## 2 Results of Literature Analysis
### Content Analysis  
To extract the insights provided in the selected literature, the BLOC-ICE systems conceptual framework developed by [PERSON] [67] was used. Based on the BLOC-ICE framework (Figure 2), the content of the literature was divided into four parts: (i) inputs for initiating AM-based SC; (ii) the SC processes such as resource allocation, manufacturing, inventory, and logistics, and decision-making to facilitate the AM; (iii) constraints that limit the functioning of the processes; and (iv) the outputs. The contents mentioned in Figure 2 are discussed below. The inputs consider material availability, demand for spare parts, uncertainty factors, supply potential, and digital files, which transmit the required information in order to manufacture the 3D printed parts using the system process. The raw and input materials are demanded and scheduled to be replenished from a particular supplier with a certain quantity at a certain period. The demand for spare parts is usually uncertain, which explains the uncertainty factors in the input stage. The supply potential is related to the supplier capacity. Initially, the raw material should be available to move to the processing stage. Then, the material is processed in the AM-based SC system to undergo different processes, including decision-making. In the processing stage, the material and other resources are allocated, and parts are manufactured, stored, and transported. Resources such as spare parts, 3D printers, and raw materials must be optimally allocated to minimize the cost and increase the efficiency of the production system to meet the demand. The control of inventory is dependent on the available storage space, quantity of raw materials, demand for spares, manufacturing capability, and logistics capability of \begin{table}
\begin{tabular}{c c} \hline \hline
**Study Type** & **Authors** \\ \hline Empirical Study & [23; 28] \\ Case Study & [39; 40; 44] \\ Scenario Analysis & [17; 20; 22; 26; 27; 29; 31; 32; 34; 35; 37; 43; 49; 63] \\ Quantitative Modeling & [1; 3; 4; 5; 6; 11; 17; 18; 25; 38; 50; 52; 53; 54; 55; 56; 64] \\ Other approaches & [9; 10; 15; 16; 24; 30; 36; 41; 51; 59; 60; 61] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: References of literature for different approaches. Figure 2: Supply chain process adopting additive manufacturing in spare parts management. packaging and transportation. Parts can be transported either through agents (such as third-party logistics providers or freight forwarders) or directly by the company to the service location. The management of the AM-based SC is supported by decision-making in which inventory, manufacturing, and maintenance strategies of the company are considered. The optimal manufacturing strategy could be to partially focused on conventional methods instead of the total dependence on the additive methods. Maintenance strategies can be implemented in different types, including corrective maintenance, preventive maintenance, condition-based maintenance, and predictive maintenance. The company decides on the maintenance approach which suits the business and assets the most. Therefore, the spare parts production system also focuses on the type of maintenance strategies used by the company. A mixture of maintenance strategies can be adopted by organizations [68]. Inventory strategy also becomes important to balance the production and storage, lead time to meet the demand through internal production or purchase of spare parts, service efficiency, and cost of handling and operation. Therefore, the decision to produce spare parts requires multi-level analysis. The output of the process is 3D printed spare parts. Note that all parts are developed by strictly adhering to the 3D digital computer-aided design (CAD) input file. The AM and SC processes that are shown in Figure 2 also show the constraints. There are various constraints or limitations which govern the conversion of inputs to the intended outputs. Multiple constraints were identified in the literature.