## 2 Welding Deformation Experiments of Unit Specim  
Butt welding experiments were conducted on each different three welding test specimens, as shown in Figure 4, to compare the deformation by the number of pieces installed in the butt welding. Flux cored arc welding was employed as a welding method. The welding was carried out manually and performed using a welding machine (HD-auto 350s+) by Hyundai Welding Machine Company. Details of operation conditions are displayed in Table 1. The root gap and groove angle are defined as shown in Figure 5. The conditions employed during welding, other than the quantity of temporary pieces, are the same in all experiments. Each specimen is of dimension \(940\times 1100\times 15\) mm. The base material is low carbon steel AH32, which is mainly used for hull blocks, and the filler material is E81T1-K2C wire type, conforming to the specification of the American Welding Society [26]. However, the thickness of the pieces is 12 mm and they are of the same material composition as the specimens. The three experimental cases analyzed, denoted specimen 1, 2, and 3, and each having a particular number of pieces installed (0, 3, and 5, respectively), are shown in Figure 4. Specim 1 is a reference for measuring the welding deformation value when no piece is installed, which will be used for comparison with the welding deformation value when pieces are installed. For specimen 2, three pieces were installed at equal distance intervals of 275 mm. This distance is the average value of 250 and 300 mm, which is the piece installation interval empirically used in the workspace. In specimen 3, the welding deformation value is measured for five pieces installed at equal intervals of approximately 183 mm. \begin{table}
\begin{tabular}{c c} \hline \hline
**Welding Condition** & **Value [Unit]** \\ \hline Current & 211–268 [A] \\ Voltage & 27–31 [V] \\ Welding speed & 101–198 [mm/min] \\ Root gap & 8.2 [mm] \\ Groove angle & 34.5 [degree] \\ Number of welding passes & 4 \\ Flow rate of shielding gas (100\% CO\({}_{2}\)) & 20 [/min] \\ Diameter of the electrode wire (E81T1-K2C) & 1.2 [mm] \\ Stick-out & 20–25 [mm] \\ Angle of welding torch & 75 [degree] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Operation conditions of butt welding. Figure 4: Welding test specimens for three experimental cases: (**a**) specimen 1; (**b**) specimen 2; and (**c**) specimen 3. Figure 5: Definition of root gap and groove angle. The specimen was fixed by tack welding at both ends of the welding line, and edges of the specimen were not constrained in order to observe the maximum deformation. The welding deformation value was measured by obtaining three-dimensional coordinate of marking points using a three-dimensional contact measuring instrument. The measuring instrument is the Metronor SOLO model with a \(\pm\)0.21 mm accuracy in a 10 m distance camera; it was suitable for measuring deformations of large structures [27]. Marking points were made at 50 mm intervals on the opposite side of the piece mounting face and more closely to the welding bead, at 20 mm intervals, in grid form. The butt welding experiment was conducted for each case in the following order: butt joint welding, piece removal, grinding, and deformation measurement, as shown in Figure 6. The number of measuring points is 504. Figure 7 presents each measuring line position in the transverse direction, x1 to x5, and longitudinal direction, y1 to y3 (y1\({}^{\prime}\) to y3\({}^{\prime}\)). Figure 8 illustrates the welding deformation measured along line x3 for each specimen. Because all three specimens had the same welded thickness, welding passes, and constraint conditions, the angular deformations shown in Figure 8 are the result of the difference in the number of installed pieces. Figure 8: Experimental results of horizontal welding deformations (line x3). Figure 6: Sequence of procedures per experiments: (**a**) Flux cored arc welding; (**b**) piece removal; and (**c**) measurement.