Weld Formation Research Articles

Orbital-Based Automatic Multi-Layer Multi-Pass Welding Equipment for Small Assembly Plates

To address the technical challenges, production quality issues, and inefficiencies caused by the heavy reliance on traditional manual processing of small assembly plates in the shipbuilding industry, this paper presents the design and analysis of a track-based automatic welding device. This equipment provides a solution for achieving batch and continuous welding in the field of automatic welding technology. The design section includes the mechanical design of the equipment’s core mechanisms, the design of the operating systems, the development of visual scanning strategies under working conditions, and the formulation of multi-layer and multi-pass welding processes. The analysis section comprises the static analysis of the equipment’s mechanical structure, kinematic analysis of the robotic arm, and inspection analysis of the device. Compared with manual welding, multi-layer and multi-pass welding experiments conducted using the equipment demonstrated stabilized welding quality for small assembly plates. Under the conditions of single plates with different groove positions and gaps, when the gap was 4 mm, processing efficiency increased by 7.35%, and processing time was reduced by 10.2%; when the gap was 5 mm, processing efficiency increased by 10.7%, and processing time decreased by 7.39%. The welding formation rate for the overall processing of single plate panels and web grooves increased by 11.48%, total material consumption decreased by 13.4%, and unit material consumption decreased by 13.5%. For mass production of small assembly plates of the same specifications, processing time was reduced by 16.7%, and there was a 41.4% reduction in costs. The equipment effectively addresses the low level of automation and heavy dependence on traditional manual processing in the shipbuilding industry, contributing to cost reduction and efficiency improvement.

Steel Catenary Riser Fatigue Assessment: Fracture Mechanics Approach Versus S-N Curve Method.

In this paper, the fatigue resistance of a full-scale Steel Catenary Riser (SCR) girth weld is investigated using the Strength-Number of cycles (S-N) curve method based on weld formation quality and fracture mechanics approaches. The test results, presented in the form of S-N curves, are superior to the design curve E in BS 7608. Compared with the S-N curve determined by a resonant bending rig, the analytical fracture mechanics, i.e., engineering critical assessment (ECA) based on BS 7910, can provide a rational estimation of full-scale girth welds. For the numerical methods, the short crack growth phase is crucial to improving the accuracy and reliability of the assessment. For the girth weld with a concave root, the geometries of the weld cap are the predominant factors for fatigue life. Although the crack initiation site is always located at the outer surface regardless of the flushed or welded caps, the weld grinding treatment is still effective in promoting fatigue life.

Dissimilar unbeveled aluminum to steel butt joint achieved by laser-arc hybrid welding-brazing

In this study, unbeveled butt joints of 2 mm thick steel and aluminum plates were welded using a laser-arc hybrid process. The influence of welding speed and wire feed speed on joint weld formation, microstructures, and mechanical properties were investigated. The results indicate that using a laser-arc hybrid heat source enables good weld formation of steel/aluminum dissimilar metals without groove preparation, even under high welding speed conditions. The steel side interface formed Fe₂(Al,Si)₅ near the steel and Fe(Al,Si)₃ near the aluminum. As the welding heat input decreased, the thickness of the intermetallic compounds gradually reduced. With an increase in welding speed or wire feed speed, the tensile strength of the joint first increased and then decreased, reaching a maximum of 104.47 MPa. Cracks propagated rapidly along the intermetallic compound region, resulting in brittle fracture characteristics. The three-point bending test showed a maximum longitudinal bending angle of 53.82° and a maximum transverse bending angle of 36.54°.

Investigation on metal vapor characteristics and keyhole/melt pool dynamics in high-power laser welding with side gas flow

High-power laser welding processes involve intense interactions between the laser beam and the base material, resulting in severe welding defects such as humping, spattering, and undercutting. Utilizing side gas flow may provide an effective approach for minimizing these defects. However, the effects of side gas flow on the dynamic behavior and weld formation necessitate further investigation. In this study, an innovative analysis of metal vapor characteristics and keyhole/melt pool dynamics in high-power laser welding with side gas flow is presented, combining experimental and simulation results. A three-dimensional transient fluid flow model was developed, uniquely integrating an adaptive heat source, evaporation-condensation processes, and metal vapor energy attenuation to provide a novel perspective on the effects of side gas flow in high-power laser welding. The results display that side gas flow could suppress plasma, increase thermal input to the melt pool, and intensify the flow of liquid metal toward the pool bottom during high power laser welding, thereby enhancing weld seam penetration. The numerical results indicate that variations in flow rate significantly impact metal vapor morphology, with higher flow rates reducing both the average area and height of the metal vapor and effectively suppressing the size of metal vapor/plasma. When the side gas flow rate is 20 l/min, with the gas flow impact point located at the keyhole opening and the nozzle height set to 3 mm, the side gas flow significantly enhances the depth-to-width ratio of the weld seam in 316L stainless steel laser welding. This work can provide guidance for suppression of weld defects in high-power laser welding of medium-thick steel components, which has important theoretical significance and application value.

Lap joining of Ti6Al4V titanium alloy by vortex flow-based friction stir welding

The current study uses a novel vortex flow-based friction stir lap welding (VFSLW) process to weld 1.4 mm thick Ti6Al4V sheets, trying to replace the diffusion bonding in the superplastic forming/diffusion bonding process. The mechanical properties and joining mechanism of the VFSLW joint were investigated. Good weld formation was obtained at 300–350 rpm and 80 mm/min. No hook defect was formed in the lap interface. The lap joint fractured across the stir zone (SZ) in the top plate under the optimal parameters. The cracks initiated from the oxidation defect, where the oxides on the workpiece surface were involved in the SZ by the vortex during the welding. It suggests that a good argon shield is very important for the VFSLW of titanium alloy. The highest tensile strength reaches ∼890 MPa, up to 95 % of the base material. The formation of an α + β lamellar structure in the SZ is due to the peak welding temperature exceeding the β-transus temperature. In the bonded zone (BZ), a very thin layer with ultrafine α grains was formed by dynamic recrystallization in the α phase field, although its two sides are α + β lamellar structures. This is because of the oxidation on the workpiece surface during the welding process and the O element is a strong α stabilizer.

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

Effect of Beam Oscillation on Weld Formation, Porosity, Grain Structure, and Mechanical Properties in Electron Beam Welding 5B70 Aluminum Alloy

Effect of Beam Oscillation on Weld Formation, Porosity, Grain Structure, and Mechanical Properties in Electron Beam Welding 5B70 Aluminum Alloy

Improvement of technology and equipment for welding vertical joints with forced weld formation

Improvement of technology and equipment for welding vertical joints with forced weld formation

Coupling effect of dynamic power and oscillation path on butt weld formation and melt flow behavior during aluminum alloys

The influence of the coupling effect between dynamic power and oscillation path on the formation of weld seams and the fluid behavior of the molten pool during laser welding of 5A06 aluminum alloy was investigated through numerical simulation and experimentation. Three power modes were compared in the experiments: equal power (EP), delayed dynamic power (D-DP), and non-delayed dynamic power (ND-DP). The experimental results show that both D-DP and ND-DP modes are favorable to improve the mechanical properties. Among them, the joints formed under the D-DP mode exhibit the best mechanical properties, with an average tensile strength reaching ≈ 99.1% of the base material, which is an increase of ≈ 35.3% and ≈ 5.6% compared to the EP and ND-DP modes, respectively. Numerical simulation results indicate that the D-DP mode effectively mitigates the average flow velocity of the molten pool, reduces the collision effects between liquid flows, suppresses the impact of fluid on the keyhole walls, and improves the stability of the keyhole and the welding process, thereby enhancing the mechanical properties of the joints.

Dynamic behavior regulation of droplet transfer based on arc-bubble control by ultrasound-induced during underwater wet welding

In comparison to welding in air, the periodic formation of unstable arc bubbles is a significant factor contributing to the unstable mass transfer process during underwater wet welding (UWW). Up to now, there is no ideal method to control droplet transfer and improve arc stability. In this study, the ultrasound-induced method (UIM) was used to regulate the droplet transition behavior and improve the process stability. The behavior features and key mechanisms of arc-bubble and droplet transfer induced by ultrasound were revealed with the employment of highspeed camera and X-ray observation, respectively. The incident angle of ultrasound was taken as a variable to reveal its effects and mechanism of action on the behaviors of arc bubble and droplet transfer, weld formation quality, microstructure, and property of weld joint. The results show that ultrasound-induced a new rising mode of arc bubble, which can significantly reduce the repulsive resistance that come from the bubble rising on the droplet transfer process. Compared with underwater wet welding without ultrasound, the average diameter of molten droplets reduces from 3.2 mm to 1.7 mm, and the droplet transfer frequency increases from 7.8 Hz to 13 Hz as the incident angle of ultrasound increases to 60°. In addition, the weld seam without obvious defects could be produced by UWW with UIM, of which the Variation coefficient of weld reinforcement is reduced from 21.3 to 11.6 and 17.4 at an ultrasonic incident angle of 30° and 45°. With increasing of ultrasound incident angle, it showed that the microhardness of the weld joint has a slight increase. In the heat-affected zone, the microhardness for the joint increased from 290 HV to 320 HV while the incident angle increased to 60°. This research shows that an appropriate incident angle of ultrasound can obtain good-quality joints which has a stable metal transfer process in underwater wet welding.

A novel method for fully penetrated U-rib-to-deck joints: Single-sided oscillating laser arc hybrid welding

U-rib-to-deck (RTD) joints represent one of the most critical and vulnerable welding details of orthotropic steel decks. Aiming for full penetration and high-level service performance, a novel method with single-sided oscillating laser-arc hybrid welding (OLAHW) technique was proposed for the RTD joint. The weld formation, microstructure and mechanical properties were extensively investigated. The results indicated that the porosity and lack of fusion (LoF) defects effectively suppressed with the beam oscillation during LAHW process. The OLAHW technique has good spatial accessibility with larger laser beam incidence angle of 20° Beam oscillation led to an increase in acicular ferrite in the fusion zone (FZ) while simultaneously a reduction of martensite in the heat effected zone (HAZ). This was related to the cooling time, and the thermal simulation results revealed that the OLAHW sample demonstrated comparable cooling times in both the Laser-FZ and arc-FZ. Consequently, beam oscillation can generated more homogeneous microstructures and microhardness. Although the microhardness of the OLAHW sample in the FZ was increased compared to the conventional arc welding (CAW) and LAHW sample, the highest microhardness value remained within acceptable limits (380 HV). Moreover, the ultimate tensile strength of the OLAHW weld sample increased by 7 % compared to the CAW weld sample. The application of the OLAHW technique demonstrates its feasibility for engineering applications in orthotropic steel decks manufacturing.

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.

Microstructure and mechanical properties in electron beam scanning welded joints of super thick titanium alloy plates

It is generally difficult to obtain good weld formation and excellent properties in super thick titanium alloy joints via conventional electron beam welding (EBW) methods due to the fact that the melt pool flow becomes more unstable as the plate thickness increases. In this study, electron beam scanning welding (EBSW) was utilized to weld 100 mm Ti–6Al–3Nb–3Zr–1Mo titanium alloy plates to improve the weld formation and impact toughness through the scanning effect. The results revealed that there were spatter and cutting defects on the surface and inner pore defect in the normal EBW joint, which could be effectively eliminated via EBSW. The decrease of the amplitude of the fluid flow rate and the change of the velocity direction were mainly responsible for this. A large amount of lamellar α phase with similar orientation was formed in the fusion zone (FZ) due to the fast cooling rate. The joint coefficient for both EBSW and EBW reached 100%, with the joint tensile strength of ∼840 MPa. The impact energy of the FZ in the EBSW joint was 70.5 J, reaching 210.4% of that of the BM (33.5 J). The impact toughness increase ratio in this study was far larger than those for Ti alloy welds ever reported, which was mainly attributed to that the high angle α colony boundaries with high preferred orientation in the FZ deflected the crack propagation direction. This study provides a reference for the strength-toughness design of EBWed joints of super thick Ti6331 titanium alloy.

Laser transmission welding of Polyphenylsulfone resin using Sn film absorbent: Weld formation control and mechanical properties enhancement

Polyphenylsulfone resin (PPSU), holding significance across various domains, was successfully welded by the laser transmission welding (LTW). In order to optimize the morphology and mechanical properties of the weld seam, the Sn film was chosen as an intermediate layer and the mechanism governing the formation control and mechanical performance was unveiled. Without the addition of Sn film, weld formation was subpar, marked by defects such as bubbles occurring in the weld seam, particularly under moderate power conditions. After introducing Sn film as a metal absorbent, the molten pool pores were stabilized and the temperature distribution was optimized during LTW process, which promoted the welding process stability and facilitated the mixing and agitation of the molten pool. The Energy-dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) were conducted on cross-sections of the weld seam. Analysis revealed the formation of newly forged metallic bonds (SnC) between the metal and the PPSU, which were instrumental in bolstering the shear strength of the weld seam. After using the Sn as intermediate layer, the shear strength of welding joints increased from 23.21 MPa to 29.14 MPa. At optimal intermediate-layer thickness, the shear fracture exhibited predominantly a plastic tearing micro-pit morphology instead of brittle fracture rock pattern.

Arc behavior and droplet transfer characteristics during oscillating laser-arc hybrid welding of 2024 Al alloy based on Zr-core-Al-shell wire

A novel zirconium (Zr)-core-aluminum (Al)-shell wire (ZCASW) combined with oscillating laser-arc hybrid welding (O-LAHW) process was employed for the welding of aluminum alloy 2024 (AA2024). The arc stability and characteristics, droplet transfer behavior and weld formation were systematically investigated. The results show that electrical signal waveform determines wire feeding rate, which affects the welding stability and weld quality. The increment in wire feeding rate increases magnetic field intensity and narrows arc cross-sectional area, which leads to arc contraction. The oscillating laser increases arc width and arc area, thereby expanding the conductive channel and greatly improving conductive ability of hybrid plasma, which promotes interactions between plasmas and helps to droplet transfer. Meanwhile, owing to the melting points differences between Zr wire and Al wire in ZCASW filler material, the melting rate of outer Al wire is larger than that of central Zr wire during welding, thereby resulting in two kinds of droplet transfer modes, and electromagnetic force and metal vapor reaction force strongly influence droplet transfer behavior. The oscillating laser improves the weld quality, which is deteriorated due to the appearance of spatters as wire feeding rate increases. When 1 m/min wire feeding rate is selected, a perfect formation is obtained. The current study offers insight into the formation mechanism of high-quality weld and welding stability during O-LAHW of AA2024 combined with ZCASW filler material.

Ultrasonic Welding of Acrylonitrile-Butadiene-Styrene Thermoplastics without Energy Directors.

Ultrasonic welding (USW) of thermoplastics plays a significant role in the automobile industry. In this study, the effect of the welding time on the joint strength of ultrasonically welded acrylonitrile-butadiene-styrene (ABS) and the weld formation mechanism were investigated. The results showed that the peak load firstly increased to a maximum value of 3.4 kN and then dropped with further extension of the welding time, whereas the weld area increased continuously until reaching a plateau. The optimal welding variables for the USW of ABS were a welding time of 1.3 s with a welding pressure of 0.13 MPa. Interfacial failure and workpiece breakage were the main failure modes of the joints. The application of real-time horn displacement into a finite element model could improve the simulation accuracy of weld formation. The simulated results were close to the experimental results, and the welding process of the USW of ABS made with a 1.7 s welding time can be divided into five phases based on the amplitude and horn displacement change: weld initiation (Phase I), horn retraction (Phase II), melt-and-flow equilibrium (Phase III), horn indentation and squeeze out (Phase IV) and weld solidification (Phase V). Obvious pores emerged during Phase IV, owing to the thermal decomposition of the ABS. This study yielded a fundamental understanding of the USW of ABS and provides a theoretical basis and technological support for further application and promotion of other ultrasonically welded thermoplastic composites.

Analysis of the dynamic behaviors of molten pool and keyhole for the oscillating laser welding of dissimilar materials stake welded T-joints with a gap

The dynamic behaviors of molten pool and keyhole have the significant effects on weld quality and joint performance. To investigate the circular shaped oscillating laser welding (OLW) of dissimilar materials stake welded T-joints with a gap between the face plate (FP) and web plate (WP), a dynamic model of molten pool and keyhole for the OLW of dissimilar materials stake welded T-joints with a gap is developed and the dynamic behaviors of molten pool and keyhole during the weld formation process are analyzed and discussed in detail. Based on the calculated results, it is found that the laser beam mainly radiates on the front wall of keyhole and the hump is formed on the rear wall of keyhole relative to the moving direction of laser beam at the FP welding stage. At the gap penetration stage, the keyhole opening at the molten pool bottom of FP shows the trumpet-shaped characteristic and the molten pool is divided into the upper and lower parts by the gap. The formed gas cavity is separated and fused with the keyhole several times at the WP welding stage. The gap around the gas cavity is disappeared after the reintegration of the upper and lower parts of molten pool. The depth of molten pool shows the periodic fluctuation characteristic with time and the fluctuation period is nearly the same as the oscillation period of laser beam during the OLW process.

Numerical evaluation of interwire angle influence on molten pool fluid dynamics and weld defects in tandem NG-GMAW of 5083 aluminum alloy

The impact of interwire angle on the fluid dynamics and weld defects in tandem NG-GMAW of 5083 AlMg alloy was investigated through experimental and simulation methods. The rotating coordinate system was employed to model the inclined arc and arc interaction, while a pulsed Gaussian distribution arc model was adopted to consider factors such as arc heat, arc pressure and drag force. Experimental results demonstrate that different interwire angles lead to different weld formation and varying levels of porosity and pore distribution. A sound weld bead with no formation defect and low porosity was achieved when the interwire angle was set at 10°. Simulation results illustrate the relationship between weld formation, bubble escape and molten pool fluid dynamics under diverse interwire angles. As the interwire angle increases, the weld surface becomes concave. At the interwire angle of 0°, the weld bead surface appears leveled and porosity tends to occur near the sidewalls due to roundabout flows in that region. At an interwire angle of 14°, roundabout flows converge at the central longitudinal section, resulting in significant porosity in this area. However, when the interwire angle is set at 10°, backward flows driven by two arcs suppresses roundabout flow throughout the entire molten pool, leading to a lower percentage of porosity area.

Formation and mechanical properties of AZ31B magnesium alloy welds by power-modulated oscillating laser

an energy-space modulated laser was proposed in welding workpieces with AZ31B magnesium alloy to enhance the efficiency of heat transfer and reduce defects of welds, and the proposed laser was power-modulated oscillating laser (PMOL). To validate the performance of the proposed technique, non-penetration welding and butt welding were conducted on the workpieces with a thickness of 5 mm. The impact of power-modulation parameters was investigated at the aspects of micro-structures, appearance, and mechanical properties of welds. The results showed that in comparison with a conventional laser (CL) or circular oscillation laser (COL), an energy-space modulated laser led to (1) an increased depth of weld penetration and (2) an enhanced coupling efficiency of laser energy. The parameters of power modulation could be optimized to reduce the defects of welds such as spatter, underfill, and thick fish scales significantly reduced; it refined the equiaxed grains in the center area of weld. When the frequency and amplitude of power-modulation were set as 50 Hz and 500 W, respectively, the mechanical properties of the weld were improved with the ultimate tensile strength of 238 MPa and an elongation ratio of 13.9 % which were 96.1 % and 58.7 % of those of the base material (BM), respectively. In comparison with the results welded by CL and COL, the ultimate tensile strength by PMOL was increased by 13.9 % and 4.4 %, and the elongation was increased by 54.4 % and 8.6 %, respectively.

Research on the Welding Process and Weld Formation in Multiple Solid-Flux Cored Wires Arc Hybrid Welding Process for Q960E Ultrahigh-Strength Steel.

This paper proposes a novel welding process for ultrahigh-strength steel. The effects of welding parameters on the welding process and weld formation were studied to obtain the optimal parameter window. It was found that the metal transfer modes of solid wires were primarily determined by electrical parameters, while flux-cored wires consistently exhibited multiple droplets per pulse. The one droplet per pulse possessed better welding stability and weld formation, whereas the short-circuiting transfer or one droplet multiple pulses easily caused abnormal arc ignition that decreased welding stability, which could easily lead to a "sawtooth-shaped" weld formation or weld offset towards one side with more spatters. Thus, the electrical parameters corresponding to one droplet per pulse were identified as the optimal parameter window. Furthermore, the weld zone (WZ) was predominantly composed of AF, and the heat-affected zone (HAZ) primarily consisted of TM and LM. Consequently, the welded joint still exhibited excellent mechanical properties, particularly toughness, despite higher welding heat input. The average tensile strength reached 928 MPa, and the impact absorbed energy at -40 °C for the WZ and HAZ were 54 J and 126 J, respectively. In addition, the application of triple-wire welding for ultrahigh-strength steel (UHSS) demonstrated a significant enhancement in post-weld deposition rate, with increases of 106% and 38% compared to single-wire and twin-wire welding techniques, respectively. This process not only utilized flux-cored wire to enhance the mechanical properties of joints but also achieved high deposition rate welding.