Sintered neodymium-iron-boron (Nd-Fe-B) magnets are licensed rare earth magnets which are the most powerful commercialized permanent magnets available today, with maximum energy product ranging from 26 MGOe to 52 MGOe. Neodymium Iron Boron is the third generation of permanent magnet developed in the 1980s. It has a combination of very high remanence and coercivity and comes with a wide range of grades, sizes and shapes. With its excellent magnetic characteristics Nd-Fe-B offers  flexibility for new designs or as a replacement for traditional magnet materials such as ceramic, Alnico and Sm-Co for achieving higher efficiency and more compact devices.

A powder metallurgy process is used in producing sintered Neodymium magnets. Although sintered Neodymium is mechanically stronger than Samarium Cobalt magnets and less brittle than other magnets, it should not be used as a structural component. Selection of Nd-Fe-B is limited by temperature due to its irreversible loss and moderately high reversible temperature coefficient of Br and Hci. The maximum application temperature is 200 °C for high coercivity grades. Nd-Fe-B magnets are more prone to oxidation than any other magnet alloys. If Nd-Fe-B magnet is to be exposed to humidity, chemically aggressive media such as acids, alkaline solutions salts and harmful gases, coating is recommended. It is not recommended in a hydrogen atmosphere.

Applications of Neodymium Magnets

Magnetic separators

Linear actuators

Microphone assemblies

Servo motors

DC motors (automotive starters)

Computer rigid disc drives, printers and speakers

Attributes of Neodymium Material

Very high resistance to demagnetization

High energy for size

Good in ambient temperature

Moderately priced

Material is corrosive and should be coated for long term maximum energy output

Low working temperature for heat applications, but higher levels of heat resistance materials are being introduced periodically

Tolerances

For as-pressed material, tolerance on the thickness (direction of magnetization) is +/– .005”. Other dimensions are +/– 2.5% or +/– .005”, whichever is greater.

According to International Magnetics Association/Magnet Materials Producers Association (IMA/MMPA) standards, visual imperfections such as hairline cracks, porosity and minor chips are commonly found in sintered magnets. A chipped edge is considered acceptable if no more than 10% of the surface is missing. Cracks are acceptable as long as they do not extend across more than 50% of the pole’s surface.

Machining

Since neodymium magnet material is prone to chipping and cracking, it does not lend itself to conventional machining methods. However, neodymium can be abrasively ground, but only with the use of liberal amounts of coolant. The coolant minimizes heat fracturing and the risk of fires caused by oxidized grinding dust.

Magnetizing and Handling

Neodymium magnets are very brittle and very strong magnetically. Therefore, it is crucial to handle these magnets with extreme care to avoid personal injury and damage to the magnets. Fingers can be severely pinched between attracting magnets. Magnets can chip if allowed to “jump at” an attracting object. It is highly recommended that when constructing rare earth magnetic assemblies, they be magnetized after assembly.