|
Manufacturing
Methods
NdFeB magnets
are manufactured in the 4 following forms:
 Sintered
- fine NdFeB powder is compacted in a die and then sintered, fusing the
powder into a solid material. There are 2 forms of pressing: die pressing
(which involves a hard die into which the powder is placed and then pressed),
and isostatic pressing (involving a special "rubber" die into
which powder is placed and then pressed with equal force in all directions
on the powder). Die pressed parts are usually made smaller than isostatically
pressed parts. Although the magnetic properties of isostatically pressed
parts are higher, the uniformity of magnetic characteristics is usually
lower than that of die pressed parts. Sintered parts normally need some
finish machining in order to meet final tolerances.
Compression
Bonded - this is a technique whereby a special form of NdFeB powder
is blended with a plastic carrier material, die pressed and then heated.
Parts made in this way can be of complex shapes and come off the tool
with close tolerances, requiring no further finish machining. They have
lower energy products than sintered materials - in the range of 10 MGOe.
The Bonded NdFeB materials are isotropic - i.e. they can be magnetized
in any direction.
Injection
Molded - NdFeB powder is blended with a plastic material and injection
molded. The resulting parts have energy products in the 5 MGOe range,
but can be made with extremely intricate shapes.
Extruded
- though not popular at present, NdFeB based flexible magnets can be made
by binding NdFeB powder with a carrier material and extruding the material
in sheet or strip form. Energy products up to about 6 MGOe have been achieved
in this way.
Comparison of NdFeB and SmCo Magnets |
| Material |
Energy
Products |
Mechanical
Strength |
Density
(lbs/in3 - gm/cm3) |
Corrosion
Resistance |
Temperature
Stability |
Cost |
| NdFeB |
10
to 48 |
Medium |
0.275
- 7.5 |
Low |
Low
to Medium |
Lower |
| SmCo |
15
to 32 |
Low |
0.300
- 8.3 |
High |
High |
Higher |
|
|
Assemblies
We are able
to manufacture metal and other components of finished sub assemblies using
our CNC machining facilities.
Assemblies
can be fabricated by adhering magnets with adhesives to suit a range of
environments, by mechanically fastening magnets, or by a combination of
these methods. Due to the relatively brittle nature of these magnet materials,
press fits are not recommended.
When multiple
magnets are assembled in repelling positions, it is advisable to use mechanical
fastening in addition to adhesives, since if adhesives were to give way,
repelling magnets may dislodge and endanger personnel using them. Our
design engineering team will be happy to assist you in designing housings
for your magnet assemblies.
Surface
Treatments
The corrosion
resistance of SmCo is considered good while that of NdFeB is considered
poor. Painting, coating, or plating is therefore highly recommended for
NdFeB. Plating NdFeB is a difficult process, and commercial plating houses
are unlikely to be able to achieve plating with good adhesion. Nickel,
Zinc, or Tin plating provides good corrosion resistance for NdFeB magnets.
We are also able to cadmium chromate or aluminum chromate plate NdFeB
using vacuum deposition techniques. A variety of organic coatings have
also been successfully developed for NdFeB, exhibiting good corrosion
resistance characteristics. For especially harsh environments, it may
be advisable to use a combination of coating techniques, or to encapsulate
the material in a sealed housing.
Machining
Some machining
operations may be performed on NdFeB materials using carbide tools, although
surface finishes thus obtained may be less than optimal. In general, NdFeB
magnets must be machined using diamond-grinding techniques.
We are fully
equipped to machine these materials to your blueprint specifications.
Bonded NdFeB
is easily machined. Coolants must be used while machining this material
in order to avoid spontaneous combustion of powder. Machining this material
removes a layer of protective coating, and re-coating for corrosion resistance
may be necessary.
Magnetizing
and Handling
All Rare
Earth magnets require extremely high magnetizing fields and special consideration
must be given to this when designing complex assemblies, if it is intended
to magnetize after assembly. Consult us if you foresee any problems.
Rare Earth
materials are mechanically weak, and magnetically very strong. They must
therefore be handled very carefully to avoid damage and injury to personnel
handling the magnets. Receiving and assembly personnel should be warned
about the dangers of handling magnetized Rare Earth magnets.
Isotropic
bonded NdFeB materials can be magnetized in any direction, or with multiple
poles. Special magnetizing fixtures are required in order to achieve multiple
pole magnetization. Such multiple pole fixtures may cost several thousand
dollars depending on complexity of design and production rate requirements.
Temperature
Effects
Magnetic
properties of NdFeB deteriorate rapidly above about 130
Centigrade, depending on the grade of material, and the permeance coefficient
of the magnet in operation. The higher the permeance coefficient the magnet
operates at, the higher the temperature it will withstand. High Hci
NdFeB materials operating at a high permeance coefficient can operate
to about 210
Centigrade.
Common
Applications for Neodymium Iron Boron Magnets
Holding systems
requiring very high holding forces, high field yoke magnets, high performance
stepper, DC, servo, linear, and voice coil motors, magnetic bearings,
magnetic couplings, loudspeakers, Halbach arrays, headphones, microphones,
magnetic separation, instrumentation, switches, relays, magnetic resonance,
sputtering, vacuum deposition, charged particle beam guidance, particle
accelerators, Undulators, Wigglers, and others.
Shapes,
Sizes, and Grades Available
In addition
to the stock shapes, sizes, and grades listed, others are available. Please
inquire. Non-standard shapes and sizes can be fabricated to blueprint
specifications from raw stock. Isotropic bonded NdFeB can be specially
formulated to meet special requirements, with energy products from 1 to
10MGOe, as required.
|
