*3.3. Sidewall Penetration*

The erosion of the sidewall was caused by the arc self regulation dynamics, which tried to establish the shortest path to electron flow, thereby increasing the melting rate. However, as the arc moved through the groove, the attachment point was continually changing, melting multiple points across the groove walls. This multiple erosion points might have detrimental effects on the mechanical properties of the joint.

Figure 7 shows the sidewall penetration caused by the root pass during welding. One observes that the standard GMAW erodes the sidewalls consistently with the oscillograms shown in Figure 2a. There, every time the arc attached to the sidewalls, intense and fast short-circuiting caused the current to increase abruptly (to fuse the extra metal and restore the compatible voltage (arc length, in constant voltage) to the current pre-set before welding). Conversely, as in the CW-GMAW, the arc was attached to the cold wire, thus there is effectively no sidewall penetration, as can be seen in Figure 6a.

**Figure 7.** Top view of the sidewall penetration caused by the root pass; the specimens were cut along the longitudinal line (dashed red line): (**a**) standard GMAW; and (**b**) CW-GMAW. Once can note that the specimens were cut along the longitudinal axis of the joint. Note: In (**b**), the mark on its front is a written identification of the sample that could not be removed.
