For those just coming across this issue in the archives, I am updating the responses to current requirements:
Go figure...
It is probably not applicable at all. Drilling is not a normal distributions, and surface finish is not a bilateral specification. See below:
AIAG PPAP 4th Edition
2.2.11.5 Processes with One-Sided Specifications or Non-Normal Distributions
NOTE: The above mentioned 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.
NOTE (cont.): 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 reasons for the non-normality (e.g. is it stable over time?) and managing variation.
For drilling, use a X hi/lo-R chart. Xbar -R chart is the worst chart you can use. See Statistical process control for precision machining . You might be able to use an X-bar-R chart for surface finish if it is bad enough to exhibit a normal distribution.
You need to do a capability study to determine the true control limits for the surface finish.
See Question 1.
See Question 1.
They originate from the capability study.
See Question 1.
Since, I have tried to ask the following question to our consultant but nothing clear for me.
My question is quite simple and I would like to ask by using the following model.
Model: Suppose that I have one new machine which operate only one process , let say drilling dia 10 +/- 0.1 mm and roughness is 6.3Rz . Our customer request us to use SPC for both value where the requirements are
1) For PPAP, Ppk must greater than 1.67
2) For ongoing SPC Cpk must greater than 1.33
Question: 1)Why we use Ppk at the PPAP stage? (Ppk is for long term study but doe not require for stability???)[/
Model: Suppose that I have one new machine which operate only one process , let say drilling dia 10 +/- 0.1 mm and roughness is 6.3Rz . Our customer request us to use SPC for both value where the requirements are
1) For PPAP, Ppk must greater than 1.67
2) For ongoing SPC Cpk must greater than 1.33
Question: 1)Why we use Ppk at the PPAP stage? (Ppk is for long term study but doe not require for stability???)[/
AIAG PPAP 4th Edition
2.2.11.5 Processes with One-Sided Specifications or Non-Normal Distributions
NOTE: The above mentioned 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.
NOTE (cont.): 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 reasons for the non-normality (e.g. is it stable over time?) and managing variation.
2) For ongoing SPC Cpk must greater than 1.33
Question: 2)Do we need to use X bar R chart during our run for PPAP?
Question: 2)Do we need to use X bar R chart during our run for PPAP?
Question 3)If yes in 2, How can we set a UCL and LCL?
Question 4) For one side spec (roughness in this case),if the requirement is Ppk greater than 1.67. It means that the average value will near 3.2Rz which also means that we have to design our process not for 6.3Rz but for 3.2Rz Otherwise, we will not earn those. For this case, it will cost a lot more, so can we use Pp for this.
Question 5) When will we apply Cpk instead of Ppk (when it stable??)
Question 6) UCL, and LCL of X bar and R chart of Cp, Cpk come from???
Question 7) Since Cpk is a study of short term, so how can we use Cp for ongoing process??