NdFeB magnets can be differentiated according to the way they are manufactured. A distinction is made between sintered magnets, polymer-bonded magnets and MIM (Metal Injection Moulding) magnets. Sintered magnets have the highest energy product compared to other types of magnets. They are produced using the classic powder metallurgy method, which means that the NdFeB powder is filled into a mould, a magnetic field is applied and aligns the particles. The part is then sintered.

The disadvantage of making sintered magnets with that method is that the geometry of the component is limited, as the parts have to be ejected from the mould after the powder has been pressed. Parts with undercuts are therefore difficult to produce.

Polymer bonded magnets, on the other hand, are produced by compounding the NdFeB powder with a polymer binder in a mixer or extruder, granulating it, and shaping it using classic plastics technology processes such as injection moulding. Although this process allows the production of complex geometries, the magnetic properties are reduced compared to sintered magnets due to the residual plastic. The advantages of the above processes are combined in the MIM process. The MIM process involves embedding the powder with a binder system consisting of polymers and additives. This creates a feedstock that can be injected into a mould using an injection moulding machine. After the binder is removed, the components are sintered to produce a metallic structure.

However, difficult process ability, due to the high affinity of the powder to oxygen and carbon pickup, remains problematic in terms of obtaining sufficient remanence and coercivity.

In this talk, a novel approach to produce NdFeB magnets from recycling material with powder extrusion moulding (PEM) is presented. The process of PEM differs from MIM in terms of moulding. In PEM, the feedstock is pressed continuously through a nozzle, whereas in MIM, it is injected into a cavity at high pressure. To align magnetic particles in the continuous PEM process, an alignment tool was designed based on magnetic flux simulation.

This presentation shows the results of debinded and sintered NdFeB permanent magnets produced by the PEM process. In order to produce anisotropic magnets, different geometries for a magnetic particle alignment tool were simulated and tested to align the magnetic particles in a continuous process. Magnetic and microstructural properties of extruded, debinded and sintered samples with different feedstock compositions produced with the new alignment tool are shown.

Stefan Rathfelder (M.Sc.)