AQL (Acceptable Quality Level) for Safety Critical Parts

Stijloor

Staff member
Super Moderator
#11
It's awfully quiet with responses to this question. Is really no one experienced in determining AQL levels?
We have Members that are very experienced, but may not have found to time to log in and respond.
What about the previous responses do you have questions/concerns about?

Hoe zeggen we dat ook al weer in her nederlands? Geduld is een schone zaak? ;)

Hang in there...:agree1:

Stijloor.
 
Elsmar Forum Sponsor
S

StorkSPA

#12
I don't have concerns about previous responses - and all are appreciated. (conclusion is: no sampling for critical features with small production batches)

But I still want to understand the issue - some measurements have to be done manually, these might be on non-critical features thus worth sampling.

Geduld is een schone zaak?
Nee, de uitdrukking is: "de zweep erover!":whip:
:D

Maar, ik zal geduldig zijn.
 

Stijloor

Staff member
Super Moderator
#13
I don't have concerns about previous responses - and all are appreciated. (conclusion is: no sampling for critical features with small production batches)

But I still want to understand the issue - some measurements have to be done manually, these might be on non-critical features thus worth sampling.


Nee, de uitdrukking is: "de zweep erover!":whip:
:D

Maar, ik zal geduldig zijn.
:lol::lmao::lol::lmao:

Stijloor.
 
S

Sturmkind

#14
StorkSPA;
If I understand correctly the regular production batch is 30 parts. The supplier requesting inspection to AQL 2.5 under Normal Inspection Level II is essentially requesting to check 5 parts of 30 with Sample Size Code Letter D 'arrowed' back up to Code Letter 'C'. Any AQL less than 1.5 (check 8 of 30 or 26.7%) will result in 100% inspection.
The assumption of General Sampling tables I, II, and III is that production is from a steady-state process which may not be the case with this product. If a discontinuous production process is used, then all bets are off on attribute sampling plans.
With 70 characteristics defined on the product have they been grouped into categories by severity and probability of non-conformance? If of the 70 let us say 5 are considered crucial. The measurement system used by your inspection fuction and that of the supplier becomes more important than a chosen AQL. The supplier may 'flinch' toward acceptance and you may 'inspect to reject'. Analysis of characteristics around the specification boundary then becomes crucial to determine the probability of 'bad' parts being accepted and 'good' parts being rejected by both parties.This is especially true if the landing gear you are purchasing is really a gear wherin much error can be attributed to 'arborology' -the ability to repeatably retain the gear upon an arbor.
Without specific product or process knowledge a type III error may be made which would be choosing the wrong characteristic(s) to measure.......
-For instance, if this is a landing strut forging the greatest threat to safety may not be a dimensional characteristic at all but discontinuities/hard spots within the forging itself.
As has been mentioned earlier intimate process & product knowledge lends itself to variable SPC, process error-proofing, and a deep review of process controls.

Both Deming and Dovich believed that sampling should either be 100% or zero for best economic yield.

What are your thoughts?
 
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