Bonded NdFeB Magnets Manufacturer in China

Step-by-Step Manufacturing Process of Bonded NdFeB Magnets

1. Raw Material Preparation and Powder Production

It all starts with high-purity ingredients: neodymium (Nd), iron (Fe), boron (B), and minor additives like dysprosium (Dy) for heat resistance or cobalt (Co) for stability.

• These are melted in a vacuum induction furnace at 1,400-1,500°C to form an alloy ingot.
• The ingot is rapidly quenched (e.g., via melt-spinning) to create ribbons or flakes, which are then milled into fine powders (1-10 microns). This “rapid solidification” preserves the magnetic microstructure.
• Powders are sieved and sometimes coated to prevent oxidation, ensuring high-quality, uniform particles.

Pro tip: Powder size and shape directly impact the final magnet’s density and strength.

2. Mixing with Binder

The NdFeB powder (70-95% by volume) is blended with a polymer binder (5-30%), such as thermoplastic (nylon) for injection molding or thermoset (epoxy) for compression.

• Mixing occurs in a high-shear mixer or extruder at controlled temperatures (room temp to 200°C) to create a homogeneous compound.
• Additives like lubricants or coupling agents improve flow and adhesion.

This step turns the magnetic material into a moldable “feedstock,” similar to plastic pellets.

3. Molding and Shaping

The compound is formed into the desired shape using techniques like:

• Injection Molding: Heated and injected into molds under pressure (ideal for complex, thin-walled parts).
• Compression Molding: Pressed into dies at 100-300 MPa and moderate heat.
• Extrusion or Calendering: For continuous shapes like sheets or rods.
• For anisotropic magnets, a magnetic field is applied during molding to align particles, boosting performance by 20-30%.

The result is a “green” part that’s solid but not fully hardened.

4. Curing and Debinding

To set the binder and remove any volatiles:

• Thermoset binders are cured in ovens at 150-250°C for hours, cross-linking the polymer for strength.
• Thermoplastic versions cool naturally or are annealed to relieve stress.
• If binders include solvents, a debinding step (thermal or solvent extraction) eliminates them without damaging the structure.

This densifies the magnet to 5-7 g/cm³ (vs. 7.5 g/cm³ for sintered), creating a lightweight composite.

5. Machining and Finishing

Bonded magnets are easier to machine than sintered ones due to their polymer content:

• Trimming, drilling, or grinding refines shapes with standard tools (no diamonds needed).
• Protective coatings (e.g., parylene or paint) are applied to shield against corrosion and moisture, as NdFeB is prone to rusting.

Tolerances can reach ±0.05 mm, making them precise for assembly lines.

6. Magnetization and Quality Testing

The molded piece is magnetized in a pulse magnetizer or electromagnet to saturate the NdFeB particles.

• Testing verifies properties like remanence (Br), coercivity (Hc), and energy product using vibrometers or pull testers.
• Inspections for defects, density, and binder integrity ensure reliability, often per ISO 9001 standards.

Final products are demagnetized for safe shipping if needed.