Optimal renewing free-maintenance warranty period and preventive replacement age for repairable products

This paper proposes a decision model for determining the optimal renewing free-maintenance warranty (RFMW) period and preventive replacement age of a general repairable product with a random workload. To model a maintenance action, if a failure occurs, either a corrective replacement or a minimal repair is performed, in case of catastrophic failure or minor failure, respectively. To avoid catastrophic failures occurring for a degraded product, a preventive replacement is predetermined for implementation at age T or at the completion of a working time, whichever comes last. During RFMW, any maintenance action (either repair or replacement) is free of charge to the customer. However, each catastrophic failure still results in a downtime cost to the customer, while a planned maintenance action increases the initial purchasing cost. The aim of this paper is to determine the optimal warranty period and preventive replacement age, from the collection viewpoint of the manufacturer as well as the customers, while minimising the corresponding expected cost rate functions. The effects of RFMW on the optimal preventive replacement model are further investigated by some comparative studies and demonstrated via a numerical example. It is shown that the proposed model provides a generalised application in maintenance theory and warranty strategy.