STATISTICAL ANALYSIS FOR LIFE EXPECTANCY OF MANUFACTURED ITEMS AND ITS APPLICATION FOR INVENTORY PLANNING OF SPARE PARTS

Abstract

The problem treated here is to find the optimal p licy for keeping spares for machines which if they break­ down hold up production. This policy is based on knowledge of life expectancy of these spares.•

The conditional failure rate of a life or failure distribution plays important role in the analysis. It is defined as

h (t)= f (t) (0-1) 1-F (t)

where f (t)is the failure. density function t I'

and F

(t)is the failure distribution - J 0

f(t) dt.

An essential step in any inventory problem is to determine the distribution of the number of failures (replacements) in a fixed length of time t.

Assume a system of n equipments where only one equipment can fail at a time. The states of the system represent the number of equipment that faile Thus the state o represents the state where all n equipmants a operating, while the staten represents the.state where non are operating. If we allow the system to start in state o, we are interested in how transitions are made to the succe­ ssively higher states. We will make the following assump­ tions.