Narrow Gap Gas Metal Arc Research Articles

Investigation of Microstructure and Mechanical Properties of High-Depth-to-Width-Ratio Horizontal NG-GMAW Joint for S500Q Steel.

A novel high depth-to-width ratio of 15:1 narrow-gap gas metal arc welding technique was developed for the welding of S500Q steel in a horizontal butt joint. The bead arrangement of the I groove was optimized to produce a high-quality connection with the upper sidewall of the joint. The microstructure and mechanical properties were observed and evaluated by optical microscopy, scanning electron microscopy, tensile testing, and micro-hardness and impact toughness testing at 1/5, 2/5, 3/5, and 4/5 thickness of the joint. The 3/5 T position exhibited the highest strength, which was attributed to the presence of finer carbide precipitates. The highest micro-hardness appeared at 4/5 T. The highest impact toughness appeared at 3/5 T. The formation of coarse granular bainite was the major reason for the decrease in impact toughness in other regions. A microscopic fracture at 1/5 T and 3/5 T was further analyzed. It was observed that the width of the fibrous zone at 3/5 T was significantly larger than that at 1/5 T. The radial zones at 1/5 T were observed to exhibit cleavage, with secondary cracks on the fracture surface.

Arc and molten pool behavior on quality of hybrid cold metal transfer and tandem pulsed narrow gap gas metal arc welds: a study

ABSTRACT This research proposes a novel hybrid cold metal transfer (CMT) and tandem Pulsed gas metal arc welding (P-GMAW) process for narrow gap welding (NGW) of high strength low alloy (HSLA) steel plates. Investigating three sets of lead and trail wire feed speed (WFS) ratios [WFSL/T - 1.4, 1, 0.7], the study delves into the complex arc and metal transfer behavior within the narrow gap. Utilizing synchronized arc images and current-voltage waveforms, the research assesses their influence on fusion and mechanical properties. The root pass employs the single wire CMT process, while filling and closing passes leverage tandem P-GMAW, effectively minimizing incomplete fusion and reducing heat input. Results indicate that a lower WFSL/T (0.7) reduces the molten pool hump and overflow within the narrow gap while enabling direct weld arc engagement with the previously deposited layer, enhancing weld penetration. WFSL/T of 1.4 and 0.7 revealed higher and lower Charpy impact toughness.

Implementation of a two-stage algorithm for NG-GMAW seam tracking and oscillation width adaptation in pipeline welding

Seam tracking and oscillation width adaptation could effectively reduce the sidewall fusion defects in automatic narrow-gap gas metal arc welding (NG-GMAW). This study proposes a two-stage algorithm to realise seam tracking and oscillation width adaptation in NG-GMAW pipeline welding. The first stage involves using the principal component analysis (PCA) eigenvectors to adjust the oscillating centre, enabling seam tracking and oscillation width adaptation for the hot and fill layer. In the second stage, dataset was prepared based on the tracking data from the first stage, which can guide the welding torch trajectory for the cap layer. Experimental results show that the proposed scheme achieves seam tracking and oscillation width adaptation with an accuracy of 0.1 mm.

Real-time seam tracking during narrow gap GMAW process based on the wide dynamic vision sensing method

Welding torch horizontal seam tracking is a crucial condition to realize automatic welding of narrow gap gas metal arc welding (NG-GMAW) robots. In the present study, a real-time welding seam tracking technology based on the passive vision sensor is proposed. To this end, a wide dynamic range (WDR) vision sensor is used to capture real-time welding images. In order to realize real-time identification of the welding torch center deviation in the process of swinging arc in a welding bead, a welding seam tracking algorithm based on the window information fusion (WIF) is proposed. In this regard, the local feature moving window recognition (LMWR) algorithm is applied to extract the groove center. Based on the improved welding image processing program, the weld pool center and welding wire center are prepared for seam tracking. In this regard, considering the trifling variation of groove and weld pool center, the welding horizontal deviation is obtained by combining them with welding wire center calculation. Aiming at establishing a correlation between consecutive images, the Kalman filter is used to estimate the deviation optimally. The tracking algorithm is successfully verified in the weld bead with a horizontal deviation, and the tracking accuracy of ±0.47 mm is achieved. The performed analyses demonstrate that the developed algorithm meets the requirements of real-time seam tracking in the GMAW process of the welding robot.

Applying Statistical Models to Optimize the Weld Bead Geometry in the Vertical Oscillation Arc Narrow Gap All-Position GMAW

Vertical oscillation arc welding for narrow gap gas metal arc welding (NG-GMAW) has a relatively simple structure, and it is widely used in all-position pipeline field welding. However, it has some shortcomings, such as incomplete fusion defects on the sidewall and interlayer. Aiming at resolving these shortcomings, a mathematical model is proposed to obtain appropriate welding parameters in different positions. In this model, the response surface methodology (RSM) based on the central composite design (CCD) was developed to study the interactions between welding parameters and the weld bead geometry. Then the analysis of variance (ANOVA) was used to evaluate the accuracy and significance of the proposed model. Finally, experiments were carried out in flat, vertical, and overhead positions to obtain the optimal parameters. The macroscopic metallography of the transversal section of the weld bead under the optimizing welding parameters showed that the weld beads were free of defects in the sidewall and interlayers.

Effects of arc interaction on lack-of-fusion and porosity in tandem NG-GMAW of 5083 Al-Mg alloy

The tandem narrow-gap gas metal arc welding (NG-GMAW) is an advanced high efficient technology for joining thick section metals. However, the common defects such as lack-of-fusion (LOF) at groove sidewalls, porosity in weld bead are still hard to be avoided, especially for joining thick section of aluminum alloy. In this study, a pulsed tandem NG-GMAW process was applied to join thick 5083 Al-Mg alloy plates. The LOF and its formation mechanism at varied arc length were investigated by observing the tandem arc interaction behaviors with high-speed photography and by synchronized recording the corresponding welding signals. The results indicate, the arc heat distribution, which is likely influenced by the tandem arc arrangement, is a critical factor to the formation of LOF. However, a properly adjusted arc length can improve the arc interaction and the weld formation. Moreover, a proper arc interaction behavior can change the direction of arc force, which makes contribution to the stirring effect on molten pool. It is beneficial to reduce porosity. The oxygen enriched pores (pore-II) caused by short-circuiting transfer were found when arc length correction coefficient (ALCC) is −15, which needs to be avoided during the welding process.

Influence of Interwire Distance and Arc Length on Welding Process and Defect Formation Mechanism in Double-Wire Pulsed Narrow-Gap Gas Metal Arc Welding

Influence of Interwire Distance and Arc Length on Welding Process and Defect Formation Mechanism in Double-Wire Pulsed Narrow-Gap Gas Metal Arc Welding

Effects of Active Gases on Droplet Transfer and Weld Morphology in Pulsed-Current NG-GMAW of Mild Steel

The current research of narrow-gap gas metal arc welding (NG-GMAW) primarily focuses on improving the sidewall fusion and avoiding the lack-of-fusion defect. However, the high cost and operation difficulty of the methods limit the industrial application. In this study, small amount of active gases CO2 and O2 were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding (NG-GMAW) of mild steel. Their effects on droplet transfer and arc behavior were investigated. A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology. When the proportion of CO2, being added into the pure argon shielding gas, changes from 5% to 25%, the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer, while it remains the pulsed spray streaming transfer when 2% to 10% O2 is added. Both CO2 and O2 are favorable to stabilizing arc and welding process. O2 is even more effective than CO2. However, O2 is more likely to cause slags on the weld surface, while CO2 can improve the weld appearance in some sense. The weld surface concavity in NG-GMAW is greatly influenced by the addition of active gas, but the weld width and weld penetration almost keep constant. This study proposes a new method which is beneficial to improving the weld bead formation and welding process stability.

Influence of interwire angle on undercutting formation and arc behavior in pulsed tandem narrow-gap GMAW

The tandem narrow-gap gas metal arc welding was adopted in this study. The effects of interwire angle on the welding process stability and arc behavior were investigated. With the interwire angle increasing, the welding process stability gets improved. The arc interruptions which frequently occur in the leading arc are eliminated when the interwire angle is >0°. The mutual electromagnetic attraction between the two arcs decreases with the interwire angle increasing due to the increased arc distance. The two arcs move from the groove bottom to the sidewalls, which transfer more heat to the sidewalls resulting in increased weld width. This leads to serious undercutting defects especially when the interwire angle is 20°. The molten metal under the arcs flows to the rear of welding pool under the action of plasma drag force, arc pressure and droplet impingement. As a result, there is no adequate molten metal to fill the sidewalls, giving rise to undercutting defects. The undercutting at the groove sidewall close to the trailing arc is smaller. This is because the liquid metal under the trailing arc is more massive, which means more molten metal flows to the sidewall, alleviating the undercutting defect.

Heat Source Characteristics of Ternary-Gas-Shielded Tandem Narrow-Gap GMAW.

The characteristics of the welding heat source for tandem narrow-gap gas metal arc welding are examined for different ternary shielding gas (Ar-CO2-He) compositions. Results of previous calculations of arc properties for bead-on-plate geometry are adapted to the narrow-gap geometry to predict these characteristics. The heat source concentration factor decreases and the maximum heat flux density increases as the helium content increases, which leads to an increased welding heat efficiency. Addition of CO2 up to around 10% also increases the heat efficiency. When the CO2 content exceeds 10%, the heat source concentration factor increases significantly and the heat efficiency decreases. The shielding gas composition also affects the heat source distribution. The heat source characteristics are applied to a computational fluid dynamic model of the weld pool to predict the weld shape, and the predictions are verified by experiment. The results indicate that the appropriate addition of helium to the shielding gas can increase the heat transferred to the peripheral regions of the arc and increase the sidewall penetration.

Molten pool behaviors and their influences on welding defects in narrow gap GMAW of 5083 Al-alloy

The welding defects such as porosity and lack-of-fusion is more likely to occur in the narrow gap gas metal arc welding (NG-GMAW) of aluminum alloy. In this study, a three-dimensional transient numerical simulation was carried out to investigate the molten pool behaviors as well as their influences on welding defects. A pulsed arc welding mode was employed, which is accompanied with elliptically symmetric arc models. Three different weld bead surface shapes i.e. the convex, flat and concave surface were achieved both by experiment and simulation with varied welding current. The flow pattern varied significantly due to the different thermal and force conditions. The formation process of lack-of-fusion defect was analyzed and the effect of flow pattern on porosity in all cases were discussed. The results indicate that the upward fluid flow near the sidewall border of molten pool facilitates the formation of lack-of-fusion defect and the downward and backward fluid flow near the sidewalls may induce the porosity.

Effects of shielding gas composition on arc characteristics and droplet transfer in tandem narrow gap GMA welding

ABSTRACTThe effects of shielding gas composition in tandem narrow gap gas metal arc welding were studied. The shielding gas included argon, carbon dioxide and helium. The arc characteristics and droplet transfer process were analysed. The results show that in the same welding parameters, the trail wire welding current is higher than the lead wire welding current. With the increase of carbon dioxide content, the welding currents of two wires decrease, and the trail wire droplet transfer mode transforms from spray transfer to projected transfer. With the increase of helium content, the welding currents increase and the lead wire droplet transfer mode transforms from projected transfer to spray transfer. The weld width is the largest when the shielding gas mixture is 80%Ar10%CO210%He.

Study on insufficient fusion of NG-GMAW for 5083 Al alloy

The lack of fusion at sidewall is one of the most frequently occurred problems in narrow-gap gas metal arc welding for joining thick plates of aluminum alloys. For better understanding the sidewall fusion mechanism and eventually solving such a problem, a series of welding experiments were carried out to investigate the sidewall penetration characteristics for 5083 Al alloys under various technological conditions. A Taguchi method was adopted to study the effect of welding current, arc voltage, and welding speed on the sidewall penetration and surface concavity, which is related to the quality of welding joint. The result shows that higher welding current or lower welding speed will contribute to a better fusion between weld bead and sidewalls; thus, optimized welding parameters can be obtained. The analysis of formation mechanism for lack of fusion defect shows that the molten pool surface tension, which is greatly influenced by temperature and oxide, is a main reason. Therefore, increasing the heat input to sidewalls by arc-swing, improving the gas protection of molten pool against oxidization, or reducing the heat dispersion of molten pool by preheating, are all effective measures for eliminating the lack of sidewall fusion defect.

Arc characteristics and metal transfer behavior in narrow gap gas metal arc welding process

During the constant-voltage welding machine employed welding process, a common phenomenon of arc attachment point moving from the bottom of the narrow gap to the sidewalls occurs, and metal transfer behavior appears greatly different. A mechanism that the arc inherent-self regulation combines the minimum arc voltage principle was proposed to elaborate the arc climbing up process along the sidewalls. The arc shape was approximately classified into three patterns by the change of arc conductive path, and the amount of the arc conductive path and its distributive symmetry determine the action of the electromagnetic force on the droplet as well as the metal transfer mode. As the number of the arc conductive paths increases, and the conductive paths distribute symmetrically, the necking process of the droplet detachment occurs more easily, and the metal transfer from globular mode to spray mode becomes more smoothly. Simulation results match the experiments and verify the mechanism proposed. In a constant-current welding power source adopted condition, the arc climbing up phenomenon cannot be observed, and a stable welding process is obtained.

Effects of shielding gas composition on arc behaviors and weld formation in narrow gap tandem GMAW

In narrow gap gas metal arc welding (GMAW), it is useful to understand the arc behaviors to ensure the weld quality. Arc behaviors are strongly affected by the shielding gas composition. In this study, a three-component shielding gas mixture was used in tandem narrow gap pulsed GMAW, and the effect of its composition on arc behaviors and weld formation were investigated. The shielding gas included argon, carbon dioxide, and helium. The arc behaviors and electrical characteristics were recorded by a high-speed camera and an electrical signal acquisition system. The results show that the arc behaviors in different shielding gas are different. The arc expands and the arc length decreases with the increase of CO2 content or helium content. The arc is the widest when the shielding gas is 80%Ar10%CO210%He. The weld shape was observed, and it was found that the weld width increases first and then decreases with increasing of the CO2 content. When the helium content is below 15%, the weld width increases as the helium content increases, but when the helium is 15%, the weld width drops due to the decrease of arc length. When the helium content is above 15%, the weld width continues to increase as the helium content increases. The largest weld width can be obtained in 80%Ar10%CO210%He.

Study on arc characteristics and their influences on weld bead geometry in narrow gap GMAW of 5083 Al-alloy

As an efficient process, narrow gap gas metal arc welding (NG-GMAW) was employed to join thick plates of 5083 Al-alloy. In this paper, arc characteristics in NG-GMAW of 5083 Al-alloy and their influence on the weld bead geometry were studied with synchronous acquisition system for various groove types, welding modes, welding current levels, and swing frequencies. The arc profiles were measured and appear to be entirely different compared with that in bead-on-plate GMAW process, meanwhile the arc size changes with varied welding mode, welding current, and arc swing frequency. Arc characteristics highly affect the weld bead geometrical parameters such as bead width, welding penetration, sidewall penetration, and weld surface concavity. Linear regressions were made between the arc characteristics and the weld bead geometrical parameters both in swing and non-swing arc process. It showed that a negative linear correlation exists between welding penetration and arc length, sidewall penetration, and arc warpage, while a positive linear correlation exists between weld surface concavity and arc warpage in non-swing arc process. In contrast, a non-linear correlation exists among them and the variation tendency remains the same in swing arc process.

Characteristics and formation mechanism of sidewall pores in NG-GMAW of 5083 Al-alloy

Narrow-gap gas metal arc welding was carried out on thick plate of 5083 Al-alloy, and the characteristics of welding pores were analyzed in terms of their size and distribution. The large pores were found to occur frequently in the weld zone adjacent to the sidewalls of narrow gap groove. Their amount and size increased along with increasing welding current and/or decreasing travel speed, which was totally different from conventional GMAW of aluminum alloy. The hydrogen was found to be the main cause to the pores by using SEM and EDS analysis. The formation of sidewall pores in narrow-gap weld beads were greatly related to the groove type, the shape of molten pool and its solidification behavior, and it was verified by polarization observation and EBSD analysis. The optimized parameters for avoiding sidewall pores and lack of sidewall fusion were 175A and 5mm/s in the narrow-gap welding of given aluminum alloy.

Evaluation on microstructure and mechanical properties of high-strength low-alloy steel joints with oscillating arc narrow gap GMA welding

Abstract with the purpose of improving weld joint quality and productivity, the oscillating arc narrow gap gas metal arc (GMA) welding was employed in welding quenched and tempered high-strength low-alloy thick steel. The microstructure and mechanical properties of weld joints were evaluated, namely micro-hardness, tensile strength, and low-temperature impact toughness. The test results indicated that mechanical properties of weld joints with oscillating arc narrow gap GMA welding were excellent and found to meet stipulated requirements. Oscillating arc narrow gap GMA welding is a promising process for welding quenched and tempered HSLA thick steels due to the low energy input and narrow square-butt groove.

Research on narrow-gap GMAW with swing arc system in horizontal position

In this paper, a novel swing arc welding system developed for horizontal narrow gap gas metal arc welding (NG-GMAW) which was used in welding and joining heavy plate structures was designed and attempted. Using this welding system, two sound heavy plate beads, i.e., “multi-layer single-pass” welding and “multi-layer double-pass” welding structures, were obtained through adjusting swing amplitude and frequency. Two different welding structures are both without sagged molten pool and interlayer slags, especially obtaining the complete sidewall penetration. All these welding features ensure the bead with higher tensile properties and hardness than the base metal, respectively. This welding system displays considerable flexibility and convenience and possesses a tremendous advantage in the auto-welding industry.

Stability of Double Wires Narrow-gap Gas Metal Arc Welding

Some special parameters of double wires narrow gap GMAW (NG-GMAW) welding can be adjusted individually, such as the angle and distance between the two wires along the welding direction and the distance between the wire and the sidewall of the groove. These parameters have great influence on the welding stability. Experiments results show that when the distance between the two wires is less than 15 mm or greater than 50 mm, the two welding arcs are in one molten pool or two independent molten pools, and the welding process is very stable. When the distance is 20～30 mm, the molten pool is transforming from single one to two independent one. Under the action of unbalanced electromagnetic force, the arc is compelled to break frequently and the stable welding process is destroyed. When the two wires are parallel along the welding direction, the welding process is stable; if the front wire is inclined to the rear wire, the wandering of the front arc is aggravated. The distance between the wire and the groove sidewall has great influence on the arc modality. When the distance is 2.5 mm, the arc burns stably between the wire and the sidewall as well as the bottom of the groove. But if the distance is less than 1.5 mm, the arc burns between the sidewall or bottom randomly, and the welding stability deteriorates.