Enhancements to statistical process control

Statistical process control (SPC) broadly defined, is the use of statistical techniques to measure and analyze variations in the input parameters of a process and their effect upon the product quality. Its use enables engineers to identify major and minor causes of production problems. This article reviews a relatively unfamiliar concept, known as process capability, whereby the variances in a production process can be quantified and compared. Then, we consider several specific types of inputs and the particular ways in which variations in them affect the variability of a product. To set the stage, however, we first discuss the ideas of process variations and process specifications in a more general sense.