What does AQL mean?
When using 3rd party QC, AQL standards are one important factor to understand how to select random samples for product inspections.
The most commonly used standard for product inspections is standard ISO 2859-1 (ANSI/ASQC Z1.4-2003). It uses the concept of AQL, or Acceptable Quality Limit.
The definition of the AQL (Acceptable Quality Limit) 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”.
A sampling size, based on the AQL tables, will be selected and then inspected for defects.
Defects are broken into 3 categories: Minor, Major and Critical. While these can vary from client to client, the typical definitions are as follow:
- A Minor defect is a discrepancy from the standards, but one that is not likely to affect the usability of an object.
- A Major defect is one that is likely to create failure of the unit for its intended purpose.
- A Critical defect is one that is deemed to be hazardous or unsafe.
According to the number of defects found for each type and according to the number of defects allowed (figures given by the AQL sampling tables), your QC company can advise you to accept or to reject your shipment.
How to use the AQL Tables?
Client can set their Acceptable Quality Tolerance but the AQL tables will help to determine the sampling size we will need to inspect according to your ordered quantity and your level of severity. You can choose Levels I, II or III, with Level III being the most stringent testing and Level I being the least. The standard level, the one used by default and by 98% of the people is the Level II. This is up to the client, but it is the recommended level.
In order to find the necessary sampling size to be inspected, you must first look at the first chart and find on the left side the range of items being produced in total. For example, if you are producing 8000 items, at Level II you have the letter L, which in the second table corresponds to a sample size of 200.
On the top of the second chart are the defect levels, ranging from 0 to 6.5 (we cut the higher values out of the chart, because they are not relevant for buyers of consumer goods).
You can choose which level to apply for your type of defect: critical, major and minor. Usually most importers will choose standard defect levels which are 0/2.5/4.0, AQL 2.5, but one can choose 0/1.5/2.5 if he wishes.
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 results belongs to you. Most importers will 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 level of found defects is acceptable to you or not.