Scheduling economic lot sizes in deteriorating production systems

The paper considers the economic lot scheduling problem (ELSP) where production facility is assumed to deteriorate, owing to aging, with an increasing failure rate. The time to shift from an ‘in-control’ state to an ‘out-of-control’ state is assumed to be normally distributed. The system is scheduled to be inspected at the end of each production lot. If the process is found to be in an ‘out-of-control’ state, then corrective maintenance is performed to restore it to an ‘in-control’ state before the start of the next production run. Otherwise, preventive maintenance is carried out to enhance system reliability. The ELSP is formulated under the capacity constraint taking into account the quality related cost due to possible production of non-conforming items, process inspection, and maintenance costs. In order to find a feasible production schedule, both the common cycle and time-varying lot sizes approaches are utilized.