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Acceptable Quality Level (AQL) is a statistical measurement used in quality control to define the maximum acceptable number of defects or deviations from a specified standard in a given sample size of a product. It is a critical concept in manufacturing and production industries, where maintaining consistent product quality is paramount.
AQL is typically expressed as a percentage or a ratio and is used to set a threshold for the acceptable level of defects that can be present in a production batch. When conducting quality inspections, a sample from the batch is examined, and the number of defects is compared against the AQL. If the number of defects falls within the acceptable range, the batch is considered satisfactory; otherwise, corrective actions may be taken to address the quality issues
Acceptable Quality Level or AQL inspection, FOR ISO, USA, Europe, UK & China
The ISO standard that corresponds to the Acceptable Quality Level (AQL) and is similar to ANSI/ASQ Z1.4 is ISO 2859-1. This standard outlines the procedures for sampling inspection by attributes and provides sampling schemes indexed by the AQL for lot-by-lot inspection.
So, if you are looking for an ISO equivalent to ANSI/ASQC Z1.4 (USA), MIL-STD-105E (USA), BS 6001 (UK), GB/T 2828.1 (China) for sampling procedures and Acceptable Quality Level, ISO 2859-1 is the relevant standard & is acceptable throughout the world
Types of Inspection Levels:
1-General Inspection Levels:
Level-1 (G-1):
This is the least stringent general inspection level. It involves a smaller sample size and is typically used when a high level of confidence in the product’s quality is not required.
Level-2 (G-2):
Level-2 is a moderate inspection level with a larger sample size compared to Level 1. It strikes a balance between the stringency of the inspection and the efficiency of the process.
Level-3 (G-3):
Level 3 is the most stringent general inspection level. It involves the largest sample size and is employed when a high level of confidence in the product’s quality is crucial.
2-Special Inspection Levels:
Level-1 or S-1:
S-1 is the least stringent special inspection level, typically associated with smaller sample sizes and less rigorous inspection requirements.
Level-2 or S-2:
S-2 is a moderate special inspection level with a balance between stringency and efficiency. It involves a larger sample size compared to S-1.
Level-3 or S-3:
S-3 is a more stringent special inspection level, often used when higher confidence in product quality is needed. It involves a larger sample size than S-2.
Level-4 or S-4:
S-4 is the most stringent special inspection level. It involves the largest sample size and is used when the highest level of confidence in the product’s quality is required.
Comparison of Acceptable Quality Levels or AQL in Table Form:
Aspect | Level-1 (G-1) | Level-2 (G-2) | Level-3 (G-3) | S-1 | S-2 | S-3 | S-4 |
|---|---|---|---|---|---|---|---|
Sample Size | Small | Moderate | Large | Small | Moderate | Moderate | Large |
Stringency | Low | Moderate | High | Low | Moderate | High | very High |
Confidence in Quality | Lower | Moderate | Higher | Lower | Moderate | Higher | very High |
This table provides a general comparison between the different levels within the general inspection category (Level-1, Level-2, and Level-3) and the special inspection category (S-1, S-2, S-3, S-4) based on sample size, stringency, and confidence in quality
General Inspection level VS Special Inspection Level Against the Lot Size & Sample size of Acceptable Quality Level or AQL:
Lot Size | Sample asize with Code Letter | Level-1 (G-1) | Level-2 (G-2) | Level-3 (G-3) | S-1 | S-2 | S-3 | S-4 |
|---|---|---|---|---|---|---|---|---|
2-8 | A=2 | A=02 | A=02 | B=3 | A=02 | A=02 | A=02 | A=02 |
9-15 | B=3 | A=02 | B=3 | C=5 | A=02 | A=02 | A=02 | A=02 |
16-25 | C=5 | B=3 | C=5 | D=8 | A=02 | A=02 | B=3 | B=3 |
26-50 | D=8 | C=5 | D=8 | E=13 | A=02 | B=3 | B=3 | C=5 |
51-90 | E=13 | C=5 | E=13 | F=20 | B=3 | B=3 | C=5 | C=5 |
91-150 | F=20 | D=8 | F=20 | G=32 | B=3 | B=3 | C=5 | D=8 |
151-280 | G=32 | E=13 | G=32 | H=50 | B=3 | C=5 | D=8 | E=13 |
281-500 | H=50 | F=20 | H=50 | J=80 | B=3 | C=5 | D=8 | E=13 |
501-1200 | J=80 | G=32 | J=80 | K=125 | C=5 | C=5 | E=13 | F=20 |
1201-3200 | K=125 | H=50 | K=125 | L=200 | C=5 | D=8 | E=13 | G=32 |
3201-10000 | L=200 | J=80 | L=200 | M=315 | C=5 | D=8 | F=20 | G=32 |
10001-35000 | M=315 | K=125 | M=315 | N=500 | C=5 | D=8 | F=20 | H=50 |
35001-150000 | N=500 | L=200 | N=500 | P=800 | D=8 | E=13 | G=32 | J=80 |
150001-500000 | P=800 | M=315 | P=800 | Q=1250 | D=8 | E=13 | G=32 | J=80 |
500001-over | Q=1250 | N=500 | Q=1250 | R=2000 | D=8 | E=13 | H=50 | K=125 |
Example Of Sample Selection Against The General & Special Acceptable Quality Level or AQL:
if the lot size is 10000 units then what should be the sample size against general inspection level-1 level-2 level-3 & special level against s1,s2,s3, and s4?.
For a lot size of 10,000 units:the sample would be as below
-
General Inspection Level-I (GIL-I):
- Sample Size: 80 units
-
General Inspection Level-II (GIL-II):
- Sample Size: 200 units
-
General Inspection Level-III (GIL-III):
- Sample Size: 315 units
-
Special Inspection Level-S1:
- Sample Size: 05 units
-
Special Inspection Level-S2:
- Sample Size: 08 units
-
Special Inspection Level-S3:
- Sample Size: 20 units
-
Special Inspection Level-S4:
- Sample Size: 32 units
ACCEPTABLE QUALITY LEVEL OR AQL CHART:
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Example Of Acceptable Quality Level Or AQL Against General Level-1 with lot size 10000 units with AQL 0.065 for Critical Faults 2.5 for Majaor Faults & 4.0 for Minror Faults.
the sample size:80 units
-
Critical Faults (Critical):
- Acceptance Number : 0
- Rejection Number : 1
-
Major Faults (Major):
- Acceptance Number : 5
- Rejection Number : 6
-
Minor Faults (Minor):
- Acceptance Number : 7
- Rejection Number : 8
Example Of Acceptable Quality Level Or AQL Against General Level-2 with lot size 10000 units with AQL 0.065 for Critical Faults 2.5 for Majaor Faults & 4.0 for Minror Faults.
the sample size:200 units
Critical Faults (Critical):
- Acceptance Number : 0
- Rejection Number : 1
Major Faults (Major):
- Acceptance Number : 10
- Rejection Number : 11
Minor Faults (Minor):
- Acceptance Number : 14
- Rejection Number : 15
Example Of Acceptable Quality Level Or AQL Against General Level-3 with lot size 10000 units with AQL 0.065 for Critical Faults 2.5 for Majaor Faults & 4.0 for Minror Faults.
the sample size:315 units
Critical Faults (Critical):
- Acceptance Number : 0
- Rejection Number : 1
Major Faults (Major):
- Acceptance Number : 14
- Rejection Number : 15
Minor Faults (Minor):
- Acceptance Number : 21
- Rejection Number : 22
Example Of Acceptable Quality Level Or AQL Against Special Level-S1 with lot size 10000 units with AQL 0.065 for Critical Faults 2.5 for Majaor Faults & 4.0 for Minror Faults.
the sample size at AQL2.5 =5 units
the sample size at AQL4.0 =5 units
Critical Faults (Critical):
- Acceptance Number : 0
- Rejection Number : 1
Major Faults (Major):
- Acceptance Number : 0
- Rejection Number : 1
Minor Faults (Minor):
- Acceptance Number : 0
- Rejection Number : 1
Example Of Acceptable Quality Level Or AQL Against Special Level-S2 with lot size 10000 units with AQL 0.065 for Critical Faults 2.5 for Majaor Faults & 4.0 for Minror Faults.
the sample size at AQL2.5 =5 units
the sample size at AQL4.0 =13 units
Critical Faults (Critical):
- Acceptance Number : 0
- Rejection Number : 1
Major Faults (Major):
- Acceptance Number : 0
- Rejection Number : 1
Minor Faults (Minor):
- Acceptance Number : 1
- Rejection Number : 2
Example Of Acceptable Quality Level Or AQL Against Special Level-S3 with lot size 10000 units with AQL 0.065 for Critical Faults 2.5 for Majaor Faults & 4.0 for Minror Faults.
the sample size at AQL2.5 =20 units
the sample size at AQL4.0 =20 units
Critical Faults (Critical):
- Acceptance Number : 0
- Rejection Number : 1
Major Faults (Major):
- Acceptance Number : 1
- Rejection Number : 2
Minor Faults (Minor):
- Acceptance Number : 2
- Rejection Number : 3
Example Of Acceptable Quality Level Or AQL Against Special Level-S4 with lot size 10000 units with AQL 0.065 for Critical Faults 2.5 for Majaor Faults & 4.0 for Minror Faults.
the sample size at AQL2.5 =32 units
the sample size at AQL4.0 =32 units
Critical Faults (Critical):
- Acceptance Number : 0
- Rejection Number : 1
Major Faults (Major):
- Acceptance Number : 2
- Rejection Number : 3
Minor Faults (Minor):
- Acceptance Number : 3
- Rejection Number : 4
Application of Acceptable Quality Level or AQL:
Manufacturing Quality Control:
AQL is widely used in towel manufacturing to establish acceptable quality standards for products. It helps ensure that the manufactured goods meet predefined quality criteria by specifying the maximum allowable number of defects in a sample.
Supplier Evaluation and Management:
Businesses use AQL to evaluate the quality of products received from suppliers. By setting AQL standards, companies can communicate their quality expectations to suppliers and establish a basis for acceptance or rejection of delivered goods.
Import and Export Compliance:
AQL is often applied in international trade to assess the quality of imported or exported goods. Customs authorities and businesses use AQL standards to determine whether a shipment meets quality requirements, facilitating smooth trade transactions.
Quality Assurance in Sampling Plans:
AQL is integrated into sampling plans, where it helps determine the appropriate sample size and acceptance criteria. This is crucial for efficient and statistically sound quality inspections, allowing for representative sampling of large production lots.
Consumer Product Safety:
In industries such as food, pharmaceuticals, and consumer goods, AQL is employed to ensure product safety and compliance with regulatory standards. By setting AQL levels, manufacturers aim to deliver products that meet or exceed safety requirements, reducing the risk of harm to consumers.
Frequently Asked Questions(FAQ) on Acceptable Quality Level or AQL:
What is AQL, and why is it important in quality control?
AQL, or Acceptable Quality Level, is a statistical measurement defining the maximum allowable number of defects in a product sample. It is crucial in quality control as it provides a standardized way to determine acceptable levels of product quality during inspections.
How is AQL determined for a specific product or industry?
AQL is determined based on factors such as industry standards, product criticality, and acceptable risk levels. It involves a careful consideration of the balance between the cost of inspection and the level of quality assurance required for a particular product.
How does AQL impact decision-making in manufacturing?
AQL guides decisions in manufacturing by setting the acceptable limits for defects. Manufacturers use AQL standards to make informed choices about accepting or rejecting production lots, ensuring that products reaching consumers meet the defined quality criteria.