Optimal just in time safety stock and buffer inventory for minimal repair and regular preventive maintenance

A regular preventive maintenance strategy is proposed for a Just-In-Time (JIT) production structure to minimise the system running cost. Due to imperfect repair the production unit is in a state somewhere between good and bad. Consequently the system's effective age reduces as time progresses. As effective age reduces, the system randomly fails to operate and undergoes minimal repair between consecutive preventive maintenance schedules. To avoid shortage during minimal repair, safety stock is built at the beginning and after every minimal repair in a preventive maintenance cycle. Towards the end of the production cycle a buffer stock is made for continuous supply during preventive maintenance action. Assuming this maintenance policy, a mathematical model is developed using probability distribution of maintenance duration and reliability of the system. Optimal values of safety stocks, buffer inventories and production cycle durations are determined. A numerical example is presented to illustrate the model. Sensitivity of the model is also analysed.