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Understanding and Implementing Acceptable Quality Limits (AQL) in Quality Control

Intro: Quality control is an indispensable period in bulk production, especially when related to private label custom.


Since the order quantity can vary from 500 to 10,000, how can we ensure the best quality?


During the inspection period, how many samples shall we select? 100% inspection can be time-consuming and labor-intensive.


So, is there any official standard or reasonable method?


We must mention the AQL, which you may have heard of in many industry inspections.

 

Intro


What is AQL?

AQL Tables - How to use AQL?

How does AQL work?

Conclusion


 

What is AQL?

The acceptable quality level (AQL) is a measure applied to products. You can define it as the worst tolerable quality level you can accept.


The AQL tells you how many defective components are considered acceptable during random sampling quality inspections.


It is usually expressed as a percentage or ratio of the number of defects compared to the total quantity.


For example, AQL 2.5 means no more than 2.5 of an order can be defective in order for it to be acceptable. If more than 2.5 of the other is defective, then it doesn't meet the buyer's and producer's agreement.


For 10,000 pieces of tote bags, AQL 2.5 demonstrates that only 250 tote bags can be defective.


But, how many samples shall we select for a 10.000 order?

 

AQL Tables

The “AQL tables” are statistical tools at the disposal of buy inspection levelers (for product inspections). They are an industry standard. Most suppliers involved in international trade are familiar with it.


The AQL tables help answer the following two questions:

  1. How many samples shall we pick?

  2. If there are defective products, how many defective products reach the bottom line?

Table 1 tells how to determine the quantity of the selected sample. If the quantity of products is 3,500 pcs, which means the lot size is 3500, the inspection level comes to G2. Then we get the letter "L."



According to the letter "L," the number of samples is 200. Then we need to know the percentage. As I have mentioned above, AQL 2.5 in 200pcs means there are no more than 10 products with major defects, and 11 products with minor defects.


But how do we define the different defects?

 

How does AQL work?

To take the AQL into practice, we have to know three defects: critical defect, major, defect, and minor defect.


  • Critical Defect:

Critical defects are those harmful elements, which possess huge risks. Such defects are unacceptable. Critical defects are defined as AQL 0.


When it comes to luggage inspections, we can define critical defects as luggage wheels in specific.


Luggage wheels are the most important component in the whole case. Its functionality and safety can be fatal in consumers' usage.


There are various kinds of luggage tests to ensure standard quality to avoid fragile luggage wheels, such as mileage testing, wheel abrasion testing, drop testing, and so on.

Drop testing

The picture above came from one of our QC. Drop testing is used to examine the durability of luggage wheels.


If the wheels are found to be broken or crackable, then we may define the problem as critical defects.


Apart from drop testing, more testing methods and concrete standards can be found here.

  • Major Defect

Major defects are usually not acceptable by the end-users, as they are likely to result in failure. The AQL for major defects is AQL 2.5.


Generally, we inspect major defects from two perspectives: functional check and visual check.


Visual check inspects defects that are obvious at first sight. For example, black dots on the fabric, rusting on metal trims, etc.


Functional check focuses on components that support the product in daily usage. For instance, zippers, and buckles decide if the tote bag is for convenient use.


More inspection subjects follow the table:

  • Minor Defects

Defects are not likely to reduce the usability of the product materially for its intended purpose, but that differ from specified standards; some end users will still buy such products. The AQL for minor defects is AQL 4.0.


Similar to major defects, minor defects also can be categorized into two parts: visual check and functional check.


Differences lie in that major defects inspire much more than minor defects.

Concrete situations:

Dirty mark-minor Untrimmed thread ends-minor Poor sewing-minor

 

Conclusion

AQL, as an inspection method, is widely used in many industries. Its high sufficiency has been verified through multiple practices.


In specific, the luggage&bag industry also takes advantage of AQL inspection. It's more like a set regulation and routine.









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