Professional Alnico Bar Magnets

Composition and Manufacturing
AlNiCo Magnets
AlNiCo magnets are metallic alloys composed primarily of aluminum (8–12%), nickel (15–26%), cobalt (5–24%), iron (balance), and trace elements like copper and titanium. These alloys are produced through two methods:


Casting: Molten alloy is poured into molds, enabling complex shapes (e.g., horseshoe magnets) with excellent dimensional precision.
Sintering: Powdered alloy is pressed and heated, yielding higher density and mechanical strength.

NdFeB Magnets
NdFeB magnets are rare-earth compounds based on the Nd₂Fe₁₄B tetragonal crystal structure. They contain neodymium (25–35%), iron (60–70%), and boron (1–2%), with optional substitutions (e.g., dysprosium for coercivity enhancement). Manufacturing involves:


Powder Metallurgy: Raw materials are melted, atomized into powder, aligned in a magnetic field, and sintered at 1000–1200°C.
Post-Processing: Machining, coating (e.g., Ni-Cu-Ni), and thermal treatment refine performance.

Magnetic Performance
Energy Product and Remanence
NdFeB magnets dominate in magnetic strength, with maximum energy products (BHmax) ranging from 220–430 kJ/m³ (30–55 MGOe), compared to AlNiCo’s 5–52 kJ/m³ (0.6–6.5 MGOe). NdFeB’s remanence (Br) reaches 1.1–1.5 T, while AlNiCo’s Br is 0.8–1.3 T, making NdFeB ideal for compact, high-torque applications like electric vehicle motors.

Coercivity
NdFeB magnets exhibit high intrinsic coercivity (Hcj = 800–3000 kA/m), enabling resistance to demagnetization. AlNiCo’s Hcj is significantly lower (40–120 kA/m), requiring careful handling to avoid magnetic field reversal. However, AlNiCo’s low coercivity allows easy magnetization/demagnetization for adjustable sensors.

Thermal Stability
Temperature Coefficients
AlNiCo excels in thermal stability, with a reversible temperature coefficient of remanence (αBr) of -0.02%/°C, compared to NdFeB’s -0.12%/°C. This means AlNiCo’s magnetic output degrades linearly with temperature, whereas NdFeB suffers exponential losses above 100°C.

Curie Temperature and Operating Range
AlNiCo’s Curie temperature (Tc = 850°C) and operational range (-250°C to 550°C) far exceed NdFeB’s Tc (310–380°C) and 80–200°C limit. For instance, AlNiCo LNGT32 maintains performance at 550°C, while NdFeB N42SH fails above 150°C. This makes AlNiCo critical for aerospace sensors and industrial furnaces.

Corrosion Resistance
Material Vulnerability
NdFeB’s iron content (60–70%) makes it prone to oxidation, necessitating protective coatings (e.g., epoxy, Ni-Cu-Ni). Even with coatings, NdFeB degrades in humid or saline environments, limiting its use in marine applications. AlNiCo, being corrosion-resistant, requires no surface treatment, making it suitable for outdoor sensors and chemical processing equipment.

Long-Term Durability
Uncoated NdFeB magnets can lose 5–10% of their magnetic strength annually in harsh conditions, whereas AlNiCo retains performance indefinitely. For example, AlNiCo magnets in military compasses have operated reliably for decades without maintenance.

Cost and Applications
Pricing Factors
NdFeB magnets cost 20–100/kg,dependingongradeandcoating,whileAlNiCorangesfrom50–300/kg due to cobalt’s scarcity. However, NdFeB’s superior strength often reduces material usage, offsetting higher unit costs.

Market Segments

NdFeB: Dominates consumer electronics (e.g., headphones, hard drives), automotive traction motors, and wind turbines due to compact size and high efficiency.
AlNiCo: Preferred in high-temperature environments (e.g., aircraft engines, gas turbines), precision instruments (e.g., gyroscopes), and magnetic clutches where adjustable fields are needed.

Environmental and Ethical Considerations
Rare-Earth Supply Chain
NdFeB production relies on neodymium and dysprosium, whose mining raises environmental and ethical concerns (e.g., radioactive waste in China’s Bayan Obo mines). AlNiCo’s cobalt sourcing also faces scrutiny due to child labor in African mines, but its lower demand mitigates impact.

Recycling Potential
NdFeB recycling is challenging but growing, with companies like Hitachi Metals recovering 70% of rare earths from scrap. AlNiCo’s metallic composition simplifies recycling, though volumes are smaller.

Conclusion
AlNiCo and NdFeB magnets serve complementary roles in technology. NdFeB’s unmatched strength and cost-efficiency make it indispensable for high-performance applications, while AlNiCo’s thermal stability and durability justify its use in extreme environments. As industries demand both power and reliability, advancements in hybrid magnets (e.g., NdFeB cores with AlNiCo shells) may bridge the gap, but for now, each material remains irreplaceable in its niche.

2. Fundamentals of Magnetic Domains in NdFeB Magnets
2.1 Domain Structure and Magnetization Processes
NdFeB magnets consist of nanoscale Nd₂Fe₁₄B grains (matrix phase) embedded in a grain boundary phase (GBP) rich in Nd and other elements. The GBP acts as a magnetic insulator, isolating grains to minimize dipolar interactions that degrade coercivity.


Domain Formation: Grains are divided into domains to minimize magnetostatic energy. Each domain has a preferred magnetization direction (easy axis), determined by the crystal structure (hexagonal Nd₂Fe₁₄B).
Domain Wall Motion: Under an external field, domain walls move to align magnetization with the field. Irreversible wall displacement causes hysteresis losses, reducing efficiency.
Nucleation of Reverse Domains: Coercivity depends on the energy barrier for nucleating reverse domains at defects (e.g., grain boundaries, voids).

2.2 Key Performance Metrics

Remanence (Br): Proportional to the volume fraction of aligned domains.
Coercivity (HcJ): Determined by the energy barrier for domain wall motion or reverse domain nucleation.
Energy Product (BH)max: Maximum energy stored in the magnet, given by Br × HcJ.

3. Microscopic Strategies for Domain Regulation
3.1 Grain Boundary Engineering (GBE)
The GBP plays a dual role: it isolates grains magnetically and provides a diffusion path for heavy rare earths (HREs) like dysprosium (Dy) and terbium (Tb), which enhance coercivity.

3.1.1 Grain Size Control

Fine Grains (1–5 μm): Reduce dipolar interactions between grains, improving coercivity. However, excessively small grains increase surface energy, promoting grain growth during sintering.
Optimized Sintering: Two-step sintering (e.g., 1,020°C for 2 hours followed by 500°C for 4 hours) achieves dense, fine-grained magnets with coercivity >2.5 T.

3.1.2 Grain Boundary Diffusion (GBD)

Process: Coat magnets with HREs (e.g., Dy/Tb) and heat them to 850–950°C. HREs diffuse along grain boundaries, forming a (Nd,Dy)₂Fe₁₄B shell around grains.
Mechanism: The shell has higher magnetocrystalline anisotropy (K₁) than the core, raising the energy barrier for reverse domain nucleation.
Example: A 3 wt% Dy coating increases coercivity from 1.2 T to 2.4 T while reducing Dy consumption by 70% compared to bulk doping.

3.1.3 Non-Rare Earth GBP Modifiers

Zirconium (Zr): Forms Zr-rich phases at grain boundaries, refining grains and improving coercivity by 10–15%.
Copper (Cu): Reduces GBP melting point, enhancing liquid-phase sintering and grain boundary wetting.

3.2 Dopant Addition and Alloy Design
Doping NdFeB alloys with specific elements alters domain wall pinning and anisotropy, optimizing performance.

3.2.1 Heavy Rare Earth (HRE) Doping

Dysprosium (Dy): Substitutes Nd in the matrix, increasing K₁ from 4.9 MJ/m³ (Nd₂Fe₁₄B) to 5.7 MJ/m³ (Dy₂Fe₁₄B). However, Dy is scarce and expensive.
Gradient Alloys: Core-shell structures with Dy-free cores and Dy-rich shells balance cost and performance. For example, a Dy-free core with a 1 μm Dy shell achieves coercivity >2.0 T.

3.2.2 Light Rare Earth (LRE) Substitution

Lanthanum (La) and Cerium (Ce): Cheaper alternatives to Nd, but reduce K₁. Partial substitution (e.g., Nd₀.₈Ce₀.₂) maintains coercivity >1.5 T while cutting costs by 30%.

3.2.3 Co and Ga Additions

Cobalt (Co): Enhances Curie temperature (T_c) from 312°C (Nd₂Fe₁₄B) to 390°C (Nd₂(Fe,Co)₁₄B), improving thermal stability.
Gallium (Ga): Reduces grain boundary viscosity, promoting densification during sintering and improving coercivity by 5–10%.

3.3 Stress and Strain Engineering
Mechanical stresses alter domain wall energy, influencing coercivity and remanence.

3.3.1 Compressive Stress

Hydrostatic Pressure: Applying pressure during sintering increases grain boundary contact, reducing porosity and enhancing coercivity. For example, 100 MPa pressure raises coercivity by 0.2 T.
Post-Sintering Annealing: Heat treatment under pressure (e.g., 500°C, 50 MPa) relieves residual stresses, improving domain alignment.

3.3.2 Tensile Stress

Surface Coatings: Epoxy or nickel coatings induce tensile stress at the surface, pinning domain walls and increasing coercivity by 5–10%.

3.4 Advanced Processing Techniques
3.4.1 Hydrogen Decrepitation (HD) and HDDR

HD: Exposes magnets to hydrogen, causing them to fracture into powder. The powder is then pressed and sintered, producing magnets with uniform domain structures.
HDDR (Disproportionation-Desorption-Recombination): Heats NdFeB powder in hydrogen to form NdH₂, Fe, and Fe₂B, then recombines them into nanocrystalline Nd₂Fe₁₄B. HDDR magnets exhibit coercivity >2.0 T due to fine grains (200–500 nm).

3.4.2 Additive Manufacturing (3D Printing)

Selective Laser Melting (SLM): Prints NdFeB magnets layer by layer, enabling complex geometries and controlled grain orientation. SLM magnets show coercivity >1.8 T, comparable to sintered magnets.
Binder Jetting: Uses a binder to shape NdFeB powder, followed by sintering. This method reduces porosity and improves domain alignment.

3.4.3 Magnetic Field-Assisted Processing

Pulsed Magnetization: Applies high-intensity pulses (e.g., 5 T) during sintering to align domains before solidification, increasing remanence by 5–10%.
Rotating Magnetic Fields: Aligns grains during compaction, reducing dipolar interactions and enhancing coercivity.

4. Microscopic Characterization Techniques
To validate domain regulation strategies, advanced microscopy and spectroscopy techniques are essential:

4.1 Electron Backscatter Diffraction (EBSD)

Maps grain orientation and size distribution, revealing how GBE affects domain alignment.
Example: EBSD shows that GBD with Dy reduces grain misorientation, improving coercivity.

4.2 Magnetic Force Microscopy (MFM)

Visualizes domain walls and their motion under external fields at nanoscale resolution.
Example: MFM reveals that Co doping increases domain wall pinning sites, raising coercivity.

4.3 X-Ray Diffraction (XRD)

Measures lattice parameters and phase composition, confirming dopant incorporation (e.g., Dy in Nd₂Fe₁₄B).

4.4 Small-Angle Neutron Scattering (SANS)

Probes domain structure statistics (e.g., domain size, wall thickness) in bulk magnets.

5. Case Studies: Performance Improvements
5.1 High-Coercivity Magnets for Electric Vehicle Traction Motors

Challenge: EV motors require magnets with coercivity >2.0 T to resist demagnetization at high temperatures.
Solution: A combination of GBD (3 wt% Dy) and HDDR processing produced magnets with:

Coercivity: 2.4 T (vs. 1.8 T for conventional magnets).
Remanence: 1.25 T (vs. 1.20 T).
Energy product: 38 MGOe (vs. 35 MGOe).



5.2 Low-Cost, High-Performance Magnets for Wind Turbines

Challenge: Wind turbines require magnets with high thermal stability but minimal Dy use to cut costs.
Solution: A La-Ce-Nd alloy with 20% Ce substitution and GBD (1 wt% Dy) achieved:

Coercivity: 1.6 T (vs. 1.4 T for Ce-free magnets).
Cost reduction: 25% due to lower Dy and Nd usage.



6. Challenges and Future Directions
6.1 Current Limitations

Dy Scarcity: Global Dy reserves may last only 20–30 years at current consumption rates.
Thermal Demagnetization: High-temperature applications (e.g., EVs) require magnets with T_c >400°C, achievable only with expensive HREs.
Scalability: Advanced techniques like HDDR and 3D printing are not yet industrial-scale.

6.2 Future Innovations

Nanocomposite Magnets: Combining Nd₂Fe₁₄B with soft magnetic phases (e.g., α-Fe) to enhance remanence via exchange coupling.
Machine Learning Optimization: Using AI to predict optimal dopant combinations and processing parameters for domain regulation.
Biodegradable Coatings: Developing eco-friendly coatings to replace toxic nickel plating.

7. Conclusion
Microscopic regulation of domain structures in NdFeB magnets—through grain boundary engineering, dopant addition, stress management, and advanced processing—enables significant performance improvements. Techniques like GBD with HREs, HDDR processing, and magnetic field-assisted sintering have demonstrated coercivity enhancements of up to 100% and energy product improvements of 10–15%. However, challenges like Dy scarcity and scalability must be addressed to realize a sustainable, high-performance magnet industry. Future research should focus on nanocomposite designs, AI-driven optimization, and eco-friendly manufacturing to meet the demands of clean energy and electric mobility.

By mastering domain dynamics at the atomic and nanoscale, NdFeB magnets can continue to drive technological innovation while reducing environmental impact.

When storing ferrite magnets, several environmental factors must be carefully controlled to maintain their magnetic properties, structural integrity, and long-term reliability. Key considerations include humidity, temperature, mechanical stress, corrosive environments, and electromagnetic interference, each with specific requirements to prevent degradation. Below is a detailed analysis of these factors and their corresponding storage requirements:

1. Humidity Control
Ferrite magnets, while inherently corrosion-resistant due to their oxide-based composition (Fe₂O₃ with SrCO₃ or BaCO₃), are still vulnerable to moisture-induced damage under prolonged exposure to high humidity.


Impact of Humidity:

Oxidation and Surface Rust: Moisture can react with impurities on the magnet's surface, leading to oxidation. This not only affects the aesthetic appearance but also weakens magnetic properties over time as rust spreads internally.
Reduced Insulation Performance: In electronic applications, humidity can compromise the electrical insulation of ferrite magnets, potentially causing short circuits or performance degradation.
Microstructural Damage: Prolonged exposure to moisture may lead to microcracks or delamination, especially in sintered ferrite magnets with fine particle structures.


Storage Requirements:

Relative Humidity: Maintain storage environments at ≤60% RH to minimize moisture absorption. Use desiccants like silica gel packets in storage containers to absorb excess moisture.
Airtight Packaging: Store magnets in sealed, moisture-proof containers (e.g., plastic bags with zip locks or vacuum-sealed packages) to prevent humidity ingress.
Ventilation: Ensure proper ventilation in warehouses to avoid stagnant air, which can exacerbate humidity-related issues.



2. Temperature Management
Temperature fluctuations significantly impact the magnetic performance and physical stability of ferrite magnets.


Impact of Temperature:

Thermal Demagnetization: Ferrite magnets lose magnetic strength when exposed to temperatures above their Curie point (typically 450–460°C for strontium ferrite). While this is rarely a concern during storage, prolonged exposure to temperatures near the upper operating limit (e.g., 180–250°C for high-grade ferrites) can cause irreversible demagnetization.
Thermal Stress: Rapid temperature changes (>1°C/sec) can induce thermal shock, leading to cracks or fractures due to the brittle nature of ferrite materials.
Coercivity Changes: Ferrite magnets exhibit increased coercivity (resistance to demagnetization) at higher temperatures, but their remanence (residual magnetism) decreases. This trade-off must be managed to ensure stable performance.


Storage Requirements:

Temperature Range: Store magnets at ambient temperatures (20–25°C) where possible. For long-term storage, maintain temperatures between -40°C and +85°C (for flexible ferrite sheets) or -55°C to +125°C (for suppression components without coatings).
Avoid Extremes: Prevent exposure to temperatures below 0°C (which can reduce pull force) or above 250°C (which may cause permanent demagnetization).
Thermal Stability: Use temperature-controlled warehouses or insulated packaging to minimize fluctuations. For outdoor storage, shield magnets from direct sunlight and heat sources.



3. Mechanical Stress Prevention
Ferrite magnets are brittle and prone to chipping or cracking under mechanical stress.


Impact of Mechanical Stress:

Impact Damage: Dropping or striking magnets can cause surface fractures or internal microcracks, compromising their structural integrity.
Vibration and Friction: Prolonged vibration or friction between magnets can lead to surface wear, generating dust particles that may contaminate nearby components.


Storage Requirements:

Isolation: Store magnets individually or in padded containers to prevent contact and friction. Use foam inserts or cardboard dividers to separate magnets.
Secure Packaging: For large or heavy magnets, use sturdy crates or pallets with cushioning materials to absorb shocks during transport.
Orientation: Store magnets in a stable position (e.g., flat on a surface) to avoid tipping or rolling, which can cause impact damage.



4. Corrosive Environment Protection
While ferrite magnets are chemically stable, exposure to corrosive substances can still degrade their performance over time.


Impact of Corrosive Environments:

Chemical Attack: Acids, alkalis, or salts can react with the magnet's surface, leading to pitting or erosion. This is particularly concerning in marine or industrial settings where corrosive gases (e.g., SO₂, H₂S) may be present.
Coating Degradation: If magnets are coated (e.g., with epoxy or nickel), corrosive environments can damage the coating, exposing the underlying ferrite material to further degradation.


Storage Requirements:

Clean Environment: Store magnets in a dry, dust-free area free from corrosive vapors or liquids. Avoid storage near chemical storage areas or industrial processes emitting corrosive byproducts.
Protective Coatings: For magnets used in harsh environments, apply protective coatings (e.g., epoxy, PTFE) to enhance corrosion resistance. Ensure coatings are intact before storage.
Sealed Containers: Use corrosion-resistant containers (e.g., stainless steel or plastic) for storage in high-risk environments.



5. Electromagnetic Interference (EMI) Shielding
Ferrite magnets can interact with external magnetic fields, potentially altering their magnetic properties.


Impact of EMI:

Magnetic Field Interference: Strong external magnetic fields (e.g., from nearby electromagnets or motors) can reorient the magnetic domains in ferrite magnets, leading to partial demagnetization.
Induced Currents: In AC magnetic fields, ferrite magnets can generate eddy currents, causing localized heating and potential thermal damage.


Storage Requirements:

Magnetic Shielding: Store magnets away from strong magnetic sources (e.g., large electromagnets, MRI machines). Use magnetic shielding materials (e.g., mu-metal) to block external fields if necessary.
Orientation Control: For sensitive applications, store magnets in a consistent orientation (e.g., north pole facing up) to minimize domain reorientation.
Isolation Distance: Maintain a safe distance (at least 1 meter) between stored magnets and magnetic equipment to prevent unintended interactions.



6. Additional Considerations

Labeling and Safety: Clearly label storage containers with "Strong Magnet Inside" warnings to prevent accidental injuries or damage to electronic devices.
Inventory Management: Implement a first-in, first-out (FIFO) system to ensure magnets are used before their performance degrades over time.
Regular Inspection: Periodically check stored magnets for signs of damage (e.g., cracks, rust) or demagnetization. Re-magnetize magnets if their pull force falls below acceptable levels.

1. Introduction to AlNiCo Magnets
AlNiCo (Aluminum-Nickel-Cobalt) magnets are a type of permanent magnet material composed primarily of aluminum (Al), nickel (Ni), and cobalt (Co), with small additions of copper (Cu), titanium (Ti), and other elements to enhance performance. They are known for their high remanence (Br), excellent temperature stability, and low reversible temperature coefficient, making them suitable for high-precision applications such as sensors, motors, and aerospace components.

However, AlNiCo magnets also have inherent drawbacks, including low mechanical strength, high hardness, and brittleness, which significantly impact their machinability. This article explores why AlNiCo magnets require large machining allowances and the dimensional accuracy achievable after machining.


2. Why AlNiCo Magnets Require Large Machining Allowances
2.1 Brittleness and Low Toughness
AlNiCo magnets are inherently brittle due to their metallic glass-like microstructure, which lacks ductility. During machining, this brittleness leads to:


Chipping and Cracking: Small cracks can propagate rapidly under cutting forces, causing edge chipping or catastrophic failure.
Surface Defects: Micro-cracks and pits may form on the machined surface, necessitating additional material removal to achieve a smooth finish.

To mitigate these issues, a larger machining allowance is required to:


Remove damaged layers caused by initial roughing.
Ensure sufficient material remains for finishing operations.

2.2 High Hardness and Tool Wear
AlNiCo magnets typically have a hardness of 450–550 HV, which is comparable to hardened steel. This high hardness accelerates tool wear during machining, leading to:


Reduced Cutting Efficiency: Dull tools require higher cutting forces, increasing the risk of workpiece damage.
Poor Surface Quality: Worn tools leave behind rough surfaces, necessitating additional grinding or polishing.

A larger machining allowance compensates for tool wear by ensuring that even after multiple tool changes, sufficient material remains for final dimensioning.

2.3 Thermal Sensitivity
AlNiCo magnets have a low thermal conductivity (approximately 12–15 W/m·K), which means heat generated during machining is not efficiently dissipated. This leads to:


Thermal Expansion: Localized heating can cause uneven expansion, resulting in dimensional inaccuracies.
Residual Stresses: Rapid cooling after machining may introduce residual stresses, leading to warping or cracking.

A larger machining allowance allows for stress relief through annealing or aging treatments before final sizing, reducing the risk of deformation.

2.4 Magnetic Property Preservation
Machining generates heat and mechanical stress, which can degrade the magnetic properties of AlNiCo magnets, particularly their coercivity (Hc) and remanence (Br). To minimize this:


Low-Stress Machining: Techniques such as grinding or electrical discharge machining (EDM) are preferred over high-stress methods like milling or turning.
Large Allowances: Ensure that only the outermost layer (which may be magnetically compromised) is removed during finishing.


3. Dimensional Accuracy Achievable After Machining
The dimensional accuracy of AlNiCo magnets after machining depends on the machining method, tooling, and post-processing techniques. Below is an analysis of common machining processes and their typical accuracy ranges:

3.1 Grinding
Grinding is the most widely used method for finishing AlNiCo magnets due to its ability to achieve high precision and low surface roughness.


Dimensional Accuracy: IT6–IT7 (ISO system) or ±0.005–±0.01 mm for linear dimensions.
Surface Roughness: Ra 0.2–0.8 μm (can be improved to Ra 0.05 μm with superfinishing).
Applications: Final sizing of magnetic poles, sensor components, and precision motor parts.

3.2 Electrical Discharge Machining (EDM)
EDM is suitable for complex shapes and hard materials like AlNiCo, as it does not rely on mechanical force.


Dimensional Accuracy: IT7–IT8 or ±0.01–±0.02 mm.
Surface Roughness: Ra 1.6–3.2 μm (requires polishing for better finishes).
Limitations: Slower than grinding and may leave a recast layer that requires removal.

3.3 Lapping and Polishing
For ultra-precision applications, lapping and polishing are used to achieve:


Dimensional Accuracy: IT5–IT6 or ±0.002–±0.005 mm.
Surface Roughness: Ra < 0.05 μm (mirror finish).
Applications: Optical components, high-precision sensors, and aerospace parts.

3.4 Turning and Milling (Limited Use)
Due to their brittleness, turning and milling are rarely used for final machining of AlNiCo but may be employed for roughing.


Dimensional Accuracy: IT8–IT10 or ±0.02–±0.05 mm.
Surface Roughness: Ra 3.2–6.3 μm (requires subsequent grinding).


4. Factors Influencing Dimensional Accuracy
4.1 Material Properties

Hardness and Brittleness: Higher hardness increases tool wear, reducing accuracy.
Thermal Expansion: Requires compensation during machining to avoid dimensional errors.

4.2 Machining Parameters

Cutting Speed: Lower speeds reduce heat generation but may increase tool wear.
Feed Rate: Fine feeds improve surface finish but slow down production.
Depth of Cut: Shallow cuts minimize stress but require more passes.

4.3 Tooling

Diamond Tools: Preferred for grinding due to their hardness and wear resistance.
Carbide Tools: Used for roughing but require frequent replacement.

4.4 Post-Machining Treatments

Annealing: Relieves residual stresses, improving dimensional stability.
Magnetic Stabilization: Ensures consistent magnetic properties after machining.


5. Conclusion
AlNiCo magnets require large machining allowances due to their brittleness, high hardness, thermal sensitivity, and the need to preserve magnetic properties. The dimensional accuracy achievable after machining depends on the process used:


Grinding: Best for high precision (IT6–IT7, ±0.005–±0.01 mm).
EDM: Suitable for complex shapes (IT7–IT8, ±0.01–±0.02 mm).
Lapping/Polishing: For ultra-precision (IT5–IT6, ±0.002–±0.005 mm).

By selecting the appropriate machining method and controlling process parameters, manufacturers can achieve the required dimensional accuracy while maintaining the magnetic performance of AlNiCo magnets.