4.9.3 Modified Process Control Requirements



I'm confused about this clause. I can't understand if it is refering to cpk's or it is taking about some product characteristic in particular.

Can anybody out there explain to me ?



Captain Nice
Staff member
I think this means - say you have a supplier who cannot keep a high Cpk because of a tight tolerance (or whatever excuse / reality). Then they have to have a tight inspection in the Control Plan compared to what they would have if they could hold a high Cpk.


I think Marc is correct. I also think that this section is a "out" for customers to specify something that may not be stated elsewhere, such as a generic performance specification or tolerance on a drawing.

We have had a couple of occasions where there was a new requirement for testing that was a result of a failure long after a product had been in production. Example, a customer is suddenly experiencing breakage, so we instituted a break test sample. This was added to our control plan. It is not necessarily stated anywhere on the customer's drawing or specifications, however.

If there is some requirement, such as a higher Cpk, you should have addressed this in APQP, including a feasibility review, anyway. So requirements above the minimums in QS9000 and APQP and Control Plan manuals should already have been addressed.


Captain Nice
Staff member
There is the problem of reality vs APQP. Supplier goes thru APQP and just about PPAP when the capability run is done, it's discovered that the measurement method of a characteristic isn't valid or the tolerance is taken up in measurement uncertainty. All the early theory simply didn't prove out or someone forgot something (yes, we are human and human systems do fail rom time to time). So - do we get the engineers to do an 11th hour engineering change to open up the tolerance? Or do we allow the supplier to carry a low Cpk with 'special' receiving inspection? Do we make a hard gage for the check or do we write a CMM program? Will an optical comparator be a better choice?

The bottom line is you continue to try to solve the problems and get on with the show. Reality is a pain in the ass. Systems developed to comply with the APQP 'philosophy' are, in my opinion, a positive control factor - This is to say I have a firm belief in defined design systems and in the APQP philosophy, if you will, as a basic control of 'holistic' and coordinated product evolution.

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