Monday, December 19, 2016

How Inspection Sampling Plan is Works in Clothing Industry?

What is Inspection Sampling Plan?
Inspection sampling plan is a chart that helps the inspector to control the quality of garment, he probably inspect the garments only a portion of the whole lot. Buyer mainly decided how many sample size he pick and what sampling plan does he follow?

Inspection Sampling Plan is a chart devised by American scientists to enable to conduct inspection of merchandise by random sampling given in this chart.

Inspection sampling plan
Fig: Inspection sampling plan in apparel industry
Inspection sampling plan have 5 parts:
  1. Lot size
  2. Sample size
  3. Acceptable quality level (AQL)
  4. Accept number and
  5. Reject
1. Lot size:
Lot size represents full consignment of goods from which samples are drawn.

2. Sample size:
Sample size is the number of goods drawn randomly for inspection.

3. Acceptable quality level (AQL):
Acceptance Quality Level (AQL) refers to the maximum number of defective items that could be considered accepted during the random sampling of and inspection.

During inspection defects are found into 3 categories:

  • Critical: Must be 100% accurate. There is no range.
  • Major: Normally 2.5%
  • Minor : Normally 4%
4. Accept number:
Accept number is quantity rejected from the sample but indicates that, if the numbers of rejects are within limit, the full lot is accepted.

5. Reject number:
If the numbers of rejects are without limit, then the full lot is rejected.

Why Quality Inspection Sampling Plan is Essential for Apparel Industry?
Buyers always try to ensure that goods delivered to them by the manufacturer must complete with the specified quality standard. The name of the plan is means of which quality standard of goods is ensured is called quality acceptance sampling plan or quality inspection sampling plan.

In this system, buyer defines quality standard of goods. Buyer worried only about those major defects which may impair functional quality of goods and thus their sale ability. Renowned buyers generally supply the seller with a list of such major defects and inform of the Inspection Sampling Plan that must be pursued.

Correctness of statistical acceptance sampling plan or statistical auditing largely depends upon weather size and color-wise sample drawing was representative of the whole lot or not.

Sampling plan is selected in such a way that quality is ensured within a statistical confidences limit of 95% or above. In garments industry, the following Acceptable Quality Levels (AQL) are used 1.5%, 2.5%, 4%, 6.5% etc. AQL means allowable percent defectives in a sample.

American military standard ABC-STD-105 defines that” The AQL is the maximum percent defective (or the maximum number of defects per hundred units) that, for purpose of sampling inspection, can be considered satisfactory as a process average.

Practically quality acceptance sampling plan & AQL started finding its use since World War-II. Large number of tables and methods has been devised to put sampling plan &AQL to proper and correct use.

Classification or types of sampling plan:
A. Based on how many times samples are randomly drawn from a lot Inspection Sampling plan is classified into 3 categories:

  1. Normal or Single Sampling Plan
  2. Double Sampling Plan
  3. Multiple Sampling Plan
For example- These categories of sampling plan are mention in below with a table.

Types of inspection sampling plan based on number of sampling


Sl.
Sampling type
Sample size
Cumulative Sample size
Acceptance
No.
Rejection No.
1.
Single Sampling Plan
50
50
1
2
2.
Double Sampling Plan
1st Sampling
2nd Sampling

50
50

50
100

1
4

4
5
3.
Multiple Sampling Plan
1st Sampling
2nd Sampling
3rd Sampling

20
20
20

20
40
60


0
0
1

1
1
2
B. Based on thoroughness or toughness of sampling, inspection sampling plans are classified in the following manner:
  1. General or Normal Sampling
  2. Relaxed or Reduced Sampling
  3. Tightened Sampling
In case, the vendor is new for the buyer, tightened sampling is used for the first two consignments at least, until confidence is created between buyer and seller. If buyer is fully satisfied with the first two consignments, normal sampling inspection may be applied thereafter. In case of general quality goods or when relationship between buyer and seller is very good relaxed sampling may find application.

For example- These categories of sampling plan are mention in below with a table.


Sl.
Sampling type
Lot size
Sample size
Acceptance
No.
Rejection No.
1.
General or Normal Sampling
50
13
3
4
2.
Relaxed or Reduced Sampling
50
13
1
2
3.
Tightened Sampling
50
5
0
1