Inspection agents utilize AQL (Acceptable Quality Limit) chart as a standard tool in quality control to evaluate the overall quality of a production lot. These tables provide a systematic approach to sampling and defect assessment, enabling inspectors to determine whether a batch meets the predefined quality standards set by the client or industry regulations.
This process ultimately helps in deciding whether the lot is acceptable for shipment or requires corrective actions.
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What is Acceptable Quality Limit?
AQL is an international standard used to determine the quality of products by inspecting a sample from each batch. It sets the maximum number of defective units that are allowed before the entire batch is rejected.
Goods in a sample are tested randomly, and if the number of defective items is below the predetermined amount, that product is said to meet the AQL. If the AQL isn't reached for a particular sampling of goods, manufacturers will review the various parameters in the production process to determine the areas causing the defects.
Read more: AQL Acceptable Quality Limit
How Acceptable Quality Limit Works?
The Acceptable Quality Limit (AQL) is a statistical tool used in quality control to determine the maximum number of allowable defects in a product lot during inspection. It works by using predefined standards to sample and evaluate a batch of goods, ensuring quality while avoiding the need to inspect every single item. Here's how AQL works:
1. Select Inspection Level
Choose the inspection level based on the importance of the product:
General Inspection Levels (I, II, III): Level II is most commonly used for standard inspections.
Special Inspection Levels (S1–S4): Used for small batches or specific tests (e.g., color matching, durability).
2. Determine Sample Size
Using an AQL sampling chart, match the batch size with the chosen inspection level to identify the sample size code letter. Find the corresponding sample size from the table. This sample will represent the entire batch.
3. Conduct Inspection
Randomly select the sample items from the batch. Inspect each item for defects, categorizing them as critical, major, or minor based on predefined criteria.
4. Compare Defects with AQL Limits
Refer to the AQL chart to find the Acceptance (Ac) and Rejection (Re) numbers for each defect category. If the number of defects in the sample is less than or equal to Ac, the lot passes inspection. If the number of defects exceeds Ac, the lot fails and may require corrective action, rework, or rejection.
5. Decision
Confirm: The batch is considered acceptable and approved for shipment or sale.
Not Confirm: The batch is rejected or flagged for additional inspection, sorting, or rework. This can be decided by the buyers. Examine your quality standard, the situation found by the inspector, and what the cause of the gap between them is.
Pre-shipment product inspections can fail for a wide range of reasons, such as bad packaging, mislabeling, poor quality and more. You need to make sure are the quality issues really that serious? So as to to provide a corrective action plan to your supplier, book a follow-up quality inspection.
Industry Differences in AQL Standards
Industries producing goods that must meet specific quality standards can greatly benefit from AQL sampling tables. These tables help identify defects early in the manufacturing process, enabling companies to enhance product quality, reduce production costs, and uphold their reputation among customers.
The AQL standards for products vary across industries. For instance, electrics product are more likely to have more stringent AQL then textile and apparel products due to higher safety risks and technical complexities.
Third-party inspection companies like GIS Inspection typically use AQL (Acceptable Quality Level) standards when conducting product inspection in Asia. The specific AQL levels chosen depend on the product type, quality requirements, and customer expectations. Below are the commonly applied AQL standards for different industries during quality control inspections:
l Electric Products: Electronics buyers and manufacturers rely heavily on AQL sampling tables to ensure their products meet safety standards and work as intended. Third-party quality inspection agencies typically adopt AQL 1.5, 4.0 when performing quality inspections for electronics and electrical products.
l Soft Goods: For textile and clothing industry, AQL sampling tables are commonly used for garments and garment quality control inspection such as holes, stains, or loose threads. This is particularly important in the fashion industry, where high-quality garments are essential to help maintain the brand’s reputation and customer loyalty. And the apparel and garment random inspection AQL standard is normally 2.5 for major defects, 4.0 for minor defects.
l Hard Goods: Hard goods include Handicraft, household product, furniture, toys, building and house furnishing product, sport, ceramic products, and stone products. We typically take AQL 2.5, 4.0 for hard goods third-party quality inspection.
l Mechanical Products: In the mechanical industry, AQL sampling tables ensure that mechanical device and machines are safe and effective. By testing random samples of finished products, manufacturers can identify any defects or inconsistencies in the manufacturing process and take corrective action swiftly.
l Chemical Products: Buyers and brands use AQL sampling tables to ensure their chemical products including chemical product chemical raw materials and chemical products, chemicals and additives, fertilizer and compound fertilizer, and household chemical product meet quality standards.
l Food: AQL sampling tables are used in the food-such as cans, aquatic products, flavorings-quality control to ensure that products meet safety and quality standards. By inspecting random samples of food products, manufacturers can identify contaminants and ensure that the product is safe for consumption.
AQL Sampling Chart
The AQL chart consists of two tables as below you can see. These tables often derived from standards such as ANSI/ASQ Z1.4 or ISO 2859-1, is a tool used to determine the sample size and acceptance criteria for quality inspections based on the lot size and chosen AQL levels.
AQL Chart: Table 1-Sample Size Code Letters
AQL Chart: Table 2- Single Sampling Plans for Normal Inspection
Acceptance sampling with AQL originated during World War II, popularized by Harold F. Dodge and Harry Remig for the U.S. military. The challenge was testing bullets for quality without destroying too many in the process. AQL sampling provided a solution, ensuring sufficient quality assurance while preserving enough bullets for use.
Today, buyers and importers widely utilize AQL standards to inspect a diverse range of consumer products, including textiles and apparel, furniture, home appliances, electrical equipment, and many other goods, ensuring quality and compliance with market expectations and regulatory requirements.
Practical Example: How to Use AQL Sampling to Inspect Air Fryer
Our client has placed an order with factory in China for 4,548 pcs air fryers. They hired a third-party product inspection company (GIS Inspection) to conduct a pre-shipment inspection at the manufacturing facility. You’ll use Table 1 to determine how many random samples the inspectors should pull.
Table 1 – Sample Size Code Letters
Since the purchase order includes 4,548 air fryers, you can look at the ‘Lot or batch size’ column on the left side of Table 1 and select the appropriate range. In this case, the correct lot size is from ‘3201 to10,000,’.
AQL Table #1 - Example
Then, we’ll select your inspection level, which determines how many products the inspector should check. As a rule of thumb, you can use General II for most consumer products.
For now, look for the intersection of the ‘Lot or batch size’ row with the ‘General II’ inspection level column. You’ll see that the ‘Sample size code letter’ is “L,”. We’ll use this code letter in the following table.
Table 2 – Single Sampling Plans for Normal Inspection
Now that we know the ‘Sample size code letter’ from Table 1 is ‘L,’ we will select it on the left side of Table 2. One column over, under ‘Sample size,’ we can see that the inspector will need to check 200 randomly selected cups from the shipment of 4,548.
AQL Table #2 - Example
To the right of the ‘Sample size,’ you’ll see various columns representing different Acceptable Quality Levels. For electronics, we have talked above, we utilize stricter AQL sampling methods: AQL levels 1.5 for major defects, 4.0 for minor defects, and 0 for critical defects.
Going by this standard, we can see that our inspector will accept a maximum of:
0 critical defect,
7 major defects, and
14 minor defects.
A shipment with 8 major defects, 15 minor defects, or 1 critical defect will fail inspection. So our inspector now has the guidelines they need to make a pass or fail decision.
You can see from the report, our inspector found 1 critical defect, 7major defects and 22 minor defects. So we have a fail result.
If you would like to learn more about AQL, read our article about How to Read the AQL Table?
Conclusion
Customers would, of course, prefer zero-defect products or services—the ideal acceptable quality level. However, sellers and customers usually try to arrive at and set acceptable quality limits based on factors typically related to business, financial, and safety concerns.
AQL is a proven statistical model that has been used for decades. Its widespread adoption across diverse industries is a testament to its effectiveness.
At GIS Inspection, we offer comprehensive inspection and audit services to help enterprises ensure products’ quality. Our experienced and professional inspectors are accredited in line with international standards. Our services include AQL sampling Inspection, factory audits, and lab testing.
Contact us today to learn more about our services and how we can help your business ensure the quality of your products.