Size and shape tolerance of NdFeB magnet

Neodymium iron boron magnets are important parts of many manufacturing products, such as motors, horns, detection instruments, etc. Users generally have certain requirements for the dimensional tolerance and shape tolerance of neodymium iron boron, because the unqualified product size will cause neodymium Iron-boron components cannot be installed, and even damage the machine. Substandard sizes often lead to the risk of batch returns.

Actility has compiled the basic requirements for dimensional tolerances and geometric tolerances in the national standards of sintered NdFeB magnets and bonded NdFeB magnets, which can be used when designing and selecting materials.

Dimensional and geometric tolerances of bonded NdFeB permanent magnet products

The size and shape tolerance of bonded neodymium iron boron permanent magnet products are different due to their application fields and shapes. Taking the ring as an example, the tolerance values of the same size and shape are divided into three categories: A, B, and C , Provide the following data for reference when designing and selecting materials. The dimensional tolerance of the product is shown in Table C.1, and the geometric tolerance of the product is shown in Table C.2.

Table C.1

Table C.2

Block shape tolerance control standard				Disc shape and position toleranc control standard
Block magnet				Block magnet
Length Dimension(mm)	Tolerance(mm)	Perpendicularity	Parallelism（mm）	Outer diameter(mm)	Tolerance(mm)	Cylindricity
L≤10	±0.03	≤0.5°	0.03	D≤10	±0.03	0.03
10<L≤30	±0.05	≤0.5°	0.04	10<D≤30	±0.04	0.03
30<L≤50	±0.05	≤0.5°	0.05	30<D≤50	±0.05	0.05
L>50	±0.08	≤0.5°	0.08	D>50	±0.06	0.06
Form and Position Tolerance Control Standard for Tile Products				Tolerance control standard for shape and position of ring products
Segment magnet				Ring magnet
Name(mm)	Dimension(mm)	Tolerance(mm)		Inner diameter(mm)	Tolerance(mm)	Coaxiality（mm）
Wall thickness	T≤10	±0.04		D≤10	±0.04	0.06
	10<T≤30	±0.05		10<D≤30	±0.05	0.08
	30<T≤50	±0.06		30<D≤50	±0.06	0.1
Length	L≤10	±0.04		50<D≤80	±0.08	0.12
	10<L≤30	±0.05		D>80	±0.1	0.15
	30<L≤50	±0.05
	L>50	±0.08
Width	W<50	±0.05
	W≥50	±0.08

Only when the measurement of size and form and position tolerance are qualified, the assembly of the workpiece is safe and reliable. Some manufacturers do not pay attention to the geometric tolerances, which makes the parts unable to be assembled, which leads to customer complaints or returns. NdFeB magnet manufacturers basically use the following two delivery standards when delivering:

• 1. Micrometer;
• 2. Pass and stop regulations.

Micrometers can only measure dimensions, but cannot measure geometric tolerances. Through-stop gauge can measure size + form tolerance. It is often the case that the measurement with a micrometer is qualified, but the stop gauge cannot pass. This is because when the dimensions are qualified, the geometric tolerances are not qualified, and assembly is still impossible.

The output of NdFeB in my country has been increasing year by year. Its workpieces are small in size and light in weight. This application advantage has happened to be the difficulty in the inspection process: large quantities and small sizes lead to large manual inspection workloads, slow inspection speeds, and low accuracy.
At present, the quality inspection workshops of most NdFeB manufacturers mainly rely on manual visual inspection. The disadvantages of manual inspection are high subjective error rate, slow detection speed, and high labor cost. These problems have become the bottleneck of the development of enterprises, and increasingly become one of the factors hindering the development of my country’s NdFeB industry.

The use of automated testing equipment is already on the line. According to industry analysis, this trend will become an industry trend to solve the dilemma of NdFeB quality inspection. With the continuous increase in output, some NdFeB companies have begun to seek innovation and change, and gradually use automated testing equipment to replace traditional manual testing.

Source: China Permanent Magnet Manufacturer – www.rizinia.com