Narrow Welding Research Articles

Study on Arc Behavior and Weld Formation of Magnetically Controlled Narrow Gap TIG Welding

Study on Arc Behavior and Weld Formation of Magnetically Controlled Narrow Gap TIG Welding

Enhancing of low-temperature deformation compatibility of pure titanium welded tube by laser welding and cold-worked in welded zone

This study is aimed to improve the low-temperature deformation behaviour of titanium heat exchange tubes by optimizing welding method and weld treatment processes. The various welding processes and cold-worked in welded zone process are adopted, and the effects of macro-morphology, microstructure and mechanical properties on low-temperature deformation behaviour are studied. The results show that the width of the laser welded joint and welded zone is 3.8 mm and 2.9 mm respectively, which is 40% and 63% of TIG welded joint. Especially, the width of heat affected zone and the grain size of laser welded joint are obviously reduced due to its concentrated energy density. The cold-worked process in welded zone can relieve the macroscopical and microstructural discontinuity between base metal, heat affected zone and welded zone. The inner weld reinforcement is eliminated to improve smooth transition and the columnar α grains in welded zone are remarkable fragmented with plenty of twins. The hardness of the welded zone after cold-worked is significantly higher than that of the base metal, resulting in base metal being the main deformation area of the welded tube at low temperature, which is beneficial to improve the deformation performance of the whole welded tube. By adapting the cold-worked and laser welding process with smooth transition and narrower weld width, the pure titanium welded tube can meet the requirement of three times low-temperature deformations.

Welding Characteristics of Medium Titanium Plates with Autogenous Laser Welding and Narrow-Gap Laser Filling Welding Modes.

Titanium and titanium alloys with a medium thickness of 5 to 12 mm are widely used for ocean platforms, military equipment and in other fields because of their light weight, appropriate strength and corrosion resistance. In this study, autogenous laser welding and narrow-gap laser welding processes were researched and compared, and the welding characteristics, weld microstructure and joint strength were analyzed. The results showed that autogenous laser welding had higher efficiency, narrower weld width and higher microstructure uniformity. Autogenous laser welding can achieve the single pass weld penetration at laser keyhole mode. The weld width of narrow-gap laser welded joint was 12.5 mm, which was nearly three times than that of autogenous laser welding. The grain size of autogenous laser welding was obviously smaller and more uniform in depth than that of narrow-gap laser welding. In the weld zone, the coarse columnar α grains grew from the fusion line, while in the heat-affected zone, equiaxed α grains with needle and sawtooth α morphologies were presented. The microhardness of the heat-affected zone was higher than in the weld zone and the base metal due to the denser needle microstructure. The tensile samples all fractured at the base metal, indicating the welded joint strength efficiency was greater than 1.

Achieving excellent properties of laser tailor-welded thin Al-Si coated press-hardened steel joint via controlling dilution rate

In laser tailor welded traditional 25 μm thick Al-Si coated press-hardened steel (PHS), a lot of ferrite was easily formed in the weld, so filling with expensive high-alloys wire is usually necessary. In this work, a new thin Al-Si coated PHS with 18 μm thickness was laser tailor welded, and a cheap low alloy wire was attempted to fill into the weld to via control the dilution rate. At a high dilution rate of 94%, the weld contained a ferrite fraction of 38%, resulting in the fracture occurring in the weld during tension and bending. At a medium dilution rate of 85%, the ferrite fraction in the weld decreased to 18%, obtaining excellent tensile and bending properties. The tensile strength and elongation of the joint reached 1528 MPa and 5.6%, respectively, with fracture being in the base metal (BM). The maximum bending load and displacement were 1291 N and 7.0 mm, respectively, and cracks initiated and propagated in the BM. This is attributed to the small amount of ferrite and stress concentration in the narrow weld. At a low dilution rate of 76%, the ferrite reduced to 6%, and the bending cracks initiated and propagated in the BM. However, the tensile specimen fractured in the weld, which should be related to the relatively low C concentration and the stress concentration at the weld toe due to the weld reinforcements.

The influence of Cu on the microstructure and properties of TC4/Q345 high-entropy joints by laser welding

FeCoNiCrCu high-entropy alloy (HEA) and Cu foils were utilized as the intermediate layer to conduct laser welding of TC4 titanium alloy and Q345 steel. Welding is performed by adding single HEA and Cu/HEA double foils as interlayer respectively. We conducted in-depth studies on the microstructure and mechanical properties of the joint by stereomicroscopy, metallographic microscope, scanning electron microscope (SEM), micro-area X-ray diffraction (XRD), nanoindentation, electron backscatter diffraction (EBSD), and tensile testing. The results indicate that the position of the copper foil significantly affects the microstructure and performance of the joint. When the copper foil is on the TC4 side, its lower melting point causes a deeper keyhole, resulting in a narrower weld bead and then reduced content of Fe and Ti in the weld. Simultaneously, the increased proportion of Cu in the weld significantly enhances the content of Cu-rich phases. In the weld zone, we observed freely distributed Cu-rich phases and Ti-rich phases generated along the interface. Under tensile loads, cracks primarily initiate and propagate along the Cu-rich phases, leading to typical delamination on the fracture surface. With the copper foil on the TC4 side, due to the increased copper content in the microstructure, the hardness of the interface between the titanium alloy and the weld decreases, while the joint exhibits the highest tensile strength, reaching a maximum of 417 MPa.

Study on molten pool flow and hot cracking of narrow gap laser welding of 316LN stainless steel for fusion reactor

In this paper, narrow-gap laser welding (NGLW) of 316LN stainless steel was studied. The results indicated that continuous laser welding with filler wire (CLWFW) and pulsed laser welding with filler wire (PLWFW) can obtain good weld formation under the transition of the wire bridge, and when the pulsed laser was a trapezoidal wave, the hot cracks of the filling layer can be greatly inhibited. The intermittent output of the pulsed laser reduced the temperature gradient of the molten pool and enhanced the morphology of the caudal region of the molten pool. Meanwhile, timely liquid backfilling effectively relieved the stress concentration of the weld, thus inhibiting the generation of hot cracks. Besides, the intermittent pulse energy input had a stirring effect on the molten pool, which disturbed the growth direction of the dendrite grain and refined the grain; consequently, the impurity elements were fully diffused, and the distribution of elements in the weld center area was more uniform.

Narrow gap multi-pass laser welding with 52M/308L double wires filler addition for SA508/316L dissimilar metals

Recently, considerable effort has been directed at the development of laser welding with wire filler addition as an alternative manufacture technique for the substantial productivity gains it would offer to the nuclear pressure vessels fabrication. However, single wire filler such as 52M and 308 L addition is difficult to take into account many properties such as the strength, toughness and resistance to stress corrosion cracking at the same time. In this work we evaluate the feasibility of applying 52 M/308 L dissimilar double wires filler addition for the multi-pass narrow gap laser welding (NGLW) of SA508/316 L dissimilar metals. The objectives of this paper is to regulate the microstructure of the welded joint by adjusting the ratio of the 52 M/308 L double wires filler. The results showed that welded joints without crack and lack-of-fusion were acquired. An excellent comprehensive property welded joint with relative high hardness and low residual stresses is acquired when the 52 M/308 L double wires proportion was 75 %:25 %. The results also indicated that a certain proportion of 308 L stainless steel wire filler addition was conducive to reducing the microhardness of the welded joint. However, when that ratio of the 308 L wire was up to 75 %, harmful element S was obtained in the precipitation zone, which might reduce the mechanical properties of the welded joints.

Research status of insufficient sidewalls penetration in narrow gap TIG welding of thick metal plates

Research status of insufficient sidewalls penetration in narrow gap TIG welding of thick metal plates

Inhomogeneous Strain Behaviors of the High Strength Pipeline Girth Weld under Longitudinal Loading.

Unforeseen failures in girth welds present a significant challenge for the pipeline industry. This study utilizes 3D Digital Image Correlation (DIC) assisted cross-weld tensile testing to analyze the strain response of high-strength thick-walled pipelines, providing essential insights into the strain migration and fracture mechanisms specific to girth welds. The results reveal that the welding process significantly affects the mechanical distribution within the girth weld. The tested Shielded Metal Arc Welded (SMAW-ed) pipe exhibited undermatched girth welds due to high heat input, while Gas Metal Arc Welding (GMAW) introduced a narrower weld and Heat-Affected Zone (HAZ) with higher hardness than the base metal, indicative of overmatched girth welds. Strain migration, resulting from a combination of metallurgical heterogeneous materials and geometrical reinforcement strengthening, progressed from the softer HAZ to the base metal in the SMAW-ed sample with reinforcement, ultimately leading to fracture in the base metal. In contrast, the GMAW-ed sample shows no strain migration. Reinforcement significantly improves the tensile strength of girth welds and effectively prevents failure in the weld region. Sufficient reinforcement is crucial for minimizing the risk of failure in critical areas such as the weld metal and HAZ, particularly in SMAW-ed pipes.

Study on the suppression of solidification cracks in narrow gap laser welding of high-strength steel based on dual-beam gradient control weld solidification

Welding solidification cracks are considered as critical defects in narrow gap laser welding, and it is of utmost importance to develop reliable measures to suppress them. The fundamental approach to curbing solidification cracks lies in controlling the solidification behavior of the weld. A novel narrow gap laser welding technology is proposed to address this issue by controlling the solidification of the weld with double laser beam in this paper. The influence of process parameters on the suppression of welding solidification cracks is explored. Additionally, the mechanism behind the dual-beam laser's ability to suppress solidification cracks are comprehensively examined through weld formation, molten pool solidification behavior and microstructure evolution. The findings demonstrate that the energy matching of the dual-beam and the spacing between the beams are crucial factors that impact the effectiveness of welding crack suppression. When the beam spacing is greater than 6 mm, this method begins to work on suppressing welding solidification cracks. Three distinct effective modes of crack suppression are identified, namely molten pool expansion, gradient solidification, and weld remelting. Among these, the gradient solidification mode proves to be the most reliable method for suppressing welding solidification cracks, as it facilitates a transformation in the molten pool's solidification mode from "enclosed" solidification to "sequential" solidification. Compared to conventional single-beam Narrow Gap Laser Welding, this approach not only effectively suppresses welding solidification cracks but also improves welding efficiency by nearly doubling the filling speed.

Synchrotron diffraction residual stresses studies of electron beam welded high strength structural steels

In recent years, there's been a strong focus on enhancing high-strength structural steels (HSSSs), making them tougher, stronger, lighter, and more weldable. However, these steels face challenges like cold cracking sensitivity (CCS) and reduced toughness with higher heat input. Therefore, exploring HSSSs with advanced welding techniques like electron beam welding (EBW) is crucial. EBW known for its innovation and precision, is gaining popularity in HSSSs applications for vehicles, construction industries etc. offering advantages like narrow welds, reduced heat-affected zone (HAZ) and low distortion. It is essential to understand the influence of residual stresses (RS) in HSSSs which ultimately affect structural integrity and fatigue life. Using EBW on HSSSs, coupled with synchrotron XRD for residual stress studies, has great potential to advance this research significantly. In this work, a 15-mm-thick EB-welded joint of S960QL and S960 M steels was used to study the RS. At an energy level of 20 keV, RS data from the synchrotron XRD method and its result on the top of welded joints for both types of steel were compared. S960 M steel showed a longitudinal tensile stress of 250 MPa at the weld toe, approximately 1.8 times higher than the 138 MPa observed in S960QL steel under similar conditions. In transverse stress, S960QL exhibits a higher stress of 279 MPa compared to S960 M 46 MPa at the weld toe, approximately 83% lower. The synchrotron method measured 76% lower LRS for S960QL compared to conventional XRD, while S960 M exhibited 55% lower LRS using the same approach.

Effect of beam current on microstructure, tensile properties and corrosion behaviour of electron beam welded zircaloy-4 joints

ABSTRACT Butt joints of zircaloy-4 were made using electron beam (EB) welding. The effect of beam current (15–20 mA) on weld zone size, microstructure, porosity, mechanical and corrosion properties has been investigated. Local temperature and cooling rate were estimated, and the average cooling rate increased from 2.4 to 6.3°C ms–1 with a decrease in beam current in the said range. Joints prepared at lower beam current possessed smoother weld surface, narrow weld bead, and fine lamellar type widmanstätten structure in the fusion zone (FZ). The length of the α-Zr lamella (from 105 to 37 µm) and interlamellar space (from 0.8 to 0.3 µm) decreased with a decrease in beam current. The XCT result revealed that porosity increased with an increase in beam current, and large-size micro pores of 180 µm were present in joints prepared at high beam current. The hardness of the welded samples increased by 13–20% than the base metal. The joint prepared with a low beam current possessed higher ductility (29%) and a minimum corrosion rate (0.0085 mmpy in 3.5 wt-% of NaCl solution) than the joint made with a higher beam current.

A new method for refinement of Ti-6Al-4 V prior-β grain structure in the alternating magnetic field assisted narrow gap gas tungsten arc welding (AMF-GTAW) via filler wire oscillation

This study presents a new method for refining Ti-6Al-4 V prior-β grain in the alternating magnetic field assisted narrow gap gas tungsten arc welding (AMF-GTAW) process by stirring the molten pool, which is accomplished directly through the use of an oscillating filler wire. The wire feed rate can be increased from 1.8 m/min to 2.2 m/min by filler wire oscillation in the traditional AMF-GTAW process with minimal heat input. This method greatly increases welding efficiency by efficiently utilizing the energy of the arc and molten pool. Using a high-speed camera, the flow behavior of the molten pool was investigated under different filler wire oscillating amplitudes. The results showed that the oscillation of the filler wire can cause a violent stir in the molten pool. By increasing the oscillating amplitude of filler wire, one can refine the columnar prior-β grain structure and attain a morphology of the upper layer of the welded joint that is nearly equiaxed with crystallographic texture, all while maintaining a fixed heat input. This is because the wire's insertion into the molten pool also creates a negative thermal gradient and the filler wire's high-frequency and high-amplitude oscillation creates an intense convection that prevents randomly oriented nuclei and/or dendrite fragments from remelting and promotes nucleation activation. The oscillating amplitude of 6 mm and the oscillating frequency of 100 Hz are the ideal values for this effect.

Development of friction stir welding method using a tilted spherical tool

The feasibility of friction stir welding (FSW) with a simple spherical tool, which has neither a shoulder nor a probe, was studied. The spherical tool allows for localised welding with narrow weld widths and extended tool life but tends to generate flashes and weld thinning. The material flow around the spherical tool during FSW of the aluminium alloys was observed in detail, and the flash generation behaviour was discussed. As a result, a new FSW method in which a spherical tool tilted to the retreating side (RS) was developed, and by expanding the flow path of the leading surface on the RS, the flow of hot material was controlled to reduce flash and smooth the weld surface.

Thick-wire swing arc narrow gap GMA welding assisted by pre-embedding cold wires

Thick-wire swing arc narrow gap GMA welding assisted by pre-embedding cold wires

Experimental analysis of the effect of ultrasonic vibration on porosity suppression in narrow gap laser welding

Abstract The welding process has a wide range of applications in aerospace, military manufacturing, machinery, and other fields, and with the continuous improvement of welding technology requirements, the inhibition of porosity in the welding process is also increasing. This study, through the narrow gap laser welding characteristics and porosity formation mechanism of the depth of analysis, for the existing narrow gap laser welding method exists in the side wall of the weld fusion is poor porosity, poor uniformity of organizational properties and other issues, proposed ultrasonic-based welding method to achieve effective inhibition of porosity. The experimental analysis of ultrasonic vibration on the formation of porosity is carried out based on narrow-gap laser welding. The peak sound pressure of narrow gap welding increases when the ultrasonic current amplitude changes from 24A to 32A. Under different ultrasonic vibration conditions, the number of welds without applied ultrasound was as high as 95, while the number of porosities gradually decreased to 48 with the increase of applied ultrasound amplitude from 12% to 37%. Furthermore, as the ultrasonic amplitude increased, the residual height decreased by 0.45 ml. In addition, at fixed ultrasonic amplitude, with the increase of laser power, the porosity increased from 0.89% to 2.21%, and the average diameter of the porosity increased from 0.29 mm to 0.43 mm. The porosity for the porosity diameter of less than 200 μm was reduced to 0.020%. The percentage of stomata with a diameter greater than or equal to 200μm increased to 2.098%. This study analyzes the inhibition effect of ultrasonic vibration on porosity to a certain extent. Moreover, the inhibition effect of ultrasonic vibration in narrow gap laser welding is significant and the smaller the laser power under the same amplitude, the better the inhibition effect, which provides a valuable reference for the research of the narrow gap laser welding process.

Process strategies for optimizing the cooling behaviour of laser-welded Tailor Welded Blanks made of advanced high strength steels (AHSS)

AHSS with 1000 MPa tensile strength show promising properties for the use in Tailor Welded Blanks (TWBs) to locally strengthen car body parts. Challenges in laser beam welding of the sheets are hardness-drops and -peaks in the heat-affected zone (HAZ) and weld, which cause risks during cold-forming. This happens due to rapid cooling caused by laser welding. A numerical approach aiming for slower cooling rates in the weld region is presented in this article. Laser welded sheets served as reference for setting up a process simulation. Models for pre-heating and a coaxial setup with power split were set up. A correlation between cooling-rate and hardness in the joining zone was established and applied to the modelled strategy. Splitting the power led to a slightly narrower weld seam and experimental pre-heating of the sheets to 600 °C could lower total seam hardening. It achieved a homogenization of the fusion zone.

Temporal power modulation in high power laser beam welding of round bars

Temporal power modulation bears an enormous potential for high power laser beam welding of round bars since all its specific challenges are faced. They can be summarised as deviating welding conditions towards the round bar‘s centre. Accordingly, a tailored amount of energy would be provided to that area. The investigations are conducted on 30 mm diameter bars of 1.4301 stainless steel with the use of a 16 kW disk laser. The modulation parameters comprise 6/12/50/100/200 Hz modulation frequency and 0.30/0.47/0.73 modulation depth or power modulation ratio. Post analysis focuses on metallographic longitudinal sections and calculations. The modulation‘s outstanding capability is creating deeper and narrower weld seams due to higher peak power and more intense evaporation of protrusions along the keyhole front wall. Therefore, more laser power is provided to the weld root and despite applying lower average power, the same weld depth is achieved. Finally, more ecological and economical welding as well as welding of more temperature sensitive materials is enabled.

A Review of Friction Welding Research Addressing the Influence, Development, Similar & Dissimilar Welding

This review paper discusses the recent research work carried out in the frictional joining of dissimilar and similar alloys through the friction welding (FW) process with various parameters and modifications. It includes further the latest developments and advances in the research on FW and the influences of FW’s process parameters on the quality of joints and their properties. The specimens’ faying surfaces can also influence the joint properties as the surface modifications stimulate or change the metal joints’ bonding according to the welding parameters selected during FW. Though the rise of friction pressure (FP) during FW improves the strength of the joints, the improper selection of parameters leads to metal damage. It feels better if the axial shortening is less than 30 mm for FW of soft metals. The axial shortening values are less than 25 mm for the hemispherical bowl-type faying surfaces under 18 bar FP and it is noted that the bevel-type tapered faying surfaces increase the shortening. FW provided very narrow weld interfaces with around 5-10 µm width. With a low FP, it was possible to obtain a maximum of 100 % efficiency by modifying their faying surfaces. The small-diameter soft material needs less FP and friction time. The microstructure modification is possible and the weld joint is shown as U and V shapes for the bowl and tapered faying surfaces. It further increases the contact area and thus increases strength.

Real-time detection and localization method for weld seam of narrow butt joint based on semantic segmentation

Structured light measurement is widely used in welding seam tracking because of its high precision and robustness. For the narrow butt joint, the positioning method by reconstructing the weld contour is not suitable for the welding of the narrow butt joint because it is difficult for the laser stripe to produce obvious deformation when projected to the weld. In this study, high-quality images with laser stripes and narrow butt joints are captured by the improved structured light vision sensor, which is equipped with an auxiliary light source. A two-step processing framework, including semantic segmentation and groove positioning, is raised to locate the feature point of the narrow butt joint. Firstly, we design the strip pooling ENet (SP-ENet), a real-time network specifically designed to accurately segment narrow weld images. Our proposed network outperforms other classical segmentation networks in terms of segmentation accuracy and proves to be highly suitable for the detection of narrow butt joint welds. Secondly, a combining method of random sample consensus (RANSAC) and iterative fitting to calculate the sub-pixel coordinates of weld feature points accurately. Finally, a trajectory smoothing model based on the Kalman filter is proposed to reduce the trajectory jitter. The above methods were tested on a self-built robotic welding experimental platform. Experimental results show that the proposed method can be used for real-time detection and positioning of narrow butt joints. The positioning trajectory is smooth, with most positioning errors less than 2 pixels. The mean tracking error reaches 0.207 mm, which can meet the practical welding requirements.