Welding Simulation Research Articles

Reliability analysis of thermal cycle method on the prediction of residual stresses in arc-welded ultra-high strength steels

The large amount of calculation time is one of the major obstacles to the industrial application of numerical welding simulation. The thermal cycle method is a newly developed approach, which can significantly reduce the computational time. The present work aims to systematically analyze the reliability of the thermal cycle method in the prediction of residual stresses in the arc-welded ultra-high strength steels (UHSS). Both numerical simulation and experiments have been performed for estimating and validating its feasibility in this study. The increasingly used ultra-high strength structural steel S960 in industrial sectors was selected for investigation here. The results indicate that the calculated longitudinal residual stress applying the moving heat source and thermal cycle method is almost the same in and near the weld, while that is quite different mainly in the base metal directly under the weld area for UHSS. The predicted transverse residual stress using the thermal cycle method and moving heat source is significantly different, especially for the transforming UHSS. Although the thermal cycle method can obviously reduce the computing time, the moving heat source gives much better agreement with experimental results than the thermal cycle method in the assessment of welding residual stresses (WRS) overall in UHSS thick plates. Thus, the thermal cycle method is not reliable to predict WRS in thick structures made of UHSS. Furthermore, it is not recommended to use the thermal cycle method in numerical welding simulation for UHSS thin-walled structures.

Effect of heat input on temperature characteristics and fusion behavior at bonding interface of CFRTP induction welded joint with carbon fiber susceptor

AbstractInduction welding is a suitable and promising technique for the assembly of thermoplastic composite structural components. In this work, the simulation and experimental research of induction welding devoted to the quality and efficient bonding of carbon fiber reinforced polyetheretherketone (CF/PEEK) laminates utilizing carbon fiber susceptors is presented. The carbon fiber susceptors that consist of carbon fabric and resin film same as base materials are prepared as heating elements to concentrate the heat generation on the welding interface. A transient three‐dimensional finite element model is developed to analyze the heating characteristics and temperature distribution during the welding process. Induction welding experiments are carried out to investigate the effect of heat input on fusion behavior at the bonding interface, focusing on macro appearances, interfacial fusion morphologies and welding defects. The results show that heat distribution at the welding interface is uneven, presenting that the temperature at the edge is higher than at the center. An increase in heat input facilitates the fusion of the joints, which is demonstrated by a smaller relative width of the fusion zone and expander effective bonding area. However, macro and micro welding defects start to appear in joints due to the massive melting, ablation and thermal decomposition of resin, which are caused by excessive heat input. The micro defects dominated by pores are divided into four types according to their positions, sizes, morphologies and causes of formation.

Predicting residual stress in a 316L electron beam weld joint incorporating plastic properties derived from a crystal plasticity finite element model

Electron beam welding is an advanced joining technique which induces narrow weld region with minimal heat affected zone and weld-induced distortion. This reduces residual stresses in the joints which can be detrimental to structural performance of components in safety critical industries. Being an autogenous process, electron- beam welding generates a highly textured, columnar microstructure in the weld zone which have distinct properties when compared to the parent material region. Determining mechanical properties of the weld material assists in accurate assessment of the joint. However, extracting weld material specimens to determine plastic properties becomes increasingly cumbersome in thinner weld joints. An alternate approach has been demonstrated in this work wherein mechanical properties were derived using the weld microstructure in a crystal plasticity finite element (CPFE) framework. The initial calibration of the CPFE parameters was done using experimental data from thick weldment. These calibrated values were used to obtain the elastic and elastic-plastic properties of thinner weld materials by deforming corresponding synthetic microstructures whose attributes were determined by Electron Backscatter Diffraction analysis. The resultant properties were incorporated in a finite element (FE) based weld simulation to determine the residual strain. These results were compared with the residual strain data obtained using X-ray diffraction and good agreement was observed.

Computational fluid dynamics simulation of hybrid laser-MIG welding of 316 LN stainless steel using hybrid heat source

Hybrid laser-MIG welding (HLMW) process is preferred for welding thick sections (>10 mm) to achieve faster and full penetration weld displaying enhanced productivity due to the synergistic effect of the laser and MIG heat sources in the weld pool. An optimum heat source model combining the effect of the laser and MIG heat source needs to be determined first for the accurate simulation of the weld pool development and temperature distribution during HLMW process. The current study first aims to determine the right hybrid heat source model for welding a 0.01 m thick 316 LN SS plate and then to study its effect on the weld pool dynamics. For this purpose, a three-dimensional (3D) transient model with ANSYS Fluent V.19.2 was designed by hybridizing laser and arc heat sources. Goldak's double-ellipsoidal mode of heat source was favoured for the arc source. A 3D conical, combined 3D conical-cylindrical and rotary Gaussian heat source model were considered for the laser source. The simulated weld pool profile and temperature distribution data obtained for the three hybrid heat sources were validated by carrying out experiments employing HLMW process with optimized welding parameters that achieve full penetration. The numerical modelling has shown that the double-ellipsoidal rotary Gaussian heat source as the appropriate model for HLMW simulation of 316 LN SS. There was good agreement between the simulated weld bead shape, size and the temperature with the experimental result. The synergy effect of the laser and MIG heat sources based on their separation distance was demonstrated using the optimized heat source model to get further insight on the weld pool dynamics and the keyhole penetration.

Weldability evaluation of X80 sour line pipe using a combination of thermal simulation and actual girth welding

The weldability studies of API 5LX80 pipes developed for sour service are very recent and limited information about its heat-affected zone (HAZ) properties can be found. This paper presents a comprehensive evaluation of HAZ using both thermal simulation and the production of actual girth weld joints. The test methodology included microstructural analysis, Charpy impact test, hardness (HV10), microhardness (HV0.1), and sulfide stress cracking tests (SCC). The intercritical coarse grain HAZ presented impact toughness reduction from values above 300 J to less than 50 J at 0 °C when heat input is increased above 1.5 kJ/mm. It can be explained by grain coarsening and martensite-austenite (MA) formation as a ‘necklace’ structure at previous austenite grain boundaries. Hardness and microhardness values for both simulated and actual HAZ were below the maximum limit of 250HV usually specified by industry. Specimens submitted to the sulfide stress cracking (SSC) tests did not present any crack demonstrating that the welded joint is appropriate for sour environments. Finally, a maximum heat input of 1.5 kJ/mm is recommended for field welding. For higher heat inputs, a deeper evaluation of HAZ toughness should be done. The results contribute to supporting the application of this material as an alternative for long-distance high-pressure pipelines with H2S.

Determination of self-adaptive slip rate at tool/workpiece interface in numerical model of friction stir welding

As a key parameter affecting the heat generation and the interface material velocity, the interface slip rate is a prerequisite for numerical simulation of friction stir welding of lightweight materials. The contact state on the tool/workpiece interface is related to friction stress and material yield strength, and a new calculation method of the self-adaptive interface slip rate was established. The interface velocity of material flow, heat generation due to friction and plastic deformation near the tool and temperature distribution were analyzed quantitatively. The calculated self-adaptive interface slip rate has a wider range than the previous used one, from a sticking dominant for the material near the inner part of the shoulder to a sliding dominant for the material near the edge of the shoulder. With application of this improved method determining the slip rate, the material flow velocity at the tool/workpiece interface is roughly in a "M" shape, which first increases and then decreases as the radial distance rises, and the maximum interfacial material velocity no longer appears at the shoulder edge. The experiments were made to validate the method. The slip rate distribution at tool/workpiece interface in (a) Previous mode; (b) Improved mode.

Multiphase and multi-physical simulation of open keyhole plasma arc welding

Plasma arc welding (PAW) is an important technique in the manufacturing industry. To improve the welding efficiency, the special keyhole mode has attracted considerable attention because it has the potential to achieve full penetration without a groove. However, rigorous process conditions are required to maintain a stable keyhole mode. For better and more widespread application in industry, a multiphase and multi-physical model is established to reveal the complicated electro-magneto-thermo-hydro-mechanical phenomena and gas-liquid-solid interactions in the keyhole PAW process. Arc backward reflection and deviation of the heating center occur because of the relative movement in the system, and molten liquid metal is pushed backward and upward to form a salient metal layer at the rear. The maximum height reaches 1.45 mm. Outflow phenomenon occurs through the open keyhole, and the outflow temperature and velocity are approximately 6000 K and 60 m/s by the calculation, respectively. The predicted weld pool and keyhole basically coincide with measured results. This study provides a comprehensive understanding of the multiphase and multi-physical interactions in the PAW process, which may help improve the associated techniques.

Atomistic Simulation of Ultrasonic Welding of Copper

Molecular dynamics simulations of ultrasonic welding of two blocks of fcc copper containing asperities under the conditions of a constant clamping pressure and sinusoidal shear displacements were performed. Two different atomistic models of blocks were simulated: Model I with no misorientation between the lattices, and Model II with a special misorientation of 78.46°. Alternating shearing results in a plastic deformation of the interface layers and is accompanied by the emission of partial dislocations. Misorientation between the joined blocks contributes significantly to an interface sliding, interface migration, and pores healing during ultrasonic processing. A significantly larger increase in temperature occurs during shearing in Model II than in Model I. The applied pressure has almost no effect on the interface temperature in both studied models. The temperature increases almost up to maximum values after the first shear cycle, and then practically does not undergo changes in the next four cycles. The temperature at the interface in Model II is significantly higher than that in Model I. The change in the porosity of the interface and its structure are analyzed. The results obtained in the present work contribute to a deeper understanding of the processes occurring at the atomic level during ultrasonic welding of metals.

Distortion simulation of gas metal arc welding (GMAW) processes for automotive body assembly

Distortion simulation of gas metal arc welding (GMAW) processes for automotive body assembly

Influence of selected alloying variations on liquid metal embrittlement susceptibility of quenched and partitioned steels

In this work, the influence of selected alloying variations on Zn-assisted liquid metal embrittlement (LME) susceptibility of Zn-coated advanced high strength steels (AHSS) is investigated. Cold-rolled AHSS alloys of different carbon (C), manganese (Mn), silicon (Si), and aluminum (Al) concentrations were continuous-annealed to generate a third generation AHSS microstructure (composed of martensite and retained austenite) via quenching and partitioning. High temperature tension tests using simulated spot-weld thermomechanical cycles revealed no significant influence of C and Mn variations on the Zn-LME susceptibility of AHSS. On the other hand, Zn-LME susceptibility was strongly correlated with the Si content of AHSS. A direct comparison of the (reacted) coating microstructures of the Si-alloyed and Low-Si AHSS variants revealed that Si in the AHSS substrate suppresses Fe–Zn alloying reactions and retards the nucleation and growth of Fe-Zn intermetallic phases at the coating-substrate interface in these spot weld simulations. The suppressed intermetallic formation at elevated Si concentrations is consistent with phase equilibria considerations in the Fe-Zn-Si ternary system. In the context of Zn-assisted LME, therefore, Si is hypothesized to aggravate LME behavior by increasing the liquid Zn availability for embrittlement and promoting direct contact between liquid Zn and the AHSS steel substrate.

Simulation and Microstructure Prediction of Resistance Spot Welding of Stainless Steel to Carbon Steel

Joining of stainless steel to carbon steel is widely used in various industries. Resistance spot welding (RSW) is a suitable process for joining steel sheets. Due to the complexity and importance of optimizing the parameters, numerical simulation of this process was considered. In this research, the electrical-thermal-mechanical simulation of RSW of 304 stainless steel to St37 carbon steel was performed using finite element method (FEM). Then, the simulated weld nugget size was compared with the experimental results of optical microscopy (OM). In addition, diffusion of metallic elements of the steels in the molten region was simulated using Fick’s equation and compared with experimental results of energy-dispersive X-ray spectroscopy (EDS). It was shown that diffusion of Cr and Ni through the weld nugget, would make a new stainless steel structure. Microstructure prediction of the heat affected zone (HAZ) was performed using Koistinen–Marburger and Leblond–Devaux equations to predict the percentage of martensite and ferrite-perlite phases during the heating and cooling stages of the specimens from room temperature to the peak temperature and cooling down under the Mf temperature. The results of this simulation were validated by scanning electron microscopy (SEM) images and shear tensile and micro-hardness test results. The simulation results showed that increasing the heat input from 1250 A during 0.5 s to 3750 A during 1.5 s, increases the percentage of martensite, from 40% to 80%, in the HAZ and widens the martensite region.

Chemical composition and weld cooling time effects on heat-affected zone hardness of line pipe steels

In the past few years, the pipeline industry in North America has faced a reported increase of pipeline girth weld failures predominantly in grade X70 pipe welded with cellulosic consumables. Weld strength matching and HAZ softening were two factors believed to have contributed to the concentration of strain during, or soon after, construction which ultimately lead to an overload failure of the girth welds. The work reported in this paper aimed to establish and clarify the correlation between steel chemical composition and the HAZ hardness in typical production girth welds and a range of weld thermal simulations. The first stage was to calibrate the influence of weld cooling rate of both thermal simulations and real welds in steels over a wide range of chemical composition, typical of commercial high strength API pipe. Second, the influence of Pcm, carbon content, Mo content and cooling time in terms of minimum and maximum hardness were investigated. The comparison between simulated HAZ's and real welds showed that thermal simulation produces samples that adequately duplicate the real condition in terms of maximum and minimum hardness and can accurately assess both hardening & softening which occur in different regions of the HAZ. The simulated samples provided increased areas of different HAZ regions in order to more accurately identify the range of hardness values across the HAZ which was then correlated to real weld hardness profiles. It is concluded that ultimate hardness in the HAZ is directly related to steel chemical composition in terms of Pcm and weld cooling rate. It is however apparent that the relative percentage change in hardness from the original parent pipe hardness (also called % HAZ softening), which is important in determining the strain capacity of the weld joint, is principally dependent upon steel processing, especially the degree and severity of thermomechanical processing. This is evident by the fact that same API pipe grades have a wide range in chemical composition and most importantly Pcm, and the response to field welding conditions can be quite different depending on weld heat input, pipe wall thickness and preheat, all of which define the weld cooling rate.

Prediction and Validation for Welding Deformation of the Upper Port Stub

The vacuum vessel (VV) as an ultrahigh vacuum pressure vessel is one of the essential components of the Chinese Fusion Engineering Test Reactor (CFETR) device. VV has strict position tolerance. The VV port stub is a typical large-scaled welded structure manufactured by electron beam welding (EBW) technique. Welding has the most significant influence on deformation. Therefore, it is essential to analyze welding deformation. A systematic welding simulation method aimed at welding deformation controlling for a large EB welded structure is proposed in this article. First, the dynamic process of EBW of 50-mm-thick ultralow carbon austenitic stainless steel was simulated based on the thermal elastoplastic theory. The weld forming mechanism of high energy density welding of the thick plate was revealed. Then the inherent strain extracted from the results of the simulation of local welding was introduced to the simulation of tailor welding of the port stub. Finally, optimal welding sequence and clamping conditions were obtained, and the reliability of the simulation was verified by the profile measurement results of the inner shell of the upper port stub.

Combination of Eulerian and ray-tracing approaches for copper laser welding simulation

Laser welding of pure copper and its alloys is a challenging process with a growing industrial interest due to the latest development in the field of electric mobility. The difficulties are mainly related to the material's high thermal conductivity and a poor absorptivity of few percent at the classical IR laser (YAG). It is also well known that such a configuration can lead to the formation of undesirable defects, such as pores or spatters as a consequence of melt pool instabilities. It has been observed experimentally that the usage of a laser at both high speed and high power tends to limit those instabilities. Although this positive influence has already been observed for equivalent materials, a physical explanation is not yet available. In this perspective, a multiphysical simulation of the process at the melt pool scale is currently being developed by using comsol Multiphysics® software. The latter includes an Eulerian interface tracking method for the liquid-gas interface (phase field) and a ray-tracing description of the laser beam to take into account the well-known beam trapping effect under a keyhole regime. For the sake of time computation, the numerical model is first developed in an axisymmetric coordinate system (r,z) to be representative of a laser spot welding process and to validate the numerical coupling methodology. The model will then be extended to a 3D welding case and used as a predictive tool to make appropriate choices on welding parameters to obtain good quality welds (stable melt pool, low porosity rate, etc.).

The Influence of the Tool Tilt Angle on the Heat Generation and the Material Behavior in Friction Stir Welding (FSW)

To improve the accuracy of numerical simulation of friction stir welding (FSW) process, the tool tilt angle must be considered as a significant parameter. In this study, specific considerations for mechanical boundary conditions in Eulerian domain is employed to investigate the tool tilt angle influence on the thermomechanical behavior in FSW. Aluminum 6061-T6 with a thickness of 6 mm under a rotational speed of 800 RPM, a transverse speed of 120 mm/min, and a plunging depth of 0.1 mm were employed for the simulations. Results showed an almost symmetric temperature profile predicted by the model without considering the tool tilt angle, while after incorporating the tool tilt angle, the peak temperature point is moved to the tool backside (around 400 °C), resulting in better material bonding, enhancing the weld joint quality. Without accounting for the tool tilt angle, the highest temperature of 389 °C is observed, while with the tilt angle the maximum temperature of 413 °C is achieved. The temperature variations at different points of the leading (around 360 °C) and the trailing sides (around 400 °C) of the welding tool were measured. It was observed that, after considering the tilt angle, as the tool moves, a smooth and quick increase for the temperature at the tool trailing side is achieved. This smooth and quick increasing of the temperature at the trailing side results in reducing the possibility of the formation of defects, cracks, and voids. Finally, comparisons showed that the model computational time is acceptable, and using Eulerian formulation leads to achieving a remarkable accuracy.

Numerical Simulation and Experimental Verification of Laser Multi-Section Welding

To address the problems of large welding deformation and splashing in the resistance spot welding of the lubricating oil cooler plate, the laser spot welding was employed, instead of the resistance spot welding, and a novel laser spot welding was proposed, i.e., laser multi-section welding. The major processes involved in this study referred to a finite element model of pulsed laser lap welding built by adopting SYSWELD simulation software, as well as the laser welding of various welding methods. The effect of different welding methods on the welding quality was studied, the parameters of the average power and the duty cycle were optimized in line with the comparative analysis of the experimentally achieved results and the numerical simulation. As indicated from the experimentally achieved results, when the new 6-sections welding method was adopted, the resulting welded joint achieved the most uniform heat input and the largest welding fusion area, and the tensile properties exhibited by the welded joints were significantly enhanced, whereas some pores remained. By altering the duty cycle, pores could be eliminated to further improve the quality of the joint. The mentioned process method could tackle down the problems facing conventional resistance spot welding. Furthermore, it was capable of improving the uneven heat input of the laser spot welding.

Effect of Laser Welding Parameters on Joint Structure of AZ31B Magnesium Alloy and 304 Stainless Steel.

The effects of laser welding parameters on the interface microstructure of AZ31B magnesium alloy and 304 stainless steel were investigated. After welding, a scanning electron microscope and ultra-depth of field microscope were used to observe the microstructure of the welded material, to analyze the effects of power on the interface morphology. The simulation of laser welding of magnesium and steel was carried out by the COMSOL software. The results showed that when the power was 15 W–20 W, the temperature did not reach the melting point of magnesium alloy, there was MgO at the welding, and the interface had poor connection strength. When the power was 35 W–50 W, the temperature reached or even exceeded the boiling point of magnesium alloy, and the interface formed hot cracks, pores, and oxides and had poor joint strength. When the power was 25 W–30 W, the temperature was between the melting point and boiling point of magnesium, and the interface had excellent connection strength.

Influence of Exoskeleton Use on Cardiac Index

This study aims to assess the whole-body physiological effects of wearing an exoskeleton during a one-hour standardized work task, utilizing the Cardiac Index (CI) as the target parameter. N = 42 young and healthy subjects with welding experience took part in the study. The standardized and abstracted one-hour workflow consists of simulated welding and grinding in constrained body positions and was completed twice by each subject, with and without an exoskeleton, in a randomized order. The CI was measured by Impedance Cardiography (ICG), an approved medical method. The difference between the averaged baseline measurement and the averaged last 10 min was computed for the conditions with and without an exoskeleton for each subject to result in ∆CIwithout exo and ∆CIwith exo. A significant difference between the conditions with and without an exoskeleton was found, with the reduction in CI when wearing an exoskeleton amounting to 10.51%. This result corresponds to that of previous studies that analyzed whole-body physiological load by means of spiroergometry. These results suggest a strong positive influence of exoskeletons on CI and, therefore, physiological load. At the same time, they also support the hypothesis that ICG is a suitable measurement instrument to assess these effects.

Numerical investigation of composite materials thermo-mechanical behaviour during ultrasonic welding in different mediums

Ultrasonic welding (USW) creates highly efficient solid-state weld for composite with low power consumption. At the joint contact, a unique diffusion layer is formed during the process, which experiences significant plastic deformation at glass transition temperatures. As the use of composite increases in marine, oil, and gas transport applications, ultrasonic welding becomes the most popular welding process for weld composites. In the marine application, there is a need to weld the part underwater, underwater welding by other conventional welding methods is too much difficult due to the high temperature generated by the welding torch. This temperature can easily break the hydrogen and oxygen bond, and this could cause an explosion underwater. This phenomenon is the same for the oil and gas transportation industry. So, to minimize the risk ultrasonic welding is the most significant welding process. This paper presents the numerical simulation of ultrasonic welding of composites in a different medium. The numerical model may provide an understanding of the thermal phenomena influencing the joining process, as well as an estimation of the impact. The simulation findings revealed that the clamping pressure, vibration frequency, and friction coefficient all have a significant impact on heat and stress produced during the process, which is crucial in determining the ultimate quality of the welded joint. The maximum temperature developed during numerical investigation of USW in the air is 80.51 °C and in water is 72.67 °C and the maximum stress developed during USW in the air is 13.22 MPa and in water is 10.21 MPa these conditions are sufficient for welding composites. According to studies, higher clamping force and welding frequency also resulted in increased distortion.

Numerical simulation and experimental study of hybrid laser-electric arc welding between dissimilar Mg alloys

Numerical simulation and experimental study of hybrid laser-electric arc welding between dissimilar Mg alloys