Lot sizing in an unreliable manufacturing system with fuzzy demand and repair time

The paper deals with lot sizing in an unreliable production system which is subjected to machine breakdown and repair in an uncertain and imprecise mixed environment. The machine failure time is random and is assumed to follow an exponential probability distribution whereas the repair time is imprecise and is characterised by a triangular fuzzy number. Two mathematical models are proposed for the production system - one with crisp demand and fuzzy repair time and the other one with fuzzy demand and repair time. In each model, the expected cost per unit time is derived in the fuzzy sense and defuzzified by using signed distance method. The optimal lot sizing decisions are obtained numerically and a comparison with those of the crisp models is made. Copyright © 2010 Inderscience Enterprises Ltd.