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Neodymium Iron Boron (NdFeB)

Neodymium magnets offer the best value when comparing performance, size and cost. They are moderate in price, very strong magnetically, and typically allow for dimensional reductions. They have poor resistance to corrosion and should have a coating or plating applied. Consideration should be given to the grade of alloy when exposing Neodymium magnets to temperatures above ambient room. Neodymium Iron Boron has good resistance to external demagnetization fields because of its high Intrinsic Coercive Force (Hci) . This resistance makes Neodymium magnets an excellent choice for electromechanical applications.

Intellectual property rights exist for commercially viable Neodymium Iron Boron magnet alloys. Many infringing manufacture’s from the Pacific Rim can offer cheap pricing because they pay no royalties to the patent holders, utilize substandard raw materials, and have poor manufacturing methods. Utilization of infringing Neodymium magnets may lead to legal issues, delays, and product failures. Dura Magnetics, Inc. only provides licensed alloys which are traceable to the patent holders. This assertion of compliant Neodymium magnet alloy is supported by on-site inspections and contractual obligations initiated with alloy producers.

Neodymium Magnets Manufacturing Process

Fully dense Neodymium Magnets are usually manufactured by a powdered metallurgical process. Micron size Neodymium powder is produced in an inert gas atmosphere and then compacted in a rigid steel mold or in a rubber mold. The rubber mold is compacted on all sides by fluid and it is referred to as isostatic pressing. The steel molds will produce shapes similar to the final product, while the rubber mold will only create large blocks (loaves). The alloy’s magnetic performance in both compacting methods is optimized by applying a magnetic field before or during the pressing operation. This applied field imparts a preferred direction of magnetization, or orientation to the Neodymium Magnet alloy. The alignment of particles results in an anisotropic alloy and vastly improves the residual induction (Br) and other magnetic characteristics of the finished magnet. After pressing, the magnets are sintered and heat treated until they reach their fully dense condition. The die pressed magnets are ground to the final dimensions, but the brick magnets from the rubber mold method are usually squared on large grinders and then sliced to the final geometry. Isostaticly pressed alloy has higher magnetic properties than the die pressed material, but it may lack the uniformity. The choice of manufacturing method is usually application driven and is typically not a concern of the customer.

Neodymium Magnets Temperature Characteristics

Sintered Neodymium Iron Boron magnets are susceptible to demagnetization when exposed to elevated temperatures. There are many grades which can withstand high temperatures, but several factors will dictate the performance of the Neodymium magnet. One of the most pertinent variables is the geometry of the magnet or magnetic circuit. Magnets which are thin relative to their pole cross-section (Magnetic Length / Pole Area) will demagnetize easier than magnets which are thick. Magnetic geometries utilizing backing plates, yokes, or return path structures will respond better to increased temperatures. The maximum recommended operating temperatures listed on the Neodymium magnetic characteristics page does not take into account all geometry conditions. Please contact a Dura team member for design assistance when elevated temperatures are involved in your application.

Neodymium Magnets Corrosion Characteristics (Surface Treatment)

Neodymium Iron Boron magnets are very susceptible to corrosion. A variety of coating and plating options are available to protect the magnet from the environment. The rapid oxidation of Neodymium magnet alloy requires rigorous surface preparation before coating or plating. Most surface treatment facilities are not familiar with this magnet alloy and are not capable of successfully coating or plating it. Neodymium Iron Boron does not take plating like other metal alloys and it will corrode from the inside-out. A Dura team member will assist with the selection of best surface treatment option for your application.

Neodymium Magnets Machining

Neodymium Iron Boron magnet material is very hard and brittle. On average the material’s hardness is 58 Rc and conventional machine tools and cutters are not appropriate. The hardness combined with the powder metal grain/crystal structure inhibits the use of carbide tools. Diamond tooling, electrostatic discharge machines (EDM), and some abrasives are the conventional means of fabrication for this magnet alloy. Another concern with machining is the volatility of the powder or dry grinding swarf. These particles can combust while machining or in swarf storage containers. Machining will also remove the “skin” of the alloy and make the material more susceptible to corrosion. Most magnet materials are machined in the un-magnetized state. Once the fabrication and cleaning operation are complete the magnet is then magnetized to saturation.

Dura Magnetics is capable of fabricating simple or complex shapes from Neodymium Iron Boron alloy. We stock a variety of standard and exotic grades for production or prototype fabrication.

A Dura Magnetics team member can help determine if custom machining is required or if “pressed to size” geometry is possible. The determining factors are usually required lead-time, cost, and the alloy required.

Neodymium Magnets Magnetizing

Neodymium magnets are extremely strong and they require a large magnetizing field. The large magnetizing fields require special equipment and neodymium magnets are not generally magnetized by customers. The anisotropic nature of sintered Neodymium magnets results in a single direction of magnetization. This direction must be observed when magnetizing and when integrating the magnet into the final assembly. Often times an indicator is used to identify a specific magnetic pole for the customer’s assembly process. This indicator can be a simple paint dot or a laser engraved mark.

The high field required for magnetizing Neodymium will often times restrict the design of the magnet or magnetic assembly. Many variables must be taken into account and a Dura team member can assist with the design process.