Synchronous Welding Research Articles

Analysis of welding conditions at synchronous operation of resistance welding machines

The paper is devoted to analysis of power losses in a resistance welding machine including supplying system and examination of welding conditions of the welding machine current in a case of synchronous (simultaneous) operation of multiple welding machines, i.e., during the conduction of welding current. Analysis of the most important contributors of power losses generated on the current path between a power source and the welded joint is carried out. The analysis is carried out for a DC (direct current) welding machine with power electronics inverter. AC (alternating current) welding machines are also taken into account. The analysis is divided in two parts. The first one is the analysis of single welding machine operation, while in the second part, coexistence (mutual operation) of two synchronous welding machines is considered. The analysis is based on results of numerical and experimental investigations. The first one is focused on calculation of power losses in the energy path (including a Sankey type power loss distribution diagrams), and the second one is based on experimental tests carried out to determine the diameter of the weld nugget and the strength of the joints, for cases of reducing the welding current. An example of simultaneous operation of welding machines was presented and discussed. The percentage voltage drops and power losses in the entire power supply path of the resistance welder are shown. The analysis carried out is extremely important from this point quality of welded joints.

Bridging microstructure and crystallography with the crack propagation behavior in Ti-6Al-4V alloy fabricated via dual laser beam bilateral synchronous welding

The microstructure evolution and crack propagation behavior were systematically and thoroughly investigated in α/β Ti-6Al-4V alloy obtained under the inhomogeneous heating effect of a coupled dual laser beam via a combination of postmortem electron backscattering diffraction analyses and numerical simulations. The effect of microstructural attributes (grain size, grain boundary, dislocation) on the fracture property and crack propagation behavior was investigated based on thermodynamic and crystallographic analyses, as well as the examinations of dislocation density and the Burgers vector. By quantifying the degree of variant selection using the degree of variant selection (DVS) equation, it was found that the higher the energy input, the weaker the variant selection, as the secondary α phase suppresses further dislocation-induced variant selection via autocatalytic nucleation and growth. The proportion of high angle grain boundaries (HAGBs) concentrated around 60° gradually increases with improving cooling rate, mainly due to the change in the tendency of martensite transformation to be induced. The grain refinement was the primary mechanism for the enhancement of Ti-6Al-4V alloy T-joints, while the suppression of crack propagation by HAGBs also played a crucial role in improving strength and ductility. The crack propagation direction frequently changes when the order is approximately parallel to the short axis of α′ martensite grains, forming a zigzag propagation path. The above findings should shed light on optimizing dual laser beam bilateral synchronous welding (DLBSW) technology to tailor the microstructure and improve the mechanical properties of Ti-6Al-4V alloy T-joints.

Numerical simulation of molten pool flow behavior and keyhole evolution behavior in dual-laser beam oscillating bilateral synchronous welding of T-joints

In the context of global warming and energy shortage, the key means to increase product competitiveness is how to achieve lightweight manufacturing of large spacecraft skin-stringer structures by welding instead of riveting. In this work, we propose dual-laser beam oscillating bilateral synchronous welding (DLBOW) by combining dual-laser beam synchronous welding (DLBW) with the oscillating process to overcome the long-standing porosity problem in T-joint welds and investigate the effect of different laser incidence angles on the porosity of the weld during welding. At the same time, the corresponding numerical model was established by computational fluid dynamics to analyze the molten pool flow behavior and keyhole evolution under molten pool coupling. This is the first time that complete wire melting process has been achieved in the T-joint dual-laser beam synchronous welding numerical model, reproducing more realistically the influence of the wire fusion behavior on the molten pool flow. Both experimental and simulation results show that the porosity is significantly reduced under DLBOW compared to DLBW; in addition, the porosity is lower when the laser incidence angle is smaller. An in-depth analysis of the numerical model reveals the mechanism of this physical phenomenon: First, the oscillation process optimizes the laser energy density distribution and reduces the peak temperature of the T-joint molten pool. The impact of the metal flow on the keyhole is weakened, which reduces the probability of bubble formation and thus significantly decreases the porosity. Moreover, for the oscillation process, the keyhole effect is more obvious at large laser incidence angles, and the actual heat input to the molten pool is larger, which makes the slender keyhole more prone to collapse and more likely to generate pores. This work provides new insight into the interrelationship between keyhole and pore in T-joint dual-laser beam synchronous welding.

Research on keyhole-induced porosity and melt flow kinetic behavior of 2219 alloy T-joint manufactured by dual laser-beam bilateral synchronous welding

Research on keyhole-induced porosity and melt flow kinetic behavior of 2219 alloy T-joint manufactured by dual laser-beam bilateral synchronous welding

Dual laser-beam synchronous self-fusion welding of Ti–6Al–4V titanium alloys T-joints based on prefabricated welding materials

Aiming at the difficulty of feeding filler wire in the dual laser-beam synchronous welding (DLSW) of Ti–6Al–4V titanium alloys T-joints, the self-fusion DLSW process based on prefabricated welding materials on the stringer was developed. Prefabricated bosses on both sides of the stringer were used as welding materials. In this paper, the influence of boss size and laser power on the weld formation was studied. The influence of microstructure transformation on mechanical properties was demonstrated. It is found that T-joints with desirable weld formation can be obtained when the boss size of 0.8 × 0.8 mm2 was applied. The temperature distribution of the T-joint during laser welding process was obtained by finite element simulation method. It indicates that the cooling rate of fusion zone is 140 °C/s, indicating that massive transformation occurs in the fusion zone. The microstructure of fusion zone characterized by acicular martensite plates α′ and a small amount of intergranular α phase meets with the cooling rate of FZ. Due to multiple strengthening effects, the average microhardness of fusion zone is 351.6 HV, which is higher than the average microhardness of base material. The pull-out strength of T-joint is not related to the weld penetration, and its average pull-out strength is 1035.5 MPa. The fracture occurred in the weld toe of the pull-out specimen, and fracture surface presents quasi-cleavage fracture characteristics.

Research on the cryogenic axial tensile fracture mechanism for 2219 aluminum alloy T-joint by dual laser-beam bilateral synchronous welding

In this paper, dual laser-beam bilateral synchronous welding (DLBSW) technology is performed to fabricate 2219 aluminum alloy T-joint. The cryogenic axial tensile strength of the DLBSW T-joint in the direction parallel to the weld at −182℃ is tested. The microstructure of T-joint, the cryogenic axial tensile strength, fracture location and tensile fracture morphology are comprehensively investigated to explore the cryogenic axial tensile mechanism. The average value of cryogenic axial tensile strength of T-joint is 415 MPa, 76.9% of base metal (BM). Under the axial tensile force, the grain deformation and intergranular cracks are respectively generated in weld seam (WS) and heat affected zone (HAZ) near the fracture location. It is found that the cryogenic axial tensile fracture mechanism of the T-joint is intergranular ductile fracture, contains cleavage fracture and microvoid coalescence fracture. The degradation of cryogenic axial tensile property is attributed to multiple factors, such as impurity phases, pores, eutectics.

Study on Medium-Thick Al-Alloy T-Joints by Dual P-GMAW Bilateral Synchronous Welding

The T-joints of medium-thick 6082 Al-alloy plates created by dual pulsed gas metal arc welding (P-GMAW) and bilateral synchronous welding were investigated to improve weld quality using the adaptive deposition method, which calculates the minimum amount of deposition according to the welding condition, groove size, and cross-sectional area, effectively reducing the heat input and deformation of the welds on the basis of weld filling. The optimized linear energy with a wire feed speed (WFS) of 9.5 m/min can ensure a well-formed weld with a complete root fusion, and high-quality T-joint welds were obtained both in root openings of 0 mm and 1 mm. The biggest penetration was 4 mm, which was four times more than that of the result from a single torch welding process. When the distance between the two welding torches exceeded 20 mm, the molten pool was completely separated, and process pores were observed in the unfused root zone. Influenced by the thermal cycles in asymmetric welding, the hardness distribution changed: the width of the softer zone at the base plate with the fore arc was smaller than that zone with the rear arc. Furthermore, dual P-GMAW bilateral synchronous welding with an asymmetric heat source can further reduce the deformation of the welded joint by about 20% compared to that of symmetric welding.

Effect of laser power on the grain morphology and microhardness of dual laser-beam bilateral synchronous welded 2219 aluminium alloy T-joint

Dual laser-beam bilateral synchronous welding (DLBSW) technology has been widely used in the connection of skin-stringer T-joint. In this study, DLBSW technology was performed to fabricate T-joint of 2219 aluminium alloy. Furthermore, the effect of laser power on grain morphology and microhardness of the T-joint was investigated. The microstructure of different parts was observed and the grain size was quantitatively analysed. The results show that the grain quantity and microhardness of the welded joint are increased significantly as the welding heat input increases. It is found that the influence of laser power on the grain size at the edge of the weld seam is greater than that in the centre of weld. Besides, the microhardness of the non-dendritic equiaxed zone decreases with the increase of laser power, which is caused by the decrease of Al element.

Research on microstructure evolution and tensile characteristics of Ti6Al4V double lap-fillet joints fabricated by dual laser-beam bilateral synchronous welding

Employing prefabricated “boss” on the substrate to replace wire feeding, an attempt is made to explore the non-filler welding process of Ti6Al4V double lap-fillet welded joints with the technology of dual laser-beam bilateral synchronous welding (DLBSW). The weld quality is evaluated in terms of bead geometry, microstructural morphology and mechanical property. An optimal range of welding speed (1.3 m/min) with constant unilateral laser power of 950 W is identified to achieve satisfactory weldments with no underfill defect and acceptable porosity. Phase transformation and microstructural evolution occurring through thermal history in different regions of the welded joint are clarified. The average length of α'-martensite in the weld seam (WS) decreases significantly as welding speed increases. A connection between dimensional variation of α'-martensite and tensile strength is developed, and the fracture mechanism of the lap-fillet joint is discussed. The existence of fine α'-martensites helps to attain high-performance joints with strength comparable to the base metal (BM). The fracture position of tensile specimens is located in the region near the weld toe where stress concentration occurs. Fractography analysis indicates that the failure of weldments is in ductile mode with the feature of a great number of dimples.

Microstructure and texture evolution of Ti–6Al–4V alloy T-joint fabricated by dual laser beam bilateral synchronous welding

The microstructure and microtexture evolution of Ti–6Al–4V T-joints produced by dual laser beam bilateral synchronous welding (DLBSW) were investigated using the optical microscopy (OM) and electron back-scattered diffraction (EBSD) and correlated with the mechanical properties of the joint. We demonstrate important differences in temperature field, grain morphology, misorientation angles and texture intensity between the base material (BM), the skin-side heat-affected zone (SK-HAZ), the stringer-side heat-affected zone (ST-HAZ) and the weld seam (WS). Through in-depth crystallographic analysis, we demonstrate that the kernel average misorientation curve of the WS is steeper and the peak misorientation angle is larger, revealing that the WS has a lower geometrically necessary dislocations density and a smaller residual strain. Due to the different orientation of each a-phase colony at the interface of the two phases, it is not conducive to the deformation mode of dislocation slip, so a large number of twins are generated in the WS. Furthermore, the WS has a strong crystal preferential orientation and the maximum polar density of the pole figure is 17.05, which is significantly higher than the polar density of the base material. It is found that the gradient of microstructure variation in the narrow HAZ is higher than that in the WS, which leads to more heterogeneous properties in the HAZ compared to the weld. This research result is consistent with the phenomenon that all the fractures of the resultant T-joints occurred in the HAZ.

Study on the grain morphology and fracture performance of T-joints for Ti6Al4V alloy manufactured by dual laser beam bilateral synchronous welding

Titanium alloys have become attractive candidates for structural materials in aviation industry, benefited from their reliable mechanical properties. In the present investigation, dual laser beam bilateral synchronous welding experiments of Ti6Al4V alloy under various welding speeds were performed using optic fiber laser. Experimental results indicate that the heat affect zone has become the weakest region of the joints theoretically. Inappropriate welding speed lead to a severe coarsening of the equiaxed grains below the lower fusion zone, which is the main reason why the tensile strength of the construction decreased significantly. Additionally, the ultimate tensile strength of the T-joint under the welding speed of 22 mm/s has reached 808 MPa, exceeding 90% of the strength of the base metal. According to the fractographs, the T-joints adopted higher welding speeds have failed in the form of microporous aggregation fracture. In contrast to the others, it can be concluded that the fracture mode of the T-joint under the lowest welding speed is a mixed fracture composed of cleavage fracture and ductile fracture.

Effect of porosity morphology and elements characteristics on mechanical property in T-joints during dual laser-beam bilateral synchronous welding of 2060/2099 Al-Li alloys

The 2 mm thick 2060-T8/2099-T83 Al-Li alloy T-joints were welded by dual laser-beam bilateral synchronous welding (DLBSW) with ER4047 filler wire. The metallurgical porosity defects under different welding parameters were investigated to study the influence of laser power and weld speed on the porosity distribution, formation mechanism and mechanical properties during DLBSW process. In order to explore the special effect of welding heat input on the difference of alloying elements content around porosity, a comparative analysis of elements content between the porosity boundary and matrix around porosity was studied. It was found that the weld porosity defects were increased significantly as the laser power increased. Besides, the heat affected zone (HAZ) and branches of dendritic crystals were the key positions of porosity nucleation and formation. The results of tensile test and SEMoffailuresurface demonstrated that porosity was one of the important factors leading to weld bead failure. In particular, the porosity in the bottom fusion zone and EQZ significantly weakened the performance of the T-joint.

The cryogenic shear property and fracture mechanism for 2219 aluminum alloy T-joint fabricated by dual laser-beam bilateral synchronous welding

The dual laser-beam bilateral synchronous welding (DLBSW) experiment with self-melting process of prefabricated bosses in the 2219 aluminum alloy T-structure, consisted of skin and stringer components, was performed. The analyses of cryogenic shear strength at −182 °C, fracture morphology and element distribution were carried out to investigate the influence of different weld structure with prefabricated bosses on cryogenic shear performance. For the T-joint with prefabricated bosses on skin, the shear crack was extended from the bottom fusion line (FL) to the skin in the bottom of weld seam (WS). For the T-joint with prefabricated bosses on stringer, the shear fracture was located at equiaxed dendrites zone near the upper FL. It was indicated that the T-joint with prefabricated bosses on skin obtained higher cryogenic shear strength, 48.4% of base metal.

Effect of Grain Size on Mechanical Properties of Double Laser-Beam Bilateral Synchronous Welding Joint

Effect of Grain Size on Mechanical Properties of Double Laser-Beam Bilateral Synchronous Welding Joint

Influence of Laser Power on Fracture Properties of TC4 Titanium Alloy T-Joint Manufactured Using Dual-Laser-Beam Bilateral Synchronous Welding

Influence of Laser Power on Fracture Properties of TC4 Titanium Alloy T-Joint Manufactured Using Dual-Laser-Beam Bilateral Synchronous Welding

Study on keyhole coupling and melt flow dynamic behaviors simulation of 2219 aluminum alloy T-joint during the dual laser beam bilateral synchronous welding

In this research, the keyhole coupling and melt flow behaviors of 2219 aluminum alloy T-joint during dual laser beam bilateral synchronous welding (DLBSW) process are investigated by simulation, which involves fluid heat transfer and fluid flow. The calculated mesh model of the T-joint is established by simplifying the equal boss of the skin. The combined Gaussian laser heat source is adopted to simulate the laser energy loaded on the base metal during the welding process. The obtained simulation results are reliably matched with the experimental results. Subsequently, not only the coupling process of two keyholes and the evolution characteristics of the coupled keyhole are analyzed, but also the characteristics of molten pool and the flow behaviors of the liquid metal are studied in detail. The results demonstrate that the keyhole profile’s oscillations continuously exist, whether before or after the keyhole coupling. The flow direction of the liquid metal near the coupled keyhole wall includes the flow parallel to the keyhole wall and that around the keyhole wall. Besides, the maximum depth of the molten pool slightly lags behind the rear wall of the keyhole. On the coupled keyhole wall and molten pool surface, the melt flow velocities are significantly greater than that inside the molten pool. The vortexes are produced near the upper and lower regions of the coupled keyhole wall.

Effect of temperature alternating load on stripping performance of Al-Li alloy T-joint manufactured by dual laser beam bilateral synchronous welding

In this work, the temperature alternating load (TAL) with four cycles is performed to the 5A90 Al-Li alloy T-joint produced by dual laser beam bilateral synchronous welding (DLBSW). The grain details, stripping strength, fracture micro-morphology and elemental composition of the samples are analyzed by optical microscope, self-designed specific fixture, scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS), respectively. The experiment results indicate that the TAL treatment has a slight decrease on the width of non-dendritic equiaxed zone (EQZ) near the fusion line. The average striping strength and post-break elongation of the TAL treated samples are separately 126.01 MPa and 3.60%, which are both reduced compared with the values 145.61 MPa and 5.54% of the untreated samples. Meanwhile, the results of fracture micro-morphology and elemental composition are utilized to investigate the decline of the tensile performance of the T-joint with the TAL treatment. It is found that the fracture features such as tear layers, shear dimples and torn pores are relatively insignificant compared to the T-joint without the TAL treatment. The non-uniformity of element distribution exists in the TAL treated and untreated sample.

Study on 2219 Al-Cu alloy T-joint used dual laser beam bilateral synchronous welding: Parameters optimization based on the simulation of temperature field and residual stress

In the current research, the dual laser beam bilateral synchronous welding (DLBSW) of 2219 Al-Cu alloy T-joint is investigated by finite element (FE) simulation of temperature field and residual stress, which aims at the optimization of the welding process parameters. The FE mesh model of the T-joint is established by simplifying the equal boss of the skin. The combined Gaussian laser heat source is adopted to simulate the laser energy loaded on the Al-Cu alloy during welding process. Furthermore, a test table of process parameters with the laser power and welding speed is designed to investigate the parameters via the simulation results. The simulation with 16 groups of parameters are performed based on the heat source model which is checked by the experimental result. Two cases of parameters are filtered from the simulation results for the hoop tensile test experiment. It is employed to estimate the tensile and yield strength of the T-joints with the filtered parameters. Welding process parameters in case 6, which are the laser power of 4300 W and welding speed of 2.5 m/min, are the optimized parameters in the test table based on the tensile strength (337.28 MPa) and yield strength (243.51 MPa) obtained by the tensile test results.

Study on the shear performance and fracture mechanism of T-joints for 2219 aluminum alloy by dual laser-beam bilateral synchronous welding

Double laser-beam bilateral synchronous welding (DLBSW) of T-joints for aluminum alloy is an advancing technology, which is significant for the aerospace panel structures in the lightweight and efficient manufacturing. In this paper, the DLBSW technology is employed in the 2219 aluminum alloy T-joint with skin and stringer. It is notable that the skin component accompanied with two bosses is designed to replace the welding wire. The influences of the microstructure, defects, and stresses distribution on the shear performance of the T-joints are investigated. It is found that the T-joint owns fewer defect and higher shear performance at a weld speed of 1.3 m/min than at the weld speed of 4.0 m/min. Although the tensile strength of the T-pull tests is superior, the shear strength of the shear tests is only about 40% of base metal (BM). Besides, the dynamic shear process of welded joint based on finite element (FE) model of laser welding process for 2219 aluminum alloy is simulated. It is indicated that the weld toe is the stress concentration zone under the shear load. The shear failure propagates direction is from the highest stress node to the lowest stress node. According to the analyzation of both experiment and simulation results, it is concluded that the formation of EQZ and high stress together contribute to the origin of shear fracture.

Effect of welding direction on deformation of Ti6Al4V alloy coplanar double lap-joint produced by dual laser beam bilateral synchronous welding

The coplanar double lap-joint is the weld type mainly used for the connection of skin and stringer. The welding deformation in the component will reduce fabrication accuracy and bearing capacity and the excessive welding deformation can even render the product unusable. In the present work, a thermal-elastic-plastic finite element model is developed to investigate the characteristics of welding deformation in the coplanar double lap-joint. The experiment is carried out to verify the accuracy of simulated results. The results of the simulation shows a good agreement with the experimental measurements. The influence of welding direction on welding deformation is studied by finite element analysis. Moreover the mechanism of deformation mode in the coplanar double lap-joint is discussed. The results show that the change of welding direction has different effects on the distribution of residual deformation. Through the analysis of simulation results, the deformation mode of the joint is similar to a concave-convex mode.