Compression bonded NdFeB permanent magnets

Compression molding is a technique in which a magnetic powder is encapsulated with the smallest amount of resin possible and then pressed into a green compact with the highest practical pressure to achieve the highest possible density. The resin, typically a thermoset epoxy, is then cured to produce a rigid magnet. This process has become increasingly popular over the last several decades, primarily because high tolerance, thin walled ring magnets with high L/D ratios can be easily and rapidly produced. A major advantage of compression molding is that the metal loading factor is the highest of any of the bonding processes and, therefore, the highest possible magnetic remanence is achieved for a given magnetic powder. Compression bonded NdFeB magnets produced by this process are now used in a wide variety of motors, typically higher end brushless stepper, spindle and servo motors. This chapter reviews three families of NdFeB magnets that are produced by this technique, including bonded Nd magnets from rapidly solidified (melt spun) powder, anisotropic bonded NdFeB magnets produced from crushed hot deformed magnets and anisotropic NdFeB magnets produced by the HDDR process.