I have a question about using MMC on the SPC feature and how will it affect the UCL on capability charts. I'm doing capability studies on the 0.25 MMC position but this could change with the size of the feature so what will UCL be for the chart?
If you HAVE to use the bonus because you can't hold the feature in the declared value (0.25) and depending on how people around this issue feel about it...
You could subtract the bonus from your actual so that the UT stays static giving you a UCL that is solvable as a single value.
On reports, report the actual with the bonus, but, with a statement as to what you are doing and why, remove the bonus from the actual.
That is if you HAVE to use the bonus.
If you don't HAVE to use the bonus, just don't use it.
You will show less control, but if you run it without any bonus and run it like I said, write a position to engineering showing the delta, I would think no one would have an issue with a higher control value given the lack of full tolerance usage.
This isn't a direct answer to your question, but it is what I would do if I was needing to submit to a customer or justify some sampling rate.
Things like true position and flatness are a totally different animal for conventional SPC. Really can't be done properly (even without MMC) since zero is your target.
MMC on True Position is not doable. As
Caemgen said, this would be the way to do it. So if your bonus exceeds the true position value, it will be 0. Otherwise, what I have done in the past is if I have a set of 30 samples, I take the smallest bonus out of the subgroup and use that as my maximum. Gives us a rough estimate on the Cpk/Ppk.
Things like true position and flatness are a totally different animal for conventional SPC. Really can't be done properly (even without MMC) since zero is your target.
Yes it can. Zero will be your boundary. With a 0 to Max, your Cpk and Ppk will be the CPU and PPU, respectively. You will not have a CPL and PPL.
Hi, this is an awesome visual tool for Position. Can you help me understand what the "Average" and "Range" numbers mean? I kind of get it, but don't know how it's calculated.
I'm sorry, your parts are too flat. Please fix your process. Alternately, you holes are jumping around from 1 inch to the right to 1 inch to the left, so your process is perfectly in control. Please proceed with production.
These are examples of how people get into trouble by simply plugging flatness or true position values into regular CpK or SPC equations.
