Welding Simulation Research Articles

Numerical investigation of the influence of pulse frequency on the weld pool size in pulsed current TIG welding

This study simulates the pulsed current tungsten inert gas (TIG) welding process to investigate the transient development of the weld pool in a 4 mm thick aluminum sheet, focusing on the effects of pulse frequency on the weld pool size. Two pulsed currents, 230 and 180 A, with a 30% background current, were examined. The 230 A current achieved full, while the 180 A resulted in partial penetration. Five pulse frequencies (1, 4, 10, 20, and 50 Hz) were analyzed. A numerical model was developed to compute heat and current fluxes on the workpiece surface. The arc profile shifted from a bell shape in high-frequency cycles to a conical shape in low-frequency cycles. The heat and current fluxes served as inputs to another model that simulated weld pool behavior for both direct and pulsed current TIG welding. The results showed that weld pool size decreased in pulsed current TIG welding. At 230 A, full penetration changed to partial penetration under pulsed current. At 1 Hz, sufficient time was available for solidification during the low-cycle period, but at 50 Hz, the weld pool remained liquid. As pulse frequency increased from 1 to 50 Hz, the weld pool depth decreased significantly, with a reduction from 2.4 to 0.9 mm at 230 A and from 1.1 to 0.34 mm at 180 A. Convection in the weld pool was influenced by temperature and was strongest at higher temperatures. The decrease in weld pool size was most pronounced between 1 and 10 Hz, stabilizing between 20 and 50 Hz. Validation against experimental macrographs demonstrated good agreement with the simulations.

Investigation on the Weldability of Developed High‐Strength Hull Structure Steel

The weldability of a developed high‐strength hull structure steel is investigated using a coarse‐grained heat‐affected zone (CGHAZ) thermal simulation and duplex double welding under a heat input of ≈20 kJ cm−1. From the results, the average impact test energy at −50 °C for the simulated CGHAZ samples is 142 J and for samples with V‐notch position 0.5 mm from the fusion line (FL) was 152 J. The impact test energies for the V‐notch position at the FL also show good toughness. The simulated samples and samples from the weld joint are machined into standard sizes to test their tensile strengths, which meet the request high strength. It is concluded that the high strength of the CGHAZ is mainly due to phase transformation and is supplemented by solid solution strengthening. The good low‐temperature toughness is mainly due to the high Ni content. All the results are comparable to the reported mechanical property test results of the weld joint of navy HSLA‐100 steel under a similar heat input. This suggests that the developed high‐strength hull structure steel exhibits satisfactory weldability.

Study of atomic diffusion behavior in diffusion welding of NiTi alloy - based on molecular dynamics

NiTi alloy with nearly equiatomic ratios of Ni and Ti, has a unique shape memory effect and biocompatibility. Atomic diffusion is a determinant factor for the diffusion welding of NiTi alloys joining. In general, the atomic diffusion may be mediated by the temperature, time and pressure and so on. Despite the importance of technology, Ni and Ti atoms’ diffusion mechanism, however, still remains un-elucidated. Few works have investigated the movement rules of atoms from the atomic scale. Molecular dynamics simulations of diffusion welding were performed for 200–800 ps to investigate the diffusion process of the NiTi alloy composite plate at temperatures of 1000, 1100, 1200, and 1300 K. The results show that the holding temperature had the greatest effect on diffusion, with pressure having the least effect. The diffusion coefficients of NiTi, Ni, and Ti were calculated at temperatures of 1000, 1100, 1200, and 1300 K, respectively. The diffusion degree of Ni atoms was higher than that of Ti atoms. The diffusion coefficients of Ni and Ti atoms satisfied the Arrhenius equation, and the diffusion activation energy of Ni atoms was lower than that of Ti atoms. Furthermore, this study demonstrates at the atomic scale that the growth of the diffusion layer at high temperatures follows the parabolic growth kinetics law.

Evaluation and Prediction of Mechanical Properties According to Welding Methods of Ni 825/A516-70N Clad Plates

In this study, the microstructures and mechanical properties of different methods of FCAW (Flux-cored arc welding) + FCAW or FCAW + GTAW (Gas tungsten arc welding) welding on Ni825/A516-70N clad plate were investigated, using a double U groove angle on a laboratory scale. The amount of specimen deformation with FCAW + FCAW welding was ~1.5 mm, and that with FCAW + GTAW welding was ~3.6 mm. In the Vickers hardness tests, the average hardness value of the FCAW + GTAW welding specimens tended to be higher, and the hardness of the steel showed the same value. Also, in the tensile tests, the maximum strength and elongation of the FCAW + GTAW specimens were found to be higher. The SEM analysis of the welding boundaries of each specimen revealed the phenomenon of grain refinement in the specimens with FCAW + GTAW welding. This was due to the slow welding speed of this welding process and the rapid cooling rate caused by the relatively low layer thickness despite the relatively high number of weld passes. The computer simulation of the amounts of deformation were similar, with a value of 1.5 mm for FCAW + FCAW and 3.6 mm for the computer simulation, indicating the credibility of the simulation. In the computational simulation of butt welding, FCAW + GTAW showed high values for both residual stress and angular strain. The L-seam and C-seam of the demo vessel size were welded under the same conditions as the actual welding. The residual stress and angular deformation in the L-seam were 849 MPa and 2.3 mm for the FCAW + FCAW and 852 MPa and 2.9 mm for FCAW + GTAW. The residual stress and angular deformation in the C-seam were 920 MPa and 0.7 mm for FCAW + FCAW and 930 MPa and 0.9 mm for FCAW + GTAW, respectively.

Gleeble® simulation of the heat-affected zones in lean duplex stainless steel 2404: Understanding the effect of cooling rates on microstructure evolution and pitting corrosion resistance

Physical simulations of single-pass welding on lean duplex stainless steel (LDSS) 2404 were performed to obtain heat-affected zones (HAZs) at different cooling rates (200–1 °C/s) to evaluate the effects on microstructure changes and corrosion resistance. The findings showed that fast cooling rates resulted in insufficient austenite formation. The austenite mainly consisted of grain boundary austenite (GBA), Widmanstätten austenite (WA), and intragranular austenite (IGA). For the highest cooling rate, there was a remarkable precipitation of high-temperature Cr nitrides (Cr2N) and a high degree of sensitization (14.90%), significantly impairing the corrosion resistance. The influence of these Cr2N on LDSS 2404 was shown to be influenced by their amount, distribution, the region where precipitation occurred (α/α boundaries and α/γ interfaces), and the cooling rates applied.

Development of a 3D Virtual Welding Simulator Using Weld Bead Created by Voxelization Technique

In this study, we developed and implemented a cost-reducing, real-time virtual welding simulator to train welder candidates. In order to make a real-time welding simulation, a three-dimensional weld bead form was designed. We used a parabola as the basic bead slice shape, considering the similarity between the parabola and the bead slice. During the welding process, the parameters of the weld bead shape are calculated at each time step using an artificial neural network. This network determines the shape of the weld bead and the depth of penetration, based on inputs received from the sensor device that tracks the motions of the torch. After the parabola’s parameters have been determined, the voxel map and corresponding hash-based octree data structure are generated in real-time. By using the voxelized data, a weld bead isosurface consisting of triangles is reconstructed with a marching cubes algorithm allowing us to generate more realistic weld seam shapes. We used multi-threaded programming for voxelization and isosurface extraction to reduce the computation cost on high-resolution virtual scenes. The isosurface extraction times for different thread counts and also a feature comparison with other simulators in the literature are shown in this paper.

Study on Microstructure and Low‐Temperature Impact Toughness in Coarse Grain Heat‐Affected Zone of EH460 Steel

Herein, the effects of peak temperature on the microstructure and low‐temperature impact toughness of coarse grain heat‐affected zone (CGHAZ) of EH460 steel are investigated by Gleeble simulation welding. The low‐temperature impact toughness of CGHAZ decreases with the increase of peak temperature. With the increase of peak temperature, the microstructure of CGHAZ gradually changes from bainite to a mixed structure composed of bainite, intragranular ferrite, side lath ferrite, and a small amount of grain boundary ferrite. The inclusions size decreases as the peak temperature increases. The existence of large‐sized inclusions is conducive to the initiation and propagation of cracks, reducing the low‐temperature impact toughness of the material.

Simulation of Friction Stir Welding of AZ31 Mg Alloys.

Friction stir welding has been extensively applied for the high-quality bonding of Mg alloys. The welding temperature caused by friction and plastic deformation is essential for determining the joint characteristics, especially the residual stress and weld microstructure. In this work, a modified moving heat source model was proposed by considering the variations in heat generation caused by friction shear stress at both the side and bottom surfaces of the tool. The application of this model was further extended to the entire welding process, especially in the plunging stage. The relative errors between the experimental and simulated peak temperatures at characteristic points were small, with a maximum of 10%, thereby validating the model for accurate temperature prediction. Furthermore, the influence of welding and rotational speed on temperature fields was systematically investigated. At relatively low welding and rotational speeds, the welding temperature increased significantly with either an increase in rotational speed or a decrease in welding speed. However, this effect gradually diminished at higher welding and rotational speeds. These results provide some valuable guidelines for controlling heat generation to improve the quality of Mg alloy welds.

Modeling the coupled bubble-arc-droplet evolution in underwater flux-cored arc welding

For the numerical simulation of underwater wet flux-cored arc welding, the most crucial issue is to investigate the intense interactions between the underwater bubble, arc plasma, and molten metal. However, it is a great challenge to couple them into a single numerical model. In this study, a 3D three-phase flow model is originally established, which successfully couples the dynamic bubble, arc, and droplet. A modified Lee model is employed to realize spontaneous phase transition from liquid water to bubble gas. According to the simulation results, the bubble evolution is divided into four main stages, and two bubble separation modes are recognized. It is found that, both the changing pressure field around the bubble and the varying flow direction of surrounding water contribute to the unique bubble evolution patterns. As for the droplet, its violent up-and-down oscillation at the wire tip is mainly caused by the opposite gas drag forces, which are produced by the turbulent gas flow inside the bubbles. The upward gas drag force can even make the neck of the droplet disappear. With different droplet detaching angles, two predominant droplet transfer modes are numerically produced; when the angle reaches 147°, the droplet is pushed away and becomes a spatter. Furthermore, the underwater arc is found to be subjected to compressions from both the radial direction due to bubble necking and the axial direction due to droplet growth. The arc temperature and velocity vary significantly not only during the whole droplet transfer period, but also within each bubble evolution cycle. To verify the reliability of the model, underwater welding experiments and visual sensing are conducted. The simulated results match well with the experimental ones, with an 8% error in the droplet transfer period and only a 1.4% error in the bubble evolution cycle.

Multi-Criteria Calibration of a Thermo-Mechanical Model of Steel Plate Welding in Vacuum

This paper proposes a procedurefor multi-criteria calibration of a thermo-mechanical model for numerical simulation of welding in the space vacuum. A finite-element model of a steel plate is created. Experimental and computational data are obtained. An inverse problem is formulated for the vector identification of five calibration parameters from the heat-flow model. They are evaluated for adequacy with controlled accuracy according to four criteria. An optimization problem is solved using a two-step interactive procedure. The parameter space studying method (PSI) has been applied to the study of multidimensional regions by means of quasi-uniform sounding. A Pareto-optimal set is defined. It is used to determine reduced ranked Pareto subsets by μ-selection. Salukvadze optimum is also determined.

Works for Me: Personalizing Skilled Trade Worker Training via Smart Hand Tools

ABSTRACTThis paper explores an approach for applying Artificial Intelligence (AI) to co‐design smart hand tools to personalize learning for future skilled trade workers in workforce training programs. The purpose of this research is to better understand the perspectives of workers in the skilled trades and to respond with co‐designed socio‐technical interventions that empower workers. The research benefits from a collaboration between The University of Texas at Austin, the City of Austin, and Austin Community College (ACC) and incorporates insights from welding instructors and students, as well as skilled trade workers and supervisors. Social science findings derived from semi‐structured interviews inform tool design implemented by an interdisciplinary research team. The participatory design approach has resulted in two prototypes: a welding simulator that uses Augmented Reality (AR) and an AI‐enabled (smart) rotary tool. This paper has implications for workforce development to address skilled worker shortages. Additionally, it contributes to ongoing research into AI and skilled trade work which is understudied compared to AI and knowledge work.

Three-dimensional simulation of finite element ultrasonic welding of aluminum alloy AA-6061

Three-dimensional simulation of finite element ultrasonic welding of aluminum alloy AA-6061

Experimental Determination and Simulation Validation: Johnson–Cook Model Parameters and Grinding Simulation of 06Cr18Ni11Ti Stainless Steel Welds

Hydrogen permeation resistance in the welded region of 06Cr18Ni11Ti steel is relatively weak due to surface defects, which need high integrity surface machining. The parameters of the welding material for 06Cr18Ni11Ti steel are currently unavailable, which causes some inconvenience for simulation studies. To fill the lack of 06Cr18Ni11Ti steel weld material parameters in the relevant literature at the present stage, the quasi-static tensile test at different strain rates and notch specimen tensile tests were conducted in this paper and determined the Johnson–Cook (J-C) constitutive model parameters and Johnson–Cook failure model parameters. Subsequently, a multi-grain grinding simulation model was built based on W-M fractal dimension theory by using the determined material parameters. The influence of processing parameters on grinding heat was analyzed. Grinding experiments were conducted to analyze the influence of processing parameters on grinding heat and grinding force. By comparing the simulation and experimental results, it is revealed that the average error is 9.37%, indicating relatively small discrepancy. It is demonstrated that the grinding simulation model built in this paper could efficiently simulate the grinding process, and the determined weld material parameters of 06Cr18Ni11Ti steel have been verified to possess high accuracy and reliability.

Interdependence of metal vapor plume and melt pool dynamics during laser beam welding under vacuum

Deep penetration laser beam welding involves the emission of hot metal vapor and particles from the keyhole, which interact with the laser beam by means of scattering, absorption, and phase front deformation. The combination of scattering and absorption leads to an extinction of the laser beam, while the phase front deformation adversely affects the beam quality. The capillary formation depends on the local distribution of the absorbed irradiance of the laser beam, which in turn is related to the material process emissions. Additionally, the process atmosphere, in particular the oxygen content, and the working pressure influence the capillary fluctuations and cause variations in welding penetration. This study introduces a measurement setup using simultaneous high-speed observation of the melt pool and the keyhole while measuring the interaction mechanisms between the laser beam and the metal vapor plume during laser beam welding under vacuum of stainless steel. The obtained measurement provides a quantification of the various interaction mechanisms between the laser beam, vapor plume, keyhole, and interdepended melt pool dynamics. These quantitative high-frequency measurements at various working pressures and laser parameters provide useful insights that are crucial for understanding the formation of weld defects, resulting in process monitoring and validation of process-oriented welding simulations.

Effect of heat input on the microstructure and hydrogen embrittlement susceptibility of the coarse-grain heat-affected zone of CrMo steels generated using a Gleeble 3500 welding simulator

The changes in microstructure and hydrogen embrittlement (HE) susceptibility of the simulated coarse-grain heat-affected zone (CGHAZ) of CrMo steels under three distinct heat input conditions were investigated. The cooling time from 800 °C to 500 °C, represented by t8/5, increased from 100 s to 200 and 400 s.. The sample with t8/5 = 100 s has a microstructure consisting of martensite and a small amount of lower bainite. When the t8/5 was increased to 200 s and 400 s, the HAZ consisted of 65.43 % martensite and 34.57 % lower bainite and 4.53 % martensite with 95.47 % bainite, respectively. The HE susceptibility was assessed by slow strain rate tensile (SSRT) testing of hydrogen-charged samples, and the HE susceptibility index (IHE) declined from 87.89 % to 61.37 % when t8/5 increased from 100 to 400 s. The high dislocation density and hydrogen concentration in the sample with t8/5 = 100 s led to intergranular fracture and incresaed HE susceptibility. The martensite lath and cementite/ferrite interface are the sites of crack initiation in the sample with t8/5 = 200 s. In the sample with a cooling time of 400 s, the martensite/ferrite interfaces are the main crack initiation sites under hydrogen charging.

Numerical Simulation and Microstructure Analysis of 30CrMnMoRe High-Strength Steel Welding.

Welding experiments were conducted under different currents for single-pass butt welding of high-strength steel flat plates. The microstructure of welded joints was characterized using OM, SEM, and EBSD, and the welding process was numerically simulated using a finite element method. According to the grain size obtained by electron microscope characterization and the temperature data obtained by simulation, the microstructure and mechanical properties of coarse grain and fine grain areas of the heat-affected zone were predicted by using the material microstructure and property simulation software. Finally, the results of mechanical properties simulation were verified through mechanical property testing.

Feasibility of autogenous welding simulation for enhancement of residual stress

Feasibility of autogenous welding simulation for enhancement of residual stress

A novel method to establish friction coefficient model for numerical simulation of inertia friction welding

The precise friction coefficient at interface determines the friction behavior in inertia friction welding (IFW), its model is the basis to precisely describe the friction behavior in the numerical simulation of IFW. To measure the friction coefficient related to the temperature, pressure, and sliding velocity, the IFW trials between 2219-O Al alloy and 304 stainless steel were conducted with the simultaneous measurement of temperature and angular velocity evolutions. Two types of friction coefficient models were established by considering whether the effects of temperature and friction pressure were independent. The S-(T&P) L model, which considered the couple effect of temperature and friction pressure, was recommended as the best suitable model with its very high accuracy and best simplicity. The proposed model was successfully used in simulating the temperature evolution of IFW between Al alloy and steel tubes. The effect of the influencing variables on the friction coefficient was also discussed.

Evolution of inclusions in Ti-Ce-Mg deoxidized steel and its effect on acicular ferrite transformation in simulated welding HAZ

The characteristics of non-metallic inclusions in Ti-Ce-Mg deoxidized steel and their influence on the microstructure and toughness of welding heat-affected zone (HAZ) were studied. Results showed that Ti-Ce-Mg deoxidation led to a refined inclusion size and an increase in the number of inclusions below 1 μm. The highest acicular ferrite fraction was obtained in the HAZ of Ti-Ce-Mg steel, and the impact toughness was significantly improved. Ti-Ce deoxidation enhanced the stability of Ti-containing oxide, while Mg treatment promoted its fine dispersion. The final formation of composite inclusions of Ti-Ce-Mg oxide with TiN and MnS enhanced the ability to induce acicular ferrite transformation.

The influence of welding-induced 3D residual stress and distortion on the ultimate strength of multi-stiffened thin plate structures under cyclic load

Stiffened thin plates made of high-strength steel are widely employed in ship hull structures. Their strength capacity is highly sensitive to the welding imperfections and potential extreme cyclic loading from harsh sea state. In this work, a thermal elasto-plastic finite element analysis is conducted to simulate the 3D distribution of welding-induced residual stress and distortion of stiffened thin plate structures with triple spans and triple bays varying the plate thickness and heat input. Experimental results provided by other scholars are used to validate the welding simulation. Afterwards, the ultimate strength and collapse behaviour of the welded structures under different load patterns are dealt with, including monotonic compression load, cyclic compression-tension load and cyclic compression load. Observation from numerical results indicates that, in general, the compressive strength is reduced in each considered cycle by the residual stress as the amplitude of cyclic compression-tension load approximates to the ultimate compressive strain. When this parameter is much greater than the ultimate compressive strain or the stiffened plate is subjected to cyclic compression load, the reduction in ultimate strength is significant in the first cycle, whereas the reduction is ignorable in the later cycles. Besides, if the buckling mode of initial deflection with antisymmetric configuration is superposed to the symmetric out-of-plane welding distortion, impact of the residual stress will be diminished as the asymmetry becomes notable.