Statistical Process Control (SPC) Capability Indices

Statistical Process Control (SPC)

Capability Indices:

Process Capability Notation :

Engineering Tolerance: Variation allowed by the specifications.

Natural Tolerance: Expected common cause variation (6sx).

X-bar: Process centre line (CLX), average of the individuals.

R-bar: Range centre line (CLR), average of the moving ranges.

Upper Spec Limit: Upper limit of acceptable variation.

Lower Spec Limit: Lower limit of acceptable variation.

Standard Deviation: Calculated using R-bar/D2.

Capability Index: Potential capability if the process is ‘centred’.

Capability Index: Capability index adjusted for a ‘non-centred’ process.