AQL for product sampling and inspection.

AQL for product sampling and inspection. 

AQL  for product sampling and inspection. So let's get started. Before we get into the details of AQL and how it's used for inspection, let's first look at why you might use sampling,instead of inspecting 100 percent of an order. Inspection of 100 percent of an order is: 

1. Costly and

2. Time consuming.

Whereas inspection of a random sample of product saves time and money, while still providing an accurate look at an order of goods.

In this way, an inspector is able to take inventory pull a random sample of goods and inspect the units in the sample to report statistically significant findings. Now let's talk about AQL. AQL stands for acceptable quality limit. For the purposes of product inspection, AQL represents the highest number of quality defects allowed in a certain ratio, or sample, of product. If the number of quality defects found exceeds this AQL, that order generally fails inspection. And in the event of a failed inspection, the importer or manufacturer may decide not to ship the finished goods, but instead to rework them or carry outsome other corrective action. Here is the AQL chart, a QC-industry standard derived from the American National Standards Institute (ANSI) and the American Society for Quality (ASQ).

Included in the chart, you'll see:

lot sizes, 

General inspection levels and 

Special inspection levels. 

On the reverse of the chart, you'll find:

Sample size code letters, 

Sample sizes, 

Acceptable quality levels, 

Accept maximums and 

Reject minimums. 

So how do you use this AQL chart to determine sample sizes? 

Let's look at an example. We'll use the example of an order of LED light bulbs to keep it simple. Imagine you have an order of 960 bulbs that you need inspected prior to shipping, and you want to know what sample size to use during inspection. First look back at the AQL chart. Find your lot size, 960 pieces, in the range of lot sizes shown. If you look to the right of that lot size range, 501 to 1200, you'll see three general inspection levels: G1, showing the sample size code "G", G2, showing the sample size code "J", and G3, showing the sample size code "K". We'll stick with the general inspection levels, since you'll typically use these for inspection, rather than special levels. And let's say you want a relatively large inspection scope, but you're working on a budget. So you choose G2-level inspection with a sample size code of "J". Now, let's turn to the reverse side of the AQL chart. Find your lot size letter "J" among the list shown on the left. You can see that the sample size corresponding to "J" is 80 pieces. Now you know your sample size: 80 bulbs. So out of your total lot size of 960 bulbs, you'll want to pull a random sample of 80 bulbs to inspect. And remember, you'll want to pull samples from different parts of the lot. So if the finished bulbs are packed in cartons, be sure to pull samples at random from multiple cartons at the front, rear, top and bottom of the lot. Otherwise, you might skew the results of your inspection. The last step in using the AQL chart for inspection involves determining the AQL, the maximum number of defects allowed in the sample for inspection to pass. Let's look at the reverse side of the AQL chart again. Notice that the chart shows a row of acceptable quality levels along the top. Product inspection generally uses three inspection levels: one for critical defects, one for major defects and one for minor defects. Critical defects are typically those that pose a safety hazard to the consumer. And you'll probably want to use an AQL of zero there, the most common choice. Major defects are those that affect the functionality of the product or might otherwise lead to returns from customers. You might use an AQL of 4.0. Minor defects typically don't affect product function and aren't likely to result in customer returns or complaints. You might use a more lenient AQL of 6.5 for minor defects. Now let's get back to your light bulbs example. You have your sample size of 80 bulbs. And you want to determine the number of critical, major and minor defects to allow. As I said a moment ago, an AQL of zero for critical defects is most common. So let's assume inspection will fail if you discover a single critical defect with the order. On the AQL chart, find your sample size of 80 pieces. Now look for an AQL of 2.5, a common standard used for major defects when inspecting consumer products. You'll see two numbers where the sample size row and AQL column meet in the middle: "5" on the left, showing the maximum number of defects acceptable, and "6" on the right, showing the minimum number of defects that will result in a failing inspection of this sample size. Now you know that if you find more than five major defects in your sample of bulbs, the order fails inspection. Look back at the AQL chart once more and find your sample size of 80 pieces. Then find the AQL 4.0, which is commonly used for minor defects when inspecting consumer products. In the middle, you find the maximum number of acceptable defects is "7" and the minimum rejected number is "8". So you now know that if you find more than 7 minor defects in the sample during inspection, the order fails inspection. Here's what an AQL result might look like in an actual inspection report. Now you've just learned: why it’s often better to inspect a sample instead of 100 percent, what is AQL and how is it used for sampling during inspection, how to determine a sample size with AQL and how to determine the number of defects allowed in a sample But wait... There are just a few more vital points you need to consider: First is that acceptable quality limits cannot be set for inspections that do NOT use AQL sampling. AQL depends on a certain statistical sampling.And AQL can't be applied without it. Second, it's generally the importer who determines AQL. An independent inspector can recommend AQL levels of 0, 2.5 and 4, for example, based on their own experience. But the importer has their own expectations for quality, and AQL is often adjusted as a result. Lastly, the importer typically has the final say in terms of whether or not to accept an order of goods. An inspection report might show that an order failed inspection, but the importer may decide that AQL was too strict and give the supplier the "OK" to ship the goods anyway.