A CONTINUOUS-FLOW MODEL FOR PRODUCTION NETWORKS WITH FINITE BUFFERS, UNRELIABLE MACHINES, AND MULTIPLE PRODUCTS

This paper presents a Bow approximation of production networks with fi nite buffers and unreliable machines. Parts of various types compete f or service before a machine, or they may be assembled before service t o yield a composite part. Up times and down times of machines have arb itrary but known distributions and service times have gamma distributi ons, or may be constant quantities. Random service times are approxima ted by piecewise deterministic variables. Acyclic networks are conside red first. The model is a combination of discrete-event simulation and analysis. The simulator keeps track of the buffer and machine states. Between two consecutive state transitions, how rates remain constant and the model calculates the cumulative flow of each part type. Compar ed to a conventional simulator, the model is superior in speed and ver y accurate. An alternative model is developed for nonacyclic productio n networks where each machine provides service to different parts repe titively. The model is employed to simulate a re-entrant production li ne under a class of heuristic scheduling policies. The optimal policy is the one that meets demand while maintaining small buffer sizes and short delays of parts.