21. Accuracy Control

Accuracy Control is based on the basic fact that there is no such thing as absolute accuracy. Whatever be the method of production, variations from design dimensions are unavoidable. However these variations are measurable and at the same time they are anticipated. Hence it is necessary to know the ranges of variations so that one can quantitatively target the end product accuracy. A system is needed to monitor and control the accuracy of interim products. Otherwise, work in succeeding stages of production will be adversely affected by inaccurate interim products. The reasons for dimensional variations in any work process can be attributed to either some Common Cause or some Special Causes. Variations caused by the so-called Common Causes reflect the status of accuracy level of the existing manufacturing process, which includes production process, machineries used etc. Whereas the so-called Special Cause variation points directly to some fault in the production line. For implementation of accuracy control system, it is necessary to have an accuracy control data base. This gives the statistical history of the accuracy level of the work processes employed in the shipyard.