Cpk and Ppk calculations for QS-9000 TE (Tooling and Equipment) Requirements

M

mibusha

#1
Cpk and Ppk calculations for TE

Can’t avoid it any longer. Must do something with CpK and PpK to satisfy QS 90000 TE requirements and to facilitate continuous improvement efforts. I’m in charge of registering 3 separate but related companies. Process capability and performance calculations are not my strong point. Three scenarios with three questions:

1)This company makes wood, plastic and metal core box patterns that are used to produce crankshafts or cylinder heads at the Ford foundries. We make anywhere from 2 to 6 at a time following Ford’s specific instructions (usually taken over the phone). All dimensions are checked to ensure they get what they asked for but no final dimensions are actually recorded anywhere. Plus they are always exact because if they aren’t, the Pattern Maker keeps working on it until it is correct. Question: What can I do to calculate CpK and PpK ?

2)Machine slides. We produce 2 to 6 at a time (total of 10 to 30 per month). All slides have a “print spec” to which we final audit for flatness, parallelism, surface fit, etc. We don’t have “batches” or enough volume to obtain samples in order to calculate CpK and PpK . We do keep all final audit reports that state the USL/LSL and measured values. Question: Is there a way to use these measurements to come up with a valid CpK and PpK ?

3)Automated Machines. These projects take from 3 to 8 months. Usually they are not full turn-key (missing the controls so won’t run). Question: How does one calculate CpK and PpK for this type of manufacturing? We can’t even do the Machine Qualification Runoff Testing (another requirement of TE) because controls are not in place and the customer does not require or want it done.


I would really appreciate help on these issues from knowledgeable folks.
 
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L

Laura M

#2
I think I've digested the scenarios and refreshed my memory enough to hopefully shed some light. I'm open for others interpretations, as my experience is somewhat limited.

First, reference the introduction “implementation” section….”however it is recognized that not all of these requirements are applicable to every organization” – unfortunately they use 4.4 – Design – as the example which is fairly obvious in regards to applicability. Having said that ‘continuous improvement” is obviously applicable, but how you go about accomplishing it may or may not involve Cpk/Ppk.

Since you mentioned facilitating continuous improvement efforts, I’m assuming you are referring to 4.2.5, and page 19 of QS, which says if you have variables data, that you need to optimize characteristics and parameters toward a target value. Your process should first be identified as “stable” – hence, SPC would apply. In the first 2 scenarios, short run SPC would seem to make sense – reference T/E supplement, page 14. Since you mention that the pattern maker works until the parts are exact, I’m not sure you even have an SPC application in the first scenario, but I would start writing down the data, and look for other CI possibilities – like first time quality, delivery timeliness, I am not personally familiar with any “custom work” scenario which would allow for SPC and Cpk to be used – but am willing to learn if anyone else is.

The Phase 1,2,and 3 process performance referred to in the T/E supplement would be regarding the product produced with the tooling. It doesn’t appear that you have the capabilities to do this. Anyway, once stability is proved, use data from your shortrun SPC charts for the process capability. Make sure you note process changes.

In the 3rd case, the Machine qualification section would apply. Since the machines are missing the controls, I would ask if you run parts manually? The SPC/CPk, PPk, would apply to the product produced by the machines. I worked with a T/E client that in some cases was just material handling equipment, no product was produced. Their qualification was the 50/20 dry run and MTBF, MTTR data. Without controls, I’m wondering how you verify your equipment can produce parts within specification today. Bottom line is the table on page 6 of T/E says, “As required by the customer.” Also take a close look at the “intent” stated in the bullets on page 6 of the T/E supplement. BTW – when do controls get installed? At the customer?


Finally, note that section 4.2 – Maintaining Process Control, in the T/E supplement refers to high volume tooling – if you are not required to “maintain process control” would imply that you shouldn’t be required to use Cpk analysis ongoing for continuous improvement either.
As stated on page 18 of QS – the continuous improvement philosophy shall be deployed throughout the organization. They couldn’t eliminate the product Cpk/PPk aspect for the T/E supplement because you do have high volume machine tool suppliers that this section could apply to.

With my training and experience to date, that’s the best I can do, and I’m open for discussion. Would love to hear from others that have been registered to T/E or the T/E registrars out there.

Now we can all probably use a refresher on Short-run SPC!
 
M

mibusha

#3
Very thourough response Laura, thanks. I think continuous improvement statistics will be the key here. Try to get data on MTTF, MCTF, etc. from the customer and then attempt to improve on it. Also count on our own improvements in delivery, cost, R&M predictions, etc. Might be able to get something from the customer on process capability but usually they don't want to be bothered. Could also do something in terms of turnaround for our repair work, and, as you suggested, first time quality. As far as Mach Runoff Qual Test-I've developed procedures for it and everyone has been trained on the requirements but...until we also install the controls it is not possible to run even one part for CPk/Ppk or 50/20hr data. Perhaps I'll see if I can follow the machine to the customer's site and participate next time around. Believe it or not, the picture is a bit clearer now.
 
M

mibusha

#5
Working on that now. Apparently we do in fact perform 20 hr runs although I haven't seen any records of it!! The machine slides are put through a rather extensive "2nd audit" to ensure that they are to customer spec. Also I was able to do some Target average and range charts to show capability and process performance.

My challenge is to document all this better than in the past. Thanks for the help.
 
L

Laura M

#6
Thought someone else might have chimed in by now? Are there any T/E certified companies that can add to my comments?
 
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