All attempts to reduce variability and defects in products reflect the implementation of quality control (QC).
QC places the primary responsibility for the quality of a product or service at the source—the maker or provider. Many companies use statistical process control (SPC) techniques to analyze where fluctuations occur in the process. SPC is based on the theory that a process has natural variations over time, but that “errors,” which can result in defective goods or poor service, are typically produced at points of uncommon (nonrandom or special cause) variations. Often these variations are eliminated after the installation of computer-integrated manufacturing systems, which have internal controls to evaluate deviations and sense production problems.
To analyze the process variations, various types of control charts have been developed by recording the occurrences of some specified measure(s) of performance at preselected points in a process. Charts, graph actual process results and indicate upper and lower control limits. For example, a process is considered to be “in” or “out of” control (i.e., stable or unstable) depending on whether the results remain within established limits and do not form telltale patterns that reflect some nonrandom or special-cause variation.
In effect, SPC charts make use of the principle of “management by exception” by requiring that workers respond to occurrences greater than some predetermined limit or that form nonrandom, telltale patterns.
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