How AQL Inspection & Test corresponds to Control of Nonconforming Product

[Douglas E. Purdy]

I would like the theoretical understanding of how an AQL Inspection & Test corresponds to the requirement for Control of Nonconforming Product. I am currently in debate with management on what I think is a conflict with the current practice.

The case being discussed involves a characterisitc that is only verified by Manufacturng Operators. The characteristic is not inspected by QC Inspectors during their Inspection Points during the manufacturing process. During Final Inspection by QC, who is performing 100% Visual Inspection of all cutting surfaces, four (4) pieces out of a lot of 1900 pieces are scrapped for a dimensional characteristic (a "narrow" characteristic). What compounds this scrapping activity is that the lot of 1900 pieces was inspected by 4 different inspectors over a five day period. There is no indication as to which of the inspectors scrapped the product and when the nonconformance was identified.

Most of the current management believes that the scrapping of the four pieces does not require any further control of the nonconforming product. The lot does not need to be sorted for the dimensional characteristic. The four nonconformances were identified during a 100% Visual Inspection by four competent inspectors over a given time period. My boss presents the rationale that since Inspection & Test to an AQL allows for acceptance of a level of nonconformity, that any nonconformity (visual or dimensional) identified during 100% Visual Inspection is sufficient and that the job does not require any further sorting - let alone 100% sorting and measurement for the dimensional requirements established internally - not an external requirement.

What would you do and why?

Thanks,
Doug

[Jim Wynne]

In Reply to Parent Post by Douglas E. Purdy

During Final Inspection by QC, who is performing 100% Visual Inspection of all cutting surfaces, four (4) pieces out of a lot of 1900 pieces are scrapped for a dimensional characteristic (a "narrow" characteristic).

How is a dimensional requirement visually verified? What is a "narrow characteristic"?

In Reply to Parent Post by Douglas E. Purdy

What compounds this scrapping activity is that the lot of 1900 pieces was inspected by 4 different inspectors over a five day period. There is no indication as to which of the inspectors scrapped the product and when the nonconformance was identified.

If there were no records, how do you know that material was scrapped? Does your system allow for scrapping of n/c parts without documentation? If so, under what circumstances?

In Reply to Parent Post by Douglas E. Purdy

Most of the current management believes that the scrapping of the four pieces does not require any further control of the nonconforming product.

You can't control what doesn't exist . If the parts are gone, they're gone.

In Reply to Parent Post by Douglas E. Purdy

The lot does not need to be sorted for the dimensional characteristic. The four nonconformances were identified during a 100% Visual Inspection by four competent inspectors over a given time period.

It sounds like the lot has had the bejeepers inspected out of it, so what would you hope to accomplish by more inspection? When would you stop?

In Reply to Parent Post by Douglas E. Purdy

My boss presents the rationale that since Inspection & Test to an AQL allows for acceptance of a level of nonconformity, that any nonconformity (visual or dimensional) identified during 100% Visual Inspection is sufficient and that the job does not require any further sorting - let alone 100% sorting and measurement for the dimensional requirements established internally - not an external requirement.

AQLs are correctly associated only with sampling inspection. If you're doing 100% inspection and applying an AQL, someone is confused. If you 100% inspect a lot and find x number of defectives, you know that there is a possibility that some defectives went undetected. What you do next is a matter of the level of risk involved and the cost of inspection vs. the potential cost of problems caused by defective parts.

Of course, this is a matter of process control, and discovery of defects should be used to help improve the process, and for that reason alone, defects should always be recorded and reported.

[Bev D]

How critical is the characteristic? will it lead to certain product failure? or will it be hard fo rthe custoemr to notice?

How effective is the visual inspection of this characteristic? Is there a chance that visual inspection coudl miss it?

[Douglas E. Purdy]

In Reply to Parent Post by Bev D

How critical is the characteristic? will it lead to certain product failure? or will it be hard fo rthe custoemr to notice?

Does it matter when it comes to control of nonconforming product? I would think that is a question for the disposition phase of the process. The dimensions for the characterisitc are per our manufacturing specifications and not some external specification.

In Reply to Parent Post by Bev D

How effective is the visual inspection of this characteristic? Is there a chance that visual inspection coudl miss it?

The QC Manager believes that the visual inspection is very effective. My problem is that the visual inspection is ONLY DOCUMENTED for the cutting surfaces NOT A COMPARATIVE VISUAL OF ALL CHARATERISTICS.

My concern is that the whole lot was not inspected for the nonconformance - but apparently this is not a concern with the rest of management.

Thanks,
Doug

[Douglas E. Purdy]

In Reply to Parent Post by JSW05

How is a dimensional requirement visually verified? What is a "narrow characteristic"?

My assumption is that the presence of a characteristic (or absence) may be made during a Visual Inspection, but they are performing a comparative visual - but not to a given standard.

In Reply to Parent Post by JSW05

If there were no records, how do you know that material was scrapped? Does your system allow for scrapping of n/c parts without documentation? If so, under what circumstances?

We have a "Scrap" Column on the Manufacturing Route where the QTY is documented for the given operation.

In Reply to Parent Post by JSW05

It sounds like the lot has had the bejeepers inspected out of it, so what would you hope to accomplish by more inspection? When would you stop?

The characteristic that was found to be "narrow" is not inspected by QC. It is verified by Manufacturing. Manufacturing verified the characteristic (no specified frequency in the Control Plan) and there were no rejections. So I would not say that the "lot has had the bejeepers inspected out of it." My question is should the lot be sorted for the dimensional non-conformance?

In Reply to Parent Post by JSW05

AQLs are correctly associated only with sampling inspection. If you're doing 100% inspection and applying an AQL, someone is confused. If you 100% inspect a lot and find x number of defectives, you know that there is a possibility that some defectives went undetected. What you do next is a matter of the level of risk involved and the cost of inspection vs. the potential cost of problems caused by defective parts.

Of course, this is a matter of process control, and discovery of defects should be used to help improve the process, and for that reason alone, defects should always be recorded and reported.

We have designated QC Inspection Points that perform dimensional inspections to a Sampling Plan during the manufacturing process. It is at Final Inspection that a 100% Visual is being performed of all cutting edges. Hope that clarifies your confusion.

So it would appear that based on the risk, you would not perform a dimensional sort of the lot - correct?

Thanks,
Doug

[Jim Wynne]

Douglas:

I'm still a bit confused (my normal state, if you ask my wife). In your initial post you said,

the lot of 1900 pieces was inspected by 4 different inspectors over a five day period.

Now you say,

The characteristic that was found to be "narrow" is not inspected by QC. It is verified by Manufacturing. Manufacturing verified the characteristic (no specified frequency in the Control Plan) and there were no rejections. So I would not say that the "lot has had the bejeepers inspected out of it." My question is should the lot be sorted for the dimensional non-conformance?

So here's what I think you mean: Production ran for x days and during that time there were no rejections. At final inspection, however, 4 pieces were rejected and scrapped. OK so far?
Then the lot has been 100% inspected, albeit not all by the same person. The inspection process identified allegedly defective parts. You want to know whether further processing should be done, and your boss doesn't think so, due to some as-yet unexplained (and perhaps misguided) AQL rationale.

In Reply to Parent Post by Douglas

So it would appear that based on the risk, you would not perform a dimensional sort of the lot - correct?

I don't know anything about the risk, so I'm not recommending anything other than making a decision based on what you know about the risk, and changing your process so that discovery and documentation of nonconforming material provides the information you need in order to improve the process.

[Douglas E. Purdy]

JSW05,

Now you have it. Sorry I was not clear. The job comes into Final Inspection in what I call sub-lots. The Final Inspection went over several days by a number of different inspectors.

So, given the Standard (ISO-9001) requirement for Control of Nonconforming Product; would you have the lot of 1900 sorted for the dimensional nonconformance OR presume that the 100% Visual during Final Inspection was sufficient? Or does it depend on the risk?

Thanks,
Doug

[Jim Wynne]

In Reply to Parent Post by Douglas E. Purdy

JSW05,

Now you have it. Sorry I was not clear. The job comes into Final Inspection in what I call sub-lots. The Final Inspection went over several days by a number of different inspectors.

So, given the Standard (ISO-9001) requirement for Control of Nonconforming Product; would you have the lot of 1900 sorted for the dimensional nonconformance OR presume that the 100% Visual during Final Inspection was sufficient? Or does it depend on the risk?

Thanks,
Doug

The known* nonconforming product is gone. What's left is a lot that may or may not contain additional defectives. Of course, you can say that about any lot of material, so it boils down to confidence. No one here can help you with that--you need to decide for yourself if the risk is worth reinspection or not. There's nothing in ISO-9000 that says you have to inspect anything. You need to do containment (make sure that the suspect lot is identified and no further processing happens until a decision is made) and you need to document your findings and decision. Other than that, it's up to you.

*Actually, "known" may not be accurate. Because the parts identified as nonconforming were scrapped, no determination can be made now as to whether "scrap" was the correct disposition. Part of control of NC material is segregation of the rejected parts until a formal disposition can be made.