Every NdFeB magnet starts as a puddle of liquid metal. The raw ingredients — neodymium, iron, boron and a few extras — are melted in a vacuum furnace, poured onto a spinning copper wheel, and frozen into thin flakes in an instant. That is the whole step in one sentence; here is why each part matters.
Why vacuum?
Neodymium reacts eagerly with oxygen. Melting in a vacuum, with a little argon gas, keeps the liquid metal clean — without it, oxides would form and quietly weaken the finished magnet.
Why a copper wheel?
The wheel is water-cooled and spins fast. When the liquid alloy lands on it, it cools almost instantly — thousands of degrees per second — and solidifies as a thin ribbon about 0.3 mm thick. Rapid cooling is the secret: it freezes the alloy into a fine, uniform structure. This process is called strip casting.
Why does that matter?
If the alloy cools slowly, iron crystals grow into large, soft dendrites — think of ice crystals forming in a slowly frozen drink. Those soft iron islands act as weak spots and quietly destroy the magnet's coercivity, its resistance to demagnetization. Fast cooling stops them from forming at all.
Why flakes and not ingots?
Early production cast thick ingots that needed long, expensive heat treatments to fix their uneven structure. Strip casting solved the problem: the thin flake is uniform from edge to edge, so every later step starts from the same good material.
The flakes leave the wheel brittle and ready for the next step, where they are turned into powder.
Read on: hydrogen decrepitation → · the whole production flow →