Sampling Plans & Control of Nonconforming Product

Douglas E. Purdy

Quite Involved in Discussions
#11
Close

Discordian said:
I'm not sure I understand...

You're saying that if a non conformance is found in the SAMPLE, but not enough to reject the LOT, then the LOT is passed through but the SAMPLE is treated as a nonconforming lot?

Is that right?
You are close. Only the samples from the lot that were found nonconforming are identified and controlled in accordance with Control of Nonconforming Product procedures. For example they will go and rework those nonconforming samples Only!

Thanks,
Doug
 
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Douglas E. Purdy

Quite Involved in Discussions
#12
Not ISO Registered - Yet!

Bev D said:
If you are in fact doing as Discordian says (typical in the 'old' days, when accept numbers were often greater than zero) and you are ISO certified - or some other variation of ISO9000 - then ANY product KNOWN to be nonconforming must follow the non conforming product procedures for identification and control. The lot 'may' have nonconforming product and in fact it 'probably' does. But you dont' KNOW that for sure. so the lot isn't nonconforming - but the defective samples are.
An auditor might question why you don't 100% inspect the lot if you find one or more defects (these days most customers and many auditors insist on c=0 inspection plans) adn that might be an awkward converstation. (Although the ISO9000 standard doesn't have any "shalls" concerning the details of sampling plans.
As for ISO Registeration, I do not want to go there. I have been working on that for over 2 1/2 years.

I have been raising the questions that you raise, that is the purpose for this thread. Management does not seem to go along with my thinking or recommendations (May be that is why we are not registered yet.), but if I can get "Registration Auditors" to question the practice - then they might change it - MAY BE!

Thanks,
Doug
 

Douglas E. Purdy

Quite Involved in Discussions
#14
I Think You Got It!

Tim Folkerts said:
This is just my opinion, but it seems that it would be very helpful to distinguish between nonconforming parts and nonconforming lots.

Ideally, every unit in every lot will be conforming:agree1:. Practically, it is often more economic to just accept a few nonconforming parts in a lot and pay less.:notme:

When you sample, you are trying to determine if the lot is noncomforming. Suppose you decide that anything up to 2 bad parts in your sample is acceptable.
  • If you find 4 bad part in the sample, then you would apply the Nonconforming Lot process (for example, 100% inspection or return the whole lot to the vendor).
  • If you find 1 bad part in the sample, you accept the lot, but apply the Nonconforming Part process to the 1 bad part (for example, destroy & throw out).
Of course, any time you discover a bad part (for example, during 100% inspection of a lot or during production), you should also apply the Nonconforming Part process.


Tim F
I believe you have captured the current practice perfectly! So you would say that this practice is acceptable - Right?

Thanks,
Doug
 

Douglas E. Purdy

Quite Involved in Discussions
#15
Not Destructive Testing

Statistical Steven said:
Not sure I understand. If the test is destructive, the sample is destroyed before any additiona investigation can be done on the sample. Since the lot is acceptable, it does not make sense to sample from the lot for additional testing. Therefore, if you have a failed part in the sample, it is documented as such, but not sure you can do much more than that. Maybe I do not fully understand the issue.
No, the example that I am using does not involve destructive testing. It invovles dimensional inspection and measurement. Sorry I did not make that clear.

Thanks,
Doug
 

Douglas E. Purdy

Quite Involved in Discussions
#16
I Agree

Coury Ferguson said:
I guess my question would be: Why are you performing 100% sorting if there are nonconforming product identified? Would it be the responsibility of the Supplier?

In my opinion, the responsibility would fall under the Supplier that furnished the nonconforming material. What do your procedures say about handling "Nonconforming Material?" And if this part/assembly is critical to completion of a delivery to your customer, than I would limit the Re-Inspection to the quantity required to meet the immediate need.

All of this is in My Opinion and are only asking for some clarification.


Coury Ferguson
I agree with your thoughts about the responsibility of the Supplier!

100% Sorting is not performed if the sampling accepted the lot. Only the samples that did not conform are then identifed and controlled in accordance with the Control of Nonconforming Product procedures. The manufacturing operation performed by the supplier is critical in the over all process, but like Tim indicated the cost for the product must be allowing this level of acceptance.

Thanks,
Doug
 

Jim Wynne

Staff member
Admin
#17
Douglas E. Purdy said:
I agree with your thoughts about the responsibility of the Supplier!

100% Sorting is not performed if the sampling accepted the lot. Only the samples that did not conform are then identifed and controlled in accordance with the Control of Nonconforming Product procedures. The manufacturing operation performed by the supplier is critical in the over all process, but like Tim indicated the cost for the product must be allowing this level of acceptance.

Thanks,
Doug
If you (or they) feel comfortable releasing lots to production that "probably" have bad parts in them, why do inspection at all?
 

Tim Folkerts

Super Moderator
#18
Jim Wynne said:
If you (or they) feel comfortable releasing lots to production that "probably" have bad parts in them, why do inspection at all?
It obviously depends on the product. If the product is critical to health or safety, you treat defects differently than if the product is merely ornamental or disposable. If 1/100 disposable razors had a dull blade, I wouldn't be overly concerned, but if 1/100 scapels was dull, that could be a big problem.

It also depends on the defect rate. The economics change a lot if the defect rate is 1 in a million vs 1 in a thousand vs 1 in a hundred vs 1 in 10 vs 1 in 2. If "probably" 1/100 blades for a disposable razor were bad, economics might say that is good enough. If "probably" 1/3 was bad, then the economics has changed.

Inspection is for major changes. Depending on the situation, "major" might mean going from 5 to 100 bad pieces in a lot, or it might mean going from 0 to 1 bad pieces.


Tim F
 

Jim Wynne

Staff member
Admin
#19
Tim Folkerts said:
It obviously depends on the product. If the product is critical to health or safety, you treat defects differently than if the product is merely ornamental or disposable. If 1/100 disposable razors had a dull blade, I wouldn't be overly concerned, but if 1/100 scapels was dull, that could be a big problem.
I understand. But the question remains: If you don't care whether bad product gets to production or not (e.g., if it doesn't create expense, hardship, or bad feelings), what's the point in doing screening?
 

Tim Folkerts

Super Moderator
#20
Jim Wynne said:
I understand. But the question remains: If you don't care whether bad product gets to production or not (e.g., if it doesn't create expense, hardship, or bad feelings), what's the point in doing screening?
I wouldn't say its a question of caring vs not caring, but rather a question of how much I care. I care enough about deer in the road to wear a seat belt, but not enough to stay at home. It's a balance.

Similarly for bad parts. There are cases where paying less is worth a few bad parts in a lot. There are cases where paying for inspection is worth avoiding unusually bad lots.

Just my $0.02


Tim F
 
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