AQL for Laymen - ANSI/ASQ Z1.4 - MIL-STD-105

[amanbhai]

Is this standard lately been revised?

 

[Vu Nguyen]

Dear Amanbhai,

I glad to know you, per your question, the standard i had used is Mil-STD-105D. Any idea please let me know.

Vu Nguyen

 

[amanbhai]

Is this standard lately been revised?

 

[Marc]

I'm not sure of the revision level / status of ANSI/ASQ Z1.4.

MIL-STD-105 is obsolete.

 

[Tim Folkerts]

Dear Tim F.,
I had understood how to look on the table X-F, but how to calculate percentage of nonconformity ? ex: 0.0502% or 0.256% ? is it a percentage of nonconformity that we inspected from sample size ?

These percentages would be the "true" defect rate. Suppose you produce many parts and the actual defect rate averaged over all the parts produced was 0.256%. If you pack these into lots of 200 pieces, then you would expect those lots to pass inspection 95% of the time. You don't calculate this number based on the sample you test.

Thank so much for your instruction, I had looked on the table and have some more questions:

1. Within the table X-F, I found some columns that has same AQL, such as: 0.65, 2.5, 4.0, 6.5. How about this ?

Row F has several different sampling plans associated with it, all of which use a sample size of 20.

• AQL 0.65: accept 0
• AQL 2.5: accept 1
• AQL 4: accept 2
• ...

The higer defect rates you are willing to accept, the higher number of defects you will accept in a sample. The different columns in Table X-Fjust correspond to the different sampling plans.

2. The percentage of nonconformity (such as: 0.053, 0.256...) How to calculte this from the lot. Ex: Lot qty: 150, Sample size: 20, AQL 0.65, Inspection level II, single.

You don't calculate these percentages based on the sample you test. If you really need to know these percentages, you would have to inspect the entire lot.

These percentages are used for "what if" type calculations. If you produced many parts and the actual defect rate averaged over all the parts produced was 0.256% (and if you packed these into lots of up to 280 pieces), then you would expect those lots to pass inspection (normal, level II) 95% of the time.


Does that help?


Tim F


P.S. As I recall, there have been some minor changes in the text at the beginning of the standards, and some minor changes to the switching rules but the tables themselves haven't changed. I have the Z1.4 1993 version, and I know there is a more recent update (2003?). I'd have to check more carefully to know the exact differences between the specific versions of MIL-STD-105 and Z1.4

 

[Vu Nguyen]

Dear Tim F.,

I got it, thanks so much.

Best regards...Vu Nguyen