Introduction to Precision Machining of Magnets

    Magnet finishing refers to the cutting of sintered magnets to a certain extent, such as grinding, parallel grinding, outer or inner diameter grinding, and magnet block cutting. Magnetic materials are brittle and have high hardness, with Rockwell hardness (C-scale) ranging from 57 to 61. Therefore, their cutting and grinding processes require the use of diamond cutting blades and diamond grinding wheels or specialized grinding wheels. The cutting accuracy is very high and usually does not require subsequent grinding. All these processes must be very careful to minimize peeling and cracking phenomena.
    In some cases, the resulting irregular magnet shape is beneficial for the processing of diamond grinding wheels, such as curved and bread shaped magnets. Products close to the final shape can be polished with grinding wheels to obtain accurate dimensions. In order to realize small batch manufacturing of complex shapes, Electrical discharge machining is usually used. For simple two-dimensional shapes, the machining speed of EDM machines is faster, while for more complex shapes, the machining speed of 3-5 axis machines is slower. Cylindrical magnets can be pressed into shape, usually using axial compression, and can also be drilled from the billet using a hollow drill. Then cut these longer solid or hollow cylinders into cylindrical magnets of various sizes.
    For mass production (usually no less than 5000), it is more economical to manufacture molds and produce according to shape. If the production cycle is short or specific properties are to be obtained, the method of cutting magnets from billets may be better. Pressing and forming can minimize waste materials such as grinding debris. The order quantity, part shape and size, and complexity determine which manufacturing method is more advisable. The delivery time can also affect this decision, as the method of obtaining small batches of parts from billets may be more efficient than ordering molds and then pressing them into shape. The production costs of these methods can sometimes not be directly estimated.
    Although it can be processed into complex shaped irregular magnets, it is more suitable for simple shapes and has higher production costs for punching, chamfering, or slotting. Some complex shapes can easily cause flux field changes, which can potentially affect the components in the assembly under stress, making it more difficult to control tolerances during production.
The sharp edges of the cut magnet are prone to peeling and scratching hands, and it is also difficult to apply coating around the sharp edges. The most commonly used method to reduce sharpness is to use a vibrating grinder for grinding, commonly known as vibration rolling, which is carried out in abrasive. The rounded corners of the edges are determined based on subsequent processing requirements, with radii typically ranging from 0.005 inches to 0.015 inches (0.127 to 0.38 millimeters).