ABSTRACT
Process stability is a requirement for process capability and a prerequisite for process efficiency. A process can be considered stable if the output parameters of interest are relatively consistent over time. Graphically plotting process output performance with time will provide a visual indication of stability. Run charts can be used to expose instability in a process. Defects create instability revealed as special cause variation. Special cause variation often affects process outputs in intermittent and irregular ways. A run chart can be prepared with sufficient data to reflect actual process fluctuation. To determine process fluctuation, select a reference point in the final operator's work pattern. Statistical process control (SPC) is also an effective tool for assessing process stability. An SPC chart differs from a run or trend chart in that a control chart has statistically based control limits and a center line. Control charts are one of the best tools for reducing process variation and maintaining stability.
