Normal magnets users need to know about how are neodymium magnets made. The process is long and tricky to understand. Making neodymium magnets involves mixing raw materials and melting and cooling them into ingots. Grind the ingots into a fine powder which is pressed into shapes sintered for strength and magnetized to create powerful permanent magnets ready for use in various technologies.
Neodymium magnets are one of the strongest permanent magnets used in various industries. They are composed of neodymium, iron, boron, which are rare earth metal alloys.
The other elements present in small amounts are dysprosium (Dy), praseodymium (Pr), niobium (Nb), and aluminum (Al). These other elements are added to enhance the various properties of magnets, from temperature tolerance to corrosion and demagnetization resistance.
When someone asks how are neodymium magnets made, the answer is simple. Thin flakes are formed by melting metals in vacuum induction furnaces and cooling them by strip casting. After breaking these thin flakes and then pulverizing them into fine powder in a jet mill, the powder is then pressed in four steps through die-upsetting. Sintering, machining, plating, and magnetization are further processes that need to be completed before getting the actual Neodymium magnets.
Don't rely on general information; explore the series of precise and controlled processes involved in the formation of these powerful magnets.
How Are Neodymium Magnets Made?
Manufacturers use various processes to make Neodymium magnets or NdFeB; we have chosen the process of making Sintered and Bonded NdFeB to share here.
What Are Neodymium Magnets Made Of?
Neodymium magnets result from a mix of metals with the main components:
● Neodymium (Nd) is a rare earth metal that gives the magnet its strong magnetic power.
● Iron (Fe) adds strength and durability to the magnet.
● Boron (B) helps in increasing the overall magnetic potential.
Small amounts of dysprosium (Dy) or praseodymium (Pr) are also sometimes part of neodymium magnets to improve their performance at high temperatures.
How Neodymium Magnets Are Made (Sintered Magnets)
1. Preparing the Materials
After mining all the important rare earth metals, the next step is to start preparing materials. For general understanding, here is one common reaction:
57 Fe + 8 B + 10 Fe₂O₃ + 7.5 Nd₂O₃ + 52.5 Ca → Nd₁₅Fe₇₇B₈ + 52.5 CaO
The first reaction for making sintered neodymium magnets takes place in a vacuum induction furnace. This involves the vacuum heating of the carefully measured raw materials in a special furnace in a controlled environment without air to prevent oxidation. This also helps in removing any unwanted gases or impurities.
In powder form, the ratio is not exactly Nd₂Fe₁₄B, and it contains magnetic grains of Nd₂Fe₁₄B mixed with small non-magnetic bits of neodymium and boron.
In making sintered NdFeB, the use of the measured quantity of elements is important because this helps in controlling the magnet's
● Magnetic strength (flux density)
● Temperature resistance (Curie point)
● Polarization
● Coercivity (resistance to demagnetization)
Manufacturers achieved the specific property by changing ingredients or chemical formulas to make perfect customized sintered NdFeB for various applications or industries. Here is an example of making a sintered magnet that can perform better at higher temperatures:
● Replace some iron (Fe) with cobalt (Co): This helps the magnet keep its strength at higher temperatures. But, it also reduces its ability to resist becoming demagnetized (this is called lower intrinsic coercivity).
● Replace some neodymium (Nd) with dysprosium (Dy): This boosts coercivity, helping the magnet keep its magnetism under tough conditions. However, it slightly reduces the magnet's maximum strength, known as the maximum energy product (BHmax).
If the main aim is to balance strength and stability, they can use both cobalt and dysprosium together.
2. Melting and Cooling
A vacuum induction furnace heats all the metals by creating electrical eddy currents until they melt and blend into a homogeneous liquid alloy.
Cool down the molten alloy in the next step and solidify it into ingots for pulverization.
3. Pulverizing the Alloy
Perform pulverization of solidified alloy ingots to transform them into fine powder in two steps:
● Hydrogen Decrepitation: In the first steps, they use hydrogen gas to break apart the ingots into a coarse powder.
● Jet Milling: Use jet milling further to mill the coarse powder into extremely fine particles. In terms of size, the particles are typically around three microns, which is smaller than a red blood cell.
4. Aligning and Pressing the Powder
Now align and press your completely fine powder to create a solid magnet with strong magnetic properties.
Aligning the Magnetic Particles
At the first point, put the powder into a mold and expose it to a strong magnetic field, which causes the tiny magnetic particles to line up in a specific direction. The alignment at this position sets the direction of the magnet's strength. But you have to fix the magnetic direction before compacting and pressing the powder.
Pressing the Aligned Powder
After alignment, the next step is to press the powder into a solid shape. This not only further fixes the magnetic orientation in place but also increases the density and strength of the magnets. During and even after pressing, keep applying the magnetic strength possible.
Manufacturers use three common methods to press the powder:
● Axial Pressing is applying pressure in the same direction as the magnetic field.
● Transverse Pressing is applying pressure at a right angle to the magnetic field.
● Isostatic Pressing is applying pressure evenly from all directions to offer a more uniform and dense structure. Now, the magnet has a fixed magnetic direction with stronger magnetism and a compact form, which makes it called anisotropic. This focused orientation gives the magnet higher strength and efficiency, especially at its poles.
5. Sintering the Compact
The magnet at this sudden position is a 'green magnet,' which is not fully dense or magnetically potent. The next step is sintering the magnet to enhance its properties.
The next step in powder metallurgy is sintering, in which makers first compress the material in a controlled, oxygen-free environment to temperatures (as high as 1080°C) just below the melting point of the alloy. This process causes the particles to fuse together and increase density and strength.
Quench or cool down the magnet after achieving the desired density to lock in the microstructure and optimize magnetic performance.
6. Machining
After sintering, the next thing is to give the magnets the exact shape with the help of the grinding process.
They use diamond-coated tools to machine the NdFeB to exact shapes and sizes, as sintered magnets are brittle and hard. Electric discharge machining (EDM) is better to use for achieving complex shape magnets.
Magnets have high-cost materials; that's why manufacturers try to minimize material loss during machining, as there is no proper way of recycling the waste available.
7. Applying Protective Coating
Neodymium magnets are prone to oxidation and corrosion and thus lose their magnetic strength and properties due to moisture. A protective layer can prevent this situation and save the sintered NdFeB from being demagnetized. After machining, the next step is electroplating the neodymium magnet with three layers of nickel-copper-nickel. Other common coatings are rubber or PTFE. This covering makes the magnet durable and strong.
8. Magnetization
Now, it's time to activate the magnetic properties of the sintered magnet, which has only the 'preferred' direction of magnetization at that time. To activate magnetic properties, they place the magnet in a fixture with a strong magnetic field for a moment. It is a big coil of wire that surrounds the magnet and uses banks of capacitors and huge voltage to pass a strong electrical current through the coil. It generates a magnetic field that aligns the domains within the magnet and results in a powerful permanent magnet.
9. Inspection
After formation, there are several ways to inspect the magnet to verify its dimensions.
● Verify the plating thickness using a coating thickness measurement system.
● Inspect the coating performance with the help of periodic testing using pressure-cooker tests.
● To verify the BH curve, manufacturers use GBS hysteresis graph measurements to verify that the magnet is fully magnetized.
Bonded Magnets
The bonded NdFeB magnet's name suggests that they are MdFeB magnets with some binder material. They are also a type of rare earth magnet composed of NdFeB magnetic powder combined with a binder material. Manufacturers first make the powder by grinding NdFeB alloy into fine particles.
They mix the fine powder with a polymer to form the final product. Bonded magnets are used as finished magnets. Many industries and products use these magnets as important components. If you compare the bonded magnets with other ones, you will find a lower amount of neodymium and a higher concentration of iron in bonded MdFeB.
Bonded Magnets Manufacturing Methods
Manufacturers use different methods to make bonded magnets. You can get a gist of familiarity by reading the manufacturing processes below.
Injection Molding
It is the process of injecting a melted thermoplastic mixture into a mold to make it cool and solidify into the desired shape and add the NdFeB powder to the mixture to create neodymium magnets. This process helps in making precisely shaped magnets and is well-suited for assembly and over-molding techniques, which results in flexibility in design.
Extrusion
Extrusion is a process in which the manufacturers force the mixture of magnetic materials through a heated barrel with the help of a large screw mechanism. They press the material through a heated die and cut it into the required length. This method is helpful in creating magnets with specific dimensions and shapes.
Calendering
Flexible magnets are formed by the calendering process, which works superbly for making continuous sheets of magnets. In this process, the producers apply heat to rollers and exert pressure on a combination of elastomer and iron powder. The rollers both stretch and smoothen the material into a uniform sheet. Such sheets are ideal for applications requiring flexible magnets.
Compression Bonding
Manufacturers refine the NdFeB powder and blend it with a plastic material in compression bonding and they start with compression molding of the mixture. Then, they carry out compression molding of the mixture. These types of molded neodymium magnets are capable of multi directional magnetization, including multipoles. This technique is often used for small motors, mobile phones, electronics, and cars. Other uses include brushless motor speakers, buzzers, and toy products.
Conclusion
The everyday user of NdFeB always wants to know the processes involved in the making of these magnets, as many believe that they are naturally made metals. The production of neodymium magnets is complex and requires care at every stage. From selecting and combining raw materials to the final magnetization, the manufacturers pay close attention to every point to get a magnet that meets the desired specifications and performance standards.
