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Waveforms of welding current and arc voltage at 9 m/min and 22 V: (a) without ultrasonic wave; (b) with ultrasonic wave.
Source publication
Ultrasonic vibration can change the dynamic behavior of the bubble and improve the process stability in underwater wet welding (UWW); thus, it has been attempted to profitably control metal transfer process. Arc signals about welding current and arc voltage together with the high-speed imaging detected in conventional UWW and ultrasonic-wave-assist...
Contexts in source publication
Context 1
... Dynamic control of current and voltage waveforms 3.1.1. Experimental group 1 Fig. 4 shows the current and voltage waveforms of conventional UWW and U-UWW at a wire feed speed of 9 m/min and an arc voltage of 22 V. As shown in Fig. 4(a), large voltage signal with long duration time appears in the waveforms of conventional UWW, and the corresponding current value is reduced to zero, and this process occurs continuously. ...
Context 2
... Dynamic control of current and voltage waveforms 3.1.1. Experimental group 1 Fig. 4 shows the current and voltage waveforms of conventional UWW and U-UWW at a wire feed speed of 9 m/min and an arc voltage of 22 V. As shown in Fig. 4(a), large voltage signal with long duration time appears in the waveforms of conventional UWW, and the corresponding current value is reduced to zero, and this process occurs continuously. According to high-speed camera image in Fig. 5, it is found that due to low arc voltage and high wire feed speed, the end of fluxcored wire has no ...
Context 3
... the action of ultrasonic wave, the arc extinction and bubble burst still exist during the U-UWW process, indicating that the regulation effect of the bubble is not obvious. Thus, the U-UWW process is still dominated by solid short-circuiting transfer mode by observing the current and voltage waveforms in Fig. 4(b). The electric signal distribution of short-circuiting transfer period is uneven, and the duration time of arc extinction does not change. There is a phenomenon of arc extinction for a long time, about 60 ms. Hence, ultrasonic wave does not improve the transfer process of solid short-circuiting which is unstable under the conditions ...
Citations
... Kim and Kim (2014) presented the direct observations of single bubble dynamics in an ultrasonic field and indicated that single bubble behavior produces four different oscillations, which are highly related to bubble size and Fig. 1. Bubble evolution process generated in UWW without (a) and with (b) ultrasonic wave (Wang et al., 2019a). acoustic pressure amplitude. ...
... Prior to the generation of heat-induced bubble, the ultrasonic system was initialized to guarantee the heat-induced bubble located at an acoustic field. As observed in Fig. 1, compared with that the rising vertically in conventional UWW, the heat-induced bubble is able to oscillate appropriately at the weld pool surface without motion upwards in U-UWW (Wang et al., 2019a). With ultrasonic wave, the volume of heat-induced bubble is increased and thus generates a large area to protect the weld pool. ...
The role of the bubble in ultrasonic-wave-assisted underwater wet welding (U-UWW) remains largely empirical, primarily due to the lack of acoustical understanding of the bubble-acoustic interaction. Hence, numerical simulation of acoustic field, using a model considering bubble effect, was carried out to investigate the effect of acoustic radiator configuration on bubble-acoustic interaction. The pressure field characteristic and its influence on time-averaged potential and acoustic radiation force at the bubble boundary were systematically studied. The results show that the degree of bubble-acoustic interaction largely relies on the synergic effects of acoustic radiator configuration and the resonant mode of acoustic field; the latter can be accomplished by tailoring radiator height. Also, acoustic radiator with a concave surface is superior to that with cylinder and stepped-plate configuration in enhancing acoustic radiation force, in which the dimensionless maximum value of 93.7 is attained at the curvature radius of 38 mm. As the resonant height increases, the amplitude of acoustic radiation force tends to decrease, which renders the beneficial role of the first resonant mode in U-UWW, i.e., the resonant height is 50 mm. The simulated acoustic field results agree well with experimental results on bubble behavior and welding stability. When the resonant height is 50 mm and the curvature radius is 38 mm, the inverse of variation coefficient of arc voltage is increased to maximum values of 4.3 and 4.9, respectively, indicating superior welding stability. It is believed that the bubble-acoustic interaction mechanism can provide vital clues in enabling the design of ultrasonic system via acoustic radiator adaption.
... The simplicity of the equipment used enables the repair of complex shaped structures at low cost [3], [4], [5]. In recent years, ux cored arc welding (FCAW) has become a focus of research at UWW, although shielded metal arc welding (SMAW) is still used today [6], [7], [8]. Metal arc welding is often used for repair welds, which is particularly important for the deep water environment [9]. ...
Underwater wet welding (UWW) is applied to repair offshore structures, underwater pipelines, water transport, docks and harbour equipment. In this study, the mechanical and microstructural properties of AH36 low carbon steel were investigated at different welding current strengths and different seawater temperatures using metal arc welding (SMAW), an underwater wet welding method. Changing seawater temperatures and welding current parameters were examined together, so that the change of seasonal variability in welding parameters and chemical structure of seawater was examined. For this purpose, in the first stage, the yield strength value of AH36 was statistically modelled using the central composite design with the response surface method with input parameters of seawater temperature (in the range of 9.7°C-25.3°C) and source current value (in the range of 49A-90A) and the best conditions were found as Optimum Yield stregth 270MPa, 17.5°C seawater temperature and 69.5 A source current value. In the second stage of the study, the data obtained from the optimisation studies were used in the multi-response optimisation model to obtain elemental exchange equations for Cr (R ² = 87.3), Ni (R ² = 64.45) and Mn (R ² = 65.74) ionised in seawater. Accordingly, it was observed that the change in Cr content in seawater is affected by source current intensity, Ni content is affected by seawater temperature and Mn content is affected by current intensity and seawater temperature together. ICPMS was used for ion exchange in seawater, EDS point analysis for chemical composition in AH36 and SEM for microstructure analysis.
... However, as Ma et al. (2021) pointed that due to the poor flexibility, local dry welding may not be suitable to be applied in the large scale of marine engineering. Compared with the other two methods, underwater wet welding (UWW) has the most application prospect in water-related engineering due to the nature of economy and simplicity as Wang et al. (2019) suggested. Since it is directly conducted in the water, problems such as the process instability, fast cooling rate, hardened microstructure with high diffusible hydrogen and cracks may hinder its further development. ...
... In general, underwater wet welding relies on a bubble to achieve a desired weld bead, and the bubble plays a multiplicity of roles during the welding process, such as stabilizing the arc (Ref. 21), promoting metal transfer (Ref. 22), reducing the appearance of spatter (Ref. ...
To reasonably characterize the features of underwater wet welding, especially the bubble effect engendered from a high concentration of heat, a three-dimensional (3D) numerical model considering bubble dynamics interaction with the boundary layer was developed. A semi-empirical method assessing the bubble growth process was incorporated into our model as boundary conditions to account for the heat loss mechanism. It is proven that the bubble configuration consideration can improve the prediction accuracy and the predicted weld profile is in good agreement with the experimental results. To reveal the contribution of bubble configuration while maintaining processing variables consistency, the influences of the equivalent contact radius of the bubble and its floating frequency on the temperature field evolution were evaluated. The results show that low floating frequency and/or high equivalent contact radius tend to depress the heat losses to water environment, prolong the t8/5 time, and enhance the weld width and penetration depth, which renders the beneficial role of optimized bubble dynamics. Under otherwise identical conditions, the equivalent contact radius of the bubble plays a much better role than the bubble floating frequency in promoting weld pool dimensions. Based on the quantified data, suggestions on the matching strategy of bubble configuration and heat input for underwater wet welding may be provided.
... Underwater wet welding suffers from poor arc stability, difficult droplet transfer, high porosity, and high diffusion hydrogen content due to the negative impacts of the water environment and arc bubbles [1,2]. Many researchers have employed external fields to control the arc bubble and metal transfer process, such as mechanical ultrasound [3], arc ultrasound [4], and mechanical constraint [5], thereby achieving the goal of decreasing spatter and enhancing the welding process stability. In addition, the tempering bead technique [6], induction heating [7], and underwater submerged arc welding [8] have been used to improve the underwater weldability of low-alloy high-strength steel. ...
Alumino-thermic additions to the flux-cored wire can be utilized to enhance welding heat input, improve welding productivity, and minimize the dependency on power sources in the air environment. In this article, the influence of Al/Fe2O3 thermite on electrical dependency, microstructural characteristics, and mechanical performance during the underwater wet welding of Q235 steel was investigated. The results revealed that adding exothermic flux enhanced the underwater wet welding appearance. The basicity of the slag steadily decreased from 1.77 to 0.73 because of the formation of Al2O3. Thermite increased the quantity and diameter of inclusions in the underwater wet weld metal. The excessive addition of Al/Fe2O3 thermite resulted in agglomerated inclusions in the weld metal. Significant microstructural changes from grain boundary ferrite to acicular ferrite were mainly caused by the de-oxidation products of the thermite process. When thermite was added to the flux-cored wire, the ultimate tensile strength first increased and then decreased, while the microhardness of the underwater wet welds showed an obviously increasing trend. The addition of exothermic flux additions to the flux-cored wire can help generate chemical heat and increase the energy required to melt the wire. This study established a link between thermite addition and joint performance, paving the way for the development and application of thermite-assisted self-shielded flux-cored wire.
... Therefore, the use of different control current waveforms at different stages of bubble growth can make the bubble show a single complete separation mode. Wang et al. [6] applied ultrasonic vibration to the bubble generated in underwater wet FCAW to change the motion characteristics of the bubble, thereby further reducing the fluctuation of the welding current, reducing the size of the droplet and increasing the transfer frequency. Zhang et al. [7] combined electrical signals with visual inspection and analyzed the influence of flux-cored wire feeding rate on the arc and weld formation during welding, and proposed that an increase in the feeding rate within a certain range is beneficial to improving the stability of the arc. ...
Based on the VOF method (Volume of Fluid Method), a non-axisymmetric three-dimensional (3D) numerical model was developed in this paper, which coupled the droplet and arc and simulated the typical globular repelled transfer process with large droplet in the underwater wet flux-cored wire arc welding (FCAW) process. The results show that in addition to the action of gravity, surface tension and self-induced electromagnetic force, the droplet is also affected by the gas flow generated by the wire, the gas flow resistance in the bubble and the force caused by metal evaporation. The rotation of the droplet around the wire axis is mainly affected by the gas flow generated by the flux core. But the angle of the droplet deviation from the wire axis is determined by all external forces. The path of current line is changed by the droplet movement, thereby constraining the behavior of the arc. In order to verify the validity of the numerical model, images of the metal transfer are collected by a high-speed camera, and the simulated values are in good agreement with the experimental ones.
... New processes have been proposed to improve the underwater wet welding quality, such as tempered bead welding [14], real-time induction heating [15] and ultrasonic [16] and pulse wire feeding [17]. In particular, ultrasonic-assisted underwater welding can effectively improve the arc stability and welding quality, and it has been studied by many researchers. ...
The ultrasonic-frequency pulse underwater wet welding (UFP-UWW) process was achieved through a constant-voltage-mode power source connecting an ultrasonic-frequency pulse power source in parallel. The arc voltage and welding current waveforms, sound signal variations, microstructural characteristics and mechanical properties at different parameters were investigated. The results showed that the ultrasonic-frequency pulse voltage and current of the UFP-UWW process displayed a periodic high-frequency oscillation on the based values of the conventional UWW process. The arc stability of the UFP-UWW process improved owing to the fact that the proportions of the unstable arc burning region could be reduced to 1.56% after the introduction of the ultrasonic-frequency pulse current. No significant changes in weld width and penetration were observed while the weld dilution rate increased to 54.2% for the combination of 40 V–30 kHz, compared with the results of the conventional UWW process. The flux-cored arc (FCA) welding arc in the air had the same frequency response to the ultrasonic excitation signal, which verified the existence of the ultrasonic-frequency vibration induced by the periodic high-frequency electromagnetic forces. The application of the ultrasonic-frequency pulse produced finer columnar grains in the welds with an average length of 315 μm, although the amount of pro-eutectoid ferrite and acicular ferrite varied little. The mechanical properties of the welded joints were also noticeably enhanced with the application of different ultrasonic excitation frequencies. The optimum tensile strength and impact toughness of the welded joint were improved by 6.7% and 21.7% when the applied ultrasonic excitation voltage was 40 V for a pulsed frequency of 30 kHz. These results facilitate the application of ultrasonic arc welding technology in the marine field.
... Some research groups are also focusing on hybrid multi-field assisted welding. For example, Wang et al. [72] and Chen et al. [73] applied magnetic field-assisted reduction of droplet size and increased transition frequency in laser-MIG hybrid welding. The combined force on the droplets is constantly changing, as the intensity of the magnetic field alters, and this causes changes in the shape of the droplets. ...
The development of advanced welding processes is of great significance, which is in order to adapt to the development of new materials and new welding environments. The discrepancies in the molten droplets, expressed by the characteristic parameters, are a reflection of the final welding quality. In recent years, more fundamental theories have been established, which have directed the optimization of the methods, through observation or numerical simulation. Innovations in methodology are made through thermal, mechanical, or hybrid effects. Based on the existing innovative methods, this paper predicts the future development directions for welding droplets.
... In recent years, the application of ultrasonic vibration is believed to be a key enabler for welding manufacturing. [21][22][23] Ultrasonic vibration serves several vital functions with respect to arc constriction, [24,25] metal transfer control, [26,27] bead morphology improvement, [28] pore elimination, [29] and WM refinement [30][31][32] in welding, paving the way to achieve desired weld quality. Due to the ultrasonic irradiation of weld pool occurring during the welding process, nonlinear effects induced by ultrasonic vibration are found to be essentially affecting WM microstructures. ...
In-depth understanding of microstructural modification and grain refinement is required to manufacture high quality products by gas tungsten arc welding. Here, we report the governing role of ultrasonic vibration in the improvement of microstructure and mechanical properties of the as-welded duplex stainless steel. We show that the columnar-to-equiaxed transition was promoted and fine equiaxed grains with no preferred crystallographic texture could be achieved involved in welding. Detailed microstructural features coupled with acoustic field simulation were carried out to reveal the mechanisms of grain refinement. This was attributed to the production of many initial nuclei or crystallites which resulted from the acoustic cavitation in the ultrasonic vibration of weld pool. Consequently, the formation of this microstructure led to a significantly increased tensile strength and maintained acceptable ductility. These findings offer a new perspective on control of grain structure in the as-welded condition by extending ultrasonic vibration to duplex stainless steel welding.
... A relatively large bubble was always maintained on the weld pool surface so that the welding process was not easily affected by these bubble dynamics (Ref. 32). The effect of the acoustic radiator with various curvature radii on the bubble-acoustic interaction was investigated, and the optimized curvature radius was found to be 38 mm (Ref. ...
The control of the bubble in underwater wet welding (UWW) plays a crucial role in improving the process stability and metal transfer behavior. However, its effects on the microstructure and mechanical properties of the welded joint have not been widely researched. We employed the bubble-acoustic interaction method to the E40 steel weldments in ultrasonic-wave-assisted UWW for the first time. The welding thermal process, microstructure, and mechanical properties of the welded joint were examined. The results demonstrate that the addition of ultrasonic vibration exerts significant effects on the heat flow conditions due to the water removal from around the weld pool, which can largely prolong the t8/5 time from 4.0 to 6.4 s and reduce the cooling rate of the weld,
leading to its microstructure modification. As a result, there is a remarkable improvement in mechanical properties, among which the increase in toughness is substantially attributed to the formation of acicular ferrite in the weld metal and the decrease of lathy martensite in the heat-affected zone. In addition, a decrease in the microhardness value of the weld metal from 249 to 229 HV0.2 was observed. Our study shows that bubble-acoustic interaction is sufficient to produce weldments with microstructure modification whilst optimizing the thermal process. The comprehensive description of joint improvement mechanisms caused by bubble-acoustic interaction was presented based on process stability control and thermal cycle analyses.
