## 2 Influence of Welding Parameters on Distortions and Residual Stress Levels  
According to [PERSON]. [PERSON] [15] and [PERSON] [16], low residual stress levels occur when deformations are not restricted, and high residual stresses emerge when deformations are restricted (see Figure 1). However, the level of residual stresses could be higher than yield stress and, at the limit, it can exceed the ultimate stress [17]. So, in the last years, some researchers have been studying the optimal parameters to minimize residual stresses [18]. These studies have been conducted using numerical [19] and experimental approaches [20] to achieve the appropriate balance between the level of residual stresses and the distortion value [21].  
The most pronounced type of distortion in butt-welded plates is angular distortion [23]; it happens more frequently than other types of distortions, such as tailing and bending, and that is the reason why it is considered the most significant type of distortion [24].  
The angular distortion is a rotation of the structure around the welding line [16]. When the transverse shrinkage is not uniform in the thickness direction, the angular distortion occurs in a butt joint [23; 25], so the welded component is distorted in angular directions around the weld interface, as it is shown in Figure 2[26].  
The welding parameters must be selected considering the results to be achieved, and the choice of those parameters can also influence the distortions on the welded component. Many studies investigated the influences of the welding parameters in such distortions.  
According to [PERSON] et al., if the voltage and the current are increased, bigger distortions are likely to occur, and the distortions decrease when the welding and feeding velocities increase [27].  
According to [PERSON] and [PERSON], minor distortions are provided with higher gas flow rates, and they are increased with higher values of voltage and current [28].  
Figure 1: Relationship between clamping degree and the level of distortion as well as the effect on residual stresses [22].  
Figure 2: Angular distortion of a butt weld [22].  
[PERSON] and [PERSON] concluded that the angular distortions can be directly proportional and influenced by the voltage and the torch travel angle. Contrarily, an opposite effect on distortions can be led with the increase in the length of the electrode and the feed rate [29].  
[PERSON] et al., based on numerical simulations, verified that the heat input has a significant influence on the welding distortion. Large heat input is apt to resulting in buckling distortion in thin-plate panel structures. A reduction in heat input is an effective method of decreasing buckling propensity [30].  
The study conducted by [PERSON] et al. found, through simulations using FEA with experimental validation, that the angular distortions increased with the rise of the angle of V-preparation [31].  
[PERSON] e al. verified in their studies that the largest transverse shrinkage occurs at the middle section of the length of the plate and it is gradually reduced to the starting and ending edges of the welding line [32].  
A different investigation about the influence on joint gap distortions, number of passes, and time gap between passes was performed by [PERSON]. [33] and [PERSON]. [34]. With the experiments carried out, it was possible to conclude that an increase in joint gap and number of passes leads to an increase in distortions. On the other hand, the distortions decrease when the time gap between the passes increases.  
The Taguchi method was used by [PERSON] and [PERSON] in research to investigate angular distortions. This investigation concluded that the increase in the current, plate length, and electrode diameter brings an increase in distortions. Concerning the time gap between the passes, it affects the angular distortions oppositely [11].