ASSESSING PROCESS CAPABILITY IN THE PRESENCE OF SYSTEMATIC ASSIGNABLE CAUSE

A process must be considered free from variation due to assignable cause before its capability can be determined. In those situations where variation due to an assignable cause occurs and is tolerated process capability cannot currently be assessed. By allowing the process capability to be considered dynamic, a procedure for assessing capability is proposed and an estimator developed for those situations where a systematic assignable cause occurs. Some statistical properties of the estimator are examined and a technique for managing a process exhibiting a systematic assignable cause is discussed. Examples from a particular class of systematic assignable cause known as tool wear are included.