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Bonded/Molded Magnets

Compression molding uses a solid binder (e.g. a plastic or thermosetting epoxy) plus the magnetic material. The end material is isotropic - the magnetising coil fixture design determines the magnetic pattern it takes.

Compression molding is cost effective when higher volumes are required compression molded magnets are best produced in tens or hundreds of thousands of magnets per production run.

Injection molding uses a solid binder (e.g. a plastic or thermosetting epoxy) plus the magnetic material but gives a greater variety of shapes and complexity of shapes compared to compression bonded. The end material is isotropic - the magnetising coil fixture design determines the magnetic pattern it takes.

Overmolding is possible with injection molding process.

Injection molded magnets are produced in tens or hundreds of thousands of magnets per production run.

Advantages & Disadvantages of Bonded Molded Magnets

Advantages

  • A higher ratio of magnetic material powder to binder gives higher magnetic performance than the injection molded magnets (higher magnetic loading)
  • NdFeB, SmCo, Alnico and Ferrite versions possible
  • Hybrid versions as well (e.g. Ferrite+NdFeB) with combined properties
  • Good tolerances – secondary machining not needed
  • Low electrical conductivity, low eddy currents

Disadvantages

  • The compression bonding process is limited to simpler shapes such as rectangles, rings, arcs and cylinders. A consistent cross sectional area is required along the pressing direction
  • Possible tooling charges for production and magnetising

Typical Applications of Bonded/Molded Magnets

  • Motors
  • Position sensors
  • Hybrid performance components

Examples: A company wanted a magnet on a joystick to activate Hall Effect sensors to give relative position information. A ferrite magnet would be too weak; a sintered NdFeB neodymium magnet would be too powerful. A compression bonded NdFeB magnet was supplied that had a performance between NdFeB and Ferrite but which had an epoxy finish, good final tolerances and would be low cost in high production quantities.