AQL - How do I find Acceptable Quality Level?

After going through the suggestions given so far I hope m'lady has found the right answers. If doubt exists I would like to add a few points. But before that I need some clarifications. You have mentioned (correct me if I am wrong)

a) (In the 1st post) "we check 100% all dimensions"
b) (In the 2nd post) "we check all dimensions 100 % for SOME customers"
c) Also (in the 2nd post) " we always check criticals, especially on parts with known problem specs."
d) (in the 1st post) "... only want to write down a certain percentage for our in-process inspection documentation"

From the above do I understand that
1) You check all dimensions on 100 % of the lot for all parts for some customers, OR

2) You check only critical dimensions on 100 % of the lot for all parts for some customers OR
3) You check all dimensions on 100 % of the lot of only the critical parts for some customers.
My next question:
4) Do you find rejections/deviations in your in-house 100 % measurements?
If yes have you analysed, determined the cause, taken corrective action and found the same effective? If there are rejections/deviations the process capability of your machines may not be adequate. (Gordon has already implied that)
5) If you have no deviations/rejections during 100 % check, does the customer report rejections/deviations?

Why am I asking these questions? Because you say that you 'need to write a procedure on our AQL...'. Since you are machining components for aerospace applications the requirements may be critical.The key to the requirement is to study the process capability of your machines (if you havn't already done that) and decide on CPk figure e.g. 1.67 that would give defectives in terms of PPM rather than AQL in terms of %age.

As for the recording of readings you can adopt any figure as long as no customer has stipulated any particular AQL.

In my experiences with Z1.4 sampling both when mandated by customers or internally determined, it just felt a bit artitrary, as if someone threw a dart backwards over their shoulder, hit the policy dartboard, and turned around and said, "OK, AQL 0.65 it is!"

Like Jupitor, I prefer closely monitoring the process (preferably in real time) using a tool like Cpk or Ppk with corrective actions trigggered below a certain value on the index that is well above 1.0. This way, instead for looking for non-conformances after the the product is finished, you anticipate them before they occur.

My only caveat is that this approach works much better with large quantity production runs that provide large statistical populations than for short-term low quantity runs.

Jupitor said:

After going through the suggestions given so far I hope m'lady has found the right answers.

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I'm not going to quote everything Jupitor wrote
I was about to write that I couldn't have written it better! Truth be told, I couldn't have written it a tenth as good

I appear to get misunderstood at times (I no longer regard English as my "native tongue" having lived in Denmark most of my life), so I'd better stress that it is a compliment from me to Jupitor.

I need a format for Sampling plan for Incoming, in process and Final inspection with minimum samples inspection.. kindly advice me

We would need more info to advise you in any detail, but in general if minimum samples is your goal, C=0 plans are the ones that meet that criteria the best.

ymsheik said:

I need a format for Sampling plan for Incoming, in process and Final inspection with minimum samples inspection.. kindly advice me

Click to expand...

What do you mean by 'format'?