The Acceptance Quality Level is a statistical tool to inspect a particular sample size for a given lot and set maximum number of acceptable defects. In order words, it is the worst tolerable process average when a continuing series of lots is submitted for acceptance sampling.
The AQL has been recently renamed from “acceptance quality level” to “acceptance quality limits”. It is the limit that customer sets which is not really acceptable. Customers prefer zero defect products or services, which is the ideal acceptable quality level. However, customers arrive and set acceptable quality limits based on business, financial and safety levels.
The AQL of a product would vary from industry to industry. Companies dealing with medical tools would have more stringent AQL, as acceptance of defective products could result in health risks. Companies usually face two possible situations, to weigh against; cost involved in testing stringent acceptable levels or spoilage due to lower acceptable levels with a potential cost of product recall. AQL is an important statistic for companies seeking Six Sigma level of quality control.
Failure to meet the requirements of customers with respect to quality is termed as defects. In practice, there are three categories of defects
Critical Defects: Defects, when accepted could lead to harm the users. Such defects are totally unacceptable. It is defined by 0% AQL
Major Defects: Defects usually not acceptable by the end users, as it is likely to result in failure. The AQL for major defect is 2.5%
Minor Defects: Defects, which are not likely to reduce materially the usability of the product for its intended purpose but slightly differs from specified standards. Some end users still go ahead and buy such products. The AQL for minor defects is 4%
What the standard says about inspection level:
The inspection level designates the relative amount of inspection. Three inspection levels, I, II and III for general use. Unless otherwise specified, level II shall be used. Level I may be used when less discrimination is needed or level III when greater discrimination is required.
Four additional special levels, S-1, S-2, S-3 and S-4 are also given in Table 1 and may be used where relatively small sample sizes are necessary and larger sampling risks can be tolerated.
What the standard says about inspection severity:
Normal inspection: use of a sampling plan with an acceptance criterion that has been devised to secure the producer a high probability of acceptance when the process average of the lot is better than the acceptance quality limit.
NOTE Normal inspection is used when there is no reason to suspect that the process average differs from an acceptable level.
Tightened inspection: use of a sampling plan with an acceptance criterion that is tighter than that for the corresponding plan for normal inspection.
NOTE Tightened inspection is invoked when the inspection results of a predetermined number of consecutive lots indicate that the process average might be poorer than the AQL.
Reduced inspection: use of a sampling plan with a sample size that is smaller than that for the corresponding plan for normal inspection and with an acceptance criterion that is comparable to that for the corresponding plan for normal inspection
NOTE 1 The discriminatory ability under reduced inspection is less than under normal inspection.
NOTE 2 Reduced inspection may be invoked when the inspection results of a predetermined number of consecutive lots
The AQL has been recently renamed from “acceptance quality level” to “acceptance quality limits”. It is the limit that customer sets which is not really acceptable. Customers prefer zero defect products or services, which is the ideal acceptable quality level. However, customers arrive and set acceptable quality limits based on business, financial and safety levels.
The AQL of a product would vary from industry to industry. Companies dealing with medical tools would have more stringent AQL, as acceptance of defective products could result in health risks. Companies usually face two possible situations, to weigh against; cost involved in testing stringent acceptable levels or spoilage due to lower acceptable levels with a potential cost of product recall. AQL is an important statistic for companies seeking Six Sigma level of quality control.
Failure to meet the requirements of customers with respect to quality is termed as defects. In practice, there are three categories of defects
Critical Defects: Defects, when accepted could lead to harm the users. Such defects are totally unacceptable. It is defined by 0% AQL
Major Defects: Defects usually not acceptable by the end users, as it is likely to result in failure. The AQL for major defect is 2.5%
Minor Defects: Defects, which are not likely to reduce materially the usability of the product for its intended purpose but slightly differs from specified standards. Some end users still go ahead and buy such products. The AQL for minor defects is 4%
What the standard says about inspection level:
The inspection level designates the relative amount of inspection. Three inspection levels, I, II and III for general use. Unless otherwise specified, level II shall be used. Level I may be used when less discrimination is needed or level III when greater discrimination is required.
Four additional special levels, S-1, S-2, S-3 and S-4 are also given in Table 1 and may be used where relatively small sample sizes are necessary and larger sampling risks can be tolerated.
What the standard says about inspection severity:
Normal inspection: use of a sampling plan with an acceptance criterion that has been devised to secure the producer a high probability of acceptance when the process average of the lot is better than the acceptance quality limit.
NOTE Normal inspection is used when there is no reason to suspect that the process average differs from an acceptable level.
Tightened inspection: use of a sampling plan with an acceptance criterion that is tighter than that for the corresponding plan for normal inspection.
NOTE Tightened inspection is invoked when the inspection results of a predetermined number of consecutive lots indicate that the process average might be poorer than the AQL.
Reduced inspection: use of a sampling plan with a sample size that is smaller than that for the corresponding plan for normal inspection and with an acceptance criterion that is comparable to that for the corresponding plan for normal inspection
NOTE 1 The discriminatory ability under reduced inspection is less than under normal inspection.
NOTE 2 Reduced inspection may be invoked when the inspection results of a predetermined number of consecutive lots
