Difference between cpkppk

This topic has 3 replies, 4 voices, and was last updated 12 years, 8 months ago by CT.

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June 2, 2007 at 12:03 pm #47148

JIJU JOSEPH
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As per the def. in this site ppk is long term process capability & cpk is short term capability. But in the second edition of SPC( AIAG Manual) cpk is the limit of natural variation and ppk is total variation(cpk+special cuase variation). Anybody canclear my doubt?
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June 2, 2007 at 1:45 pm #156855

SS
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Both definition are same. Actually, short term capability of a process is due to natural variation or common cause variation whereas Long term capability includes both common cause and special cause variation.
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June 2, 2007 at 2:36 pm #156856

Fake Gary Alert
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Cp & Cpk are used for short-term capability and Pp,Ppk are used for long-term capability.
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June 2, 2007 at 5:46 pm #156859

CT
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Cp = Process Capability.
Cpk = Process Capability Index. Adjust for Non-Centered Distribution
Pp = Process Performance.
Ppk = Process Performance Index. Adjust for Non-Centered Distribution
Ppk produces an index number (like 1.33) for the process variation. Cpk references the variation to your specification limits. If you want to know how much variation is in a process, use a Ppk measurement. If you want to know how that variation will affect the ability of your process to meet customer requirements, you should use Cpk.
CT
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