How Are Neodymium Magnets Made? Neodymium magnets are made by a sophisticated process that includes some very high-tech metallurgical methods comprising powder metallurgy and advanced process metallurgy.
Dozens of process steps must be followed very precisely to make Neodymium magnets –also known as NdFeB -for the chemical symbols of Neodymium, Iron and Boron.
Process variations are used to achieve the properties necessary for various grades. These variations include compositional differences, morphological (crystal shape) differences and process differences.
Below, we will walk through many of the major processing steps.
Manufacturing Process Steps of Neodymium Magnets
Let’s review the processing steps. The production of Neodymium magnets depends on advanced materials engineering and processes. Here are the main steps:
- Rare Earth Ore is discovered and mined.
- Ore is processed and refined
- Refined metal has elements added to create rare earth alloy
- Melting (raw material) and strip casting
- Hydrogen Decrepitation
- Jet Milling
- Pressing Under External Magnetic Field
- Cold Isostatic Pressing
- Machining and Grinding
- Packing and Shipping
Neodymium Magnet Processing Steps
There are many major production steps –plus numerous sub steps- in the manufacture of high-quality, high-tech Neodymium magnets. Each step is highly important, and each step is an essential part of a highly refined operation.
Here are the major steps.
- Step #1 Rare Earth Ore Mining
First, the rare earth ore is discovered and then mined. Most rare earth mines are open pit, so the ore is removed with large equipment after removing any soil overburden.
- Step #2 Ore Processing and Refining
Next, the Rare Earth Ore is crushed and milled. Then the ore goes through a flotation process where it is mixed with water and special reagents to separate the rare earth elements from the tailings. Depending on the source of the ore, the concentrate may also undergo electrolytic refining. Rare earth metals can be refined and extracted electrochemically, or by distillation, ion exchange or other techniques.The concentrate (refined ore) is then smelted. This means it is heated up to very high temperatures (~1500°C) so the valuable metals can be separated from unusable materials in the ore.
Rare Earth Elements are often found with other valuable metals, such as precious metals and even significant quantities of base metals like copper and nickel, so multiple steps are taken to separate them.
Extraction of rare earths is difficult because many of them have very similar properties, making refinement a challenge. This is one of the cost factors; because the refinement methods require the use of expensive chemicals and time –consuming processes.
For example, it’s not well known, but about 20-30% of the Neodymium in Neodymium magnets is really Praseodymium. In fact, the alloy used to make magnets is called PrNd because these two elements are chemically so similar that not only are they too similar to easily separate, but they are also so similar that it would make only a small difference in the quality of the magnet.
- Step #3 Alloying
During the alloying process, small additions of other metals are made to NdFeB alloy to refine and modify the micro structure of the final product, enhancing its magnetic properties and enhancing the effects of other processes.
- Step #4 Strip Casting
Alloyed NdFeB is now ready for melting and strip casting. It is heated in a vacuum furnace and a stream of molten metal is forced under pressure onto a cooled drum where it is rapidly cooled at approximately 100,000 degrees-per-second. The high cooling rate produces very small grains of metal that help simplify and enhance the effect of the downstream processing. Also, small grains are an important part of producing high-quality magnets.
Vacuum strip casting furnace rapidly solidifies NdFeB magnet material to create very small grains
- Step #5 Hydrogen Decrepitation
While the grains are very small from strip casting, the material from strip casting comes out of the caster in sheets that must be reduced to powder in order to make magnets. The next step after this is Hydrogen Decrepitation –a process that introduces hydrogen to purposely disintegrate the magnet material. The metal is now brittle enough that it can easily be broken into smaller pieces, which is why it is called Hydrogen Decrepitation. In the processing of most metals, processors avoid the introduction of hydrogen into them.
Hydrogen embrittlement can be a major problem for many metals. In this case, the hydrogen is purposely introduced in order to make the material disintegrate. Then it is easy to grind it even smaller in a subsequent operation. The decrepitated material is now ready for the next step.
Hydrogen Decrepitation is a process step used in the production of Neodymium magnets to create extremely small grains in the material.
- Step #6 Jet Milling
The Jet Mill uses a high-speed stream of cyclonic inert gas to grind pieces of NdFeB metal into powder. The metal impinges on other pieces of metal powder inside the cyclone.The cyclone automatically classifies the particles by size as they go through the system, so a narrow –and very favorable- particle size distribution is maintained.
The cyclonic air flow naturally separates the particles and prevents the material from having contact with the sides of the pressure vessel due to the gas flow pressure and velocity because different particle sizes have different aerodynamics.
The jet mill is a very clean and effective way to grind NdFeB metal down to powder
- Step #7 Pressing Under External Magnetic Field
The powder is kept in an inert gas atmosphere and handled in glove boxes before going to the automated press. The powder enters a mold and is pressed between plates while under a strong magnetic field forming a block of material.The magnetic field orients the grains so that the magnetic domains remain aligned in the designed direction for all subsequent processing steps.
The magnetic field can be oriented two ways: 1) in alignment with the block or 2) perpendicular to the block.Sintered Neodymium magnets are typically pressed perpendicular to the block in order to achieve the highest anisotropy (strongest north-south magnetization)
How are neodymium magnets made
Pressing in a perpendicular magnetic field
- Step #8 Cold Isostatic Pressing
The block of material is bagged and submerged into a cold isostatic press (CIP) under great pressure. This removes any remaining air gaps in the block, which comes out of this press quite a bit smaller than it was when it went in.
- Step #9 Sintering
The pressed block is removed from the bag and sintered. Sintering is a process where the blocks are placed in a furnace at a very high temperature just below the melting point of the metal. At this temperature of >1000oC, the individual atoms have a lot of motion, which allows the blocks to develop their full magnetic and mechanical properties.
The magnetic domains maintain the same orientation they had before sintering. At this temperature, full density is achieved and the blocks have shrunk to their final size.
Neodymium magnet material achieves full density in the sintering furnace
- Step #10 Annealing
After sintering, there are pent-up stresses in the metal from all the movement during sintering, so the blocks are heat-treated again in a step fashion at lower temperatures to reduce the stresses.
The blocks are ramped up to a high holding temperature for a set time and then they are ramped down to a lower holding temperature. Once the holding time is achieved, the now stress-free blocks are slowly cooled to room temperature.
- Step #11 Cutting, Machining and Grinding
NdFeB magnets have had a lot of value added by now due to all of the prior steps. Cutting, machining and grinding are performed according to a strict control plan, and waste is minimized by design.
Wire cutting is performed with very fine wire to minimize kerf losses. Machining and grinding are minimized by close controls throughout the previous processes. Waste material is reused and recycled.
Wire cutting machines are used to cut magnets precisely and economically
- Step #12 Surface Treatment
Most Neodymium magnets now get a final surface treatment before leaving the plant. The baseline treatment is nickel-copper-nickel electroplate, which protects the magnet from corrosion in most typical use environments.
Some end users specify no coating at all for various reasons. Others specify coatings with greater protection than Ni-Cu-Ni can offer.Aluminum-Zinc offers much greater protection than NiCuNi. IVD aluminum is another choice specified by end users. Epoxy is a very good coating for intense environments and is specified by end users with applications where magnets could be exposed to salt fog.
BJMT applies corrosion-resistant coatings for all types of environments. This is a continuous spray aluminum-zinc coating line.
- Step #13 Testing
Testing and evaluation are performed on magnet material at almost every process step, and records of every data point are kept. With such intensive testing requirements, BJMT keeps a substantial inventory of test equipment in house to maintain and improve product quality, production efficiency and cost.
Rigorous testing insures only top-quality products are shipped to the customer
- Step #14 Magnetizing
One of the last steps is magnetizing. The material is placed inside an electric coil which is energized to produce a very strong magnetic field for a short time. After the coil is de-energized, the magnetic field in the magnet remains.
NdFeB Compositional and Processing Differences
High-temperature Neodymium magnets generally require the addition of Heavy Rare Earth Elements (HREE) like Dysprosium and Terbium. The HREEs improve the magnet’s resistance to demagnetization at high-temperatures and in the presence of opposing magnetic fields.
The relative rarity of the HREEs has led a few of the leading NdFeB companies to develop methods and processes for reducing or eliminating the need for HREEs in high-temperature NdFeB magnet grades.
Grain Boundary Diffusion
In recent years, a few leading NdFeB magnet manufacturers have created high-temperature/higher Coercivity grades of NdFeB magnets without HREEs (or with greatly reduced HREE) by improving control of grain size and shape, and through the use of Grain Boundary Diffusion.
Grain Boundary Diffusion (GBD) is a method of selectively introducing HREE into the Grain Boundary phase of the magnet. GBD creates high Coercivity with greatly reduced quantities of HREE like Dysprosium and Terbium, alleviating concern over the use of these rare and expensive HREEs.
Crystalline Shape and Size
In many metallurgical systems, the material’s properties are influenced by the shape of the individual crystals –or grains- in the metallic structure, as well as the average shape and size of the grains throughout the microstructure. Tight controls on processes can lead to improvements in magnetic properties at high temperatures while reducing the need for HREEs.
Each manufacturing process must be carefully monitored to verify that each step is carried out with precision to achieve quality, performance and economy.
Production of NdFeB Magnets Require a Large Capital Investment
These processes require large capital equipment investments. For example, vacuum strip casters, hydrogen decrepitation equipment, jet milling equipment, magnetic orienting presses, cold isostatic presses, and sintering and annealing furnaces are required just to make magnet blocks. Each of these is a major CAPEX cost.
Very precise cutting, machining and grinding equipment make the magnet blocks to size. Since the magnet material is prepared by a powder metallurgy process and may other processes, a substantial amount of value has been added to the parts by the time they get to machining and grinding processes.
Cutting is planned very carefully. Wire cutting is done with very thin wire to minimize kerf losses. Grinding is used when necessary, but it is well-planned to keep material losses as small as possible.
Electroplating and other coating operations all require significant capital in order to produce high-quality products in an economical and environmentally-friendly way.
Neodymium Magnets are Being Used for More Applications
Neodymium magnets power so many devices that it’s easy to lose track of them all. Almost every Hybrid and Electric Automobile depends on Neodymium magnets. Wind power turbines, marine propulsion, air conditioners, mobile phones, audio devices and many more applications all depend on Neodymium magnets to achieve sleek form factors that create downstream economies in many new systems.
Industrial motors made with NdFeB magnets configured for high up-time with efficiencies over 95% are saving electricity and conserving natural resources. Neodymium (NdFeB) magnets are creating more capabilities in smaller spaces in more applications than ever before.
NdFeB magnets deliver the highest performance in the smallest volume of material, making them a very attractive choice for designers of an increasing number of demanding applications.
Neodymium magnets are being seen in the most dynamic applications in new energy and automotive markets
Cost-Per-Unit-Weight –There’s More to the Story
A simple price-per-kg calculation doesn’t tell the whole story when evaluating a highly engineered material like NdFeB. Many winning designs factor in the cost-per-unit of magnetic field strength, which brings a ripple-effect of system cost saving throughout the system.
For example, if an engineer designs a permanent-magnet-based system that has high power requirements coupled with size or space constraints, there is a strong likelihood that the system will use Neodymium magnets. Neodymium magnets offer nearly 20 X’s the magnetic field-per-unit-volume that ferrite magnets offer, and they do it at nearly 1/10 the weight, so a design that uses NdFeB magnets will potentially create a ripple effect that reduces the size of the entire system.
Of course, each type of magnet has its place, and there are many winning designs that use different types of magnets.
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