laser-GMA Hybrid Welding Research Articles

Direction-independent laser-GMA hybrid welding with coaxial wire feed and annular beam

Conventional laser gas metal arc hybrid welding (LB-GMA hybrid welding) is used as an efficient joining process in several high-tech steel processing production facilities. However, the use of the LB-GMA hybrid welding is often limited to the joining of linear weld seams as the welding process has a preferred welding direction due to lateral positioning of the laser beam and welding wire electrode. Reorienting the welding direction, therefore, often results in weld defects since changing the welding direction also requires a geometric manipulation of the GMA torch in relation to the laser beam optics. This means a considerable additional effort that is necessary if this efficient welding process is to be used for geometrically complex weld seam contours. Furthermore, the conventional LB-GMA hybrid welding process has a high adjustment complexity. Within this work, a direction-independent laser GMA hybrid welding head with an annular beam and coaxial wire feed is used. The annular laser beam with homogenous intensity profile is formed by a special processing head, split and reassembled around the coaxial wire. Due to the coaxial arrangement of the wire electrode to the annular beam, the hybrid process is in theory direction independent. As a result, there should not be any irregularities in the weld seam, when the welding direction is changed. The annular beam considerably reduces the complexity of adjustment and improves reproducibility. The focus of this work is to qualify the process for joining geometrically complex weld contours and to investigate possible advantages of the directional independence of the coaxial LB-GMA hybrid welding process. For this purpose, fillet welds in lap joint configuration with a sheet thickness of 2 mm each at different weld contours (different direction changes, corners, radii) are discussed. By performing a DoE-based sensitivity analysis, influencing factors on the quality of the generated weld are analysed.

Investigation of weld formation and porosity in 5052 aluminium alloy laser-GMA hybrid welding assisted by magnetic field with different orientations

Steady magnetic field with both orientations including longitudinal magnetic field (LMF) and transverse magnetic field (TMF) was used. The influence of LMF and TMF on weld formation, porosity and mechanical property of 5052 aluminium alloy laser-gas metal arc (GMA) hybrid welding was investigated. The shielding effect of hybrid plasmas on laser energy was weakened by TMF, leading to an increase in weld depth under TMF. Porosity rate was significantly reduced to 2.61% under TMF, because keyhole stability was improved, escaping channels for bubbles were increased, and solidification time of molten pool was prolonged. As a result, the highest tensile strength (174.7 MPa) of hybrid weld was obtained at TMF, owing to the lowest porosity rate.

Numerical analysis of heat transfer and fluid flow characteristics and their influence on bead defects formation in oscillating laser-GMA hybrid welding of lap joints

In this study, the accuracy of the model developed for oscillating laser-GMA hybrid welding has been improved by integrating more experimentally measured parameters, such as the droplet velocity, transient arc power, and fusion area on sheets at the transverse cross-section. The effects of lateral distance of hybrid heat source relative to the top sheet edge on heat transfer and fluid flow in weld pool are numerically simulated. It is found that with more offset of the hybrid heat source to the top sheet, a larger depression and stronger lateral flow occur in weld pool, which leads to a delayed and weak backwards flow. These characteristics of heat transfer and fluid flow play a great role in the formation of weld bead defects of lap joint configuration, such as irregularity, discontinuity, lack of fusion at the top sheet. Compared to the experimental investigation, the numerical simulation provides not only quantitative description of the occurrence of those weld bead defects but also a deep physical insight into the whole process. Thus, it is useful for the parameter optimizations and further applications of this hybrid welding process.

Effects of process parameters on weld bead defects in oscillating laser-GMA hybrid welding of lap joints

The oscillating laser-GMA hybrid welding tests with lap joint configuration were conducted to observe the behaviour of welding arc, metal transfer and weld pool. Temperature distribution in the resultant lap joint was monitored. Based on the observations and the resultant morphology and geometry of weld bead, effects of three important process parameters, i.e. welding speed, laser beam oscillation and lateral distance of hybrid heat source relative to top sheet edge (LDHS), on the weld bead defects were examined. Consequently, occurrence mechanisms of the weld defects were proposed. LDHS influenced the defects such as non-uniform weld bead width, discontinuity and lack of fusion at top sheet, whilst the undercutting defect occurred at the top sheet if welding speed exceeded 6 m min−1. The laser beam oscillation could disperse the high concentrated power density of single-mode laser to avoid deep penetration channel through bottom sheet, but had little effect on the weld geometry.

Numerical simulation of temperature field, fluid flow and weld bead formation in oscillating single mode laser-GMA hybrid welding

A three dimensional numerical model of oscillating single mode laser-GMA hybrid welding process with lap joint and arc inclination configuration has been developed for the first time. The model is used to investigate the temperature field and fluid flow corresponding to the aforesaid welding process and weld configuration. An asymmetric distribution of arc heat and a cylindrical volumetric distribution of laser heat are established to describe the heat transfer from the combined heat source to the workpieces. The droplet with predefined temperature and velocity is impinged on the weld pool at a given fillet weld angle. Arc pressure, electromagnetic force, Marangoni force and buoyancy are also considered in the model with some modifications with respect to the lap joint and arc inclination configuration. Results show that the droplet impingement process has a significant influence on the weld geometry, temperature field and fluid flow pattern due to the transfer of mass, energy and momentum into the weld pool. These unique temperature fields and flow patterns are characteristic to the lap joint and arc inclination configuration. The proposed model exhibits close correspondence with the experimental results with respect to weld geometry.

Fatigue strength of hybrid welded 22MnB5 overlap joints

Abstract In order to reduce the weight of automotive parts, lightweight materials like the press hardened AlSi coated high strength steel 22MnB5 is used. This steel enables a reduction of wall thicknesses and simultaneously ensures a high stiffness of the part, e. g., the B pillar. The usage of these steels requires suitable joining technologies. Therefore, a laser GMA hybrid welding process for fillet welds in overlap configuration was designed. This process provides high welding velocities and process tolerances against gaps and misalignments. In this case a single-mode fiber laser was used in order to reduce the thermal impact. Due to the fact that the laser focus spot has only a small diameter of 25 µm, a beam oscillation was used in order to distribute the laser energy over the melt pool width. This paper is focused on the cyclic load tests which were carried out and analyzed by the staircase method. The influences of laser power and oscillation width are dominating, whereas welding velocity and wire velocity have only a minor influence. By analyzing the failure location and crack propagation of specimens after the cyclic load test, the influence of the AlSi coating can be determined. Coating agglomerations at the fusion line of the melt pool are origins of crack initiation. This is attributed to the formation of brittle intermetallic phases.

Effect of the welding process and filler material on the fatigue behavior of 960 MPa structural steel at a butt joint configuration

Ultrahigh-strength steels are being used more and more frequently in the engineering industry. Normally, the welding of these steels is more demanding. The welding requires a controlled heating and cooling rate. In this study, the S-N curves were determined for the laser, the laser-gas metal arc hybrid (Laser-GMA hybrid welding, LHW) and the gas metal arc welding (GMAW) welded joints according to the recommendations of the International Institute of Welding (IIW) by using a constant amplitude loading and a stress ratio of R = 0.1. The frequency of loading varied between 4 and 10 Hz. The tested material was direct quenched steel with a yield strength of 960MPa and a thickness of 6 mm. The total amount of tested specimens was 51. The fatigue test results have proven to be close to the IIW recommendations and the differences between various welding processes were minor. Instead of welding process or filler material, the main factor influencing the fatigue behavior was the geometry of the weld. Consequently, the proper welding parameters should be applied in every welding process in order to achieve a smooth joint geometry and, thus, a high fatigue resistance.

Hybrid welding with fiber laser and CO2 gas shielded arc

Argon-rich shielding gas was replaced by 100% CO2 gas for cost reduction in fiber laser-GMA hybrid welding of double-side welded T-joints. The welding process using 100% CO2 gas was characterized by a large number of spatters, while the penetration depth of a weld was increased and porosity was reduced. With the objective of obtaining a buried-arc transfer for the reduction of spatter formation, the welding parameters were optimized by observation with a high-speed video camera. Reduced arc voltage, arc leading arrangement and shortened wire extension were necessary to achieve a buried-arc transfer. A significant reduction in spatter generation could only be obtained by the procedure that the relative distances between the two heat sources in the X and Y directions were controlled to produce a proper profile of the arc cavity that could trap any spatters generated. A regulating action of a keyhole was observed to remove the disturbances in the melt flows caused by the arc short-circuiting, and high quality joints with good appearances and very few spatters could be produced.

Laser-GMA hybrid welding of API 5L X70 with 23 mm plate thickness using 16 kW disk laser and two GMA welding power sources

Hybrid processes have been established for the joining of thick plates. The presented approach enables single side welding of thick metal plates by combining a laser beam and two gas metal arc (GMA) welding torches in one setup. By using this hybrid process for joining high material thicknesses, manufacturing time can be significantly reduced in comparison to conventional multilayer arc welding processes. Additionally, new joint designs can be used to reduce filler metal consumption. In order to benefit from these economic advantages, and to make use of brilliant high power lasers in pipeline manufacturing, this hybrid process needs to run robustly for common gap and tolerance ranges. The process time, compared to conventional methods, will be significantly decreased, due to the use of disk lasers with a maximum output power of 16 kW combined with two high power GMA subprocesses. For process development, American Petroleum Institute (API) 5L X70 pipeline steel plates with a thickness of 23 mm have already been joined in a flat position using a single weld pass. Based on these parameter studies, the process limitations have been determined with regard to energy input, gap bridgeability, vertical edge offset, and a lateral offset of the energy sources from the weld joint. The robustness of the hybrid process developed has been demonstrated in experiments representative of the pipeline application.

Investigations of properties in hybrid welds at 40-mm sheet thickness

Laser gas metal arc hybrid welding (laser-GMA hybrid welding) offers capabilities for improving the economy of welding in comparison to conventional welding processes due to characteristics concerning material and seam design. Research into this process was restricted to a sheet thickness range of between 6 and 12 mm for steel. However, for steel, container, vehicle or ship engineering in particular, structures (components) with large wall thicknesses are of special interest. These structures are currently welded by using the submerged arc welding process, which requires a high input of energy, welding material and working time. The objective of this project was to determine the influence of the reduction of the weld volume and energy per unit length of weld on the formation of residual stresses and their effects on the fatigue strength of hybrid welded sheets with large wall thicknesses. As a result, better qualities with regard to fatigue strength and toughness have been achieved for hybrid welded joints in comparison to submerged arc-welded joints for wall thicknesses of 40 mm.

Solidification cracking in laser GMA hybrid welding of thick-walled parts

Laser GMA hybrid welds, producing partial penetration, were conducted on stiff tubes made of S460NH. Experiments, using a design-of-experiments plan were conducted to examine the influence of the welding parameters on the occurrence of solidification cracks. Results say that cracks diminish, when high levels of arc power are applied, while their number increases with rising laser beam power. The weld velocity had no measurable impact.

Prevention of porosity by oxygen addition in fibre laser and fibre laser–GMA hybrid welding

Prevention of porosity in partial penetration fibre laser and fibre laser–gas metal arc hybrid welding is investigated. It is found that modulation of laser power prevents porosity formation in fibre laser welding, but that this method is not effective in hybrid welding. However, the addition of a small amount of oxygen to the molten pool can prevent porosity formation in both fibre laser and hybrid welding. This is attributed to stabilisation of the keyhole. During welding, oxygen reacts with dissolved carbon to form carbon monoxide (CO) in the keyhole. The CO partial pressure in the keyhole prevents the intense interaction between laser beam and molten metal, thus stabilising the keyhole. The role of CO formation is confirmed by the enhancement of porosity suppression with increased carbon content of the base metal.

Gap Bridging Ability in Laser GMA Hybrid Welding of Thin 22MnB5 Sheets

In this paper, laser GMA hybrid welding of thin ultra-high-strength steel sheets (22MnB5) is investigated. A single-mode laser beam oscillating transversal to the welding direction is used in order to minimize the heat input during the process. The sheets have a thickness of 1.5mm each and are fixed in overlap configuration. The gap between the sheets was 0.8mm during experiments in order to simulate typical gap width in industrial manufacturing processes. It is shown that a stable weld seam has been achieved for this gap width in case of a welding speed of 6m/min. The gap bridging ability is caused by the interaction of the arc and the laser beam process. The laser beam process produces deeper penetration in the bottom sheet. Thus, the arc is stabilized by the laser beam.

30CrMnSi激光-GMA复合焊接工艺参数对焊缝成形的影响

30CrMnSi激光-GMA复合焊接工艺参数对焊缝成形的影响

30CrMnSi激光-GMA复合焊接工艺参数对焊缝成形的影响

30CrMnSi激光-GMA复合焊接工艺参数对焊缝成形的影响

Specific properties of ferritic/austenitic Dissimilar Metals Welded Joints

This paper addresses several peculiar properties of ferritic/austenitic welded joints (Black and White Joints-BWJ) of thin sheets, which are emerging nowadays due to cost saving and satisfactory service performance. Starting from 3D thermal field modelling approached by considering Goldak’s double ellipsoidal heat source, together with a contribution of the authors, a 2D FEM-based model was used for arc welding of low carbon steel (CS) and stainless steel (SS) of thin sheets (3 mm). Conclusion helped to conduct experiments of BWJ arc welding (MMA and TIG), and laser-GMA hybrid welding, whilst infrared thermographic measurements were compared with the FEM results. Besides microstructural examination and mechanical characterization (hardness and tensile), fracture toughness and stress corrosion tests were performed on the BWJ laser hybrid welded. Whilst the model has offered important qualitative information about the asymmetric thermal field and the heat apportionment on the molten metal pool formation, the experiments have shown inadequate microstructures and constitutions of the welds for MMA and TIG welding, with respect to laser-GMAW hybrid joints. The description of the experimental program focused on B&W laser-GMA hybrid welding of thin plates aiming a characterization procedure using fracture mechanics methods is briefly presented.

Influence of oxygen on weld geometry in fibre laser and fibre laser–GMA hybrid welding

The effect of oxygen on weld geometry during keyhole mode welding has been investigated by adding a small amount of oxygen to the shielding gas during fibre laser and fibre laser–gas metal arc hybrid welding. The results indicate that the penetration depth increases and the weld width decreases with increasing oxygen concentration. This effect is attributed to the formation of a deeper keyhole when oxygen is present. The addition of sulphur up to 1500 ppm in the molten pool has no significant effect on the penetration depth. This behaviour indicates that the Marangoni convection and surface tension are not the main reasons for the deeper weld penetration when oxygen is added to the shielding gas. The increase in the penetration depth owing to oxygen addition is consistent with the formation of CO by reaction between dissolved carbon and oxygen. Rapid generation of CO in the keyhole expands the keyhole and results in deeper weld penetration.

Single-Pass Laser-Gma Hybrid Welding of 13.5 mm thick duplex stainless steel

Single-pass solid-state laser welding of plates in the thickness range of 10 to 20 mm became possible with the invention of the fibre laser. This new technique provides excellent beam quality at powers as high as 20 kW or more, and has proved applicable in several industrial applications. By replacing conventional methods with the fibre laser, it is possible to avoid multiple-pass welding that requires time-consuming bevelling. The high energy density of the fibre laser beam also reduces the heat input and consequently the distortion. However, the rapid solidification and cooling associated with laser welding can cause imbalance of the microstructure of duplex stainless steel weldments, where excessively high ferrite contents may reduce the corrosion resistance and the ductility of the material. The solution is normally to add nickel-based filler wire and to increase the heat input. By using a hybrid welding process where the laser beam and the gas metal arc (GMA) process act in a common process zone, filler metal can be added to the molten pool at higher heat input and at the same time, higher welding speed and deeper penetration can be achieved. In this work, 13.5 mm thick 2205 (EN 1.4462, UNS S31803) was fibre laser-GMA hybrid welded in a single-pass using 14 kW of laser power and ISO 22 9 3 N L as filler wire for the GMA process. The resulting welds were free from defects, with smooth surfaces and full penetration. The investigation examines the weld metal microstructure and the effect on corrosion resistance and mechanical properties. The option to add nickel foil, when hybrid welding, was also investigated, as comparison, and the effect on austenite formation was evaluated.

Effect of laser and laser hybrid welding on the corrosion performance of a lean duplex stainless steel

The use of duplex stainless steel increases steadily worldwide and the fluctuations in nickel price the recent years have contributed to further growth. The lean duplex grade Outokumpu LDX 2101® (EN 1.4162, UNS S32101) has a low nickel content and is alloyed with nitrogen and manganese to give a balanced microstructure. It means that good austenite formation is obtained even when laser welding autogenously (without filler). This is in contrast to most other duplex grades, for which laser welding is normally associated with high ferrite fractions, known to reduce the ductility and corrosion performance. Nd:YAG, CO2 and fiber laser welding of LDX 2101® has been performed with and without filler wire and as laser hybrid welding with gas tungsten arc (GTA) and gas metal arc (GMA). The microstructure was evaluated and related to the corrosion performance, and the mechanical properties are presented. The austenite formation in autogenously laser welded LDX 2101® is not sufficient to completely avoid chromium nitride precipitation and the weld metal pitting resistance is consequently affected. This is particularly seen when fiber laser welding. The mechanical properties of all welds were on a similar level with those of the base metal, while the corrosion performance and ductility were marginally to significantly lower. Use of filler wire when Nd:YAG laser welding and Nd:YAG laser-GTA hybrid welding with and without filler wire, and nitrogen additions to the GTA shielding gas improved the austenite formation and hence the pitting resistance. CO2 laser and CO2 laser-GMA hybrid welding proved to result in most austenite and generally showed the highest pitting resistance of all laser welds.

Numerical study of alloying element distribution in CO 2 laser–GMA hybrid welding

This article addresses the physical assumptions and mathematical models required to precisely predict molten metal flow in CO 2 laser–GMA hybrid welding and assesses that welding phenomena can be explained by the consequent simulation results. To this end, three-dimensional transient simulations of CO 2 laser–GMA hybrid welding for the laser trailing the arc are conducted by combining the arc welding model and the laser welding model without any interactive effect between the two. Additionally, based on the hypothesis that fluid flow inside a molten pool might affect the alloying element distributions, an additional conservation equation is newly suggested and united with the aforementioned models to examine the hypothesis and the validity of the models. It is found that similar fusion zones and alloying element distributions are predicted by numerical simulations, although for a laser- and material-dependant quantity ε, which is the function of material properties and laser wavelength and decides the reflectivity together with incident angle in the simplified Fresnel’s reflection model, the theoretical value of 0.08 rather than the compensated value of 0.2 is used in the simplified Fresnel’s reflection model for steel and CO 2 laser. It is thought that these are not only strongly affected by molten metal flow but also the assumptions and models used in the flow calculation are appropriate. However, in spite of the good prediction results, it is deemed that many effects overlooked in this study should be investigated in further studies.