Magnet Making Process and Manufacturing Methods

Magnet Making Process

There are several processes for manufacturing magnets, but the most common method is PM(Powder Metallurgy). In this process, the appropriate composition are pulverized into fine powder, pressed and heated to densify via "liquid phase sintering". Therefore, these magnets are often referred to as sintered magnets. Ferrite, Samarium Cobalt (SmCo) and Neodymium-iron-boron (Neo) magnets are manufactured by this way. Unlike ferrite, which is a ceramic material, all rare earth magnets are metal alloys.

How are SmCo and NdFeB Magnets are Manufactured

Right raw materials are melted in an induction melting furnace under vacuum or inert gas. The molten alloy is either poured into a mold, placed on a cooling plate, or machined in a strip caster. These solidified metal "lumps" are pulverized to form a fine powder range from 3 to 7 μm.The very fine powder is chemically active and can spontaneously ignite in the air, so it must be protected from exposure to oxygen.

There are several ways to press the powder, all of which involve aligning the particles so that at the finished part, all magnetic areas point in a prescribed direction. The first method is called axial or transverse prssing. In this process, powder is placed on a cavity tool on the press and the punch enters the tool to compress the powder. Before compaction, apply alignment fields. The compaction "freezes-in" this alignment. In axial  compaction, the alignment field is parallel to the compaction direction. In transverse pressing, the field is perpendicular to the compaction pressure. As the small powder particles are elongated in the direction of magnetic alignment, transverse pressing yields better alignment, thus a higher energy product. The powder is pressed in a hydraulic or mechanical press to limit the shape to a simple cross-section that can be pushed out of the mold cavity.

The second compaction method is called isostatic pressure, in which a flexible container is filled with the powder, the container is sealed and the container is placed into isostatic pressure. Using a liquid, either hydraulic fluid or water, pressure is applied to the outside of the sealed container, pressing it equally on all sides.The main advantage of making magnet blocks by isostatic pressure is that very large blocks can be made usually up to 100×100×250 mm - and because of the pressure applied on all sides, the powder is kept in good alignment to produce the highest possible energy product.

Pressed parts are load in the "boats" for plating into a vacuum sintering furnace.  inert gas or Special temperature and the presence of vacuum is specific to grades and types  of magnets being produced. Both rare earth materials are heated to a sintering temperature and allowed densification. After sintering, SmCo has requirements for  "solutionizing" treatment. After reaching the room temperature, the two materials were tempered at low temperature.During sintering, the shrinkage of the magnet is about 15-20% linearly. Finished magnets surface rough and approximate size. They also have no external magnetic field.


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