Weld Geometry Research Articles

A review on TIG welding technology variants and its effect on weld geometry

This paper focuses on the major developments in the tungsten inert gas (TIG) welding technology for improving weld penetration depth during the welding process. TIG welding is an established arc welding process and it is extensively used for welding thin sections of almost all ferrous and non-ferrous material. However, the growing interest of industries in utilizing the process for welding mid-thick sections components led to numerous innovation in the TIG welding process. In this article, major variants of the TIG welding process i.e. pulse TIG, activated TIG, keyhole TIG, multi-electrode TIG welding process and its associated mechanism is described to understand the concept of improvement in weld penetration depth during the welding process. Furthermore, a systematic discussion on weld bead geometry obtained by different TIG welding process, starting from the mid of 2000 s to till date is presented. The major motive of this review paper is to explore the potential of the TIG welding process and provide a state-of-the-art to the industries as well as the academic world.

Modeling and optimization of weld bead profile with varied welding stages for weathering steel A606

The profile of the welding bead changes with the welding process parameters during the gas metal arc welding (GMAW) process, the top reinforcement disappears, and the penetration becomes sunken when the excessive welding heat input is applied. However, little research work is specially planned to cope with the studying of welding bead under these circumstances. A systematic study of the relationships among the welding process variables and welding bead geometric features as well as optimization of the welding quality is presented. The influences of the welding technological parameters (voltage, welding speed, and wire feed speed) on the welding geometry were revealed, and the models correlating them were established. The features of the weld bead geometry were composed of top reinforcement width, top reinforcement height, penetration depth, bottom reinforcement width, and bottom reinforcement height. By the desirability function approach, the recommendation of suitable welding parameters to meet the contradicting demands of multiple bead geometric features is fulfilled. The microstructure in different welding regions and mechanical performances of the welding joints produced by the verification test were also studied.

Electron-Beam Welding of Laser Powder-Bed-Fused Inconel 718

This study explores the application of Electron-Beam Welding (EBW) for joining Laser Powder-Bed-Fused Inconel 718 (L-PBF IN718) superalloy. Three different levels of electron beam speed and beam current were explored to give nine different electron beam heat inputs for experimentation. To define the weld characteristics microhardness, tensile, and fractography analysis using scanning electron microscopy, optical microscopy, and energy dispersive spectroscopy were conducted. Typical nail-shaped weld geometry was observed with penetration depth proportional to heat input. Most welded samples exceeded the yield strength (600MPa) and tensile strength (920MPa) requirements from the ASTM F3055 specifications for additively manufactured IN718, however, the specimens did not meet the ductility requirements (27%). Brittleness of the weld was attributed to the presence of brittle secondary phases in the weld matrix, and unfused metal powder of adjacent L-PBF layers. Post-processing heat treatments were recommended to improve the weld quality while improving the ductility of EBW joints.

Numerical and databased investigations on the fatigue of cruciform joints with gaps

The paper deals with investigations on the fatigue resistance of the load-carrying cruciform joint with gaps. The aim is to define limits of specific acceptable imperfections, since these do not always necessarily affect the fatigue strength. Different geometrical influences on the fatigue strength of the load-carrying cruciform joint with gaps are analysed numerically. Numerical simulations comprise effective notch stress calculations, which have been compared to fatigue test results from literature, documented in a fatigue test database. A larger gap in combination with a smaller weld size leads to the unfavourable failure at the weld root. For the specific geometrical configurations, borderline functions defining the failure location on the basis of local weld geometry have been defined. Finally, the most interesting configurations are presented, which will be tested experimentally in a subsequent fatigue test program.

“ICMPC” Effects due to tool design during FSW process of aluminium alloy AA7075 T-6

ABSTRACT The present study explores the implications of friction stir welding (FSW) geometries of instruments on AA7075 T-6 welds. For tougher materials, it is assumed that threaded FSW instruments are beneficial, like AA7075 T-6. However, the structure of the tool shoulder and the concavity of the shoulder surface also play an important role in determining the quality characteristics of friction stir welds. The effect of threaded FSW instruments on using various shoulder diameters, pin diameters, AA7075 aluminium alloys were investigated. Diameters, concavity of the shoulder surface and speeds. Experiments were to research the effects of these instruments on welds of AA7075 with respect to welding cross-sectional area, tensile strength, and percent elongation. A mathematical trend using response, the effects of the tool geometries on the welds were predicted to the regression analysis of surfaces, diameter of the shoulder and concavity of the shoulder surface. The relationship effects of the control variables (geometrical parameters of the instrument) on the responses such as weld power, weld cross segment and percent elongation have been investigated. The modelling approach developed in this study was found to be sufficient to predict the effects of the FSW instrument welding geometrical variables.

Decisive impact of Filler-free joining processes on the Microstructural evolution, tensile and impact properties of 9Cr-1Mo-V-Nb to 316 L(N) dissimilar joints

Filler-free (FF) welding processes namely, Activated Tungsten Inert Gas welding (ATIG), Laser Beam Welding (LBW), and Friction Stir Welding (FSW) were utilized for joining the nuclear grade 9Cr-1Mo-V-Nb ferritic-martensitic steel and 316 L(N) austenitic stainless steel. A comparative investigation was made by assessing the weld geometries, metallurgical features, material mixing proportions, carbon diffusion behaviour, and mechanical properties of the post-weld heat-treated (PWHT) dissimilar weld joints. Geometries of the weld zones were observed with the transverse and longitudinal macrographs. Metallurgical features were examined by optical microscopy (OM) and Scanning electron microscopy (SEM). Three-phase microstructures were identified in the dissimilar weld zones (DWZ). The elemental distributions were identified by Energy-dispersive X-ray spectroscopy (EDAX). The mixing proportions of the dissimilar alloys and the formation of δ-ferrite in the dissimilar heat-affected zones (HAZ) and DWZ were analytically quantified. Moreover, the diffusion activity of carbides/interstitial carbon atoms was examined by Secondary ion mass spectroscopy (SIMS). In the FSW joints, the intermingled microstructures are recorded with high and stabilized hardness values as compared to the DWZ of the ATIG and LBW joints. In the transverse tensile test, all FF joints were failed at the 316 L(N) base metal (BM) region. Tensile and impact testing of all weld metal indicated that, the weld metal region of the LBW joint exhibited higher strength and lower toughness as compared to the ATIG and FSW joints. The presence of untransformed, recrystallized fine equiaxed austenite along and refined martensitic structure arranged in an alternate layers within the weld metal region of FSW joint caused the higher toughness property than the ATIG and LBW joints.

Pulsed Nd: YAG Laser Parameters Effect on Welding Uncoated Advance High Strength Steel (AHSS) for Automotive

Pulse wave (PW) welding technique has become more adequate process to produce a deep penetration welding with smaller fusion zone and heat affected zone for automotive steel joint. A 1.6 mm thickness of N22CB boron steel from advance high strength steel (AHSS) type was welded by using PW mode from a low power Nd: YAG laser. The process parameters studied in this paper are pulsed energy, Ep, focal length, F, and welding speed, S. Bead-on-plate (BOP) welding was used in this experiment. The effect of parameters on the weld pool geometry was studied. Higher pulsed energy gives high weld penetration and higher weld width, contributing to the bigger weld pool size. Positive defocus position of focal length produces weld geometry with high penetration depth and smaller bead width compared to negative defocus position. Lower welding speed could produce deep penetration depth as the high heat input produced.

Effects of wheelset flexibility on locomotive–track interaction due to rail weld irregularities

Irregularities of rail joints ordinarily induce high-frequency impacts on wheel–rail contact systems, which may further influence vehicle–track interaction. In this study, a three-dimensional locomotive-track coupled dynamics model that uses the wheelset flexibility was developed. The wheelset rigid motion and elastic deformation are calculated based on the multi-body dynamics theory and finite element method, respectively. The effectiveness of this model was validated. The effect of wheelset flexibility on locomotive–track interaction due to rail weld irregularities is analysed by comparing the dynamic responses obtained using the rigid model and the proposed rigid–flexible coupled model. The proposed model is applied to the sensitivity analysis of the wheelset response to the rail weld geometry irregularity. The results show that the dominant frequency of the wheel–rail force or axle–box acceleration is 81 Hz, which is the 1st bending modal frequency of the wheelset. The P2 resonance frequency is easily excited owing to impacts of rail weld irregularities, which may induce the formation of locomotive wheel polygonization. The wheelset acceleration was more sensitive to the wavelength than the depth of the rail weld irregularities. The wavelength characteristics can be significant in vehicle vibration-based condition monitoring of rail weld irregularities.

Isogeometric Analysis and Bayesian Optimization on Efficient Weld Geometry Design for Remarkable Stress Concentration Reduction

Shape optimization combined with Isogeometric Analysis will be an efficient design method since exact Computer Aided Design geometries can be used for numerical analysis thanks to the same basis functions. In this study, authors developed an in-house research software JWRIAN-IGA and applied it to optimize the weld geometries of two models, namely a T-joint fillet weld and an elongated boxing fillet weld to reduce stress concentration. A gradient-free stochastic global optimization algorithm, Bayesian Optimization was used to sought optimal geometry parameters. It was shown that the optimized geometry was efficiently designed and the stress concentration in the welds for both cases was greatly reduced.

Peridynamic analysis of fatigue crack growth in fillet welded joints

Fatigue assessment is one of the significant factors to be considered for estimating design life of structures and structural reliability during operation. Especially, for welded structures, high stress concentration, residual stresses, weld geometry and weld quality make the structure more vulnerable to fatigue failures. Therefore, approaches that are more effective are required for estimating fatigue performances of welded structures. Existing classical methods to predict the crack propagation under cyclic loadings have some difficulties in treating complicated patterns of crack growth. However, peridynamic theory has advantages on dealing with discontinuities. In this study, a peridynamic fatigue model, which is a bond damage model of remaining life, is validated by considering ASTM E647 standard compact tension test for the crack growth. After validating the PD model, the fatigue performance of the fillet welded joint is presented by predicting the fatigue crack growth under cyclic loading conditions.

A study on simulation analysis for laser-welded I-core sandwich plate with different material properties and T-joint weld characteristic

Stiffness and strength of sandwich plate vary depending on similar (SI) or dissimilar (DSI) material element (faceplate or core) and laser weld geometry. The issues of I-core sandwich plate characteristics are essential to attain practical sandwich plate application. Hence, research on different material properties and T-joint weld characteristics of I-core sandwich steel plate presents a positive understanding of various character factors that affect sandwich plate bending performance. In this paper, the I-core sandwich steel plate characteristic was investigated using finite element analysis (FEA). The 3-point bending with a fine meshing, interaction of elements, and load applied was kept constant. The partition size at the laser weld geometry is smaller, and the partition size continuously grows when further away from the weld geometry. The result shows that a combination of weak and strong material on either element will reduce I-core sandwich's stiffness and strength unless strong material is assigned at the faceplate and core. Moreover, there is a significant change when rootgap is present. This influencing the centric and eccentric of the weld. The weld width produces a perfect bending as wholesome T-joint, yet to achieve such traits is impossible in reality but possible when the weld length is closer to the length of the core. The exploration of these characteristics in response to I-core sandwich steel plate holds a good response in engaging for the multiple variables that affect the plate's stiffness and strength.

Use of a stepped preparation to improve the damage tolerance of grade 91 steel welds

ABSTRACT Damage equivalent to that seen over very long times in Grade 91 steel welded components was successfully formed in laboratory, feature sized samples tested under controlled conditions. This paper compares the creep behaviour of welds made using a typical preparation with results for novel step weld geometries. When well-designed the step geometry offsets the heat affected zone (HAZ) in the through thickness of the weld which would be equivalent to the pressure boundary in a pipe. The step in the weld profile thus provides benefit to in-service performance because it prevents the rapid link up of aligned creep cavitation that forms in the HAZ of welds made using typical preparations. The results demonstrate that a well-designed step weld geometry increases the creep rupture life and improves damage tolerance. In turn, the increased duration of stable crack growth promotes the opportunity for detection of creep damage using nondestructive testing methods.

An Approach to Improving the Mechanical Properties of Friction Stir Spot Welded Joints on the Basis of Hook Formation Mechanism

Background: Partial metallurgical bond (namely 'hook') is formed between the overlapped metal sheets during friction stir spot welding (FSSW). The geometry of hook is found to significantly affect the mechanical performance of FSSWed joints, while that how to adjust hook geometry to a better state remains to be studied. Methods: The conventional FSSW joints under different plunge depths and dwelling time were obtained. The cross-sectional morphology of each spot weld was investigated to clarify the material flow behavior and deduce the formation mechanism of hook. The tensile shear strength and fracture features were examined to reveal the effect of hook geometry on the mechanical properties. Results: The weld geometry affects the tensile shear strength of FSSWed joints by determining their fracture modes. The formation mechanism of hook is deduced by a material flow model. In the toolplunging stage, the faying interface is broken by upward-flowing materials, hook is therefore initiated and driven up gradually. During the tool-dwelling stage, hook continues to migrate to the lowpressure zone, surrounding the stir zone. Conclusion: The uncertainty of crack-propagating endpoint along hook makes it difficult to ensure the mechanical properties of welds. If the hook endpoint has not yet reached the low-pressure zone at the end of welding process, welds with ideal hook geometry can be obtained. Target friction stir spot welds were produced by the use of a tool possessing smaller pin diameter.

Laboratory-Scale Processing and Performance Assessment of Ti\u2013Ta High-Temperature Shape Memory Spring Actuators

Ti75Ta25 high-temperature shape memory alloys exhibit a number of features which make it difficult to use them as spring actuators. These include the high melting point of Ta (close to 3000 °C), the affinity of Ti to oxygen which leads to the formation of brittle α-case layers and the tendency to precipitate the ω-phase, which suppresses the martensitic transformation. The present work represents a case study which shows how one can overcome these issues and manufacture high quality Ti75Ta25 tensile spring actuators. The work focusses on processing (arc melting, arc welding, wire drawing, surface treatments and actuator spring geometry setting) and on cyclic actuator testing. It is shown how one can minimize the detrimental effect of ω-phase formation and ensure stable high-temperature actuation by fast heating and cooling and by intermediate rejuvenation anneals. The results are discussed on the basis of fundamental Ti–Ta metallurgy and in the light of Ni–Ti spring actuator performance.

Evaluation of Cyclic Loading Effects on Residual Stress Relaxation in Offshore Wind Welded Structures

Monopile foundations contain welding residual stresses and are widely used in industry to support offshore wind turbines (OWTs). The monopiles are subjected to hammering loads during installation and cyclic loads during operation, therefore the influence of residual stress redistribution as a result of fatigue cycles must be evaluated in these structures. The existing empirical models to predict the residual stress redistribution in the presence of cyclic loading conditions are strongly dependent on the material, welding process and loading conditions. Hence, there is a need to predict the residual stress redistribution using finite element simulations. In this study numerical analyses have been conducted to predict the initial state of residual stress in a simplified weld geometry and examine the influence of subsequent cyclic loads on the relaxation behavior in residual stress profiles. The results have shown that fatigue cycles have a severe effect on residual stress relaxation with the greatest reduction in residual stress values observed in the first cycle. Moreover, the numerical prediction results have shown that the stress amplitude plays a key role in the extent of residual stress relaxation in welded structures.

Selection of parameters in nanosecond pulsed wave laser micro-welding

The digital control of the latest nanosecond pulsed wave (PW) fibre lasers allows very high flexibility in controlling the application of the total energy to a workpiece, which brings several advantages to the joining process. By choosing different pulse shapes in different spatial profiles, it is possible to apply low energy per pulse with high precision and accuracy resulting in lower heat input. Since the energy of each pulse is insufficient to generate melting, these lasers operate at very high pulse repetition frequencies near continuous wave (CW) regime. Nevertheless, the peak powers of PW lasers are much higher than CW. In this research, the effect of peak power, pulse energy, pulse width, pulse repetition frequency and duty cycle has been studied. The experimental work was conducted in bead on plate of austenitic stainless steel to investigate the effect of laser on the weld geometry, i.e. depth of penetration and width. An empirical model, previously established for CW mode, which enables the achievement of a particular penetration depth independent of the beam diameter, was redesigned and tested for PW mode. The “pulse power factor model” allows the laser user to select a weld profile that meets certain quality and productivity requirements independent of the laser system. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of different system parameters by keeping a constant trade-off between pulse power factor and interaction time.

Geometry and Distortion Prediction of Multiple Layers for Wire Arc Additive Manufacturing with Artificial Neural Networks

Wire arc additive manufacturing (WAAM) is a direct energy deposition (DED) process with high deposition rates, but deformation and distortion can occur due to the high energy input and resulting strains. Despite great efforts, the prediction of distortion and resulting geometry in additive manufacturing processes using WAAM remains challenging. In this work, an artificial neural network (ANN) is established to predict welding distortion and geometric accuracy for multilayer WAAM structures. For demonstration purposes, the ANN creation process is presented on a smaller scale for multilayer beads on plate welds on a thin substrate sheet. Multiple concepts for the creation of ANNs and the handling of outliers are developed, implemented, and compared. Good results have been achieved by applying an enhanced ANN using deformation and geometry from the previously deposited layer. With further adaptions to this method, a prediction of additive welded structures, geometries, and shapes in defined segments is conceivable, which would enable a multitude of applications for ANNs in the WAAM-Process, especially for applications closer to industrial use cases. It would be feasible to use them as preparatory measures for multi-segmented structures as well as an application during the welding process to continuously adapt parameters for a higher resulting component quality.

Improvement on the tensile properties of 2219-T8 aluminum alloy TIG welding joint with weld geometry optimization

An applicable method to improve the tensile properties of 2219-T8 aluminum alloy TIG welding joints is attractive in manufacturing of large propellant tanks. In this work, tensile properties of 2219-T8 TIG welded joints was improved by adjusting the weld geometry using multi -pass welding with swing. The effects of weld geometry on the tensile properties of joint were investigated. And the geometry parameters were optimized by an orthogonal experiment design. The joints with tensile strength coefficient of 70 % and elongation over 4% were acquired after weld geometry optimization. The improvement mechanisms of weld geometry attributed to the reduced strain variation rate and stress concentration at the weld toe.

Fatigue life estimation of the weld joint in K-node of the offshore jacket structure using stochastic finite element analysis

Several methods for finite element modelling and analysis of tubular welded joints are described in various design codes. These codes provide specific recommendations for modelling of the welded joints, using simple weld geometries. In this paper, experimental strain range results from two full-scale semi-automatically welded K-nodes tests are compared to corresponding finite element models. Three dimensional (3D) scans of the weld surfaces have been developed for the automatically welded K-joints. These 3D scans are included in the finite element (FE) models to determine the accuracy of the FE models. Some discrepancies are observed between finite element predictions and test results. Finite element model updating has been applied to improve the accuracy of the developed finite element models. The results are compared to a FE model with a simple weld geometry based on common offshore design codes and a FE model without any modelled weld. The results show that the FE model with 3D scanned welds are more accurate than the other FE models. The precise location of weld toe in the 3D scanned weld is difficult to locate in the FE model, thus stochastic finite element modelling is performed to analyse the probabilistic hot-spot stresses. The results show large variations in the hot-spot stresses. It can be concluded that it is necessary to evaluate the probabilistic nature of stresses for calculating fatigue lives of welded tubular joints in offshore structures.

Laser wobble welding of fluid-based cooling channel joining for battery thermal management

Aluminium alloys are increasingly used to fabricate cooling channels for the thermal management of Li-ion batteries. Cooling channel fabrication involves a number of manufacturing operations including material extrusion, forming and joining/welding. In general, welding of aluminium alloys is challenging as they are both highly reflective and thermally conductive. To address the joining challenges, this paper is focused on developing an optimised joining process to connect a thin, flanged cooling channel to the thick module manifold of the battery thermal management system to create a watertight joint with high mechanical strength. As continuous seam welding was required, laser welding was the preferred as it is a non-contact process combining high speed and precision. For this application, 0.4 mm Al cooling channel was welded with 1.5 mm Al endplate/module manifold using a wobble head integrated with 1 kW CW fibre laser system. The effect of process parameters including line energy, incident angle, laser power, welding speed and beam offset were investigated to optimise both the weld geometry and strength. Microstructure, micro-hardness and grain formation analyses were carried out to understand the metallurgical behaviour of the weld. Beam offset had the most significant effect on the responses such as weld strength, throat thickness and modified throat thickness, and laser power had a significant influence on two key geometric features of the fusion zone, i.e. penetration depth and weld width. Weld strength was optimised using a developed surrogate model and a maximum load of 646.89 N was achieved using 0.2 mm beam offset, 331.82 W laser power and 659.10 mm/min welding speed. Using this optimum combination, a leak-proof cooling channel and module manifold joint were produced for battery thermal management.