Weld Seam Geometry Research Articles

Laser Weld Seam Curved Path Effect on 6063 Aluminum Alloy Strength and Temperature Distributions: COMSOL Numerical Simulation

To improve the welding performance of aluminum alloys, a thermal source model of an irregular weld seam was established. COMSOL software was used for numerical simulation of the weld seam geometry effect on the temperature and stress fields in laser welding, which results were experimentally validated. The results show that the ellipsoidal laser welding melted micropool exhibited quasi-steady-state temperature field characteristics. The temperature gradient and thermal stress showed an increase followed by a decline. The temperature fluctuation amplitude of the square-tooth-shaped weld seam exceeded that of the arc-toothshaped one. The temperature evolution of the broken line tooth-shaped weld seam showed a slightly increasing trend, except for the inflection point. The experimental average tensile strength of the weld seam was the highest, reaching about 210 MPa, i.e., roughly 85% of the base material (245 MPa), which coincided with the COMSOL-based temperature field simulation results. With increasing deformation amplitude and transition radius, the maximum tensile force, tensile strength, and elongation at fracture showed an increasing trend. However, the deformation amplitude should be below a certain limit because its increase elongates the welding path and reduces the distance between weld seams, resulting in serious heat accumulation. The tensile fracture morphology of the 6063-T6 base material was curved shear, with shallow toughness pits, small tearing edges at the edges, and small granular objects, indicating small plastic deformation during the fracture process. The tensile fracture of the welded part spanned the weld seam and the base material, and the fracture occurred along the tangent direction of the weld seam. The fracture surface was smooth, the tearing edges at the edge of the toughness pit shifted along the weld seam direction, forming many co-directional slip bands, with highly pronounced plastic deformation.

Evaluation of the fatigue resistance of butt-welded joints in towers of wind turbines — a comparison of experimental studies with small scale and component tests as well as numerical based approaches with local concepts

Wind turbines must endure a high number of load cycles during their service lifetime. Therefore, the fatigue strength verification plays an important role. Butt-welded joints are one of the most common structural details in the tower structure of wind turbines. In general, the nominal stress method is used for their fatigue verification. The Eurocode 3 part 1–9 is the current design standard for this field of application and defines the fatigue resistance by pre-defined FAT-classes. This paper presents recent results of fatigue tests on small-scaled specimens and large components with transverse butt welds to discuss the validity of the FAT-class. In addition, results from numerical simulations for the verification with the effective notch stress and the crack propagation approach are used for comparison. For this purpose, macroscopic measurements of the weld seam geometry and a 3D scan were used for a realistic consideration of the notch effect in the simulation. Based on the consistency between the numerical results and the fatigue tests, the influence of the seam geometry on the fatigue resistance was worked out. Furthermore, a prediction of the fatigue strength of butt-welded joints with plate thicknesses up to 80 mm was carried out.

Influence of NIR-laser radiation on the underwater arc welding process with flux-cored wire

The combination of laser radiation and electric arc as hybrid welding is used successfully in industry. In the underwater area, this technology is currently being researched but is not yet part of the industry. This paper demonstrates laser-stabilized arc welding with flux-cored electrode for underwater applications where the laser power density of the laser radiation does not result in a deep penetration welding effect. Steel samples (S235-JR) with a thickness of 10 mm were examined as bead-on-plate welds with a laser power density of 0.7-2.8 x 104 W/cm² at a wavelength of 1030 nm. The addition of laser radiation at low laser power density stabilizes the arc and produces a homogeneous weld seam. The process behavior and stability are characterized by measuring the current and voltage signals and analyzed regarding the laser beam and current source parameters. The metallographic analyses are used to compare the weld seam geometry and the microstructure properties.

Effect of partial and global shielding on surface-driven phenomena in keyhole mode laser beam welding

Partial shielding by means of local gas supply has proven to be very effective in reducing spatter. Besides the effect of gas-induced dynamic pressure, the shielding of oxygen is also highly relevant for melt pool dynamics and spatter formation due to the growth of oxides and the influence on surface tension. Therefore, this paper addresses the effect of local supplied argon on oxide growth and seam topography during keyhole mode laser beam welding of high-alloy steel AISI 304. To determine the shielding quality, the results are compared to laser beam welding in a global argon atmosphere. The topography of the upper weld seams was analyzed by scanning electron microscopy (SEM). An X-ray microanalysis (EDX) in line scan modus was performed to determine and to locate the elements which are covering the specimen surface. The chemical state of the found elements was quantified by X-ray photoelectron spectroscopy (XPS). In a last step, high-speed synchrotron X-ray imaging was performed to separate the effect of the gas-induced pressure and the gas-induced shielding on keyhole geometry. The results show that a local supply of argon contributes to a significant difference in oxide growth, affecting melt pool convection and weld seam geometry. It was further shown that the effect of gas flows at low flow rates is primarily because of oxygen shielding, as no significant difference in keyhole geometry was found by high-speed synchrotron X-ray imaging.

Impact of laser beam shaping on weld pool and seam geometry in butt-joint welding with filler wire

Beam shaping offers a promising solution to address various challenges in laser-based processes. This study explores the use of an adaptive beam shaping solution using a deformable mirror for high-power continuous wave lasers. Specifically, the impact of three different elliptical beam shapes on weld pool geometry, weld cross section in butt-joint welding with a filler wire is investigated. The results reveal that beam shaping significantly affects the weld pool and cross section, with elliptical beam shapes resulting in wider fusion zones in two tested cases and more uniform weld bead compared to a typical circular beam. These findings highlight the potential of beam shaping for enhancing consistency and quality in laser beam welding.

Influence of process parameters on single weld seam geometry and process stability in Laser Hot-Wire Cladding of AISI 52100

Steels with high carbon content can hardly or not at all be welded, but are of great interest for cladding applications due to their high hardness. In this study, the influence of process parameters on weld seam geometry and process stability is investigated when welding AISI 52100 bearing steel using the laser hot-wire cladding process. Process stability is evaluated using actual and set values for the wire feed rate and current parameters to determine a process window for a stable welding process. Weld seams are measured and analyzed in terms of width, height, contact angle, and shape. The effect of the process parameters on the weld seam geometry is investigated and appropriate mathematical functions to describe the geometry are determined. Process parameter sets in the range of 1-2 m/min wire feed rate and 45-75 A hot wire current were investigated. Unstable parameter sets occur clustered at high wire feed rate of 2 m/min for all hot wire currents. In addition, the process is unstable at high hot wire current of 75 A and low wire feed speed of 1 m/min. The remaining parameter sets resulted in a stable process. The investigated functions parabolic, cosinusoidal and circular arc for the mathematical description of the weld seam geometry, no clearly significant result could be determined. Only a trend towards the circular arc function and the parabolic function is apparent.

Fatigue Strength Assessment of Laser Beam Welded Joints Made of AA7075 and Magnetic Pulse Welded Joints Made of AA7075 and 3D‐Printed AlSi10Mg

The use of 7000 aluminum alloys has an important role in future lightweight structures in the field of mobility due to the low density and high strength. However, these alloys can only be fusion welded to a limited extent because welding defects can rarely be prevented. For this reason, investigations are carried out to identify the most suitable welding parameters for two processes: laser beam and magnetic pulse welding. Herein, laser beam welding is successfully used to manufacture a roll‐formed and longitudinally welded pipe made of AA7075 and joined by magnetic pulse welding with a 3D‐printed lug‐tube made of AlSi10Mg. The fatigue strength of these pipe joints and of laser beam welded butt joint specimens is determined using load‐controlled fatigue tests. For the characterization of the specimens, cross sections are prepared and examined metallographically, which reflect the local weld seam geometry in the joining area. A fatigue assessment is made using linear‐elastic approaches. The reference radius concept is applied to map the influence of geometric notches on the fatigue strength, assuming linear‐elastic stress–strain behavior. It is shown that the recommended notch stress fatigue class FAT 178 (von Mises stress) can be applied for a safe and reliable fatigue assessment.

Numerical modeling of defect formation in friction stir welding

This study presents an investigation of welding defect formation in joining AZ61 magnesium alloy with friction stir welding by means of a 3D finite element model. The numerical model was created and analyzed in the ABAQUS software. This numerical model uses coupled Eulerian Lagrangian formulation, modified Coulomb's friction law, Johnson-Cook material law, mass scaling technique, and temperature dependent friction coefficient values. The numerical model was validated with experimental results in terms of heat input, temperature distribution, plastic deformation type-amount, and weld defect formation in the weld zone. In friction stir welding, the heat input with a certain tool simply changes directly proportional to the ratio of tool rotation speed to tool feed rate for constant tool compressive force. In the numerical model, as in the experimental study, when the ratio of tool rotational speed to tool feed rate is 2, low heat input results in insufficient plastic deformation, leading to the formation of weld defects in the form of void. When the ratio of tool rotational speed to tool feed rate is 3, however, it was observed that sufficient heat input is provided, and no welding defects occur. The generated numerical model enables the determination of the welding defects that occur in the form of voids in the friction stir welding in a very short processing time. Besides, weld seam geometry can be predicted quite accurately with this model.

Investigation of deposition welding in vertical and horizontal position with a coaxial laser wire welding head

Deposition welding of components using the laser metal deposition (LMD) process is a proven method of creating 3D structures. It is used for the manufacturing of components, the repair of machine parts and for cladding. Up to now, claddings have mainly been investigated in the flat welding position. Some investigations on deposition welding in vertical orientation are available with different processes. For the cladding of large components, welding in the vertical direction offers advantages. So far, there are no investigations on the LMD process with coaxial wire feeding when welding in vertical direction. Therefore, in this study, the influence of the welding direction, i.e., vertical down and vertical up weld seams, and the influence of the welding speed are investigated. Single weld seams, claddings and a wall are welded. A stable welding process could be achieved for a welding speed parameter window of 100 to 1000 mm/min. The results show that there is a statistical correlation between the welding direction and the waviness of the weld seams. Vertical up weld seams have a lower waviness. Another influence on the waviness is the welding speed. As the welding speed decreases, the waviness increases. The weld seam geometry is strongly dependent on the welding direction. With vertical down weld seams, the width and height of the weld seam vary depending on the distance welded. This can be attributed to the influence of the gravitational force. Vertical up weld seams, on the other hand, have a more uniform shape.

Empirical Model for the Description of Weld Seam Geometry in Coaxial Laser Hot-Wire Deposition Welding Processes with Different Steel Wires

Claddings are used to protect areas of components that are exposed to particular chemical, physical or tribological stresses. The aim when developing a cladding process is to achieve a cladding with low waviness in order to reduce the amount of machining required. Computational models and FEA simulations can be used to determine process parameters for claddings with low rework including a prediction of the height and width of a single weld seam aswell as the development of welding strategies. In this paper empirical models describing the geometry of single weld seams on a substrate manufactured with a coaxial laser hot-wire cladding process are investigated for three steel wire materials and different welding parameters. The coordinates of surface points of the weld seams were detected using a laser scanning microscope and post-processed by a self-created script. In order to describe the cross sectional shape of the weld seams, the parameters of parabolic, cosinusiodal or circular arc model functions are derived from the surface data using a fitting algorithm. For the tested wire materials, an effect of the wire material on the shape of the weld seam was not observed. The investigations also show that regardless of the varied welding parameter set or wire material, a circular model function appears to be the most suitable model shape for describing the cross sectional weld seam geometry in coaxial laser metal deposition with hot-wire. The regression residua using a circular arc model function ranged from 18.9 upmum to 34.6 upmum, which indicates a good approximation.

Optical Coherence Tomography for 3D Weld Seam Localization in Absorber-Free Laser Transmission Welding

Quality and reliability are of the utmost importance for manufacturing in the optical and medical industries. Absorber-free laser transmission welding enables the precise joining of identical polymers without additives or adhesives and is well-suited to meet the demands of the aforementioned industries. To attain sufficient absorption of laser energy without absorbent additives, thulium fiber lasers, which emit in the polymers’ intrinsic absorption spectrum, are used. Focusing the laser beam with a high numerical aperture provides significant intensity gradients inside the workpiece and enables selective fusing of the internal joining zone without affecting the surface of the device. Because seam size and position are crucial, the high-quality requirements demand internal weld seam monitoring. In this work, we propose a novel method to determine weld seam location and size using optical coherence tomography. Changes in optical material properties because of melting and re-solidification during welding allow for weld seam differentiation from the injection-molded base material. Automatic processing of the optical coherence tomography data enables the identification and measurement of the weld seam geometry. The results from our technique are consistent with microscopic images of microtome sections and demonstrate that weld seam localization in polyamide 6 is possible with an accuracy better than a tenth of a millimeter.

CO2 laser based welding of borosilicate glass by Laser Glass Deposition

Due to its thermal and chemical resistance, borosilicate glass finds a wide range of applications in optics, chemical laboratories and in glass apparatus engineering. For the manufacturing of complex glass components, the welding of semi-finished glass products is essential. In the majority of industry, this is realized by operating gas burners in manual processes with low efficiencies. Here, laser-based processing offers the advantage of local heating with high efficiency, since borosilicate-glass has a high absorption for CO2-laser radiation. For this purpose, the welding partners are heated with the CO2-laser, while a borosilicate rod is fed under an angle into the welding zone. In this paper, the welding of borosilicate glasses in butt and 90°-angles using CO2-laser irradiation is demonstrated. Prior to the manufacturing of the weld seams with additional material and the examination via 3-point bending tests, parameter studies are performed for the welding of blind weld seams with regard to the weld seam geometry.

Local Shielding Gas Supply in Remote Laser Beam Welding

The use of shielding gases in laser beam welding is of particular interest for materials interacting with ambient oxygen, e.g., copper, titanium or high-alloy steels. These materials are often processed by remote laser beam welding where short welds (e.g., up to 40 mm seam length) are commonly used. Such setups prevent gas nozzles from being carried along on the optics due to the scanner application and a small area needs to be served locally with inert gas. The article provides systematic investigations into the interaction of laser beam processes and parameters of inert gas supply based on a modular flat jet nozzle. Based on the characterization of the developed nozzle by means of high-speed Schlieren imaging and constant temperature anemometry, investigations with heat conduction welding and deep penetration welding were performed. Bead-on-plate welds were carried out on stainless steel AISI 304 for this purpose using a disc laser and a remote welding system. Argon was used as shielding gas. The interaction between Reynolds number, geometrical parameters and welding/flow direction was considered. The findings were proved by transferring the results to a complex weld seam geometry (C-shape).

Finite element modelling of concrete-filled spiral-welded stainless-steel tube columns under concentric and eccentric axial loading

This study investigated the capacity of finite element modelling (FEM) approaches to predict the experimentally obtained behaviour of concrete-filled spiral-welded stainless-steel tube (CF-SWSST) short and long columns. Using the ABAQUS software, FEM was carried out of 24 CF-SWSST column tests. Nominal outside diameter to thickness ratios, effective length to diameter ratios and load eccentricity to diameter ratios equal to 51–114.5, 4.5–12.0, and 0–0.4 had been considered for the tests that were modelled. The distinct spiral weld seam geometry of the SWSST was explicitly considered in the FEM. Widely reported and accepted FEM modelling approaches and material models were adopted for this work. The concrete damaged plasticity model was utilised for the concrete core, while the stress–strain behaviour of stainless-steel was modelled using a modified Ramberg-Osgood relationship. On average, the capacities predicted by the FEM for the CF-SWSST columns were found to be non-conservative. The non-conservativeness was higher for specimens under concentric axial loading and increased with column and section slenderness. The actual to predicted capacity ratios were much closer to 1.0 for eccentrically loaded CF-SWSST columns, with conservative capacities predicted for eccentrically loaded specimens with the smallest section slenderness. For load eccentricity to diameter ratios of 0.15 and 0.4, there was negligible difference in the prediction conservativeness. Compared to analogous concrete-filled spiral-welded mild-steel tube columns, the FEM predictions obtained for the CF-SWSST columns were notably less conservative. This suggested that separate material constitutive models may be warranted for the FEM of CF-SWSSTs compared to their mild-steel counterparts. For the modelled eccentrically loaded specimens, the FEM predicted globally flexurally deformed states which agreed with those obtained experimentally, though the local buckling patterns were not replicated. In addition, the FEM qualitatively captured the experimentally obtained bending stiffness and strain variations. A modelling sensitivity study found that the FEM results were effectively equivalent even when the SWSSTs were modelled as plain seamless tubes.

Finite element modelling of concrete-filled spiral-welded mild-steel and stainless-steel tubes in flexure

This study investigated the capability of widely-used finite element modelling (FEM) methods, to predict the flexural capacity behaviour of concrete-filled spiral-welded mild-steel and stainless-steel tubes (CF-SWMSTs and CF-SWSSTs). For this purpose, twelve CF-SWMST and CF-SWSST flexural tests each were modelled using the ABAQUS software. The main parameters that had been varied in the respective tests were the outside diameter to thickness (D/t) ratio and infill concrete strength. The nominal D/t of the modelled specimens were in the range 51–114.5, while the infill concretes were of nominal grades 20 and 50 MPa. The moment capacities predicted by the FEM were observed to be, on average, conservative for the modelled CF-SWMSTs. The predicted flexural capacities were more closely in agreement with the corresponding experimental capacities for the CF-SWSSTs. The respective average actual to predicted moment capacity ratios were 1.07 and 1.00, respectively. The experimental and predicted deformation modes were also in qualitative agreement, with local buckling also being predicted by the finite element models. Though the experimentally obtained local buckling patterns were not exactly replicated, there was, nonetheless, good qualitative agreement. This study provided evidence of the capacity of commonly used FEM approaches, relating to CFSTs, to act as a predictive tool for CF-SWMSTs and CF-SWSSTs in flexure. Given the distinct difference in capacity prediction conservativeness, the study also indicated that separate material model formulations may be warranted for CF-SWSSTs compared to CF-SWMSTs. The predicted results were also found to be negligibly sensitive to explicitly modelling the spiral weld seam geometry, even though it was the default case adopted for the FEM in this study.

Finite element modelling of concrete-filled spiral-welded mild-steel tube short and long columns

The capability of finite element modelling (FEM) to predict the experimentally observed behaviour of concrete-filled spiral-welded mild-steel tube (CF-SWMST) columns was assessed in this study. FEM was carried out of 24 previously reported CF-SWMST short and long column tests using the ABAQUS software. The tube length to outside diameter ratio (L/D) of the short and long columns were 3.0–3.3 and 9.0–10.0 respectively while the nominal outside diameter to thickness ratios (D/t) of the specimens were in the range 51–114.5. Load eccentricities of 0, 0.15D, and 0.4D had been considered for the specimens in the respective tests. Widely used and well-established modelling procedures, previously reported for concrete-filled steel tube (CFST) columns, were adopted for the analyses. The concrete damaged plasticity model in ABAQUS was used as the constitutive model for concrete. The specimen geometries were represented using solid hexahedral elements, while the spiral weld seam was also explicitly modelled. With respect to the reported experimental axial capacities, the FEM provided conservative load capacity predictions for the CF-SWMST specimens with D/t ratios less than 100. The prediction conservativeness increased with increasing load eccentricity and decreasing section slenderness. For the eccentrically loaded CF-SWMST columns, the predicted globally deformed states agreed with those observed experimentally, though the local buckling patterns were not replicated in the FEM. The results indicated that the decrease in strength enhancement of the concrete core due to confinement with increasing section slenderness was possibly underestimated by the material models that were used. The FEM results were also found to be negligibly sensitive to the explicit consideration of the spiral weld seam geometry with equivalent behaviour being predicted even when the spiral welded tubes were modelled as plain tubes.

Influence of electron beam welding parameters on the weld seam geometry of Inconel 718 at low feed rates

Abstract Ni-based superalloys are well established in various industrial applications, because of their excellent mechanical properties and corrosion resistance at high temperatures. Despite the high development stage and a common industrial use of these alloys, hot cracking remains a major challenge limiting the weldability of the materials. As commonly known, the hot cracking susceptibility during welding increases with the amount of precipitation phases. Hence, a large amount of highstrength Ni-Alloys is rated as non-weldable. A new approach based on electron beam welding at low feed rates shows great potential for reducing the hot cracking tendency of precipitation-hardened alloys. However, geometry and properties of the weld seam differ significantly in comparison to the common process range for practical uses. The aim of this study is to investigate the influence of welding parameters on the seam geometry at low feed rates between 1 mm/s and 10 mm/s. For this purpose, 25 bead on plate welds on a 12 mm thick sheet made of Inconel 718 are carried out. First, the relevant parameters are identified by performing a screening. Then the effects discovered are further studied by using a central composite design. The results show a significant difference between the analyzed weld seam geometry in comparison to the well-known appearance of electron beam welded seams.

Influence of electron beam welding parameters on the weld seam geometry of Inconel 718 at low feed rates

Abstract Ni-based superalloys are well established in various industrial applications, because of their excellent mechanical properties and corrosion resistance at high temperatures. Despite the high development stage and a common industrial use of these alloys, hot cracking remains a major challenge limiting the weldability of the materials. As commonly known, the hot cracking susceptibility during welding increases with the amount of precipitation phases. Hence, a large amount of highstrength Ni-Alloys is rated as non-weldable. A new approach based on electron beam welding at low feed rates shows great potential for reducing the hot cracking tendency of precipitation-hardened alloys. However, geometry and properties of the weld seam differ significantly in comparison to the common process range for practical uses. The aim of this study is to investigate the influence of welding parameters on the seam geometry at low feed rates between 1 mm/s and 10 mm/s. For this purpose, 25 bead on plate welds on a 12 mm thick sheet made of Inconel 718 are carried out. First, the relevant parameters are identified by performing a screening. Then the effects discovered are further studied by using a central composite design. The results show a significant difference between the analyzed weld seam geometry in comparison to the well-known appearance of electron beam welded seams.

Numerical Simulation and Experimental Validation of the Cladding Material Distribution of Hybrid Semi-Finished Products Produced by Deposition Welding and Cross-Wedge Rolling

The service life of rolling contacts is dependent on many factors. The choice of materials in particular has a major influence on when, for example, a ball bearing may fail. Within an exemplary process chain for the production of hybrid high-performance components through tailored forming, hybrid solid components made of at least two different steel alloys are investigated. The aim is to create parts that have improved properties compared to monolithic parts of the same geometry. In order to achieve this, several materials are joined prior to a forming operation. In this work, hybrid shafts created by either plasma (PTA) or laser metal deposition (LMD-W) welding are formed via cross-wedge rolling (CWR) to investigate the resulting thickness of the material deposited in the area of the bearing seat. Additionally, finite element analysis (FEA) simulations of the CWR process are compared with experimental CWR results to validate the coating thickness estimation done via simulation. This allows for more accurate predictions of the cladding material geometry after CWR, and the desired welding seam geometry can be selected by calculating the cladding thickness via CWR simulation.

Strategies for Increasing the Productivity of Pulsed Laser Cladding of Hot-Crack Susceptible Nickel-Base Superalloy Inconel 738 LC

A novel repair strategy based on decoupled heat source for increasing the productivity of wire-assisted pulsed laser cladding of the γ’-precipitation strengthening nickel-base superalloys Inconel 738 low carbon (IN 738 LC, base material) and Haynes 282 (HS 282, filler material) is presented. The laser beam welding process is supported by the hot-wire technology. The additional energy is utilized to increase the deposition rate of the filler material by increasing feeding rates and well-defining the thermal management in the welding zone. The simultaneous application of laser pulse modulation allows the precise control of the temperature gradients to minimize the hot-crack formation. Accompanying investigations such as high-speed recordings and numerical simulations allow a generalized statement on the influence of the adapted heat management on the resulting weld seam geometry (dilution, aspect ratio and wetting angle) as well as the formation of hot-cracks and lack of fusion between base and filler material. Statistical analysis of the data—the input parameters like laser pulse energy, pulse shape, hot-wire power and wire-feeding rate in conjunction with the objectives like dilution, aspect ratio, wetting angle and hot-cracking behavior—revealed regression functions to predict certain weld seam properties and hence the required input parameters.