Can you only use the industry standard AQL form to determine the sample size suitable for your product inspection
? According to AQL standard, what is the maximum number of defects allowed to accept orders?
For most importers, it is no secret that product inspection is an important process to determine whether the goods meet their expectations. However, many importers do not understand the sampling methods used by quality control professionals to inspect their products. You may see AQL charts, but you don't know what the various parts of the chart mean or how to use them. Or you may not know how to interpret the AQL results displayed in the inspection report.
You can use a simple AQL calculator to quickly get the information you need. However, understanding how the table works can help you interpret the results of the inspection and decide how to take action on them. Therefore, let's continue the step-by-step process of QC inspection using AQL form.
4 steps to determine sample size and defect tolerance using AQL table
Since the U.S. military adopted the sampling procedure during World War II, several acceptance sampling standards have come and gone. Today, most quality control inspectors Use ANSI ASQ z1.4 standard AQL form, which is the table we focus on here. This chart will help you decide how many units are randomly selected from the total order quantity for inspection and the maximum number of acceptable defects in the finished product.
1. Select inspection type and inspection level
The inspection type will be "general" or "special" as shown in the two columns in the first part of the table. You probably want to use general because it represents the primary sample size you will use for the examination. Special inspection types are reserved for specific types of product tests and other inspections, which you only need to perform on a small part of the order.
Many inspection levels divide each type of inspection. The leftmost column includes higher inspection levels, representing a larger range and contributing to a larger sample size. For example, most general examinations belong to the most popular "GII". Importers who need less thorough inspection and importers with relatively limited inspection budget can choose "Ig" for smaller inspection samples. Importers who pay more attention to quality can choose "gIII" to obtain larger samples.
2. Find the sample size letter corresponding to the selected batch size and inspection level
Batch is the quantity of each SKU or item in your order. You may need to consider merging similar SKUs for inspection, because checking multiple SKUs individually will greatly increase the time and cost of inspection.
Suppose you are using AQL to check 3000 watches you purchased from a factory in Yiwu, China. There are five different SKUs in the order, but because they are only different in color, you chose to combine SKUs and control them as one. Find your hands in the range indicated in the hands column, from "1201 to 3200".
If you select the general inspection level GII, you will find that the letter "K" appears at the intersection of the batch size row and the inspection level column. This is your "sample size code letter", which represents the sample size in another part of the AQL chart. You will use this in conjunction with an acceptable quality level to determine how many units to extract for inspection.
3. Select your AQL for inspection
In the second part of the AQL chart, you will find the acceptable quality level (AQL) at the top and the sample quantity code letter on the left. You can clearly see that your sample number code letter K corresponds to a sample number of 125 units. Where's your AQL?
Your AQL represents your relative tolerance for quality defects, that is, the worst average percentage or ratio of acceptable defects. A higher AQL represents a higher tolerance. This is not to say that your goal is to have some defective units in your order. Instead, you should limit the number of defects you are willing to accept in your order. This is why some professionals began to use the acceptable quality limit of the term rather than the acceptable quality level of the original term.
If you have classified quality defects as "serious", "major" or "minor", you will usually use a unique AQL for each type (related: 3 types of quality defects in different products). In this example, we used 0%, 2.5%, and 4% AQL for critical, major, and minor defects, respectively.