Manufacture process neodymium magnet
Vacuum Melting
Compositions of neodymium, iron , iron-boron, dysprosium and minor additions including cobalt , copper , gallium, aluminum and others are mixed and induce-melted to form Nd2Fe14B phase and other necessary structures required for high performance permanent magnets. The melting temperature reaches over 1300o C. Usually repeated melting is needed to be produce an even phase and structure distribution.
Crushing
The ingots from vacuum melting process are crushed into coarse powder directly , or strip cast followed by HDDR processing into coarse powder.
Jet Milling
The coarse powder further milled into required particles sized about 3 microns in diameter by a jet miller . Those particles become single-domain and anisotropic which are critical for producing a high coercivity magnet. Jet milling is the most effective way to mill the particles so far.
Pressing
Compact the fined powder to re-produces block magnets. Usually a magnetic field is applied during pressing to align those anisotropic particles in order to produces maximum magnetic output in particular direction. There are two pressing methods, transverse and axial , depend on different application. Isostatic pressing is normally used to further densify magnets to 75-80%.
Vacuum Sintering
The compacted magnets are sintered ate temperature above 1000 o C and for many hours to be solidifiedand compacted further more up to 99% by shrinking its body. A required microstructure between particles for high performance permanent magnets is also formed in this stage. Some following heat-treatments are needed to stabilize the magnets.
Machining
Shrinkage and distortion during sintering is too difficult to control adequately and magnets normally need at least a "clean up" grind on the surface. Small parts are cut or sliced precisely forma big block to meet the demanding tolerances and different shapes.
Surface Treatment
Various surface treatments can be applied on the final products . They include zinc, nickel ,Ni-Cu-Ni multi-layer, e-coating , epoxy and others. They provide different surface finishing, appearance and corrosion resistance, applicable in different application environments.
