How Neodymium Magnets Are Made

The journey starts far upstream: rare earth ore is mined, chemically separated into individual oxides — an involved solvent-extraction process and a major reason supply is geographically concentrated — and reduced to neodymium and praseodymium metal. At the magnet plant, the recipe is assembled: roughly Nd₂Fe₁₄B stoichiometry with grade-specific additions — dysprosium or terbium for high-temperature classes, cobalt, aluminum, copper, and other minor elements that tune corrosion and coercivity (the composition behind every line of the grades chart).

The charge is vacuum-induction melted and strip cast: poured onto a water-cooled rotating wheel that freezes it into thin flakes in a fraction of a second. The rapid quench creates the fine, uniform microstructure — thin Nd₂Fe₁₄B grains with well-distributed Nd-rich boundaries — that modern high grades depend on. Slower book-mold casting, the old method, can't reach today's N48+ properties.

Magnet properties are decided at the scale of a single crystal grain, so the alloy must become a powder of near-single-crystal particles:

• Hydrogen decrepitation (HD): the strip-cast flakes are exposed to hydrogen gas, which the Nd-rich phase absorbs and swells on — cracking the material apart along grain boundaries into coarse, friable granules. Elegant, low-energy, and the reason NdFeB in hydrogen environments is a corrosion concern later (noted in the material comparison).
• Jet milling: the granules are accelerated in nitrogen gas streams and shattered against each other down to ~3–5 µm — each particle approximately one crystal, each with one easy axis of magnetization. No grinding media, no contamination.
• Oxygen is the enemy: micron NdFeB powder oxidizes eagerly (and is pyrophoric — the industrial-scale version of the swarf warning in the safety guide), so everything from milling onward runs under inert gas.

The powder is compacted in a die inside an applied magnetic field. The field physically rotates each micron particle so its easy axis points the same way; the press then locks the alignment into a fragile "green" compact at roughly chalk strength. This is the step that fixes the magnetization direction forever — everything in the magnetization directions guide traces back to this moment.

• Field-parallel vs. transverse pressing: the geometry of field versus press direction affects achievable alignment (and thus Br) — transverse-field pressing yields the highest grades.
• Isostatic pressing: for large blocks and the best alignment, powder in a flexible mold is squeezed uniformly by fluid pressure after field alignment.
• Special orientations need special dies: true radial rings require dies that generate a radial orienting field during pressing — the specialized capability that separates true radial rings from glued segment assemblies.

Green compacts are vacuum-sintered at roughly 1,000–1,100 °C, where the Nd-rich boundary phase becomes liquid and fuses the grains into a dense solid — the parts shrink about 15–20% linearly in the process. A lower-temperature annealing treatment then optimizes the grain-boundary structure that gives the material its coercivity.

• Shrinkage is why pressed tolerances are loose: as-sintered dimensions vary a percent or more, so precision comes from grinding afterward — never from the die alone.
• Grain-boundary diffusion (GBD): the modern refinement — heavy rare earths (Dy/Tb) diffused into the surface after sintering concentrate exactly where coercivity needs them, at the grain boundaries. GBD delivers high-temperature classes with far less heavy rare earth, expanding the grade/class combinations available (the shifting "limited" cells in the grades chart availability matrix).
• The lot is born here: a sintering lot shares one furnace history and one set of measured properties — the unit behind the per-lot material certificate described in How Magnets Are Tested.

Sintered NdFeB is hard, brittle, and unmachinable by conventional cutting — every finished surface is produced by abrasive and electrical methods on unmagnetized blanks:

• Diamond grinding — surface, OD/ID, and double-disc grinding hold the standard ±0.05 mm and tighter where paid for.
• Diamond slicing — large sintered blocks are sliced into many thin parts, the economical route for small blocks and discs.
• Wire EDM — arcs, complex profiles, and shapes grinding can't reach; slower and priced accordingly.
• Coolant everywhere: all of it runs wet, both for the brittle material and because dry NdFeB swarf is a fire hazard.

Machining is the largest controllable slice of part cost — the geometry and tolerance decisions in the pricing guide and RFQ guide all cash out at this station.

Bare NdFeB corrodes, so nearly every part is coated: multi-layer electroplated NiCuNi as the standard, epoxy (often over plating) for harsher exposure, zinc for economy, parylene or gold for medical and specialty needs. Parts are cleaned, barrel- or rack-plated depending on size and geometry, and coating thickness (typically 15–25 µm for NiCuNi) is verified by XRF.

Two buyer-relevant details from this station: coating consumes dimensional tolerance (state whether your dimensions apply before or after coating), and coating adhesion — not adhesive strength — is often the true limit of bonded joints, as covered in the bonding guide.

Until now the parts have been magnets-in-waiting — oriented but uncharged. Magnetizing is a capacitor bank discharged through a fixture coil: a millisecond pulse of several tesla saturates the material along its pressed axis. Simple axial parts use standard solenoid fixtures; multipole patterns use custom fixtures whose conductor layout defines the pole pattern (the NRE item flagged in the directions guide).

Because charging is fast and portable, parts can ship unmagnetized and be pulsed after assembly — easing handling, enabling bond-then-magnetize production, and sidestepping air-freight field limits entirely.

Quality runs through the whole line — alloy chemistry at melt, powder size at milling, density after sintering — and converges at final inspection:

• Material properties per lot: hysteresisgraph measurement of Br, Hcb, Hcj, BHmax against grade minimums → the material certificate.
• Part-level magnetics: helmholtz-coil total moment; pole scans for multipole and radial parts.
• Dimensional, coating, and visual checks per drawing and workmanship standard.

The full toolkit and how to write acceptance criteria against it is the subject of How Magnets Are Tested & Measured; for regulated programs the same data feeds PPAP and compliance documentation (see the compliance guide).