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Magnet Manufacture

Manufacture of Rare Earth Magnets

NdFeB magnets are currently marketed under the two broad classifications of sintered and bonded.

Bonded magnets are usually isotropic with a maximum energy product up to 12MGOE. These magnets are manufactured by compressing a mixture of NdFeB alloy flakes with a resin as a bonding agent followed by heat treatment to set the resin. The alloy flakes are made using a melt spun rapid quenching process developed by Delco Remy, a division of General Motors. The magnets are then magnetised as required.

Sintered magnets are anisotropic and have a typical maximum energy product in the range between 27 to 48 MGOE.

There are two possible processes for manufacture of high energy anisotropic Neodymium based rare earth magnets. One process uses melt spun isotropic crushed ribbon, hot pressed and plastically deformed which results in domain alignment and anisotropy. This process is still in the development stage.

The other process used widely is a classical powder metallurgical process used by AMS. Cast alloy slabs, produced from molten alloy of the right composition are crushed mechanically to minus 3 mm in size and then milled to 3-5 µm powder.

The powder particles are magnetically aligned in an electromagnetic coil then pressed to shape in a mechanical or isostatic press. The pressed compacts are then sintered at 1100°C, finished to size by grinding or slicing, and magnetised in an electromagnetic coil at a very high magnetic field.

Whilst the basic process appears simple, in practice very strict controls at every operation must be maintained. Powder of the alloy is extremely pyrophoric, bursting into flames in contact with air. All operations must be carried out under inert atmosphere. Even a minute presence of oxygen will render powder useless. Other important parameters are particle alignment, particle size distribution and sintering parameters.

AMS has the know-how and ability to produce the very best in bonded and sintered magnets. We are backed by knowledge of the Applied Magnetism Section of CSIRO in magnetic circuitry and the latest magnetic measurement equipment.