4.9.2 Maintaining Process Control - Maintaining ongoing process capability



If one reads this element literally, and I do mean literally, it borders on the absurd. "The supplier shall maintain(or exceed) process capability or performance as approved via PPAP. Should one interpret this to mean if a PPAP is submitted showing a short term capability of 2.0, that a 2.0 would have to be maintained ongoing? This contridicts the PPAP Manual page 8 which talks about a lower Ppk of 1.33 ongoing as opposed to a 1.67 which is required for ppap submission. Our registrar is hanging on the literal and I have a feeling we are being hung period. I would like someone elses intrepretation. Thanks, Mike
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Staff member
The PPAP manual is a guide and as such is not auditable so you have to stick with the QS9000 book as the focus of your compliance

I'm not savvy on how they are interpreting the capability aspect of your question. I'll take a looksie if I get a few minutes this weekend and see what the books say.

Anyone else want to field an opinion on this issue?

Lyndon Diong

I flip through the manual but could not locate that statement. Where exactly does that statement come from?

Lyndon Diong

Disregard my previous message. I found that statement in the Third Ed. I think Cpk is just one of the indicator of process capability.
If your Cpk is 2 as approved via PPAP, which exceeds 1.33. During production your Cpk is 1.7 which also exceeds 1.33. Therefore you are maintaining the Cpk exceeding 1.33 as approved via PPAP.
Does this sound logical?


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Staff member

Please cite where in the new QS the statement is that contradicts the PPAP manual. I'll look closer at it and give you my read. I think what you are asking is this: "If I submit PPAP with a capability Ppk of 2.0 is that my minimum Ppk through out the life of production?"

Christian Lupo

I'll agree with Chad on this one. If there was one thing that was reiterated time and time again while I was becoming a QS certified auditor, it's that there are 3 documents that make QS-9000: The QSR manual, PPAP, and the QSA. These three document are mandatory. FMEA, APQP, MSA, and SPC are "optional". The way the QSR reads they are mandatory options if there is such a thing.

Chad Nunnery

A slight correction to what was stated earlier. Since indicates "The supplier shall fully comply with all requirements set forth in the Production Part Approval Process (PPAP) manual," I believe this means that the PPAP manual is auditable.

Lyndon Diong

1) Am I right to say that full PPAP requirements are applicable to suppliers to Ford, GM and Chrysler, but partially (with modification) applicable to party seeking third party registration?
2) Could someone response to MSHELLEY's question? If that (4.9.2)is taken literally, I need to list all Ppk values for different products submitted and and compare them against current values. This is a lot of work. I prefer a fixed value e.g. > 1.33.

Scott Knutson

I'm going to agree with what Christian has said. If you look at the document progression chart on page 6 of the third edition, it clearly shouws that the QS9000 manual and PPAP are to "define customer requirements". APQP, FMEA, etc. are listed under "Customer Reference Manual," though this goes against what LRQA recently told a large manufacturer going through a QS9000 certification audit.

Roger Eastin

I think the wording in the PPAP manual is somewhat confusing on page 8. It looks like the Big 3 want to "hedge" a little bit. It's clear that they may not be satisfied with Ppk between 1.33 and 1.67, even though according to their criteria, this assumes that the process is stable. They clearly want Ppk above 1.67. I would say that if your process is submitted with a Ppk of 2.0, then this needs to be maintained throughout the product's production life. It looks like if you submit with a certain Ppk, then that's what the Big 3 (or auditor) expects to see as the ongoing "requirement" for your process. I would take the statement under 4.9.2 as the overriding requirement for Ppk.
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