Bonded NdFeB materials are composite materials consisting of melt spun neodymium iron boron powder (NdFeB) dispersed in an engineering thermoplastic or thermoset matrix. Injection moulding uses polyamides, or polyphenylene sulphide for higher operating temperatures, whilst epoxy resins are most commonly used in compression moulding.

The proportion of NdFeB powder to polymer matrix can be varied to achieve the desired magnetic performance. Very high volume fractions of the magnet powder are possible.

NdFeB metal is susceptible to corrosion, but the polymer matrix in injection moulded NdFeB contributes to a much better corrosion resistance than its fully dense counterpart, partly by prevention of penetration of corrosion beyond the surface. Thus injection moulded NdFeB magnets do not normally require coating. However, for compression moulded NdFeB products, a coating is recommended because of a degree of inherent porosity.

The magnetic temperature stability is determined by the NdFeB powder with coefficients dependent upon composition:

B r = - 0.07 to - 0.13%/°C and H cJ = - 0.4%/°C. PROCESSING

PROCESSING
Processing begins with the controlled mixing and dispersal of the NdFeB powder into molten thermoplastic or thermoset matrix material. This mixing is conducted using highly specialised state-of-the-art compounding equipment due to the high volume fraction of filler being used. Additives may be incorporated at this stage to influence compound properties and behaviour. The resultant compound is in pelletised form as the feedstock for the injection moulding process and powder form as the feedstock for the compression moulding process.

Magnet production is carried out on adapted injection moulding machines, often operating fully automatically. Shapes with a high degree of complexity can be produced, for example, gears, snap fits and undercuts. It is possible to incorporate shafts, bushes and other inserts into the process thereby greatly simplifying magnetic assemblies.

Compression moulding is carried out by axial pressing. The process operates fully automatically with statistical process control being used to ensure consistent green density. Components are thermally cured to cross link the thermoset matrix material and so develop mechanical properties in the component. Magnetic properties of parts produced by this route can be higher than those produced by injection moulding, and tooling costs are lower, although this is at the expense of the shape complexity possible with injection moulding.

Precise dimensional control is achieved in both processes and usually the component does not require further machining.

Components may be coated (if compression moulded) and magnetised before final inspection, packing and despatch.