AAOM Handbook

INTERNAL

AI.05 Is the Process Capable? Context

The Capability Histogram and Control Charts of a process can be used to track its KPI’s. If review of a KPI determines that the process is stable, the next step is testing for process capability. In the least demanding case, a capable process is one where the range of variation in performance fits the specification to the required confidence level (the confidence level specifies the percentage of the variation that must lie within the specification limits). If the process is meeting specifications then nothing further needs to be done until either the process or specifications change. If the process is not meeting specifications then the issue should be evaluated to determine if the impact justifies further analysis and implementation of control actions. Purpose To determine if the process is capable of meeting its specifications. Quantity One decision on each KPI – is the process capable or not? Quality The Capability of a process is not tested if the process is not stable. The tests to be applied for determining capability are:  The distribution fits the expected shape.  The range of variation evident in the performance will fit within the specification limits to the required confidence level, and  The performance is located within the specification limits to the required confidence level. Resources This task is completed by the manager responsible for the process performance. Time Process capability will only change after there is either an indicated change in process stability or the process specifications are changed. Therefore the minimum requirement is to review capability after;  a change in process stability, and  the process performance has reached a stable state, and  there are sufficient data points to make a reasonable judgement (hopefully 25 but certainly more than 7), or  there is a change to the process specifications.