NdFeB magnet grinding and polishing is the finishing stage that converts a sliced magnet block into a dimensionally precise component ready for coating and assembly. Slicing gets the magnet close to final dimensions — but “close” is not close enough for motor lamination stacks, precision sensors, or direct-drive generators where parallelism tolerances of ±2 μm and surface roughness below Ra 0.5 μm are standard requirements.
This page covers the complete NdFeB magnet grinding and polishing workflow: the process sequence from sliced blank to finished magnet, surface quality requirements by application, double-sided lapping equipment selection, and key parameters for achieving tight TTV control.
The NdFeB Post-Slicing Workflow Overview
NdFeB magnet grinding and polishing follows a fixed sequence. Each stage removes a defined amount of material and delivers a specific surface condition to the next operation.
Sliced blank → Rough grinding → Double-sided lapping → Fine polishing → Coating
Sliced blank condition: Wire saw slicing produces Ra 0.5–1.5 μm surface roughness and TTV (total thickness variation) of 5–15 μm across a typical 50 × 25 mm magnet. For many applications, this is insufficient — motor magnets require TTV ≤ 5 μm, and sensor magnets require TTV ≤ 2 μm.
Rough grinding: Removes slicing damage and brings the magnet to near-final thickness. Typically 50–150 μm removed per face using resin-bonded diamond wheels. Output: Ra 0.3–0.8 μm, TTV 3–8 μm.
Double-sided lapping: Processes both faces simultaneously on rotating lapping plates with abrasive slurry. Achieves tight parallelism (TTV ≤ 1–2 μm) and consistent thickness across a full production batch. This is the step that determines dimensional accuracy for assembly.
Fine polishing: Optional for applications requiring Ra < 0.1 μm. Used for sensor magnets, precision assemblies, and magnets going into high-frequency servo applications where surface condition affects eddy current losses.
Coating: Ni, Zn, or epoxy coating applied after polishing. Surface condition at the end of lapping directly affects coating adhesion — rough or contaminated surfaces cause premature coating failure.
그만큼 자석 슬라이싱 기계 upstream determines how much material needs to be removed in grinding. Diamond wire slicing produces shallower subsurface damage than ID saw or blade cutting, which reduces the grinding stock required and shortens finishing cycle time.
Surface Quality Requirements by End-Application
NdFeB magnet grinding and polishing targets vary significantly by application. Over-specifying surface quality wastes cycle time; under-specifying causes assembly problems downstream.
| 애플리케이션 | Ra Target | TTV Target | Parallelism |
|---|---|---|---|
| EV traction motor magnets | ≤ 0.8 μm | ≤ 5 μm | ≤ 10 μm |
| Servo motor magnets | ≤ 0.4 μm | ≤ 3 μm | ≤ 5 μm |
| Wind turbine generator magnets | ≤ 1.0 μm | ≤ 8 μm | ≤ 15 μm |
| Precision sensor magnets | ≤ 0.2 μm | ≤ 2 μm | ≤ 3 μm |
| Speaker magnets | ≤ 1.5 μm | ≤ 10 μm | ≤ 20 μm |
| Medical / MRI magnets | ≤ 0.1 μm | ≤ 1 μm | ≤ 2 μm |
For most motor magnet production, the governing specification is TTV rather than Ra. A magnet that meets Ra but has 8 μm TTV will create uneven stack height in a laminated assembly, producing air gap variation that reduces motor efficiency and generates vibration.
NdFeB Magnet Grinding and Polishing: Double-Sided Lapping Equipment
Double-sided lapping is the core equipment in NdFeB magnet grinding and polishing. The workpieces are loaded into carrier plates between two horizontal lapping plates rotating in opposite directions, with abrasive slurry flowing between plate and workpiece. Both faces are lapped simultaneously, producing matched parallelism that single-sided grinding cannot achieve.
Three machine sizes cover the production range from R&D to mass production:
13B-6LY/P — R&D and Small Batch Production
- Lapping plate diameter: Φ210 mm
- 최적: Material qualification runs, prototype magnet evaluation, small-volume specialty production
- TTV achievable: ≤ 2 μm with calibrated slurry
그만큼 13B Lapping Machine is the entry-level machine for NdFeB lapping. Its compact footprint allows installation in existing workshop space without dedicated finishing areas.
16B-5LY/P — Mid-Volume Production
- Lapping plate diameter: Φ390 mm
- 최적: Motor magnet production lines at mid-volume
- TTV achievable: ≤ 1.5 μm
그만큼 16B-5LY-P Lapping Machine is the most common configuration for mid-volume NdFeB production. Its 5-carrier plate design allows larger batches without sacrificing parallelism control. Servo-driven pressure control maintains consistent lapping force as the carrier plates orbit.
22BF-5LY/P — High-Volume Production
- Lapping plate diameter: Φ480 mm
- 최적: High-volume EV motor magnet production
- TTV achievable: ≤ 1 μm
그만큼 Double Sided Polishing 22BF handles both lapping and fine polishing modes — slurry composition determines the output surface condition. Switching from lapping abrasive to polishing compound in the same machine eliminates a transfer step for applications requiring fine-polished surfaces.
Grinding and Polishing Process Combinations
Not every NdFeB application requires the full grinding-lapping-polishing sequence. The process combination depends on starting surface quality from slicing and the final specification required.
Combination A — Grind + Lap (most common):
Used for EV motor magnets, servo magnets, and most industrial applications. Rough grind removes slicing damage, lapping achieves final parallelism. Typical stock removal: 80–200 μm total per face. Achieves Ra 0.3–0.8 μm and TTV ≤ 3 μm.
Combination B — Lap only (high-quality slice input):
When wire saw slicing produces Ra < 0.8 μm with consistent kerf width, direct lapping without rough grinding is possible. Saves cycle time versus Combination A, but requires tight process control at the slicing stage.
Combination C — Grind + Lap + Polish:
Required for sensor magnets, medical applications, and high-frequency servo motors. Polish stage uses 0.5–1.0 μm diamond or alumina slurry on a polishing pad. Achieves Ra < 0.1 μm.
For arc-segment magnets used in motor rotors, the sequence includes an additional arc grinding step after flat lapping. Vimfun’s Arc Magnet Grinding Machine VMG4-90 그리고 내외측 호 연삭기 process the curved faces of arc magnets to the required inner and outer radius dimensions and surface finish.
Achieving ±2 μm Tolerance and TTV ≤ 1 μm
Hitting ±2 μm thickness tolerance and TTV ≤ 1 μm consistently across a production batch requires control of four variables:
Carrier plate flatness. The lapping carrier plates must be flat to within ±0.5 μm. Worn or warped carriers are the most common cause of TTV drift in production. Inspect and dress carriers every 500–1,000 cycles.
Slurry concentration and temperature. Abrasive concentration affects removal rate and surface finish. Temperature changes alter slurry viscosity and removal rate. Maintain slurry at 20–25°C with closed-loop temperature control for consistent batch-to-batch results.
Lapping pressure. Vimfun lapping machines use servo-controlled pressure, not fixed weight. This allows pressure profiling — higher pressure at the start of the cycle for fast stock removal, lower pressure at the end for surface quality. Typical pressure: 0.5–2.0 N/cm² depending on magnet size and slurry.
Conditioning rings. Conditioning rings running at the inner and outer edges of the lapping plate maintain plate flatness during production. Without conditioning, lapping plates develop a convex or concave profile that transfers to the workpiece. See our double-sided lapping machine overview for conditioning ring specifications.
Coating Compatibility After NdFeB Magnet Grinding and Polishing
NdFeB magnets require protective coating before assembly — bare NdFeB corrodes rapidly in humid environments. The surface condition after lapping affects coating quality and adhesion.
Ni/Cu/Ni (triple-layer nickel): The most common coating. Requires Ra ≤ 0.8 μm and a clean surface free of embedded abrasive. Electroless or electrolytic plating, 15–25 μm total thickness.
Zinc coating: Lower cost than Ni, used for less-demanding applications. Tolerates Ra up to 1.2 μm. Salt spray resistance 48–96 hours.
Epoxy coating: Applied by spray or dip, 15–30 μm. Requires the smoothest substrate — Ra ≤ 0.5 μm — for uniform coverage. Preferred for high-temperature motor applications where metallic coatings may delaminate.
Phosphate + epoxy: Two-step process used for magnets with complex geometries. The phosphate conversion layer provides adhesion base; epoxy top coat provides corrosion resistance.
Surface contamination from lapping slurry is the most common cause of coating adhesion failure. Thorough ultrasonic cleaning after lapping, followed by DI water rinse and drying before coating, eliminates this failure mode.
Vimfun NdFeB Lapping and Grinding Equipment Lineup
| 기계 | 유형 | Work Area | 최적 용도 |
|---|---|---|---|
| 13B-6LY/P | Double-sided lapper | Φ210 mm | R&D, small batch |
| 16B-5LY/P | Double-sided lapper | Φ390 mm | Mid-volume production |
| 22BF-5LY/P | Double-sided lapper + polisher | Φ480 mm | 대량 생산 |
| VMG4-90 | Arc magnet grinder | 90° arc range | Motor arc segments |
| Inner/Outer Arc Grinder | Arc magnet grinder | Custom arc radius | Complex arc geometries |
For specifications, pricing, and sample lapping trials on your NdFeB material, contact our engineering team through the 자성 재료 solution page.
에 따르면 Arnold Magnetic Technologies NdFeB processing guide, surface finish after lapping directly correlates with assembly yield in precision motor stacks — operations achieving TTV ≤ 2 μm consistently report 8–12% lower assembly rejection rates compared to those relying on single-sided grinding alone. The Magnetics Business & Technology journal documents similar findings across servo motor and sensor magnet applications.
