In the last article, we explained the different inspection levels that can be used. Another basic concept rings familiar to many importers, but is often not clearly understood: the AQL (Acceptance Quality Limit).

There is no such thing as zero defect

First, as a buyer, you have to know what proportion of defects is tolerated on your market. If you are in the aviation business, any defective part might cause a disaster, so your tolerance will be very, very low. But you will have to accept a higher percentage of defects if you source consumer products made by hand in China.

An objective limit is necessary

So, how many defects are too many? It is up to you, as a buyer, to make this decision. There are two reasons why you should not leave this to the inspector’s judgment: 

1.  When it comes to giving instructions to an inspector, you should never leave gray areas—as they might open the door to corruption.
2. Your supplier should have clear criteria for acceptability, or they will see rejections as unfair. The AQL is the proportion of defects allowed by the buyer. It should be communicated to the supplier in advance.
   

The three categories of defects

Some defects are much worse than others. Three categories are typically distinguished:

• Critical defects might harm a user or cause a whole shipment to be blocked by the customs.
  
• Major defects are not accepted by most consumers, who decide not to buy the product.
  
• Minor defects also represent a departure from specifications, but most consumers would still buy the product.

For most consumer products, the critical defects are not allowed, and the AQL for major defects and minor defects are 2.5% and 4.0% respectively. Remark: a professional inspector will notice defects and evaluate their category by himself. But it is better if the buyer himself describes the most frequent defects and their categories. .

How to read the AQL tables

The master tables included in the relevant standards are commonly called AQL tables. Let’s take an example.

 

You buy 8,000 widgets from a factory, and you choose the normal inspection level. In the table below, you see that the corresponding letter is L.

 

 

 

 

 

 

 

Now let’s turn to the next table. (It is only appropriate for normal-level inspections). The letter L gives you the number of samples to draw at random: 200 pcs. And what about the AQL? Let’s say you follow the usual practice of tolerating 0% of critical defects, 2.5% of major defects, and 4.0% of minor defects. The maximum acceptable number of defects is 7 major and 10 minor. In other words, the inspection is failed if you find at least 1 critical defect and/or at least 8 major defects and/or at least 11 minor defects

Additional notes, for accuracy

• The number of defects is not the only cause for acceptance of refusal. The products can be refused because they are not conform to the buyer’s specifications, even though their workmanship is very good.
  
• If you have two different products (made with different processes or in different factories), you should do two separate inspections. If you inspect them together, one product might be accepted even though it presents too many defects. Why? Because the better workmanship of the other product might “compensate” for its poor quality.

Now you know how many samples should be selected, and how many defects can be tolerated. But when should inspections take place? After production is finished? Won’t it be too late for corrections if quality problems are discovered? These topics will be covered in the next article.

 

Renaud Anjoran is the founder of Sofeast Quality Control, a third-party QC firm specializing in garments and textile in China. He also writes on the Quality Inspection blog. You can contact him at info@sofeast.com.