June 29, 2021

Quality control: What is the AQL?

Most of the inspections made in Chinese factories are prepared and conducted by inspectors who follow the AQL standard. This standard defines the accepted defects limits according to the client’s expected quality, hence the name, Acceptance Quality Limit (previously Acceptance Quality Levels).

In other words, the AQL standard gives the number of products to inspect & the maximum number of defects the buyer is willing to accept.

In order to optimally use the AQL standard, the buyer must first set two critical tasks:

Build a clear and exhaustive list of checkpoints,
Finalise the quality levels expected from the production.

We will see below how to do this. But first let’s see what is the AQL.

How does the AQL work?

The AQL standard is made of two tables. Used properly, they tell the inspector to see the quantity of products to check and when to accept or reject the production.

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Why do we use the AQL?

The AQL standard that is most widely used by inspection professionals is the ANSI ASQ Z1.4 that was developed by the American National Standards Institute (ANSI) and the American Society for Quality (ASQ). It offers many advantages over the other inspection methods.

1. It limits waste

When the tests require the inspector to destroy a product (or a part of it), both the factory and the buyer prefer to limit the number of products tested. In that case, the AQL helps limit waste while keeping a clear idea of the quality level.

2. It reduces time and cost

Rightly so, many buyers think that the more products they inspect, the more confident they can be about the quality of an order. Indeed, there’s no better clarity than a test over 100% of the production. However, buyers must keep in mind that inspecting 100% of the production raises costs and time spent.

Let’s see what it takes to inspect 100% in terms of time and cost:
For example, you order 3500 computer displays from a factory in Shenzhen. It takes 2 minutes to perform all the required tests on ONE display. Totally, it takes 117 hours to test 3500 computer screens. That’s 15 days of non-stop inspections (8 hours a day). Inspections costs are based on man/day, so if a single inspector asks for $349 ; for 15 man/day, expect to pay around $5235, that’s a huge amount compared to the price of the goods. Furthermore, not many buyers are willing to wait 15 more days after production to ship their products. And no factory will accept to store the goods and monopolise factory workers for 15 days of inspections after production.

The AQL comes handy, allowing to check a sample size of the production within a day or two while keeping a clear view of the quality.
It’s also financially much more interesting for the buyers.

3. why not use a fixed percentage then?

Studies show that the inspection sample size does not equally grow with the order size. So the number of products to inspect should not be strictly linked to the order quantity. AQL inspections give equally reliable results without the need to check as many products.

How does AQL look like?

The AQL standard is construed of two tables. TABLE A, called “Sample Size Code Letters”, gives a letter that matches a sampling size. TABLE B, called “Single Sampling Plans for Normal Inspection” gives the number of accepted and rejected defects.

How to use the AQL tables?

The first table tells the sampling size. The second one defines the number of accepted and rejected defects based on acceptance levels.

1. Table A: setting the sampling size

A. Lot size = order quantity

The Lot Size is the quantity of your order for one type of product. If you order different products, you should consider them as different “lots”. In the table, lots are displayed as ranges. So if your order is 3,500 units, you follow the line “3201 to 10000”.

B. General inspection levels

Choose General Inspection Levels if your checkpoints require tests on all of the sampling size. There are 3 levels going from smaller (I) to bigger (III) quantity. You can choose the inspection level according to your budget and the risk you’re willing to take. Note that most of the inspections in China use Level II.

Lower inspection level means cheaper cost but higher risk.
Higher inspection level means higher cost but more clarity.

C. Special inspection levels

As the name suggests, these levels are used for special tests or inspection procedures that do not need to be performed on the whole quantity of the sampling size. So, Special Inspection Levels lead to smaller sampling sizes.

D. Sample size code letter

The letters in the middle of the table give an indication on the sampling size and range from A (smallest batch) to R (biggest batch).

2. Table B: collecting the accepted and rejected quantities

A. Sample size

This column gives you the sample size according to the letter that you collected from the first table.

B. Acceptance quality levels

This is your tolerance for defects in your order. That corresponds to the highest percentage of goods with a type of defect that you’ll allow. For example, you could accept to have a scratch defect on only 1.5% of your order. In that case, you should choose AQL 1.5.

C. AC= accepted defect quantity

This shows the quantity of defects you can accept.

D. RE = rejected defect quantity

This shows the quantity of defects from which you can refuse the order.

E. Vertical arrows

Sometimes, your sample quantity and the AQL do not give you “Ac” and “Re” right away. The arrows lead you to the advised “Ac” and “Re”.

Defining the checkpoints

The best practice asks buyers to define all the checkpoints before the mass production starts. That way, you make sure the factory understands your expectations in terms of quality, lowering the risk of defects during the production.

Once you have made a list of checkpoints, you may want to assign them different levels of tolerance. Inspectors classify defects in 3 categories:

Minor: defects that are unacceptable in high quantities but generally won’t result in product returns.
Major: defects that would likely result in product returns but don’t pose a safety risk to the user.
Critical: defects that violate regulations or pose a threat to user safety.

Here’s how most inspectors assign Inspection Levels to defect categories:

Minor -> AQL 4
Major -> AQL 2.5
Critical -> AQL 0

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Let's check with a practical example

You purchased 2500 tablets and want to control their quality through AQL standard. In the first table, “Sample Size Code Letters”, check the line corresponding to your order quantity: “1,201 to 3,200” and the column “General Inspection Level II”, which is the standard for normal inspections in China. We get the letter K.

Let’s check the second table, “Single Sampling Plans for Normal Inspection”, to have concrete information regarding the quantity of inspected items and the limits for accepted and rejected defects. The letter K from the first table tells us that we should inspect 125 tablets. Our inspectors advise AQL 4 for minor defects, AQL 2.5 for major defects and AQL 0 for critical defects.

We now have a look at your checkpoints and the defects found:

Checkpoints in minor defect category = 10 accepted defects. Refuse order from 11 defects.
Checkpoints in major defect category = 7 accepted defects. Refuse order from 8 defects.
Checkpoints in critical defect category = 0 accepted defects. Refuse order from 1 defect.

Assuming that each tablet can be inspected in 2 minutes, this inspection can be done in 1 day by 1 inspector (meaning 1 man/day).
It should be mentioned that if you want to inspect 100% of this order, it will take 11 man/days.

Is AQL enough?

The AQL standard is very useful for all the appearance defects (size, colour, etc.). Nevertheless, it does not reflect the overall quality status of your order because it does not include the inspections of:

On-site tests for functionality, safety and performance,
Regulations and distributor requirements.

You should not rely on the result of the AQL tests only, but on the final inspection report result, given by the inspection company.

To sum up the AQL

A professional inspection company usually advises their clients on the inspection method according to the buyer’s requirements. However, it is not done all the time, and early in the process the responsibility falls on the shoulder of the buyer to provide a comprehensive list of checkpoints that are categorised (minor, major, critical). They also should share with the inspectors their situation in terms of risk aversion, financial budget and schedule. Eventually, most of the buyers agree to follow the AQL standard, giving them an objective view of the order’s quality while keeping fees quite low.

You have quality issues?

A word of advice from ASIACTION experts

Most of the QC companies offer a very limited assistance before, during or after the inspections. They ask you to fill in their long inspection forms (usually not very user-friendly), to prepare the booking with the factories and to follow the inspection schedule with these factories. After the inspection they usually send you an inspection report with little to no explanation. Basically, you end up all by yourself trying to decipher the report and to fix the potential problems with a Chinese factory far from you.

At Asiaction, our team in China personally helps you build up the checkpoints and their categorisation in a clear inspection sheet. We then are completely available during the booking and the inspection. We send urgent warnings if necessary during or right after the QC. After the inspection, we send you a comprehensive report and our experts are still available for any clarification.

Most importantly, ASIACTION have experts who advise and help you to resolve cases with your Chinese suppliers after the QC.

If your QC report presents defects leading to a failed status of the order, contact us to get our help on negotiation with the factories whether you prefer to have a discount, to fix the problems or to refuse all or a part of the order.