB Magnets

Magnet

Laminated back iron

Magnetic Fixture

Magnetizing current pulse

Center iron piece

Magnet

Motor housingHall sensor or

probe

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

Mid airgap Flux Density for the Closed Magnetic Circuit

Magnet Saturation analysis during magnetization

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. 1. Anisotropic Neo (Original magnet in the motor)

2. Isotropic bonded neo made using CCM

3. Isotropic bonded neo made using CDC

Dynamometer Test Setup for Motor Characteristics Measurement

Measurement of back-emf constant

Effect of Different Magnets on Seat Motor Performance - Test Setup for Motor Testing

Effect of Different Magnets on Seat Motor Performance - Motor Performance before Thermal Aging

Motor current and speed at various load torques before

thermal aging of the magnets

Motor efficiency and output power 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.

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.

Type of MagnetAnisotropic Neo (Original

Magnet in Motor)Isotropic Neo using

CCMIsotropic Neo using CDC

kb (mV/rpm) before thermal aging4.52 3.98 4.25

kb (mV/rpm) after thermal aging at 1204.40 3.93 4.16

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 current and speed at various load torques after

thermal aging of the magnets 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.

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