## 3 Materials and Methods
### Experimental Procedures
#### 3.2.2 Butt-Joint Welding Process  
The weld beads were performed in the flat position (1G) with the pulling technique, and the parameters were selected within the range recommended by ESAB (as indicated in Table 4). After the fit tests, the welding parameters were selected as indicated in Table 5.  
Figure 4: Experimental set-up for measuring distortions of specimens.  
Figure 5: Control grid created in the samples.  
Each welding sequence was made in triplicate to guarantee that the experiments would not be affected by human, material, or machine flaws, improving the precision of the investigation. The welding sequences performed were divided into three groups:  
* SM: Symmetrical method.
* BM: Backward method.
* SP: Single-pass method with one step.  
Figure 7 shows the sequences, indicating the sequence and order of each step, the Figure 7a is the symmetrical method, Figure 7b the backward method, and the Figure 7c the single pass.  
It was observed that the base metal had a few geometrical discontinuities before the welding process and, because of that, to obtain a higher control of the distortions that were really caused by the welding process, the measurements were performed before and after the welding (Figure 8). The distortions which already existed before were considered and properly compensated for in the analysis.  
The order of the methodology used is represented in the flowchart of Figure 9. To prepare GMAW butt joints previously, it was necessary to cut carbon steel sheets in agreement with the defined dimensions, followed by a cleaning process using a cloth and solvent (acetone), and then creating a control mesh, drawing orthogonal lines at same distances. Before performing the welding of sheets, a control measurement which is used as reference values was implemented; these measurements were taken using the C-Track 780, HandyPROBE, and MetraSCAN 3D system. The welding process was carried out according to the sequence presented in Figure 7 and using the welding parameters defined in Table 5. The welded sheets were measured with the same equipment used to measure references values. So, a methodology using computerized equipment was performed to measure distortions, making it possible to obtain the coordinates in the operational space with metrological precision.  
As cited by [PERSON] [15] and [PERSON] [16], when deformations are restricted, high residual stresses arise and, for that reason, the samples were not fixed during the welding procedures. As a consequence of that, the deformations were not restricted in any time of the experiments.  
Figure 6: Steel sheets samples for welding process.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Welding Parameters** & **Used Values** \\ \hline Voltage & 22.4 V \\ Travel angle & 15\({}^{\circ}\) \\ Shielding gas flow & 14 L/min \\ Welding speed & 0.30 m/min \\ Feeding speed & 4.5 m/min \\ Electrode extension (_Stick-out_) & 19 mm \\ \hline \hline \end{tabular}
\end{table}
Table 5: Parameters used in welding of top joints.  
The welding parameters were chosen in order to have a uniform distribution of the stands and ensure a better structural and visual aspect of the whole weld. Moreover, the welding was performed in flat position (1G) with the pulling technique.  
The equipment used for data acquisition was the C-Track, which measures coordinates in the space, interconnected with HandyPROBE and MetraSCAN 3D using the softwares Metrolog X4 and VXelements.  
Figure 8: Arrangement without movement restrictions during the welding process in top joints.  
Figure 7: Butt-joint welding sequences, (**a**) symmetrical method (SM), (**b**) backward method (BM), and (**c**) single-pass method (SP).