The service parts control problem

This paper addresses itself to obtaining a theoretical understanding of the service parts control problem. After formulating general relations among the production pattern, product life characteristic, and product still in use quantity, and also relations among the production pattern, product life characteristic, part life characteristic, and service parts demand quantity, a computer program to seek these relations for any form of production pattern, product life characteristic, and part life characteristic was developed, using this program, the behavior of the product still in use quantity curve and the service parts demand curve was investigated. This revealed that from the viewpoint of controlling spare parts the product still in use quantity curves can be classified into three groups according to the coefficient of variation of the product life probability density function. Service parts demand curves can be classified into eight types. Based on these findings the policy to control service parts is framed. The paper also deals with the problem of how to design part reliability, from the viewpoint of controlling spare parts, by taking into consideration the holding cost of spare parts, the classification of product still in use quantity curves, the difficulty of predicting product life, and the relative easiness of estimating part life.