AQL - How do I find Acceptable Quality Level?

qmslady - 2009 · May 18, 2009

howste said:
There are several items that caught my attention:

Your procedure says that all parts will be 100% inspected, but it fails to mention how the person doing the inspection knows what characteristics will be measured. Will they also inspect 100% of all print dimensions and notes?

(Yes we always inspect the prints, but do I need to mention that? Isn't it a given?)

Your procedure says "measurements taken by the operator shall be recorded randomly up to 10% of the lot or customer requirements (which ever is less)." This means that if your customer specifies that more than 10% of the measurements will be recorded, you'll ignore their requirement and just do 10% anyway. I don't think that's what you really want it to say.

(This is the part that bugged me all weekend. All dims will be checked, the "random" is the actual part, i.e. Part #5 is marked on the part, and all the dims will be taken and recorded. But I still don't think "random" is the word I'm looking for. And at first I had (whichever is more) but I wasn't sure if that was right, now I know.)

Since you're not doing sampling, why do you have the C=0 sampling table and reference MIL-STD-1916?

(Like I said before, I need to justify "why" we only "write down" a percentage instead of 100%, the auditor says we need a "sampling plan" to do this. So I am taking out the part that says we don't have one.) No one is perfect and sometimes, one gets by us to the customer and is sent back for rework or is scrapped.)

Also, your procedure References AS9100-2008. It should be either 2004 or 2009. There is no 2008 version.

(I didn't find anything (rev.) saying which year and assumed it was "2008" because that's when the revision was made. But since it came out in "2009" I didn't know for sure. Isn't this year a reference to the ISO standard rev.? Or is it for the AS9100 rev.? They have both been revised.)

I hope this helps...

I wasn't sure how to answer each question, so I put my answers in parenthesis..
Thanx for your help...waiting for your reply... :read:

QMSLADY

Gordon Clarke · May 18, 2009

qmslady said:
Like I said before, I need to justify "why" we only "write down" a percentage instead of 100%, the auditor says we need a "sampling plan" to do this. So I am taking out the part that says we don't have one.) No one is perfect and sometimes, one gets by us to the customer and is sent back for rework or is scrapped.

Did the auditor really mean "sampling plan" as litteraly as you've taken it?
It could be what ws said/implied was
"What do you do when you don't do 100% inspection"?

If I were you I'd also be curious as to why "one gets by you" occasionally. Is it the same dimension/chararteristic (type) and/or by the same operator?

Bev D · May 18, 2009

I think the troubling part that remains unanswered is the random recording. We understand that you are inmeasuring all dimensions on all parts. Good without SPC and proven capability most arespace Customers require 100% final inspection.

However, you still need to justify why you are only recording some of the measurements. You also need to specify how you will "randomly" determine which parts will be recorded. Are you going to use a random number generator each time?

qmslady - 2009 · May 18, 2009

qmslady said:
I wasn't sure how to answer each question, so I put my answers in parenthesis..
Thanx for your help...waiting for your reply...QMSLADY

I have been taking in all the advice and see how my "words" can be confusing...

The 3rd party auditor said and I quote, "You can't just say that you are writing down 10% of the parts that you inspected, even tho you inspected all of them. You must justify how you arrived at that percentage as a "statisically valid" number. To do that you need an SPC, if you like, I could come and show your inspectors how to do this." For a fee of course

.

You may ask why am I saying 10%? Because it is what we "do" to show "in process" inspections and uniform conformity. If one is out of print, we stop until the non-conformity is fixed.

As for the "one getting by us", that was at another company I worked for. Also AS9100 and the customer requirement stated 10% inspection. Although I checked all dims, and every part, it was the nature of the material to change with temperture. :yes:

It was teflon. The company did not require a controlled environment and the lots were 750 to 1000 parts(small). While I ran them nominal, they could change drastically if it was very hot or very cold (in the building) while I was running them, so sometimes it happened that there some out of print, but not very often. Made me crazy! :biglaugh:

I attached my revision for more critique...anybody game?

QMSLADY

Gordon Clarke · May 18, 2009

qmslady said:
I attached my revision for more critique...anybody game?
QMSLADY

I've made some changes (suggestions) so now I'm opening up for critique too

Bev D · May 18, 2009

You still haven't answered your auditor's question about why you will only record 10% of the parts you measure. what is your statistical rationale fro 10% (v.s. all, min/max or a simple conforms notation which are the traditionally accepted approaches) and how will you ensure randomness?

Additionally you say the operator will measure 100% of all dimensions on all parts before during and after each of the machining processes. Really? isn't that over kill? How will this be done and why? I can see measuring every part as it completes a machining operation. That makes sense.
I know there are inprocess measures on dimensions that require multiple cuts but these typically aren't recorded and aren't required to be recorded even for aerospace.

Gordon Clarke · May 18, 2009

Bev D said:
You still haven't answered your auditor's question about why you will only record 10% of the parts you measure. what is your statistical rationale fro 10% (v.s. all, min/max or a simple conforms notation which are the traditionally accepted approaches) and how will you ensure randomness?

And that is why I've eliminated all percentages (except 100%) from my "suggestions" in the file I included in my last response.
M'Lady you seem determined to make life difficult for yourself

qmslady - 2009 · May 18, 2009

Bev D said:
You still haven't answered your auditor's question about why you will only record 10% of the parts you measure. what is your statistical rationale fro 10% (v.s. all, min/max or a simple conforms notation which are the traditionally accepted approaches) and how will you ensure randomness?

Additionally you say the operator will measure 100% of all dimensions on all parts before during and after each of the machining processes. Really? isn't that over kill? How will this be done and why? I can see measuring every part as it completes a machining operation. That makes sense.
I know there are inprocess measures on dimensions that require multiple cuts but these typically aren't recorded and aren't required to be recorded even for aerospace.

Hi Bev,

I'm not sure what you mean by multiple cuts. And on the "before, during and after" I meant the prints, program, etc. before, the part is inspected after each process or "op" and then again when it is finaled.

She is the one that said we had to have an SPC if we were not going to write down all the dims every time we inspected the part. The AQL chart (suggested by the auditor) she says, is to show our 'statistical rationale'.

Before she brought this up, I didn't even know it existed...as I stated a while back...I am new to this company and starting from scratch...as an Internal Auditor at the last company I was with, I was also a lathe machinist, tool crib manager and purchasing agent for company of about 45. I asked her how we were able to get by with this at the last company, she said "They had a procedure for an AQL of 1.0%". That still doesn't tell me "how" one arrives at a statisically valid conclusion without a chart.

Are you telling me I need to take some samples before I can use the chart? What are you trying to tell me?

I don't need to spend anymore time spinning my wheels this week, I have been working on this since Monday the 11th...and I'm still not sure of what is being asked of me.

Some direction would be good at this point...Thanx...QMSLADY

"All regulations are subject to interpretation"...

qmslady - 2009 · May 18, 2009

Gordon Clarke said:
And that is why I've eliminated all percentages (except 100%) from my "suggestions" in the file I included in my last response.
M'Lady you seem determined to make life difficult for yourself

O.K.
Don't you think I already thought about that? If you don't state it you don't have to do it. But she (Auditor) told me that that would not work. Just like Bev. D was saying, How do I assure them that it's every tenth part of 100? Or that it's random and not selective? It really isn't random and it is selective that we write down, say...every fifth part. Why can't we just say that ? That we are writing down every fifth part to show we are staying in conformity as we process the part? If the Standard is open to interpretation...Then this is how I understand 8.2.4...The exact words of the clause (2009 rev. C) "When the organization uses sampling inspection as a means of product acceptance," we don't use sampling as means of acceptance, we inspect 100% "the sampling plan shall be justified on the basis of recognized statistical principles and appropriate for use." and "Evidence of conformity with the acceptance criteria shall be maintained." My acceptance criteria is my print and my First article passing inspection. If I wanted to use the ZBA CHART to show my selection of recording, not just certain dims, but parts with all the critical dims. I am checking all and writing some, I am 'basing my selection on the statistical principles of a recognized chart' am I not?...
It's late...I'm tired...time to go home...will check in tomorrow...thx qms

Gordon Clarke · May 18, 2009

qmslady said:
But she (Auditor) told me that that would not work.

She "told" you, but did she put anything in writing? Every third, fifth or tenth etc. item would be random - at least in the sense that the person doing the inspection wouldn't be "choosing" what to take.

I stopped long ago believing everything I heard and read. You have a practical background - have more faith in your own judgement. I've never met an auditor yet that was infallible :notme:

AQL - How do I find Acceptable Quality Level?

qmslady - 2009

Gordon Clarke

Bev D

Heretical Statistician

qmslady - 2009

Gordon Clarke

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Heretical Statistician

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