Statistical Process Control(SPC): Knowledge Capsule…If you refer any book on Quality, it is defined as “fitness to use” or “variablity reduction”.
Walter Shewhart in 1924 developed a tool named as Control chart and withing years it is used extensively as a prominent Quality tool in manufacturing companies. Control chart is an application of SPC which a quality control method.
Every product goes to lot of processes and it is important to keep process under control to avoid the production of wastes. Control chart is an oline tool that establishes upper control line(UCL), center line(CL) and lower control line for any process. Note that UCL, CL and LCL may or may not be the specification limit of product.
For example, for a particular product suppose the specification is 19.5-20.5, control limits for process may be fractions or in terms of no. of defects.
Control charts are classified as :
1. Control charts for variables: Include X-bar chart, R-chart and IMR Chart
2. Control chart for attributes: Include p- chart, np- chart, c- chart, u- chart and U- chart