Sintered NdFeB magnets are made with several steps. At first, a alloy is formulated based on the properties
of final permanent magnets supposed to reach. The alloy is produced in a vacuum furnace. Then the alloy is crushed into
a powder form. Sintered NdFeB permanent magnets are formed by powder metallurgical process. These magnets can be die
pressed or isostatically pressed. During the pressing process, magnetic fields are applied with assistance of specially
designed fixture to align magnetic "domains" and optimize the magnetic performance of these magnets. Then pressed magnets
are placed into a furnace under protective atmosphere for sintering. After sintering the magnet shape is rough, and need
to be machined and ground to achieve desired shape and size. A surface coating is usually applied on NdFeB magnets.
Zinc or nickel coating is common used as a protective layer. Other materials such as cadmium chromate, aluminum chromate,
tin or polymer (epoxy) are also used for this purpose.
Polymer-bonded magnets can be produced with close tolerances off tool, with little or no finishing required.
Polymer-bonded NdFeB permanent magnets can be made by both compression moulding and injection moulding. The sintered
magnets usually require some finishing operations in order to hold close mechanical tolerances. The sintered magnets,
however, provide better magnetic properties than bonded magnets. |
