Rare earth bonded magnets with versatility on shaping and high density, composed of isotropic Nd-Fe-B powder and thermoplastic resin (Nylon-12, PBT and PPS), were developed with warm compression molding.
(1) Compounds with magnet powder volume fraction of 80vol.%, composed PBT or Nylon-12, have versatility on shaping and compressibility at relatively low pressure. Coin-shaped magnets with a thickness of 0.3mm and ring magnets with a wall-thickness of 0.4mm were moldable with these compounds at the pressure of 250MPa. The properties of these bonded magnets were as follows: pore=0vol.% in substance, density =6.2Mg/m³ and (BH)max=97.9kJ/m³ (12.3MGOe).
(2) Compounds with magnet powder volume fraction of 90vol.% have higher compressibility than the compounds for compaction molding at high pressure. This is because that viscosity of resin during the molding is easy to optimize and spring-back after molding is small in warm compression molding. The properties of the magnet were as follows: density=6.7Mg/m³ and (BH)max=115kJ/m³ (14.4MGOe) at pressure of 1250MPa.
In this way, warm compression molding is applicable to extensive compounds through adjusting the molding condition.