AQL - How do I find Acceptable Quality Level?

qmslady said:

"I" am not the one making these rules. There are procedures that B.T. had in place before I came here. If they are spinning "their" wheels by recording useless information, then I need to tell them to stop. But...

I went out on the floor and questioned some of the guys about how they determine these things since you all put the question to me. They are writing down "critical dims" for parts with less than .002 tolerance and using the 10 % method. I asked one guy, after picking up a part, "which one is this?" He smiled and shrugged??? I asked "How do I know you aren't writing down the same piece over and over?" He says "I guess I'll have to write it on the part". O.K.

Click to expand...

I'm getting the notion that B.T. is extremely like the following scenario:

Start with a cage containing five monkeys. Inside the cage, hang a banana on a string and place a set of stairs under it.
Before long, a monkey will go to the stairs and start to climb towards the banana. AS soon as he touches the stairs, spray all of the other monkeys with cold water.
After a while, another monkey makes an attempt with the same result all the other monkeys are sprayed with cold water.
Pretty soon when another monkey tries to climb the stairs, the other monkeys will try to prevent it.
Now, put away the cold water. Remove one monkey from the cage and replace it with a new one. The new monkey sees the banana and wants to climb the stairs. To his surprise and horror, all of the other monkeys attack him. After another attempt and attack, he knows that if he tries to climb the stairs, he will be assaulted.
Next, remove another of the original five monkeys and replace it with a new one. The newcomer goes to the stairs and is attacked. The previous newcomer takes part in the punishment with enthusiasm! Likewise, replace a third original monkey with a new one, then a fourth, then the fifth. Every time the newest monkey takes to the stairs, he is attacked.
Most of the monkeys that are beating him have no idea why they were not permitted to climb the stairs or why they are participating in beating the newest monkey.
After replacing all the original monkeys, none of the remaining monkeys have ever been sprayed with cold water.
Nevertheless, no monkey ever again approaches the stairs to try for the banana. Why not? Because as far as they know that's the way it's always been done around here.

And that, my friends, is how a company policy begins.

Maybe you should get it printed and hand it out when talking to your co-workers

Good Morning G. C. ")

That was great!! And that about sums it up around here!! I was wondering when i started here why the last auditors left...there is a lot of resistance to change by the management and employees. They say they want it, need it and must have it to go forward. When I try to implement it I get all kinds of reasons about "that's always how its been done around here" and " I don't see the need to change that because it's how we do it". Obviously, its not working anymore. I can only go as fast and as far as "they" will let me. There is a lot of resistance to this "sampling plan" testing. I have a QMS meeting this morning and of course this will be the main topic, as I will not let this go until it gets resolved. It will also be the topic next week if its not resolved and I get another meeting! (Bumping my head against the wall).
I'll check in later...Thanx...qms

Hi GORDON...

I left everything the way you had changed it and tried to answer your question with this...

5.1 MONITORING, MEASUREMENT AND ANALYSIS
The appropriate department employee or authority shall inspect the part produced or the product supplied to verify conformity. Parts produced shall be inspected for conformity to customer print requirements for First part, during manufacturing and as a final inspection. Any critical dimensions, (.002 tolerances or less) as specified by QA, shall be monitored and measured by the operator during each operation. The customer's critical requirements, the inspection results, and numbering sequence for each part inspected shall be recorded on Operator Inspection Sheet Form 7.5.1.3-10 and the sequence number written on the correlating part with a black Sharpie marker.

I had already changed it to this yesterday:

5.1 MONITORING, MEASUREMENT AND ANALYSIS
The appropriate department employee or authority shall inspect the part produced or the product supplied to verify conformity. Parts produced shall be inspected for conformity to customer print requirements for First Article, during processing, and Final Inspection. Critical dimensions with tolerances at .002 or less shall be monitored and measured by the operator for every part. Print minimum and maximum requirements, tolerances, inspection results, and numbering sequence determined by QA according to customer requirements, shall be recorded on Form 7.5.1.3-10 and the sequence number marked on the correlating part with a black Sharpie marker.

Either way, they both sound about the same to me. But I still have the problem of validating "determined by QA or as specified by QA"...right? Where did QA get their info? "They" tell me the customer has not specified any requirement other than the print. So, how much authority does QA have making this rule?

AS9102 states (regarding FAI) "In the absence of any contractual requirement, compliance is not mandatory. However, the supplier (that's us) must have a process and should utilize AS9102 for guidance." If it works for the 1st Article, why not the rest of the parts? The Scope of this standard states, "The purpose of this standard is provide a consistant documentation requirement for aerospace components."

Am I mis-interpreting this? AS9100, 4.2.4-"Records shall be established and maintained to provide evidence of conformity..." 8.2.4 Evidence of conformity with the acceptance criteria shall be maintained."
Our "acceptance criteria" is the customer's print requirements and therefore their release of the product. Our records provide the evidence of conformity according to the customer's print requirements. We do not use "sampling inspection" as a means of acceptance.

Almost time for my meeting...gotta go...qms

qmslady said:

That was great!! And that about sums it up around here!!

Click to expand...

I thought you'd be needing a "pick-me-up" so that's why I sent the "policy" story
I was being serious about you copying and printing it. Maybe not handing it around, but at least have it on your desk Even in the tight-xxxxx organization ifthere isn't any humour it's time to look for a new job.

If management is asked to make a decision it's usually easier to say "No" than "Yes" or hum and haw and avoid answering directly. Therefor don't ask and do what you feel should be done. Then management, if they don't agree, have to come out into the open if they want things to remain at status quo.

Don't forget - we're probably quite a few by now that will want to know what happens.

A very bad translation of saying by a Danish poet (Piet Hein) is:
"If you always do what you've always done,
You'll always get what you know must come".

Gordon's right about going ahead and doing. As a "young puppy engineer" I was told, "It's always better to beg for forgiveness than to ask for permission."

walt76661 said:

Gordon's right about going ahead and doing.

Click to expand...

Good grief Walt - thanks
Can I print, frame and hang that up on my wall?

Well...that's another meeting skipped, second week in a row...so much for "management commitment"...

Guess I'll just have to take Walt up on his statement and get things moving myself...

There is one person "above" me who will have a cow, a horse, and a litter of kittens, that I didn't ask before proceeding. A lot of what needs to be done around here is with the machinists and making them aware of the changes and what their part is, in the scheme of "QMS".

My husband and I like to use the saying; What's the definition of insanity? "To keep doing the same thing over and over again and expecting a different result"...

P.S. Did anyone have any comments about my last post?
QMSLADY

Tim Folkerts said:

AQL is roughly the fraction defective that would usually be accepted. If AQL = 1, then most lots with 1% defective would be accepted. The defect rate that will usually be rejected is several times higher. This doesn't really seem to be what you want.

If you want to be (fairly) sure that (most of) the parts are good, then this thread on reliability and sample size gives some good advice. https://elsmar.com/Forums/showthread.php?t=33830 (Note that the sample sizes are nearly nearly independent of sample size. So picking a fixed samlpe size - like "60" - is statistically more valid than picking a fixed % -- like "10%".)

If you can record & analyze the actual numbers, then you might be able to justify smaller sample sizes. For example, 30 good parts all near the center of the specs would be much better than 30 good parts all hugging one spec limit.




It almost sounds like you are saying

• "we test all the parts because it is valuable and important that all the parts are good."
• "we record some of the results just because it was written into the procedures."

This might be a good place to try some root cause analysis to find out why the procedures are set up this way - like "5 Whys". "Why do we record just some of the data?" ... "Then why ...?"


Tim F

Click to expand...

Thanks Tim,
I will do that and I did look at your links...I printed out the one from Reliasoft. I have a software program(trial) that has the ability to do this. I just didn't know what to put where or how many to put in for a sample or for acceptance. I have managed to understand some of it. It will print out the OC, ASN, AOQL, etc. and has the ability to "match the plan". It has many choices that I'm not sure of choosing. Like "single, double, & multiple" with "switching-limited, switching full, Reduced, tightened, normal...and so on. When I choose to edit the program there are more choices. It will let me put my own AQL and Sample size instead of choosing it for me.

I get confused when I read the charts afterwards, I don't know if it's telling me how many will fail or pass. Like under the AQL .95% it will say something like .0023456???? How do I know what number should be there? I keep playing with it and reading all the info I can to better understand what to put in the right places and choose the right catagories. Like Defective units or defects per unit or both. It has choices for ANSI Z1.4 and 1.9, which, I'm told, that is the specs we should be using. But I can't get anything on them without paying for it. Around here that's like asking for ice water in the desert. I'm looking this print out over and it is helping me to choose better, especially with your other comments earlier...so...Thanks again...QMSLADY ")

Let's take step back. If you aren't doing sample inspection you don't need to know how to use an AQL for this situation. PERIOD.

Your original question was how to justify - statistically - only recording 10% of the measurements when you always perfrom 100% inspection. This has NOTHING to do with sampling. Your company has simply always done this. I'm sorry, but you cannot justify an irrational non-statistical choice by attempting to wrap it in a sampling table. The fact is - as you have stated - that your company just wants to record 10% and be done with it. Fine. Just tell your auditor that. any attempt to make it sound like you have statistical rationalization will only trip you up.

Simply write into the procedure that you inspect 100% of the parts. The machinist will record the first part and every 10th part after that. Keep it simple. If your auditor has a problem with that, then you will have your leverage to change. The auditor shouldn't have a problem with it although he may find it a bit different than what he is used to....

If you keep trying to somehow justify it with sampling tables or whatever, you will only get the auditor's **** detector pinging and you will have a very bad day...


If you choose to continue to learn about AQLs and sampling (not a bad thing) you might want to take it to a new thread...However, if your company is having trouble with the whole 10% recording thing, I doubt very much that it will be an easy go to get to sample inspection. Most Aerospace companies require that you have real SPC and can prove capability prior to allowing sampling in lieu of 100% inspection.

qmslady said:

There is one person "above" me who will have a cow, a horse, and a litter of kittens, that I didn't ask before proceeding.

Click to expand...

Great. He can then quit his job and be a farmer.