## 2 Results of Literature Analysis
### Content Analysis
#### 2.2.1 Inputs for AM Based Supply Chain  
Very few researchers have focused on the input of AM-oriented SC systems. Although the SC system may be strategically designed for spare parts management, SC efficiency depends on uncertainties, demand changes, and changes in the supply potential. The type of materials required for printing can differ based on the type of spare part. Uncertainties in demand can cause problems in material availability, and this can impact the decisions to be made in the SC. Decision models based on stochastic programming may be used to analyze the impact of uncertainty in AM, such as the work of [PERSON] et al. [11], such that the spare parts management system becomes profitable with AM. [PERSON] et al. [29] demonstrated the utility of a system dynamics-based model to compare the costs and emissions between AM and conventional manufacturing. The authors mention that spare parts supply adopting AM is superior to conventional manufacturing in terms of both costs and carbon emissions. [PERSON] et al. [35] analyzed the performance of three SC configurations for aircraft spare parts by considering demand characteristics, manufacturing and logistics lead time, and cycle service level factors for three supply configuration scenarios: conventional, centralized, and distributed. The author obtained the demand for the spare parts, lead time, and required safety inventory for each of the regional distribution centres, service locations, and original equipment manufacturer for the three scenarios. They showed that AM has the potential to increase the efficiency of aircraft SCs. A study on the spare part demand characteristics with AM was provided by [PERSON] [53]. The author examined the impact of spare parts demand on AM operations and SC performance. Demand rate effects were studied for both regular and emergency spare parts. [PERSON] [19] integrated the demand factor and arrival rate for cost and SC comparisons. The author mentioned that the demand arrival rate is a critical factor in the overall system performance of the AM-based spare parts SC. In addition, any change in the demand arrival may cause turbulence in the operating costs. The author found that a mixed supply chain configuration would outperform the centralized (where AM machines are located at centralized distribution centres) and decentralized configurations (where AM machines are deployed at each service location), especially when the demand frequency and technology development reach a certain stage. Additionally, this form of mixed configuration allows the simultaneous allocation of AM machines at regional distribution centers and service locations. [PERSON] [9] investigated the issues and industrial perceptions of adopting digital spare parts. The author provided possibilities, obstacles, networks, and requirements of digital spare parts and mentioned that long-tail products are potential candidates for digital distribution, especially long-tail spare parts, such as digitization results in the reduction of inventory and transportation costs. [PERSON] et al. [15] introduced the photogrammetry technique which is utilized to obtain a 3D model of spare parts in the automotive industry. This technique facilitates the creation of the 3D object model, meshes and fixes its surface, and finally prints it. [PERSON] [20] studied five scenarios in spare parts SC by considering a digital distributor. The author mentioned that when digital files of the production system are used, the role of the logistics service provider will be reduced. The authors analyzed the scenarios by assuming that the service provider is a spare parts carrier, a digital distributor, an AM decision-maker, a selector of the manufacturer, or an AM service provider. [PERSON] found that the individual roles of such service providers would change based on the capability of the service provider. This indicates that with AM, the service provider should also change its business model. [PERSON] [23] evaluated the current economic and technical feasibility of digital spare parts.