SPC mis applied?
JSW05 said:
.....is x-bar/R charting with a minimum of 25 subgroups and 100 data points with sampling done during the PPAP production run....
I have never understood the requirement for x-bar/r with subgroups of 4.
It seems to ignore rational subgrouping. In my process at least we collect all the PPAP run parts, so I use X and mR charts. I lost a pitched battle with a Chrysler SQE and finally had to do it by the book.
I did extensive comparisons with the data using both methods and the conclusions drawn were the same using either method.
I could not get an explanation why I should arbitrariy grouping 4 parts together that were not collected as a sample of 4. The best he could do was "the book says so".
Anyway the customer is always right I guess.