3.1.2. Cyclogrammes

Figure 4 shows typical cyclogrammes for GMAW specimens where one can notice that in the root pass (Figure 4a) the number events corresponding to short-circuits (region inside the dashed rectangle) are larger than the arc burning area (darker region, upper left-side of the dashed square). Ultimately, this cyclogramme points out an unstable condition where the arc burning region is smaller compared to the perturbed region.

As reflected by oscillograms, the fill pass was more stable, with some short-circuits and high voltage points, indicating large variations in arc length (see Figure 4b). In the cap pass (Figure 4c), one can notice a larger short-circuit region with slight variation in arc length. The results also suggest

that there was a high variation in current, probably due to an increased quantity of metal to melt, interpreted by the power source as an increase in wire feed speed (higher melting speed).

Figure 5 shows the cyclogrammes for the CW-GMAW condition. One observes that, by comparing the cyclogrammes for root pass between standard GMAW and CW-GMAW, the arc burning operation range for CW-GMAW is shorter, indicating that this was more stable than the root in GMAW condition. One observes the complete absence of short-circuits (see Figure 5a). The cause of such stabilization should be attributed to the cold wire feed. Meanwhile, comparing the fill/cap condition (Figure 5b) between CW-GMAW and GMAW, one finds short-circuits events where voltage dropped below 20 V, along with variations in arc length, suggested by high values of voltage for the same range of current.

**Figure 4.** Cyclogrammes for the GMAW specimens: (**a**) root pass; (**b**) fill pass; and (**c**) fill pass.

**Figure 5.** Cyclogrammes for the GMAW specimens: (**a**) root pass; (**b**) fill pass; and (**c**) fill pass.
