Control Charts in Quality Assurance

Control Charts in Quality Assurance   Introduction The purpose of control charts is to find if a process is stable and in-control, or unstable and out-of-control. When a process is stable, or “in control,” this suggests that it's predictable and affected only by normal random causes of variation. An unstable or “out-of-control” process is suffering from an equivalent common causes of variation, but it's also suffering from “special” or “assignable” causes. If you are successfully centralizing all important process variables, and your incoming raw materials are relatively consistent, then your process should be stable and in control. Control Chart Basics A control chart consists of a time trend of a crucial quantifiable product characteristic. In addition to individual data points for the characteristic, it also contains three lines that are calculated from historical data when the method was “in control”: the road at the centre corresponds to the mean average for the data, a...