Capability Test
For a good analysis capability is necessary to follow certain assumptions, they are:
1) Analyze data stability through the CR (coefficient Robustness) which is defined as:
CR = Standard Deviation Short Term / Long Term Standard Deviation
CR> = 0.8 – stable Process
Note: If the process is not stable, not impossible to do analysis capability, because the
capability is calculated state of the process at that time, and may not represent the capability
of the process.
2) Normality of Data Analysis
3) Place data in SPC and examine whether there outliers. Using IR chart.
Remember that SPC was developed based on data normality. If the data is not normal, you
will have to determine new control limits, based on the best distribution that your data
originated. This way you can determine outlier of your process, and eliminates them or not.
3a) If the data is normal, we can make direct capability analysis using Cp, Cpk, Pp and Ppk
3b) If the data is not normal terms to follow the following premise:
3b1) Making Box-Cox analysis in order to make non-normal data for normal data. If Pvalue> 0.05, you could transform the data and can use them to calculate Cp, Cpk, Pp and Ppk.
3b2) If the transformed data are not normal, you have to return the natural data and
find better distribution that fits your data. If pValue>0.05 calculate process capability using the
best distribution
3b3) If P value<0.05 from distribution, you will have calculcar capability using non-parametric
data. Using smooth curve. This methodology is based core Kernel.O Kernel method is a method
for non-parametric density estimation curves where each point is weighted by distance from a
central value of the core. The idea is to focus each observation x where you wish to estimate
the density, a window b defining the x and neighborhood points belonging to the pet.
This methodology allows us to calculate Cp, Cpk, Pp and Ppk
Remember that Cp process capability looking future. Cpk is centralization of the process
looking future. Pp is performace of the process looking for today, your current data and Ppk
process is centralizing data looking today or current data.
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Below show PFM – Capability Analyse…
PROCESS FLOW MAP - CAPABILITY ANALYSE
START
1
DATA COLLECT
STABILITY TEST
CR>=0,8
NORMALITY TEST
NO
NORMAL
CURVE ?
MAKE BOX-COX
TRANSFORMATION
YES
PUT DATA SPC CHART
(IR) AVAILABLE
OUTILIER´S
SPECIAL
CAUSE ?
DATA ANALYSE
REMOVE DATA
?
YES
NO
NO
YES
SIM
MAKE NORMALITY TEST
NORMAL
CURVE ?
NO
MAKE BOX-COX
TRANSFORMATION
NORMAL
CURVE?
FIND BEST
TRANSFORMATION FOR
DATA
NO
YES
YES
NO
CALCULATE Cp, CpK,SIM
Pp,
Ppk, DPMO AND SIGMA
LEVEL
PVALUE>=0,05 ?
YES
NO
PROCESS
CAPABLE?
YES
END
USING BRAINSTORM,
ISHIKAWA, X.Y MATRIX ,
FIVE WHY, AND 5W2H
IMPROVE PROCESS
1
MAKE ANALYSE NO
PARAMETRIC DATA
Smooth Curve