Mean

n

Median

STDEV

Cp Cpk % out of tolerance

Min/Max

Compare with

Calculate Difference

Diff mean normally

Diff median not normally

Diff variation normally

Diff variation not normally

Normally test

Correlation

Regression

Kurtosis

Skewness

For commercial use

75 EURO

To check if the production process is capable to produce within specification limits. The Cp Cpk Pp and Ppk are used together with Control charts in Statistical process control (SPC).

What is the difference between Cpk vs Ppk or Cp vs Pp?

The Cp and Cpk is used when a process is under statistical control. For not production environment (testing, new process or setting) use the Pp and Ppk!

Violet

the process is The Cp value of a data-set is only calculated if the min and max tolerance are available.

With a higher Cp value the variation is smaller and it is possible to produce with a higher quality.

Violet

the process is With a higher Cpk value the data set is better within tolerance.

Two sided table | |||

Cpk Ppk | Sigma level | % out of tolerance | PPM out of tolerance |

0.33 | 1.0 | 31.73 | 317310.508 |

0.50 | 1.5 | 13.36 | 133614.403 |

0.67 | 2.0 | 4.55 | 45500.264 |

0.83 | 2.5 | 1.24 | 12419.331 |

1.00 | 3.0 | 0.27 | 2699.796 |

1.17 | 3.5 | 0.05 | 465.258 |

1.33 | 4.0 | 0.01 | 63.342 |

1.50 | 4.5 | 0.001 | 6.795 |

1.67 | 5.0 | 0.0001 | 0.573 |

1.83 | 5.5 | 0.000004 | 0.038 |

2.00 | 6.0 | 0.0000002 | 0.002 |

1 is no subgroups the STDEV within will be estimated and the Cp and Cpk will be calculated.

>1 there are subgroups and the Cp and Cpk are calculated with the estimated STDEV within.

So the the following data is filtered

- Drift of the process in time
- Tool wear
- Drift due different operators
- Drift due material batches

Data file

USL = Upper specification limit

LSL = Lower specification limit

= STDEV within

- Do a Gauge R&R and try to improve the measurement.
- Label the data in subgroups to identify the factors that can cause that the process is not in control.

Red

the data set is not according the normal distribution.The Pp value of a data-set is only calculated if the min and max tolerance are available.

With a higher Pp value the variation is smaller and it is possible to produce with a higher quality.

Red

the data set is not according the normal distribution.With a higher Ppk value the data set is better within tolerance.

Red

the data set is not according the normal distribution.calculate the value out of the t distribution.

% out of tolerance

s = STDEV

USL = Upper specification limit

LSL = Lower specification limit

Data file

- http://en.wikipedia.org/wiki/Process_capability_index
- http://www.itl.nist.gov/div898/handbook/pmc/section1/pmc16.htm
- http://en.wikipedia.org/wiki/Three_sigma_rule
- http://en.wikipedia.org/wiki/Parts-per_notation