Sintered NdFeB magnets are manufactured by a powder metallurgical process which involves the sintering of powder compacts under vacuum. Magnets may be produced in large blocks for subsequent processing or as tailor made components made by die pressing. Coatings may be applied depending on the expected environment.
All the magnets require very careful processing since the powders are very reactive with moisture and oxygen. It means that controlled atmospheres are required at all stages in production, from the raw alloy to the sintering at around 1100ˇăC.
The production of NdFeB magnets begins with melting of the alloy and the careful addition of special elements to enhance the particular properties required of the finished magnet. The ingot is then crushed and milled to a fine powder under protective atmosphere. Depending on the type of magnet being produced, the powder is either isostatically pressed into a block or die pressed to a particular component shape. During the compaction it is important to apply a large alignment field to orientate the particles for the preferred magnetic direction.
The compacts are transferred to furnaces which operate under high vacuum. The sintering process is completed by a separate heat treatment stage to develop the magnetic properties.
Finishing of the magnets may be by grinding to the required tolerance or slicing a large block into the desired shape.
All sintered NdFeB magnets are characterised by being hard and potentially brittle compared to steels. Magnets based upon samarium cobalt are more stable to harsh environments but are much less economic than neodymium iron boron materials. Where there may be high temperatures there are grades of NdFeB to survive up to 200ˇăC. Where there is a poor environment a range of protective coatings is available.
All sintered NdFeB magnets are difficult to magnetise and each application should consider the merits of in situ or prior magnetisation.
Components may be magnetised before final inspection, packing and despatch.