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Bonded/Molded/Plastic Magnets

Bonded/Molded Magnets - Overview

 

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 of Bonded/Molded

  • • 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 of Bonded/Molded

  • • 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

  • • 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.

 
 

Injection Molded (Plastic) Magnets

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 of Injection Molded (Plastic) Magnets

  • • More complex shapes are possible
  • • Overmold, insert mold, etc all possible
  • • NdFeB, SmCo, Alnico and Ferrite versions possible
  • • Hybrid versions as well (e.g. Ferrite+NdFeB) with combined properties
  • • Low electrical conductivity, low eddy currents
  • • Good tolerances. More resistant to chipping than compression bonded
 

Disadvantages of Injection Molded (Plastic) Magnets

  • • Injection molded magnets offer lower magnetic performance than the compression bonded magnets (due to lower magnetic loading)
  • • Possible tooling charges for production and magnetising
 

Typical Applications of Injection Molded (Plastic) Magnets

  • • Motors
  • • Sensors
  • • Injection molded rotor assemblies
  • • Insert molded magnetic components
  • • Overmolded magnetic components
 

Example

A company required a ring magnet with multiple poles around the outer circumference for rotary movement sensing. An injection molded ferrite magnet was magnetised with a dedicated magnetising fixture to create the required multiple pole pattern. The ring also had a slot added to fit onto the keyway on a shaft to locking in place in the assembly.