Final process capability results - What I am supposed to present? Cp and CpK?


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There are SC's for which the team will prepare Cpk and same for all CC's such as bolt tightening.
There's something that is not clear for me - what do you mean that I have to back up CC's with SPC of process parameters? can you clarify for me ?
Disregard this, I made a quick read at the documents in the link and I interpreted poorly. :yuk:

The document in the link states "continuous manufacturing process control" (IATF CSR page 40). For example, in an injection molding process a machine can normally obtain outputs per each shot, like melt cushion or injection time. In case your melt cushion deviates from a defined tolerance you could reject the part or stop the machine automatically. If you'd be injecting a part with a CC you can use SPC provided you also have this type of control, i.e. 100% automatic control. Another example of a process where this is applicable -that I know- is resistance welding.

If I have understood correctly I and the team have to do SPC (calculating Cpk) for all Significant and Critical characteristics listed in SCCAF/PFMEA/Control Plan ? is that correct ?
That is not correct. If you could have poka-yokes or automatic controls for all special characteristics then you would not need SPC. Those controls are more likely to prevent shipping NOK product. You would opt for SPC as an alternative to the higher costs of other detection methods in processes which have potential to be stable, and/or when you want to track a trend in the process (e.g. tool wear in stamping)

I would also pay attention to Johnnymo62's advice and stick to Ppk, as in the documents provided.

and another thing still not clear for me - For process crimping, terminal crimp height is SC, but it is quite difficult to do process capability (Cpk) on all terminals being used in production, so from one machine we must make 125 consecutive samples(crimped terminals) measure this characteristic, put the data in the software, set LSL and USL and check what is the variability. I see the things that way, but not sure if it is correct.
For me Cpk should be used in my case, not Ppk since Ppk is used for process performance, not process capability if I am not mistaken.
Since the topic you have been assigned is "final process capability results" I would advice you to read through the doc Ford specifics for PPAP pages 7-9.

I do not think 125 consecutive parts from one machine is a suitable demonstration of final process capability. There is a lot of variation that you are not addressing.

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