Bonded magnets are lauded for complex shape, high dimensional precision, tight tolerance, without additional mechanical machining, and suitable for mass production. Bonded magnets are a kind of composite material which composed of magnetic powder and binder. Magnetic performance of magnetic powder plays a decisive role in the bonded magnet’s magnetic properties. The volume fraction of binder and interior porosity will directly influence remanence and Max. Energy product of magnet, but its intrinsic coercivity is not affected by above two factors in principle. The isotropic magnets with melt-spun Nd-Fe-B nanocrystalline powder accounts for more than 80% of bonded rare earth magnets market, then other 20% are occupied by anisotropic Nd-Fe-B, Sm-Fe-N and Sm-Co magnets. Besides varies choices of magnetic powder, binder with different physical and chemical properties also add more diversity to the bonded magnets. The commonly used binder includes thermosetting resin, thermoplastic resin, rubber, and thermoplastic elastomer, thus correspond to four kinds of molding process: compression molding, injection molding, calendering and extrusion molding. Magnets with different molding process also have different magnetic properties, shape adaptability, dimension and geometrical tolerances, therefore, compression molded magnets and injection molded magnets are more widely used among them.
