Magnets Manufacturing Method
Neodymium Magnet Manufacturing Method
Fully dense Neodymium Magnets (also known as neo magnets, neodymium iron boron, neo, or rare earth magnets) are usually manufactured by a powdered metallurgical process. Micron size Neodymium and iron boron 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) of Neodymium magnet alloy.
The Neodymium 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 rare earth magnet. After pressing, the Neodymium 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 to create Neodymium Magnets is usually application driven and is typically not a concern of the customer.
Samarium Cobalt Magnet Manufacturing Method
Fully dense Samarium Cobalt rare earth magnets are usually manufactured by a powdered metallurgical process. Micron size Samarium Cobalt powder is produced and then compacted in a rigid steel mold. The steel molds produce shapes similar to the final product, but the mechanical properties of the alloy usually inhibit complex features at this stage of the manufacturing process.
The various elements that compose a samarium cobalt magnet – samarium, cobalt, copper, zinc, and iron.
The Samarium Cobalt’s magnetic performance is optimized by applying a magnetic field during the pressing operation. This applied field imparts a preferred direction of magnetization, or orientation, to the Samarium Cobalt 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 Samarium Cobalt magnets are sintered and heat treated until they reach their fully dense condition. The rare earth magnet alloy is then machined to the final dimensional requirements and cleaned.
AlNiCo Magnet Manufacturing Method
Alnico is a cast or sintered alloy consisting primarily of iron, aluminum, nickel, cobalt, with minor amounts of other elements including copper and titanium. Alnico is produced by conventional foundry methods using resin bonded sand molds or powder metal manufacturing methods. Alnico is suitable for complex geometries and configurations not achievable with other magnet materials.
Various Alnico alloys are achieved by modifying the chemistry and manufacturing process. These alloys can be tailored to obtain a variety of magnetic properties and characteristics. For example, specialized casting techniques are used to achieve the unique crystalline grain orientation found in the Alnico 5-7 grade.
Most Alnico produced is “oriented” and this is where the alloy’s properties are optimized by imparting an “alignment.” The alignment or orientation occurs during a heat treatment process which is unique to Alnico. The direction of orientation for most Alnico material is determined during this process which involves heating the casting or sintered part above its Curie Temperature and then cooling it at a controlled rate in the presence of a directionalized magnetic field. The actual shape of the magnetic field as well as its intensity can be optimized during this process.
Magnets which have been processed in this fashion are Anisotropic in nature and exhibit a preferred direction of orientation. Unoriented materials (Alnico 2) are available for those applications which require the specialized magnetizing capabilities of a non-aligned material. Unoriented Alnico is also typically more cost effective than oriented or anisotropic alloys.
Alnico MachiningFinal shaping of the Alnico materials is achieved by abrasive grinding and cutting where close tolerances are required, otherwise it is desirable to use the part with as-cast features.
Alnico magnets produced by the powder metal method lend themselves to shapes with more features. A conventional tool is required to facilitate the “pressing” operation and this can add cost, but finish machining is typically not necessary because the parts can be made to size or near net size.
Ferrite (Ceramic) Magnet Manufacturing Method
Ceramic or Ferrite Magnets are produced by calcining a mixture of iron oxide and strontium carbonate to form a metallic oxide. A multiple stage milling operation reduces the calcined material to a small particle size. The powder is then compacted in a die by one of two methods. In the first method, the powder is compacted dry which develops an isotropic magnet with weaker magnetic properties, but with better dimensional tolerances. Oftentimes, a dry pressed magnet does not require finish grinding. In the second method, the powder is mixed with water to form slurry. The slurry is compacted in a die in the presence of a magnetic field. The applied field creates an anisotropic magnet which exhibits superior magnetic properties, but usually requires finish grinding.
The compacted parts which approximate the finished geometry are then sintered at high temperatures to achieve the final fusion of the individual particles. Final shaping is achieved by diamond abrasives. Usually the pole faces of the ceramic (ferrite) magnets will be ground and the remaining surfaces will exhibit “as sintered” tolerances and physical characteristics.