Neodymium Magnet Manufacturing Process
Neodymium magnets are made through a series of advanced steps monitored to ensure a premium yield of high-grade materials. The processes involved merge advanced metallurgy and powdered metallurgy within the scope of sophisticated metallurgical methods. Being the most-trusted rare earth metals, neodymium magnets must undergo careful preparation to preserve the quality of the end products and deliver a range of magnet grades.
Neodymium magnets are composed of three key elements — neodymium, iron, and boron — mixed in varying proportions based on the market requirement or industrial use. Neodymium magnets can be sintered, hot pressed, or bonded, based on the selected manufacturing processes. These processes thus hugely affect the type of yield obtained.
Below, we review the steps in making a Neodymium magnet of different classes.
Alloy Preparation
The alloy of neodymium is prepared by adding other elements in trace quantities to the mix of Neodymium, iron, and boron. This enhances the magnetic properties of the alloys and optimizes the effects of the subsequent processes after the preparation of the alloy. Common elements used as alloys are aluminum and niobium.
Before alloying, neodymium is extracted from its ore, which occurs as an open pit requiring heavy industrial equipment for a clean extraction. Like any other chemical process involving the separation of an element from its ore, the rare earth metal’s ore is crushed and then subjected to floatation. This means that the ore is mixed with considerable volumes of water diluted by special reagents to separate the core element from accompanying compounds.
This process is the first critical step in making pure magnets, as the concentrate (core element) must be as pure as possible. To achieve this, the ore, after floating, undergoes refining. The refining and extracting processes follow different methods including electrolytic, catalytic, ion exchange, or electrochemical refining.
Getting the concentrate from the ore is costly and a factor in the unit price of different magnets. Neodymium, the core element, shares several similar properties with other elements found in its ore. Praseodymium, another rare element, has numerous uncanny properties like neodymium such that separating the two becomes an arduous task. Thus, Neodymium magnets often contain up to two-tenth of praseodymium, as their magnetic properties are keenly alike.
Cobalt and nickel are easily found in monazite and bastnasite, the primary ores of Neodymium. They are extracted from the concentrate through multiple, time-consuming steps. Once extracted, though, they are kept in separate vessels for future applications, as they are suitable catalysts for a range of industrial processes.
Melting
Melting and strip casting is crucial to the crystallization of the magnetic grains. The alloyed NdFeB (Neodymium-Iron-Boron) is heated to a molten form in a vacuum furnace, before being compelled to cool (cast) under extremely high-pressure rates. This super cooling converts the molten NdFeB to small grains that ease the downstream movement of the magnet and set it up for a solid manufacturing process.
How do you check that the casting is complete? The NdFeB grain must be homogenous, with the neodymium phase equally distributed along the granular circumference of the magnets’ crystals.
Hydrogen Decrepitation
Decrepitation is a process that involves the breaking down of heated crystals into powdery form. It is a risky procedure often avoided during the industrial production of different substances, as it converts them into a brittle form.
In manufacturing Neodymium magnets, this brittleness is necessary. When decrepitated, the disintegrated material is fully ready for the next stage, which is the pressing of the NdFeB powder.
The crystals gotten after molting are exposed to sufficient measures of hydrogen to disintegrate the material, hence the process is called hydrogen decrepitation. Now brittle, the crystals can be broken down into tinier particles, hence the importance of passing Neodymium magnets through this process.
Jet Milling
Jet milling is a considerable alternative to decrepitation. It relies on high-speed inert gas set up in a piece of cyclonic equipment to crunch the crystal grains into powder. The cyclone will classify the different grain particle sizes as they are converted, ensuring that they maintain a favorable particle size during the process.
As they are separated through cyclonic airflow, the particles are prevented from having contact with the pressure vessel due to the velocity of the gas flowing through the cyclone.
Pressing
Here, the possible anisotropic effects of magnets are achieved. Anisotropy is a phenomenon where the value of a material varies with a change in direction. In magnetism, anisotropy addresses the necessary directional couplings for the strongest magnetization effects, particularly south-north coupling.
The powder obtained through decrepitation or milling is placed in an inert gas system (to prevent oxygen or air from reacting with the mixture) and kept in gloves boxes before being shipped into molds. In the molds, the powder is subjected to an external magnetic field and pressed between plates. The effect of the magnetic field is to align the powder in an outlined direction throughout the remaining manufacturing processes.
If the alignment of the powdery form occurs in the direction of the applied field, then it is lateral to it. The alignment can likewise happen perpendicular to the field, in cases where sintered magnets are the desired product. Remnant air gaps in the block can be removed by submerging the block in a cold isostatic press. The block becomes smaller than it was when entering the press.
Sintering
It is at this stage that manufacturers value even more the need for pressing the NdFeB powder molds. Sintering doesn’t affect the magnetic features or orientation of the NdFeB material.
Instead, it is a process where the molds are placed in a furnace set to temperatures of around 1200F, close to the melting point of the NdFeB alloy. The extreme temperature excites the component atoms of the alloy, prompting atomic motion that strengthens the compactness of the metal as they develop magnetic and mechanical properties.
The process ends with the shrinkage of the mold. But the magnet is only half ready.
Annealing
The processes leading up to the production of fine, strong magnets require utmost patience. Manufacturers of premium Neodymium magnets agree that after sintering, many magnet shapes still contain internal stress, due to random excitation of the constituent atoms, which may reduce their ductility or render them too hard for suitable use.
Thus, annealing is introduced to remove any internal stress existing in magnets. The sintered blocks are sent for heat treatment at low temperatures to displace the pent-up stress. The heating is alternated between high and low temperatures until the holding time is achieved when the magnets can then be cooled to room temperatures.
Machining
The present shapes of the magnet blocks aren’t the desired shapes applicable in different industrial processes. Hence, under strict guidelines, cutting and machining are done to transform the outer shape of the magnets.
Yet, even with close monitoring, industrial machines will certainly chip away some part of the molten block while cutting. These chipped parts are recycled as waste material and can be reused during the production of other magnets.
Grain Boundary Diffusion
Earlier, we talked about other ingredients added to NdFeB magnets to improve their strength and magnetite. One class of magnets is the Heavy Rare Earth Elements, known in the industry as HREEs. They aid the resistance of a magnet to demagnetization activities and the effects of an external magnetic field acting on it.
The downside of depending on HREEs for optimum, 100% magnetic enhancement is this: HREEs are rare to find and expensive to refine. To address this, manufacturers introduce a method known as grain boundary diffusion which cuts the volume of HREEs needed to affect a magnet’s property.o
In grain boundary diffusion, manufacturers selectively introduce HREEs like Dysprosium and Terbium into the magnet’s grain boundary phase. This guarantees effective dispersion of the HREEs with the minimum quantity used, thus preventing the worry of procuring large volumes of HREEs. It is up to manufacturers to determine if this step is important for producing magnets.
Coating
Why coating?
In industrial processes, the coating protects products from extreme atmospheric conditions, prevents iron objects from rusting, preserves shelf life, and stops the occurrence of spontaneous chemical reactions when products are brought in contact with volatile elements.
Magnets are brittle and are prone to chipping and breaking. They also have a delicate core mixture of NdFeB, which can quickly react with oxygen. To prevent these, Neodymium magnets are cleaned and coated. The choice coating materials are usually of three layers of nickel, copper, and nickel, giving them a nickel-copper-nickel plating.
The coating is done before a magnet is saturated with magnetic charges; the heat applied during coat can strip off the magnetic features of a magnet, and the magnetic field in the magnet can alter the electroplating procedure. Other suitable coatings are gold and polytetrafluoroethylene (PTFE).
An alternative to coating is electrophoresis coating, reserved especially for bonded magnets (magnets made up of a magnetic part and a non-magnetic part). In some spaces, the coating is called surface treatment.
Magnetizing
What’s a magnet without magnetic properties? After coating, the magnet is magnetized by placing it in an electric capacitor and subduing the capacitor to an external magnetic field. The field energizes the capacitor during a brief window of magnetization, and when the field is removed, the coil loses its magnetism but the magnetic field created in the magnet tarries.
Permanent magnets can be magnetized to become anisotropic or isotropic, given the desired direction of magnetization.
Inspection of Magnets
Before shipping, magnets are subjected to a degree of tests to determine their shelf life –
Quality Check
During the different phases of manufacturing, testing and evaluation are performed on the materials. The data obtained are recorded and tallied against known standards, and the feedback obtained suggests what, if any, improvements are needed.
Counting Quantity
How many pieces of magnets are packed in a single magnet shipment? What are the desired weights of the magnets, and the obtained weights? Are there discrepancies in the magnet size? Manufacturers crosscheck the output of the production process to ensure alignment with industry requirements.
Grade Inspection
Neodymium magnets come in different grades. The standard magnets are effective under temperatures of up to 80C. Anything above this and the magnets are graded into categories such as SH, EH, etc. This affects the unique processes of making different magnets. After production, magnets are identified and sorted based on their different grades to avoid colossal errors of putting a magnet in the wrong grade.
Saturated Product Magnetization
While magnetizing, manufacturers test to ascertain that the magnet has reached full saturation. The strength of a magnetic material is directly proportional to the strength of its magnetic field. If the magnetic field is stripped off, the magnet is not ready for shipping.
Packaging and Shipment
Magnets exert a magnetic field around objects that are receptive to magnetism. Unlike many industrial products that are transported in numerous ways, magnets require special wrapping based on the mode of transportation:
Ordinary
Generally, magnets should be shipped in carton boxes with enabled shielding features. This is done by padding the interiors or using a steel-lined box. The padding adds to the weight of the container and should be considered when shipping magnets.
Rust-free
Though coating prevents magnets from undergoing volatile reactions with oxygen in air or water, continuous exposure of magnets to oxygen will eventually wear out the nickel-copper-nickel layer. The shipment vessels should be airtight at all times.
By Ship or Air
In a previous post, we discussed the criteria for transporting Neodymium magnets by air. The magnetic field can alter the plane’s navigation. They have a strong shattering pull and can cause bodily harm if not handled with great care. Likewise, ships are susceptible to the effects of magnets and require special packaging for transportation. If uncertain, seek the opinions of an expert before packaging and shipping out your magnets.
Where To Buy?
At ROBO Magnetic, we ship and deliver the most refined neodymium magnets in swift time, getting you all set up within one week of receiving your order. To get started, fill out a request form, and we’ll take it over from there.
