Abstract
Determining the best tool replacement time is important for minimizing overall manufacturing costs. Utilizing the yield index, the true process yield for dynamic processes with tool wear can be estimated, and the tool wear problem can be controlled. However, no measurement is free from error or uncertainty, a realistic approach is to assume that observed data contain a degree of imprecision. Thus, this study applies the fuzzy theory to the tool wear control problem. A decision rule is proposed to determine the appropriate time to replace a tool.