By John N. Zorich
Manufacturing involves an attempt to produce items that as closely as possible meet design specifications (e.g., size, strength, etc.). However, all production processes exhibit variation – that is, no two items are identical. What method can we use to reduce such variation? The classic and still most widely used method is called SPC or “statistical process control”.
SPC is a statistical tool that objectively identifies when it is worthwhile to perform a formal investigation of manufacturing variation, in order to identify and reduce its cause. SPC continually adjusts its sensitivity in order to ensure that such investigations are performed only when there is a reasonable chance of identifying causes of variation. SPC also provides information that can be used to estimate what % of items is being produced “in specification”.