Welding Simulation Research Articles

An improved recoil pressure boundary condition for the simulation of deep penetration laser beam welding using the SPH method

Deep penetration laser beam welding is simulated using the mesh-free Lagrangian Smoothed Particle Hydrodynamics (SPH) method. The physical phenomena modeled are the elastic material behavior of the solid phase, the fluid dynamics of the liquid phase including temperature-dependent surface tension, heat transfer by heat conduction, and the phase transitions melting, solidification, and evaporation. The energy input of the laser beam is determined by a ray-tracing scheme that calculates the absorbed irradiance distribution in the capillary. Based on the locally absorbed irradiance, an improved recoil pressure model is introduced and compared with a temperature-dependent model frequently used in the literature. To transfer the momentum of the recoil pressure to the surrounding melt, two boundary conditions based on either dynamically detected boundary particles or surface forces are presented and validated using simple examples. The results show that the recoil pressure is a key factor for the formation of a deep capillary and the acceleration of the melt around the capillary. Comparison of capillary geometry and melt pool size from simulation and experiment shows good agreement for the irradiance-dependent recoil pressure model.

The Microstructure Prediction during the Welding Process of Fe–C–Si Steel Using Physical and Numerical Simulation: A Comparative Study

Overall, medium‐carbon, multiphase steels subjected to welding processes can be described as difficult and require dedicated process conditions. In these investigations, an attempt is made to characterize the welding process of commercial 55Si7 steel with a high carbon equivalent (CE = 0.73). An experimental tungsten inert gas (TIG) welding process is performed by the use of preheating. Then, to understand and explain the processes during welding, a numerical (finite element method [FEM]) and physical (dilatometry) simulation is carried out. Measurement points located in the heat‐affected zone (HAZ) are selected based on the obtained data of thermal cycles. Significant differences in the results obtained with the three approaches are assessed and indicated. The cause of the discrepancies in the test results is also identified. The essence of the implementation of material data, which precisely defines the kinetics of phase transformation, is confirmed. A detailed analysis of the contribution of the phases is performed, together with their morphological assessment, as well as the hardness distributions are conscientiously compared. Moreover, it seems that the segregation of the chemical composition of austenite and the initial microstructure plays a crucial role in terms of the quality of the prediction.

Influence of welding sequences on induced residual stress and distortion in pipes

A three-dimensional (3D) finite element (FE) model based on thermal-elastic-plastic approach in SYSWELD® was employed to investigate the effects of welding sequences on induced residual stresses and radial distortion in AISI 316L stainless steel welded pipes. To mesh the model, the HYPERMESH® processor was utilized and the model was then exported to SYSWELD® for further thermo-mechanical analysis. The Goldak's double ellipsoidal moving heat source model was employed in SYSWELD® to obtain the volumetric heat flux density in the Gas Metal Arc Welding (GMAW) simulation process. A neural-network program was suitably trained and used to predict the parameters of Goldak's model. The obtained numerical models using predicted Goldak’s parameters were then successfully validated by experimental results in terms of size of welding pool and the temperature distribution. Four different welding sequences (concepts) were investigated and compared: three quarters and one full circumferential welding. These welding sequences were anticipated to create the least residual stress and distortion in pipe welding. The results demonstrate that the welding sequences significantly influence induced residual stresses and distortions in magnitude and in distribution. For the full circumferential welding concept, which was proposed in this study, the residual stresses and distortion present more uniform distribution along the circumferential direction than those in quarter welding sequences. The magnitude of welding distortion was also significantly lower in the full circumferential concept when compared to the quarter welding concepts. The FE results of residual stresses in the full circumferential welding sequences were accurately validated by experimental tests.

Entire-Process Simulation of Friction Stir Welding — Part 2: Implementation of Neural Networks

To further understand the structure-parameter-property relationships of friction stir welded aluminum alloy joints, a nested neural network was proposed to map the macro- and microstructural response. The uncoupled effect of each primitive parameter on the joint performance was depicted. Reducing heat input and keeping an adequate load-bearing area of the welding nugget zone were proven to be the sufficient and necessary conditions to obtain high load-bearing performance. The entire-process simulation strategy showed great potential for prediction and optimization of the macro- and microstructural response of complex and large components.

Welding simulation using a reduced order model for efficient residual stress evaluation

Abstract In this paper, to evaluate the residual stress of welded structures efficiently, we propose a welding simulation method utilizing a reduced order model. To construct the reduced order model, a finite element model is divided into a target part and an omitted part. For the heat transfer analysis, a thermal boundary condition is newly defined and applied to the target part, to compensate for the heat loss induced by neglecting the omitted part. For the thermal elastic plastic analysis, a reduced model for the target part is constructed using the automated static condensation method. The performance of the proposed welding simulation method adopting the reduced order model is verified by solving several welding problems, and it effectively reduces computational costs while predicting the residual stress with little loss of accuracy.

Entire Process Simulation of Friction Stir Welding — Part 1: Experiments and Simulation

Understanding structure-parameter-property relationships in friction stir welding of aluminum alloys is a challenge despite its wide application in load-bearing components. In this paper, we propose a combined strategy for mapping the macro- and microstructural responses of these joints. A combined model based on experiment validation was adopted for the prediction of tensile strength. This included the computational fluid dynamics model, precipitation evolution model, dynamic recrystallization and recovery model, and computational solid mechanics model. The comparison between the experimental results and the combined model proved the rationality and accuracy of this numerical model.

Numerical Prediction of Strength of Socket Welded Pipes Taking into Account Computer Simulated Welding Stresses and Deformations.

The paper presents a numerical model based on the finite element method (FEM) to predict deformations and residual stresses in socket welding of different diameter stainless steel pipes made of X5CrNi18-10 steel. The next part of the paper concerns the determination of strength properties of a welded joint in terms of a shear test. A thermo-elastic–plastic numerical model is developed using Abaqus FEA software in order to determine the thermal and mechanical phenomena of the welded joint. This approach requires the implementation of moveable heat source power intensity distribution based on circumferentially moving Goldak’s heat source model. This model is implemented in the additional DFLUX subroutine, written in Fortran programming language. The correctness of the assumed model of thermal phenomena is confirmed by examinations of the shape and size of the melted zone. The strength of the welded joint subjected to shear is verified by performing a compression test of welded pipes as well as computer simulations with validation of the computational model using the Dantec 3D image correlation system.

A novel systematic numerical approach on determination of heat source parameters in welding process

The double-ellipsoidal heat source concept, established by Goldak, has been extensively employed to represent the energy distribution in a broad range of arc welding simulation processes. However, the Goldak's parameters need to be exactly and efficiently defined for accurate arc welding simulation. In this study, a novel procedure was proposed to accurately predict the Goldak's parameters in Gas Tungsten Arc (GTA) Welding simulation. A developed three dimensional (3D) Finite element (FE) analysis was performed to generate thirty sets of normalized input (welding pool characteristics) and outputs (Goldak's parameters). The relevance between Goldak's parameters and welding pool characteristics were established using two regression models and Artificial Neural Network (ANN) computing systems. Linear and quadratic regression models and ANN were compared for evaluation of accuracy of the parameters. Analysis of the results indicated that ANN slightly transcends both regression models, even though the regression models and ANN were able to suitably predict Goldak's parameters for welding simulation. Hence, Goldak's parameters for the welding numerical model were estimated and employed from the ANN model. 3D FE analysis based on thermal-elastic-plastic model using predicted Goldak's parameters were then conducted and validated by the experimental tests in terms of the size of welding pool, temperature distribution and induced residual stress. In the proposed procedure, the data set in training process was obtained using an efficient FE model analysis, which eliminates the cost and time associated with plenty of experimental tests.

Welding simulation of railway bogie frame side beam: Analyses of residual stresses, clamping forces, distortion and prediction of fatigue S-N curves

This paper presents numerical analyses of a welding simulation of a bogie frame side beam. The simulation is based on an analytical thermal model coupled with a non-linear structural finite element model using shell elements enabling the welding simulation of large structures. The predicted clamping forces, distortions, and residual stresses for different clamping conditions and plate thicknesses are analysed in terms of manufacture. A new fatigue model based on the endurance limit approach is proposed using residual stresses to predict the S-N curves. The predicted S-N curves with the proposed model showed close correlation with the S-N curves for class F and class F2 welds of the BS7608 standard, demonstrating its validity and potential use in design.

Finite element simulation of multi-layer repair welding and experimental investigation of the residual stress fields in steel welded components

Finite element simulation of multi-layer repair welding and experimental investigation of the residual stress fields in steel welded components

Sequentially combined thermo-mechanical and mechanical simulation of double-pulse MIG welding of 6061-T6 aluminum alloy sheets

Double-pulse MIG (DP-MIG) welding is an efficient aluminum alloy jointing technique, which can form heterogeneous aluminum alloy welded sheets with different microstructure and mechanical properties. In order to accurately analyze and predict mechanical properties of welded structures, the geometrical features, local material properties and residual stresses of different welded zones should be synthetically considered in the numerical simulation. This work proposes a sequentially combined thermal-mechanical and mechanical simulation to accurately characterize the mechanical properties of the welded joint through the finite element analysis (FEA) method. The thermo-mechanical simulation was carried out to analyze the transient temperature field and residual stress distribution, which are conductive to build mechanical simulation model with detailed geometric features, the corresponding local material properties as well as attached residual stress. Subsequently, the mechanical simulation was performed to investigate the stress distribution of the welded joint. The deformation behavior and load-carrying capacity of the welded joint from numerical simulation are all in good agreement with corresponding experimental study, which indicates the feasibility and superiority of the developed sequentially combined thermal-mechanical and mechanical simulation method. Also, the stress distribution of the welded joints analyzed by numerical simulation reveals that the fracture evolution mechanism depends on whether the reinforcement has been removed from the welded specimen. The existence of the weld reinforcement leads to the increase of shear stress under tensile condition; hence, the fracture morphology includes equiaxed dimples and elongated dimples. When the reinforcement is removed, the mechanism is trans-granular and inter-granular mixed fracture in the welded zone; otherwise, trans-granular fracture occurs in the heat-affected zone.

Numerical simulation of the stationary shoulder friction stir welding of Ti-6Al-4V

Numerical simulation of the stationary shoulder friction stir welding of Ti-6Al-4V

Sensitivity of Solid Element Spot Weld Modeling Methodology to Nugget Diameter

<div class="section abstract"><div class="htmlview paragraph">A vehicle’s structure has more than 4000 spot welds, which can be considered as one of the main design criteria that affects the general stiffness as well as the durability of an automobile. Considering the essential role of finite element-based simulations of the spot-welded structures on the design phases of vehicle development, accuracy of analyses can be considered as one of the main concerns to meet the design objectives. This study examines the sensitivity of solid element spot weld modeling technique to nugget diameter. Comparative stress and multi-axial low cycle fatigue analyses are conducted for the inspection of the effect of weld diameter on solid element spot weld simulations. Displacement contours as well as local stress profiles at the vicinity of the spot welds are examined to evaluate the effect of nugget diameter on general stiffness and safety. Multi-axial low cycle fatigue analyses are conducted for the specimens composed of U-profiles, and different thickness levels are simulated for a set of nugget diameters. Simulation results are compared with the low cycle fatigue tests’ life cycles to determine the accuracy of the solid element spot weld modeling methodology and its sensitivity to nugget diameter.</div></div>

Infrared Visual Sensing Detection of Groove Width for Swing Arc Narrow Gap Welding

To solve the current problem of poor weld formation due to groove width variation in swing arc narrow gap welding, an infrared passive visual sensing detection approach was developed in this work to measure groove width under intense welding interferences. This approach, called global pattern recognition, includes self-adaptive positioning of the ROI window, equal division thresholding and in situ dynamic clustering algorithms. Accordingly, the self-adaptive positioning method filters several of the nearest values of the arc’s highest point of the vertical coordinate and groove’s same-side edge position to determine the origin coordinates of the ROI window; the equal division thresholding algorithm then divides and processes the ROI window image to extract the groove edge and forms a raw data distribution of groove width in the data window. The in situ dynamic clustering algorithm dynamically classifies the preprocessed data in situ and finally detects the value of the groove width from the remaining true data. Experimental results show that the equal division thresholding algorithm can effectively reduce the influences of arc light and welding fume on the extraction of the groove edge. The in situ dynamic clustering algorithm can avoid disturbances from simulated welding spatters with diameters less than 2.19 mm, thus realizing the high-precision detection of the actual groove width and demonstrating stronger environmental adaptability of the proposed global pattern recognition approach.

Using double ellipsoid heat source model for prediction of HAZ grain growth in GTAW of stainless steel 304

The grain growth in HAZ of austenitic stainless steels during welding is an important metallurgical change that affects the mechanical properties. In this study, the finite element simulation of heat transfer in GTAW of stainless steel 304 is investigated using double ellipsoid heat source model. The simulation results are compared with the results obtained from the analytical Rosenthal model and also experimental data. The simulated peak temperatures are close to the experimental results at the measurement points (the maximum relative difference is 10%), while the Rosenthal model has a maximum relative difference of 34%. It is also observed that the simulated weld pool size is also better compatible with the experimental results than the Rosenthal model. Additionally, the calculated grain size based on the simulation results is also more consistent with the experimental data than the Rosenthal model, particularly near the fusion boundary.

Investigation of welding parameters effects on temperature field and structure field during laser-arc hybrid welding

Thermo-structural weak coupling model was adopted in numerical simulation of laser-arc hybrid T-joint welding. Gauss surface heat source and Rotary-Gauss body heat source were used to form a combined heat source in the temperature field analysis and simulate the arc and laser heat source. The laser-arc hybrid overlaying welding test of 304 stainless steel was carried out, and the weld molten pool morphology was obtained by metallographic corrosion test. The test results of a molten pool morphology show that the combination heat source can better simulate the laser-arc hybrid welding process. The effects of laser power, arc power and welding speed on residual stress and deformation of T-joint in laser-arc hybrid welding were studied by orthogonal experiments. Experimental results show that the arc power has great influence on the depth-width ratio, the laser power has great influence on the welding residual stress, and the welding speed has great influence on the thermal deformation. Through quantitative analysis and comparison, the optimal parameters were found during laser-arc hybrid welding.

Analysis of Local Strain Evolution during Electron Beam Welding of Hot Crack Sensitive Nickel Base Conventionally Cast Alloy 247 LC CC

Among different joining methods, the electron beam welding is recently applied for manufacturing of turbine components from temperature-resistant nickel-based conventionally cast Alloy 247 LC CC. However, the high tendency to hot cracking, in particular the formation of solidification cracks, remains a major challenge. Experiments indicate a significant reduction in hot cracks if the welding is performed outside the common welding parameter range. To understand these observations, a study of local thermo-mechanical conditions during electron beam welding of Alloy 247 samples was carried out using numerical simulations. The results were subsequently compared with reference test welds. For this purpose, a finite element model for coupled transient thermal and mechanical analysis was created and used. The work presents a comparative analysis of the evolution of strain components in brittle temperature range during cooling, considering the distribution and orientation of the cracks. Various relations between local strain kinetics and crack appearance, with notable influence of the plastic strain vector, were observed. Finally, the aspects of assessment of hot crack susceptibility with aid of thermo-mechanical welding simulation are discussed.

Numerical Simulation of Ultrasonic Spot Welding of Superelastic NiTi Alloys: Temperature Distribution and Deformation Behavior

Abstract Ultrasonic spot welding (USW) has attracted increasing attention due to its high-throughput solid-state bonding mechanism, which shows great potential in the semiconductor and automotive industries for joining of metal sheets. However, the short welding cycle makes it challenging to effectively monitor the temperature history and deformation of the workpieces during the process. In this study, a three-dimensional (3D) finite element analysis model for USW of superelastic NiTi shape memory alloy (SMA) with Cu interlayer was developed using ansysworkbench. The thermal-stress coupled phenomena including the heat generation and stress distribution during the welding process were simulated and analyzed. First, a superelastic constitutive model for NiTi SMAs was constructed. The distribution of temperature and stress fields was then obtained by thermal-stress analysis using the direct coupling method, and the superelasticity of SMAs was observed. The simulation results showed that the highest temperature occurred in the center of the welding area during USW, which is proportional to the welding time and inversely proportional to the clamping pressure. In addition, the maximum stress occurred at the center of the contact surface between upper NiTi and Cu interlayer. After that, the validity of the simulation results was verified by setting up a thermocouple temperature measurement platform to collect the temperature data, which exhibited a good agreement with the simulated results. The simulation procedure demonstrates its potential to predict temperature and stress distributions during the USW process.

Droplet spatter suppression in laser lap welding of galvanized sheets using additional coaxial annular laser source

This study is to prevent droplet spatter in laser welding of galvanized sheets. Three-dimensional welding simulation model is also established and analyzed to reveal the relationship between keyhole oscillation and flow behavior. It is found major reason for droplet spatter is the impact force of the reflux and eddy of the metal pool toward the keyhole. Keyhole oscillates seriously and reflux impact causes energy exchange discontinuity, making the keyhole opening intermittent closed in traditional Gaussian laser source alone. While certain output proportion of coaxial annular and Gaussian laser source could considerably improve impact resistance on the reflux and suppress droplet spatter obviously. Weld appearance is relatively beautiful and harmonious, with few undercuts, collapses and humps.

Numerical simulation of ultrasonic welding for CFRP using energy director

For ultrasonic welding of carbon fiber-reinforced plastics (CFRPs), a sharp shaped resin called the energy director (ED), is usually inserted between them. In this study, finite element analyses for ultrasonic welding of CFRPs were performed using a two-dimensional model. The effects of the shape of the ED on the temperature increase, deformation history, and dissipated energy behaviors are discussed. Flat and triangular ED shapes are considered. From the results, it is easier for a triangular ED to increase the temperature than for a flat ED, and hence, the consumed energy and time are less for a triangular ED than for a flat ED. However, in the triangular ED, the temperature is distributed significantly, that is, there is a very high temperature at some point and a very low temperature at other points. Thus, unexpected chemical reactions, such as oxidation, may occur. This study concludes that a triangular ED is not always better than a flat ED. In any case, it was found that an abrupt temperature increase was caused by a synergistic effect. That is, the increase in temperature causes the viscoelastic and frictional dissipated energy to be remarkable, and the increase in the dissipated energy increases the temperature.