NdFeB Magnets
Manufacturer in China

Step-by-Step Manufacturing Process of Sintered NdFeB Magnets

1. Raw Material Preparation and Alloying

High-purity elements—neodymium (Nd: 25-35%), iron (Fe: 60-70%), boron (B: 1-2%), and additives like dysprosium (Dy) or terbium (Tb) for heat resistance—are sourced.

• These are melted in a vacuum induction furnace at 1,400-1,500°C to form an ingot, preventing oxidation.
• The ingot is strip-cast (rapidly cooled on a wheel) into thin ribbons, which are then hydrogen-decrepitated or jet-milled into fine powders (2-10 microns).

Powder quality is paramount—any oxygen contamination can degrade performance.

2. Powder Blending and Alignment Preparation

Powders are blended for uniformity, often with lubricants to aid pressing.

• For anisotropic magnets (standard for high performance), particles are aligned in a magnetic field during subsequent steps.
• The blend is stored in inert atmospheres to avoid reactions with air or moisture.

This ensures a consistent starting material for compaction.

3. Pressing and Compaction

The powder is die-pressed under 500-1,000 MPa in a hydraulic press, forming a “green” compact.

• A strong magnetic field (10,000-20,000 Oe) is applied during pressing to align the crystal grains, creating anisotropy.
• Isostatic pressing may follow for even density, achieving 50-60% theoretical density.

Shapes like blocks, cylinders, or arcs are formed here, though complex geometries require post-machining.

4. Sintering and Densification

The green compact is sintered in a vacuum furnace at 1,000-1,100°C for 1-4 hours, fusing particles into a dense solid (7.4-7.6 g/cm³).

• Liquid-phase sintering occurs as low-melting phases help bond grains.
• Controlled cooling prevents cracks, and the process is done under argon or vacuum to minimize oxidation.

This step locks in the magnetic properties, with grain boundaries refined for high coercivity.

5. Heat Treatment and Machining

Post-sintering, magnets undergo annealing at 500-900°C to optimize microstructure and relieve stresses.

• Machining uses diamond tools or wire EDM to achieve precise shapes, as sintered NdFeB is very hard.
• Protective coatings (e.g., nickel, zinc, epoxy, or parylene) are applied via electroplating or spraying to combat corrosion.

Tolerances can be as tight as ±0.01 mm for demanding apps.

6. Magnetization and Quality Testing

The finished magnet is magnetized in a pulse magnetizer with fields up to 50,000 Oe.

• Testing includes hysteresis loop analysis for Br, Hc, and BHmax, plus checks for density, microstructure, and defects using X-ray or ultrasonic methods.
• Compliance with standards like RoHS ensures no harmful substances.

Approved magnets are often shipped demagnetized for safety.