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How a Neodymium Magnet is Made

A neodymium magnet also known by the acronyms NdFeB, NIB or simply Neo is a permanent magnet made from an alloy of neodymium, iron, and boron. The exact ingredients depend on the grade or strength of magnet being produced. Higher values indicate stronger magnets.

 

IT BEGINS WITH THE MIX

Preparation of materials determines the type of magnet to be produced. A combination of Cobalt and Dysprosium will result in increased intrinsic coercivity and properties improved at elevated temperatures. After selection, these elements are placed into a vacuum induction furnace where they are heated by creating electrical eddy currents. After that melted to form the alloy material. It is done in a vacuum to avoid contaminants affecting the reaction. This mixture is then cooled to form ingots before being ground into tiny grains in a jet mill. Each particle is typically only three microns in size, smaller than a cell in your body!

 

INGOTS ARE THEN PRESSED

The super-fine powder is then pressed into a mold to form a solid with a preferred magnetization direction. This technique is known as die-upsetting. Simultaneously, magnetic energy is applied to the mold. The magnetism comes from a coil wire that acts like a magnet when electrical current is passed through it. It is usually performed at temperatures as high as 725 C. The solid then goes through a second pressing whereby it’s reduced to half its original size and its magnetism induced becomes parallel to that of the magnet. When the particle structure of the magnet matches the direction of magnetism, the magnet created is referred to as an anisotropic magnet. At this stage, manufacturers can give the block more acute properties.

 

AFTER PRESSING IS SINTERING

At this point, the magnetized material is demagnetised and will be re-magnetised later in the process. The compression in this stage will result in the particles adhering to each other. The temperatures involved will be below its melting point to avoid liquefaction. This is because at this stage the material would be far too soft and crumbly to be useful. This process takes place in an oxygen-free, inert environment.

 

THEY MUST COOL

Almost there, the heated material gets rapidly cooled using a technique known as quenching. This rapid cooling process minimizes areas of poor magnetism and maximizes performance. This is the stage when the raw magnets are machined into their desired shape. Less complex materials are shaped using Electric Discharge Machine (EDM), and more complex is shaped by diamond plated cutting tools.

 

TO LOOK PRETTY, THEY GET A PLATING

The last step before the material is re-magnetised is vital. Because neodymium magnets are so hard and oxidize so quickly, making them prone to breaking and chipping, they must be coated, cleaned, dried and plated. There are many different types of coating that are used with neodymium magnets, the most common being electroplating with nickel-copper-nickel mixture, but they can be coated with other metals and even rubber or PTFE. This helps them to retain their magnetic properties even in the presence of moisture.

 

WE HAVE A MAGNET

The magnets now are almost ready but not yet fully magnetic. Their pole directions have been aligned, but their magnetism hasn’t been activated. Therefore will not attract or repel as strongly.

After the plating process, the finished material is re-magnetised by placing it inside a coil, which, when an electric current is passed through it produces a magnetic field three times stronger than the required strength of the magnet. This is such a powerful process that if the magnet is not held in place, it can be flung from the coil like a bullet. The use of an industrial magnetizer is preferred. The process of creating this magnet is intricate, and the way the magnet is formed will affect how it functions.

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Published in Physics of Magnets