What to Report when Using C=0 Sampling Plan

R

RosieA

We use a C=0 sampling plan for receiving inspection. When there is a defect found in the sample, we generally move to 100% rather than return the lot.

What should be reported as the reject quantity in this case? Should it be the total lot quantity, or just the number of rejects that were found in the 100% inspection?

What seems to be happening is that QA is recording the entire lot quantity, (which makes it to me at the end of each month) while the debit and SCAR to the supplier reports what was actually found non-conforming.

Needless to say, our suppliers are confused, because the ppm# they see from me on their supplier Scorecard, does not match what is being reported to them through the Buyer or SCAR.
 

Stijloor

Leader
Super Moderator
Re: What to Report when Using C=0 Sampling Plan ?

A Quick Bump!

Can someone help Rosie?

Thank you very much!!
 

Steve Prevette

Deming Disciple
Leader
Super Moderator
What should be reported as the reject quantity in this case? Should it be the total lot quantity, or just the number of rejects that were found in the 100% inspection?

SSP: First, you have to report that the "test" failed. And your C=0 Sampling Plan ought to have in it what is the policy for when a test fails. Simply resampling the whole lot is not necessarily a good practice. At what point would you reject the lot and send it back? Is that recorded in the plan?

What seems to be happening is that QA is recording the entire lot quantity, (which makes it to me at the end of each month) while the debit and SCAR to the supplier reports what was actually found non-conforming.

SSP: What do they record when a lot passes the C=0 test? They should similarly record when the test fails. Then, if there is supplemental information that should be recorded, and a final declaration of pass or fail on the lot.

Needless to say, our suppliers are confused, because the ppm# they see from me on their supplier Scorecard, does not match what is being reported to them through the Buyer or SCAR.

SSP: True, whatever the message is, it needs to be consistent, and in accordance with the sampling plan.

In general, a big failing of sampling plans I review is they never specifiy a "get out of jail" path if the test were to fail.
 

Mike S.

Happy to be Alive
Trusted Information Resource
Re: What to Report when Using C=0 Sampling Plan ?

Steve gives good advice.

If we reject a supplier's lot via C=0 sampling, we usually return the entire lot for the supplier to replace it or do the 100% sorting themselves, in which case the entire lot quantity is held against the supplier as far as quality rating calculation.

If it is in our best interest to do the sorting (urgent need) we hold the actual qty of nonconforming parts we find in the lot against the supplier.

In either case, we demand a good, strong, RCCA response to keep it from happening again. But that is a whole different discussion....
 
R

RosieA

Thanks Steve and Mike.

We almost always do the 100% sort because we need the material for production.

Our C=0 plan calls for two outcomes to a failed test, RTV or sort. The issue is what gets recorded in the Receiving Inspection plan...I think I'm reading this right, that the plan should indicate a failure for a specific reason (which we do) and the quantity would be the results of the 100% inspection.

We calculate ppm on quantity received vs. quantity rejected, not by lot.

Did I read your responses correctly?
 

Steve Prevette

Deming Disciple
Leader
Super Moderator
Yes. Though - please consider the risk that 100% inspections are rarely 100% effective, so if you are having repeated failures of the sampling plan, you likely have repeated unsatisfactory materials coming through. Worse, if the supplier is aware that all you do is pay for your own 100% sort, what incentive do they have to improve?
 
R

RosieA

Re: What to Report when Using C=0 Sampling Plan ?

Good point. We do debit for material, but not all plants debit for time and labor when doing the 100% sort.
 

Bev D

Heretical Statistician
Leader
Super Moderator
Back to basics: What do you want your supplier to do? And what does your supplier need to know in order to do it

If it was me, I'd want to know that the test failed AND what the defect rate of the lot was. since the defect rate calcualted from a smaller sample has larger possible deviation from the true defect than a larger sample, I woudl want to know the total number that failed. it might be acedemically interesting to compare the total defect rate to the number of defects found in the sample inspection, but that probability space is quite well documented and it really isn't helpful to me in improving my processes to know that you got lucky, or I got lucky in your sample inspection.

If you really want me to improve my process you'll focus my efforts away from deflective conversations about samping inspection and keep me focused on the 'actual' defect rate. (no 100% isn't 100% accurate, but an estimate from a large sample - even 100% - is more precise than an estimate from a small sample.

And if you really want to have a cost incentive, charging me for all of the defective parts you found and the labor it took to determine that, then you have to tell me how many defecgts were found.
 

Mike S.

Happy to be Alive
Trusted Information Resource
Are the rejections usually the same part and/or supplier being rejected over and over again, or are the failures usually unique, or do you have both situations going on?

Especially if there is a repeat failure for a given part, I would make it one of my top priorities to work with that supplier to make this problem stop ASAP.

Get all the internal support you can (Purchasing, Program Management, your boss, etc.) and lead the effort to kill these kinds of problems that expose your company to liability to one degree or another and waste. Sometimes it is a battle, sometimes a supplier never "gets it" and needs to be replaced. But I have had horrible suppliers whom I eventually helped get turned around and in one case 2 years later they were our very best supplier, so success is possible.
 
R

RosieA

I think I need to refocus this thread a bit....my problem is not that we are or are not driving corrective actions, (we are) or doing 100% inspection or not, it's how does the reject get reported for the metrics....as 100% reject or as the real number of rejects found during the 100% inspection.

Just an FYI, I understand and agree with what everyone is saying, and am proud that we have dropped our supplier ppm by 70% in the three years my department has been around. My question, however, is how the initial reject from the C=0 sample gets reported.
 
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