Optimal Preventive Maintenance Schedule based on Lifecycle Cost and Time-Dependent Reliability

Reliability is an important engineering requirement for consistently delivering acceptable product performance through time. It also affects the scheduling for preventive maintenance. Reliability usually degrades with time increasing therefore, the lifecycle cost due to more frequent failures which result in increased warranty costs, costly repairs and loss of market share. In a lifecycle cost based design, we must account for product quality and preventive maintenance using time-dependent reliability. Quality is a measure of our confidence that the product conforms to specifications as it leaves the factory. For a repairable system, preventive maintenance is scheduled to avoid failures, unnecessary production loss and safety violations. This article proposes a methodology to obtain the optimal scheduling for preventive maintenance using time-dependent reliability principles. An optimization algorithm maximizes the time for preventive maintenance by improving the system reliability, so that the lifecycle cost stays below a specified target. The lifecycle cost includes a production, an inspection, and an expected variable cost. All costs depend on quality and/or reliability. Preventive maintenance is performed at the time when the improved reliability falls below an acceptable reliability target. The methodology also identifies the most critical component(s), or failure modes, which if repaired, will improve the system reliability the most. We demonstrate the proposed approach using an automotive roller clutch example.