Designing with Permanent Magnets: 10 Tips

Reducing the air gap can increase useful field, but halving it does not universally double the field. Magnet dimensions, leakage and return-path geometry matter. Use a circuit model or measurement, as illustrated by K&J’s gap-field measurements.

Back iron can change flux concentration and leakage. Calculate its section and saturation in the intended geometry instead of assigning a fixed percentage benefit.

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. 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.

Specify the finished coated dimensions and account for layer variation and edge coverage. Specify the coating formulation, thickness on each face, edge coverage, substrate preparation and cure. Agree a corrosion test method, exposure duration and acceptance endpoint for the actual part, then request its report. Salt-spray hours are not a service-life guarantee.

Use assembly datums and tolerance analysis to identify critical features. Confirm process capability for those features. A number from a different ring construction is not a universal machining capability.

Anisotropic material has a preferred easy-axis structure established during manufacture. Later magnetization must work with that structure. Isotropic bonded material permits different magnetizing patterns, subject to fixture and geometry. Magnequench’s product documentation distinguishes the powder and magnet routes.

Assess attraction forces, brittle fracture and assembly access for the actual magnet. Use appropriate fixtures, spacers and packaging based on that assessment.

Use a magnetic circuit model or FEA to compare the design, then validate representative parts and assemblies. Simulation does not guarantee a fixed number of saved prototype iterations.

Define bonding, mechanical retention, coating and the dimensional stack. Test the intended joint and structure under the relevant temperature, speed and environmental duty.

Review the drawing and acceptance plan before tooling. Confirm the specific material, process, inspection and exporter responsibilities.