Bead Profile Research Articles

Energy reconstruction and metallurgical characteristics in 316L NG-LWFW with assisted wire wobbling by numerical and experimental analysis

A novel, new approach of narrow gap laser wire feeding welding (NG-LWFW) with electromagnetic assisted wire wobbling is proposed to solve incomplete sidewall fusion and improve solidification morphology. The energy distribution and fusion zone formation during multi-pass NG-LWFW process are clarified. The melt pool is driven into sidewall position and the melted metal accumulates towards that side groove, leading to the increase of sidewall penetration with concave bead profile. The simulation results show that the wire wobbling obviously reduces peak temperature of melt pool and increases sidewall temperature. The heat affected zone (HAZ) width reduced, and a finer and diversity weld microstructure is presented. As multi-pass welding proceeds, the former weld is heat-treated by the latter weld, leading to the re-melting of columnar grains and increasing diversity of interlayer grains. The columnar crystal zone is refining and a narrower dendrite spacing of δ-ferrite phase is found with deposited filling layers. The micro-hardness of weld centerline shows an overall increase trend and the impact energy increases with denser dimples from the bottom layer to upper layer.

Computational minimization of over-deposition at corners of trajectories in Laser Metal Deposition

Avoidance of over-deposition at trajectory corners is relevant in Laser Metal Deposition (LMD) for Additive Manufacturing. Currently available LMD hardware only allows constant material feed (g/s). Therefore, gliding speed of the material dispenser is the remaining tuning variable for controlling metal over-deposition at corners. Existing literature reports trial–error physical experiments, addressing only particular corner angles. In response, this manuscript reports the implementation of a voxel-based simulator of the bead geometry, taking into consideration bead profile, dispenser velocity, material feed, and bead curve geometry. We use it to evaluate two constant-feed tailored-velocity strategies for minimizing material over-deposition at corners.

Effect of Laser Pulse Duration on Tensile and Electrochemical Behavior of Laser-Welded Dual-Phase Steel

Dual-phase steels having excellent combination of strength and ductility are extensively used in automotive industry for the manufacture of car body structure involving welding and joining significantly. The present study assesses the tensile and electrochemical behavior of butt welded dual-phase 780 steel grade produced using pulsed Nd:YAG laser with varying pulse duration in the range of 1.5 to 3.6 ms. Numerical modeling has been done to know the temperature profile during welding. Systematic analysis of welded joint bead profile, microstructure, tensile test results, and fractographic features revealed the effect of pulse duration on the fusion zone, heat-affected zone softening, and also allowed the estimation of critical size of the soft zone near to the failure location under tensile loading. With an increase in pulse duration, welded joint concavity reduced from 35 to 6% which improved the mechanical performance of the welded joints. Welded joints with higher pulse duration enhanced the resistance against galvanic and pitting corrosion due to the formation of the oxide layer, finer martensitic microstructure in the fusion zone and a smaller amount of weld defects.

Data-driven multi-objective optimization of laser welding parameters of 6061-T6 aluminum alloy

In this paper, a data-driven multi-objective optimization approach using optimal Latin hypercube sampling (OLHS), Kriging (KRG) metamodel and the non-dominated sorting genetic algorithm II (NSGA-II) is presented for the laser welding process parameters on 6061-T6 aluminum alloy. The experiments are designed by OLHS and carried out to obtain the data results. The complex relationship between the process parameters and the bead profile geometry is established by KRG using the data results. The accuracy of the established KRG metamodel is validated using experiments. Then, NSGA-II is used to explore the design space and search the Pareto optimal solutions of process parameters. Besides, the validation experiments were carried out to obtain ideal LW bead profile, which shows that the approach can bring dependable guidance for LW experiments.

Recycling of steel slag as a flux for submerged arc welding and its effects on chemistry and performance of welds

The slag generated by the steel plant has been utilized to produce submerged arc welding flux. The flux produced by recycling steel slag has been applied in the submerged arc welding process. The effects of recycled slag on the chemical composition, microhardness, and microstructure of weld metal have been evaluated. For chemical composition, weld pads were prepared and beads on plates for bead geometry were deposited. It has been found that the chemistry of welds deposited using recycled steel slag is acceptable in accordance with ASME specifications. It is further observed that the addition of 10% CaCO3, 20% SiO2, and 6% MnO to the steel slag during recycling provided 0.10% carbon, 0.11% Si, and 0.8% Mn, respectively, in the weld metal. The microstructure of welds produced using recycled steel slag contains acicular ferrite which is desirable for improved tensile and impact strength. The microhardness of weld metal prepared using recycled steel slag is 220.9 VHN, which is more than that of weld metal deposited with fresh flux. Smooth surface appearance and desirable bead profile having deeper penetration were obtained. It is interesting to note that the cost of recycled steel slag is economical by 62% in comparison with equivalent virgin flux available in the market. The developed technology after fine-tuning will be transferred to the industry for practical applications.

Effect of Welding Parameters on the Weld Bead Profile of Submerged Arc Welded Low Carbon Steel Plates

Welding of thick and long steel sections with minimal requirements of etch preparation has posed a challenge to the fabricators to have a reliable and good quality joint. Such requirements are successfully catered to by the submerged arc welding process which was developed in early 40s to weld thick hull sections of naval ships. The process has since been used extensively in heavy fabrication industries like ship building, pressure vessel and rail industries. The strength and quality of weld produced is decided by its bead parameters like depth of penetration, bead width and reinforcement height. It has been found that weld parameters like wire feed rate, voltage welding speed nozzle to plate distance, torch angle and flux composition have influence on bead parameters. Present work is an attempt to develop a mathematical relation between bead parameters and input parameters so that an empirical relation can be developed between them Full factorial approach with 2 levels and 3 factors is used and graphical depictions are used to analyse the result

A shape control strategy for wire arc additive manufacturing of thin-walled aluminium structures with sharp corners

• Self-overlapping in WAAM of thin-walled structures with sharp corners is revealed. • A corner cross-section model for WAAM is established. • Travel/welding speeds at corners are optimized by using the developed model. • An improved deposition quality at corners can be achieved through using the proposed shape control strategy. Wire Arc Additive Manufacturing (WAAM) of large thin-walled aluminium structures in the aerospace field has significant advantages over traditional subtractive approaches. The technique is based on arc welding and wire filler material, and the thin-walled structures are built up layer-by-layer. However, for the parts with sharp corners, the shape control poses a challenge due to the occurring of an inevitable self-overlapping of the deposition at corners. Since aluminium alloys are sensitive to heat, the undesired materials stacked at corners with excessive heat input reducing not only the shape accuracy of the deposited structures, but the stability of the deposition process also. In this paper, a shape control strategy was proposed to reduce shape errors through local optimization of deposition parameters at corners. A corner cross-section model correlating the relationship between the process parameter and bead profile in the self-overlapping area was firstly established. Accordingly, the parameter of the welding speeds at the corner areas were locally optimized with the proposed bead model. The performance of the present corner cross-section model was then investigated in terms of corners with the angle degree varied from 15° to 60°. Finally, the proposed shape control strategy was implemented through experiments on a thin-walled aluminium structure with varied sharp corners. It can be found that the accumulative height errors varied with the change of the angle degree of the corners. At the corner with the angle of 60°, the height error reduced from 3.56 mm to 1.75 mm corresponding to the average building height of 55.2mm. More than 50 % in error reduction was achieved indicating the considerable improvement of the proposed control strategy. This is critical in process planning to achieve better shape accuracy and material efficiency in the WAAM of thin-walled aluminium structures with sharp corners.

Imperfections and Modelling of the Weld Bead Profile of Laser Butt Joints in HSLA Steel Thin Plate

In many applications that use high strength steels, structural integrity depends greatly on weld quality. Imperfections and the weld bead geometry are influencing factors on mechanical properties of the welded joints but, especially in the fatigue strength, they cause a great decrease. The proper knowledge of these two factors is important from the nominal stress approach to the fracture mechanics approaches. Studies concerning the profile and imperfections of the weld bead in laser welding for thin plates of high strength steels are scarce. In this work, these two aspects are covered for five series single and double-welded joints, butt joints in a 3 mm thick HSLA steel, welded in a small range of welding parameters. The actual profiles captured with profilometer were modeled with proposed geometric parameters achieving an adequate fit with values of the coefficient of determination ℜ2 greater than 0.9000. Description of imperfections includes the distributions of porosity and undercuts. The evaluation of the weld quality, taking as guide the ISO 13919-1 standard determined B and D levels for the welded series while based on the stress-concentrating effect, showed a greater detriment in those series with undercuts and excessive penetration. The analysis of variance validated the results of the different combinations of laser welding parameters and showed, for the factorial experimental design, a more significant effect of the welding speed.

Optimal weld bead profiles in the conduction mode LBW of thin Ti–6Al–4V alloy sheets

<abstract> <p>Day by day laser welding (LW) is gaining industrial importance. Good quality of weld joints can be realized through this process. Because this process yields low distortion and small weld bead. Aerospace, nuclear, automotive, and biomedical industries are opting for the lightweight and corrosion resistance titanium alloys. This paper deals with the generation of optimal weld bead profiles in the conduction mode laser beam welding (LBW) of thin Ti–6Al–4V alloy sheets. Laser beam diameter, power and welding speed are the 3 LBW parameters, whereas, bead width, depth of penetration, heat affected zone and maximum temperature are the performance indicators (PIs). 3 levels are set for each LBW parameter. Taguchi's L<sub>9</sub> OA (orthogonal array) is selected to minimize the numerical simulations. ANSYS Fluent V16.0 with Vc++ code is used to develop a generic model. %Contribution of each process variable on the PIs is assessed performing ANOVA analysis. The range of PIs is assessed adopting the modified Taguchi approach. A set of optimal LBW parameters are identified considering a multi-objective optimization technique. For these optimal LBW parameters weld bead width is minimum, and the depth of penetration is maximum. Empirical relations for PIs are developed and validated with simulations. Utilizing the Taguchi's design of experiments, empirical relations are developed for the performance indicators in laser beam welding (LBW) simulations performing few trial runs and identified the optimal LBW process parameters.</p> </abstract>

Activated flux TIG welding of dissimilar SS202 and SS304 alloys: Effect of oxide and chloride fluxes on microstructure and mechanical properties of joints

Low depth of penetration limits the use of favored tungsten inert gas (TIG) welding process for joining of ferrous and non-ferrous metals, demanding weld bead profile of high quality. This article aims to study the effect of chloride and oxide fluxes viz. calcium chloride (CaCl2) and ferric oxide (Fe2O3) on micro-structural and mechanical properties of TIG welded joints of dissimilar SS304 and SS202 steels. Results reflected that use of oxide and chloride fluxes significantly affects the weld bead geometry, bead dimensions and penetration. The use of oxide flux resulted in complete penetration and approximately linear root of weld with good fusion of both the base metals. Fusion zone showed columnar dendritic cast grain structure while coarse grain structure was obtained in heat-affected zone. Fusion zone hardness was higher than SS304 base metal and an opposite trend observed for SS202 irrespective of welding condition. Fine grained heat affected zone hardness was higher than coarse rain for all welding conditions.

Determination of heat source model for simulating full penetration laser welding of 316 LN stainless steel by computational fluid dynamics

The selection of appropriate heat source model is vital in predicting the temperature distribution and visualizing the dynamic fluid flow behaviour during Laser keyhole welding of Type 316 LN stainless steel. Three-dimensional (3D) numerical models were designed utilizing ANSYS Fluent by employing different heat source models. Different heat source models considered include volumetric heat sources namely Goldak double ellipsoidal, 3D conical, a coalition of 3D conical and cylindrical heat source, 3D volumetric Gaussian and Rotary Gaussian. The simulation was carried out by solving the fundamental conservation equations of mass, momentum and energy. The predicted weld bead profile by different heat sources were compared with the actual weld bead obtained from the laser welding experiment on 0.0055 m thick 316 LN stainless steel (SS) plates. It was found that simulation results of the conical-cylindrical combined (CCC) model exhibited good agreement with actual weld bead dimensions and thermal data obtained during the experiment. Therefore, the conical-cylindrical heat source model is recommended for CFD simulation of full penetration laser welding of 316 LN stainless steel for studying the effect of variation of laser power and surface active element on the weld pool development.

Numerical simulation of the influence of oxygen content on the weld pool depth during activated TIG welding

The required amount of surface-active element dissolved in the weld pool remarkably influences the depth of penetration during activated tungsten inert gas (A-TIG) welding process. This is mainly attributed to the changes in the surface tension coefficient sign by oxygen content, which in turn controls the reversal of fluid flow and the nature of heat transfer. It emphasizes that there is a strong correlation between the surface-active element oxygen content and the development of the weld pool. This research intends to find out the critical oxygen content required in the weld pool to cause complete reversal of Marangoni flow and its influence on the weld bead dimensions by numerical simulation during A-TIG welding. Three-dimensional evolution of thermal and velocity fields in the weld pool is simulated using ANSYS Fluent for 200 A and 300 A welding currents respectively by altering the dissolved oxygen levels in a 0.01 m thick 316 LN stainless steel (SS) plate. The simulated weld bead profile for varying dissolved oxygen levels is validated for 300 A current by carrying out A-TIG welding experiments in a 0.01-m–thick plate with different fluxes in order to achieve the diverse amounts of oxygen content in the weld pool. The simulated and experimentally obtained weld bead dimensions exhibited good agreement for various dissolved oxygen contents in the weld. The complete reversal of fluid flow has been found to occur in the weld pool when the dissolved oxygen in the weld pool is 335 ppm at 300 A and 200 ppm at 200 A current.

Optimization of weld strength for laser welding of steel to PMMA using Taguchi design method

Dissimilar joining of 304 stainless steel to PMMA is accomplished by a Nd: YAG pulsed laser. The light and process were represented by laser peak power, welding speed, defocus, pulse duration, pulse frequency and Ar gas flow rate, as these experiment parameters have significant effects on joints strength, weld width, joints quality and appearance. The welding parameters were optimized by an orthogonal experiment design, then the validation and optimization experiments were carried out to obtain the best combination of process parameters. A maximum weld strength of the joints of 974 N was achieved (the joints efficiency reached 70% of the base PMMA), much larger than ever reported. Bead profiles such as bead width and mechanical strength were investigated, and five types of 304 stainless steel-PMMA welded joints and three kinds of fracture model have been proposed.

Estimation Method of Interpass Time for the Control of Temperature during a Directed Energy Deposition Process of a Ti-6Al-4V Planar Layer.

Directed energy deposition (DED) provides a promising additive manufacturing method to fabricate and repair large metallic parts. However, it may suffer from excessive heat accumulation due to a high build rate, particularly during a wire feeding-type DED process. The implementation of interpass time in between two depositions of beads plays an important process role to passively control the interpass temperature. In this study, a method to estimate the proper interpass time using regression analysis from heat transfer finite element analysis is proposed for maintaining the interpass temperature during a wire feeding-type DED deposition of a planar layer. The overlapping beads of a planar layer are estimated using a polygonal-shaped bead profile in the finite element model. From the estimated proper interpass time, a selected proper interpass time scheme (PITS) is suggested for practical implementation. The selected PITS is applied in a thermo-mechanical finite element model to evaluate the temperature distribution and its effects on the depth of the melt pool, the depth of the heat-affected zone (HAZ), displacement, and residual stresses. By comparing the predicted results with those using a constant interpass time scheme (CITS), the selected PITS shows better control in reducing the depths of the melt pool and HAZ without severely inducing large displacement and residual stresses.

Parametric Formula for Stress Concentration Factor of Fillet Weld Joints with Spline Bead Profile.

The existing parametric formulae to calculate the notch stress concentration factor of fillet welds often result in reduced accuracy due to an oversimplification of the real weld geometry. The present work proposes a parametric formula for the evaluation of the notch SCF based on the spline weld model that offers a better approximation of the real shape of the fillet weld. The spline model was adopted in FE analyses on T-shape joints and cruciform joints models, under different loading conditions, to propose a parametric formula for the calculation of the SCF by regression analysis. In addition, the precision of parametric formulae based on the line model was examined. The magnitude of the stress concentration was also analyzed by means of its probability distribution. The results show that the line model is not accurate enough to calculate the SCF of fillet weld if the weld profile is considered. The error of the SCF by the proposed parametric formulae is proven to be smaller than 5% according to the testing data system. The stress concentration of cruciform joints under tensile stress represents the worst case scenario if assessed by the confidence interval of 95% survival probability.

Experimental and numerical studies on gas tungsten arc welding of Ti–6Al–4V tailor-welded blank

The effect of gas tungsten arc welding (GTAW) process parameters and its impact on the titanium TWB was studied experimentally as well as using numerical simulation. Bead characteristics of BoP trials (bead on plate) were analyzed based on Taguchi L27 orthogonal array by taking welding current (115 A, 125 A, 135 A), welding speed (4.1 mm/s, 5.8 mm/s, 7.5 mm/s) and arc length (3 mm, 4 mm, 5 mm) as process parameters. The bead width and depth of penetration for all trials were measured by using the weld expert system. Based on the bead characteristics, optimized GTAW process parameters (135 A, 4.1 mm/s and 3 mm) were identified for making the TWB by joining 2–1.6-mm-thick Ti–6Al–4V sheets. The tensile test of the prepared Ti–6Al–4V TWB was conducted in the universal testing machine. The COMSOL and ABAQUS software packages were used for the numerical simulation of TWB to assess the bead profile and tensile properties. The prediction made from the temperature distribution curve related to phase change near weld zone, exactly matched with the experimental work. The joint strength of TWB observed to be around 982 MPa and 1005 MPa was evaluated experimentally and conducting ABAQUS simulation work. The tensile test results were comparable with each other within the acceptable error level.

Multi sensor based strategies for accurate prediction of friction stir welding of polycarbonate sheets

High performance thermoplastic is often used in automotive and aerospace sectors. Friction stir welding (FSW) has been a suitable method for joining these thermoplastic materials. However, the process characteristics vary dynamically, even at same parametric conditions due to process disturbances. While quite a few studies have been reported in experimental investigation, the usage of sensors for the process monitoring during welding has not been explored. Therefore, the present paper focuses on various sensor-based approaches on process monitoring. The study includes an in-depth experimental investigation for joining of polycarbonate sheets using full factorial design of experiments. Three different tool pin profiles like cylindrical, square and triangular have been selected, whereas tool rotational speed and traverse speed are considered as primary process variables. Various statistical time domain features of the force and torque signals starting from average, its deviation and root mean square as well as thermal cycle based weld peak temperature and its cooling rate were found to have a strong correlation with weld bead profile. The axial force and thermal cycles were found to be the major indicators of joint strength efficiency rather than torque as per regression models developed by using response surface methodology. Finally, an attempt has been made for improving the joint strength predictability by using various sensor-based approaches. This work can be used potentially to real time welding process monitoring in industrial sectors.

Numerical Investigation on Molten Pool Dynamics and Defect Formation in Electron Beam Welding of Aluminum Alloy

Penetration depth fluctuations and spiking defects, which appear almost simultaneously during partial penetration electron beam welding (EBW) of aluminum alloy, lead to weakened joint strength. In this study, a novel dynamic heat source model, which can be used to understand the coupling behavior between the electron beam and keyhole wall, is proposed to simulate the EBW process. While studying molten pool patterns, the formation mechanism of weld defects is also discussed in detail. In addition, a corresponding experimental test is carried out as verification. The weld bead profile and dimensions predicted by simulations agree well with the experimental data. The periodic oscillation of the molten pool is the root cause of the penetration depth fluctuations. The simulation results show that spiking defect formation has four crucial steps: keyhole collapse, liquid metal backfilling, cutting by the molten pool boundary and liquid metal backfilling. The findings from this work provide a fundamental understanding of the formation mechanism of the penetration depth fluctuations and spiking defects during EBW of aluminum alloy to improve the weld bead quality.

Analysis of copper sheets welded by fiber laser with beam oscillation

Laser welding of Copper is a challenge due to its high thermal conductivity, low absorptivity of laser light and facility to dissolve oxygen favoring the formation of oxides. However, recent developments suggest that these problems can be overcome by power spatial modulation of the laser beam. This paper presents results on laser welding with beam oscillation (wobbling effect) performed on Copper plates. The effect of the major welding parameters on the weld surface aspect and bead profile are discussed, as well as the microstructure evolution. An interesting feature was observed in the microstructure of the fusion zone in the form of circular shaped bands which result from the solidification front of the weld metal as the laser oscillates and travels continuously. No defects were seen in the welds suggesting this variant of laser welding has potential for industrial applications where high thermal and/or electrical conductivities are required.

Mechanism investigation of the influence of the magnetic field on the molten pool behavior during laser welding of aluminum alloy

Magnetic field-assisted welding provides a promising approach to suppress defects and improve weld bead properties significantly. In this paper, a full factorial experiment was conducted to study the mechanism of the influence of the magnetic field on the weld profile of aluminum alloy laser welding. Furthermore, a three-dimensional numerical simulation model simultaneously considering the free surface of the keyhole, and the effect of the magnetic field is developed to reveal the mechanism of the influence of the magnetic field on the weld bead profile by analyzing molten pool behavior. It was found that the magnetic field can reduce the width of the weld bead while increasing the depth and middle width of the weld bead. The magnetic field distribution in the weld bead was numerically simulated and validated. The simulation results demonstrate that the liquid motion in the magnetic field can induce a Lorentz force in a direction opposite to the flow velocity. The magnetic field can suppress both the lower-to-upper region and center-to-edge molten flows of the molten pool, which reduces the heat transfer from the tip of the keyhole to the molten pool surface and from the center to the boundary of the molten pool. This can provide a concept to reveal the underlying mechanism of the influence of the magnetic field on the weld bead profile. This work could contribute to gain insight into the influence of a magnetic field on aluminum alloy laser welding.