N
narakorn
Dear Folks
I am a project manager in the automotive parts company in Thailand. Our company got ISO9000 last year and now going for QS9000.
I have learn a lot about SPC in the past cople year. However, most of the materials are only mention about theory of SPC. None of them explain how to start. This made me mad. Since, I have tried to ask the following question to our consultant but nothing clear for me. Two days ago, I found this web page and hope that someone out there can give me a light.
My question is quite simple and I would like to ask by uning 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 boths 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???)
2)Do we need to use X bar R chart during our run for PPAP?
3)If yes in 2, How can we set a UCL and LCL? (If the answer is, we can have it after we finish sampling, then calculate, so what about during the sampling, how can we sure that our process is in control, and if the number of require subgroup is large, we don't to end up do it all over again after finish sampling????)
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 e use Pp for this.
5) When will we apply Cpk instead of Ppk (when it stable??)
6) UCL, and LCL of X bar and R chart of Cp, Cpk come from???
7) Since Cpk is a study of short term, so how can we use Cp for ongoing process??
That would be all of my questions. Sorry for a long question but really need answer.
Regards,
Narakorn Ratchapolsitte
PS: Sorry for my English, it does not be our first langauge here in Thailand
------------------
I am a project manager in the automotive parts company in Thailand. Our company got ISO9000 last year and now going for QS9000.
I have learn a lot about SPC in the past cople year. However, most of the materials are only mention about theory of SPC. None of them explain how to start. This made me mad. Since, I have tried to ask the following question to our consultant but nothing clear for me. Two days ago, I found this web page and hope that someone out there can give me a light.
My question is quite simple and I would like to ask by uning 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 boths 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???)
2)Do we need to use X bar R chart during our run for PPAP?
3)If yes in 2, How can we set a UCL and LCL? (If the answer is, we can have it after we finish sampling, then calculate, so what about during the sampling, how can we sure that our process is in control, and if the number of require subgroup is large, we don't to end up do it all over again after finish sampling????)
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 e use Pp for this.
5) When will we apply Cpk instead of Ppk (when it stable??)
6) UCL, and LCL of X bar and R chart of Cp, Cpk come from???
7) Since Cpk is a study of short term, so how can we use Cp for ongoing process??
That would be all of my questions. Sorry for a long question but really need answer.
Regards,
Narakorn Ratchapolsitte
PS: Sorry for my English, it does not be our first langauge here in Thailand
------------------