Welding Of Sheets Research Articles

Effect of adhesive on friction stir spot welding of AZ31B magnesium alloy sheets

ABSTRACT AZ31B magnesium alloy sheets were lap-joined with adhesive only, friction stir spot welding (FSSW) only, and also with FSSW after adding adhesive between sheets. The produced joints were comparatively studied regarding joint cross-section geometrical features and defects that occurred at joint interface, microstructure, microhardness, tensile shear strength, and fracture surface evaluation. For joints made with FSSW only, cracks formed at underside of top sheet just above interface of sheets. However, joining with FSSW while there is adhesive between sheets eliminated formation of cracks and enabled weld width to enlarge significantly. Additionally, adhesive presence at interface of sheets joined by FSSW drastically reduced hook defect formation in the weld . The hook sizes of joints of FSSW with adhesive were so small as to be negligible compared to those of FSSW adhesive-free. Consequently, joints of FSSW with adhesive had much higher tensile shear strength. However, due to their brittle fracture, they displayed much less ductility than adhesive-free FSSW joints. The joints made via just adhesive had the lowest strength and elongation. Microstructure and microhardness of joints made by FSSW without and with adhesive were slightly different from each other. The main factors determining joint strength were adhesive, hook and weld size.

Experimental and finite element investigation of resistance spot welding of mild steel sheet covered aluminum alloy, AA 2017

Experimental and finite element investigation of resistance spot welding of mild steel sheet covered aluminum alloy, AA 2017

Elucidating the process mechanism in Mg-to-Al friction stir lap welding enhanced by ultrasonic vibration

The composite structures/components made by friction stir lap welding (FSLW) of Mg alloy sheet and Al alloy sheet are of wide application potentials in the manufacturing sector of transportation vehicles. To further improve the joint quality, the ultrasonic vibration (UV) is exerted in FSLW, and the UV enhanced FSLW (UVeFSLW) was developed for making Mg-to-Al dissimilar joints. The numerical analysis and experimental investigation were combined to study the process mechanism in Mg/Al UVeFSLW. An equation related to the temperature and strain rate was derived to calculate the grain size at different locations of the weld nugget zone, and the effect of grain size distribution on the threshold thermal stress was included, so that the prediction accuracy of flow stress was further improved. With such modified constitutive equation, the numerical simulation was conducted to compare the heat generation, temperature profiles and material flow behaviors in Mg/Al UVeFSLW/FSLW processes. It was found that the exerted UV decreased the temperature at two checking points on the tool/workpiece interface from 707/671 K in FSLW to 689/660 K in UVeFSLW, which suppressed the IMCs thickness at Mg-Al interface from 1.7 µm in FSLW to 1.1 µm in UVeFSLW. The exerted UV increased the horizontal materials flow ability, and decreased the upward flow ability, which resulted in the increase of effective sheet thickness/effective lap width from 2.01/3.70 mm in FSLW to 2.04/4.84 mm in UVeFSLW. Therefore, the ultrasonic vibration improved the tensile shear strength of Mg-to-Al lap joints by 18 %.

Studies on welding of thin stainless steel sheets with pulsed nanosecond fiber laser in butt joint configuration

In this work, we report full penetration welding of 1.6 mm thick AISI 304L stainless steel sheets in a butt joint configuration using a pulsed nanosecond fiber laser of an average power of 200 W. The welding was carried out by a focused laser beam oscillating in a circular path. The effects of beam oscillation parameters, e.g., amplitude, frequency, and weld speed, on weld morphology and microstructure were studied. Electron back scattered diffraction was used to characterize the weld microstructure and to map the distribution of austenite and ferrite phases in the weld. The solidification mode of the weld was found to change from the equilibrium FA (Ferrite-Austenite) to AF (Austenite-Ferrite) to A (Austenite) on an increase in the cooling rate with a concomitant drop in the fraction of δ-ferrite. The welds were found to be without any cracks with the sporadic presence of porosities. The welds were found to be mechanically strong.

Friction Stir Welding of Unequal-Thickness Magnesium Sheets with a Cover Sheet

Friction Stir Welding of Unequal-Thickness Magnesium Sheets with a Cover Sheet

Solidification crack elimination in TIG welding of Al7075: Experimental investigation and modified RDG modelling

Although solidification crack susceptibility modelling has been a point of interest for many years in fusion welding of aluminum alloys, the underlying mechanism of solidification crack elimination is not yet fully understood. To contribute in closing this knowledge gap, the present study investigates and proposes a new modified Rappaz-Drezet-Gremaud (RDG) physical model in autogenous and heterogeneous TIG welding of Al7075 sheets. The core novelty of the new model is that it includes the shrinkage strain rate, which allows to better capture the effects of capillary pressure, coherency point, as well as final dendrite or grain size in the fusion zone. In agreement with the experimental results and previous models, the new model shows that the defining mechanism of eliminating solidification cracks in heterogeneous joints is the capacity of nanoparticles to initiate heterogeneous grain nucleation, altering the fusion zone grain morphology from dendritic to fine equiaxed, with only little impact of the resulting grain size. This leads to two main effects causing reduced solidification crack susceptibility: (1) a reduction in coherency point by about 15 % from 902 K to 879 K, which reduces strain accumulation on the coherent solid network; (2) a considerable increase in capillary pressure across the entire mushy zone, allowing to maintain the total pressure at void/liquid interfaces in the positive range, which prevents the growth of potentially formed voids between grains at any temperature during solidification. In contrast, dendrite widths below 68 μm are required to prevent solidification cracks in autogenous joints without TiC nanoparticles, indicating a greater role of grain refinement. Overall, the proposed model highlights the more determinant role of the temperature-dependent solidification shrinkage strain rate in solidification crack susceptibility as it is an order of magnitude greater compared to the temperature-independent thermal contraction strain rate that has been the main or sole focus of previous models.

Laser butt welding of thin stainless steel 316L sheets in asymmetric configurations: A numerical study

Laser butt welding of thin metal sheets is a widely used fusion-based joining technique in industrial manufacturing. A comprehensive understanding of the complex transport phenomena during the welding process is essential for achieving high-quality welds. In the present work, high-fidelity numerical simulations are employed to investigate the influence of various symmetric and asymmetric welding configurations on the melt-pool behaviour in conduction-mode laser butt welding of stainless steel sheets. The analysis focuses on the effects of laser power density, heat source misplacement and different welding scenarios, including plates with a root gap, high-low mismatches, and dissimilar thicknesses, on the molten metal flow and heat transfer. The results show that advection is the dominant mechanism for energy transfer in the melt pool, and its contribution increases with higher laser power. The non-uniform temperature distribution over the melt-pool surface induces Marangoni shear forces, driving the flow of molten metal and leading to the formation of vortices and periodic flow oscillations within the pool. The effects of various types of asymmetries on the thermal and molten metal flow fields, as well as the process stability, are thoroughly examined and compared with symmetrical welding configurations. These comprehensive simulations provide valuable insights into the fluid flow dynamics and thermal field evolution during laser butt welding of thin metal sheets. The knowledge gained from this study can facilitate process optimisation and guide the improvement of weld quality in practical applications.

Analysis on TIG Arc During Welding of Magnesium Alloy Sheet by a Combination of Spectral Diagnosing and Langmuir Probe Detection

Analysis on TIG Arc During Welding of Magnesium Alloy Sheet by a Combination of Spectral Diagnosing and Langmuir Probe Detection

COMPARISON OF ORBITAL AND MANUAL WELDING FOR MANUFACTURING STAINLESS STEEL HEAT EXCHANGER

The main purpose of this study, the fabrication of tube-to-tube sheet welds ofan acid cooler exchanger, which is produced with stainless steel material, was examined usingdifferent welding methods. The tubes were subjected to two different welding methods usinga tungsten electrode. In orbital welding, the machine places the tube on a mandrel andautomatically performs the welding based on the manually inputted tube diameter. At the endof each tube weld, the mandrel is transferred to the next tube by the welder. In manualwelding, the entire tube-to-tube sheet weld is performed by the welder. Welds were madeusing the same material, same diameter, and same thickness of tubes for both orbital welding and manual welding. As a result, the test results and quality controls for both weldingmethodswere examined.

The role of filler wire and scanning strategy in laser welding of difficult-to-weld aluminum alloys

AbstractLaser welding of dissimilar aluminum alloys has gained interest over recent years, especially for the production of lightweight components. Pore and crack formation is one of the most critical factors to be taken into consideration for such applications, in particular when one or more parts are produced by die casting or additive manufacturing (AM). Current laser systems offer several methods for defect reduction and process control, while optimized process strategies must be correlated to key factors influencing welding outcomes. In light of these aspects, the current paper investigates the welding of AA6082 sheets with AlSi10Mg parts produced by AM in a lap-joint configuration typical of battery housings in the e-mobility industry. Both laser welding with and without filler wire are investigated, along with the potential advantages of using a wobbling scanning strategy, in order to understand the impact of process strategies on weld bead quality. The importance of process parameter optimization is highlighted for all of the employed strategies, with special emphasis on defects, weld bead chemical composition, joint morphology, and dilution between the materials involved. The findings demonstrate that by introducing filler wire and employing active wobbling, highly reflective alloys can be welded correctly (porosity below 1%, equivalent ultimate strength up to 204 MPa) with good tolerance to variations in process parameters, while filler wire can be excluded in high-productivity welding where linear scanning is employed and detailed optimization of process parameters is performed (porosity below 2%, equivalent ultimate strength up to 190 MPa).

Laser welding in e-mobility: process characterization and monitoring

The global automotive industry is shifting to e-mobility, where the main challenge is addressed to battery’s mass-production. To keep up with the market demand, high speed production rates and quality products must be accomplished. Since laser welding of dissimilar thins sheets has earned rising demand for battery electrodes connections, a defect-free welding process has to be performed on behalf of a closed-loop monitoring system that updates corrective and/or preventive actions in order to obtain a reliable, “zero waste, zero stop” process. However, nowadays photodiode systems do not allow real-time modification of the parameters, they only tell, at the end of the process, if any signal has gone out of threshold. The objective of this paper is to find correlations between the data collected by the monitoring system with the typical process characteristics of laser welding. Materials investigated are pure copper 300 µm and aluminum 400 µm, processed by means of different sources, length tracks, wavelengths and scanning heads. In this contribution, a Precitec system has been implemented as a possible economical and industrial-oriented solution.The experimental data was analyzed offline and the relationships between technological and signals outputs were evaluated by means of statistical analysis with MATLAB for both Al-Cu and Cu-Al configuration. Findings plotted stable signals if high speeds were set. Results further suggested the power to be the most influent variable for the closed-loop monitoring system and the dependance on the first material irradiated and the laser source used to define the threshold value for the control of the welding process.

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.

Friction stir spot welding of aluminum and steel sheets using a consumable sheet

Friction stir spot welding of aluminum and steel sheets using a consumable sheet

Acoustic monitoring of weld strength in ultrasonic metal welding by tracking welding stages

Ultrasonic metal welding (USMW) is a welding technique often used in the electronic and automobile industries. However, the strength of the welds it produces is influenced by a large number of variables, making USMW difficult to monitor. There is therefore a need for monitoring parameters which can be used across a large number of influencing variables. Such parameters should be closely related to the welding process and the evolution of the weld strength during welding. The goal of this paper is to investigate the usability of the horn and anvil vibrations at the welding frequency as such monitoring parameters. In this study, the horn and anvil vibrations were tracked during welding of copper sheets using laser vibrometers, compared to results in the literature to identify welding stages, and compared to the evolution of the weld strength. To avoid any low sample size bias, 120 welds were used. Their envelopes and their rate of change were extracted and used to identify welding stages. The results showed that the strength of a weld plateaus when it reaches its stage of maximum strength, and that this stage can be identified by both the horn and anvil vibrations using features derived from the envelopes and their rate of change.

Study on mechanical and microstructural properties of advanced high-strength welded sheet metal

Continuous research is carried out in the automotive industry to decrease the weight of automobile bodies without reducing durability. For this purpose, the use of welding sheet metal is one of the successful techniques. Welded sheets are formed by combining two or more flat materials with different thicknesses and different mechanical properties, using the welding method, before being shaped in order to provide superior properties. This situation requires more attention during the shaping stages. It is important to calculate the pressures to be applied to the welding areas and to apply the shaping steps in a way that will not reduce the material strength. For this reason, the production stages of the dies to be used in the manufacture of these parts are just as important. In this study, an innovative die design is carried out for the production of welded sheet metal. The microstructure and mechanical properties of the welded sheet formed by the die were examined. The effect of the forces applied to the welding areas on the material and the mechanical properties of the materials of different thicknesses were determined. Within the scope of the study, microstructure analysis, hardness and tensile tests were carried out and the results were examined. When the results obtained were examined, it was seen that the strength and hardness values of the samples obtained from the welded area were higher than the other areas.

Development of resistance spot welding technology applying multi-stage adaptive control for narrow pitch spot welding of high strength steel sheets

In order to expand the application of high strength steel sheets to automotive bodies, stabilizing nugget diameter of resistance spot welds is required in the presence of several industrial disturbances. This study aims to ensure the nugget diameter of high strength steel sheets regardless weld spacing by utilizing adaptive control technology based on real-time feedback of heat quantity. Short weld spacing leads to expulsion from the sheet surface applying conventional adaptive control welding for mild steel sheets, whereas decrease in nugget diameter due to reduction of effective welding current for high strength steel sheets. On the other hand, two-stage adaptive control method enables to ensure nugget diameter regardless of steel strength even with 10 mm weld spacing, in which heat quantity was controlled independently in each stage of welding. The mechanism of these phenomena was revealed by verifying the influence of physical properties of steel and welding current pattern on the shunting phenomena using numerical simulation.

Influence of tool pin shape and rotation speed for friction stir spot welding of AZ91 magnesium alloy sheets

Abstract Light weight design is believed one of the most effective ways to enhance performance, reduce fuel consumption and harmful gases for air and land vehicles. Hence, welding lightweight metals like magnesium alloys is very important. Friction stir spot welding joints of 2 mm thick AZ91 magnesium alloy sheets by overlapping two of them were performed utilizing two welding tools having conical and triangular pin at 800, 1200 and 1600 revolution per minute (rpm) tool rotational velocities for each tool to identify the pin shape and rotation speed impact on microstructure and mechanical features of the created joints. The stir zones of the joints contained smaller grains, therefore had higher hardness in comparison to AZ91 base metal, thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ). The lowest hardness values were found in HAZ of the welds. Hardness fell slightly with a rise in rotation speed for both tools because of more heat input. Strength of the joints manufactured applying the triangular pin tool was better because this pin mixed materials better, thus created joints with bigger welding area and greater hardness. The strongest weld was fabricated by applying triangular pin tool and 1600 rpm.

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.

A General Analytical Solution for Two-Dimensional Columnar Crystal Growth during Laser Beam Welding of Thin Steel Sheets

A technique for calculating the main solidification parameters for a two-dimensional columnar crystal growth during complete penetration laser beam welding of thin steel sheets was developed. Given that the weld pool interface is described by Lamé curves (superellipses) within the horizontal plane of growth, general analytical solutions were derived for the geometry of the crystal axis and the corresponding growth rate and cross-sectional area of the crystal. A dimensionless analysis was performed to provide insights on the dependence of the solidification parameters on the shape and dimensions of the rear part of the weld pool boundary. The derived solutions were applied for the case of complete penetration laser beam keyhole welding of 2 mm thick 316L austenitic chromium-nickel steel sheets. It was shown that the reconstruction of the weld pool boundary with Lamé curves provides higher accuracy and flexibility compared to results obtained with elliptical functions. The validity of the proposed technique and the derived analytical solutions was backed up by a comparison of the obtained solutions to known analytical solutions and experimentally determined shapes and sizes of the crystals on the top surface of the sheet. The dimensions of the calculated crystal axis correlated well with the experimentally obtained results.

Welding of AA6061-T6 Sheets Using High-Strength 4xxx Fillers: Effect of Mg on Mechanical and Fatigue Properties.

Al-Si-Mg 4xxx filler metals are widely used in aluminum welding owing to their excellent weldability and capability for strength enhancement by heat treatment. However, weld joints with commercial Al-Si ER4043 fillers often exhibit poor strength and fatigue properties. In this study, two novel fillers were designed and prepared by increasing the Mg content in 4xxx filler metals, and the effects of Mg on the mechanical and fatigue properties were studied under as-welded and post-weld heat-treated (PWHT) conditions. AA6061-T6 sheets were used as the base metal and welded by gas metal arc welding. The welding defects were analyzed using X-ray radiography and optical microscopy, and the precipitates in the fusion zones were studied using transmission electron microscopy. The mechanical properties were evaluated using the microhardness, tensile, and fatigue tests. Compared to the reference ER4043 filler, the fillers with increased Mg content produced weld joints with higher microhardness and tensile strength. Joints made with fillers with high Mg contents (0.6-1.4 wt.%) displayed higher fatigue strengths and longer fatigue lives than joints made with the reference filler in both the as-welded and PWHT states. Of the joints studied, joints with the 1.4 wt.% Mg filler exhibited the highest fatigue strength and best fatigue life. The improved mechanical strength and fatigue properties of the aluminum joints were attributed to the enhanced solid-solution strengthening by solute Mg in the as-welded condition and the increased precipitation strengthening by β″ precipitates in the PWHT condition.