The main shapes of sintered NdFeB magnet products include square pieces, cylinders, rings, tiles, sectors and various special-shaped products. In actual production, large pieces of blanks are mostly produced first, and then the final products are obtained through post-processing according to the user's size requirements.
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Sintered NdFeB magnets are prepared by powder metallurgy. The material has high hardness, high brittleness and is easy to break; and the heat release, corrosion and defects during the processing will damage the magnetic properties. Therefore, it is necessary to select a suitable processing method based on these characteristics. At present, sintered NdFeB machining is mainly based on traditional cutting, grinding, chamfering, drilling, etc., and there are also EDM cutting, laser processing, ultrasonic processing and other methods.
The cutting process is mostly completed by slicers, EDM wire cutting machines, wire saws or laser cutting machines.
Slicer: Use a high-speed rotating thin-sheet inner circular diamond drill tool to automatically cut the NdFeB magnet. Cutting oil is used as a cutting coolant during the slicing process. The advantage is that it does not require customized special tools, has strong flexibility, and is suitable for sample processing and truncation processing. However, due to low processing efficiency and yield rate, and weak verticality guarantee ability, batch slicing production has gradually been replaced by multi-wire cutting machines (wire saws).
Multi-wire saw cutting: Use a fixture to fix the workpiece on the workbench, and use the roller cloth diamond wire. The high-speed diamond wire (wire diameter 0.15~0.2mm) rubs against the magnetic steel to achieve material cutting. The cutting process is cooled by cutting fluid. The main feature is that multiple workpieces can be cut at the same time, with high production efficiency, good yield rate and yield rate, strong verticality guarantee ability, and suitable for batch continuous processing. However, special rollers need to be customized for products of different specifications.
Electric spark wire cutting: Use molybdenum wire electrodes to generate high-frequency electric sparks on neodymium iron boron magnetic steel to melt it locally, and control it by computer to make the electrode wire cut according to the predetermined trajectory. The advantage of electric spark wire cutting is high processing accuracy, which can be used for slicing of tile-shaped and special-shaped products and cutting of large magnets. The disadvantage is that the cutting speed is slow, and the melting area of the cutting surface has a greater impact on the magnetic properties.
Laser cutting: The laser beam is converged on the magnetic material, the magnetic material melts and vaporizes, and the disappearing area forms a slit. Laser cutting is a non-contact processing, which has the characteristics of small impact on the environment, high processing accuracy, and can process inclined surfaces, and has broad application prospects. However, the changes in temperature and stress during the processing have a certain impact on the performance of the magnet, and when cutting thicker products, the divergence of the laser beam causes a slope in the cutting section.
Mainly refers to the processing method of grinding the surface of the workpiece with a grinding disc or a grinding wheel. The commonly used grinding methods for square NdFeB magnets are: vertical grinding, flat grinding, double-end grinding, etc. Cylindrical and annular NdFeB blanks often use centerless grinding, square grinding, internal and external grinding, etc. Tile-shaped, fan-shaped, and special-shaped magnets can use multi-station forming grinders.
Surface grinder: It is used for surface grinding of magnetic materials and can also perform multi-faceted processing. Generally, a horizontal axis rectangular table surface grinder (flat grinding) or a vertical axis circular table surface grinder (vertical grinding) is used to neatly stack the flat surface of the magnetic steel as the reference surface and fix it on the disk workbench with a baffle clamp, etc., and a grinding wheel is used for reciprocating surface grinding.
Double-end surface grinder: The conveyor belt passes the product continuously, and the two grinding wheels are located on both sides of the product. The horizontal axis double grinding head is used to rotate and drive the grinding wheel (the two grinding wheels produce an inclination angle), and the two planes of the product are ground under the rotation of the grinding wheel. The double-end surface grinder has high processing accuracy and small surface roughness. It is the most widely used symmetrical plane processing equipment in NdFeB machining.
Centerless grinder (or square circular grinder): The centerless grinder is used for the external cylindrical grinding of cylindrical blanks, and the square circular grinder is used for the circular grinding of square bar magnetic steel. The magnetic steel passes through the guide wheel and the grinding wheel in turn through the feeder and the guide rail. The guide wheel drives the magnetic steel workpiece to rotate on the pad iron, and the grinding wheel grinds the outer circle of the magnetic steel to the required diameter.
Internal and external cylindrical grinder: Fix the magnetic steel workpiece by the fixture, and then make the grinding head move along the inner or outer circumference of the workpiece, grind the magnetic steel workpiece to the set size of the inner and outer circles, and grind the surface flat and remove burrs. It is mostly used for the internal and external surface processing of circular ring products.
Forming grinder: It can grind various planes, curved surfaces or grind complex forming surfaces through special grinding wheels (grinding wheel shaping). It is suitable for grinding without motorized feed to meet the shape requirements of different types of products. It is usually used for mechanical chamfering or special-shaped product processing of products.
Sintered NdFeB is very prone to breakage or fragmentation during the drilling process, so specific equipment and processes are required for punching operations. Commonly used equipment for NdFeB internal hole processing includes boring machine tools, instrument lathes and bench drilling machines.
Hole boring machine tools (trepanning machines): A device that uses diamond ring cutters, the product is fixed by the chuck and driven by the spindle to rotate, and the tool feeds to realize internal hole processing of the product. Hole boring lathes are usually used to process NdFeB products with inner holes of more than 8mm. Holes and reamer can be completed by special hole boring and reaming tools.
Instrument lathe: The instrument lathe clamps the magnetic steel product through the fixture, drives the product to rotate continuously through the spindle motor, and the fixed alloy tool drills the rotating workpiece. It is mainly used for drilling and trepanning of cylindrical, circular and small square products, and the processing hole diameter is less than 5mm.
Benchtop drilling machine: A device that uses self-made tooling to position the product and carbide tools to rotate and feed to achieve drilling processing on the product; the main difference from the instrument lathe is that the workpiece of the instrument lathe rotates and the tool is fixed; while the workpiece of the benchtop drilling machine is fixed and the tool rotates. Therefore, the benchtop drilling machine can be used for the processing of through holes, blind holes and step holes of special-shaped products.
Ultrasonic drilling machine: The ultrasonic energy is concentrated to the drill position through the transducer, and the high-frequency mechanical vibration of the drill drives the abrasive suspension to achieve impact perforation through high-speed impact, friction and cavitation. Ultrasonic drilling has high precision, efficiency and qualified rate, and can be applied to small hole processing of magnetic steel.
NdFeB magnetic products are easily knocked and cornered during grinding, slicing, punching and other processing. The sharp corners produced are very easy to cause edge knocking and corner dropping, and the tip effect during electroplating will make the coating uniformity worse. Therefore, after machining, the magnetic steel is usually chamfered, including mechanical chamfering and vibration chamfering. Common chamfering equipment includes vibration chamfering machine and drum chamfering machine
Vibration chamfering machine: Through the vibration deviation generated by the vibration motor, the magnetic steel and abrasive in the working tank are driven to move up and down, left and right or rotate and rub against each other, so that the surface of the product is smooth and rounded. Commonly used abrasive media include silicon carbide, brown corundum, etc.
Drum chamfering machine: The NdFeB magnetic steel product, abrasive and grinding liquid are placed in a sealed horizontal drum. The rotation of the drum causes the product and the abrasive to rotate centrifugally and rub against each other, which plays a chamfering role.
