Heat Transfer In Welding Research Articles

Effect of inclined magnetic field and chemical reaction on Casson fluid flow over a stretching surface with Cattaneo–Christov double diffusion

This investigation discusses the significance of studying the behavior of non-Newtonian fluids, specifically the Casson fluid, subjected to an electrically conducting and stretching sheet. The study also explores the effects of an aligned magnetic field, Cattaneo–Christov double diffusion, viscous dissipation and chemical reactions on heat and mass transfer, respectively. The partial differential equations governing the flow problem are transformed into ordinary differential equations through the utilization of similarity transformations. Furthermore, the shooting technique is implemented in MATLAB to solve the ODEs. The influence of physical parameters, such as the magnetic field parameter, Eckert number, Prandtl number and chemical reaction parameter, on the velocity profile, temperature distribution, concentration profile, skin friction coefficient, Nusselt number and Sherwood number is studied and presented in graphical and tabular forms. It is found that increasing the Prandtl number causes a drop in the temperature profile. Moreover, the presence of thermal radiation and the Eckert number significantly amplifies the temperature distribution. When the magnetic number undergoes a substantial increase, there is a notable decrease in the velocity profile, and simultaneously, the temperature profile experiences a noticeable rise. Additionally, increase in the chemical reaction parameters leads to a decrease in the concentration profile. The skin friction coefficient, local Nusselt number and Sherwood number exhibit significant reductions as the Casson parameter increases. Additionally, a MATLAB built-in function named bvp4c is incorporated to verify the computed results. The practical implications of the Cattaneo–Christov heat flux model include microelectronics, microfluidic devices, processes involving rapid heating or cooling, such as laser welding or pulsed laser ablation and heat transfer in biological tissues.

Final assessment of multifactor experiments of heat transfer in the underwater wet welding

The multifactorial nature and interconnection of phenomena occurring during welding, especially under water, are important for deepening knowledge in this area. An analysis of the research carried out and the solutions obtained in the field of underwater wet welding of low-carbon steels shows that in this area, adequate assessments of the effectiveness of various types of welding with comprehensive consideration of the interaction of various physical phenomena, significantly different in nature from each other, have not been obtained. Integrated approaches to the assessment and analysis of heat transfer coefficients from the side of the arc combustion surface and from the opposite side are proposed. For the first time, the potential values were calculated as a change in the values of heat transfer indicators for various welding conditions based on verified experimental data. The ultimate goal of the work is to calculate the cooling rates of the metal of the welded joint, which will subsequently make it possible to predict the mechanical properties of the weld metal and the likelihood of the formation of hardening structures.

The effect of weld bead heat input on the performance of thick 3CR12 stainless steel welds

3CR12 is a low cost special stainless steel containing 12% chromium. It is widely used in material handling, road transport, rail transport, power generation and petrochemical applications due to its favorable corrosion performance. 3CR12 is a weldable material, but it has challenges such as poor ductility, poor toughness of 3CR12 stainless steel welds, unfavorable microstructure and cross-sectional properties of the weld bead. This is due to the welding heat input and heat transfer across beads, which causes cracking due to property changes. When welding a thick stainless steel section, the hardest heat affected zone (HAZ) is created due to uneven heating and cooling in the weld metal and base material, which is susceptible to cold cracks and residual stresses, resulting in welding defects and unfavorable material properties. Welding thick 3CR12 stainless steels can be accomplished by using a variety of welding techniques. In order to restore undesirable material qualities, the majority of welds require a post-weld heat treatment (PWHT). However, critical PWHT factors such as duration, weld geometry, and unsupported loads during the hot phase of the weld do not always allow the process to be effective. This process results in prolonged downtime since the holding time in the PWHT cycle can be very long, especially with thick-walled 3CR12 steel members. There are other methods that are currently used to weld or repair thick 3CR12 steels. Among these other methods, the use of controlled temper bead welding technique which potentially could mitigate the above mentioned problems is mentioned. The approach involves using the heat input of the weld bead as a way of introducing the heat into the previous weld bead. This is achieved by varying the heat input in order to improve the mechanical performance of the previous weld bead and thus the overall weld integrity. Welding procedures for 3CR12 recommend the use of minimum heat to avoid weld defects and unfavorable material properties. This study was carried out to investigate the effect of the heat input of the weld bead on the mechanical properties of thick welds made of 3CR12 stainless steel. By utilizing inert gas (MIG) welding, two heat input levels were used in the process: low heat input averaged at 1.53 kJ/mm and high heat input averaged at 2.1kJ/mm. The heat input was varied by changing the welding parameters, for example the average welding voltage ranging from 28V to 30V, the average welding current from 120 A to 150 A and the average feed rate between 1.77mm/sec to 2.0mm/sec.

Temperature field simulation and asymmetric heat transfer distribution of dissimilar steel welded with external transverse magnetic field

During the welding process of Q235 mild steel to 304 L stainless steel, the difference in their thermal properties and magnetic permeability deflects the arc to the mild steel side, resulting in unstable welding process, poor weld formation, and reduced penetration depth. In this paper, a method of applying an external transverse magnetic field acting on the welding arc is proposed to overcome the adverse effects of arc deflection. The experimental results show that the welding depth of Q235/304 L can be significantly improved by magnetically controlled arc welding process. In order to understand the asymmetric heat transfer distribution of dissimilar steel under the action of external transverse magnetic field, a new type of deflection heat source was constructed. The influence of transverse magnetic field deflection arc on heat source parameters was considered, and the welding temperature field of Q235/304 L was simulated to study the welding temperature field of dissimilar steel under the action of magnetic field. In the error analysis, the maximum error of the deflected heat source model is less than 16 %, and the average error is less than 7 %. Compared with the asymmetric heat source model, the constructed heat source model is more accurate in calculation. The depth of melt and temperature variation around the weld under different excitation currents were studied. The weld forming and welding heat transfer law of dissimilar steel with external transverse magnetic field are obtained, which could be used to further improve the welding quality of dissimilar steel.

Revealing the acoustic effects on heat transfer and material flow in ultrasonic assisted friction stir welding of dissimilar Al/Mg alloys

Development of a reasonable constitutive equation is critical to realize accurate numerical prediction of ultrasonic vibration-assisted friction stir welding (UVaFSW) of dissimilar Al/Mg alloys and deepen the understanding of the synchronous interaction between the ultrasonic vibration exerted on the tool and the tool induced thermo-mechanical behavior. Considering the thermal activation and dislocation evolution mechanisms, the calculation method of acoustic stress work based on the change of dislocation strain energy is redefined, and a modified acoustic-plastic constitutive equation is developed. The modified constitutive equation was applied to the computational fluid dynamics (CFD) model combined with the volume of fluid (VOF) method and quantitative analysis was conducted on the acoustic effects on heat generation, material flow and intermixing in UVaFSW of Al/Mg alloys. The results indicate that the exerted ultrasonic vibration has a little effect on the total heat due to the multiple effects of acoustic softening, acoustic antifriction and additional acoustic heat, but can promote the material flow around the tool and expand the material intermixed region. The experimental research validates the calculated results, and it is indicated that the flow stress and temperature field calculated by the improved constitutive equation have higher accuracy in UVaFSW of Al/Mg alloys.

General thermomechanical model of FSW based on a characteristic temperature for deformation and heat transfer

This paper presents a coupled model of heat transfer and plastic deformation in friction stir welding (FSW), accounting for the temperature profile in the substrate near the pin. This approach is analogous to the boundary layer analysis in fluid mechanics and is based on the methodology of scaling and calibration based on published data. A model focusing on common conditions in FSW, such as relatively slow translation and high rotation velocities, a thin shear layer and the influence of the shoulder on the maximum temperature was reformulated. This paper extends previous work by considering the heat flow into the pin and an improved criterion for determining the temperature at the edge of the shear layer. The results are a set of updated closed-form expressions for the maximum temperature, the thickness of the shear layer, the shear stress around the pin, torque and thermal effect of the shoulder, applicable to all metals. The predictions from this model are verified against a comprehensive database of published experiments. Applications of this model also include the accelerated determination of procedure variables and the generalization of maps of process limits.

Role of Surface-Active Element Sulfur on Thermal Behavior, Driving Forces, Fluid Flow and Solute Dilution in Laser Linear Welding of Dissimilar Metals

Understanding heat and mass transfer and fluid flow in the molten pool is very helpful in the selection and optimization of processing parameters, and the surface-active element has an important effect on the heat and mass transfer in laser welding of dissimilar metals. A three-dimensional (3D) numerical model coupled with a sub-model of surface tension, which considers the influence of local temperature and the concentration of surface-active element sulfur at the gas/liquid surface, is used to analyze the thermal behavior, driving forces, fluid flow, and solute dilution during laser linear welding of 304SS and Ni. The relationship between surface tension, driving forces, and the temperature coefficient of surface tension with the spatial distribution of temperature and the surface-active element sulfur is quantitatively analyzed. The simulation results show that the molten pool is fully developed at 45 ms, and the collision of inward and outward convection, with the maximum velocity reaching 1.7 m/s, occurs at the isotherm with a temperature between 2200 K and 2500 K. The temperature-gradient term and concentration-gradient term of surface shear stress play different roles in different positions of the free surface. The local sulfur concentration changes the temperature sensitivity of the surface tension at different sides of the free surface and further determines the transition of convection. Complex fluid flow promotes solute dilution, and the distribution of solute becomes uniform from the front to the rear of the molten pool. The Ni element is transferred to 304SS mainly at the rear side. The work provides theoretical support for the control of joint quality by changing the content of surface-active elements in dissimilar welding.

Numerical and experimental study on melt-pool heat transfer and weld characteristics in dual-mode fiber laser welding of aluminum alloy

A dual-mode fiber laser consisting of center and ring beams has attracted significant attention in the laser welding field owing to its ability to stabilize melt pools and reduce defect formation. In this study, a dual-mode fiber laser was adopted for butt welding of an aluminum alloy. Experimental and numerical investigations were conducted to analyze the weld characteristics and heat transfer phenomena during the process. The use of both the center and ring beams produced a funnel-like weld shape because of the low ring beam intensity, resulting only in the melting of the upper part of the workpiece. As the ring beam power increased, the temperature gradient near the solidification front, acting as a driving force for fluid flow, decreased. This contributed to the relatively gentle fluid flow and the smooth bead surface. It was also found that an increase in ring power lowered the cooling rate of the melt zone near the weld edge. Therefore, the average grain size of the weld zone increased with an increase in the ring power. The results of this study provide fundamental insights into the mechanism of dual-mode fiber laser welding.

Heat generation and transfer in micro resistance spot welding of enameled wire to pad

The single-sided micro resistance spot welding (MRSW) of enameled copper wire to pad is widely applied in electronics manufacturing. The welding quality is significantly influenced by the process of heat generation and transfer which are gradually changing and quite uncertain in production. This work is to investigate the thermal process variation under the common influence factors of electrode wear and thermal contact conductance (TCC). Multi signals such as dynamic resistance and electrode temperature were detected to analyze the welding process. A finite element model of electrical-thermal-mechanical coupling was established to simulate the heat generation and transfer in MRSW. The coupled model was validated by comparing the simulated results of temperature and voltage with the experimental measurement. The results show that the electrode wear in single-sided MRSW of enameled wire to pad causes an increase in the resistance and temperature of electrode tip rather than decrease, and it requires reducing the welding parameters instead of increasing. In case of electrode wear, maintaining a consistent temperature rise of electrode tip helps to ensure welding quality. Due to the insulation coating of enameled wire, the normal TCC between electrode tip and workpieces significantly changes in the MRSW process and rapidly rises after the decomposition of insulation coating. TCC needs to be controlled within a reasonable range to prevent insufficient or excessive heat transfer in production.

Effect of Surface-Active Element Oxygen on Heat and Mass Transfer in Laser Welding of Dissimilar Metals: Numerical and Experimental Study

The effects of the surface-active element oxygen on the laser welding of 304 stainless steel (304SS) and nickel were numerically and experimentally studied in pure argon and argon–oxygen mixed gas atmospheres containing 21% oxygen (AMO). In this study, the molten pool morphology, thermal behavior, solidification phenomenon, correlation between dilution and convection flow, and microhardness of welding joints were analyzed. As a result of oxygen effects, the molten pool was deeper, the maximum temperature was higher, and the maximum flow velocity was lower in the AMO. The cooling rate (GR) and combination parameter (G/R) were studied by the direct simulation of temperature gradient (G) and solidification growth rate (R). Combined with the solidification microstructure, it was found that oxygen had little effect on grain size. The major elements Fe, Cr, and Ni within the solidified molten pool in the AMO were uniformly diluted, while the distribution of the above elements was non-homogenous in pure argon. Stronger flow and multiple directions of convection inside the molten pool contributed to uniform dilution in the AMO. The distribution of microhardness was similar to the content of Cr, and the microhardness at the substrate interface of the joint was higher in the AMO than in pure argon. The preliminary conclusions of this study provide in-depth insights into the effects of surface-active element oxygen on heat and mass transfer in laser dissimilar welding.

Simulation of Heat Transfer in Laser Transmission Welding

Abstract A numerical simulation of the heat transfer during laser transmission welding is presented. A finite difference approach was used to solve the one-dimensional unsteady-state heat conduction problem and to investigate the effect of welding conditions on the time-dependent temperature profiles for PA 6. For the needs of the simulation, the process was divided into heating and heat redistribution periods. The absorption coefficient of the laser-transparent part was measured experimentally and that of the laser-absorbing part was fitted using experimental data. The predicted temperature profiles were combined with experimental meltdown data to estimate the heat-affected zone thickness in the welded specimens. Good agreement was found between the estimated and measured heat-affected zone thickness values.

Simulation of transient heat transfer and phase transformation in laser beam welding for low alloy steel and studying its influences on the welding residual stresses

The welding process causes high local heat input on the material, which leads to microstructural changes in the base material, followed by the development of residual stresses in the welded components. This has a significant impact on the performance of the welding joint. Therefore, it is crucial to effectively predict the effect of temperature, metallurgical and structural changes on the component, which can be achieved by numerical simulation.The main goal of this work is to mathematically investigate the influence of thermo-metallurgical phase transformations on the welding residual stresses which was induced by laser beam welding in low alloy steel (S235JR). In this study, two separate numerical simulation models were analyzed using the software Abaqus CAE. One numerical model describes the thermo-mechanical behavior and the other describes the thermo-metallurgical-mechanical behavior of the system which was realized using UEXPAN user subroutine. In this user subroutine, the kinematics of phase transformation was computed using the modified Johnson-Mehl-Avrami and Kolomogorov while considering a nucleation and growth process that controls the dissolution of the initial microstructure. The generation of martensitic transformation has been accounted by the Koistinen-Marburger equation. In the next step, the phase transformation subroutine has been integrated with a structural model along with a special temperature step function to realize the effect of thermal strain and the strain caused by phase transformation on the welding residual stresses. The computed residual stresses of both the models were compared with the experimentally measured residual stresses using the hole drilling method. These results show that the inclusion of phase transformations has a significant effect on the residual stresses of the welded component.

Modeling of Melt Flow and Heat Transfer in Stationary Gas Tungsten Arc Welding with Vertical and Tilted Torches.

A 3D numerical simulation was conducted to study the transient development of temperature distribution in stationary gas tungsten arc welding with filler wire. Heat transfer to the filler wire and the workpiece was investigated with vertical (90°) and titled (70°) torches. Heat flux, current flux, and gas drag force were calculated from the steady-state simulation of the arc. The temperature in the filler wire was determined at three different time intervals: 0.12 s, 0.24 s, and 0.36 s. The filler wire was assumed not to deform during this short time, and was therefore simulated as solid. The temperature in the workpiece was calculated at the same intervals using heat flux, current flux, gas drag force, Marangoni convection, and buoyancy. It should be noted that heat transfer to the filler wire was faster with the titled torch compared to the vertical torch. Heat flux to the workpiece was asymmetrical with both the vertical and tilted torches when the filler wire was fully inserted into the arc. It was found that the overall trends of temperature contours for both the arc and the workpiece were in good agreement. It was also observed that more heat was transferred to the filler wire with the 70° torch compared with the 90° torch. The melted volume of the filler wire (volume above 1750 °K) was 12 mm3 with the 70° torch, compared to 9.2 mm3 with the 90° torch.

Computational Investigation of Heat Transfer and Mass Flow in GTA Welding of AA6061 Plates

Computational approach or numerical simulation is a trend in recent manufacturing technology, in the present study a computational approach is made for a pulse type GTAW to analyze the heat transfer and mass flow behavior using FEA software ANSYS 19.0. Transient thermal simulations are carried at three different heat inputs in the form of voltage and currents with the welding speed of 70mm/min. The heat source profiles are obtained with the different heat inputs from experimental investigations. The same heat source profiles are modeled using the Solid EDGE software and called in the ICEM CFD to generate grids with unstructured tetrahedral mesh and grids are also made for the workpiece by modelling for a dimension of 150mm × 100mm having 6mm thickness same as the experimental workpiece. The generated Finite element model is called in ANSYS Workbench for transient thermal simulations to obtain the temperature distributions and the heat source models are also called in ANSYS Fluent for velocity field. The heat source models selected and the temperature field obtained from the computational numerical simulations are in good agreement with the experimental results indicating validation of the simulation process made.

Analysis of heat and mass transfer in ultrasonic vibration-enhanced friction stir welding of 2195 Al–Li alloy

Ultrasonic vibration (UV)-enhanced friction stir welding (UVeFSW) is used for welding of 2195 Al–Li alloy plates. A model is developed to study the heat and mass transfer in UVeFSW of 2195 Al–Li alloy. It reveals that additional UV in FSW could reduce the heat flux and temperature at the contact interfaces when compared to those in conventional FSW. Although the temperature is slightly decreased with additional UV, the acoustoplastic effect of the UV could reduce the flow stress and viscosity in the shear zone, resulting in an enhanced fluidity of the plastic material with a higher flow velocity. It is demonstrated that the variations of viscosity, strain rate and flow stress around the tool at the same radial distance are more severe at low heat input condition, such as with a low rotation speed or a high welding speed. The model is validated by the experimental data.

Thermal modelling of alternating current square waveform arc welding

The instantaneous change of polarity during the welding with square waveform alternative current (AC) creates two distinct but partially overlapping weld-pools. The conventional ellipsoidal heat source model lacks the versatility to embody the overlapping weld-pools in the numerical simulation. A new overlapping double ellipsoidal heat source model is proposed to simulate the thermal behaviour of the AC square waveform welding process. The dimensions of the overlapping heat source are determined first by solving the steady-state heat conduction equation. The heat source so developed is then used in finite element analysis for the computation of the transient temperature distribution. The numerical model is validated by comparison with the experimentally measured thermal cycle. The effect of process parameters, namely welding current, electrode negative ratio, current frequency, on the thermal behaviour and weld-pool geometry is analyzed. The interplay between the process parameters and the thermal cycle due to AC square waveform are the significant findings of the present work, e.g., increase in frequency stabilizes the arc on the cost of lowering the peak temperature. The computationally affordable welding heat transfer models, such as the present investigation, pave the way to resolve shop-floor significant issues such as residual stress and distortion.

Influencing mechanism of an external magnetic field on fluid flow, heat transfer and microstructure in aluminum resistance spot welding

ABSTRACT The magnetically assisted resistance spot welding (MA-RSW) method provides a promising approach for improving weld performance. However, the MA-RSW process involves complex multiphysics fields that make numerical modeling very challenging. Thus, most resistance spot welding (RSW) models adopt electrothermal-mechanical coupling and ignore the influence of fluid flows caused by electromagnetic forces on nugget growth. In this paper, a magnetohydrodynamic (MHD) model, which couples the electric, thermal, magnetic and flow fields, is developed to explore the influencing mechanism of an external magnetic field (EMF) on the flow patterns and microstructures of aluminum resistance spot welds. Numerical results show that the application of an EMF can lead to the formation of Lorentz force in the liquid nugget, which transforms the flow pattern from an in-plane flow to a combined in-plane and out-of-plane flow. The flow velocity of molten metal in the MA-RSW process is 5 times higher than that of the RSW process, and the maximum temperature of the MA-RSW model is reduced from 774°C in the MHD RSW model to 725°C. Therefore, the MA-RSW joint exhibits a 25.5% larger nugget diameter, a more than 20% finer grain structure, and fewer defects than the RSW joint in the experimental results.

Influence of tool tilt angle on heat transfer and material flow in friction stir welding

The tool tilt angle is an important factor determining the microstructure and properties of friction stir weld joints. In this study, both experiments and numerical simulations are made to investigate the influence of tool tilt angle on heat generation, temperature field and material flow behavior in friction stir welding (FSW). The tool tilt angle induced non-contact area between tool shoulder and workpiece is determined under different sets of process parameters, and numerical simulations are conducted. It is found that the crescent-shaped uncontacted area gets larger when either the tool rotation rate or the welding speed increases. Compared with the case of 0° tool tilt angle, a tilted tool produces stronger forging effect at trailing side, a larger region of high temperature at the trailing advancing side, a higher peak temperature and more intensified material flow around the tool. With consideration of tool tilt angle and pin thread in the new model, the predicted peak temperature at tool/workpiece interface and the thermo-mechanically affected zone match well with the measured ones.

Heat transfer and fluid flow and their effects on the solidification microstructure in full-penetration laser welding of aluminum sheet

Understanding the behaviors of heat transfer and fluid flow in weld pool and their effects on the solidification microstructure are significant for performance improvement of laser welds. This paper develops a three-dimensional numerical model to understand the multi-physical processes such as heat transfer, melt convection and solidification behavior in full-penetration laser welding of thin 5083 aluminum sheet. Solidification parameters including temperature gradient G and solidification rate R, and their combined forms are evaluated to interpret solidification microstructure. The predicted weld dimensions and the microstructure morphology and scale agree well with experiments. Results indicate that heat conduction is the dominant mechanism of heat transfer in weld pool, and melt convection plays a critical role in microstructure scale. The mushy zone shape/size and solidification parameters can be modulated by changing process parameters. Dendritic structures form because of the low G/R value. The scale of dendritic structures can be reduced by increasing GR via decreasing heat input. The columnar to equiaxed transition is predicted quantitatively via the process related G3/R. These findings illustrate how heat transfer and fluid flow affect the solidification parameters and hence the microstructure, and show how to improve microstructure by optimizing the process.

Metal flow of weld pool and keyhole evolution in gas focusing plasma arc welding

Establishing an open keyhole throughout work-piece is the key to penetrate work-piece fully in gas focusing plasma arc welding. In order to study heat transfer, metal flow and keyhole surface evolution in gas focusing plasma arc welding, the three dimensional mathematical model is developed. Arc heat model and plasma arc pressure model are used to describe heat and force action in gas focusing plasma arc welding. Temperature field, fluid flow in weld pool and keyhole evolution are simulated. It is found that metal in weld pool front flows bypass keyhole wall toward weld pool back. Center line of keyhole channel is crocked instead of going along z-axis. The calculated weld shape agrees with the experimental data basically. This work may enrich theoretical knowledge about the complicated thermal physical process and provide basic data to guide welding application in gas focusing plasma arc welding.