Optimal tool replacement and resetting strategies in automated manufacturing systems

As a result of tool wear in machining processes there is a change in the di mensions of parts produced. To minimize the cost of producing parts out of specifications and to minimize the overall tooling cost, the optimal tool r esetting and replacement intervals need to be determined. In this paper, th e optimal cost models are proposed for tool replacement and resetting by us ing renewal functions. The tool life as well as tool reset times are modell ed as inverted normal distributions. Numerical solutions are presented for the proposed models. To illustrate the application of the models, a case st udy of machining a part on a Mazak CNC machine is presented. The dimensiona l changes of various surfaces of the machined parts are monitored along wit h the corresponding tool wear as a function of time. The data obtained have demonstrated the validity of the proposed models, their underlying assumpt ions, and they illustrate the utilization of such an analysis in a flexible manufacturing system, where such CNC machines are the integral part of the system.