USING DISCRETE-EVENT SIMULATION FOR DESIGN AND OPERATION OF FLEXIBLE MANUFACTURING SYSTEMS

Described in this paper is an application of a discrete-event simulation model for the Mazatrol FMS system manufactured by Yamazaki Mazak, one of the leading machine tool companies in the world, to analyze various causes of machine idle times. The Mazatrol FMS is a module-type FMS which consists of the maximum of 8 horizontal machining centers, 1 to 4 load/unload stations, a stacker crane, pallet stockers among others. Presentation of a conceptual framework for the machine idle times and their causes is followed by detailed simulation results. Simulation indicates that the utilization of machining centers during the normal operating period is at least 92.7% and is reasonably high, under the conditions of enough work load for each machine and no equipment failure. It is also shown that the main causes of the machine idle times differ depending on the periods in which they occur during the entire makespan. The increase of routing flexibility, which is known to be an important factor for the reduction of the makespan, is found to give little effect on the machine utilization. On the other hand, the results show that the number of pallets is an important factor for high machine utilization. The simulation results are expected to provide useful information for efficient operation of FMSs in general, and of the Mazatrol FMS in particular. Suggestions are given on how simulation results could be used to improve the system utilization on the medium-range as well as the short-term planning of FMSs.