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Xiamen U Polemag Electronics & Technology Co., Ltd.
Brand holder
Main Products:Magnet Products
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Quality control procedure

Here we would like to explain the quality management procedure of neodymium magnets, which are well-known typical rare earth magnets. On our website, we have introduced the production sites, with the cooperation of our OEM manufacturer in China. (The procedures for quality management also differ slightly due to the different production procedures depending on the material such as ferrite magnet, samarium cobalt magnet etc.) In order to prevent defected products from being shipped out, design, production and finishing procedures are managed and inspected strictly by our company’s employees that have been assigned in China. We are committed to improvements and identifying the source of any issues by traceability, in the event of any failures.

 

No. Procedure Facility Characteristics Method Processing for failed products Images
No. Product Procedure Specification tolerance for production procedure, Control method Sample Management adjustment method
Worker Check
Allowance Frequency/time Allowance Frequency/time Worker Check
1 Acceptance of raw material   1 Structure   Work standard ICP analysis device   4 units Each batch Inspection statistical handbook ICP analysis report Return product

2 Appearance Visual check 4 barrel (cartons) Technical instructions
Inspection for alloyed Pr Nd 3 Contents ICP analysis device 4 units
2 Preparation of material Polishing cutter 1 Appearance   Inspection for changes, rust, oxidization, impurities Visual check All inspected Each batch   Re-treat
3 Melting   1 Mixing of materials
Weight inspection
  Instruction book for ratios of mixing materials Adjustment device for electrical scoreboard Once Each batch   Mixed procedure book   Re-treat Re-adjust  
4 Melting Vaccuum melting furnace 1   Recovery rate 97%-99.5% Adjustment device for electrical scoreboard   1pc Each input Daily record of melting Trend diagram  
2 Vaccuum pressure Instruction diagram for melting procedure Vaccuum gauge Once Each input   Daily record of melting inspection Separation limit
3 Argon pressure   Barometer   Each time
4 Cooling Time
5 Appearance after molding   Instructions for molding procedure Visual check   1pc Each batch  
Record of appearance inspection after making molding template
Separation limit  
6 Thickness after molding Instructions for molding procedure Micrometer 4pcs Each input Record of thickness inspection after making molding template  
5 Roasting under nitrogen environment (heat treatment) Nitrogen incinerator 1   Vaccuum pressure <=1Pa Vaccuum gauge Once Each input 1pc At each time of replacement HP original record HP record Separation limit
2 Nitrogen pressure 0.1-0.2Mpa Barometer
3 Conformity 2-2.5h Time
4 Dehydrogenation temperature 550°C-590°C Temperature control device
5 Dehydrogenation time 6-8h TImer
6 Cooling 3.5-4h
6 Pulverizing Puliverizing jetmill 1 Particle size   3.5-4.0 micron Measurement device for average sizes   Once Each barrel Daily report of size inspection (Average value)X-R chart Separation limit


2 Contains oxygen   Oxygen analyzer 100%
All inspected
Each batch   Record of pulverizing  
3   Separation rotation speed 3000-4500r/min Speedometer 100%
All inspected
Each batch 1pc Every day Record of pulverizing
7 Weighing powder Scale 1 Scale Measurement of weight of powder Production plan adjustment Scale 1 type Each time Each size 3 timesEach time 1 type Each time Record of molding Record of molding Re-make
8 Molding Magnetic forming machine 1   Magnetization current >40(A) Ammeter 100%
All inspected
Each time Each size 1pc Each time Record of molding Record of molding Reprocessing
Adjustment


2 Magnetization trend >=1500mT
>=1200mT
Gauss meter Once Each time Each size
3 Molding size   Production adjustment Caliper 1pc Each time Each size 3 timesEach time Re-make
4 Appearance No chips, impurities Visual check 100%
All inspected
Each size
5   Packaging
No air leaks after suction
No air leaks after suction
No air leaks after suction
 
Parallel magnetization 6 No air leaks Separation identification
9 Separation agent Nitrogen cartridge 1 Appearance   Parallet magnetization and oil removal, no oil leaks   100%
All inspected
Each time Once Each time Record of sintering Record of molding Separation identification  
2 Amount of oxygen contained   <1ppm Oxygen content meter Each time  
10 Sintering Vaccuum incinerator 1   Weight inside the incinerator Instructions for sintering Calculation (single weight x total) Once Each input Once Each time Record of sintering Record of sintering Separation limit





2 Sintering temperature Instructions for production Electrical scoreboard, temperature adjustment device 100%
All inspected
3 Sintering time
4 Tempering temperature
5 Tempering temperature
6 Vaccuum pressure Instructions for sintering Vaccuum gauge Once
11 Magnetic properties inspection   1 Calibration device   Coil for calibration Testing device for magnetic properties   Once Every day    
2 20+/-3°C
Br
Specification record Check regulations for sampling for material inspection Record of properties NdFeB Record of properties Separation or lowering of grade
3 20+/-3°C
Hcb
4 20+/-3°C
Hcj
5 20+/-3°C
(BH)max
6 Density Precision measurements >=2 PCS Each batch   Record of density testing Separation  
12 Centerless grinding Centerless 1 Dimension   Production adjustment Micrometer   AQL=1.00 Each batch   Record of grinding procedure Re-treat  
2 Appearance inspection, cracks, pinholes, chips, rust, finish
Appearance inspection, cracks, pinholes, chips, rust, finish
Finish, work standard
Finish, work standard
Visual check 100%
All inspected
Record of grinding procedure Separation
3 Chamfering Micrometer >=4 PCS Re-treat
4 Magnetization Measurement using micrometer of demagnetized magnet  
13 Bonding of material Bonding base 1 Perpendicular   Production adjustment Visual check 100%
All inspected
Each size   Record of cutting procedure Limit
Attaching material   2 Perpendicular Place the work piece perpendicular to the blade Anglemeter for blade
Cutting Cutter 3 Cutting speed Heavy hammer
3kg-6kHeavy hammer
3kg-6k
Scale
4 Cutting size Production adjustment Micrometer Each batch Re-treat
Removal of adhesive agent, cleaning
Removal of adhesive agent, cleaning
  5 Boiling time 1.5h-2h TImer Limit  
14 Pre-surface treatment inspection   1 Dimension   Work standards for pre-surface treatment Micrometer   AQL=1.00 Each batch   Sample record 100%
All inspected


2 Appearance inspection, cracks, pinholes, chips, cutting marks or scratches, sealing oil, flatness, holes, number of defects Visual check 100%
All inspected
Re-treat
3 Circulatory Micrometer 4% Separation
Re-treat
 
4 Magnetism Measurement using micrometer of demagnetized magnet Re-treat  
5 Number of pieces Instructions Instructions/measurement device 100%
All inspected
  100%
All inspected
Sample record Supplement  
17 Finish inspection Magnetization device 1 Dimension   Instructions Micrometer   AQL=1.00 Each batch   Record of sample of finished product Re-treat
2 Appearance inspection, cracks, pinholes, chips, cutting marks or scratches, rust, holes or surface treatment Work standards for measurements Visual check 100%
All inspected
3 Coating thickness Instructions Coating thickness gauge 2-6 PCS Record of coating thickness inspection  
4 Coating
Corrosion
Instructions for salt spray Salt spraying test 1-6 PCS Record of salt spraying
5 Coating
Corrosion
Surface magnetic flux density, work standard Gauss meter 10-80 PCS Sample record Select only defected products after inspection of all products
6 Total magnetic flux value Total magnetic flux value, work standard Fluxmeter 10-80 PCS
7 Number of pieces Production adjustment Instructions/measurement device 100%
All inspected
  100%
All inspected
Supplement  
18 Packaging   1   Packaging method Packaging specification Visual check     Twice At each time of replacement   Packaging record Re-treat


Sampling inspection

The below standard for sampling inspection is one of the standards set by Japanese Industrial Standards Committee. The inspection standard and number of samples (N) can be determined as necessary. The variability, tolerance and standard deviation is dependent on, and determined by the number of samples. Inspection standard: JIS Z9015/Inspection standard S4/AQL 1%

 

Lot size Strict inspection Average inspection Lenient inspection
(Number in 1 lot) Number of samples Number required for pass Number of samples Number required for pass Number of samples Number required for pass
Below 0 Below 0 Below 0
15  Below 0 Below 0 Below 0
16  Below 0 Below 0 Below 0
26  50  Below 0 Below 0 Below 0
51  90  Below 0 Below 0 Below 0
91  150  Below 0 Below 0 Below 0
151  280  13  Below 0 13  Below 0 Below 0
281  500  13  Below 0 13  Below 0 Below 0
501  1,200  20  Below 0 20  Below 0 Below 0
1,201  3,200  32  Below 1 32  Below 1 13  Below 1
3,201  10,000  32  Below 1 32  Below 1 13  Below 1
10,001  35,000  50  Below 1 50  Below 1 20  Below 1
35,001  150,000  80  Below 1 80  Below 2 32  Below 1
150,001  500,000  80  Below 1 80  Below 2 32  Below 1
500,001    125  Below 2 125  Below 3 50  Below 2

Appearance inspection

Appearance inspections are all conducted visually. Since the inspections are visual inspections, unfortunately it is not possible to prevent all defects in appearance and other failures. The permissible range for appearance defects varies according to the size. In principle, the permissible ranges are determined as below. Permissible ranges are determined beforehand and set forth in the product specification for products for which appearance is considered important and require mechanical strength. It is not possible to completely prevent chips and scratches on magnets as they have similar physical characteristics to china and glass and thus break easily. Therefore, unless there is a large chip that may weaken the magnetic characteristics or surface treatment that is stripping off which may lead to corrosion, the product will be accepted under concession.

 

 

Boundary sample for appearance

Item Diagram Dimension A B C Accepted number of defects Remarks Pass Fail
Chipped pole face φ5 ≦1.0mm ≦1.0mm ≦0.5mm ≦1pc There must be surface treatment on the chipped area  
φ10 ≦2.0mm ≦2.0mm ≦1.0mm ≦1pc
φ20 ≦2.0mm ≦2.0mm ≦1.0mm ≦1pc
φ30 ≦2.5mm ≦2.5mm ≦2.0mm ≦1pc
φ40 ≦2.5mm ≦2.5mm ≦2.0mm ≦1pc
φ50 ≦3.0mm ≦3.0mm ≦2.5mm ≦1pc
Chipped pole face φ5 ≦1.0mm ≦1.0mm ≦0.5mm ≦2pc
There must be surface treatment on the chipped area
φ10 ≦2.0mm ≦2.0mm ≦1.0mm ≦2pc
φ20 ≦2.0mm ≦2.0mm ≦1.0mm ≦2pc
φ30 ≦2.5mm ≦2.5mm ≦2.0mm ≦2pc
φ40 ≦2.5mm ≦2.5mm ≦2.0mm ≦2pc
φ50 ≦3.0mm ≦3.0mm ≦2.5mm ≦2pc
Pinhole All ≦0.5mm - - ≦2pc
There must be surface treatment on the pinhole area
       
Scratches Scratches, ex. by nails are not acceptable
There must be surface treatment on the scratched area
     
Crack All not acceptable Determine whether it is a crack or streak      
Discoloration due to rust There must be no discoloration due to rust and no areas may be have any bulging or paint stripping off  


※1 All items will be determined by visual inspection.※2 In cases which the inspection standards are set according to the boundary samples, the boundary samples shall take precedence.


Magnetic measuring device

There are various types of magnetic measuring devices that measure magnetic forces, depending on the inspection purposes. Below are typical measuring devices that are used mainly in the magnet industry.

 


Manufacturer Type Hall effect element
probe
Image of probe Neodymium magnet
φ10mm×10mm
Remarks
Denshijiki Industry Co. GM-4002 T-401 506.5mT Floor standing type
T-402 535.1mT Floor standing type
KANETEC Co. TM-601 TM-601PRB 488.0mT Mobile type
Simple accuracy device
Magfine Corporation   Magnetic calculator   494.1mT Predicted values based on magnetic calculations


Difference in measurement results due to difference in measurement device and probe. Testing material neodymium magnet φ10mm×10mm

Testing device for magnetic characteristics
 
Standard Magnets

A magnet that corrects or calibrates errors of tesla/gauss meters and fluxmeters are called standard magnets. Since tesla/gauss meters are precision devices, errors may occur due to age and environment. Even if such errors occur, these testing devices are designed so that they cannot be manually corrected. Therefore, standard magnets are used to conduct regular tests of the meters in order to calibrate any errors. The standard magnets are also regularly tested at a testing institution to check they meet magnet industry standards.

 
 

 
Fluxmeter

A fluxmeter measures the total flux and can accurately and quickly inspect a large volume of magnets to check which ones have a large or small variation in the characteristics. It is suitable when all the products need to be inspected or a large volume inspection is required. The unit used is Wb or Mx. It is necessary to build a search coil that suits the magnet to be tested so that it is possible to measure the variation of the total flux when the magnet is removed from the search coil.

 

 


 
BH analyzer

The BH analyzer measures the magnetic characteristics of magnetic material which then makes it possible to find out the demagnetization characteristics and energy product that is necessary for designing magnetic circuits. It can also check whether the values of the magnetic characteristics which are set forth for each magnetic material are within the specification range. In order to measure the characteristics, a powerful electromagnetic field and a power-supply device with a high voltage is required. It is mostly used at magnet manufacturing plants and magnet research and development institutions.

 

 

 
Tesla meter, gauss meter

The tesla meter or gauss meter measures magnetic flux density. A hall effect device is set up on the magnet surface or other surface and the density of the magnetic flux that passes through an area of 1cm2 . According to the definition of magnetic flux density, when 1 Mx of magnetic flux perpendicularly intercrosses, the magnetic flux density is 1 gauss. The unit commonly used for measuring devices is tesla or gauss. It is most widely used out of all the magnetic testing devices since it can easily check magnetic characteristics. The measurement values may largely vary because they are easily affected by the testing environment and testing method. Therefore even if the same magnet is tested by the same person in the same environment, in some cases, the measurement values may differ largely depending on the manufacturer, type, accuracy of the probe(hall effect device) , points measured on the surface and room temperature. Since the measurement enviroment criteria depend on the usage environment, absolute values like dimension tolerances cannot be indicated. For that reason, there may be a large difference in the measurements values indicated on our products and customer's measurement values. Measurement methods and environments differ according to the manufacturer and the testing standards within the industry are also not the same. The testing environment and magnetic flux density that shall serve as the standard shall be determined based on the testing environment used by the user.