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 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
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 for Injection Molded (Plastic) Magnets
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.