## 2 Materials and Methods  
### Experimental Plan and Setup  
Bead-on-plate trials were deposited by the GMAW process using metal-cored wire on 1.25 Cr-0.5 Mo substrate. The Metalloy 80B2 (Hobart Brothers (TRI-MARK) company) wire with a diameter of 1.2 mm was used for investigation. Metalloy 80B2 is a metal-cored wire that was used for single or multi-pass welding of chromoly steels. The shielding gas of 98% Ar and 2% O\({}_{2}\) was used. The chemical composition of the base plate and wire are as shown in Table 1. The experiment was conducted on a PRO MIG-530 GMAW setup (Miller). Figure 1 represents the complete arrangement of the experimental setup used in the present study. This setup includes a wire feeder, power source, computer interface, automated nozzle controller, welding torch, working table, shielding gas cylinder and a special-purpose machine. The computer interface helps to run the code designed for a particular bead deposition. The code was directly linked with the automated controller, which controls the movement of the nozzle in X, Y and Z directions. Before initiating any program, shielding gas was provided through the setup so that the deposited material does not come in contact with any atmospheric gases. The base metal was clamped from both sides and the material was deposited with the help of the torch, which has the flexibility to move in any required direction. To measure the temperature around the heat-affected zone, a thermocouple was installed between the base plates.  
Single bead deposition was taken on the base plate following an experimental matrix produced through the Box-Behnken design (BBD). In the present study, wire feed speed, travel speed, and voltage were chosen as the input parameters based on device ability and the analysis of recent studies. On the basis of the recent literature and machining capabilities, the constant length of each bead was taken as 90 mm along with a constant gas flow rate of 15 L/min and an arc length of 3 mm. Table 2 shows the experimental conditions used in the present study. [PERSON] and [PERSON] utilize the response surface methodology (RSM) method to obtain an optimal response using a proper arrangement of the experimental  
\begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Grade** & **Cr** & **Mn** & **Mo** & **C** & **Si** & **S** & **Fe** \\ \hline
**1.25 Cr-0.5 Mo** & 1.1–1.5 & 0.4–0.66 & 0.45–0.65 & 0.05–0.17 & 0.50–0.80 & 0.025 & Balance \\ \hline
**Metal-cored wire** & 1.25 & 0.78 & 0.47 & 0.07 & 0.42 & Balance \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition of base material and wire.  
matrix. RSM design reduces the experimentation required, thereby saving the cost of work material and time. In addition, the BBD technique of RSM generates a correlation between the machining variables and responses. A total of 15 trials were taken by changing the 3 machining variables at 3 levels.  
The impact of the designated variables was studied on BW and BH. Each single bead deposition was cut at a cross-section to evaluate the BW and BH. Optical microscopy was employed to determine the BW and BH. Each experiment was repeated three times, and an average value of that was taken for analysis. Figure 2 shows the optical micrographs of the specimens of single bead deposition as per the BBD design.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Values** \\ \hline Travel speed, S (mm/min) & 425; 455; 485 \\ Voltage, V (V) & 19; 20; 21 \\ Wire feed speed, WFS (m/min) & 4; 5; 6 \\ Length of bead, (mm) & 90 \\ Gas flow rate, (L/min) & 15 \\ Arc length, (mm) & 3 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Experimental conditions of WAAM process.  
Figure 1: Experimental setup of the WAAM process.