## 2 Materials and Methods
### Cost Model  
The total cost of fabricating a part was estimated by considering the direct raw material cost, the indirect cost, and the fixed cost [63]. Specifically, the direct raw material cost referred to the raw material purchase cost that was calculated based on the raw material market price \(P_{raw\ material}\) (USD/g) and the weight of the part \(w\) including both the main part and the support structure, calculated as follows.  
\[w=\rho_{raw\ material}\times\left(V_{build}+V_{support}\right)\times\left(1+r _{loss}\right) \tag{2}\]  
\(\rho_{raw\ material}\) is the density of the raw material (g/mm\({}^{3}\)), \(V_{build}\) is the main part volume (mm\({}^{3}\)), \(V_{support}\) is the support volume (mm\({}^{3}\)), and \(r_{loss}\) is the material loss rate.  
The indirect cost referred to all time-dependent costs that were associated with the capital investment and the fabrication process including the consumables like compressed air, Argon gas, and filters. The fixed cost \(C_{fixed}\) was defined as all the fixed costs for each fabrication including machine setup and maintenance. The total cost was formulated as Equation (3).  
\[C_{total}=\left(\hat{C}_{indirect}\times T_{build}\right)+C_{fixed}+w\times P _{raw\ material} \tag{3}\]  
In this equation, \(T_{build}\) denotes the total build time (hr) for fabricating the entire part and is estimated by using the machine control software EOSPRINT 2.0 in this research. \(T_{build}\) is consisted of the time for fabricating the main part \(T_{main\ part}\) and the time for fabricating the support structure (\(T_{support}\)). The \(\hat{C}_{indirect}\) refers to the indirect cost rate (USD/hr) and it was calculated using the equation below.  
\[\hat{C}_{indirect}=\hat{C}_{air}+\hat{C}_{Argon}+\hat{C}_{filter}+\hat{C}_{ blade}+\left(C_{machine}/N_{machine}+C_{occupancy}+C_{Maintenance}\right)/M+\left(E_{build} \times P_{energy}\right) \tag{4}\]  
In this equation, \(\hat{C}_{air}\) is the cost rate of the compressed air (USD/hr), \(\hat{C}_{Argon}\) is the cost rate of the Argon gas consumption (USD/hr), \(\hat{C}_{filter}\) is the cost rate of filter usage (USD/hr), \(\hat{C}_{blade}\) is the cost rate of the blade usage (USD/hr), \(C_{machine}\) is the purchasing cost (USD), \(N_{machine}\) is the lifetime of the machine (year), \(C_{occupancy}\) is the occupancy cost per year (USD/year), \(C_{Maintenance}\) is the maintenance cost per year (USD/year), \(M\) is the maximum capacity of the machine (4,000 hrs/year), \(E_{build}\) is total energy consumption per build (kW) and \(P_{energy}\) is the average price of electricity (USD/kWh).  
In addition, the fixed cost was calculated by considering the labor cost for machine setup and the cost of replacing and refinishing the build platform.  
\[C_{fixed}=C_{setup}\times t_{setup}+C_{platform}/N_{use}+C_{Refinishing} \tag{5}\]  
\(C_{setup}\) is the salary of the labor (USD/hr), \(t_{setup}\) is the time required to setup the machine, \(C_{Precument}\) is the build platform price (USD), \(N_{use}\) is the total number of runs per build platform, and \(C_{Refinishing}\) is the platform refinishing cost. Parameters' values that are used in the cost calculation are shown in Table 2.