the potential outcome still depends on the specification. Specifying the magnet as consisting of several zones, with specific homogenous coercivity requirements, is an initial challenge. This is a compromise enabling the standard IEC 60404-5 on cut-off specimens to be utilised.
The largest potential is obtained by a real, three-dimensional profile of heavy rare earths and coercivity for the respective zones. Magnet users are still reluctant to go in this direction, as it results in quality assurance to standard IEC60404-5 no longer being possible at the part level.
The final release testing of a magnet is shifted to the release at the machine level, at a test bench. In parallel, all production processes need to be fixed by a magnet supplier – akin to existing automotive standards.
Why insist on a part-level release as the exception for a sintered 3D-GBD NdFeB magnet?
Lamination sheets or hardened surfaces of shafts are good examples that show that not all parts of an electrical machine can be measured at the part level, but in fact, need machine-level testing.
The local-diffusion approach does not require additional effort in magnetic-circuit engineering. The counter field distribution is calculated anyway and can be given as part of the specification to the magnet supplier. Furthermore, the scenario for inserting the magnets into the machine needs to be discussed. In the case of non-oriented insertion, where the side with higher coercivity is not necessarily at the required position, the hot spots need to be mirrored symmetrical in order to enable a randomly oriented insertion solution. Otherwise, markings need to be applied.
Finally, in order to enable a local diffused 3D-GBD magnet, an individual discussion with quality assurance and production teams needs to take place for each project, in order to define the degree of willingness to accept inhomogeneity. The variety of possibilities with 3D-GBD is immense and should be evaluated, in particular, for projects with huge volume demand like EV projects for automotives.
