Inventory Models for Maintenance and Repairable Items
In this chapter, we discuss the management of maintenance items – items that do not go into the final product but those that support the production of a product. Maintenance items such as spare parts, coolants, lubricants, sensors etc. have been traditionally classified into three groups – fast-moving items, slow-moving items, and rotables. Fast-moving items may be managed using one of the deterministic or stochastic techniques learned in the earlier chapters. However, the same techniques may not be applicable to manage slow-moving items because their consumption (demand) is random, and reliability of historical records is low. Despite the demand being low because the time between failures is far and in between, organizations would still need to maintain an inventory of slow-moving parts. This is because they may not be available a few years later as original equipment manufacturers would no longer be producing those parts, or would have changed their design. Rotables are repairable items that are reconditioned and made available for service. The characteristics of this type of item as well as its demand pattern make it unsuitable to apply inventory management techniques we learned earlier in this book to manage this class of spares. Analytical as well as graphical techniques, suitable for management of slow-moving inventories as well as rotables, have been discussed in detail in this chapter.