Welding Temperature Field Research Articles

Study on Morphology, Microstructure and Properties of 6063-T6 Aluminum Alloy Joints in MIG Welding

In this paper, a metal inert gas (MIG) shielded welding method was used for high-quality welding of 6063-T6 aluminum alloy sheet with a thickness of 2.5 mm. The welding process of MIG welding was accurately simulated and the welding temperature field and thermal cycle curve were calculated using a combination of Gaussian body heat source and double ellipsoidal heat source. As the welding current increased from 75 A to 90 A, the reinforcing phase precipitated under the microstructure of the joint gradually became larger and re-solidified into the body, resulting in a reduction in mechanical properties. When the welding current is 85 A, the pitting resistance of weld forming and weld area reaches its optimum. At this time, the tensile strength of the joint is up to 110.9 MPa, the elongation is up to 16.3% and the Vickers Microhardness is up to 46.9 HV.

Numerical Simulation of Welding Temperature Field, Stress Field, and Strain Field of Fillet Joint in Different Welding Sequence

For welding temperature field, stress field, and strain field in fillet joints, using the double ellipsoid heat source, the ABAQUS software platform is used to simulate and analyze the welding process of fillet joints with four different application sequences. By setting up observation points, the study analyzed the distribution of the temperature field, stress field, and strain field of the simulated welding process for these four application cases. The results show that in the vertical weld direction, the welding sequence has a large effect on the transverse residual stress; the use of isotropic welding, butt weld first and then welded fillet weld program, the maximum total deformation and angular deformation produced are the smallest.

Multiple effects of forced cooling on joint quality in coolant-assisted friction stir welding

To understand the multiple effects of forced cooling on the joint quality in coolant-assisted friction stir welding and the underlying mechanism, commercial pure aluminum AA1050 was welded by liquid–CO2–assisted friction stir welding (FSW) within a large process parameter range. The cooling effects on the weld formation, microstructure, and mechanical properties were investigated by comparison with conventional FSW. The microstructure evolution during the liquid–CO2–assisted FSW process was revealed by EBSD characterization together with thermal cycle measurement and short-time annealing. The results show that the process parameter window was narrowed by the liquid CO2 cooling. Forced cooling led to weld surface grooves and interior cavities under “too cold” welding conditions. The grains in the weld zone were refined and the areas of the weld cross-section were reduced by the forced cooling, resulting in the tensile strength of the joint being improved but the elongation being reduced. The thermal cycle shows that the liquid CO2 cooling compressed the welding temperature field by decreasing the heating rate and increasing the cooling rate, giving rise to the decrease in deformation temperature at the stirring stage. The low deformation temperature promotes dynamic recrystallization by changing the way of recrystallization and thus refines the grains. Further, the liquid CO2 cooling suppresses the grain growth which should have happened in natural cooling. Combining the above two aspects, the grain in the weld zone was refined and the tensile properties of the joints were changed. Nevertheless, the contribution of decreasing the deformation temperature to the grain refinement is more significant than that of increasing the cooling rate.

Study on the Microstructure and Properties of Flash-Butt Welding Joints of High Nitrogen Steel

A thermomechanical coupling model for the solid-state flashing process of high nitrogen steel was established, based on finite element simulations and experiments. The effect of flash current on the microstructure and mechanical properties of the welded joint was investigated, and the temperature field of the flash-butt welding (FBW) process was simulated. The phase composition of the joint was determined according to the phase diagram and cooling curve. In addition, the joint with optimal parameters was subjected to full immersion corrosion tests. The results demonstrated that the interface structure was composed of austenite and δ-ferrite with a thyristor angle (flash current) of 45°. The microstructure of the overheated zone (OZ) was composed of austenite, ferrite and a small amount of the M2 phase, in which the heat-affected zone exhibited a single-phase austenite microstructure. The joint hardness displayed a “V” shaped distribution with the lowest interface hardness. As the flash current increased, the hardness and tensile strength of the interface area of the joint first increased and then decreased, with a maximum tensile strength of 902 MPa at 45°. During the full immersion corrosion tests, the joint exhibited the most serious corrosion in the interface center and gradually reduced corrosion on both sides.

Temperature and residual stress field analysis in double-pulse MIG welding of AA6061-T6 aluminum alloy thin sheets

Accurately predicting the weld temperature field and post-weld residual stress field is of utmost significance for comprehending the composition of welded structures and enhancing their service performance. In this study, the double-pulse MIG welding process of AA6061-T6 aluminum alloy thin sheets was investigated. A dynamic combined heat source model, consisting of double ellipse and double ellipsoid heat sources, was proposed based on weld bead morphology and the current variation during the welding process. The temperature and residual stress fields were numerically simulated and experimentally measured using thermocouple temperature measurements and blind hole methods, respectively. Simulation results of the combined heat source model were found to be accurate and in good agreement with the experimental data. The effects of welding fixtures and convective heat transfer coefficients on the results were also considered. The welding temperature and post-weld residual stress properties of the welded structure were thoroughly examined. During the welding process, the highest temperature is about 1500 °C and the maximum longitudinal residual stress occurs in the heat-affected zone, which is approximately 250 MPa, slightly lower than the yield strength of the base material.

Application of finite element analysis in structural analysis and computer simulation

Abstract In today’s highly developed technology, computer and Internet technology has seen a climax of innovation and its application areas are becoming more and more extensive. Computer simulation technology is the direction of computer development proposed in recent years, which can change our way of life to a greater extent. In order to explore the role of finite element analysis in structural analysis and computer simulation, this paper uses ANSYS finite element analysis combined with structural analysis methods and verified by computer simulation examples of welding thermal cycles. The results show that the computer simulation of the simulated temperature curve trend and the experimentally measured temperature curve is basically the same. Absolute error curve increases first and then decreases, basically at 11 s when the maximum, followed by a rapid decline, and then gradually slow down the rate of decline, and eventually converge on 200 °C or 180 °C or so. Such a computer simulation in a certain range to be able to more accurately simulate the welding temperature field, the study of welding problems is very valuable reference. For the simulation speed of computer simulation, combined with the structural analysis of finite element analysis, the running time was reduced by an average of 3.58 min, and the overall efficiency was improved by 21.81%. It shows that the FEA method can effectively reduce the running time and significantly improve the running efficiency. In summary, finite element analysis can optimize common problems in structural analysis, strengthen the analysis effect, and expand the application of computer simulation technology.

Microstructure and Mechanical Properties of TA2/Q235 Laser Weld Joint with Copper Interlayer.

For the dissimilar metal welding needs of TA2 titanium and Q235 steel, preliminary trials were conducted using laser welding methods, and the results showed that the addition of a copper interlayer and the bias of the laser beam toward the Q235 side allowed for an effective connection. The welding temperature field was simulated using the finite element method, and the optimum offset distance of 0.3 mm was obtained. Under the optimized parameters, the joint had good metallurgical bonding. Further SEM analysis showed that the microstructure of the bonding area between the weld bead and Q235 was a typical fusion weld pattern, while that of the bonding area between the weld bead and TA2 was in brazing mode. The microhardness of the cross-section showed complex fluctuations; the microhardness of the weld bead center was higher than that of the base metal due to the formation of a mixture microstructure of copper and dendritic Fe phases. The copper layer not involved in the weld pool mixing had almost the lowest microhardness. The highest microhardness was found at the bonding site of TA2 and the weld bead, mainly due to the formation of an intermetallic layer with a thickness of about 100 μm. Further detailed analysis revealed that the compounds included Ti2Cu, TiCu and TiCu2, showing a typical peritectic morphology. The tensile strength of the joint was approximately 317.6 MPa, reaching 82.71% of that of the Q235 and 75.44% of the TA2 base metal, respectively. The fracture occurred in the unmixed copper layer.

Influence of Heat Input on Microstructure and Mechanical Properties of Laser Welding GH4169 Bolt Assembly—Numerical and Experimental Analysis

By conducting the numerical and experimental analysis, the influence of heat input on the microstructures and mechanical properties of laser welding GH4169 bolt assembly is systematically investigated. The weld formation, temperature field, and residual stress distribution during laser welding by using the finite element modeling are consistent with experimental results. The numerical simulation results show that the increase of heat input imparts lower residual stresses and higher temperature gradient. During the process of laser welding, the steepest temperature gradient and the peak residual stress arise in the fusion zone (FZ). In addition, the dissolution of γ″ and γ′ toward the fusion line increases in heat affected zone (HAZ), but only Laves phase is observed in FZ. With increasing heat input from 24 to 48 J mm−1, the ultimate tensile strength of welded joints decreases. Both the lowest microhardness values and tensile failure of GH4169 alloy laser welded joint are in FZ. Herein, it is that the relationship among the heat input, microstructures, and mechanical properties of GH4196 bolt assembly in laser welding is systematically established, which will be of guiding significance for the selection of welding parameters in aerospace.

Measurement of weld penetration for variable-groove weldment using dual-band imaging and neural network

For the process of gas metal arc welding, the online measurement of weld penetration has always been a research hotspot, and high-precision penetration monitoring can lay the foundation for penetration control. This study developed a novel method for measuring the weld penetration of variable-groove weldments using dual-band imaging and a neural network. First, a welding temperature field measurement system was constructed using a colour charge-coupled device (CCD), and the feasibility of using the output images from the red and green channels of the CCD for colorimetric temperature measurement was investigated. Then, a welding temperature field measuring algorithm based on a network model was investigated. Compared with the traditional temperature measurement algorithm, the proposed algorithm can measure the welding temperature field with higher precision. The distribution characteristics of the temperature field were extracted by means of the histograms of oriented gradients (HOG) algorithm. Finally, based on a back-propagation (BP) neural network, a weld penetration prediction model for variable-groove weldments was built, and the distribution features of the temperature field were used as the model input. The experimental results reveal that the proposed back bead penetration measurement method for variable-groove weldments can achieve the high-accuracy penetration measurement, which has broad application potential.

Unbalanced thermal field assisted thermo-compensated resistance brazing welding 6061 aluminum alloy to 304 stainless steel

The reliable Al/steel resultant welded joint with a large contact area was of great significance in electrolysis cells to produce aluminum. Herein, a large-area 6061 aluminum alloy/304 stainless steel dissimilar welds were successfully obtained by unbalanced thermal field assisted thermo-compensated resistance brazing welding(abbreviated as UTC-TC-RBW). In the present study, the heating distribution conditions of the joint were adjusted based on the introduction of the auxiliary welding current, forming an unbalanced temperature field. The whole welding temperature field of the joint was improved significantly with the increase of the auxiliary current, which promoted the interdiffusion of Al and Fe elements at the interface. Hence, the connection area between Al alloy and steel was increased gradually. The final interface between Al alloy and steel was changed to the Al(s.s) diffusion layer and Fe2Al5 layer. XRD results proved the presence of these phase compositions. When the auxiliary current was 0.3 kA, the maximum thickness of the Al(s.s) diffusion layer and Fe2Al5 layer reached 5.25 μm and 0.86 μm. The final load of the obtained joint with the auxiliary current of 0.3 kA was the maximum and reached 1789.7N, which was approximately 3 times that of the joints without auxiliary current.

Numerical analysis modeling of temperature field in swing-arc narrow gap GMA welding with additional wire

Numerical analysis modeling of temperature field in swing-arc narrow gap GMA welding with additional wire

Numerical Simulation of Temperature Field in Ultra-Narrow Arc Welding of Thick-Walled Steam Turbine Valve Body Material

The welding problems of large and thick plates are becoming more prominent as the application of large-scale and thick-plate metal structures grows. Due to the issue of excessive welding deformation between the 60mm thick steam turbine valve body and the pipe joint, a new process method is employed to connect. In this paper, the welding technology of flux strip confined arc ultra-narrow gap is proposed to carry out welding test on the ZG13Cr9Mo2Co1NiVNbNB cast steel test block of steam turbine valve body material with a thickness of 60 mm. The welding temperature field is measured by means of a K-type thermocouple and numerical simulation. The results show that the thermal cycle curve obtained by the homogeneous body heat source simulation is basically consistent with the thermal cycle curve measured during the experiment, and the simulation results of the molten pool morphology are also consistent with the actual macroscopic morphology of the weld.

Welding Quality Detection for Variable Groove Weldments Based on Infrared Sensor and Artificial Neural Network

Connecting a variable groove weldment is always challenging, and it is necessary to monitor the course of the work and optimize the welding process parameters in real time to ensure the final welding forming quality. Welding penetration is an important index to appraise the welding forming quality; the visual sensing method for molten pool is the main method for detecting the weld penetration, but its detection accuracy is affected by the arc light. In this paper, a welding penetration sensing method for variable groove weldments based on the welding temperature field distribution is proposed. Firstly, a set of temperature field measurement system for a weldment is developed by means of an infrared sensor. Secondly, in the direction perpendicular to the welding direction, a linear temperature distribution feature extraction algorithm based on Gaussian fitting is studied; in the direction parallel to the welding direction, the linear temperature distribution feature extraction algorithm based on the thermal cycle parameters is studied, and the feasibility of using the extracted linear temperature distribution features to identify the weld penetration of a variable groove weldment is analyzed. Finally, taking the extracted linear temperature distribution features as input, using an artificial neural network, the prediction model for the welding penetration of a variable groove weldment is established. The experimental results showed that the weld penetration sensing method put forward in this paper can realize high-precision weld penetration sensing and has high reliability, which solves the problem that weld penetration sensing is affected by arc light to a great extent.

Numerical simulation analysis of laser-arc hybrid welding of austenitic stainless steel

Laser-arc hybrid welding heat source has high energy density, and the temperature field is very uneven and unstable. It is impossible to systematically study the welding temperature field only through process tests. For this reason, the calculation of the thermal process of hybrid welding is of great significance to the systematic study of the temperature field of hybrid welding. In this paper, the laser-arc hybrid welding process of 8mm thick austenitic stainless steel was simulated by SYSWELD software. The results indicate that with the increase of laser energy, the melting time increases, and the peak temperature rises from 1,230°C to about 2,000°C; When the laser energy is 3.0 kW, the welding deformation reaches the minimum value of 0.68 mm, but the peak value of equivalent stress is high, which is 476.8193 MPa. When the arc voltage increases, the peak temperature rises from 1,650°C to 1,850°C, and the melting time increases. The arc voltage has little effect on the equivalent stress of the weld and has a clear impact on the welding deformation. When the voltage is 18 V, the maximum deformation reaches 2.191 mm.

Comparison of welding temperature fields, residual stress distributions and deformations of Gas Tungsten Arc (GTA) and ultrasonic–wave–assisted gas tungsten pulsed arc (U–GTPA) welded DP780 steel joints

Considering the excellent anti-corrosion property in chlorinated mediums and comprehensive mechanical properties of dual phase steel, this kind of steel plate will be widely used in the future. However, when ordinary welding methods are used to weld these steel sheets, large deformation usually occurs during local heating due to the lower stiffness of sheet joints. Based on a thermo-elastic-plastic Finite Element Analysis (FEA) method, considering both material non-linearity and geometric non-linearity, the temperature field and deformation of DP780 steel thin-plate welded joints using Gas Tungsten Arc (GTA) welding and Ultrasonic-wave-assisted Gas Tungsten Pulsed Arc (U-GTPA) welding is simulated. Through the combination of experiment and numerical simulation, the difference in the simulation process for the weld deformation of sheet joints caused by GTA welding with and without acoustic-controlled arc is clarified. In particular, the effects of acoustic-controlled arc and external confining positions on the weld deformation, and residual stress distribution of duplex phase steel joints welded by two welding methods are compared. The research results indicate that the welding heat source of U-GTPA has a smaller acting range on the workpiece and a higher peak temperature (up about 200 °C) than that of GTA. Replacing the traditional GTA with U-GTPA can reduce weld deformation, the maximum buckling deformation of welded sheet is only 4.2 mm and the rate of deformation is reduced by 60%. The numerical simulation confirmed that the high longitudinal tensile stress ranges in U-GTPA-welded joints are narrower than that in GTA-welded joints, but the maximum longitudinal residual stress generated by U-GTPA welding is greater than that generated by GTA welding. Furthermore, the stress distribution in the fusion zone and its surroundings, as well as the out-of-plane deformation of the steel sheet can be further controlled by optimizing the confining positions. The selection of the appropriate restraint positions is also an important factor to the optimization of the U-GTPA welding process.

Numerical simulation and ultrasonic measurement on welding residual stresses of full penetration U-shaped stiffening ribs

In order to study the distribution of welding residual stresses in single-sided and full penetration double-sided welded U-ribs, numerical and experimental investigations were carried out considering different deck thicknesses. The birth–death element technique and the heat transfer analysis method were utilized to obtain the welding temperature field and the stress field. The accuracy of the numerical simulation was verified by using the ultrasonic method and the hole-drilling method. The proposed formulas of residual stresses as a function of the weld length in full penetration double-sided welded U-ribs were regressed. The results show that the stress distribution of double-sided welded U-ribs is consistent with that of single-sided welded U-ribs, but double-sided welded U-ribs produce more complex and adverse residual stresses. With the increase of deck thickness, the peak value of the residual stresses in the weld has no significant change and is stable at about 380 MPa. But the residual stresses in the region around double-sided U-rib welds are generally larger than those of the single-sided U-rib welds, and they decrease with the increase of the deck thickness. When the thickness increases to 18 mm, the maximum decrease reaches about 80 MPa. In addition, the calculation errors of new formulas are very small. The accuracy and reliability of numerical simulation results has been verified.

Numerical modeling for the mechanism of shoulder and pin features affecting thermal and material flow behavior in friction stir welding

A three-dimensional transient computational fluid dynamics model is developed to analyze the influence of rotational/non-rotational shoulder and pin characteristics on the thermal and material flow behavior in friction stir welded (FSW) aluminum alloy joints. Four tool designs with rotational/non-rotational shoulder and the pin with/without triple facets are considered. The heat cycle of the rotational and non-rotational shoulder friction stir welded joint (RS-FSW and NRS-FSW) is simulated and experimentally verified, and the welding temperature fields are analyzed. The welding peak temperature of the RS-FSWed joint is the highest, and the non-rotational shoulder significantly reduces the welding peak temperature and the range of the heat-affected zone (HAZ). The rotational shoulder promotes material flow and enhances flow velocity, whereas the non-rotational shoulder reduces both. An increase in the triple facets on the pin facilitates the material flow during NRS-FSW. Viscosity is a physical quantity associated with the welding temperature and strain rate, which is affected by the tool characteristics. The deformation zone caused by the tool is related to the viscosity of the material, the closer the tool, the lower the viscosity of the material. The viscosity of the material gradually increases with an increase in the distance from the tool surface.

Investigation of welding temperature field and residual stresses of corrugated steel web girders

This paper proposes a new approach for obtaining the welding temperature field and stress distribution in a corrugated steel web girder. This approach was validated by comparing the control temperatures (obtained from finite element modelling of CO2 gas shielded welding) of a corrugated steel web girder with experimental findings. Moreover, the effects of different welding speeds on welding residual stress were analysed. The control point temperatures obtained using modelling corresponded closely with those of the observed data. The welding residual stress was primarily affected by the longitudinal residual tensile stress and increased as the distance to the weld decreased. The welding speed had an insignificant effect on the residual stress distribution but a significant effect on the residual stress peak. The findings of this study can serve as a reference for the analysis of the welding temperature and stress fields of corrugated steel web girders.

Analysis on friction stir welding process of 7022 aluminum alloy

The state of the simulation technology widely used in friction stir welding (FSW) studies requires greater and greater accuracy. An analysis is made of an FSW dynamic heat source model and related information. The model is combined with results from FSW experiments and the welding temperature field. A relationship is obtained for the friction coefficient between the tool and welding materials with temperature. By incorporating tool force measurements and analysis, a simulation model which is much more in line with actual FSW results is thus established. In the simulation process, the temperature of each part of the tool, the material model, fixture constraints, and the role of tool–material forces are analyzed and discussed in detail. In the new model, the different input heats on the advancing and retreating sides on the shoulder, the pin surround, and top of the pin are distinguished. The mechanical properties of the materials with change in temperature and the constitutive equations for the welding, before and after, are obtained. The contact relationship between the fixture and workpiece was built. In the welding process, the forces of the tool toward the welding material were applied. The 7022 aluminum alloy FSW process was simulated by the constructed simulation model. The temperature field, residual stress, and deformation in the simulations were in good agreement with the experiment results.

A computational framework based on FEA, ML and GA for estimation of welding residual stresses

The present work describes a computational framework based on finite element (FE) analysis and machine learning (ML) and genetic algorithm (GA) to accurately estimate and minimize the residual stresses in welding. The FE analysis comprises of sequentially coupled thermal and mechanical analyses that are nonlinear due to temperature-dependent thermal/mechanical properties. In the FE analysis, the effective stress function (ESF) algorithm is used for accurate computation of the temperature-induced elasto-plastic stress field during welding. The ESF algorithm accounts for the large variation of yield curves due to temperature changes in welding. To improve the accuracy of the thermal and mechanical analyses, an optimization process combining supervised machine learning and binary coded genetic algorithm is utilized. This optimization technique is implemented to derive an accurate phase-change model for the thermal FE analysis of SS304, which is otherwise a burdensome and costly task to obtain from calorimetric experiments. The results obtained through the derived phase-change model are validated through welding time-temperature distribution reported for a welding experiment in literature. The same optimization process is further used to obtain a set of weld operating conditions (such as weld voltage, current, welding speed, and the gap between plates) for SS304 that reduce the tensile residual stresses. It is found that the accurate estimation and reduction of welding residual stresses can be realized by using the present computational framework. • A detailed FE analysis is presented for the estimation of residual stresses in welding. • ESF algorithm implemented in the FE analysis is found very useful. • An optimization methodology is proposed based on machine learning and genetic algorithm. • Proposed optimization scheme is used to estimate the phase-change model and weld parameters. • Accuracy in estimation of welding temperature field is improved and tensile residual stress is minimized to a certain extent.