Every product requires an inspection before you can release it, so when manufacturers mass-produce, they need to find a way to speed up the inspection process. One way to do this is Acceptance Quality Limit (AQL), a standard sampling method to determine the quality of a batch of products.
However, not all regions and products have the same requirements for quality, so you will need to choose between various AQL levels to test your product. This test will limit the number of defective units in each released batch.
What is AQL?
AQL is shorthand for Acceptance Quality Limit, meaning the worst tolerable quality level according to ISO 2859-1:1999. The limit represents the most defective units a sample size can have before rejection of the entire produced batch. Its purpose is to help the buyer decide whether they should accept or reject a specific order of manufactured products.
These are international standards to ensure product quality in any item being inspected, but the AQLs can vary between products. Products can have minor, major, and critical defects that would determine the percentage of products in a batch with that particular issue without needing to discard the entire thing.
Also, inspections can be costly depending on the sample size, so figuring out the best risk to cost ratio is imperative to select the number of products to be tested and the AQL ratings for each defect.
An AQL is necessary for your production. It ensures you release high-quality products that meet your customers’ needs without causing them harm. A suitable AQL will help your business in the long-run, despite a higher initial cost.
Minor, Major, and Critical Defects
Every form of production has three categories of defects: minor, major, and critical. These categories have different ratings that state the maximum percentage of products that can be defective. As the defects become more vital to the product’s usability, the limit decreases.
A minor defect is a small deviation from the specifications. This defect does not affect the product’s performance and is unlikely to deter the customer from purchasing it. These are rated at 4.0%, meaning that up to 4.0% of the products can have that defect in a given batch without being rejected. An example would be a missing decorative stud. While not ideal, it has minimal impact on the product.
Major defects include those that may not be accepted by the consumer, though they do not greatly impact the functionality. These defects reduce the value of the product but do not make it unacceptable to use.
They usually have a rating of 2.5%. One example of a major defect would be a visible dent in a car door. Consumers would be less likely to buy the product, but it does not impact performance.
The most stringent category is critical defects. A critical defect is unacceptable and dangerous to use. It greatly deviates from the specifications and industry standards, so that consumers should not be able to purchase it.
These defects are usually rated at 0% because they should never be sold. An example of a critical defect is a microwave that operates with an open door. This issue could be extremely dangerous, so it should not pass an inspection.
Overall, every mass-produced batch will have at least one defective unit. However, not all defects are created equal. By setting different AQL levels for each issue, you can sift out the dangerous products from the imperfect ones to inspect your production line.
AQL tables are charts that help you determine the number of samples needed for inspection, and the number of allowable defective products based on the AQL. ISO 2859 includes these tables, and they have equivalents in all global standardization organizations. After choosing an AQL, the chart helps the buyer and manufacturer agree on inspection standards.
You can use an online AQL calculator to find a suitable sample size and number of allowable defective units without tables. However, understanding the charts will help you determine if your product needs a larger or smaller sample size or AQL based on some of the below factors that a calculator cannot quantify.
AQL Table Inspection Levels
Three different inspection levels define the quantity that quality control will pick from for checking:
- Inspection Level I: the smallest sample size, designed for general inspections
- Inspection Level II: mid-sized sample, most commonly chosen because of its balanced risk to cost ratio
- Inspection Level III: large sample size, best for products with rigorous specifications, provides the most representative result of the quality, chosen the least because of its high cost and potential loss
Factors that Determine Your AQL Limit
Determining the severity of each defect depends on several factors, including the audience, the purpose, and consumer preferences.
Depending on the scope of your product, you may have to change your AQL based on the market. Different countries and cities have various tolerance standards for critical, major, and minor defects. The values mentioned above of 0%, 2.5%, and 4.0% are North America and Europe’s standards.
Understanding the quality expectations of your target audience and the regional standards will help you determine the severity of your AQL.
Inspections aren’t free, and larger sample sizes cost more to inspect. A larger sample size has a higher time, labor, and monetary cost to perform an inspection, but it will provide the most accurate result. If you are testing a riskier product, like a prescription drug, a larger sample size may be worth the extra costs to avoid causing harm to consumers.
Not all products require surgical precision to be sold. For example, if a batch of candleholders has some products with misshapen dishes, it’s not as big of an issue as an airplane with a deformed wing.
Items designed for transportation, ingestion, pharmaceuticals, electronics, and appliances have more rigorous inspection standards than something like clothes or decorations. Critical issues with those products could kill someone, so they need much lower AQL ratings than other items. Also, riskier products require a larger sample size, and thus a higher AQL table inspection level than safer products.
These sensitive products undergo more designing, testing, and prototyping, and their factories monitor their manufacturing processes more closely to minimize defects before testing. As such, they are able to pass AQL ratings sub 1%.
Beyond the wider audience, you’ll also need to consider the target consumers’ preferences. Depending on their personal standards, they will accept different quality levels. By understanding what people want, manufacturers can create products that meet their needs while also releasing them in the quality they want.
There aren’t any set rules in selecting the best AQL for your production. By understanding your products’ purpose, industry, and target consumers, you can determine the severity a defect would have on your item and thus figure out what level of inspection the batch must undergo.
Keep in mind that all markets have a high level of competition, so you need to create a high-quality product in order to succeed. One way to do so is by choosing the perfect AQL. To save time and money, you need to make the right decision the first time, so you may want to consult an expert.
Here at Jonble, we can help you choose your AQL limits and perform inspection and quality control. We guarantee on-site inspections of manufacturers in all provinces of China. We assess the raw material, the production progress, the packaging, and loading to determine the quality, ensuring you release the best products.
Feel free to contact us for more information or if you have any questions.