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Sintered Nd-Fe-B Magnets

Nd-Fe-B

The successful development of Nd-Fe-B magnets marked the birth of the third generation of rare earth permanent magnets.

Sintered Nd-Fe-B magnets (also known as neodymium magnets) are currently the most powerful magnets in terms of magnetic properties.

They are particularly suitable for mass production of various shapes and sizes, and can achieve precise dimensional control during processing.Thanks to these advantages, sintered Nd-Fe-B magnets have been widely used in numerous commercial fields, such as high-performance motors, brushless DC motors, magnetic separators, magnetic resonance imaging (MRI), sensors, loudspeakers, consumer electronics, and green energy.

PROCESSING SHAPES OF ND-FE-B

MAGNETIC PROPERTIES 01

Material Grades

The grade of sintered Nd-Fe-B magnets is usually defined by the format: letter N + number + letter(s). The letter N is the abbreviation of the rare earth element Neodymium. The number represents the maximum energy product (BH)max of the magnet, with the unit being Mega Gauss-Oersted (MGOe) in the CGS system. One or two letters may be added after the number to indicate the intrinsic coercivity (Hcj) and the maximum operating temperature of the magnet. Common grade designations are:

Medium

High

Super High

Ultra High

Extra High

Abnormally High

Their corresponding Hcj (intrinsic coercivity) should be greater than 14, 17, 20, 25, 30, and 35 kOe respectively. Correspondingly, the maximum operating temperatures of the magnets can reach 100℃, 120℃, 150℃, 180℃, 200℃, and 230℃ respectively.

MAGNETIC PROPERTIES 02

Material Performance

Neodymium-Iron-Boron Magnet Grades Summary Product List & Reference Guide

Neodymium iron boron (NdFeB), or "neo" magnets offer the highest energy product of any materialtoday and are available in a wide range of shapes, sizes and grades. agnetic properties will differdepending upon alignment direction during com paction and upon size and shape.

Neodymium Iron Boron.pdf

8.4MB

PHYSICAL PROPERTIES OF MATERIALS

In addition to permanent magnetic properties and corrosion resistance, the operational stability of sintered Nd-Fe-B magnets is also closely related to their unique physical properties. Besides conventional density and hardness, the physical properties of sintered Nd-Fe-B magnets include mechanical properties, electrical properties, and thermal properties.

Mechanical Properties

Mechanical properties mainly include: compressive strength, tensile strength, and flexural strength. These three indicators have a significant impact on the machinability and long-term service performance of sintered Nd-Fe-B magnets.

Electrical Properties

The electrical properties of alloy materials are usually characterized by resistivity. Sintered Nd-Fe-B magnets have relatively low resistivity, so they are prone to eddy current loss when applied in high-speed rotating machinery.

Thermal Properties

The thermal properties of sintered Nd-Fe-B magnets are usually measured by the coefficient of thermal expansion. The thermal expansion of sintered Nd-Fe-B magnets will directly lead to dimensional changes; if there is a large difference in thermal expansion between the magnet and the assembly material, the magnet will generate a certain amount of stress in the magnetic device due to dimensional changes, which may cause mechanical damage and degradation of magnetic properties.

SURFACE TREATMENT

Surface Protection Treatment

Surface protection treatment is an indispensable process for sintered Nd-Fe-B magnets. The neodymium-rich phase exhibits a strong tendency to oxidize and will form a galvanic cell system with the main phase in a humid environment. Eventually, the neodymium-rich phase is corroded, and the main phase particles gradually peel off from the magnet body.

Two Processes

The surface protection treatment of sintered Nd-Fe-B magnets can be divided into wet processes and dry processes. Common wet processes include: electroplating, electroless plating, electrophoresis, spraying, and dip coating. Dry processes include physical vapor deposition (PVD) and chemical vapor deposition (CVD).

MAGNETIZATION

Axially Magnetization

Diametrically Magnetized Magnet

Axially Multipole Magnetization

Diametrically Multipole Magnetization

Radially Magnetization

MACHINING

Wire Cutting (Electrical Discharge Machining/Wire Electrical Discharge Machining, EDM/WEDM): Suitable for parts with complex shapes and high dimensional accuracy requirements. Diamond Grinding Wheel Cutting: Used for simple cutting and splitting processing.

Grinding

Commonly used diamond grinding wheels for surface grinding, cylindrical grinding, internal grinding, etc. High dimensional accuracy and surface quality can be achieved.

Drilling and Forming

Small holes or special-shaped holes are usually drilled with diamond drill bits. Special shapes are achieved through a combined process of grinding + wire cutting.