REPAIRABLE SPARE PARTS PROVISIONING IN A PRODUCTION SITUATION WITH MULTIPLE IDENTICAL UNITS

In the planning of a production support system, the provision of an adequate amount of spares is an important issue. The system effectiveness, as measured by average unavailability, average downtime, and probability of stock-out situations, is largely dependent upon spares quantity. In this paper, mathematical formulations for these parameters have been given for a typical production situation with a number of identical and repairable units. Unit failure and repair rates have been assumed to be constant whereupon the system behavior could be easily represented by a transition rate diagram. The paper presents a computerized solution procedure for generation of state transition matrix, evaluation of state probabilities for steady state situation and computation of system parameters. Presentation of spare provisioning policies in graphical forms has been discussed with two representative plots. The minimum required spare quantity can be easily obtained from such plots. Formulation of cost-optimal spare provisioning policy and the effect of storage failures have also been discussed with some representative results.