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How are neodymium iron boron magnets manufactured?

How are neodymium iron boron
magnets manufactured?

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Neodymium iron boron ring magnetic disc Neodymium magnets are made from a combination of iron, boron, and neodymium. To create neodymium magnets, manufacturers usually follow these steps:
Iron, neodymium and boron being poured into an oven

Step 1 – Strip casting

First, a combination of iron, boron and neodymium are ground up and melted in a vacuum induction furnace at 14426.7°C (26000°F).

Wonkee Donkee says "Strip casting is the name given to heating up a group of different metals until they are molten and then cooling them down together into a solid"
No oxygen in a vacuum A vacuum induction furnace removes the oxygen from the materials at the same time as heating them. The oxygen needs to be removed from the compound as iron and neodymium oxidise very easily.
Ball milling making magnet powder

Step 2 – Milling

After the metals have cooled and solidified, they are broken up into small chips which are then ground down to a fine powder using a ball mill and mixed together thoroughly. A ball mill is a type of grinder used to grind metals into a very fine powder.

Moulds for different shaped magnets

Step 3 – Moulding

The powder is then weighed and pressed into moulds, which can be any shape of magnet, and vacuum packed to stop the powder from oxidising.

Pressing machine

Step 4 – Pressing

The moulds are placed into a pressing machine which places a total of 21000psi of pressure onto them. The vacuum packing is then removed before the next step.

Wonkee Donkee says "Psi stands for the amount of pressure there is per square inch inside the machine"

Step 5 – Sintering

The shaped metal is then placed into an electric oven, which heats the metal compound gradually from 250°C (482°F) to 900°C (1652°F).

Extremely hot thermometer The magnets can take from 20 to 36 hours to be heated depending on the quality of the end magnet. A top quality magnet will take a lot longer in the oven than a low quality one, as a slower temperature rise will produce a greater magnetic force.

For more information on sintering, see the Magnets glossary

Electrical discharge machine

Step 6 – Machining

After the magnets have been removed from the oven and left to cool, they are ground down to the correct size. To do this, an electrical discharge machine will take off millimetres of metal until the exact size of magnet is achieved.

Neodymium iron boron ring magnetic disc

Step 7 – Coating

The magnets are then coated to prevent them from oxidising.

For more information on the types of plating and coatings, see the page What are magnets coated with?


Step 8 – Magnetising

Finally, the mixture of iron, boron and neodymium is magnetised. A magnetising machine envelops the magnet in a high strength magnetic field by sending 2400 volts of electrical current through the magnet to create a permanent neodymium magnet.

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