**4.4 Optimized welding processes**

Aiming at reducing the values of deformations and RS's, the market has been promoting the improvement of welding processes, such as, for example, better stability in metal transfer, methods of controlling the waveform of sources,

**249**

**Figure 9.**

*CW-GMAW process scheme.*

*Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

the other investigated processes.

residual welding stresses.

into the arc atmosphere in the CW-GMAW process.

feedback of parameters during the process, reduction of heat input on the material to be welded, among these processes the CW-GMAW (CW)® stands out. It is a process derived from the GMAW process. The CW-GMAW process uses the feeding procedures to those of the GTAW process with automated feeding, it presents itself as an alternative to increase productivity without increasing the heat input in the melting arc/puddle system. The respective process uses the introduction of an additional wire, at room temperature, in the atmosphere of the arc, generated by the main wire, through an independent feeder and an injector connected to the welding torch [70, 75–78]. In detail, **Figure 9** illustrates the entry of the non-energized wire

It is possible to highlight several advantages of the CW-GMAW process over conventional processes, among which we have the one presented in the work of [70, 75]. The authors pointed out that the introduction of an additional wire improves the melting rate, tending to decrease the heat input to the workpiece, thus, there is a decrease in the values of distortions and consequently of RS. Distortions levels were compared using the GMAW, Surface Tension Transfer (STT) and CW-GMAW processes [70]. With the global deformation values, **Figure 10**, it was possible to observe that the CW-GMAW process obtained the lowest global distortion value, in comparison with

In another study, RS values were compared using two measurement techniques, X-ray diffraction and Acoustic Birefringence (BA), using the GMAW and CW-GMAW processes [63]. The analyzes were performed in simple deposition welds, on ASTM 131 grade AH32 naval steel plates, rigidly attached to a support to ensure a condition close to that found in real welding, simulating the dimensional restriction levels of a welded structure. After the deposition of the welds, the values of AB and XRD were measured at previously established points, in the regions of the base metal, heat-affected zone (HAZ) and weld metal (WM). Through **Figure 11** the measurements obtained by XRD showed that the use of the CW-GMAW process decreases the longitudinal stresses in the region near and in the weld bead, a difference was not observed for the transverse stresses. BA measurements showed that the difference between longitudinal and transverse residual stresses tends to decrease when using the CW-GMAW process, compared to the GMAW. These results suggest that the addition of an extra wire to the conventional process reduces the amount of heat supplied to the welded joint and, consequently, prevents the generation of

#### *Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

*Welding - Modern Topics*

**Figure 8.**

generated values consistent with those found in numerical studies [71–73]. Similarly, the results are corroborated by the work of [69], where it was observed that the welding sequence that provided the lowest distortion value must be performed from a more rigid point (central part) to one of less rigidity (extremities), resulting in less flexion of the panel and consequently lower values of RS. Exp. 5 obtained values very close to Exp. 2, due to the greater control of the temperature differential applied to the welded sheet and to a more uniform distribution of residual stresses [71]. However, this gain in the distortion values must be well considered, since a

The VSR process has achieved great prominence in the relief of RS's induced by thermal processes, such as welding, casting, but not those induced by cold work, being applied in several materials, low and medium carbon steels, stainless steels and aluminum alloys, not having an expected effect on copper alloys. VSR offers several advantages compared to the PWHT (Post Weld Heat Treatment) process: low time and energy spent, low thermal deformation and no change in the mechanical or metallurgical properties of the material [11, 65]. However, there are numerous conditions that must be considered when using the VSR and PWHT processes. Within the conditions employed by the authors, a lower RS value was obtained for

The basic premise of this method is the relief of the workpiece RS with a region where the natural stress has been changed. When the part is subjected to vibrations below its new frequency, the metal absorbs energy, gradually redistributing the stresses and the resonant frequency returns to the point corresponding to a residual, or almost free, state [20]. The search for greater productivity for the arc welding process has generated efforts by researchers to develop the VSR process, to act during the welding process, that is, Vibration assisted welding (VAW), which can reduce most expenses related to post-weld vibrations or heat treatments [74].

Aiming at reducing the values of deformations and RS's, the market has been promoting the improvement of welding processes, such as, for example, better stability in metal transfer, methods of controlling the waveform of sources,

longer time was used to make the stiffener joint.

**4.3 Vibratory stress relief (VSR)**

*Overall distortion of the experiments.*

the use of both processes.

**4.4 Optimized welding processes**

**248**

feedback of parameters during the process, reduction of heat input on the material to be welded, among these processes the CW-GMAW (CW)® stands out. It is a process derived from the GMAW process. The CW-GMAW process uses the feeding procedures to those of the GTAW process with automated feeding, it presents itself as an alternative to increase productivity without increasing the heat input in the melting arc/puddle system. The respective process uses the introduction of an additional wire, at room temperature, in the atmosphere of the arc, generated by the main wire, through an independent feeder and an injector connected to the welding torch [70, 75–78]. In detail, **Figure 9** illustrates the entry of the non-energized wire into the arc atmosphere in the CW-GMAW process.

It is possible to highlight several advantages of the CW-GMAW process over conventional processes, among which we have the one presented in the work of [70, 75]. The authors pointed out that the introduction of an additional wire improves the melting rate, tending to decrease the heat input to the workpiece, thus, there is a decrease in the values of distortions and consequently of RS. Distortions levels were compared using the GMAW, Surface Tension Transfer (STT) and CW-GMAW processes [70]. With the global deformation values, **Figure 10**, it was possible to observe that the CW-GMAW process obtained the lowest global distortion value, in comparison with the other investigated processes.

In another study, RS values were compared using two measurement techniques, X-ray diffraction and Acoustic Birefringence (BA), using the GMAW and CW-GMAW processes [63]. The analyzes were performed in simple deposition welds, on ASTM 131 grade AH32 naval steel plates, rigidly attached to a support to ensure a condition close to that found in real welding, simulating the dimensional restriction levels of a welded structure. After the deposition of the welds, the values of AB and XRD were measured at previously established points, in the regions of the base metal, heat-affected zone (HAZ) and weld metal (WM). Through **Figure 11** the measurements obtained by XRD showed that the use of the CW-GMAW process decreases the longitudinal stresses in the region near and in the weld bead, a difference was not observed for the transverse stresses. BA measurements showed that the difference between longitudinal and transverse residual stresses tends to decrease when using the CW-GMAW process, compared to the GMAW. These results suggest that the addition of an extra wire to the conventional process reduces the amount of heat supplied to the welded joint and, consequently, prevents the generation of residual welding stresses.

**Figure 9.** *CW-GMAW process scheme.*

#### **Figure 10.**

*Overall distortion of the experiments for each process.*

**Figure 11.** *Comparative between longitudinal and transverse RS with GMAW and CW-GMAW measuring by XRD.*

The authors [68] presented evidence that the use of the CW-GMAW process reduces the residual stress and increases the resistance to fatigue, when compared to samples welded by the conventional GMAW process. The weld bead was made on plates with V joints of ASTM 131 grade A steel. Through a micrographic analysis it was shown that welding by the CW-GMAW process promoted a decrease in the amount of intergranular ferrite and an increase in hardness in the HAZ. SN fatigue resistance curves can be seen in **Figure 12**. Analysis of the results revealed that, for lower levels of reliability, joints manufactured using the GMAW process have a fatigue life at high voltage amplitude levels and greater fatigue life at lower stress amplitudes. However, when a higher level of confidence is considered, weldments made using the CW-GMAW process showed greater resistance to fatigue at both high and low amplitude stress levels.

The versatility and low cost of application of the CW-GMAW process is presented by [76], the authors developed a study on the viability of narrow bevel welding (Narrow Gap Welding-NGW). The tests showed an improvement in stability with the CW-GMAW process instead of the GMAW, and an increase in the melting rate, from 4.9 to 9.7 kg/h, promoting a complete filler weld with just 3 passes (root, filler and finishing), **Figure 13**.

Through high speed filming, in the GMAW process the arc attaches to the side wall, causing erosion and leading to welding discontinuities shown in **Figure 13e**, while for CW-GMAW welding this is not observed, **Figure 13a**. For a better understanding of the metal transfer mechanism [76], welds were deposited on a metal plate with the addition of increasing amounts of extra wire, shown in **Figure 14**.

**251**

**Figure 12.**

**Figure 13.**

**Figure 14.**

*respectively.*

*(c) CW-GMAW additional wire of 1.0 mm.*

It was found that as the amount of additional wire increases, the position fixing the arc changes from the weld pool to the additional wire, promoting greater stability during the welding process. When larger amounts of additional wire, 140% mass

*Influence of the addition of additional wire on the cathode point of the arch: (a) represents the GMAW process, and (b) and (c) represent CW-GMAW welding with the addition of 60 and 140% additional wire,* 

*Appearance and cross section of the bead for welds: (a-d) CW-GMAW; (e-h) GMAW.*

*Fatigue life for different levels of reliability: (a) GMAW, (b) CW-GMAW additional wire of 0.8 mm, and* 

*Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533* *Welding Residual Stresses to the Electric Arc DOI: http://dx.doi.org/10.5772/intechopen.93533*

#### **Figure 12.**

*Welding - Modern Topics*

**Figure 10.**

**Figure 11.**

*Overall distortion of the experiments for each process.*

The authors [68] presented evidence that the use of the CW-GMAW process reduces the residual stress and increases the resistance to fatigue, when compared to samples welded by the conventional GMAW process. The weld bead was made on plates with V joints of ASTM 131 grade A steel. Through a micrographic analysis it was shown that welding by the CW-GMAW process promoted a decrease in the amount of intergranular ferrite and an increase in hardness in the HAZ. SN fatigue resistance curves can be seen in **Figure 12**. Analysis of the results revealed that, for lower levels of reliability, joints manufactured using the GMAW process have a fatigue life at high voltage amplitude levels and greater fatigue life at lower stress amplitudes. However, when a higher level of confidence is considered, weldments made using the CW-GMAW process showed greater resistance to fatigue at both

*Comparative between longitudinal and transverse RS with GMAW and CW-GMAW measuring by XRD.*

The versatility and low cost of application of the CW-GMAW process is presented by [76], the authors developed a study on the viability of narrow bevel welding (Narrow Gap Welding-NGW). The tests showed an improvement in stability with the CW-GMAW process instead of the GMAW, and an increase in the melting rate, from 4.9 to 9.7 kg/h, promoting a complete filler weld with just 3

Through high speed filming, in the GMAW process the arc attaches to the side wall, causing erosion and leading to welding discontinuities shown in **Figure 13e**, while for CW-GMAW welding this is not observed, **Figure 13a**. For a better understanding of the metal transfer mechanism [76], welds were deposited on a metal plate with the addition of increasing amounts of extra wire, shown in **Figure 14**.

**250**

high and low amplitude stress levels.

passes (root, filler and finishing), **Figure 13**.

*Fatigue life for different levels of reliability: (a) GMAW, (b) CW-GMAW additional wire of 0.8 mm, and (c) CW-GMAW additional wire of 1.0 mm.*

#### **Figure 13.**

*Appearance and cross section of the bead for welds: (a-d) CW-GMAW; (e-h) GMAW.*

#### **Figure 14.**

*Influence of the addition of additional wire on the cathode point of the arch: (a) represents the GMAW process, and (b) and (c) represent CW-GMAW welding with the addition of 60 and 140% additional wire, respectively.*

It was found that as the amount of additional wire increases, the position fixing the arc changes from the weld pool to the additional wire, promoting greater stability during the welding process. When larger amounts of additional wire, 140% mass

more is inserted into the system, the cathode point moves to the additional wire, which is being feed, shown in **Figure 14c**. This change in the cathode point for the additional wire allows for a more stable welding, thus there is no erosive effect on the wall base metal, the smallest variation in the heat input value for the CW-GMAW points to the stability of the process and its ability to increase the deposition rate without changing the welding heat input.
