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- Common Quality Assurance Processes and Tools
- Capability, Accuracy and Stability - Processes, Machines, etc.

J

Thanks all of you two!

as far as I know ,in AIAG SPC manual Cpk is Process Capability Indies,Ppk is Process Performance Indies,Cpk>1.67,Ppk>1.33:but in VDA2 Cpk is long-term Process Capability ,Ppk is Preliminary Process Capability ,Cpk>1.33,Ppk>1.67.

Howard Atkins, I still need you help, I want know the Formulas of Ppk in VDA4.1. what is more,I want know the Formulas of σtot in page 137 of VDA 4.1 3rd edition.

as far as I know ,in AIAG SPC manual Cpk is Process Capability Indies,Ppk is Process Performance Indies,Cpk>1.67,Ppk>1.33:but in VDA2 Cpk is long-term Process Capability ,Ppk is Preliminary Process Capability ,Cpk>1.33,Ppk>1.67.

Howard Atkins, I still need you help, I want know the Formulas of Ppk in VDA4.1. what is more,I want know the Formulas of σtot in page 137 of VDA 4.1 3rd edition.

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jinzhoujun said:

as far as I know ,in AIAG SPC manual Cpk is Process Capability Indies,Ppk is Process Performance Indies,Cpk>1.67,Ppk>1.33:but in VDA2 Cpk is long-term Process Capability ,Ppk is Preliminary Process Capability ,Cpk>1.33,Ppk>1.67.

I do not think that there is any real difference

R

Whether Ppk is called "process performance" or "preliminary process capability", all it really means is that all or most of the data is known - meaning that you can use standard deviation in the denominator. Cpk uses an estimate (e.g. some constant factor of a range value) to determine sigma, and is more often long term (as in the case of getting the data from current control charts).