Laser-arc Hybrid Welding Process Research Articles

Influence of advanced laser-arc hybrid welding and conventional MIG process on microstructure, mechanical properties and corrosion resistance of dissimilar joints

The purpose of this paper is to study the technological potential advantages and quality of dissimilar metal (austenitic stainless steel and ferritic stainless steel) joint welded by advanced laser-arc hybrid process and compared it with a conventional metal inert gas welding process on key grounds like weld geometry, structure-property co-relationship, in order to encourage its industrial recommendation for this dissimilar metal combination. The characterization was accomplished by using an optical microscopy, scanning electron microscopy and energy dispersive spectrometer. Results indicated the full depth of penetration in both the processes; however, narrower weld bead and absence of heat affected zone achieved with laser-arc hybrid welding. Equiaxed dendritic microstructure comprised of massive acicular ferrite was observed in laser-arc hybrid welding, while, in case of metal inert gas welding process, cellular dendritic microstructure and type-II boundary was examined. Laser-arc hybrid welding showed higher hardness, higher tensile strength and low impact energy due to rapid cooling rate. Magnetic induction method (ferritoscope) revealed higher ferrite content in the laser-arc hybrid welding process. The modified strauss test revealed intergranular corrosion in the ferritic base metal.

Hybrid laser-arc welding of thick-walled ferromagnetic steels with electromagnetic weld pool support

The hybrid laser-arc welding (HLAW) process provides many advantages over laser welding and arc welding alone, such as high welding speed, gap bridgeability, and deep penetration. The developments in hybrid laser-arc welding technology using modern high-power lasers allow single-pass welding of thick materials. This technology can be used for the heavy metal industries such as shipbuilding, power plant fabrication, and line-pipe manufacturing. The obvious problem for single-pass welding is the growth of the hydrostatic pressure with increasing thickness of materials leading to drop-out of molten metal. This phenomenon is aggravated at slow welding velocities because of increasing weld seam width followed by a decrease of Laplace pressure compensating the hydrostatic pressure. Therefore, weld pool support is necessary by welding of thick materials with slow welding velocities. The innovative electromagnetic weld pool support system is contactless and has been used successfully for laser beam welding of aluminum alloys and austenitic and ferromagnetic steels. The support system is based on generating Lorentz forces within the weld pool. These are produced by an oscillating magnetic field orientated perpendicular to the welding direction. The electromagnetic weld pool support facilitates a decrease in the welding speed without a sagging and drop-out of the melt thus eliminating the limitations of weldable material thickness.

Hybrid laser/arc welding of 304L stainless steel tubes, part 2 – Effect of filler wires on microstructure and corrosion behavior

The effect of filler wire used in hybrid laser arc welding (HLAW) of AISI304 corrosion resistant steel (CRS) on microstructural alteration and pitting corrosion resistance were studied, utilizing the scanning electron microscope, X-ray diffraction (XRD), and cyclic potentiodynamic polarization analysis (CPPA). According to the XRD patterns, the dominant phase formed within the fusion zone was γ-austenite coupled with primary δ-ferrite as the minor phase. The calculated amount of δ-ferrite inside the FZ was slightly higher than the amount for the base metal that could be attributed to the higher cooling rate in the weld region. From the microstructural point of view, observation showed that the formation of δ-ferrite dendrite was consistent with the ferrite-austenite solidification mode, predicted by the pseudo-binary diagram. In terms of corrosion resistance, CPPA results revealed that the HLAW process had no negative effect on general corrosion properties of the joint for various filler wires. A316LSi wire generated the weld with the most superior pitting resistance and the smallest hysteresis loop associated with the lowest unstable passive region. This process resulted in the best passivation and re-passivation behavior with respect to the base metal.

Characteristics analysis of droplet transfer in laser-MAG hybrid welding process

The droplet transfer, plasma morphology and droplet morphology of laser arc hybrid welding process are collected and analyzed using high speed camera. The force magnitude and acceleration of motion droplets in the arc space are calculated by the image processing and mathematical calculations. The value and distribution of the recoil force from the metal vapor on droplets are calculated. The results show that the globular transfer mode corresponds to the welding current is approximate 180 A; the streaming transfer mode corresponds to the welding current is approximate 200 A. The laser has a compress effect on the arc, and the compression on the surface of the weld pool is stronger. The acceleration of the droplet detachment from wire is 70 m/s2 and 50 m/s2 for arc welding and laser arc hybrid welding separately. In the actual welding process, the reaction force of metal vapor on molten droplets is very small, when the distance between droplet and keyhole in the surface of the weld pool is 3 mm. The pressure difference on the surface between upper and lower of the droplet is great, which results the droplet coalescence and the transfer frequency slows down.

Finite element analysis of residual stress in hybrid laser-arc welding for butt joint of 12 mm-thick steel plate

As a high-efficiency and high-quality welding process, hybrid laser-arc welding (HLAW) has significant potential of application in welding thick plate. Understanding the features of welding residual stress benefits the optimization of HLAW process. In the present study, based on thermal elastic–plastic theory, a three-dimensional finite element model is developed to predict the residual stress and distortion in HLAW for butt joint of 12-mm-thick steel plate. GMAW heat input and laser energy are modeled as one double-ellipsoid body heat source and one cone body heat source with enhanced peak density along the central axis, respectively. Residual stresses and distortions are calculated for single-pass and multi-pass hybrid welding processes. The results show that the distribution features of longitudinal and von Mises equivalent residual stresses in single-pass hybrid welding are similar to that in multi-pass hybrid welding. A large tensile stress is generated at the weld zone and its vicinity. Compared with GMAW, the zone with high residual stress in hybrid welding is decreased largely, but there is no improvement in peak residual stress. Among three cases, the distortion in single-pass hybrid welding has the lowest value.

Study on the Characteristics and Mechanics of Droplet Transfer in Laser Arc Hybrid Welding Process

Study on the Characteristics and Mechanics of Droplet Transfer in Laser Arc Hybrid Welding Process

Study of gap and misalignment tolerances at hybrid laser arc welding of thick-walled steel with electromagnetic weld pool support system

The hybrid laser arc welding (HLAW) process provides many advantages such as improved gap bridgeability, deep penetration and misalignment of edges, that is why the process is used increasingly in industrial applications e.g. shipbuilding, power plant industry and line-pipe manufacturing. The obvious encountered problem for single pass welding in flat position is the gravity drop-out at low welding velocities. With the usage of an electromagnetic weld pool support system, which is based on generating Lorentz forces within the weld pool, wide seams followed by reduced welding velocities could be achieved in this study leading to the realization of a gap bridgeability up to 1 mm, misalignment of edges up to 2 mm and a single pass weld up to 28 mm thickness with a 20-kW fibre laser. These developments expand the boundaries of the HLAW process for different industrial applications. As a result, less accurate preparation of the edges would be sufficient, which saves time for manufacturing.

Improving weld bead homogeneity in short arc GMAW processes applying low power diode lasers

Using laser and arc power in equal parts, laser-arc hybrid welding processes are successfully adapted by the industry. This paper shows the stabilizing effects of diode lasers on short arc GMAW (gas metal arc welding) which deliver just a fraction of the supplied arc power. In a comprehensive comparison the stabilized and the sole GMAW processes are confronted and differences regarding process behavior and weld bead properties are pointed out. The tests were carried out with DC01 (1.0330) plates of 1 mm thickness deploying lasers using a mean laser intensity of 1,1 x104 W/cm². Adding this low amount of intensity provides stability to the weld process and results in weld beads of higher homogeneity. The process behavior is characterized by the transient current and voltage curves which are analyzed in regards to consistency and uniformity. Metallographic analysis is employed to compare the weld bead dimensions at different energy ratios.

Effect of Laser-arc Hybrid Welding Energy Parameters on Welding Stability

The high-speed camera was used to collect the droplet transfer pattern and arc pattern of the laser-arc hybrid welding process. Using the methods of image processing and mathematical statistics, the effects of different laser and arc power conditions on the welding stability were studied. The results show that the melting width depends on the welding current, the depth of penetration depends on the laser power, the droplet transition pattern, the actual filament spacing and the arc length determine the welding stability of the laser arc hybrid welding.

Effect of the welding direction on the microstructural characterization in fiber laser-GMAW hybrid welding of 5083 aluminum alloy

Thick plates of 5083 aluminum alloy are welded with double-side hybrid welding method, and the effects of different heat source positioning arrangement on porosity formation, microstructure and mechanical property of the welding joints are studied. The results show that relative stable arc and stable process can be obtained in laser-arc hybrid welding (LAHW) process, and the weld bead with lower porosity level can be achieved. Fewer air involved in the weld pool, better stability of the keyhole and the easier escape of bubbles from the weld pool are the three ways to suppress the porosity. In both arc-laser hybrid welding (ALHW) and LAHW processes, the columnar grains are found in the fusion boundary, while equiaxed grains are observed in the weld center. In LAHW process, although the grain size is larger, the strength of the joint is higher, which is attributed to less porosity formation, the slight loss of Mg, more second-phase particles with uniform distribution, and the formation of dislocation with higher density in the joints.

Hybrid laser/arc welding of thick high-strength steel in different configurations

In this investigation, hybrid laser/arc welding (HLAW) was employed to join 8-mm-thick high-strength quenched and tempered steel (HSQTS) plates in the butt- and T-joint configurations. The influences of welding parameters, such as laser power, welding speed, stand-off distance (SD) between the arc of gas metal arc welding, and the laser heat source on the weld quality and mechanical properties of joints, were studied to obtain non-porous and crack-free fully-penetrated welds. The weld microstructure, cross-section, and mechanical properties were evaluated by an optical microscope, and microhardness and tensile tests. In addition, a finite element model was developed to investigate the thermal history and molten pool geometry of the HLAW process to join the HSQTS. The numerical study demonstrated that the SD had a paramount role in good synergy between the heat sources and the stability of the keyhole. For the butt-joint configuration, the results showed that, at a higher welding speed (35 mm/s) and optimum SD between the arc and laser, a fully-penetrated sound weld could be achieved. A non-porous weld in the T-joint configuration was obtained at a lower welding speed (10 mm/s). Microstructural evaluations indicated that the formation of residual austenite and the continuous network of martensitic structure along the grain boundary through the heat affected zone were the primary reasons of the softening behavior of this area. This was confirmed by the sharp hardness reduction and failure behavior of the tensile coupons in this area.

Hybrid Laser-Arc Welding of the High-Strength Shipbuilding Steels: Equipment and Technology

Hybrid laser-arc welding (HLAW) allows getting weld joints with thickness up to 35mm for one pass, provide good quality formation of joints, minimal thermal deformations, the productivity in 10 times more in comparison with arc welding. In addition, replacement arc welding to the HLAW allows economizing filler materials, shielding gas and consumable electricity more than 4 times. Therefore, HLAW is actually technology for basic engineering branches and especially for shipbuilding. The Institute of Laser and Welding Technologies (ILWT) developed laser and hybrid laser-arc welding technologies for different type of steels and alloys including high-strength shipbuilding steels. Also ILWT produced portal and robotic systems for HLAW process realization. Portal system for hybrid laser-arc welding of panels with dimensions 6x6 m using at the manufacturing of flat curvilinear sections in the shipbuilding is depicted in the article. Results of experimental researches of the hybrid laser-arc welding parameters influence on the formation and mechanical properties of weld joint are described at the publication also. Experimental part was made with using of the portal system.

Numerical study of the effect of laser-arc distance on laser energy coupling in pulsed Nd: YAG laser/TIG hybrid welding

A three-dimensional (3-d) computational fluid dynamics (CFD) based model in which a ray-tracing algorithm was combined with the volume of fluid (VOF) method was used to simulate a pulsed Nd: YAG laser /tungsten inert gas (TIG) hybrid welding process. The calculated weld cross sections in pure laser welding and hybrid welding process were validated by the experimental results, respectively. Then, the variations of keyhole shape and laser energy coupling behaviour in the laser-arc hybrid welding process were calculated at three different laser-arc distances. It was found that the laser-arc distance would affected the shape of keyhole generated in the laser-arc hybrid welding process, thus influencing the laser energy coupling efficiency. In the initial stage of each laser pulse, small laser-arc distances favoured the generation of keyholes and multiple reflections of laser beam within keyhole. However, as the laser irradiation time increased, the smaller the laser-arc distance, the more liquid metal were found around the keyholes, which was more favourable to the expansion of keyhole in radial direction. As a result, the aspect ratio of keyhole, the reflection time of laser beams in keyhole, and the laser energy absorbed by keyhole wall decreased. Given that the interaction between laser and arc was neglected, the maximum keyhole depth increased with reducing laser-arc distances, while the total laser energy coupling efficiency decreased as the laser-arc distance was reduced.

The effect of welding direction in CO2 LASER - MIG hybrid welding of mild steel plates

In this paper, hybrid laser-arc welding process has been studied based on the relative position of the laser and the arc (i.e. laser-leading and arc-leading arrangement) and, the effects of welding parameters, such as the laser power, arc current, arc voltage and the welding speed on the weld bead were investigated. The study indicates that the welding direction has a significant effect on the weld bead and weld pool behaviour. The result shows that laserleading configuration shows better bead characteristics when compared to arc-leading configuration. This is because in the laser-leading case molten metal flow is inward, while in the arc-leading case the metal flow is outward leading to variation in solidification front resulting in lack of synergic effects of both processes.

A study of droplet transfer behavior in ultra-narrow gap laser arc hybrid welding

Laser arc hybrid welding became a useful method to weld thick plates. But a sound weld is not so easy to obtain because of the uncontrollability of droplet transfer state, especially in ultra-narrow gap welding process. In this study, V-like ultra-narrow gap welds were carried out using 80 % Ar + 20 % CO2 blend as shielding gas. A high-speed video system was used to observe the droplet transfer behaviors. The results showed that the transfer mode did not change with the same welding current. The transfer mode changed from the short circuiting transfer to the mixture of the short circuiting and the globular transfer and then to spray transfer as the welding current increased. The relationship between the droplet transfer process and the welded defects was studied to obtain high-quality weld joint with a stable transfer process. The optimal parameter window between welding current and groove size was found. Only when the welding current was 200 to 270 A and groove gap was 2 to 3 mm, can a good welded joint be got. Finally, 30-mm-thick plate with 5.49-mm maximum groove gap was welded well by one pass laser autogenous welding and seven passes laser arc hybrid welding process.

Analysis of influence of initial gap of laser-arc hybrid butt welds on inherent strain and welding deformation of a pipe structure

Although the laser-arc hybrid welding process has the advantages of smaller deformation and wide freedoms using different energy ratios, some initial dimension errors such as initial gap or initial mismatch before welding assembly have a significant influence on the final shape of welded structures. In this paper, a thermal elastic-plastic finite element model was developed to investigate the temperature fields and plastic strains in butt joints of steel plates with three different initial gaps (0.2 mm, 0.5 mm, and 1.0 mm). Four inherent deformation parameters, longitudinal inherent shrinkage, transverse inherent shrinkage, longitudinal inherent bending, and transverse inherent bending, were calculated and compared with different initial gaps. Finally, welding deformation in a steel pipe structure with five weld lines was predicted by the inherent strain theory.

Application of Taguchi Approach to Optimize Laser-Arc Hybrid Welding Parameters of Galvanized Steel

This study aims to establish the weld quality of the Nd:YAG laser-MIG hybrid welding on galvanized steel (SGACC60). In order to do so, the Taguchi analysis optimized the laser-arc hybrid welding process for SGACC60 by varying four parameters: welding speed, welding current, laser-arc distance and shielding gas. The experiment produced 18 combinations of these four essential welding parameters, which were estimated in terms of ultimate tensile strength, welding depth and width ratio, and hardness. The optimum result exhibited that the tensile strength of welds was approximately 101% of that of the base metal, and that their hardness was within the acceptable range (the maximum value 350 Hv).

Effect of welding parameters and the heat input on weld bead profile of laser welded T-joint in structural steel

The high power fiber laser has become one of the most efficient energy sources for deep penetration welding processes used in heavy manufacturing and marine industries. Combinations of cost-efficient, easily automatable process together with fairly mobile and flexible welding equipment have raised high expectations for improved quality and economic feasibility. In this study, the fillet welding of a low alloyed structural steel was studied using a 10 kW fiber laser. Plates of 8 mm thick AH36 were welded as a T-joint configuration in flat (1F) and horizontal (2F) positions using either an autogenous laser welding or a hybrid laser arc welding process. The effect of heat input on the weld bead geometry was investigated using one variable at a time approach. The impact of single process parameter such as laser power of 4.5–6 kW, welding speed of 0.5–2.5 m/min, beam inclination angle of 6°–15°, focal point position of −2 to +2 mm, and welding positions of 1F and 2F were studied. All welds were visually evaluated for weld imperfections described in EN ISO 13919-1 standard. Penetration depth, geometries of the fusion and heat affected zones, and hardness profiles were measured. Produced joints have a high depth to width ratio and a small heat affected zone; full penetration welds with acceptable weld quality on both sides of the joint were produced. The parameter configurations for optimizing the welding processes are proposed.

Effect of Cut Quality on Hybrid Laser Arc Welding of Thick Section Steels

From an industrial point of view, in a laser cutting-welding production chain, it is of great importance to know the influence of the attainable laser cut quality on the subsequent hybrid laser arc welding process. Many studies have been carried out in the literature to obtain lower surface roughness values on the laser cut edge. However, in practice, the cost and reliability of the cutting process is crucial and it does not always comply with obtaining the highest surface quality. In this study, a number of experiments on 25mm steel plates were carried out to evaluate the influence of cut surface quality on the final quality of the subsequent hybrid laser welded joints. The different cut surfaces were obtained by different industrial cutting methods including laser cutting, abrasive water cutting, plasma cutting, and milling. It was found that the mentioned cutting methods could be used as preparation processes for the subsequent hybrid laser arc welding. However, cut quality could determine the choice of process parameters of the following hybrid laser arc welding.

Arc characteristics and metal transfer process of hybrid laser double GMA welding

Hybrid laser gas metal arc (GMA) welding can provide higher productivity than either autogenous laser welding or GMA welding alone. In order to further enhance the welding efficiency of the hybrid laser arc welding process, a novel triple-heat-source welding system entitled hybrid laser double GMA welding was proposed in this study. This hybrid welding system was established based on a double GMA welding and laser welding system. During the hybrid welding process, two consumable electrodes kept alternative arcing at relatively low welding current while they changed to arc synchronically at relatively high welding current. This research is mainly focused on the mechanism of the alternative arcing phenomena and the influences of wire feed speed and laser beam on the arc alternating process. It was found that the arcing period decreased with the increase of wire feed speed which was positively correlated with the welding current. The arcing period also decreased with the introduction of the laser beam into the arc welding system. The arcing period can be decreased as short as possible until it was equal to the pulse period of the welding power source. Based on the analysis of the driving forces acting within the molten weld pool, it can be inferred that the hybrid laser double GMA welding process could be in favor of homogeneous alloying elements distribution and weld metal microstructure.