**1. Introduction**

In a general context, the welding area currently develops on the conceptual and technological foundations of Industry 4.0, as well as the latter actively collaborates to advance the former. Welding joining processes have never presented so many changes in their techniques as in recent years. This is mainly due to the insertion of arc welding in additive manufacturing [1, 2], as robotic systems have sought to improve the manufacture of parts and components by deposition or coating of flat and tubular surfaces for any type of materials. Whether carbon steel [3] or special alloys [4, 5]. However, the difficulty of implementation and the cost of additive manufacturing favor more

traditional processes such as the electric arc to remain for longer acting as the front line of the metalworking industry in the welding segment.

Thus, processes such as GMAW (Gas Metal Arc Welding) and FCAW-G (Flux Cored Welding with Gas Protection), among others, still remain firm, being used in the manufacturing and heavy assembly industries such as shipbuilding, oil industry, in addition to construction of structures and pipelines for the power generation industry, for example. Thus, it is known that the mentioned processes have high deposition rates, weld metal quality, in addition to versatility in their applications, which consolidates them in the market. However, due to the excessive need to increase productivity, many variants have emerged in order to assist in this procedure.

Currently, there are some aspects of the GMAW process, with the Cold Wire–Gas Metal Arc Welding (CW-GMAW), the Double Cold Wire–Gas Metal Arc Welding (DCW-GMAW), and the Hot Wire–Gas Metal Arc Welding (HW-GMAW). CW-GMAW and DCW-GMAW welding contributed significantly to increased productivity [6, 7]. CW-GMAW welding allowed for narrow bevel welding with 4 mm gap [8]. Furthermore, it is responsible for reducing the level of residual welding stresses [9] and increasing fatigue strength [10]. On the other hand, the HW variant presents as its main characteristic the increase in productivity, with the possibility of variation in penetration [11]. These variants have the possibility to achieve deposition rates ranging from small percentages from 10% to more than 100% of extra molten metal, also influencing the formation of microstructures such as acicular ferrite, which contribute to increase the properties, mainly mechanical, of the weld metal. In this context, some variants of the GMAW process will be presented below, some of which have already been tested, and others are still being tested for possible field applications, thus showing the importance of these welds for the academy and the manufacturing industry, assembly, and maintenance.
