## 2 Results of Literature Analysis
### Content Analysis
#### 2.2.2 Process
[17] investigated the determination of the optimal location and number of manufacturing sites and trade-offs between the cost of production, transportation, and inventory through a location-dependent model followed by a cost minimization supply model. The authors applied the proposed methodology to an aviation case study and found that the decentralized configuration was only suitable for low-volume products. [PERSON] et al. [16] proposed real green time allocation and scheduling architecture for large-scale distributed additive manufacturing task allocation for healthcare spare parts and personal protective equipment (PPE). The proposed architecture was designed because of the failure of global SCs, which led to a severe shortage of PPE and spare parts. The authors found that the utilization of 3D printers was improved, and the workload between them was balanced. The study mentioned that the allocation of 3D printers, raw material, and human resources should be conducted in such a way that it ensures the efficiency and effectiveness of AM. The research on different strategies of analysis methods in decision making for AM is reviewed in the section below, according to Figure 2. Decision-making is focused on three main strategies: inventory, manufacturing, and maintenance. As mentioned earlier, both quantitative and qualitative analyses can be adopted for decision making on the adoption of AM for spare parts logistics. * _Inventory Strategy_  
[PERSON] et al. [54] investigated the reduction of the overall system lead time through the addition of different percentages of AM spares into the inventory mix. The authors proved that AM provides agility and positively affects lead times associated with spare parts replenishment, resulting in less capital tied up in spare parts inventory. Taking the example of AM for spare parts supply in the aircraft industry, [PERSON] et al. [35] mentioned that the focus of inventory strategy with AM would be to reduce the safety stock of spare parts in the SC. Owing to the high value of products in the aircraft industry, any addition of safety stock can lead to a significant increase in the cost of SCs. The authors analyzed two situations to understand their impact on inventory: producing slow moving parts in a centralized location and aggregating demand for the utilization of the AM capacity, and deployment of AM in service locations to reduce the cost of transportation and inventory. The authors mentioned that if a company adopts the centralized approach, its strategy would be to build an inventory based on historical demand so that the customer service level is decreased. [PERSON] et al. [72] assessed the switch from conventional manufacturing of slow-moving spare parts to additive manufacturing based on models and concepts of inventory management. The authors found out through the empirical dataset which they used that the switch to AM technology would result in an overall system cost reduction of 6.4%. The authors explored the opportunities for the digitization of spare parts and their implications for inventory management and after-sales services. * _Manufacturing Strategy_  
[PERSON] et al. [5] measured the performance of SC simulations in their study using the following key performance indicators: service level, inventory level and cost, production time and cost, lead time, stock-outs number and costs, and supply costs. The authors mention that AM has the capability of highly customized manufacturing, but it may be good for manufacturing batches with a lower volume. The authors developed a simulation model to study the AM for spare parts for elevators. They mentioned that the model could support choosing a manufacturing strategy in an SC based on the total cost, lead time, and service level. The authors indicate that based on the demand, the manufacturing capabilities might have to be changed at different locations, and the decision makers should be open to adding or removing AM facilities in some locations.