Narrow Gap Groove Research Articles

A comparison of the swing and non-swing arc behavior in arc ultrasonic assisted narrow gap GMAW

The arc ultrasonic technology was applied to the swing arc narrow gap GMA welding process of aluminum alloy. The ultrasonic energy acts on the welding process by superimposing an ultrasonic current on the basis of pulsed welding current. The arc behavior will be significantly different from that in the conditions of non-narrow gap and non-swing due to influences from the narrow gap groove constraint and the arc swing. In this paper, the behavior of swing arc and non-swing arc at different positions in narrow gap groove are compared, and the influence mechanism of arc ultrasonic on arc behavior is analyzed. Results indicate that the arc expands after superposition of ultrasonic current, and that the arc behavior is different at different positions of the narrow gap groove. In the sidewall, the expansion degree of the non-swing arc is obviously greater than that of the swing arc. The swing arc area increases by 50.33% at most, and the non-swing arc area increases by 117.94% at most. In the groove bottom, the expansion degree of the swing arc is greater than that of the non-swing arc. The average area and width of the swing arc in the groove are nonlinear relationships with the ultrasonic current amplitude and a linear positive correlation with the ultrasonic frequency, respectively. Arc swing and ultrasonic action make the arc length longer. The difference in speed between arc expansion and contraction and the oscillation of arc plasma under the arc ultrasonic action together promote arc expansion.

Research on Filling Strategy of Pipeline Multi-Layer Welding for Compound Narrow Gap Groove.

With the increase in transmission pressure and pipe diameter of long-distance oil and gas pipelines, automatic welding of the pipeline has become the mainstream welding method. The multi-layer and multi-pass welding path planning of large-diameter pipelines with typical narrow gap grooves are studied, and a welding strategy for pipeline external welding robot is proposed. By analyzing the shape of the weld bead section of the narrow gap groove and comparing the advantages and disadvantages of the equal-height method and the equal-area method, the mathematical model of the filling layer is established. Through the test and analysis in the workshop, the predicted lifting value meets the actual welding requirements. The microstructure of the weld was analyzed by SEM. The main structure of the weld was fine acicular ferrite, which could improve the mechanical properties of the welded joint. After multi-layer filling, the filling layer is flush with the edge of the groove. The establishment of this model lays a foundation for the formulation of welding process parameters for large-diameter pipes and the off-line programming of welding procedures.

Effect of Alternating Magnetic Field on Arc Plasma Characteristics and Droplet Transfer during Narrow Gap Laser-MIG Hybrid Welding

In this paper, the morphological characteristics of arc plasma and droplet transfer during the alternating magnetic field-assisted narrow gap groove laser-MIG (metal inert gas) hybrid welding process were investigated. The characteristics of arc plasma and droplet transfer, electron temperature, and density were analyzed using a high-speed camera and spectrum diagnosis. Our results revealed that the arc maintained a relatively stable state and rotated at a high speed to enhance the arc stiffness, and further improved the stability of the arc under the alternating magnetic field. The optimum magnetic field parameters in this experiment were B = 16 mT and f = 20 Hz, the electron temperature was 9893.6 K and the electron density was 0.99 × 1017 cm−3 near the bottom of the groove, which improved the temperature distribution inside the narrow gap groove and eliminated the lack of sidewall fusion defect. Compared to those without a magnetic field, the magnetic field could promote droplet transfer, the droplet diameter decreased by 17.6%, and the transition frequency increased by 23.5% (owing to the centrifugal force during droplet spinning and electromagnetic contraction force). The width of the weld bead was increased by 12.4% and the pores were also significantly reduced due to the stirring of the magnetic field on the molten pool.

Influence of wire feeding speed on the melting behavior and formation of narrow-gap joint by laser welding with filler wire

The influence of wire feeding speed during laser welding with a filling wire was investigated by high-speed imaging and mechanical analysis of the droplet. A force relationship was found to analyze the droplet transition behavior at the end of the welding wire in the narrow-gap groove. Welding defects, mainly including nonfusion and porosity, were studied to reveal the formation mechanism and propose affective solutions. In this paper, it was found that the droplet transition was determined by the position of the melting end of the wire in the narrow-gap groove under the same parameters. The sidewall transition, the liquid bridge transition, and the spreading transition were found at different wire feeding speeds. As the wire feeding speed increases from 3 to 6 m/min, the weld depth increased 40%, the maximum weld width decreased 16%, and the minimum weld width increased 8%. More nonfusion and porosity defects and poor weld formation would appear at excessive wire feeding speed.

Studies on the formation mechanism of incomplete fusion defects in ultra-narrow gap laser wire filling welding

Austenitic stainless steel has many excellent properties and it has been extensively used in rail transit trains. Ultra-narrow gap laser wire filling welding is the preferred welding method to connect austenitic stainless steel. However, with this method, it is easy to form defects such as lack of fusion in the welding process. In order to clarify the mechanism of incomplete fusion defects, this article analyzed incomplete fusion defects from the groove design and the welding wire transfer behavior, integrating with high-speed photography and finite element simulation. It is found that the form of narrow gap groove has a close relationship with the formation of fusible defects. Besides, under the condition of globular transfer, all the complicated recoil force, blocking effect of the large droplet on laser energy, the eruption of metal vapor and turbulence of the molten pool caused by large droplet transfer will cause violent disturbance of the molten pool and seriously affect its heat conduction effect. The base metal incompletely melting, the lack of transfer driving force on the droplet and the failure of droplet wetting and spreading on the sidewalls of the groove are the main causes of welding non-fusion defects. Designing reasonable groove, ensuring the stability of wire feeding, adopting liquid bridge transfer mode and appropriately increasing heat input are conducive to reduce the occurrence of incomplete fusion, which is essential to improve the welding quality and enhance the safety of rail vehicles.

Numerical analysis of arc physical properties in narrow gap TIG welding

The arc physical properties of the plate-butt welding and narrow gap welding were simulated. The narrow gap groove affects the arc properties, and the narrow gap welding arc has its special properties. The shielding gas flows along the longitudinal direction in the narrow gap groove, and the arc temperature field constricts transversely but expands longitudinally. The high-temperature region expands and the welding heat efficiency increases. The current density is larger for narrow gap welding, which induces the larger Lorentz force to accelerate the plasma flow. The axial and radial plasma flow velocities are both larger for narrow gap welding, which leads to the larger arc pressure and shear stress. The results have good agreements with the experiments results.

Investigation on microstructure and properties of narrow-gap laser welding on reduced activation ferritic/martensitic steel CLF-1 with a thickness of 35 mm

Reduced activation ferritic martensitic (RAFM) steel is chosen as a structural material for test blanket modules (TBMs) to be constructed in International Thermonuclear Experimental Reactor (ITER) and China Fusion Engineering Test Reactor (CFETR). Chinese specific RAFM steel named with CLF-1 has been developed for CFETR. In this paper, a narrow-gap groove laser multi-pass welding of CLF-1 steel with thickness of 35 mm is conduced by YLS-15000 fiber laser. Further, the microstructures of different regions in the weld joint were characterized, and tensile impact and micro-hardness tests were carried out for evaluating the mecharical properties. The results show that the butt weld joint of CLF-1 steel with a thickness of 35 mm was well-formed using the optimal narrow-gap laser filler wire welding and no obvious defects was found such as incomplete fusion cracks and pores. The microstructures of backing layer is dominated by lath martensites and the Heat-Affected Zone (HAZ) was mainly filled with two-phase hybrid structures of secondary-tempering sorbites and martensites. The filler layer is similar to the backing layer in microstructures. In tensile tests, the tensile samples from different parts of the joint all fractured at base metal (BM). The micro-hardness of weld metal (WM) was found to be higher than that of BM and the Heat-Affected Zone (HAZ) exhibited no obvious softening. After post weld heat treatment (PWHT), it can be observed that the fusion zone of the autogenous welding bead and the upper filling beads mainly consist of lath martensites which caused the lower impact absorbing energy. The HAZ mainly included two-phase hybrid structures of secondary-tempering sorbites and martensites and exhibited favorable impact toughness.

Research on the “jump sidewall” behavior and its signal characteristics in narrow gap P-MAG welding

Arc “jump sidewall” phenomenon is observed during P-MAG welding in narrow gap conditions. The mechanism and formation conditions are analyzed, and the phenomenon is found to be the arc channel re-establishment process, which results from large changes in the welding current. The arc channel position is the result of the balance between the electric field force and the magnetic field force. The current characteristics of P-MAG welding in a narrow groove provide adequate conditions for a “jump sidewall” phenomenon. The influences of a narrow gap groove on droplet transfer and arc signal of P-MAG power supply with modified I-I external characteristics are discussed. The research results lay a foundation for arc sensor-based welding seam tracking technology in narrow gap P-MAG welding.

Technical Challenges in Narrow-Gap Root Pass Welding during Tandem and Hybrid Laser-Arc Welding of a Thick Martensitic Stainless Steel

As part of a collaborative program to develop advanced manufacturing processes for next-generation hydraulic turbines, this study investigated the technological challenges for joining 25-mm thick martensitic stainless steel (MSS) plates using tandem and hybrid laser-arc welding. Although candidate materials for the intended application typically include wrought AISI 415 and cast CA6NM, a martensitic 410 stainless steel (SS) was especially selected in this study due to its greater crack sensitivity. A narrow-gap groove was designed to minimize the amount of 410NiMo filler metal required to fill the groove using a multi-pass single-sided welding technique. All the welding trials were performed using a 5.2 kW fiber laser. The root-pass quality was characterized in terms of weld bead geometry, defects and microstructure. The main technical challenges observed for the root pass were lack of penetration, lack of fusion and cracking, as detailed in this work.

Assessing mechanical properties of the dissimilar metal welding between P92 steels and alloy 617 at high temperature

In this study, a new welding technology of dissimilar materials, Cr-based P92 steels and Ni-based Alloy 617 is introduced and demonstrated to investigate its reliability. Firstly, multi-pass dissimilar metal welding between P92 steel and Alloy 617 was performed using DCEN TIG welding technology, buttering welding technique and a narrow gap groove. After welding, in order to understand characteristics of the dissimilar metal welds, metallurgical micro-structures analysis by optical observation and static tensile strength assessment of the dissimilar welded joints were conducted at 700°C.

Development of gap sensing system for narrow gap laser welding

Narrow gap welding with an oscillation laser beam is one of the effective processes for thick plate welding. To put this welding process into practical manufacturing, a groove-sensing system using image processing for narrow gap welding with an oscillation laser beam is used. This developed system uses still images of the weld zone taken by a coaxial CMOS camera. It can recognize the position of the groove wall by analysing the brightness distribution in the still image. It can then control the oscillation width and the laser-irradiated area by calculating the groove width and the groove centre position. Some narrow gap welding experiments were performed to evaluate the performance of the developed system. The results revealed that the developed system is effective for narrow gap welding with an oscillation laser beam. Using this system, the narrow gap groove can be welded even if the groove width has changed during the welding 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.

Study on microstructures and mechanical properties of super narrow gap joints of thick and high strength aluminum alloy plates welded by fiber laser

The welding of thick high strength aluminum alloy plate was exceedingly difficult. Traditional arc welding was prone to softening the welded joints and involves multilayer; meanwhile, multi-pass welding may cause great residual welding stress, and deformation resulted in dampening the wide expansion of the welding structure of thick high strength aluminum alloy plates. Therefore, it was urgent to develop advanced materials and welding technologies to enhance the comprehensive mechanical properties of welded joints. Fiber laser boasted the advantages such as perfect monochromaticity and high quality light beam. In order to decrease the thermal loss of the welding heat source on the matrix, small power fiber laser and super narrow gap groove were applied for the effective welding of the 20-mm thick 7A52 aluminum alloy. The welding adopted multilayer and single pass welding with the groove width no wider than 4 mm. The weld was composed of four layers and the size was no wider than 4.5 mm, which was basically consistent with the widths of the whole. The parent metal was welded with 5183 alloy and 5E06 alloy. Fiber optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), and tensile testing machine were employed to investigate the influence of Er-Zr microalloying aluminum alloy welding wires upon the microstructure and mechanical properties of the welded joints.

Solidification cracking susceptibility of modified 9Cr1Mo steel weld metal during hot-wire laser welding with a narrow gap groove

Hot-wire laser welding with a narrow gap groove was applied to ASTM A213 grade T91 steel in the application of ultra super critical boilers. A filler wire according to AWS A 5.28: ER90S-G was used. The effect of the depth-to-width ratio (D/W) of a weld shape on the susceptibility to solidification cracking was investigated. With a groove width of 3 mm, solidification cracking did not occur with a D/W ratio of less than 0.6 and more than 1.2. The hot-wire laser welding method with a narrow gap groove seemed to be efficient for practical use, when the higher D/W condition was used without solidification cracking. The high temperature strain, which occurred during solidification, was computationally calculated in order to make clear the effect of D/W ratios on the susceptibility of solidification cracking in theory. From in situ observation using a high-speed camera of the hot-wire laser welding phenomena, a three-dimensional Finite Element Method (FEM) was simulated to estimate an equivalent plastic strain in the weld metal during welding. An approach to the moving heat source consistent with such phenomenon was proposed and validated based on experimental measurements. The simulation results presented that a moving heat source by hot-wire laser welding was able to produce a particular weld shape at a higher D/W ratio with a lower strain rate, which corresponded with the relationship between D/W ratios and solidification cracking in experiments. Therefore, such a hybrid process is a very interesting alternative process to reduce the solidification cracking in narrow gap welding, especially in modified 9Cr1Mo steel.

FE-calculated stresses in a multi-pass butt-welded pipe—A simplified approach

The development of stresses in a multi-pass butt-welded pipe is studied numerically by use of the finite element method (FEM). A simplified approach is employed where rotational symmetry is assumed, where the complex temperature history experienced by the pipe material during welding is not followed in detail, and where effects of phase transformations are disregarded. Two different weld grooves, a narrow gap groove and a conventional single-U groove, are compared with respect to the calculated welding residual stress field and the radial deflection. Somewhat smaller stresses and larger deflections are found for the narrow gap groove. Calculated stresses and displacements are qualitatively in good agreement with experimental results reported elsewhere, especially for the narrow gap groove.