How are the Neodymium Magnets Made?
Sintered neodymium magnets are made with several steps. At first, a Nd-Fe-B alloy is formulated based on the magnetic characteristics 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 neodymium 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 tolerances. A surface coating is usually applied on neodymium magnets. Zinc or nickel coating is common used as a protective layer. Other materials such as cadmium chromate plating or aluminum chromate plating, tin or polymer (epoxy) are also used for this purpose.
Both neodymium magnets and SmCo magnets can be made either in sintered or polymer-bonded magnets. The polymer (such as epoxy)-bonded magnets can be produced with close tolerances off tool, with little or no finishing required. CMS Magnetics supplies polymer-bonded neodymium permanent magnets made by both compression moulding and injection moulding. The sintered magnets usually require some finishing process in order to hold close mechanical tolerances. The sintered magnets, however, provide better magnetic properties than bonded magnets.