Background

This case study with Hitachi Rail examined how combining component maintenance activities and overhaul plans will help reduce the cost of asset fleet management. 

A classic maintenance problem of repair/renewal problem arises from the need to maintain an asset by replacing failed critical components to keep the asset functioning until a renewal (overhaul) action is due. The decision to be made is when the overhaul should take place i.e. to provide an optimal replacement/overhaul strategy. On executing those strategies, a schedule for maintenance and overhaul activities of multi-asset systems needs to be developed. The scheduling of maintenance for multi-asset systems is crucial to the operations of the system as financial or human resource constraints are usually stronger than individual systems due to the workload increased for maintenance personnel.

The fleet under consideration consisted of 30 trains where one of the key components that require regular replacement are their brake discs. The replacement of the brake discs are based on the wear through usage. Moreover,  the trains are required to be overhauled before 500k miles of operation. The overhaul activity is only allowed on one train per week to meet availability constraints and a window of 30 weeks is determined to complete the overhaul at the end of the fleet life cycle.

The problem under consideration was to determine the optimal time for replacing brake discs on each train as well as the overhaul slot (week) to allocate to each train.  

Approach

A regression model was used to predict the time for each brake to cross the wear threshold and to determine the replacement time. In particular we considered the dependency between the wear of inner and outer discs of the brakes to improve our prediction. However, the slot allocated to the train for overhaul influenced the overall costs as an earlier slot could remove the need to replace brake discs since the discs will have to be replaced again during overhaul. The overhaul slot allocation problem was framed and solved using the traditional "Assignment Problem" approach to minimise the overall fleet maintenance and overhaul costs. 

Benefits

Our model resulted in a overall cost saving over the overhaul cycle for the fleet of more than £200,000 compared to the overhaul program that was in place.

Researchers

• Nipat Rasmekomen

Publications

• Rasmekomen, N., Parlikad, A.K., “Maintenance and overhaul scheduling of transportation assets,” In Proc. 2nd IET Asset Management Conference, London, Nov 2012.