acceptance quality levels

8/13/2019 Acceptance Quality Levels

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Acceptance Quality Levels

How to Use MIL-STD-105E


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Primary Concept1. The AQL is designed to most often accept lots of material having defect

percentages equal to the AQL value

2. The process average was measured and is stable and acceptable

3. The part is either good and bad. In case of evaluating a single complexproduct, the characteristic is either acceptable or unacceptable

4. The defects are randomly distributed, and the sample is taken randomly

5. The probability of finding a defect stays the same as samples are taken

The part is defective if only one characteristic ormore are defective

The characteristic is either good and bad.


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Random SampleRandom Sample Sample is taken by using random number table Each part to be check is assigned a random number

Formation the Lot Lot or batch consist of units of products of a single type, grade, class, size orcomposition


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AQL Process Average OP curveConcept of AQL Sampling Procedure To accept material that has a process average less defective than the AQLlevel

Probability of

acceptance

% Defective0 100 %

100 %

Operational characteristic Curve

Theoretical Curve

A lot of parts that has a defect percentageequal to or less than the AQL percentdefective will always be rejected

Actual Curve

The shape of the curve is depend onsample size. As sample size increase for aparticular AQL, the shape is close to thetheoretical curve

Theoretical curve

Actual curve


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Probability of Finding a Defect

Probability Distribution used Binomial Distribution

For Sample sizes 80 or less Poisson Distribution

For sample sizes more than 80

Probability (k non-conforming items out of N chosen) =

where k = 0, 1, 2, N -1, N

p = probability of an item being non-conforming,

The Poisson equation is given by:

P (no. of non-conformities = k) =

where k = 0, 1, 2, 3, ...

l = average rate of non-conformities

e = 2.71828...

Assumption

The probability finding a defect staythe same as a sample is removed

from the population


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Normal - Tightened Reduced

Use Normal First !Criteria for change from normal to reduced Ten consecutive lots must be accepted by normal inspection during theoriginal inspection

Total number of defect must be meet the respective table Production must be at a steady rate Reduced inspection must be considered desirableCriteria for change from reduced to normal

Lot rejection on original inspection or accept number is exceededCriteria for change from normal to tightened inspection Two out of two, three, four or five consecutive lots or batches are rejectedduring original inspection


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AQL Simulation Determine the lots size of products Determine the quality level of the production Select the sampling plan on the AQL table, start from normal inspection Prepare the sample, using random table Inspect the sample and judge the lots Try to use another level of inspection


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Acceptance Quality Level (AQL) Lot Size

1. Lot Size S1 S2 S3 S4 GI GII GIII02~08 A A A A A A A09~15 A A A A A B C16~25 A A B B B C D26~50 A B B C C D E51~90 B B C C C E F91~150 B B C D D F G

151~280 B C D E E G H281~500 B C D E F H J501~1200 C C E F G J K1201~3200 C D E G H K L3201~10000 C D F G J L M10001~35000 C D F H K M N35001~150000 D E G J M P Q

Special inspection standard General inspection Standard

Note : refers to Mil Std 105 e if in doubt

Level is represent the degree of discrimination need, where level I is used when lessdiscrimination. Level II is generally use.

The Sx Levels are use when relatively small sample sizes are needed and large samplingrisk can be tolerance


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Acceptance Quality Level (AQL)

Sample Size

AC RE AC RE AC RE AC RE AC RE AC RE AC RE AC RE A 2B 3C 5 0 1

D 8 0 1E 13 0 1F 20 0 1 1 2G 32 0 1 1 2 2 3H 50 0 1 1 2 2 3 3 4J 80 0 1 1 2 2 3 3 4 5 6K 125 0 1 1 2 2 3 3 4 5 6 7 8

L 200 1 2 2 3 3 4 5 6 7 8 10 11M 315 1 2 2 3 3 4 5 6 7 8 10 11 14 15N 500 1 2 2 3 3 4 5 6 7 8 10 11 14 15 21 22

Acceptance quality standard0.65 1 1.5 2.50.1 0.15 0.25 0.4

Note : refers to Mil Std 105 e if in doubt

acceptance quality levels

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