Pulsed Gas Tungsten Arc Welding Research Articles

Effect of the thermal field on the microstructure of dissimilar welded joints between TWIP steel and 2205 duplex stainless steel

This study reported a theoretical-experimental analysis of dissimilar metals duplex stainless steel (DSS) grade 2205 and twinning induced plasticity (TWIP) steel joined. Welded joints were performed in autogenous mode and using filler metal (ER2209) by the pulsed gas tungsten arc welding (GTAW-P) process. Critical weld regions were characterized metallographically using LOM and SEM. Microstructural changes such as the morphology and contents of ferritic and austenitic phases were correlated to the temperature ranges estimated numerically by a finite element (FE) model, which considered the variation of the percentage dilution in the fusion zone (FZ). The average variation between experimental and numerical results was up to 6.75%. SEM chemical analysis and line scanning analysis corroborated the diffusion of Al, Mn, Cr and Ni in the FZ of the autogenous joint. Small concentration gradients promoted a homogenous chemical composition of the ferritic and austenitic phases in the filler metal joint. The FZ exhibited an austenitic phase coarsening due to the elevated temperatures (1506°C–1803 °C, DSS 2205 side). Wetting problems were observed in both weldments producing prominent interfaces between the welded metal (WM) and the heat-affected zone (HAZ). Other weld defects such as underfilling, undercuts and lack of fusion were also detected. When a high TWIP steel volume was melted (filler metal joint), WM hardness increased compared to the autogenous joint. The hardness increment (2–5% in the DSS 2205) combined with the lack of fusion brought about the failure of the filler metal joint during the bend test.

Multi-layer deposition mechanism in ultra high-frequency pulsed wire arc additive manufacturing (WAAM) of NiTi shape memory alloys

Ultra high-frequency pulsed gas tungsten arc welding (UHFP-GTAW)-based Wire Arc Additive Manufacturing (WAAM) was used to fabricate thin walls of NiTi shape memory alloys. The transient heat and fluid flow are critical during fusion-based additive manufacturing, since they impact the as-built microstructure. In this work, a three-dimensional numerical model, which includes the force, surface Gauss heat source and periodic droplet transfer models, was developed to simulate the deposition of 5 layers. The gravity, buoyancy, electromagnetic, surface tension, arc pressure and arc shear stress are considered in the developed force model. An improved free surface tracing method using the volume of fluid (VOF) technique was proposed to more effectively track the free surface of the molten pool with the computational fluid dynamics (CFD) software FLUENT. The multiphysics phenomena associated to the process, namely the temperature and velocity fields of the molten pool, were studied. The model was then validated by experiments. It is revealed that the microstructure of the as-built parts is refined by the UHFP current power which induces significant vibration of the molten pool. These findings lay the foundations for optimizing the WAAM process aiming at fabricating high quality and complex NiTi parts. • Ultra high-frequency pulsed WAAM is used to promote grain refinement in as-built NiTi parts. • Development of a numerical modeling approach to understand the deposition mechanism and its effect on the molten pool. • The ultra high-frequency current promotes significant vibration of the molten pool thus inducing grain refinement. • Good agreement between experimental and modelling approaches was achieved.

Dynamic molten pool behavior of pulsed gas tungsten arc welding with filler wire in horizontal position and its characterization based on arc voltage

To explore the dynamic behavior of molten pool and to find the electric characteristic signals reflecting the weld penetration states and degree for the fixed-point wire-filled pulsed gas tungsten arc welding (GTAW-P) of thin pipes in 2G position, molten pool images from different directions and arc voltage were sensed. During a peak current period, critical penetration occurred, with the molten pool behavior that the topside molten pool height collapsed sharply and was approximately 0.5 mm, and then rose to approximately 1.5 mm during the next base current period. With the increase in backside molten pool width, the oscillation amplitude and frequency of topside molten pool during the base current period increased and decreased, respectively. The oscillation amplitude reached the maximum when over penetration occurred. Such molten pool behaviors could be extracted from the arc voltage signals. The change in average peak voltage (ΔU⁎) could reflect the occurrence of critical penetration. The average base voltage (Ub¯) and the fluctuation of base voltage (ΔUb) increased linearly with the increase in backside molten pool width, which are reliable characteristic signals for the weld penetration degree. The effects of wire filling and base current on the dynamic molten pool behavior and characteristic signals were investigated. Experimental results showed when the base current is 10 A ̶15 A, Ub¯ and ΔUb can effectively characterize the weld penetration degree.

Influence of Different Frequency Pulse on Weld Bead Phase Ratio in Gas Tungsten Arc Welding by Ferritic Stainless Steel AISI‐409L

The objective of the present experimental work is to obtain an appropriate welding parameter on pulsed current gas tungsten arc welding (GTAW) ferritic stainless steel AISI 409L with a thickness of 4.5 mm. Frequency affected penetration, and the ratio of bead width to penetration (aspect ratio) is the main objective of the research. A Taguchi L9 orthogonal array with three level four factors was chosen to execute the bead on plate welding. It leads to optimize the input process parameters on main effect plot via analysis of variance, and it has imposed to determine their contribution level of each parameter with respect to responses. Taguchi optimized conditions for butts weld with the pulsed TIG and its surface morphology, and mechanical characteristics of AISI 409L weld was investigated. A full penetration with an optimal aspect ratio was accomplished using high‐frequency pulsing, according to the findings. The mechanical properties were characterized using Vickers microhardness and tensile tests on the base material and weld metals. Microstructural study revealed that these variables have a greater impact on the bead profile. Pulsed TIG showed maximum UTS of 445 MPa and a minimum of 385 MPa, with an average of three samples of 415 MPa. The weld metal in all of the zones had influenced superior tensile strength (UTS) as compared to base metal, according to the findings. The obtained strain percentage for both butt and TIG welds, however, was smaller than that of the parent metal. The formation of martensitic was attributed for the higher tensile strength with minimized ductility of the pulsed TIG welds. Furthermore, results on the hardness are in concurrence with the tensile experiments, as the zone for fusion has a higher hardness than the base metal. Corrosion behavior of the parent metal and welded specimen was analyzed using a potentio‐dynamic polarization technique. The electrochemical behavior of base material and weld samples confirmed that the overall corrosion resistance is better in parent material than the other zones.

Hot corrosion performance of bare and pulsed current welded Fe-based A-286 alloy in chlorine and sulphur environment

This present research work focuses on the hot corrosion performance of the base metal, weldment, and weld metal of A-286 alloy in sodium sulphate (Na2SO4)–5% sodium chloride (NaCl)–7.5% sodium metavanadate (NaVO3) (3SM) atmosphere at 700 °C. A pulsed current gas tungsten arc welding process is employed to make a similar joining of A-286 alloy using the filler material ERNiCrMo-3. The corrosion kinetics of the specimens has been determined using the thermo-gravimetric technique. The phase compositions of the reaction products are studied by X-ray diffraction, and the surface morphology of the scales is explored by scanning electron microscope analysis. The corroded samples are subjected to a cross-sectional study to ensure the corrosion attack and scales thickness using a SEM with elemental mapping technique. The result indicates that weldment showed better corrosion resistance than bare metal. A thick oxide scale could be found in the bare metal specimen than the weld metal. In the case of base metal, the formation of non-adherent and porous iron (III) oxide (Fe2O3) leads to rapid corrosion. The weight gain of weldment is about 1.96 and 1.13 times less than bare alloy and weld metal.

Joint Penetration Monitoring in Low-Frequency Pulsed GTA Root Pass Welding of Medium-Thick Steel Plates

Welder-dependent manufacturing is no longer suitable for the modern production of a high-performance nuclear pressure container. The high-quality root pass welding of medium-thick steel plates is the main challenge to obtain a sturdy reactor vessel, especially to generate one-sided welding with back-formation bead without a backing. Herein, low frequency and large duty-cycle pulsed gas tungsten arc welding (GTAW) was employed to weld the medium-thick steel plates with a 5-mm root face and 2-mm root opening. The arc characteristic and weld pool dynamic behavior in the proposed GTA root pass welding was investigated by a high-speed camera, and a deflection phenomenon of arc tail flame was first found. The correlations of the characteristic parameters of the arc tail flame, including the deflected angle and length, with the weld joint penetration and welding speed were also analyzed in detail. The results showed a negative correlation to the welding speed and a positive correlation with the weld joint penetration. A sound weld bead was formed at a range from 15 deg and 20 mm to 19 deg and 27mm. Based on the above relationship, a new method using these two characteristic parameters was proposed to identify the weld joint penetration in the root pass welding, and its fundamentals were completely demonstrated by the dynamic change of the keyhole. Its feasibility was also demonstrated by the experiment combined with the weld pool dynamic-dependent theoretical analysis.

Mechanical and Microstructural Properties of AL 5754 Alloy Joined by GMAW and GTAW

The purpose of this study is to examine the effect of double pulse Gas Metal Arc Welding (GMAW) and Gas Tungsten Arc Welding (GTAW) on metal droplet transfer, weld bead geometry, weld pool profile and to examine the mechanical properties of the Al 5754 alloy weld joints. Al 5754-Al 5754 aluminum alloy plates were welded with ER 5356 welding wire. No significant defects were found, and full penetration joints were created. The effect of arc welding parameters on the speed and appearance of welding were investigated by means of macrostructure and microstructure characterization of fusion zone. Also, the characters of tensility and micro-hardness being of the welded specimens were measured.

Effects of CNTs addition on the microstructure and microhardness of stainless steel alloy/carbon-manganese non-alloyed steel welding

In recent years some progress has been made about the addition of Carbon Nanotubes (CNTs) in the stainless steel metal matrix by pulsed Gas Tungsten Arc Welding (P-GTAW). Despite that, there is lack of information regarding to microstructural modifications induced by CNTs in dissimilar welding. In this sense, we present the welding of nanocomposite based on Nickel/Carbon Nanotubes-stainless steel 316L alloy (Ni/CNTs-SS 316L), as the welding metal, on carbon-manganese (C-Mn) non-alloyed structural steel, as the base metal. The microstructure of manufactured specimens with/without nanocomposite was characterized by: optical microscopy; Raman spectroscopy; scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and electron backscattering diffraction (EBSD). Moreover, Vickers tests were performed from the welding metal (WM) to the base metal (BM) before/after temper treatment in order to investigate the microhardness changes. The results show that dilution rate and grain size for specimen with nanocomposite was higher than without nanocomposite; the CNTs affected the misorientation angle and texture of the WM; the topside microhardness from WM with Ni-CNTs was on average 30.40% higher than BM; and, in transverse cross-section microhardness was 31% higher than control sample on average at fusion line zone. These results indicate that addition of CNTs in the metallic matrix by dissimilar welding is a fertile ground for new studies applicable to manufacturing industry.

Improvement of hot corrosion resistance of dissimilar weldments by current pulsing in a simulated power plant environment

Hot corrosion studies are of utmost importance for welded components in the power plant industry as well as for industries which deal with exposure to the high-temperature corrosive environment. The failure of welded components at high temperatures has often led to the reduced service life of a component and catastrophic disasters. This has been a significant engineering challenge in the design of welded components. It is generally seen that the failure of the welded sections mostly occurs because of the deposition of molten salt over the weldments which accelerate the hot corrosion reactions. In this present research work, two dissimilar base materials, AISI 4340 and AISI 304L have been welded with two different welding processes namely continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) while making use of ERNiCr-3 as filler material. A comparative study of the dissimilar welded plates was carried out by simulating a molten salt environment at 600°C involving hot corrosion behavior. By analyzing the microstructure and thermo-gravimetric data, it is concluded that the pulsed current gas tungsten arc welding process has superior corrosion resistance properties while using ERNiCr-3 as the filler material as compared to the continuous current gas tungsten arc welding process.

Prospects of pulsed current arc welding on aerospace grade Hastelloy X

The conventional constant current arc welding of Hastelloy X (Ni-Cr-Fe-Mo) leads to the solidification and liquation cracks in the weldment. The higher heat supplied in constant current weldment develops the secondary carbide precipitates. It promotes the development of hot cracks in the weldment. In this study, joining of Hastelloy X plates was carried out by constant current gas tungsten arc welding (GTAW) and pulsed current gas tungsten arc welding (PCGTAW) with C263 filler wire. The result discovered that no hot cracks were formed in the weldment. In constant current mode, Cr-rich and Mo-rich Cr23C6 (M23C6), Fe2MoC, Fe3Mo3C (M6C), and Cr2Ti precipitates were observed. Whereas, in pulsed current mode, Ni3(Al, Ti), Ni3Ti, Co3Ti, Cr2Ti precipitates are found due to the segregation of Co, Al, and Ti. No Cr-rich and Mo-rich carbide phases identified in pulsed current weldment due to rapid cooling rate and higher thermal gradient observed during solidification. The tensile results revealed that 8.23% increase in the ultimate tensile strength and a 29.62% increase in elongation of pulsed current mode welding compared to constant current welding. Further, the microhardness and impact toughness of PCGTAW is 3.32% and 5.45% higher than GTAW, respectively. In pulsed current welding, better mechanical properties were identified compared to constant current welding. The nonappearance of Cr and Mo-rich phases and refined microstructure in the weldment are the main reason for better strength.

Multipass dissimilar joints for SS316L to Inconel625 using gas tungsten arc welding

Dissimilar material welding of SS316L and Inconel625 joints growing in heat exchanger applications like nuclear, power plants and petrochemical industries. The current work reports on multipass welding of SS316L and Inconel625 dissimilar material analysis effect of Gas Tungsten Arc Welding (GTAW) process. Four trials were conducted with L4 orthogonal array. These welds are prepared by using ErNiCrMo-3 and ERNiCr-3 filler wire. The analysis of weldability, distortion, residual stress, and tensile strength of the weldments. Least distortion was observed for pulsed current GTAW process. Tensile residual stress was spotted at welding zone. Tensile strength shows the fracture occurred in the base plate of the SS316L for all the trails.

A Proposed Mechanism of Hot-Cracking Formation During Welding Fan-Shaped Test Specimen Using Pulsed-Current Gas Tungsten Arc Welding Process

Solidification cracking is a significant problem during the welding of fully austenitic stainless steels. The present work is considered as the first trial to investigate and propose a mechanism of hot cracking formation when welding the Fan-shaped cracking test specimen, using the pulsed current gas tungsten arc welding process (PCGTAW). The specimen lateral expansions perpendicular to welding line due to thermal effects, plus the transverse expansion due to crack opening are sensed and recorded to detect the crack behavior with time. The stages of crack formation are filmed by a high-speed photography of the weld pool and solidification process at a speed of about 1000 fps. Additionally, some microscopic examinations using Scanning Electron Microscope (SEM) and Electron Probe Micro-Analyzer (EPMA) are performed on the welds. The results helped in establishing a proposed mechanism for the formation of hot cracks in full–austenitic stainless steel welds done on a Fan-shaped test specimen. The proposed mechanism suggests three stages during hot cracking formation; the crack initiation, propagation, and ceasing. The occurrence of a hot crack during welding mainly depends on the way by which the molten zone solidifies, and which solid phase will primarily solidify. This affects, in turn, the segregation of the chemical elements, which found to have a great role in crack initiation. Moreover, the weld metal structure type, together with the thermal stresses in conjunction with the applied strains on the weld joint play a great role in the crack expansion and ceasing. The present work is considered the first trial done to propose a mechanism of hot-cracking formation during welding the Fan-Shaped test specimen using Pulsed-Current Gas Tungsten Arc welding process.

Prediction of welding quality characteristics during pulsed GTAW process of aluminum alloy by multisensory fusion and hybrid network model

To implement predicting and controlling of welding quality are significant during pulsed gas tungsten arc welding (GTAW) process. In this paper, a multi-sensor system has been developed to synchronously obtain arc voltage, welding current, arc power, arc sound and weld pool images during pulsed GTAW process. The convolutional neural network (CNN) is designed to extract the visual feature of weld pool images. Besides, the time-frequency domain features of arc voltage, welding current, arc power, arc sound are also extracted. These features constituted a 19-dimensional feature vector. The long short-term memory (LSTM) network is used to fuse the extracted 19-dimensional features and learn time series information from the fused features. Further, the LSTM network can predict the different welding states 0−2 s in advance: normal penetration, lack of fusion, sag depression, burn through and misalignment. Finally, the proposed hybrid network model, CNN-LSTM, is verified to be effective with high accuracy and robustness.

Numerical analysis of internal flow of molten pool in pulsed gas tungsten arc welding using a fully coupled model with free surface

A fully electromagnetic, fluid flow and heat transfer coupled model with free surface is proposed to analyze the internal flow of weld pool with the strong interaction of arc plasma in pulsed gas tungsten arc welding. Governing equations are solved in the whole domain including the tungsten cathode, arc plasma and weld pool without simplifications; the level set method, the Marangoni effect and the local thermodynamic equilibrium (LTE) diffusion approximation are used to treat the interface between the plasma arc and weld pool. The originality of this paper is providing a fully coupled model both with free surface and varying surface tension gradient to reveal the oscillating behaviour of arc plasma and internal flow of molten pool in a pulsed - GTAW process, especially with high peak current and low frequency. By considering the pulsed current ranging from 80 A to 400 A with oscillating frequency of 10 Hz and validating the model with experiments, the fully coupled model shows that the multiphysics-based simulation methodology could reveal the physical essence of periodically expansion and compression of arc plasma and fluctuations of molten pool subjected to pulsed current, The dynamic variations (the current density, electric potential, magnetic flux density, temperature, arc flow and internal flow of weld pool) and driving mechanisms of internal melt flow (The Marangoni effect due to varying surface tension gradient, Lorentz force, arc pressure, shear stress) are quantitatively analyzed, the computed arc plasma behaviour and molten pool profiles are in reasonable agreement with the corresponding experimental and calculating results, revealing that the arc plasma and the molten pool both have a very fast response to the varying current as a whole electromagneto-hydrodynamic system, while the internal flow of molten pool also exhibits nonlinear characteristics as a result of the Marangoni effect.

Deep learning-empowered digital twin for visualized weld joint growth monitoring and penetration control

This paper presents an innovative digital twin to monitor and control complex manufacturing processes by integrating deep learning which offers strong feature extraction and analysis abilities. Taking welding manufacturing as a case study, a deep learning-empowered digital twin is developed as the visualized digital replica of the physical welding for joint growth monitoring and penetration control. In such a system, the information available directly from sensors including weld pool images, arc images, welding current and arc voltage is collected in pulsed gas tungsten arc welding (GTAW-P). Then, the undirect information charactering the weld joint geometry and determining the welding quality, including the weld joint top-side bead width (TSBW) and back-side bead width (BSBW), is computed/estimated by traditional image processing methods and deep convolutional neural networks (CNNs) respectively. Compared with single image source, weld pool image or arc image, the CNN model performs better when taking the 2-channel composite image combined by both as the input and the state-of-the-art accuracy in BSBW prediction with mean square error (MSE) as 0.047 mm2 is obtained. Then, a decision-making strategy is developed to control the welding penetration to meet the quality requirement and applied successfully in various welding conditions. By modeling the weld joint cross section as an ellipse, the developed digital twin is visualized to offer a graphical user interface (GUI) for users perceiving the weld joint growth intuitively and effectively.

Weldability and weld strength of dissimilar joint between UNS S32750 and Monel 400 developed by PCGTAW process

Dissimilar weldments of Monel 400 and UNS S32750 are widely used in pressure vessels and marine industries where the weldments are exposed hot corrosion and can withstand this effect as they offer excellent corrosion resistance and improve the service life. This research paper aims at investigation on the weldability and welding strength of dissimilar welded joints of UNS S32750 and Monel 400 developed by pulsed current gas tungsten arc welding technique. ERNiCrMo-4, ERNiCrMo-3 and ER309L fillers were used to join the base metals. Mechanical properties were demonstrated by using tensile test, impact toughness test and microhardness. The ultimate strength of ERNiCrMo-4 weldment was increased by 16.2% and 20.2% when compared to ERNiCrMo-3 and ER309L weldments, respectively. The fracture has occurred under direct tension test in all the cases at the base metal of Monel 400. The superior impact toughness value (169 J) was observed in ERNiCrMo-4 filler weldment than the ERNiCrMo-3 (144 J) and ER309L (76 J) filler weldments. The average hardness number of ERNiCrMo-4 filler weldment (318 HV0.1) was higher than those of ERNiCrMo-3 (306 HV0.1) and ER309L (286 HV0.1) filler weldments.

Microstructure and Mechanical Properties of Fe-36Ni and 304L Dissimilar Alloy Lap Joints by Pulsed Gas Tungsten Arc Welding.

High-quality joining of dissimilar alloys between Fe-36Ni alloy and 304L stainless steel is essential in the manufacturing of LNG tanker. In this study, lap joints of Fe-36Ni and 304L dissimilar alloys were fabricated by a pulsed gas tungsten arc welding (P-GTAW) process. The effects of low-frequency pulse on the appearance, microstructure and mechanical properties of the Fe-36Ni/304L lap joints was investigated. With the increase of frequency, the feature sizes of α (the transition angle of the upper surface of Fe-36Ni to the surface of the weld bead) and R (shortest distance between weld root and weld surface) exhibited downtrend and uptrend, respectively, while La (the maximum weld width of lower sheet) and P (the maximum weld penetration of lower sheet) changed in a smaller range. Fusion zone (FZ) is mainly composed of γ phase and M23C6 during solidification, and M23C6 particles are distributed on the grain boundaries of the cells, which reduced the mechanical properties of joint. The average hardness between 110 HV1 and 136 HV1 is lower than that of the base metals. Fractures of all joints located at the Fe-36Ni side near the weld, and a dimple fracture in all samples indicated a ductile fracture. This study found that the heat input values remain 198.86 J mm−1 and increased pulse frequency can improve the maximum tensile force. The average maximum tensile force of the lap weld is 11.95 kN when pulsed frequency is 15 Hz.

Arc Characteristics and Weld Bead Microstructure of Ti-6Al-4V Titanium Alloy in Ultra-high Frequency Pulse Gas Tungsten Arc Welding (UHFP-GTAW) Process

To resolve the problem of grain coarsening occurring in the fusion zone and the heat-affected zone during conventional gas tungsten arc welding(C-GTAW) welded titanium alloy, which severely restricts the improvement of weld mechanical properties, welding experiments on Ti-6Al-4V titanium alloy by adopting ultra-high frequency pulse gas tungsten arc welding (UHFP-GTAW) technique were carried out to study arc characteristics and weld bead microstructure. Combined with image processing technique, arc shapes during welding process were observed by high-speed camera. Meanwhile the average arc pressure under various welding parameters were obtained by adopting pressure measuring equipment with high-precision. In addition, the metallographic samples of the weld cross section were prepared for observing weld bead geometry and microstructure of the fusion zone. The experimental results show that, compared with C-GTAW, UHFP-GTAW process provides larger arc energy density and higher proportion of arc core region to the whole arc area. Moreover, UHFP-GTAW process has the obviously effect on grain refinement, which can decrease the grain size of the fusion zone. The results also revealed that a significant increase of arc pressure while increasing pulse frequency of UHFP-GTAW, which could improve the depth-to-width ratio of weld beads.

Development of Pulsed Current Arc Welding to Preclude Carbide Precipitates in Hastelloy X Weldment Using ERNiCr-3

In this study, gas tungsten arc (GTA) and pulsed current gas tungsten arc (PCGTA) welding on Hastelloy X were performed using ERNiCr-3. The welded plates are free from the porosity, inclusion, liquation cracks, and hot cracks. The weld bead profile shows a lower bead width in PCGTA than GTA weldment. The segregations of Cr, Mo, Nb, and Ti were identified in GTA with the development of Fe3Mo3C (M6C), Fe2MoC (M3C), Cr23C6, Cr2Ti, Ni8Nb phases. While in PCGTA, Nb and Ti segregations alone were observed with the formation of phases like Ni3Ti, Cr2Ti, Ni8Nb, respectively. The presence of γ prime precipitate (Ni3Ti) observed in PCGTA improved the ultimate tensile strength (UTS) by 8.56% compared to GTA. The UTS and ductility were found inferior in both the weldments when compared to the base metal. This is due to the precipitation of Ni8Nb phase and the existence of Cr2Ti phase, respectively. The PCGTA weldment also shown improved microhardness by 12.21% and impact energy by 9.78% compared to GTA, respectively. The refined crystallite size and precluded carbide precipitates in PCGTA are responsible for the enhanced properties.

Arc sound model for pulsed GTAW and recognition of different penetration states

Weld defect detection based on arc sound signal in pulsed gas tungsten arc welding (GTAW) has been a hot research topic in industry and academia. However, arc vocal mechanism model of pulsed GTAW remains to be studied further. In this paper, a sensing system is developed to collect arc voltage, welding current, arc sound, and weld pool images synchronously during pulsed GTAW process. Theoretical researches and experiments verify that the arc sound signal of pulsed GTAW is proportional to the change rate of the instantaneous arc power input. Furthermore, an arc sound excitation model is proposed to explain the mechanism of arc sound signal. The model inputs are arc voltage and welding current; the model output is the arc sound signal. The experiments prove that the proposed excitation model is a non-linear model. Therefore, a dynamic long short-term memory (DLSTM) network model is designed to identify the non-linear model. Furthermore, the effects of different penetration states on arc sound signal are discussed in combination with the proposed arc sound excitation model. Finally, a novel method based on DLSTM model is built to recognize different penetration states: lack of fusion, normal penetration, and burn through. The proposed method was verified to be effective with high accuracy and robustness.