What are CPK and PPK? What is the difference between them?

What are CPK and PPK? What is the difference between them?

A: CPK is complex process capability index.
The abbreviation used by modern enterprises to representProcess Capability. Strong process capability can produce products with high quality and reliability.
PPK is an index used to calculate the process capability or process capability in SPC Central Control drawing. It refers to the process performance of sample data when there is a deviation in the process.

Difference between CPK and PPK:

1. CPK
This is mainly because of the variation between sub-groups. Therefore, data must be grouped. That is to say, the collection value is grouping, involving sub-groups, sub-group capacity, and collection frequency. It targets a long-term process. When CPK is used, the process must be controlled.

2. PPK is the effect of overall variation. It does not take into account the value collection process. It can be used continuously or intermittently.

3. The evaluation process of PPK is a stable process, PPK may not be a stable process, and the sample capacity of CPK is 30 ~ 50, PPK sample size is greater than or equal to 100; CPK rating is a single batch (several hours
Or a few days), PPK reviews multiple batches (weeks or months ). CPK = 1.33 (1.5 deviation) is 4 σ level, the pass rate reaches 99.379%. Based on PPAP manual in the automotive industry
The acceptance criteria for CPK in the mass production phase are ≥ 1.67. But ≥0. 5 indicates that it is acceptable and needs to be improved.
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4. CPK-Process Capability Index (short-term)

5. PPK-Process Performance Index (long-term

6. "PPK is the capability evaluation of small batch production before entering mass production. Generally, the requirement is greater than or equal to 1.67. CPK, after entering mass production, to ensure that the quality of products in mass production is not
To ensure the same control capability as the small batch production, the evaluation of production capacity generally requires ≥ 1.33. In general, CPK needs to use the control limit of PPK for control.