Neodymium Magnets for Servo Motors
Custom NdFeB arc segment, bread-loaf, and multipole ring magnets for PMSM servo rotors — SH/UH/EH grades stable to 200°C, machined to ±0.02 mm, flux-matched to ≤±2% per pole for low cogging torque. IATF 16949 certified, manufacturing since 1992.
Mainrich Magnets is a vertically integrated manufacturer of neodymium magnets for servo motors — custom arc segment, bread-loaf, block, and multipole ring NdFeB magnets for the permanent-magnet synchronous motor (PMSM) rotor that drives your CNC axis, robot joint, or injection molding machine. Servo motors punish magnets harder than most industrial drives: peak drive currents apply strong demagnetizing fields, rotor temperatures run 20–30°C above winding temperature, and every micrometre of geometric variation shows up as measurable cogging torque. We manufacture to ±0.02 mm precision tolerance, bin magnets to ≤±2% per-pole flux deviation, and validate knee-point performance at your rated operating temperature — with no MOQ on custom orders, from prototype lots to multi-million-piece annual programs.
Supply-chain continuity: Dy and Tb for our SH/UH/EH servo grades are sourced exclusively through MIIT-licensed channels, and our Grain Boundary Diffusion (GBD) process cuts heavy-rare-earth content substantially versus conventional sintered NdFeB — directly reducing your exposure to China's rare-earth export controls. Export licensing for Dy/Tb-containing grades is handled case by case; see our rare-earth export compliance guide for how we manage documentation and timelines.
The difference between specifying N42SH and N42UH for a servo motor can be the difference between a ten-year service life and a field failure within eighteen months. A magnet driven past its knee-point temperature under peak current demagnetizes irreversibly — torque drops, position accuracy degrades, and the motor fails in service. Send us your thermal profile and we verify the grade before you commit to tooling.
Five Servo Applications — Five Different Magnet Specs
Servo motors span very different duty cycles and thermal environments. Each application drives a different grade, shape, and tolerance requirement.
CNC Feed-Axis & Spindle Servos
Machine tool feed axes demand minimal cogging torque for surface finish quality; spindle servos add sustained 120–150°C operation. Precision-ground arc segments in N45SH, flux-matched per rotor set.
N45SH · ±0.02 mm · ≤±2% fluxRobot Arm & Cobot Joint Servos
High-pole-count frameless PMSM joints need compact arc or ring magnets with high energy density in tight axial space. N48UH GBD keeps coercivity at 180°C joint temperatures. See our robotics magnets page for joint actuator detail.
N48UH GBD · Tmax 180°CAGV / AMR Drive Servos
Warehouse AGV and AMR wheel drives prioritize cost-effective flux density with moderate 100–120°C thermal load and high lot-to-lot consistency across large production volumes.
N45SH · high volume · NiCuNiInjection Molding Machine Servos
Electric injection molding machines run high-duty-cycle clamp and injection axes near hot barrels — sustained heat soak pushes rotor temperatures toward 180–200°C. N42EH holds coercivity where lower grades demagnetize.
N42EH · Tmax 200°C · knee 170°CPick-and-Place & Packaging Servos
High-speed pick-and-place axes cycle at extreme accelerations — low rotor inertia and consistent step response matter most. Thin-wall arc segments or bonded multipole rings keep the rotor light and the torque ripple low.
Thin-wall arcs · rings · low inertiaMagnet Grades Servo Motor Engineers Specify Most
Selected by peak rotor temperature and demagnetization margin under peak drive current — these are the grades most commonly specified for servo motor programs at Mainrich. All values from our production line, tested per IEC 60404.
Most Popular
N45SH Arc Magnets
View Arc Magnets →
High Power Density
N48UH GBD Magnets
View Custom Magnets →
High Temp
N42EH Arc Magnets
Full Grade Chart & Selector →GBD is standard on all our SH, UH, and EH servo grades. Heavy rare earths (Dy/Tb) raise intrinsic coercivity and shift the knee-point temperature upward, but they also drive cost and export-control exposure. Mainrich applies Grain Boundary Diffusion to concentrate Dy/Tb at the grain boundaries where it matters — achieving the same Hcj and knee-point at significantly lower heavy-rare-earth loading than conventional sintered NdFeB. Lower Dy/Tb per magnet means lower bill-of-material cost and a smaller export-license footprint per shipment.
What Sets Our Servo Motor Magnet Manufacturing Apart
Four capabilities that matter specifically for servo motor programs — beyond what a catalog magnet supplier controls.
Per-Pole Flux Binning
Magnets are flux-tested and shipped in matched rotor sets with ≤±2% per-pole deviation — the spec that controls cogging torque and torque ripple in your assembled motor.
Precision Grinding (mm)
±0.05 mm standard, ±0.02 mm precision, ±0.01 mm ultra-precision on request — full dimension inspection reports and B-H curve data with every OEM shipment.
Grain Boundary Diffusion
Standard on SH/UH/EH grades — the same knee-point and Hcj at substantially lower Dy/Tb content, cutting cost and export-control exposure.
16949 Certified
PPAP documentation, FMEA, control plans, and MSA studies — the quality system servo OEMs and Tier-1 automation suppliers audit for.
Export compliance for Dy/Tb servo grades: Under China's 2025 rare-earth control framework, UH/EH grades containing Dy and Tb require export licensing per shipment. Mainrich sources through MIIT-licensed channels and manages the licensing process on your behalf — timelines are case by case and depend on end-use documentation, so tell us your target delivery date early and we plan the license window into your schedule. Details: China's 2025 dual-use export controls explained.
Servo Magnet Tolerances Decide Your Cogging Torque
Two servo rotors built from the same drawing can behave differently on the test bench. The difference is almost always the magnets — geometric variation and per-pole flux variation both distort the air-gap field and show up as cogging torque, torque ripple, and audible noise.
Every dimensional deviation in an arc segment — radius, thickness, chord width — creates local irregularities in the air-gap flux distribution. Every difference in magnetization strength between poles adds a once-per-revolution torque disturbance that your servo loop has to fight. For machine tool and robotics applications, we control both:
| Precision Level | Dimensional Tolerance | When to Specify |
|---|---|---|
| Standard finishing | ±0.05 mm | Industry standard — covers most motor applications |
| Precision grinding | ±0.02 mm | High-precision servo motors, machine tool axes |
| Ultra-precision | ±0.01 mm | Special requirements — evaluated per drawing, higher cost |
| Per-pole flux deviation | ≤±2% | Flux-matched rotor sets for high-end servo and robotics |
Arc Segment Dimension Capability
All dimensions machined to your drawing. Magnetic properties tested to IEC 60404 standard conditions.
| Parameter | Description | Typical Range |
|---|---|---|
| OD / OR | Outer diameter / outer radius of the arc | Custom per drawing |
| ID / IR | Inner diameter / inner radius of the arc | Custom per drawing |
| Width (W) | Chord width across the arc face | 3–180 mm |
| Length (L) | Axial length of the segment | 1–180 mm |
| Thickness (T) | Wall thickness (OR minus IR) | 1.5–100 mm |
| Arc angle (α) | Included angle of the segment | 0–180°, per design |
Size limits: maximum L50 × W180 × H80 mm or L180 × W80 × H50 mm; minimum L1 × W3 × H2 mm. For geometries outside these ranges, send your drawing — we quote in 24 hours with DFM feedback on tolerance, coating, and magnetization direction. New to custom magnets? Our custom magnet ordering process walks through drawing requirements, sampling, and qualification step by step.
Coating for servo motor magnets: NiCuNi (triple-layer nickel, 96 h salt spray per ISO 9227) is the standard for enclosed servo housings and is compatible with the epoxy adhesives used in rotor assembly. Specify an epoxy topcoat (500 h+ salt spray) for washdown zones, coolant splash, or condensation-prone environments. We confirm coating compatibility with your bonding or press-fit assembly method during DFM review.
Buyers compare grades and prices, but for servo motors the spec that separates suppliers is flux consistency. We flux-test every magnet and ship matched sets at ≤±2% per-pole deviation — because a rotor built from unmatched magnets fights its own cogging torque for the life of the motor.
Vertically Integrated NdFeB Manufacturing
Every servo motor magnet we ship is made start-to-finish in our own plant — from raw material to magnetized, flux-tested, matched rotor sets. No outsourced steps, no traceability gaps.
Servo Motor Magnet Grades & Specifications
Production data from our line — Br values are typical, magnetic properties tested per IEC 60404. All grades available as arc segments, bread-loaf segments, blocks, or rings. Send your drawing for DFM review and a quote within 24 hours.
| Grade | Br typ. (T / kGs) | Hcj (kA/m) | Tmax | Knee-Point | Dy/Tb wt% | Recommended Servo Application |
|---|---|---|---|---|---|---|
| N45SH GBD | 1.37 / 13.7 | ≥ 1592 | 150°C | 120°C | 2.5 / 0.5 | General industrial servo, CNC feed axes, AGV |
| N45UH GBD | 1.37 / 13.7 | ≥ 1990 | 180°C | 150°C | 1.5 / 2.0 | High-dynamic CNC spindle servos |
| N48UH GBD | 1.41 / 14.1 | ≥ 1990 | 180°C | 150°C | 1.0 / 2.5 | High-power-density compact servo, cobot joints |
| N42EH | 1.33 / 13.3 | ≥ 2388 | 200°C | 170°C | 1.0 / 3.0 | Injection molding, heavy-duty high-temperature servo |
| Custom | Per engineering specification — full N35–N52 / N35H–N33AH range available | See full grade chart & selector | ||||
Segmented / laminated magnets for high-frequency servo drives. Servo PMSMs driven by PWM inverters at high switching frequencies induce eddy currents in the magnet body, heating the rotor from the inside. Mainrich supplies laminated NdFeB — multiple insulated slices per pole — to cut those losses in high-speed spindle and high-frequency servo applications. Mention your inverter switching frequency in your RFQ and we advise whether segmentation pays off for your design.
Arc Segment, Bread-Loaf, or Multipole Ring?
Servo rotor magnet shape is a trade-off between cogging performance, assembly cost, and tooling investment. We manufacture all three — and advise which fits your rotor design and production volume.
Arc Segments
The standard choice for surface-mounted PMSM servo rotors. Flexible tooling, proven reliability, and the lowest cost path from prototype to medium volume. Precision-ground faces control the air gap.
Prototyping · medium volume · SPM rotorsBread-Loaf Segments
Flat base, curved top — the varying magnet thickness shapes the air-gap flux toward sinusoidal, reducing cogging torque without the cost of a skewed stator. A built-in skew effect in a single part.
Low cogging · smooth torque · SPM rotorsMultipole Rings
One ring replaces a full set of glued segments — superior flux uniformity, better concentricity, and no gluing labor in your assembly line. The high-volume choice for compact, high-precision servo rotors.
High volume · automated assembly · BLDC/servoBuilding an interior permanent magnet (IPM) servo rotor instead? IPM topologies use rectangular block magnets inserted into rotor lamination slots — often segmented to control eddy-current losses. For ring-based designs, see our neodymium ring magnets. Either way, send the rotor cross-section with your RFQ and we recommend shape, grade, and magnetization pattern together.
Proven in Servo Motor Serial Production
What qualifying Mainrich as your servo motor magnet supplier looks like in practice — a representative program in continuous serial supply, running under a formal quality agreement.
European Industrial Automation OEM — CNC Servo Motors
Custom arc segment magnets for servo motor rotors in CNC machining centres. Qualified under IATF 16949 audit with knee-point verification at 130°C per batch. Zero demagnetization failures over 3 years of continuous supply.
What Ships with Every Servo OEM Order
Every production lot is delivered with the documentation your incoming inspection and quality system need:
• Full dimension inspection report
• B-H curve data at reference temperature
• Per-pole flux test records for matched sets
• Material certification and RoHS/REACH declarations
• PPAP package on request (IATF 16949 programs)
Servo Motor Application Scope
Mainrich supplies neodymium magnets for servo motors across the full range of motion-control applications.
- CNC Feed-Axis Servos — precision-ground N45SH arc segments, flux-matched sets for minimal cogging on machine tool axes
- CNC Spindle Servos — N45UH GBD, laminated options for high switching frequencies and sustained thermal load
- Robot Arm & Cobot Joint Servos — compact N48UH GBD arcs and rings for high-pole-count frameless PMSM joints
- AGV / AMR Drive Servos — N45SH in high volumes with tight lot-to-lot consistency for warehouse automation fleets
- Injection Molding Machine Servos — N42EH for 180–200°C heat-soak environments near hot barrels
- Pick-and-Place & Packaging Servos — thin-wall arcs and bonded multipole rings for low-inertia, high-acceleration axes
Related Products & Resources
Frequently Asked Questions
The questions servo motor design engineers and procurement managers ask us most.
Should I specify SH, UH, or EH grade for my servo motor?
It depends on your motor's maximum operating temperature and demagnetization risk:
- SH — max operating temp 150°C: machine tool feed axes, standard industrial servo motors
- UH — max operating temp 180°C: high-power-density servo motors, cobot joints, automotive applications
- EH — max operating temp 200°C: injection molding machines, extreme thermal environments
- AH — max operating temp 220°C: ultra-high-temperature servo applications
The difference between selecting N42SH and N42UH for a servo motor can mean the difference between a ten-year service life and a field failure within eighteen months. We recommend specifying the grade from the peak rotor temperature under worst-case operating conditions, plus a safety margin — and we provide DFM feedback on your drawing to recommend the optimal grade for your thermal profile.
At what temperature do servo motor magnets start to demagnetize?
Demagnetization onset depends on the grade's intrinsic coercivity (Hcj), not a single universal temperature:
- Standard grade (no suffix) — starts losing flux above ~80°C
- SH grade — stable up to 150°C
- UH grade — stable up to 180°C
- EH grade — stable up to 200°C
- AH grade — stable up to 220°C
For servo motors we typically recommend SH, UH, or EH grades depending on your peak operating temperature. We also offer grades with Hcj > 2785 kA/m (>35 kOe) for maximum demagnetization resistance. Share your motor's thermal profile and we'll recommend the most cost-effective grade with adequate safety margin.
How do magnet tolerances affect cogging torque?
Significantly. Both geometric tolerances (dimensions, concentricity) and magnetic tolerances (magnetization uniformity, per-pole flux consistency) directly influence cogging torque. Variations in arc radius, thickness, or width create irregularities in the air-gap flux distribution; inconsistent pole magnetization adds torque ripple and vibration.
For high-precision servo motors, we control: ±0.05 mm standard dimensional tolerance, ±0.02 mm precision tolerance on request, and ≤±2% per-pole flux deviation for high-end servo and robotics applications. Tight tolerances mean lower cogging torque, smoother motion, and longer servo life — and we provide full dimension inspection reports and B-H curve data with every OEM shipment to verify consistency.
Arc segment, bread-loaf, or multipole ring — which shape for my rotor?
Each shape has distinct trade-offs. Arc segments and bread-loaf segments are the most common: easy to manufacture, lower tooling cost, proven reliability — the right choice for prototyping and medium-volume production, with bread-loaf profiles adding a cogging-reduction benefit. Multipole rings offer superior flux uniformity, higher efficiency and torque, better mechanical concentricity, and eliminate gluing labor — the right choice for high-volume, high-precision servo motors built on automated assembly lines.
Our recommendation: arc segments for prototyping and medium volume (flexible, lower tooling cost); multipole rings for high-volume, high-precision programs (better consistency, lower assembly cost). We support all three shapes and provide DFM feedback to help you choose the optimal geometry for your rotor design and volume.
Do Dy-containing UH/EH grades face China export controls, and how should I plan lead times?
Yes. Since April 2025, China's MOFCOM has placed Dy/Tb-containing NdFeB magnets — including UH, EH, and AH grades — under a strict non-automatic export licensing regime. Each shipment requires a dual-use export license; review times are highly variable, with 60–120+ days common and no statutory deadlines; approval depends on the quality of end-use documentation. The October 2025 controls are suspended until November 10, 2026, but the April 2025 controls remain in effect — full background in our guides on China's 2025 dual-use export controls and rare-earth magnet export compliance.
Our planning advice: for UH/EH/AH grades, notify us at least 8–12 weeks before your required delivery date so the export license is secured in time. For standard grades (N–SH), normal lead times apply — prototypes in 7–15 days, mass production in 20–30 days. We handle the entire export licensing process on your behalf; you provide the end-use documentation, and sharing your application details upfront expedites the review.