NdFeB Thermal Demagnetization: Temperature Limits and Grade Selection for EV and Robotics Motors

Select the grade using the actual hot demagnetization curves, the magnetic circuit working point and the worst opposing field. A suffix is a nominal material class, not a guaranteed motor temperature limit or a chemical recipe. A quoted temperature class is conditional on the material and magnetic working point. It does not mark a universal onset of irreversible loss.

For a simple passive magnetic circuit, the permeance load line relates B and H through the circuit geometry and crosses the material demagnetization curve at the working point. It is not a line starting at Br. Applied stator fields and nonuniform geometry require a more complete model. Use the actual curve at the worst magnet temperature and opposing field. Hcj alone does not specify the knee shape.

Calculate the local reverse field, rotor position, magnet temperature and duration for the actual stall, short-circuit or field-weakening case. No fixed multiple of normal field applies to every motor. Establish a test and allowable irreversible loss with the motor designer.

The reported N45H magnetic comparison and the separate historical 50H Dy-reduction example have different scopes. See the GBD evidence and limitations. Finished-part savings require a quotation and qualification of the proposed route.

Confirm the treated faces and diffusion distance for the geometry. A fixed maximum thickness or automatic substitution between grades is not established by the reported comparison.

Define magnetic measurement conditions before and after the agreed thermal or fault exposure. A total magnetic-moment test and an assembled-motor back-EMF test answer different questions. Control temperature, speed, fixture and uncertainty when comparing them. Investigate losses against the agreed acceptance criterion rather than a universal 2% threshold.

Mainrich’s sintered NdFeB range is N30 to N56, with no AH grades. The top grade depends on the temperature series: N56, N54M, N52H, N52SH, N50UH and N45EH. Grades up to N52SH can be made without a Chinese export licence, so we offer those first; UH and EH grades need a licence, applied for per order.

Confirm the grade, suffix, geometry and production route for each drawing. This summary does not offer every combination; grades outside it in educational examples are not Mainrich supply offers. Agree tooling, sample quantity, inspection and production milestones in the quotation. Export release depends on any required authorization.

No standard prototype quantity or fixed delivery interval is promised here. A suffix does not establish a fixed price premium or additional production time.