Magnetic feed material and its use in producing bonded permanent magnets by additive manufacturing

A method for producing a bonded permanent magnet, the method comprising:

• (i) blending thermoplastic polymer and particles having a hard magnetic material composition to produce a blended magnet-polymer mixture, wherein said thermoplastic polymer has a melting point of at least 175° C., and said particles having a hard magnetic material composition are present in said blended magnet-polymer mixture in an amount of at least 75 vol %;
• (ii) feeding said blended magnet-polymer mixture into a pre-feed hopper having a powered auger at an outlet of said pre-feed hopper, wherein said outlet feeds directly into an inlet of a temperature-controlled barrel extruder;
• (iii) feeding the blended magnet-polymer mixture from step (ii) into said temperature-controlled barrel extruder at a fixed feed rate of 5-20 kg/hour, pushing said blended magnet-polymer mixture from said inlet to an outlet of said temperature-controlled barrel extruder, and subjecting said blended magnet-polymer mixture to an increasing temperature from said inlet to said outlet of said temperature-controlled barrel extruder, wherein the temperature at said outlet is at least the glass transition temperature to no more than 10° C. above the glass transition temperature of said blended magnet-polymer mixture;
• (iv) feeding said blended magnet-polymer mixture at said outlet of the barrel extruder directly into an extruding die, wherein said extruding die is set at a temperature below the temperature of said outlet of the barrel extruder and below the glass transition temperature of said blended magnet-polymer mixture, to cool and harden said blended magnet-polymer mixture;
• (v) passing the blended magnet-polymer mixture from step (iv) through said extruding die at a fixed speed to produce a shaped and hardened form of said magnet-polymer mixture exiting said extruding die at said fixed speed;
• (vi) cutting said shaped and hardened form of said magnet-polymer mixture at regular intervals as said shaped and hardened form of said magnet-polymer mixture exits said extruding die at said fixed speed, to produce hardened pellets of said magnet-polymer mixture, wherein said hardened pellets are of uniform size by virtue of said fixed speed and cutting at regular intervals;
• and
• (vii) feeding said hardened pellets into an additive manufacturing device and operating said additive manufacturing device, by at least hot extruding said hardened pellets through a die or nozzle of said additive manufacturing device and repeatedly depositing discrete amounts of the extruded material in designated locations, to produce a bonded permanent magnet having the composition of said hardened pellets.