![]() |
|
![]() |
Free
desktop six sigma, DPMO/PPM, Yield, Cpk calculator and converter
|
Distribution Centered |
||||
# of parts | +/- 3 Sigma | +/- 4 Sigma | +/- 5 Sigma | +/- 6 Sigma |
10 | 97.33% | 99.94% | 99.9994% | 99.999998% |
20 | 92.74 | 99.87 | 99.9989 | 99.999996 |
30 | 92.21 | 99.81 | 99.9983 | 99.999994 |
40 | 89.75 | 99.75 | 99.9977 | 99.999992 |
50 | 87.36 | 99.68 | 99.9971 | 99.999990 |
60 | 85.03 | 99.62 | 99.9966 | 99.999988 |
70 | 82.76 | 99.56 | 99.9960 | 99.999986 |
80 | 80.55 | 99.49 | 99.9954 | 99.999984 |
90 | 78.40 | 99.94 | 99.9948 | 99.999982 |
|
||||
Distribution Shifted One Sigma |
||||
# of parts | +/- 3 Sigma | +/- 4 Sigma | +/- 5 Sigma | +/- 6 Sigma |
10 | 79.42% | 98.66% | 99.968% | 99.9997% |
20 | 63.07 | 97.33 | 99.937 | 99.9994 |
30 | 50.09 | 96.03 | 99.905 | 99.9991 |
40 | 39.78 | 94.74 | 99.873 | 99.9989 |
50 | 31.59 | 93.47 | 99.842 | 99.9986 |
60 | 25.09 | 92.21 | 99.810 | 99.9983 |
70 | 19.93 | 90.98 | 99.779 | 99.9980 |
80 | 15.82 | 89.75 | 99.747 | 99.9977 |
90 | 12.57 | 88.55 | 99.715 | 99.9974 |
Interpreting the Capability Indices
Compare the abnormal and normal indices. Capability indices are quite sensitive to assumptions of the distribution.
A Capability index is a statistic, subject to statistical error.
Most Engineers or Black Belts consider a capable process to be one that has a Cpk of 1.33 or better, and a process operating between 1.0 and 1.33 is "marginal." Many companies now suggest that their suppliers maintain even higher levels of Cpk.
A Cpk exactly equal to 1.0 would imply that the process variation exactly meets 3 Sigma. A Cpk exactly equal to 1.33 would imply that the process variation exactly meets 4 Sigma. If the process shifted slightly, and the out of control condition was not immediately, if not sooner, detected, then the process would produce scrap. This is the reason for the extra .33. It allows for some small process shifts to occur that could go undetected. The Table located here, provides an indication of the level of improvement effort required in a process to meet these escalating demands, where "PPM Out of Specification" refers to the average defect level measured in parts per million, (PPM).
Using Defects Per Unit To
Benchmark Different Products
Given equivalent design margins and levels of process control, DPU is proportional to parts count.
Therefore, we can benchmark different products if we know (or can estimate), DPU and parts count.
We normalize products with different parts count by calculating PPM/part
PPM/part = DPU ------------------------ Parts Count To achieve this in six sigma, you can use our free software.
Also see DPO, (defects per opportunity), and DPMO, (defects per million opportunities).
|
Copyright � 2005 Six
Sigma SPC / Jim Winings All Rights Reserved
|
|
Last Updated: Sunday, 16-Apr-06 17:15:27 PDT