Weld Bead Geometry Research Articles

Effects of Heat Input on Weld-Bead Geometry, Surface Chemical Composition, Corrosion Behavior and Thermal Properties of Fiber Laser-Welded Nitinol Shape Memory Alloy

Bead-on-plate laser welding was carried out on 1-mm-thick Nitinol sheets at different heat input values. The variations in weld-bead geometry and variations in microstructures across the bead were studied. The effects of heat input on surface layer composition of the welded samples, corrosion properties and phase transformation temperature were examined. From x-ray photoelectron spectroscopy (XPS), it was clear that relative intensity of elemental Ni peak was higher in parent material and the oxidation state of Ti was Ti4+. It was further observed from Auger electron spectroscopy (AES) that the Ti to Ni ratio on the top surface of the welded samples was more than 1, and as a result of this the stability of TiO2 layer was enhanced, which eventually helped to improve the corrosion property of the welded samples. The polarization resistance of the welded samples was increased by more than ten times compared to that of the un-welded samples. From differential scanning calorimetry (DSC), it became evident that phase transformation temperatures got changed due to welding.

Effect of beam shape and spatial energy distribution on weld bead geometry in conduction welding

The size of a projected beam onto a workpiece and its intensity distribution profile defines the response of the material to the applied laser heat. This means that not only the processing parameters, but also the optical set-up and process tools define the process and the resulting weld profile. In high power laser delivery systems the beam propagation characteristics of the laser beam can vary during processing. A change of the focal distance, for instance, alters the spot size projected on the workpiece as well as its intensity distribution. Some dynamic optical systems can also change the shape of the projected beam. Galvo-scanners induce a small distortion to the projected beam from circular to elliptical when the mirrors deflect the beam across the working domain. This continuous change of the spatial energy distribution may affect the process stability and material response locally. This work examines the influence of changing the shape of the projected beam and its energy distribution on the weld bead profile in conduction laser welding, which is also relevant to laser cladding and additive manufacture. It has been found that for the same optical set-up and system parameters, different bead profiles can be obtained with different degree of distortion of the beam profile. In addition, different intensity distribution profiles led to different penetration depths for the same nominal beam diameter and energy density due to the difference in peak intensity.

Manipulating the melt propagation of short arc gas metal arc welding with diode lasers <1 kW for improvement in flexibility and process robustness

The processes that were performed for the studies on manipulating the melt propagation of the short arc gas metal arc welding process were carried out with a diode laser emitting with mean intensities of maximum 1.1 × 104 W/cm2 and a wavelength of 1025 nm on 1.0330 low carbon steel with a thickness of 1 mm. To determine the ability of the laser to manipulate the melt, investigations in terms of static displacement and dynamic movement of the laser beam via a scanner optic were executed. By displacing the laser spot statically and parallel to the weld, the shape of the bead can be influenced, and furthermore misalignments of fillet welded sheets up to 3 mm can be compensated. The extent of displacement and the influence of the laser energy on the weld bead geometry were examined through metallographic analysis regarding the width and height of the beads as well as the shift in position. The use of a two-dimensional scanner optic adds the potential of moving the melt in nonlinear shapes. The high speed camera footage is examined to visualize the melt dynamics in displacement operation. For comparing the weld properties of weld beads with and without laser stabilization in static and dynamic operations, the transient current and voltage curves are recorded and evaluated regarding alterations of the mean values.

Geometrical, microstructural and mechanical characterization of pulse laser welded thin sheet 5052-H32 aluminium alloy for aerospace applications

Abstract Pulse laser welding of 0.6 mm-thick AA5052-H32 was performed to determine the optimum set of parameters including laser pulse current, pulse frequency and pulse duration that meets the AWS D17.1 specifications for aerospace industry. The microstructure and mechanical properties of the weldments were also investigated. Relationships between the parameters and weld bead geometry were found. High quality weld joints without solidification crack that met AWS D17.1 requirements were obtained at (I) high pulse energy (25 J) and high average peak power (4.2 kW) and (II) low pulse energy (17.6 J) and low average peak power (2.8 kW). The weld joint formed at lower heat energy input exhibited finer dendritic grain structure. Mg vapourisation and hard phase compound (Al0.5Fe3Si0.5) formation decreased in the weld joint formed at lower heat energy input. Consequently, the tensile strength of the weldment formed at lower heat energy input (168 MPa) is by a factor of 1.15 higher but showed ∼29% decrease in hardness (111 HV0.1) at the joint when being compared with the weldment formed at higher heat energy input. Appropriate parameters selection is critical to obtaining 0.6 mm-thick AA5052-H32 pulse laser weld joints that meet AWS D17.1 requirements for aircraft structures.

Ti–6Al–4V TIG Weld Analysis Using FEM Simulation and Experimental Characterization

This study involves thermal, metallurgical and mechanical analysis during tungsten inert gas welding of Ti–6Al–4V alloy aiming at optimizing the welding current to enhance the mechanical properties. Firstly, a 3D transient FEM simulation of TIG Ti–6Al–4V weld using ABAQUS software, based on a Gaussian distribution of power density in space, has been built to predict the effect of welding current on the heat input, weld bead geometry, temperature and residual stresses distribution across the welding line. Secondly, a validation of FEM with the experimentally measured temperature distribution and welding bead geometries has been presented. Finally, experimental study of the effect of TIG welding current, the suitable range predicted from FEM, on the microstructure, hardness and tensile strength of 12-mm-thick alloy plate is discussed. Using FEM, the suitable range of welding current was predicted to be 130–170 A. There was a close agreement among the experimental results and the FEM simulation data. It has been found that low welding current of 130 A results in high tensile strength and hardness of the welding joint. This is attributed to low heat input, high cooling rate and the formation of a fine grain structure containing martensite-phase with low values of residual stresses.

Influence of weld parameters on weld regimes and vaporization rate in electron beam welding of Ti6Al4V alloy

Electron beam welding (EBW) is the most preferable and efficient joining technique to weld titanium alloys, since it provides a vacuum atmosphere and eliminates the use of shielding gas during the welding process. The present work is focused on understanding the electron beam weld parameters which controls the weld limits, microstructural and mechanical properties and vaporization rate of metal elements in the Ti6Al4V alloy. The influence of power density on characteristics of electron beam welded Ti6Al4V alloy at constant linear energy conditions is examined. The welding experiments were performed to evaluate the weld geometry, weld regimes, microstructural properties and microhardness characteristics using fundamental parameters such as power density and interaction energy per unit volume (IE). Moreover, the vaporization heat transfer model of the EBW process is developed by employing Fourier’s law of heat conduction to estimate the vaporization rate of Ti6Al4V alloying elements. The rate of vaporization of major alloying elements of Ti6Al4V is analysed with respect to power density. Based upon the results obtained, it is witnessed that the weld bead geometry, weld limits and grain size are controlled by power density for constant linear energy conditions. Also, the solidified microstructure in the weld zone at different power density significantly effects the final strength of the weld joint. The conduction and keyhole weld limits are identified for power density values below 0.31 W cm−2 and above 2.12 W cm−2, respectively. The transition mode welding in the Ti6Al4V alloy is identified by a nominal increase in aspect ratio for a wide range of power density and IE values. The results also established that the size of β grain in the fusion zone reduces with increase in power density at constant linear energy condition. Also, the average α1 martensitic grain size in the weld zone is determined to be higher in keyhole welds (128 µm) relative to conduction welds (48 µm) on account of higher solidification rate. In effect, the solidified martensitic phases influence the microhardness distribution proportionately across the weld sample of Ti6Al4V alloy. Vaporization of metal elements of the Ti6Al4V alloy is induced in few milliseconds and evaporation rate of ‘Al’ element is least followed by ‘Ti’ and ‘V’ elements. It is also observed that by reducing the power density from 2.54 to 2.12 W cm−2, keyhole mode welding can be acquired and vaporization rate of ‘Al’ is reduced by 20.5%.

Segmentation of Weld Defects Using Multiphase Level Set by the Piecewise-Smooth Mumford-Shah Model

This paper deals with the problem of the X-ray image segmentation used to detect weld defects for a non-destructive testing task. In this work we have implemented a multiphase method using the Mumford and Shah piecewise smooth model to extract the size and the texture information of defect and its region. Using this model which is more robust to the noise and less sensitive to the position of the initial curve, we have obtained a maximum of information for several regions in the X-ray image (the geometry of weld beads and defects). Our results show that the model developed can do at the same time the image segmentation and restoration.

Effects of Welding Speed and Pulse Frequency on Surface Depression in Variable Polarity Gas Tungsten Arc Welding of Aluminum Alloy

A three-dimensional (3D) numerical model with the volume of fluid method is developed for high-speed variable polarity gas tungsten arc welding (VP-GTAW) of aluminum alloys. It predicts the thermal flow field in the weld pool, the weld pool surface deformation, and solidified bead geometry during VP-GTAW in successive welding passes. Verification of the numerical model was performed by comparing the calculated results with metallography of welded cross-sections. The prediction showed reasonable accuracy in predicting weld bead geometry. The prediction average relative errors of the bead width and depth of penetration are less than 7%. The deformed weld pool surface, the fluid flow in the weld pool, and maximum fluid temperature in the workpiece based on the developed model, are discussed in detail. The effects of welding speed and pulse frequency on surface depression are studied. The results show that the maximum fluid temperature is closely correlated to the welding speed and pulse frequency. Further, the upper and lower limit of maximum fluid temperature would provide a clue by which the surface depression and the pitch of humps may be recognized. An increase in welding speed will lead to the increase of the pitch of humps, but the reverse is true in the pulse frequency. These detailed physical insights facilitate the prediction of welding surface defects in the high-speed VP-GTAW of aluminum alloy.

Effects of process parameters on the quality aspects of weld-bead in laser welding of NiTinol sheets

ABSTRACTThe effects of process variables, like scan speed and laser power, on the quality of bead-on-plate welding of NiTinol sheets were investigated. The measured quality aspects for the weld-bead profile were bead geometry, changes in microstructure, variation of microhardness value along the weld-bead, extent of oxide contamination during welding, Ti/Ni ratio after welding, changes in tensile strength of the welded samples and corrosion behavior of the welded and parent materials. The laser weld-bead profile changed from the shape of a stemless wineglass to that with a prominent leg. Dimensional aspects of weld-bead geometry showed a decreasing trend with increasing scan speed. However, an increasing trend of the same was observed with power. The Ti/Ni ratio on the top surface after welding was found to decrease with scan speed at a particular power. Oxide contamination during welding followed the same pattern of variation as that of the Ti/Ni ratio. Microhardness values gradually increased from the weld centerline to the base metal. Formation of brittle intermetallic compounds reduced the tensile strength of the material after welding. A dual failure mode for the welded sample was observed, whereas a single mode of failure was detected for the parent material. The corrosion properties of the welded samples were better than that of the parent material.

CFD modelling of weld pool formation and solidification in a laser micro-welding process

The application of developed thermal models has demonstrated that parameters, such as power, scanning velocity and spot diameter of laser beams have considerable effects on the formation of weld pools. The properties of the weld metal are heavily dependent on the solidification microstructure, and an accurate prediction of the weld pool solidification requires consideration in both the thermodynamics and kinetics of solidification. The computations we presented for a transient three-dimensional model show the aspects of weld pool formation and solidification in a quantitative manner. Our focus was the examination of heat transfer and fluid flow analysis in laser micro-welding of thin stainless-steel sheet (SUS304) using the computational fluid dynamics (CFD) approach. In this research work, a useful linkage between the laser micro-welding parameters and the geometry of the micro-weld can be derived from the results, and informative guidance was achieved as to how the width, depth and length of the weld pool differ during laser micro-welding as a function of spot diameter, scanning velocity and laser power. The simulation results have been compared with two sets of experimental data to predict the weld bead geometry and solidification pattern made on thin stainless steel sheet using a continuous wave (CW) fibre laser. The reasonable agreement between the simulated and experimental results, demonstrates the reliability of the computed model, and the results can be used to determine the laser micro-welding conditions necessary to achieve an appropriate target microstructure. However, the results allow estimation of acceptable ranges of welding variables, to attain the required micro-weld geometry.

Effect Of Welding Speed On Weld Bead Geometry And Percentage Dilution In Gas Metal Arc Welding Of SS409L

Abstract Welding process parameters are the controlling factor for percentage dilution and weld bead geometry (bead width, bead height and penetration). Percentage dilution and weld bead geometry are very important factors to determine the quality of the joints. Present work aims to investigate the effect of welding speed (300, 400 and 500 mm/minute) on percentage dilution and weld bead geometry. Gas metal arc welding of ferritic stainless steel SS409L with austenitic stainless steel filler wire ER304L using pure argon gas has been done. The study of percentage dilution and weld bead geometry has been carried out. It has been found out that with increasing welding speed, bead width, bead height and penetration decreases but percentage dilution first increases with the welding speed parameter and then decreases with further increase in these values.

Effect of Arc Length Correction on Weld Bead Geometry and Mechanical Properties of AISI 316L Weldments by Cold Metal Transfer (CMT) Process

Abstract Cold Metal Transfer (CMT) joining process is a clean and economical process in arc welding, which has higher productivity and good quality when comparing with traditional arc welding processes. The joining process has the characteristics like low heat input and low distortion while welding sheet metals. The influence of correction in arc length on the weld bead geometry of AISI 316L using ER 316L filler wire by a single variable is investigated in this research. The results depict that the effect is non-linear on the joining process. By optimizing the arc length correction full depth of penetration was achieved with low heat input, reduced bead width and top reinforcement. Also the uniaxial test and micro-vickers hardness test results reveal that there was improvement in tensile strength and hardness value. The tensile strength for the best joint was 569 MPa and Vickers hardness value of 210 HV. It was observed that the joints exhibited better strength compared to the base metal for 10% arc length correction.

Analysis of Residual Stress by the Hole-Drilling Method and Hardness in Dissimilar Joints of Austenitic Stainless Steel AISI 316L and Inconel 718 Alloy by Autogenous GTAW Process

Stainless steel and nickel alloy have high corrosion resistance in high-temperature environments due to the high Cr content present in their chemical composition, being widely used in components of nuclear reactors, petrochemical industries, etc. Through proper processes and procedures, it becomes possible to join these alloys. However, this union can generate detrimental factors in its performance, among them, the residual stresses. In this work, the residual stresses generated by the autogenous GTAW process, due to different interpass temperatures on the weld bead geometry, were analyzed by the Hole-Drilling technique in dissimilar welding joints of stainless steel AISI 316L and Inconel 718 alloy. In addition, the Vickers microhardness measurements were carried out to evaluate the hardness profile in the cross section of the weld bead covering base metal (BM), heat affect zone (HAZ) and weld metal (WM). We found that in the interface region between BM and HAZ of each dissimilar joint metal, residual stresses increased above 300 MPa, while hardness increased above 160 HV.

Arc Behavior Study Using Welding Current Module and its Impact on Residual Stress and Weld Bead in Anti-Phase Synchronized Twin-Wire Gas Metal Arc Welding

The importance of twin-wire welding in increasing the deposition rate is known for a long, but its application in gas metal arc welding is limited due to the arc-stability related issues. An unstable welding arc causes irregular weld bead and material loss in the form of spatters. Previous investigations indicate that the problem can be addressed through arc-stability induced by dissimilar twin-arcs as the electromagnetic field concentrates around the arc with higher current. The present study is intended to reduce the twin-arcs' interactions and to improve the arc stability in twin-wire gas metal arc welding by evaluating different conditions at lead and trail wires. Further, their influence on the residual stresses and weld bead geometry is studied. Bead-on-plate-welds are carried out. A data acquisition system is used to capture the electrical signals during welding. The results indicate that the unequal currents at trail and lead wires provide stability to the arc that also results in a shift in residual stresses from compressive to tensile along the weld transverse direction. In addition, the maximum residual stress is located at the weld toe. When the current difference between the trail and lead wire is more, the arc produces stable metal transfer with uniform heating and cooling that results in reduction in stresses and improvement in weld quality.

Weldability Evaluation of 409 FSS with A-TIG Welding Process

Abstract Tungsten inert gas (TIG) welding process is widely known for producing defect free sound quality welds. However, low depth of penetration in single pass is a major disadvantage of the existing TIG welding process. Flux assisted tungsten inert gas (A-TIG) welding is growing as a solution low penetration. In the current work, the weldability of the 409 ferritic stainless steel (FSS) with A-TIG welding process have been evaluated. Effort have been made to demonstrate the impact of the different components like activating flux and its quantity on the weld bead geometry.

Effect of oxide fluxes on activated TIG welding of AISI 316L austenitic stainless steel

In this work, activated TIG (A-TIG) welding on 8 mm thick plates of AISI 316L stainless steel was carried out. The effect of various single component fluxes and a multi-component flux on weld bead geometries was analysed. The multi-component flux mixture resulted in though thickness penetration in a single pass. Metallography of different zones was observed and weld zone was found to exhibit austenitic-ferritic microstructure. Delta ferrite content was measured with Ferritoscope and increase in delta ferrite content was observed in A-TIG weld zones as compared to base metal. From microhardness measurements, weld zone was found to be harder than the base metal due to increase in delta ferrite fraction.

Studies on Numerical Simulation of Temperature Distribution in Laser Beam Welding of 304L Austenitic Stainless Steel

A numerical simulation of temperature distribution in laser welding of 304L austenitic stainless steel have been investigated in the present research work. A three-dimensional Gaussian conical moving heat source has been implemented in the present numerical simulation using ANSYS software package. Temperature-dependent thermal physical properties of 304L austenitic stainless steel have been considered, which affects the temperature profile in the weldment. The effect of laser welding process parameters, namely, average beam power, welding speed, and laser spot diameter on weld bead geometry have been studied. The temperature distribution obtained from the numerical results at different positions away from the weld line were found to be in good agreement with the experimental results. The shape of the weld pool profile obtained through numerical simulation are in good agreement with the experimental results. Mechanical properties of the welded joint have also been studied. The ultimate tensile strength of the laser welded sample was equal to the base metal 304L austenitic stainless steel.

Effect of Submerged Arc Welding Parameters on Hard Facing with Different Proportions of Alloy Mix upon Mild Steel

The optimum values of various parameters and their levels were determined for minimum dilution level in SAW process. The element infusion in hard facing was determined by optical emission spectra analysis. This study will help the engineers to select the proper parameters for required weld bead geometry. Also to use various elements and ferro-alloys in proper composition to develop localized alloying on mild steel to reduce wear losses.

A Three-Dimensional Numerical Model for Predicting the Weld Bead Geometry Characteristics in Laser Overlap Welding of Low Carbon Galvanized Steel

Laser welding (LW) becomes one of the most economical high quality joining processes. LW offers the advantage of very controlled heat input resulting in low distortion and the ability to weld heat sensitive components. To exploit efficiently the benefits presented by LW, it is necessary to develop an integrated approach to identify and control the welding process variables in order to produce the desired weld characteristics without being forced to use the traditional and fastidious trial and error procedures. The paper presents a study of weld bead geometry characteristics prediction for laser overlap welding of low carbon galvanized steel using 3D numerical modelling and experimental validation. The temperature dependent material properties, metallurgical transformations and enthalpy method constitute the foundation of the proposed modelling approach. An adaptive 3D heat source is adopted to simulate both keyhole and conduction mode of the LW process. The simulations are performed using 3D finite element model on commercial software. The model is used to estimate the weld bead geometry characteristics for various LW parameters, such as laser power, welding speed and laser beam diameter. The calibration and validation of the 3D numerical model are based on experimental data achieved using a 3 kW Nd:Yag laser system, a structured experimental design and confirmed statistical analysis tools. The results reveal that the modelling approach can provide not only a consistent and accurate prediction of the weld characteristics under variable welding parameters and conditions but also a comprehensive and quantitative analysis of process parameters effects on the weld quality. The results show great concordance between predicted and measured values for weld bead geometry characteristics, such as depth of penetration, bead width at the top surface and bead width at the interface between sheets, with an average accuracy greater than 95%.

Parametric optimisation of gas metal arc dissimilar welding on AISI 304 stainless steel and low carbon steel

The weld-bead geometry and mechanical properties of the AISI 304 stainless steel and low carbon steel gas metal arc dissimilar weldments were optimised within a process window (wire feed rate (66-96 mm/s), voltage (19-25 V) and welding speed (3-6 mm/s)). The variations of the weld-bead width and mechanical properties with the processing parameters were analysed and presented. Significant changes in the microstructure of the weld zone with the heat energy inputs were observed. All the three utilised parameters contributed significantly to the bead width, ultimate tensile strength (UTS) and hardness of the weldments. The welding speed contributed most significantly to the UTS and bead width while the voltage has the most significant effect on the hardness. Optimum weld qualities including continuous joint, high tensile strength (422 MPa) and high hardness (112 HB) were found at 84 mm/s wire feed rate, voltage of 25 V and speed of 3 mm/s.