Magnet manufacturing processes
- Each company use their preferred manufacturing processes of magnets; we make in the following text a compilation of the most used and standardized.
Description of the magnet production process
Although there are different methods of manufacturing magnets, the principle of powder metallurgy is one of the preferred and, therefore most used. The material of the magnet to be manufactured is made in a powder or fine-grained compound so that it is ready for liquid phase sintering. The permanent magnets that have gone through this manufacturing process are sintered magnets. As some examples of magnets that have been magnetized in this way, the samarium-cobalt magnets (SmCo) and neodymium magnets with iron and boron components (NdFeB) should be mentioned here. These are rare earth magnets, all made of metal alloys. A completely different class of magnets are ferrite magnets, also known as ceramic magnets.
Production processes for Neodymium magnets and SmCo magnets
The raw materials to be used are melted in an induction melting furnace. The molten mass is cooled in a mould. According to another processing method, the molten mass is loaded into a strip melting machine, cooled and converted into a thin, uniform metal strip. After curing, crushing and spraying of the metal to a particle size of 3 to 7 microns is done. This is done in a vacuum, using an inert gas, as the metal powder by its chemical reactivity must not come into contact with oxygen in the air.
The dust compression process can be performed in several ways, but always with the aim of achieving a uniform alignment of the elementary magnets. In the first type, axial or transverse pressing, the powder is placed in a cavity of a tool. By means of a press, a punch is pressed into the mould, thus compressing the powder.. By means of a press, a punch is pressed into the mould, thus compressing the powder. Immediately before compression, an external magnetic field is applied to align the elementary magnets. Compression maintains alignment. The characteristic of axial (parallel) pressing is a magnetic field direction parallel to the compression pressure. If, on the other hand, the magnetic field is perpendicular to the compaction pressure, this is known as transverse pressure. The result of transverse pressing is a higher energy product, as the small dust particles align in the direction of the magnetic field.
After a second isostatic pressing process, the powder is placed in a flexible container, closed and an external magnetic field is applied. The container is now placed in an isostatic pressed compartment. The outside of the container is pressurized and evenly compressed by means of hydraulic oil or water. This method has a useful advantage on that the production of larger magnetic blocks of up to 100 x 100 x 250 mm is possible. Due to the uniform compression, the powder also remains in its alignment. The result is a very high energy product. The pressed bodies are packed and placed in a vacuum sintering furnace. In the compacted state, rare earth materials are brought to sintering temperature. For the SmCo material, a "solubilizing" treatment is required after sintering. During subsequent cooling, the bodies shrink in the longitudinal direction by approximately 15-20% and then have a rough surface. In this state, the subsequent permanent magnets do not yet have an external magnetic field.
Magnetization and calibration of magnets
Sintered magnets have a rough surface, are very fragile and very hard. Their Rockwell hardness is HRC 57 - 61. The magnets obtain their final shape after being with diamond discs. The surfaces are smoothened by grinding with diamond or special grinding wheels. However, since cutting with a diamond blade is very precise and can be carried out with a high surface quality; there is often no need for subsequent grinding. Processing sintered magnets requires a lot of sensitivity; otherwise it can easily cause splinters and cracks.
When the processing of the external magnet is complete, magnetization is the last step. This can be generated with an electromagnet or with a hollow cylinder, which is equipped with permanent magnets of certain sizes and shapes.
When calibrating magnets, a magnetic field of known magnitude is compared with the magnetic field values of the magnets to be calibrated. In this way, a relationship is determined between the known nominal values of the magnetic fields and the actual values of the magnets.
In the production of magnets, each step must be carried out with great care, as permanent magnets are very hard and fragile. It is particularly important that these delicate treatments avoid cracks and splinters in the magnet to be produced. The handling of the magnets for their final completion requires a great deal of experience, acquired through many years of study of the extensive field of magnetism. Use our help and support for an optimal solution to your magnetic problems and contact us at any time.