Acceptance Sampling Plans

Acceptance Sampling Plans

4.1 Acceptance Sampling Basics

It is the process of inspecting a sample of units taken from a batch that is performed for the purpose of accepting or rejecting the entire batch.

Acceptance Sampling

QUALITY

Defensive strategy in the face of possible deterioration in quality.

Alternative to prosecute a batch

Zero inspection

This is when a batch is accepted or shipped without any inspection.

• 100% inspection

It consists of checking all the items in the batch to remove those that do not meet the established specifications.

Alternative to prosecute a batch

100% inspection

DISADVANTAGEIt can lead to further inspection errors and sometimes the productit is damaged.

• It is used in those cases where the products are high risk and if they pass defective, a great economic loss can be generated.

Alternative to prosecute a batch

Acceptance Sampling

When the inspection is carried out with destructive testing.

When the cost of 100% inspection is too high compared to the cost of passing defective units.

When the seller has had excellent levels of quality and a reduction in the inspection quantity is desired.

DISADVANTAGES

• Risk of accepting bad batches and rejecting good ones.It provides less information about the product's quality level. More time and knowledge is required to plan and document sampling.

TYPES OF SAMPLING PLANS

PLANS BY VARIABLES

• It is when each unit of the sample is measured a continuous variable and a statistic is calculated with the data.

• The value of such a statistic is compared with a value of tables, with which the whole batch will be accepted or rejected.

PLANS BY ATTRIBUTES

When each item in the sample is classified as conforming or non-conforming; The number of non-conformers is used to accept or reject the batch.

POR ATRIBUTOS

Sampling by attributes: single, double, and multiple

• Simple sampling plan

If the number of defective items is less than or equal to a certain number c the batch is accepted; otherwise it is rejected.

n articles

BY ATTRIBUTES

Plan de muestreo de aceptación por atributos (N,n,c)

c= Acceptance number

N=6000; n=200; c=2

BY ATTRIBUTES

• Plan de muestreo doble

Attribute-based plan in which up to two samples can be taken to decide whether a batch is accepted or rejected.

BY ATTRIBUTES

• Double sampling plan

Example:From a batch of 3 000 pieces, a sample n1= 80 is taken:Accept the lot; if the defective units are less than or equal to c1 = 1 Reject the lot; If the defective parts are greater than C2 = 4. Take a second sample of n2 = 80 units when neither of the two previous cases occurs. If the number of defective units in the two samples is less than or equal to c2 = 4, the batch is accepted; but if it is larger, the batch is rejected.

BY ATTRIBUTES

• Multiple Sampling Plan

Attribute-based plan that consists of a generalization of the double sampling plan, where two or more samples can be extracted to accept or reject the batch.

Acceptance sampling is a particular form of inspection, inthat batches are simply accepted and rejected, but it does not improve the quality.