Exam 11: Process Capability

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A process is under control if the amount of variation present in the process remains constant over time. Process centering must also be constant over time. If both of these are constant, then process behavior is predictable enabling decisions to be made about process performance.

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6 σ = 0.0048
Cp = 2.08
Cpk = 1.958
The process is capable though not quite centered.

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$$\begin{array} { c } \sigma = - \frac { \mathrm { s } - \mathrm { bar } } { \mathrm { C } _ { 4 } } = \frac { 1 } { 0.693 } = 1 \\\mathrm { Cp } = - \frac { 36 - 30 } { 6 ( 1 ) } = 1.0 \\\mathrm { Cpk } = \frac { { 2 } } { 3 } = 0.66\end{array}$$
Where:
$$\begin{array} { l } Z ( u ) = \frac { 36 - 32 } { 1 } = 4 \\Z ( I ) = \frac { 32 - 30 } { 1 } = 2\end{array}$$ The process is not centered and just barely capable.