Sintered neodymium - iron - boron (NdFeB) magnets are widely used in various fields due to their high magnetic performance. The manufacturing process of these magnets is complex and involves several key steps.

Raw Material Preparation

The first step is to prepare the raw materials. High - purity neodymium (Nd), iron (Fe), boron (B), and sometimes other alloying elements such as dysprosium (Dy) and terbium (Tb) are carefully selected. These elements are typically in the form of metals or metal compounds. The purity of the raw materials is crucial as impurities can significantly affect the magnetic properties of the final product. For example, even trace amounts of certain elements can reduce the coercivity and remanence of the magnet.

Melting and Alloying

The prepared raw materials are then melted together in a high - temperature furnace. This melting process is carried out under a controlled atmosphere, usually an inert gas like argon, to prevent oxidation. The alloying process aims to achieve a homogeneous mixture with the desired chemical composition. The temperature and time of melting are precisely controlled. After melting, the alloy is cast into ingots, which are then crushed into small pieces for further processing.

Milling and Powder Preparation

The alloy pieces are milled into fine powders. There are different milling techniques, such as ball milling. During ball milling, the alloy pieces are placed in a container with grinding balls. As the container rotates, the balls collide with the alloy pieces, gradually reducing them into fine powders. The particle size of the powders is carefully monitored as it affects the magnetic properties and the subsequent sintering process. Generally, a narrow particle size distribution is preferred.

Magnetic Alignment and Pressing

The milled powders are then placed in a die and subjected to a strong magnetic field. This magnetic field aligns the magnetic moments of the powder particles in a specific direction. After alignment, the powders are pressed under high pressure to form a green compact. The pressing process gives the magnet its initial shape and density.

Sintering

The green compact is sintered in a high - temperature furnace. Sintering is a crucial step as it densifies the compact and improves the magnetic properties. During sintering, the powder particles bond together, and the microstructure of the magnet is formed. The sintering temperature is typically around 1000 - 1100 °C, and the heating and cooling rates are carefully controlled. After sintering, the magnet has a relatively high density and good magnetic performance.

Machining and Surface Treatment

The sintered magnet may need to be machined to achieve the final desired shape and dimensions. Machining processes such as cutting, grinding, and drilling are used. After machining, surface treatment is applied to protect the magnet from corrosion. Common surface treatments include electroplating (such as nickel - copper - nickel plating), epoxy coating, and passivation.