Double-sided Welding Research Articles

Studies on A-TIG welding of Low Activation Ferritic/Martensitic (LAFM) steel

Low Activation Ferritic–Martensitic steels (LAFM) are chosen as the candidate material for structural components in fusion reactors. The structural components are generally fabricated by welding processes. Activated Tungsten Inert Gas (A-TIG) welding is an emerging process for welding of thicker components. In the present work, attempt was made to develop A-TIG welding technology for LAFM steel plates of 10 mm thick. Activated flux was developed for LAFM steel by carrying out various bead-on-plate TIG welds without flux and with flux. The optimum flux was identified as one which gave maximum depth of penetration at minimum heat input values. With the optimized flux composition, LAFM steel plate of 10 mm thickness was welded in square butt weld joint configuration using double side welding technique. Optical and Scanning Electron Microscopy was used for characterizing the microstructures. Microhardness measurements were made across the weld cross section for as welded and post weld heat treated samples. Tensile and impact toughness properties were determined. The mechanical properties values obtained in A-TIG weld joint were comparable to that obtained in weld joints of LAFM steel made by Electron beam welding process.

Double-sided laser beam welded T-joints for aluminum aircraft fuselage panels: Process, microstructure, and mechanical properties

T-joints consisting of 1.8 mm thick AA6156-T6/AA6056-T4 aluminum alloys have been fabricated by double-sided laser beam welding using eutectic alloy AA4047 filler wire. The effects of the incident beam position, the incident beam angle, and the beam separation distance on the weld properties were investigated. The microstructure and mechanical properties were identified using optical microscopy, scanning electron microscopy, and tensile testing. The optimal incident beam position was determined to be 0.2 mm yielding a 40–50° seam angle. It was found that the weld penetration was increased significantly as the incident beam angle increased. The doubled-sided welds were not fused in a common molten pool and no longer symmetry when the beam separation distance exceeded to 1.5 mm. Five distinct zones were identified between the fusion zone center and the base material which consisted of: the cellular dendrite zone, parallel dendrite zone, partially melted zone, over-aged zone, and base material. The tensile strength depended on the weld penetration, and the failure originated at the weld toe on the skin side. The fracture mechanism of the head tensile test and hoop tensile test was found to be brittle fracture and ductile fracture, respectively.

Simulation of collision behavior on magnetic pressure seam welding of aluminum sheets

This paper deals with dynamic deformation process on magnetic pressure seam welding of aluminum sheets. Numerical analysis of the dynamic deformation process of the aluminum sheets is made by a finite element method. In this analysis, the metal sheets (100 mm width, 1 mm thickness) are modeled with plane-strain quadrilateral elements. A collision point velocity between the aluminum sheet surfaces was very high at an initial collision point, but it decreased continuously during the welding. A collision angle between the aluminum sheet surfaces was 0 degree at an initial collision point, but it increased continuously during the welding. The collision angle in a double-sided magnetic pressure seam welding process increased more quickly than that in a single-sided magnetic pressure seam welding process.

不锈钢激光-电弧双面焊接头熔化特征分析

不锈钢激光-电弧双面焊接头熔化特征分析

不锈钢激光-电弧双面焊接头熔化特征分析

不锈钢激光-电弧双面焊接头熔化特征分析

铝合金激光电弧双面焊接特性

铝合金激光电弧双面焊接特性

A comparative study of laser-arc double-sided welding and double-sided arc welding of 6 mm 5A06 aluminium alloy

In order to study the interactions between the two heat sources in both laser-arc double-sided welding (LADSW) and double-sided arc welding (DSAW), some welding characteristics including weld configuration, energy efficiency, weld microstructure and mechanical properties of the both processes were contrastively investigated. The results show that the weld cross-section of LADSW within the proper welding parameter takes on the combination of typical weld profiles of gas tungsten arc welding and laser welding, while the DSAW takes on a quasi-symmetrical shape. The energy efficiency of LADSW is higher than DSAW, probably due to the higher heat transfer efficiency in laser welding and stronger effect of laser on the arc. The weld microstructures of the both processes characterized by scanning electron microscope mainly consist of α and β phase, whereas the grain size and second-phase particle size vary a great deal for the different heat input. The tensile strength of LADSW is 91.7% of base metal, compared with that of 82.3% of DSAW, and the elongation is also higher than DSAW. The fracture micromorphology of LADSW indicates a more typical dimple fracture than that of DSAW. It is considered that the better mechanical properties of LADSW are attributed to the finer grain size.

Simulation of Temperature Field during Double-Sided Multi-Layer TIG Welding and Determination of its Thermal Efficiency

In order to provide effective guarantee for the prediction of residual stress and deformation after welding process of large-sized aluminum alloy structures, temperature field and thermal efficiency during double-sided multi-layer TIG welding of aluminum alloy was studied. By integratedly considering temperature-depended material properties, convection, radiation, filling rate of solders, et al, numerical analysis about the form of molten pool and temperature field was given. Element birth and death technique was taken during the simulation. Double-sided multi-layer TIG welding experiment was carried out and sample of cross section of weld seam after welding was prepared. By trying different thermal efficiency for calculation, simulation result consistent with experimental result was obtained finally, making the present thermal efficiency as the aim result for study. Confirmation was given by comparing temperature value from experiment with simulation one.

Numerical and experimental study on prediction of thermal history and residual deformation of double-sided fillet welding

Distortions occur in almost every arc welded joint. The nature of the created distortion depends on several parameters including the welding speed, plate thickness, welding current, voltage, and restraints applied to the job. The distortions and thermal history of a joint can be measured experimentally but the measurement procedure may be costly and time-consuming. In the present work a numerical elasto-plastic thermomechanical model has been developed for predicting the thermal history and resulting angular distortions of submerged arc welded double-sided fillet joints. A moving distributed heat source was used in the finite element modelling of the double-sided fillet welding to create a realistic simulation of the process. The effect of filler metal deposition was taken into account by implementing a birth-and-death process for the elements. The transient temperature distributions were predicted using temperature-dependent material properties. The angular distortion profiles were predicted based on the transient temperature distributions of the fillet welds. The model yielded results that match the experimental values (with a variation of 5–10 per cent for the maximum values of the distortions and a variation of 8 per cent for peak temperatures).

The Realization of Low Stress and Nonangular Distortion by Double-Sided Double Arc Welding

Control welding residual stress and distortion is extremely important in manufacturing industry. Double-sided double arc welding (DSDAW), which can control residual stress and angular distortion, is developed. Because arc distance between fore and rear torches is the key effective factor of angular distortions in DSDAW, its effects are not clear on the stress and angular distortions. In this study, numerical simulation is used to predict the transient temperature and welding distortion and stress with different arc distances. Meanwhile, the transient temperature and angular distortion are measured. The calculated results are in good agreement with the experimental results. The effects of arc distance on the angular distortion and stress are investigated. Lower stress and nonangular distortion is obtained at arc distances of 0 mm and 50 mm.

Arc characteristics of laser-TIG double-side welding

Based on the experiments of laser-TIG double-side welding (LTDSW) for aluminium alloys, the influence of laser radiation on the arc behaviours of the opposite side was investigated. Generally, with the variation of laser power, there are three typical arc shapes: arc column convergence, arc root constriction and arc expansion. An important point to notice is that the laser keyhole preheating will induce the arc column convergence in the LTDSW. The arc voltage in the LTDSW is lower than that in TIG welding over the entire range of the experimental currents. Moreover, with increasing welding current, the difference in arc voltage between TIG welding and LTDSW is diminished because of the self-stabilisation of the arc burning at high currents. The complex transformation of arc behaviours has a great effect on the arc current density and its stability. The laser generated hot spot or laser induced plasma will have a higher temperature and greater electron density than neighbouring regions, and will offer the line of least resistance or the lowest potential drop. Hence, it is very reasonable that the arc voltage should descend under the influence of laser radiation, and the arc electrons should compress and root to the hot spot or plasma zone.

Numerical simulation of three-dimension stress field in double-sided double arc multipass welding process

A new high-efficiency method for welding thick plates of low-alloy high-tensile steel which does not require back chipping – double-sided arc welding (DSAW) – is provided in this paper. Backing run adopts double-sided pulse gas tungsten arc welding, and other passes adopt double-sided gas metal arc welding. Three-dimensional numerical models of DSAW with 50 mm plates are developed to predict the stress distribution by using finite-element analysis, computer parallel processing technology and multiple jobs design, and are compared with single arc welding (SAW). The analysis of the interpass stresses indicates that the stresses of the back and cover pass are to be regarded as the key point in multipass welding. To verify the calculated results, the residual stresses and transient temperature of back run weld measured individually agree approximately with the calculated results, which illustrates that the backing run and residual stresses of DSAW are lower than those of SAW.

Fundamental studies on in-process controlling angular distortion in asymmetrical double-sided double arc welding

It is extremely important to reduce and control residual angular deformation from the welding processes which has negative effects on fabrication accuracy in the manufacturing industry. A new method, asymmetrical double-sided double arc welding (ADSAW), is studied due to control residual angular distortion. Because arc distance between fore and rear torches and welding parameters are the key effective factors of angular distortions in ADSAW, but it is not clear about the effects of them on the angular distortions. In this study, experiments are carried out to investigate the thermal character and the effects of arc distance and welding parameters on the angular distortion in ADSAW. Meanwhile, a 3-D thermal elastic plastic finite element model is developed to simulate transient temperature and welding deformation with different arc distance and heat input. The simulated results are in a good agreement with the experimental measurements. The influence on welding deformation of the arc distance and heat input is investigated. In addition, the distortion mechanism and control strategy of angular distortion are clarified through numerical simulation.

Abnormal macropore formation during double-sided gas tungsten arc welding of magnesium AZ91D alloy

One of the major concerns during gas tungsten arc (GTA) welding of cast magnesium alloys is the presence of large macroporosity in weldments, normally thought to occur from the presence of gas in the castings. In this study, a double-sided GTA welding process was adopted to join wrought magnesium AZ91D alloy plates. Micropores were formed in the weld zone of the first side that was welded, due to precipitation of H 2 as the mushy zone freezes. When the reverse side was welded, the heat generated caused the mushy zone in the initial weld to reform. The micropores in the initial weld then coalesced and expanded to form macropores by means of gas expansion through small holes that are present at the grain boundaries in the partially melted zone. Macropores in the partially melted zone increase with increased heat input, so that when a filler metal is used the macropores are smaller in number and in size.

Investigations into the effects of electron beam welding on thick Ti–6Al–4V titanium alloy

Electron beam welding (EBW) of titanium alloy Ti–6Al–4V is not an easy task and finding the correct welding parameters is one of the critical activities when the product is intricate in shape. The procedure adopted to weld 17.5 mm thick joint in a spherical titanium gas bottle using EBW is presented here. Available EBW machine was capable of welding full penetration joint only up to 12.5 mm in titanium. Single sided partial penetration weld yielded poor result in production welding due to repeated defects like lack of fusion, root porosities, weld bead depression, under cut, etc. A two-pass double side welding technique was developed, and a joint thickness of 21 mm was decided so that a partial penetration weld can be attempted with lesser beam power. The extra material kept at the root of the weld can be machined off after welding. Single pass was made from one side of the joint producing a partial penetration weld with a penetration of nearly 19 mm. The second pass was made from the reverse side of the joint producing a similar partial penetration weld with almost the same penetration as that of the first weld. Trial welds were carried out and considerable difficulties were encountered in developing the welding procedure for establishing a defect free weld. Fusion zone voids and root porosities were observed and techniques were developed which eliminated their occurrence. Systematic weld qualification was carried out on coupon level and mechanical property and microstructure evaluations were carried out to ensure the joint integrity. Based on the technology developed and parameters arrived, the final specimen was welded. After passing through non-destructive tests, it was subjected to hydraulic proof pressure test with strain gauges and acoustic emission sensors for validating the capability of the technology developed. It has qualified all the test requirements as per the specifications and has been used for aerospace applications.

Heat transfer and fluid flow in fusion type PA-GTA double-sided welding

In comparison with conventional single-sided arc welding, double-sided arc welding powered by a single power supply has remarkable advantages in enhancing penetration, minimizing distortion and improving welding production. In this paper, a three-dimensional steady numerical model is developed for the heat transfer and fluid flow in a fusion type plasma arc (PA)–gas tungsten arc (GTA) double-sided welding process. Based on the numerical model, the distributions of the fluid flow and temperature field are calculated. Numerical results show that the peak temperature and temperature gradient in the weld pool in the PA side are higher than the values in the GTA side. Within the weld pool, the electromagnetic force drives the melted metal to move from two sides to the central part of the weld pool, and this effect is positive to penetrating the workpiece. The fluid flow of the melted metal in the free surface of the weld pool is fiercer than the flow within the weld pool, and the biggest flow velocity of the melted metal occurs in the free surface in the PA side. A comparison of the cross section of the weld bead with the experimental result shows that the numerical model's accuracy is reasonable.

Numerical simulation of dynamic development of keyhole in double-sided arc welding

Double-sided arc welding (DSAW) is a novel process for joining metals that is capable of achieving deep narrow penetration in a single pass with minimized distortion. A clear understanding of the process fundamentals is critical in order to fully examine the potential of DSAW, to guide the further developments of the process, to direct the practicability study, and to design the process parameters. This paper aims at developing a numerical model for examining and simulating the dynamic keyhole establishment process, which will be a key in developing an effective control technology for DSAW. The model is used to determine the geometrical shape of the keyhole and the weld pool, and the temperature distribution in the workpiece. Quantitative information on the establishment of the keyhole in DSAW, such as the transient development of the keyhole and the weld pool, the increase rate of the depth of the surface depression, the time interval from full penetration to the keyhole establishment, the minimum span of the weld pool for describing the conditions required to complete the keyhole establishment, and variation of the overflow height of the weld pool surface on the plasma arc welding side, has been obtained through numerical analysis. The DSAW experiments show that the predicted weld cross-section is in agreement with the measured one. The results lay a foundation for guiding the further development of the DSAW process and its effective control.

Numerical simulation of heat transfer and fluid flow in a double-sided gas-tungsten arc welding process

Double-sided arc welding powered by a single power supply is a new type of welding process developed recently at the University of Kentucky. Experiments show that this process has advantages over conventional single-sided arc welding in enhancing penetration, minimizing distortion, improving solidification structure and welding aluminium without the necessity of using filler metal for cracking prevention. In this paper, a three-dimensional transient numerical model is developed for the heat transfer and fluid flow in double-sided gas-tungsten arc welding, including flat-position welding and vertical-up position welding. Based on a non-uniform staggered grid system, the governing equations are solved numerically using the SIMPLEC algorithm. The roles of the surface tension gradient, electromagnetic force and buoyancy force in determining the fluid flow and weld penetration are analysed and compared with those in the conventional arc welding process. The computed weld geometry is compared with experimental results and it is found that the computational results agree with the experimental results with reasonable accuracy.

Numerical analysis of temperature field during double-sided arc welding of thick materials

Double-sided arc welding (DSAW) is a novel arc process developed at the University of Kentucky in which the workpiece is disconnected from the power supply and the two torches are used to establish two arcs on the both sides of the workpiece to close the current loop. As a result, the welding current is forced to flow through the workpiece along the thickness direction. This configuration and current flow direction improve the concentration of the arc energy distribution and provide a mechanism to guide the arc into the keyhole. Hence, DSAW process is capable of achieving deep narrow penetration and symmetrical welds. However, despite the progress in process development, there is a lack of a clear understanding of the physical processes and phenomena occurring in the weldment. In this study, a numerical model is developed to compute the temperature field and history in double-sided arc weldment. Using this numerical model, the temperature distributions and profiles at different cross-sections and along different lines of interest have been computed and compared with the results in regular plasma arc welding. It was found that DSAW process has advantages in obtaining deep narrow penetration, in producing symmetrical hour glass-shaped welds, in reducing the sensitization zone, in lowering the temperature gradient along the thickness, thus lowering the thermal distortion and residual stress, and in decreasing the sensitization duration.

Sensing and Control of Double-Sided Arc Welding Process

The welding industry is driven to improve productivity without sacrificing quality. For thick material welding, the current practice is to use backing or multiple passes. The laser welding process, capable of achieving deep narrow penetration, can significantly improve welding productivity for such applications by reducing the number of passes. However, its competitiveness in comparison with traditional arc welding is weakened by its high cost, strict fit-up requirement, and difficulty in welding large structures. In this work, a different method, referred to as double-sided arc welding (DSAW) is developed to improve the arc concentration for arc welding. A sensing and control system is developed to achieve deep narrow penetration under variations in welding conditions. Experiments verified that the pulsed keyhole DSAW system developed is capable of achieving deep narrow penetration on a 1/2 inch thick square butt joint in a single pass.