What is acceptable quality level | Acceptable quality level in textile and apparel industries

What is Acceptable quality level (AQL)?

• Acceptable quality level is one of the most frequently used quality assurance tools. It is defined as the total number of acceptable defective pieces within the samples that the buyer will accept from the manufacturer.

• In one sentence, AQL is the least tolerable defective product.

• Acceptable quality level varies depending on the factory, buyer, and product. Generally, the critical the product the higher the AQL.

• In any business, before accepting the product quality is checked. This checking is done by the buying office merchandiser and also third party quality checker (QC). The samples are collected on a random basis.

Levels of Acceptable quality level (AQL):

There are 3 levels of acceptable quality level. Defending on these levels sample number is decided for a product.

AQL level 1:

• If the manufacturer has passed all the previous quality inspection successfully then the buyer may decide to follow AQL level 1.

• In AQL level 1 only 80 samples are inspected.

• Although it takes less time and money, AQL level 1 very risky and it is generally not followed.

AQL level 2:

• This is the standard inspection level.

• In AQL level 2, 200 samples are inspected.

AQL level 3:

• This is a stricter inspection level.

• A total of 315 samples is checked that are randomly selected.

• It takes more time and money to follow AQL level.

• AQL level 3 is generally used in the case of high-value products.

Acceptable quality level (AQL) standard:

There are 6 types of AQL standards. They are-

1. Acceptable quality level 1% (1 per 100 garments can be defective)

2. Acceptable quality level 1.5% (1.5 per 100 garments can be defective)

3. Acceptable quality level 2.5% (2.5 per 100 garments can be defective)

4. Acceptable quality level 4% (4 per 100 garments can be defective)

5. Acceptable quality level 6.5% (6.5 per 100 garments can be defective)

6. Acceptable quality level 10% (10 per 100 garments can be defective)

Sampling plan of AQL:

There are 3 types of sampling plans in acceptable quality level (AQL). They are-

1. Single sampling plan

2. Double sampling plan

3. Multiple sampling plan.

What is Single sampling plan?

When the acceptance or rejection decision of a lot is taken based on a single sample collection plan, then it is called single sampling plan. Let’s assume the number of samples collected is n, the number of acceptance is a, the number of rejection is r. If the number of defective units d ≤ a, then the sample will be accepted, and if the defective unit d ≥ r, then the sample will be rejected.

What is double sampling plan?

When the decision of acceptance or rejection decision of a lot is taken based on two sets of samples, then it will be called double sampling plan. It is especially useful when the first sample is neither good nor bad and it is difficult to take a final decision based on the first sample. But if the first sample is really bad then the lot can be rejected without inspecting the second set of samples.

Let’s assume,

Size of the first sample = n1

Acceptance number of the first sample = a1

Defective unit in the first sample = d1

Size of the second sample = n2

Defective unit in the first sample = d2

Acceptance number of first + second sample= a2

If d1+d2 ≤ a2, then the sample will be accepted.

If d1+d2 ≥ a2, then the sample will be rejected.

What is multiple sampling plan?

When the decision of acceptance or rejection decision of a lot is taken based on multiple sets of samples, then it will be called multiple sampling plan.

If the size of the sample = n1

Number of acceptance = a1

Number of rejection = r1

Number of defective samples = d1

If, r1> d1 > a1, then the buyer may decide to use a multiple sampling plan.

Also read: 

Different types of defect in garment manufacturing | List of 12 major quality defects found in the finished garment with images

Inspection levels in acceptable quality limit (AQL):

Each type of sampling plan can follow 3 inspection level:

1. Normal inspection

2. Tightened inspection

3. Reduced inspection

What is normal inspection?

• This type of inspection is conducted under normal conditions.

• This type of inspection is mostly conducted.

• No excessive time, money requirement.

What is tightened inspection?

• It has a stricter acceptance criterion.

• If the initial quality reports are not satisfactory and if it is marked as ‘sufficiently poor’, then this type of inspection can be used.

• Required excess time and money and it is also not good for the image of the manufacturing company.

What is reduced inspection?

• It is the opposite of tightened inspection.

• It means the sample size for inspection will be smaller than the normal sample size.

• If the initial quality reports are highly satisfactory and if it is marked as ‘sufficiently good’, then this type of inspection can be used.

• Required less time and money than normal inspection.

AQL in garments or apparel industry:

In the garments or apparel industry AQL level 2 is used. Which means 200 samples are inspected.

For apparel, defects are classified into 4 categories. For these defects, different inspection levels are used.

1. Critical defect (Goods are not going to function properly and can even harm the consumer): There is no room for error. The goods have to be 100% accurate.

2. Major defect (Consumer will notice the defect of the good and may even return it): AQL level 2.5% is used.

3. Minor defect (Customer may not even realize the defect, there is a very little chance of return): AQL level 4% is used.

4. Slight defect (Defect can only be identified by the manufacturer and the buyer): AQL level 6.5% is used.

Acceptable quality level (AQL) formula:

Average defective item = No. of defects in inspection/(Total no. of item inspection *100)

AQL chart in textile: