What does AQL?
AQL, or Acceptance Quality Limit, is defined as “quality level that’s worst tolerance in standard ISO 2859-1, it’s a statistical tool to inspect a particular sample size for a given lot and set maximum number of acceptable defects.
In order words, it is the worst tolerable process average when a continuing series of lots is submitted for acceptance sampling.
There are normally three limits chosen, one for critical, major and minor. Usually, each of these three limits is different for each category, and most Asia exporters are familiar with type of setting,
AQL also named “acceptance quality level” before, it is an important statistic for companies seeking Six Sigma level of quality control. and the AQL of a product would vary from industry to industry,
Companies dealing with extreme sports equipment or medical tools would have more stringent AQL, as acceptance of defective products could result in health risks.
Keywords: AQL Table/ANSI AQL Chart:
The standard definition of Acceptance Quality Limit (AQL) is “the maximum defective percent (or the maximum number of defects per hundred units) that, for purpose of sampling inspection, can be considered satisfactory as a process average”.
Keywords: three types of defects for consumer goods:
- Critical Defects: Totally unacceptable defects, when accepted could lead to harm the users. or regulations are not respected. It is defined by 0% AQL
- Major Defects: Defects usually not acceptable by the end users, the AQL for major defect is 1.5 or 2.5%
- Minor Defects: Defects, which are not likely to reduce materially the usability of the product for its intended purpose but slightly differs from specified standards. most end users won’t mind it. The AQL for minor defects is 4%
Keywords: lot size in AQL Chart
Quantity of each product is the lot size, if you ordered different products, then each product consider as a seperate lot.
Keywords: General Inspection level (G-I, G-II, G-III)
Different inspection levels will command different numbers of samples to inspect. General Level II in single sampling plans is the normal used sampling method.
Keywords: Special Inspection level (S-1, S-2, S-3, S-4)
The special levels can be applied in cases where only few samples should be checked, mostly the special levels are used only for certain on site testings, and spot check during container loading supervision.
Keywords: ASQ Z1.4
ANSI/ASQ Z1.4-2003 (R2013): Sampling Procedures and Tables for Inspection by Attributes is an acceptance sampling system to be used with switching rules on a continuing stream of lots for Acceptance Quality Limit (AQL) specified.
It provides tightened, normal, and reduced plans to be applied for attributes inspection for percent nonconforming or nonconformities per 100 units.
How to use the AQL Table?
The AQL table will help you to determine the sampling size, we will need to inspect according to your ordered quantity and your level of severity (G-I, II or III).
And the standard level, the one used by default and by 98% of buyers is the level G-II for a standard AQL inspection.
If your order has multiple references, ideally we should at least inspect a level II on each reference.
Indeed, for a standard order, the standard level II from the AQL table gives the minimum sampling size we should check per reference if we do not want to take additional risks.
If we inspect a G-II sampling size on a multiple references orders, then the AQL sampling size is diluted and divided by the number of references, increasing the risks as the sampling size must be representative enough.
In order to find the necessary sampling size to be inspected, we look at the first chart and find on the left side the range of items being produced in total.
You have the choice of levels I, II and III, with Level III being the most stringent testing and level I being the least. as we said above, Level II is the standard and is most often used.
For example, if you are producing 8000 items, at AQLChart level II you have the letter L, which in the second table says to inspect 200 items.
|General inspection levels||Special inspection levels|
On the top of the second chart are the defect levels, ranging from 0 to 6.5. You can choose which level to apply for your type of defect: critical, major and minor. (More: product inspection standard)
Usually most importers will choose standard defect levels which are 0/2.5/4 but one can choose 1/1/1 if he wishes or 0/1.5/2.5 like in the automotive industry.
Using the standard 0/2.5/4 defect levels and a sample size of 200, we see that if you have more than 0 critical defects, 10 major defects or 14 minor defects, you should reject your shipment.
Of course the decision about what to do after your received the inspection reports belongs to you, inspection only can give suggestions.
So most importers will put AQL into the purchase contract and inspection checklist to avoid any misunderstanding in production, suppliers will be clear with your quality requirementss.
Importers will also wish to discuss all inspection findings with their vendor/manufacturer in order to improve whatever possible. In case the inspection results are very close to AQL limits, it is important that you double check if the AQL of found defects is acceptable to you or not.
|Sample size||G-II AQL 0/1.5/2.5||G-II AQL 0/2.5/4.0|