Common machinery workmanship for sintered neodymium magnet

The main shapes of sintered neodymium iron boron magnets include square, cylinder, ring, tile/arc segment, sectors, and various irregular shapes. In actual production, large raw magnets are usually produced firstly, and then machinery into required dimension.

Sintered Nd-Fe-B is prepared by powder metallurgy, with high hardness, high brittleness and easy fracture of Hardness; And the exothermic, corrosion and defects in the processing will damage the magnetic properties, so it is necessary to select appropriate processing methods according to these characteristics. At present, the machining of sintered neodymium iron boron mainly involves traditional cutting, grinding, chamfering, drilling, etc. In addition, there are also methods such as electric discharge cutting, laser processing, ultrasonic processing, etc.

1. Slicing (cutting) process

Slicers, electric discharge wire cutting machines, wire saws, or laser cutting machines are often used to complete the cutting process.

Slicer: Using a high-speed rotating thin inner circular diamond drill tool to automatically cut neodymium iron boron magnet, the slicing process uses cutting oil as the cutting coolant. The advantage is that there is no need for customized special tools, with strong flexibility, suitable for sample processing and cutting processing. However, due to low processing efficiency and yield, as well as weak verticality assurance ability, batch slicing production has gradually been replaced by multi wire cutting machines (wire saws).

Multi wire saw cutting: fix the product on the workbench with the tooling fixture, rub the high-speed running diamond wire (wire diameter 0.15~0.2mm) with the magnet through the roller cloth diamond wire to achieve material cutting, and use Cutting fluid to cool the cutting process. The main feature is that it can cut multiple products simultaneously, with high production efficiency, yield rate, and yield rate. It has a strong ability to ensure verticality and is suitable for continuous batch processing. But specialized rollers need to be customized for different specifications of products.

Electric spark wire cutting: Using molybdenum wire electrodes to generate high-frequency electric sparks on neodymium iron boron magnet, causing local melting. Controlled by a computer, the electrode wires are cut and processed according to a predetermined trajectory. The advantage of electric discharge wire cutting is its high machining accuracy, which can be used for slicing tile shaped and irregular products and cutting large magnets. The disadvantage is that the cutting speed is slow, and the melting zone of the cutting surface has a significant impact on magnetic properties.

Laser cutting: Using a laser beam to converge on a magnetic material, the material melts and vaporizes, forming a slit in the disappeared area. Laser cutting is a non-contact machining method with low environmental impact, high machining accuracy, and the ability to process inclined surfaces. It has broad application prospects. However, changes in temperature and stress during the processing have a certain impact on the performance of the magnet, and when cutting thick products, there is a slope in the cutting section due to the divergence of the laser beam. 

2. Grinding process

Mainly refers to the processing method of grinding the surface of a product with a grinding disc or grinding wheel. The commonly used grinding methods for block neodymium iron boron magnet include vertical grinding, surface grinding, double end grinding, etc. Cylinder and ring neodymium iron boron raw magnet often use centerless grinding, square into round grinding, internal and external grinding, etc. Tile shaped, sector shaped, and irregular magnet can be formed using a multi-station grinding machine.

Surface grinding machine: used for surface grinding of magnetic materials, and can also perform multi sided machining. Generally, a horizontal axis rectangular table surface grinding machine (surface grinding) or a vertical axis circular table surface grinding machine (vertical grinding) is used. The magnetic steel flat surface is neatly stacked as a reference surface and fixed on the disk workbench with baffle fixtures, etc., and a grinding wheel is used for reciprocating surface grinding.

Double end grinding machine: A conveyor belt is used to continuously pass through the product, with two grinding wheels located on both sides of the product. The grinding wheels are driven by horizontal axis double grinding head rotation (the two grinding wheels generate an inclination angle), and the two planes of the product are ground under the rotation of the grinding wheel. Double end grinding machines have high machining accuracy and low surface roughness, making them the most widely used symmetrical plane machining equipment in neodymium iron boron machining.

Centerless grinding machine (or square into round grinding machine): Centerless grinding machine is used for outer circle grinding of cylindrical raw magnets, while square into round grinding machine is used for rounding of square magnet bars. Through the feeder and guide rail, the row magnet passes through the guide wheel and grinding wheel in sequence. The guide wheel drives the row magnets to rotate on the pad iron, and the grinding wheel grinds the outer circle of the row magnet to the required diameter.

Internal and external grinder: fix the row magnet through the fixture, and then make the grinding head move along the internal or external Circular motion of the products to grind the magnet to the set size of the internal and external circles, and make the surface smooth and remove burrs. Mainly used for the internal and external surface processing of ring magnets.

Formed grinder: It can grind various flat surfaces, curved surfaces, or complex formed surfaces through special grinding wheels (grinding wheel shaping), suitable for grinding without the need for motorized feed to meet the shape requirements of different types of products. Usually used for mechanical chamfering or irregular product processing of products.

3. Drilling processing

The drilling process of sintered neodymium iron boron is prone to fracture or fragmentation, therefore specific equipment and processes are required for drilling operations. The commonly used equipment for processing neodymium iron boron inner holes includes drilling machines, instrument lathes, and desktop drilling machines.

Drilling machine: A device that uses diamond circular cutting tools, and the product is fixed by a chuck and driven to rotate by a spindle. The tool feed is used to process the inner hole of the product. The hole cutting lathe is usually used to process neodymium iron boron products with an inner hole of more than 8mm. By using specially designed cutting and reaming tools, drilling and reaming can be completed.

Instrument lathe: The instrument lathe clamps magnetic steel products using a fixture, drives the product to rotate continuously through a spindle motor, and drills the rotating products using a fixed alloy tool. Mainly used for punching and threading cylinder, ring, and small square/block/rectangle products, with a machining aperture of less than 5mm.

Desktop drilling machine: a type of equipment that uses self-made tooling to locate products, and hard alloy cutting tools to rotate and feed, to achieve drilling and machining of products; The main difference with instrument lathe is that the product rotates and the tool is fixed while the desktop drilling machine, the product is fixed and the tool rotates. Therefore, desktop drilling machines can be applied to the processing of through holes, blind holes, and step holes in irregular products.

Ultrasonic Hole punch: the ultrasonic energy is concentrated to the drill bit position through the transducer, and the high frequency mechanical vibration of the drill bit drives the abrasive suspension to achieve impact perforation through high-speed impact, friction and cavitation. Ultrasonic drilling has high accuracy, efficiency, and qualification rate, and can be applied to small hole machining of magnets.

4. Chamfering:

During the processing of grinding machines, slicing, punching, and other processes, neodymium iron boron magnets can easily generate sharp corners that can cause edges and corners to fall off, and the tip effect during the electroplating process can lead to poor uniformity of the coating. Therefore, after machining, the magnets are usually chamfered, including mechanical chamfering and vibration chamfering. Common chamfering equipment includes vibration grinding chamfering machine and roller chamfering machine.

Vibration grinding chamfering machine: The vibration deviation generated by the vibration motor drives the magnets and abrasive in the working groove to move up, down, left, right, or rotate and rub against each other, thereby making the product surface flat and smooth, while grinding round edges and corners. Commonly used abrasive media include silicon carbide, brown alumina, etc.

Roller chamfering machine: It places neodymium iron boron magnets, abrasives, and grinding fluid into a sealed horizontal roller. The rotation of the roller causes the product to rotate and friction with the abrasives, playing a chamfering role.

We will choose the most economical and efficient processing methods based on product size specifications and geometric tolerance requirements. For the quality of processed products, we should mainly focus on dimensional tolerances, geometric tolerances, and appearance. Common defects in machining including: size deviation, poor verticality profile, missing corners, cutting thread, scratches, grinding marks, corrosion, hidden cracks, etc.