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Process Capability 3 - Six Sigma Functions
  • 민경현
  • 2019-01-09
  • 5
복사본 Process Capability 3 - Six Sigma Functions.xlsx (838 KB), 2019-01-09 13:16:30

This model illustrates some of @RISK's six sigma functions. (This file is very similar to the file Theo Statistical Functions 3 - Quality Calculations, except that six sigma functions aren't used in that file.) The normal samples for the components in row 15 are not only uncertain inputs, but they have also been designated as @RISK outputs. In addition, the RiskSixSigma property function has been appended to each RiskOutput function in row 15 to indicate the lower and upper specification limits and the targets in rows 4-6. (This property function can be added automatically through the Add Output button by clicking the fx button and then using the Six Sigma tab.)

Once output cells include the RiskSixSigma property functions, histograms of them, such as the one for component 1 shown, automatically have marks for the target and specification limits. In addition, various six sigma statistical functions can be used, as illustrated in rows 19-21 with the RiskCpk, RiskPNC, and RiskDPM functions. For example, the Cpk index for each component is 1, meaning that each specification limit is about 3 standard deviations from the target. PNC stands for percentage nonconforming, and DPM means defective parts per million, both standard statistics reported in a six sigma analysis.

Note that the six sigma functions in this model apply only to the individual components. There are no specification limits for the system as a whole, which functions only if each of the components is within its specification limits. So the system has to be analyzed as illustrated in cells C24 and C25

 

 



 시뮬레이션 결과를 살펴보면 각각의 components들의 Cpk 가 품질 기준이 되는 1.3보다 작아 개선이 필요하다는 것을 알 수 있다.

다음으로 각각의 Components들의 결합된 시스템의 양품률을 시뮬레이션 한 결과 0,9928이며 반대로 불량률을 계산하면 1-0.9928로 0.007된다.

즉 Six Sigma 지표인 PNC가 0.0072가 되는 것이고 DPM(100만개당 불량갯수)는 7200개가 된다.

DPM 7200의 해당하는 Cpk는 약 0.82에 해당하며 시스템 전체적으로 보았을때 이 시스템으 개선의 여지가 크다는 것을 파악할 수 있다.