**1. Introduction**

GMAW as a welding process presents a high degree of production, reliability, and automation capacity. With the appropriate parameter configuration, it allows welding in almost all positions and with almost all existing metal alloys. One peculiarity of the GMAW process is that, depending on the intensity of the current and voltage, different types of metal transfer can be observed. The metal transfer mode characterizes the way molten metal is deposited. The three main modes of metal transfer are short circuit, globular, and spray. The most relevant parameters involved in the process can be mentioned: amperage, voltage, welding speed, and stick out. Another peculiarity is that the process can be defined as chaotic; involves the interaction of several nonlinear welding variables; and presents a stochastic behavior. Therefore, great efforts are made to select the appropriate procedure to ensure the highest quality.

Quality can be defined as the union of a client's requirements with respect to a product. In the particular case of welding, the main objective is to get a weld bead as close as possible to the requirements. The welding quality can be monitored in two moments: online while the process is running and offline after the welding bead is obtained.

The offline evaluation considered geometric factors such as proper penetration, reinforcement, and the length of the pieces. Destructive tests can be carried out and consist of taking samples of weldments to evaluate the metallic continuity, mechanical strength, and other determining factors for the correct performance in service. Sometimes these tests lead to the destruction of the body tested. On the other hand, Wu et al. [1] affirm that online quality control allows the saving of financial resources through the reduction of defects in the production line. For this purpose, sensors for visual imaging, sound acquisition, infrared cameras, and ultrasonic sensing methods have been implemented.

Contact tip: It is a torch device that has the function of guiding and supplying

CTWD (contact tip to work distance): It is often confused with the distance between the contact tip and the work piece, which coincides when the nozzle front

Stick out: It is the length of free wire after it has passed through the contact tip. The gas composition aims to stabilize the arc and protect the welding material from atmospheric gases such as nitrogen and oxygen, which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with the electrode, the arc, or the welding metal. Depending whether the gas is inert (Ar or He) or active (CO2, or mixtures including N2 or O2), it can sbe classified as metal

The weld bead geometry depends directly to the parameters that govern the process. **Figure 2** outlines these geometric parameters in the cross section of a weld bead. The most important parameters affecting penetration and geometry in the GMAW process are welding current, arc voltage, torch travel speed or welding

According to [6] the process parameters of GMAW can be divided into five basic

• Fixed, that cannot be modified by the operator and it is defined in the process

• Adjustable offline, that can be modified only before starting the process.

• Quantifiable offline, that is measurable only after the process ended.

Workpiece: composed of the metal bodies to be joined by the weld.

Electrode: It is the consumable copper-coated steel electrode that melts with the

voltage to the wire.

*Stability on the GMAW Process*

electric arc and transfers to the melting pool.

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

cut is also the same as the contact tip front cut.

active gas (MAG) or metal inert gas (MIG).

groups (as shown in **Figure 3**):

design.

**Figure 2.**

**5**

*Weld bead geometric characteristics [5].*

speed, stick out, torch tilt, and the diameter of the electrode.

• Adjustable online, that can be modified during the process.

• Quantifiable online, that is measurable during the process.

One concept that is strongly correlated to the online quality is the control of the process stability. According to Ponomarev [2], the stability of the GMAW process is evaluated online by three factors: metallic transfer regularity, arc stability, and the operational behavior of the welding process. Meneses [3] also ensures that the higher the transfer stability, the higher the penetration and the lesser the amount of spatter.

The objective of this work is to present a bibliographical review of the scientific literature related to weld quality evaluation, focused mainly on those studies that present qualitative and quantitative indexes to evaluate the stability of the GMAW process. The chapter is structured as follows: Section 2 discusses Stability Control in the GMAW process; Section 2.1 discusses GMAW process operation; Section 2.2 discusses factors that affect stability; Section 2.3 presents a Summary of Stability index; and finally, Section 3 reveals a synthesis of the study and future research directions.
