Analyzing Warranty Data of Repairable Systems

Systems can be categorized into two basic types: one-time or nonrepairable systems and reusable or repairable systems. In the latter case, under continuous operation, the system is repaired but not replaced after each failure. For example, if a water pump in a vehicle fails, the water pump is replaced and the vehicle is repaired.

A repair of a complex system typically does not make a system as good as new. Generally a repair is just enough to get the system operational again. That is, the repair addresses only what failed and does not restore the system to its original condition when first put into service. When we repair a system doing only what is necessary to get the system operational again, this is called “minimum repair.” The repairable systems models and methods in RGA 6 are appropriate for the common practical situation where the systems under consideration are not replaced when they fail, but are repaired under the minimum repair strategy and put back into service.

The system under study may be part of a larger system. For example, a transmission is a complex system that is part of a larger system such as an automobile, truck or helicopter. So, in terms of the RGA 6 methods, both the fleet of transmissions and the fleet of vehicles can be analyzed. In this article, we will address fleet analysis directed toward addressing warranty failures.

Economical Life Model for Repairable Systems
One consideration in reducing the cost of maintaining repairable systems is to establish an overhaul policy that will minimize the total life cost of the system. However, an overhaul policy only makes sense if the systems suffer from wearout problems. In other words, the β parameter of the Crow-AMSAA model should be greater than 1. Implementing an overhaul policy if wearout is not present is not economically beneficial, because an overhauled unit would have the same or a higher probability of failing compared to a unit that was not overhauled. If we assume that there is a point at which it is cheaper to overhaul a system than to continue repairs, what is the overhaul time that will minimize the total life cycle cost while considering repair cost and the cost of overhaul?

This article presents a methodology, implemented in RGA 6, for estimating the optimum overhaul time based on the Economical Life Model for Repairable Systems.