**3. Synthesis of the study and future research directions**

To synthesize the study, an analysis of the documentation was obtained, the metadata of the document collection was exported in Information Systems Research (RIS) format, and a bibliometric analysis was performed using the VOSViewer software. A graph with groups of the main authors and their relationship of coauthorship (taking five as a frequency of occurrence of the author's surname) is presented in **Figure 11**. It is possible to identify as the largest cluster the Chinese authors, followed by smaller groups of Brazilian and Indian authors, highlighting that there is little cooperation between those groups.

**Figure 12** shows the most used terms in the area that can be defined as keywords.

**Figure 11.** *Authors and their relationship of co-authorship (two as a frequency of occurrence of the author's surname).*

**Figures 13** and **14** show a summary of the signals and methods used to measure or estimate the indexes. Consequently, the current and voltage signals are widely used, as well as the camera in the image processing and the microphone for the analysis of acoustic signals.

Also, it is possible to classify the indexes into groups according to their purpose, those that are oriented to the monitoring of the metallic transfer, and the analysis of the stability of the arc and the process in general. **Figure 16** shows the percentage by group; **Figure 17** shows the technique used to develop the indexes for those groups.

It is important to emphasize that these concepts are widely correlated.

**Figure 14.**

**Figure 15.**

**Figure 16.** *Percentage by group.*

**19**

*Methods used to estimate the indexes.*

*Stability on the GMAW Process*

*DOI: http://dx.doi.org/10.5772/intechopen.90386*

*Parameters and variables used in the studies.*

**Figure 15** summarizes the parameters and variables used in the studies showing that among the most influential in the stability of the process, current, voltage, wire feed speed, short-circuit time, arcing time, and short-circuit frequency can be mentioned.

**Figure 12.** *Cluster of terms (two as a frequency of occurrence of the term).*

**Figure 13.** *Sensors used to measure.*
