Even though the AQL chart and AQL table can help you breakdown the numbers, you will need an AQL calculator to get the numbers quickly and enhance accuracy. The AQL calculator is a simple and highly convenient tool to calculate the required sample size quickly. You only need to input your lot size, inspection level, inspection type, and limits. The calculator will provide you with an accurate sample size according to the AQL standard. Using the AQL calculator is an effective way to streamline your AQL sampling process.
At Tetra Inspection, we are dedicated to helping importers, suppliers, and manufacturers to access the insight, services, and tools they need to streamline AQL sampling and inspection. You can rely on our AQL calculator to determine your AQL sample size for inspection. Tetra AQL calculator is robust, accurate, and also allows you to determine the number of tolerated defects by selecting the appropriate AQL Level. It is easy, simple, and accurate.
How is AQL applied in practice?
As an importer, even though the ideal acceptable quality level is zero-defect products, you may have to settle for acceptable quality. AQL will help you monitor and avoid batches with unsatisfactory quality levels. If you and your supplier settle on AQL of 1%, the number of defects in the batch from the supplier should not exceed 1%. So, only 10 products can be defective in a batch composed of 1000 products. The importer rejects the entire batch if the number of defective products is 11 or more. The defective products over and above the predetermined number or percentage are known as Rejectable Quality Limit (RQL). RQL is an unsatisfactory quality level. If the quality level falls somewhere between AQL and RQL, it is known as Indifference Quality Level (IQL).
It is important to note that AQL is not constant across all industries. For instance, AQL for healthcare products is more stringent since any defects pose a higher risk to the end-user. Some companies use different settings based on AQL defects. AQL defects are quality issues highlighted during random inspections. They are categorized into three groups:
- Critical defects. These are serious defects that can harm the end-user severely. Importers usually use AQL of 0.0 for critical defects. If inspectors find a single critical defect in the selected sample size, the entire order fails the inspection.
- Major defects. These defects are less serious but are not acceptable by the end-users since they increase the risk of product failure. Importers typically assign the AQL standard of 2.5% to major defects.
- Minor Defects. They are small defects with a low impact on safety and the usability of the product. Most importers use the AQL standard of 4% for minor defects.
Each defect is not interpreted similarly by all inspection companies. But, importers and suppliers can agree on an AQL standard that is acceptable to both parties based on the level of risk they assume. Once an AQL standard is agreed on, it will be used as a reference during pre-shipment inspections. To determine the acceptable percentage for each type of defect in a shipment, order, or batch, you’ll use the AQL chart with AQL table, AQL sampling plan table, and AQL sampling chart, or the AQL calculator.
What’s an AQL Table?
Acceptable Quality Limit table refers to the ANSI ASQ Z1.4 table used by QC professionals for AQL sampling during the inspection. This AQL sampling plan is designed to help in determining the right sample size for inspection and the acceptable number of defects. Insight into the dynamics of the AQL table can also enhance your understanding and the interpretation of inspection results. It is vital for data-driven decision-making.
How to use AQL sampling plan table
While the AQL sampling plan table might seem intimidating, it is easy to use. It is divided into three columns for lot or batch size, sample size code letter, and sample size level I, with one larger section on the right for AQL. The AQL section consists of three sub-sections for AQL 2.5, AQL 4.0, and AQL 6.5, with Acceptable (Ac) and Rejectable (Re) column each.
AQL stands for “Acceptance Quality Limit” and indicates the percentage of defective units compared to the total units in a batch, order, or shipment. In ISO 2859-1, AQL is defined as the “quality level that is the worst tolerable.” It is an important statistical tool for quality control that leverages the capabilities of the Six Sigma methodology developed by Motorola. Quality control professionals can help importers doing business with manufactures and suppliers overseas to conduct pre-shipment inspections. The inspector checks for quality issues related to performance, usability, functionality, and aesthetics by inspecting a sample of the entire shipment. An inspection certificate is issued to certify that products meet the quality levels.
Importers and suppliers operating in the global marketplace have to adopt strict quality control measures to avoid issues down the line. While tapping overseas production is vital for success in the globalized market of the 21st century, it comes with numerous pitfalls. Determining the quality of the products before shipping is the biggest challenge facing importers and suppliers. To ensure each shipment meets quality level, importers, suppliers, manufacturers, and shipment inspection companies can use AQL.
AQL sampling plan table
You only need the number of units in your order or shipment and countercheck with the parameters on the lot or batch size column. Find the accurate range where the units in your shipment or order fall. If your order has 2000 units, it will fall on 1,201-3,200 range in the lot or batch size column. This lines up with the letter “K” on the sample size code letter column and 125 units on the sample size level I. For your order of 2000 units, you will need to sample 125 units and determine whether it is acceptable or rejectable based on the corresponding numbers on the AQL section:
- For AQL 2.5, only 7 defects are acceptable, while 8 defects or more are rejectable.
- For AQL 4.0, only 10 defects are acceptable while 11 defects or more are rejectable.
- For AQL 6.5, only 14 defects are acceptable while 15 defects or more are rejectable.
This provides you and your inspector with a reference for inspection of your order in the future to determine the quality level. The AQL sample size of 125 units for inspection should be chosen randomly to guarantee the accuracy of the results. Apart from the AQL sampling table, you can also use the AQL chart.
What is the AQL chart, and how does it work?
The AQL chart consists of two Acceptable Quality Limit tables and used to determine the sample size for inspection and the acceptable defective units. This AQL sampling chart offers more options, inspection levels, and standards for unique use cases. But, the AQL chart is just as easy as the AQL sampling plan table.
Table 1 on the AQL chart is Sample Size Code Letters, which is divided into three columns for lot or batch size, special inspection levels, and general inspection level. The special inspection levels column is reserved for particular types of product testing. The lot or batch size column represents the number of units in your order. If your order is 2000 units, it will fall between 1,201 and 3,200 in the lot or batch size column.
AQL Sampling table in AQL chart
Even though the general inspection levels consists of level I, II, and III, the best practice is to use level II (GII). Your selection for 2000 units from the lot or batch size column will correspond with K in the GII. Once you attain “K” as your sample size code letter, you can proceed to Table 2 on the AQL chart.
Table 2 on the AQL chart has three columns for sample size code letter, sample size, and acceptable quantity levels. The letter ‘K’ from Table 1 goes on the sample size code letter column of Table 2. It lines up with 125 units as the AQL sample size for the inspection.
AQL for normal inspection table
On the AQL columns, you line up your AQL sample size of 125 units with the appropriate levels. If you are ordering consumer products, you will use 0.0 for critical defects, 2.5 for major defects, and 4.0 for minor defects as the AQL standards. For AQL 2.5 in the chart, 7 major defects are acceptable, and 8 or more major defects are rejectable. For AQL 4.0 in the chart, 10 minor defects are acceptable, and 11 minor defects or more is rejectable (See AQL 4.0 in the chart below).
AQL 4.0 in normal inspection table
Any critical defects are rejectable. Once you’ve acquired the accurate AQL sample size and the AQL limits for your order, you can use this normal inspection table to conduct AQL inspections.
What is AQL inspection?
AQL inspection is a process of determining whether the percentage of defective units in shipment is acceptable before shipping to the customer. The inspector selects the sample randomly from the shipment and inspects for defects based on the acceptable and rejectable number of defects from the AQL table. For large orders, the best practice is to select the sample randomly from different batches over several production runs. The quality limits and AQL sample size will guide your AQL inspection and help the inspector to decide whether to pass or fail the shipment.
After completing the AQL inspection, the inspection agency will issue a shipment inspection certificate. It certifies that the products pass the quality level and accompanies the shipment until it is delivered to you. If you operate in Asia, you will need pre-shipment inspection certificates. The inspector can conduct a pre-shipment inspection before production commences and issue a pre-shipment inspection report. The inspection report is attached to the documents for your shipment. To streamline the process, you will have to use the AQL calculator to get AQL sample size, limits, and all the numbers you need quickly.