Spare parts models have typically focused on the number of spares physically required to maintain system availability and optimize replacement policies, such as block or age replacement and variants thereof. In an era where additive manufacturing (AM), or 3D printing, as it is popularly known, has come of age for end-user parts, considerations must be added to traditional ways of thinking about spare part inventories. In aviation, large amounts of money are spent on spare parts, and owing to long lead times, large numbers of stock keeping units (SKUs) must be kept in inventory, driving up cost and the requirements of inventory storage space. Spare parts that are not consumed in a timely manner can become obsolete due to innovations, or can be damaged, lost, or stolen. This dissertation shows how AM can be used to optimize spares inventory and maintenance activities through a simulation for the replenishment of a modular system. The approach opens up a discussion on the new cost variables that become relevant when AM spares are also employed along with spares from traditional methods. A simulation model using two scenarios is presented, where only traditionally manufactured spares are used in the first (baseline), and the second is a hybrid of AM spares and those from traditional methods. The simulation shows that the introduction of 15% of additively manufactured spares to the inventory mix for maintenance spares reduced the overall replenishment lead time for a system by 14.4%, from 98.4 days to 84.2 days. It is also argued that AM introduces variables that express benefits that can be realized throughout the system’s lifecycle, particularly in the later stages. It is concluded that a spares inventory strategy that uses both AM and traditionally manufactured spares is not only viable, but also an important option in the optimization toolbox.
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