Showing papers on "Butt welding published in 2017"

Microstructural characteristics and mechanical properties of the dissimilar friction-stir butt welds between an Al–Mg alloy and A316L stainless steel

Abstract: In this research, dissimilar butt joining of an Al–Mg alloy (AA5083) to austenitic stainless steel (A316L) by using friction-stir welding (FSW) process was examined. FSW parameters and joint design were optimized, owning to achieve the best joint strength. The processed FSWs at the optimized traverse speeds of 16, 20, and 25 mm/min with the sound surface appearance were considered for further cross-sectional investigations, microstructural characterizations, and mechanical testings. In situ reactions at the interface of Al–Mg alloy and stainless steel during FSW processes were studied by using field emission-scanning electron microscopy (FE-SEM) and line-scan energy-dispersive X-ray spectroscopy (EDS) analysis. As expected from the monitored thermal histories during FSW joining, the features indicating the formation of tunneling like defects were observed at low heat inputs (low w/v ratios). Moreover, some discontinuous thin intermetallic layers (with the thickness of ∼0.5 μm) were formed at the joint interface at the expressed processing conditions. Mechanical performances of the prepared dissimilar joints were assessed during transverse tensile loading and Vickers indentation micro-hardness testing. The joint strength ratio to the ultimate tensile strength (UTS) of the weakest base metal (BM) was improved up to ∼93 %, as all of the dissimilar FSWs failed from the Al–Mg base alloy, with a Vickers hardness enhancement of ∼460 % at the interface.

The effect of shoulder coupling on the residual stress and hardness distribution in AA7050 friction stir butt welds

Abstract: The effect of shoulder coupling in friction stir welding (FSW) on the distribution of residual stresses, microstructure and hardness has been investigated by comparing welds manufactured with a conventional tool, using different levels of downforce, to joints produced using a stationary shoulder (SSFSW). The welds were produced in AA7050-T7651 6.35 mm plate with the same travel speed and similar power levels. Reducing the tool downforce in FSW led to a decrease in the overall shoulder input power, but a minimal reduction in the weld zone hardness and peak residual stresses. In contrast, relative to FSWs made with a similar input power, the stationary shoulder led to much more significant microstructure and property changes including a reduction in the HAZ width, an increase in the minimum weld zone hardness level and a significant reduction in the peak tensile residual stresses (by ~ 25%). With SSFSW, the improvement found in the hardness and residual stress distribution from eliminating the energy dissipated by the tool shoulder could be directly correlated to a reduction in the weld temperature and narrowing of the thermal field, which reduced the size of the HAZ and region of plastic misfit responsible for the weld residual stresses. By comparing the results with previous work it was found that, apart from using a stationary shoulder, the most important welding parameter affecting the weld zone peak tensile stresses was the travel speed, with longitudinal residual stresses doubling upon increasing the travel speed from 100 to 400 mm/min.

Finite Element Simulation of Temperature and Strain Distribution during Friction Stir Welding of AA2024 Aluminum Alloy

Abstract: Friction Stir Welding (FSW) is a solid state joining process and is handy for welding aluminum alloys. Finite Element Method (FEM) is an important tool to predict state variables of the process but numerical simulation of FSW is highly complex due to non-linear contact interactions between tool and work piece and interdependency of displacement and temperature. In the present work, a three dimensional coupled thermo-mechanical method based on Lagrangian implicit method is proposed to study the thermal history, strain distribution and thermo-mechanical process in butt welding of Aluminum alloy 2024 using DEFORM-3D software. Workpiece is defined as rigid-visco plastic material and sticking condition between tool and work piece is defined. Adaptive re-meshing is used to tackle high mesh distortion. Effect of tool rotational and welding speed on plastic strain is studied and insight is given on asymmetric nature of FSW process. Temperature distribution on the workpiece and tool is predicted and maximum temperature is found in workpiece top surface.

Disk Laser Weld Brazing of AW5083 Aluminum Alloy with Titanium Grade 2

Abstract: Disk laser weld brazing of dissimilar metals was carried out. Aluminum alloy 5083 and commercially pure titanium Grade 2 with the thickness of 2.0 mm were used as experimental materials. Butt weld brazed joints were produced under different welding parameters. The 5087 aluminum alloy filler wire with a diameter of 1.2 mm was used for joining dissimilar metals. The elimination of weld metal cracking was attained by offsetting the laser beam. When the offset was 0 mm, the intermixing of both metals was too high, thus producing higher amount of intermetallic compounds (IMCs). Higher amount of IMCs resulted in poorer mechanical properties of produced joints. Grain refinement in the fusion zone occurred especially due to the high cooling rates during laser beam joining. Reactions at the interface varied in the dependence of its location. Continuous thin IMC layer was observed directly at the titanium–weld metal interface. Microhardness of an IMC island in the weld metal reached up to 452.2 HV0.1. The XRD analysis confirmed the presence of tetragonal Al3Ti intermetallic compound. The highest tensile strength was recorded in the case when the laser beam offset of 300 μm from the joint centerline toward aluminum alloy was utilized.

Joining lightweight components by short-time resistance spot welding

Abstract: Resistance welding is a very cost- and energy-efficient welding process for thin sheets with wide distribution in the automotive manufacturing. With the challenges of lightweight construction in this area, new high-strength steel grades, light metals, and fiber-reinforced plastics are increasingly used. Hence, to that, adjustments of the welding processes are required. New process variants such as the resistance element welding (REW) are used to join mixed compounds of lightweight components and steel. Similar to the welding of functional elements, a low energy input in the base material is targeted, so only a small thermal influence of the materials occurs. This requires new approaches to short-term welding, to be presented in this paper. The content is based on a bilateral research project with a welding machine manufacturer. The influence of adhesive on REW joints is described. In addition to the produced joints, the mechanical properties and the process parameters are shown.

Control of welding distortion during gas metal arc welding of AH36 plates by stress engineering

Abstract: Welding residual stress and distortion are strongly linked together. One of the ways to control or reduce the welding distortions is the manipulation of the generated stresses during welding, and final residual stresses exist in the workpiece (stress engineering). In this paper, the control of gas metal arc butt welding distortion of 500 × 250 × 6 mm3 AH36 plates by means of additional heat sources is studied using experimental and numerical approaches. To understand the distortion reduction mechanism, 3D finite element model has been constructed and validated by temperature, distortion and residual stress measurements together with microstructure investigation. The numerical results are compared to that of the experimental measurements.

Vision and spectroscopic sensing for joint tracing in narrow gap laser butt welding

Abstract: The automated laser beam butt welding process is sensitive to positioning the laser beam with respect to the joint because a small offset may result in detrimental lack of sidewall fusion. This pro ...

Development of friction stir welding technologies for in-space manufacturing

Abstract: Friction stir welding (FSW) has emerged as an attractive process for fabricating aerospace vehicles. Current FSW state-of-the-art uses large machines that are not portable. However, there is a growing need for fabrication and repair operations associated with in-space manufacturing. This need stems from a desire for prolonged missions and travel beyond low-earth orbit. To address this need, research and development is presented regarding two enabling technologies. The first is a self-adjusting and aligning (SAA) FSW tool that drastically reduces the axial force that has historically been quite large. The SAA-FSW tool is a bobbin style tool that floats freely, without any external actuators, along its vertical axis to adjust and align with the workpiece’s position and orientation. Successful butt welding of 1/8 in. (3.175 mm) thick aluminum 1100 was achieved in conjunction with a drastic reduction and near elimination of the axial process force. Along with the SAA-FSW, an innovative in-process monitor technique is presented in which a magnetoelastic force rate-of-change sensor is employed. The sensor consists of a magnetized FSW tool that is used to induce a voltage in a coil surrounding the tool when changes to the process forces occur. The sensor was able to detect 1/16 in. (1.5875 mm) diameter voids. It is concluded that these technologies could be applied toward the development of a portable FSW machine for use in space.

Numerical simulation of residual stresses induced by TIG butt-welding of thin plates made of AISI 316L stainless steel

Abstract: The paper herein presented refers to the numerical simulations of a TIG butt-welding process applied to thin plates made ​​of an AISI 316L austenitic stainless steel. Finite element (FE) thermal analyses were initially carried out in order to obtain the transient temperature distributions in the plates, and, subsequently time-dependent thermal results were used in the FE structural analyses, in order to calculate the residual stresses and deformations introduced by the welding process. A double Gaussian distribution – namely a double ellipsoid -, with front and rear dimension's areas of the arc defined based on real weld bead's measurement, was used as the heat source model (power density), and it was considered that it moved at constant speed. Numerical results calculated were in good agreement with the experimental residual stresses measured by the hole-drilling method, showing the adequacy of the method implemented and its potential to estimate residual stresses and distortions. In fact, it was found a deviation of 19 % for the maximum principal stress calculated, while for the minimum principal stress a deviation value of 9 % was obtained; in addition, the simulated weld bead presented slight deviations from the macrograph sample and the differences related to the depth of the weld pool were around 2%.

Development of Activated Flux, Optimization of Welding Parameters and Characterization of Weld Joint for DMR-249A Shipbuilding Steel

Abstract: The present investigation aims to develop activated flux for joining of DMR-249A steel using activated tungsten inert gas (A-TIG) welding process and characterize the fabricated weld joint. The various combinations of fluxes were prepared to decide suitable flux for DMR-249A steel. The design of experiment was carried out for optimization of welding parameters to achieve the desired depth of penetration. The square butt weld joints were fabricated on 10 mm thick plates employing A-TIG welding using developed flux and optimized process parameters employing double side welding procedure. The microstructural investigations and hardness, tensile and impact tests were carried out on the base metal and weld joint. The strengths, ductility and impact toughness of the joints were found to be comparable with that of the base metal.

Influence of Filler Alloy Composition and Process Parameters on the Intermetallic Layer Thickness in Single-Sided Cold Metal Transfer Welding of Aluminum-Steel Blanks

Abstract: Hybrid components made of aluminum alloys and high-strength steels are typically used in automotive lightweight applications. Dissimilar joining of these materials is quite challenging; however, it is mandatory in order to produce multimaterial car body structures. Since especially welding of tailored blanks is of utmost interest, single-sided Cold Metal Transfer butt welding of thin sheets of aluminum alloy EN AW 6014 T4 and galvanized dual-phase steel HCT 450 X + ZE 75/75 was experimentally investigated in this study. The influence of different filler alloy compositions and welding process parameters on the thickness of the intermetallic layer, which forms between the weld seam and the steel sheet, was studied. The microstructures of the weld seam and of the intermetallic layer were characterized using conventional optical light microscopy and scanning electron microscopy. The results reveal that increasing the heat input and decreasing the cooling intensity tend to increase the layer thickness. The silicon content of the filler alloy has the strongest influence on the thickness of the intermetallic layer, whereas the magnesium and scandium contents of the filler alloy influence the cracking tendency. The layer thickness is not uniform and shows spatial variations along the bonding interface. The thinnest intermetallic layer (mean thickness < 4 µm) is obtained using the silicon-rich filler Al-3Si-1Mn, but the layer is more than twice as thick when different low-silicon fillers are used.

Narrow-gap laser welding using filler wire of thick steel plates

Abstract: Thick-section steel has been widely used in many heavy industries. Traditionally, very thick steel plates could be welded by using submerged arc welding and other welding processes. However, there were more or less drawbacks in these welding methods. Laser welding, a high-energy density welding method, is being considered for such structures to improve the production efficiency and reduce the residual stresses of the joints. In this study, butt joints with narrow gap were welded using a high-power CO2 laser. The effect of welding parameters including the relative position between the laser beam and the filler wire, welding speed, and the distance from the intersection of the beam and wire to root of the groove on the weld bead geometry and welding defects was studied. Additionally, high-speed photography was introduced in the experiment as an efficient method to record the total process of welding, especially the transfer of molten drop. The study found that when the beam was focused on the center of the groove, the filler wire could be melted successfully even though it would tremble slightly during welding process. The optimized distance from the intersection of the beam and wire to groove root was 3 mm. Later, butt weld joints of 70-mm-thick steel plate without lack of fusion can be obtained under optimized welding parameters.

Friction stir butt welding of Al-Cu bilayer laminated composites: analysis of force, torque, and temperature

Abstract: The effect of the layer in contact with tool (Al or Cu) and the depth of plunge on friction stir butt welding of Al-Cu bilayer laminated composites produced by cold roll welding were studied. The measurement of weld cross sections and variations of the axial load and torque during welding process showed that material flow is influenced by the material which is in contact with the shoulder. Being Al layer in contact with the shoulder led to higher force and torque during welding, and a defect-free weld could be obtained in this manner. By welding from Cu side, a higher plunge depth was needed to develop enough force and torque and thereby a defect-free weld. The amount of material swept by the shoulder and flow stress of the material in contact with shoulder have determined the force and torque and also temperature during welding.