The permanent magnet production processes mainly include sintering, casting, bonding, and hot pressing deformation. One of these permanent magnet production processes may be suitable for the production of several types of magnets, but in actual production, adjustments and improvements in certain procedures and details must be made according to the characteristics of the magnets themselves.
Classification of Permanent Magnet Production Processes
Sintering Process
The sintering process utilizes powder metallurgy and is currently the most widely applied production method, suitable for the production of sintered neodymium-iron-boron, permanent ferrite, samarium-cobalt, and sintered aluminum-nickel-cobalt magnets.
Casting Process
Casting refers to the process of melting solid metal into liquid form and pouring it into a specifically shaped mold, allowing it to solidify into shape. For permanent magnets, the casting process is primarily used for the production of cast aluminum-nickel-cobalt magnets.
Compared to sintered aluminum-nickel-cobalt, cast aluminum-nickel-cobalt exhibits higher magnetic performance and can be processed into various sizes and shapes.
The sintered aluminum-nickel-cobalt process is simpler, with smaller size tolerances and better machinability.
Bonding Process
The bonding process involves uniformly mixing permanent magnetic material powder with adhesives and other additives in a certain ratio and then preparing composite permanent magnetic materials using methods such as pressing, extruding, and injection molding.
Compared to sintered and cast permanent magnets, the outstanding advantages of bonded permanent magnets include high dimensional accuracy, no deformation, no need for secondary processing; great freedom in shape, allowing the production of various forms such as strips, sheets, tubes, rings, or other complex shapes according to actual usage needs; ease of automated large-scale production; and high mechanical strength. However, its disadvantages include lower magnetic performance and limited high-temperature applications.
Hot Pressing Deformation Process
The hot pressing deformation process is another method for producing neodymium-iron-boron magnets. This process can produce isotropic and anisotropic neodymium-iron-boron magnets. The magnets produced through this method exhibit high magnetic performance, with a maximum radial magnetic energy product reaching 240–360 kJ/m3. Moreover, they possess high heat resistance, with operating temperatures reaching up to 180 °C. The magnetic rings have a nanocrystalline structure, high density, and use an epoxy resin electrophoretic coating, offering excellent corrosion resistance.
The Importance of Permanent Magnet Production Processes
| Determining Magnetic Performance Indicators: Permanent magnet production processes directly affect key performance parameters of magnets, such as remanence, coercivity, and maximum magnetic energy product. For instance, in the production of neodymium-iron-boron magnets, the magnetic field orientation forming process enables magnetic powder particles to align in specific directions, significantly enhancing the magnetic strength and directionality of the magnets to meet the demands of high-performance applications.
| Affecting Dimensional Accuracy and Shape Complexity: Different permanent magnet production processes can achieve varying levels of dimensional control precision and complex shaping of magnets.
| Ensuring Mechanical Properties and Reliability: Permanent magnet processes such as sintering and heat treatment are crucial for the hardness, toughness, and fracture resistance of magnets. Proper process parameters can increase the mechanical strength of the magnets, making them less prone to damage from external impacts or vibrations during use, thereby prolonging their lifespan.
Applications of Permanent Magnet Production Processes
| The sintering process is the most widely used production method, suitable for sintered neodymium-iron-boron, permanent ferrite, samarium-cobalt, and sintered aluminum-nickel-cobalt magnets.
| The casting process is primarily used for the production of cast aluminum-nickel-cobalt magnets.
| The bonding process is mainly for producing various types of bonded magnets, such as bonded neodymium-iron-boron, bonded samarium-cobalt, and rubber magnets.
| The hot deformation process is primarily used for the production of hot-pressed neodymium-iron-boron magnets.
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