Hi everyone. Is there a Cpk requirement for automotive industry stated in TS16949? I couldn't find it in the manual. Maybe 1.67 is still the standard practice?

My memory is that this is a customer specific requirement, not TS16949 general requirement Typically, they make a distinction among critical characteristics, key characteristics, and significant characteristics as well as between "capability" shown by PPAP and actual during real production.

Here's a sample clause from a customer specific requirement:

Characteristic mmmmmmmmmmmPPAPmmmmmmmmOn-going production

CriticalmmmmmmmmmmmPp/Ppk > 2.0 n=50mmmmmCp/Cpk > 1.67
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmm& Continuous Improvement

Key mmmmmmmmmmmmPp/Ppk > 2.0 n=40mmmmmmCp/Cpk > 1.67
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmm& Continuous Improvement

Significant mmmmmmmmPp/Ppk > 1.67 n=30 mmmmmCp/Cpk > 1.33
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmm& Continuous Improvement

Hi everyone. Is there a Cpk requirement for automotive industry stated in TS16949? I couldn't find it in the manual. Maybe 1.67 is still the standard practice?

TS16949 - 8.2.3.1 states "The organization shall maintain manufacturing process capability or performance as specified by the customer part approval process requirements"

Most of our customer requirements state 1.67 for the PPAP. Others state a minimum of 1.33. Some have no specified requirement.

Dave

My memory is that this is a customer specific requirement, not TS16949 general requirement Typically, they make a distinction among critical characteristics, key characteristics, and significant characteristics as well as between "capability" shown by PPAP and actual during real production.

Interesting this! Just the other day I was at an interview being asked just this very same question!!

My answer was in line with the quotation above, unfortunately I am not as capable as y in quoting from the standard. Now I do know that in real life (eg business life) things are a tad more complicated. But the interview setting wasn’t the place to elaborate on such practical issues.

However the MD doing the interview insisted that it was not the customer but more the tools themselves, those that you use in production that decides issues of capability.
Why would he say this? Could it be something that is/was true in the world of the old QS 9000??
And please could someone help me with this? Another issue at the interview concerned the relation between the old QS and ISO TS. I was under the impression that QS is to be phased out and replaced by TS. The MD however was very adamant about the fact that TS standard is only there to enhance the QS and that they would continue to coexist. I really would appreciate if someone could tell what goes here.

Cheers!

However the MD doing the interview insisted that it was not the customer but more the tools themselves, those that you use in production that decides issues of capability.
Why would he say this? Could it be something that is/was true in the world of the old QS 9000??

The capability that you achieve is based on the tolerances and the tools.
You must build the tool in a more accurate manner to achieve a higher capability as it must be in the middle of the tolerance. The capability is based on how much the MD is prepared to pay for the tooling.
The customer decide you need the equipment to comply


And please could someone help me with this? Another issue at the interview concerned the relation between the old QS and ISO TS. I was under the impression that QS is to be phased out and replaced by TS. The MD however was very adamant about the fact that TS standard is only there to enhance the QS and that they would continue to coexist. I really would appreciate if someone could tell what goes here.

Cheers!

You are right at the end of 2006 QS 9000 ceases to exist, the confusion could be that for the customer requirements the handbooks for PPAP, APQP,SPC,FMEA and MSA can remain the same

There is also the confusion of the 2 standards "co-existing" until December of 2006. Both QS and TS are active systems until that time.

Dave

Don't forget the little caveat found in AIAG PPAP 4th edition (2.2.11.5, NOTE) that Cpk's cannot be calculated if the distribution is non-normal, such as precision machined diameters and lengths. For more information, see Statistical process control for precision machining (http://elsmar.com/Forums/blog.php?b=79)

Let's get back to basics.

My understanding of SPC and Cpk < 1.67 was that if you do not meet it, then 100% testing is required.

If you are 100% testing, then provided you understand the influence of GR&R and you factor in an appropriate guardbanded test limit, you should be ok. (There should be a test and/or yield hit !)

Provided you then do seperate QA sample which should be to a clipped distribution, AOQ should be zero. Provided there is no test escape possibility proven over a large sample size, your customer should be ok with that.

Don't forget the little caveat found in AIAG PPAP 4th edition (2.2.11.5, NOTE) that Cpk's cannot be calculated if the distribution is non-normal, such as precision machined diameters and lengths.
The Note in question doesn't say that Cpk "cannot be calculated if the distribution is non-normal," it says,
The above mentioned [Cpk] acceptance criteria (2.2.11.3) assume normality and a two-sided specification (target in the center). When this is not true, using this analysis may result in unreliable information. These alternate acceptance criteria could require a different type of index or some method of transformation of the data. The focus should be on understanding the reasons for the non-normality (e.g., is it stable over time?) and managing variation. (Emphasis added).

For more information, see Statistical process control for precision machining (http://elsmar.com/Forums/blog.php?b=79)
This is where "understanding the reasons for non-normality" comes in. :agree1:

My understanding of SPC and Cpk < 1.67 was that if you do not meet it, then 100% testing is required.


The 4th Edition PPAP manual says that if the index is equal to or greater than 1.33 and less than or equal to 1.67,
The process may be acceptable. Contact the authorized customer representative for a review of the study results.For an index result < 1.33, it says,
The process does not currently meet the acceptance criteria. Contact the authorized customer representative for a review of the study results.

(Emphasis added).


Good emphasis. I would have emphasized assume normaility, too. :agree1:

At least the caveat gets people to look at that section....:tg: