Showing papers on "Butt welding published in 2022"

Improving intermetallic compounds inhomogeneity of Ti/Al butt joints by dual laser-beam bilateral synchronous welding-brazing

Abstract: To regulate the inhomogeneous interfacial reaction during laser welding-brazing of Ti/Al dissimilar alloys, an advanced method of dual laser-beam bilateral synchronous welding-brazing was proposed. The formation mechanism of the intermetallic compounds (IMCs) with various dual laser-beam input was analyzed. The experimental results revealed that sound brazing joints with homogeneous serrated-shaped IMCs along the Ti/Al interface were obtained when the laser power on both sides is the same. An interesting phenomenon can be found that the thickness of IMCs layer on both sides is thicker than the middle. The highest bonding strength of Ti/Al butt joints could reach up to 71% of aluminum alloy base metal due to homogeneous serrated-shaped IMCs with a thickness of 3–4 μm.

Influence of contact behavior on welding distortion and residual stress in a thin-plate butt-welded joint performed by partial-length welding

Abstract: Partial-length butt-welded joint is a typical weldment which is often used in vehicle parts such as car door and body. In order to clarify the influence of contact behavior on the final distortion and residual stress distribution in thin-plate butt-welded joints, a computational approach considering multiple nonlinearities was proposed based on ABAQUS code, and a series of three-dimensional thermal–elastic–plastic finite element models were developed to simulate welding distortion and residual stress in mild steel thin-plate butt-welded joints performed by partial-length welding. Meanwhile, the corresponding experiments were carried out to verify the calculation accuracy of the proposed computational approach. Moreover, the influence of initial gap size on welding distortion and residual stress was numerically and experimentally examined. Based on the simulated results, the formation mechanism of welding deformation in the thin-plate partial-length butt-welded joint was also discussed.

Improving intermetallic compounds inhomogeneity of Ti/Al butt joints by dual laser-beam bilateral synchronous welding-brazing

Abstract: To regulate the inhomogeneous interfacial reaction during laser welding-brazing of Ti/Al dissimilar alloys, an advanced method of dual laser-beam bilateral synchronous welding-brazing was proposed. The formation mechanism of the intermetallic compounds (IMCs) with various dual laser-beam input was analyzed. The experimental results revealed that sound brazing joints with homogeneous serrated-shaped IMCs along the Ti/Al interface were obtained when the laser power on both sides is the same. An interesting phenomenon can be found that the thickness of IMCs layer on both sides is thicker than the middle. The highest bonding strength of Ti/Al butt joints could reach up to 71% of aluminum alloy base metal due to homogeneous serrated-shaped IMCs with a thickness of 3–4 μm.

Ultrasonic vibration-induced thinning of intermetallic compound layers in friction stir welding of dissimilar Al/Mg alloys

Abstract: Frictions stir welding (FSW) and ultrasonic vibration enhanced FSW (UVeFSW) of dissimilar Al/Mg alloys were conducted, and the intermetallic compounds (IMCs) layers formed at Al/Mg interface in welds were characterised by TEM. It was found that the IMCs thickness was significantly reduced in UVeFSW, and the IMCs were generated by solid-state atomic diffusion in butt joints under the used welding conditions since the measured temperature at the tool/workpiece interface was far below the eutectic points. The EBSD characterisation showed that ultrasonic vibration improved the degree of grain recrystallization on both sides of the IMCs layers and promoted the consumption of dislocations, which resulted in a reduced diffusion rate of atoms. Therefore, the growth of IMC layer was suppressed in UVeFSW.

Buckling distortion investigation during thin plates butt welding with considering clamping influence

Abstract: Welding induced buckling is generally considered as the most complicated type of out-of-plane welding distortion during thin plate section fabrication, which will significantly influence the fabrication accuracy and cost. Thin plates of 3 mm thickness with dissimilar materials were experimentally butt welded together beforehand, while clamping constraint by fixture jig and additional plate was employed. After cooling down and clamping release, out-of-plane welding distortions were measured, and characteristic of welding buckling behavior can be observed. Advanced thermal elastic plastic (TEP) FE computation with solid elements models of examined butt-welded joints were then carried out. Welding induced buckling can be represented without considering clamping constraint, while much larger difference between computed results and measurement data was obtained. When the influence of clamping constraint employed during welding experiment was considered, good agreement for both deformed tendency and magnitude of out-of-plane welding distortion can be represented. With the clarification of mechanism based on the comparison of longitudinal residual stress, plastic strain as well as shrinkage force, clamping can significantly reduce magnitude of out-of-plane welding distortion, which still could not avoid the occurrence of welding induced buckling, as well as the change of deformed shape pattern.

Experimental study on tensile fracture mechanism of butt joints in multi-celled CFST walls

Abstract: Multi-celled concrete filled steel tubular walls (MCFSTWs) have been widely used in engineering practice. A high MCFSTW can be constructed by assembling two medium-height wall segments that are butt welded with the connector. At the connecting part between two wall segments, the connector, welding seams and steel plates of upper and lower wall segments form the butt joint. Since the butt joint is susceptible to tensile fracture, it is necessary to investigate its tensile fracture mechanism. In this paper, 12 specimens representing different parts of the butt joint are tested under tension and they include 6 types with different configurations. These specimens are designed by using connectors with different shapes and considering different welding conditions. The test results are analyzed and validated against the numerical simulation considering the ductile damage criteria. Based on the reliable finite element (FE) model, a simplified model is established to study the fracture performance of the complete butt joint. Finally, reliable design recommendations based on the experimental results and supplement FE analysis are summarized for improving the tensile performance of butt joints in MCFSTWs.

Statistical Characterization of Stress Concentrations along Butt Joint Weld Seams Using Deep Neural Networks

Abstract: In order to ensure high weld qualities and structural integrity of engineering structures, it is crucial to detect areas of high stress concentrations along weld seams. Traditional inspection methods rely on visual inspection and manual weld geometry measurements. Recent advances in the field of automated measurement techniques allow virtually unrestricted numbers of inspections by laser measurements of weld profiles; however, in order to compare weld qualities of different welding processes and manufacturers, a deeper understanding of statistical distributions of stress concentrations along weld seams is required. Hence, this study presents an approach to statistically characterize different types of butt joint weld seams. For this purpose, an artificial neural network is created from 945 finite element simulations to determine stress concentration factors at butt joints. Besides higher quality of predictions compared to empirical estimation functions, the new approach can directly be applied to all types welded structures, including arc- and laser-welded butt joints, and coupled with all types of 3D-measurement devices. Furthermore, sheet thickness ranging from 1 mm to 100 mm can be assessed.

The role of thermal contribution in the design of AA2024 friction stir welded butt and lap joints: mechanical properties and energy demand

Abstract: Although in recent times the use of solid-state welding processes as friction stir welding (FSW) has become increasingly widespread, for some joint morphologies, as lap joints, there are still significantly less data available on both process parameters optimization and energy consumption. In the present paper, the authors investigated the possibility of enhancing the joint quality in two different configurations, i.e. lap and butt joints, taking into account specific thermal contribution (STC) conferred to the weld. Strength, micro-hardness and microstructure were evaluated on the produced AA2024 aluminum alloys butt and lap joints. The surface response method (RSM) was used to investigate the effects of the main process parameters and to identify optimal technological parameters in terms of joint resistance, while the specific energy consumption (SEC) of the entire process was acquired with the aim to provide design guidelines taking into account, at the same time, mechanical performance and environmental impact. It was found that the same optimal range of revolutionary pitch can be identified for both the configurations. Additionally, maximizing welding speed, for a given revolutionary pitch, contributes to significantly reduce the environmental impact of the process with no detrimental effect on the joint performance.

Rotational speeds and preheating effect on the friction stir butt welding of Al-Cu joints

Abstract: Friction Stir Welding (FSW) used for welding similar and dissimilar materials especially to join sheet Al alloys. In this study, commercial pure aluminum and copper sheets (Al/Cu) with a thickness of 3mm were joined. We first preheated on the Cu side by pinless welding tool. Three different tool rotational speeds of 700, 1000 and 1500 rpm were used while the axial load and transverse speed were kept constant at 7.5 KN and 30 mm/min, respectively. We measured different parameters to determine the best rotational speeds for welding. Such as Field Emission Scanning Electron Microscopy (FESEM) and X-Ray Diffraction (XRD) analysis which showed that at 700 rpm there are three elements: Al, Cu and oxygen are present. While at 1500 rpm formation of different Intermetallic Compounds (IMCs). At 1000 rpm the interface has only Al and Cu in a uniform structure this result is due to the sufficient frictional heat generated at 1000 rpm and it considered perfect welds with acceptable mechanical properties.

Laser welding of 16MnCr5 butt welds with gap: resulting weld quality and fatigue strength assessment

Abstract: Abstract For laser welding, gaps should normally be avoided to ensure stable weld processes and high weld quality. Nonetheless, sometimes, gaps are resulting from non-optimal weld preparation in industrial applications. Within this investigation, the effects of a defocussed beam and laser beam oscillation on gap bridging abilities at reduced ambient pressure were investigated. For reference purpose, conventional laser welding with zero gap at ambient pressure was performed, too. The resulting weld geometry was investigated and correlated to gap bridging strategies and weld quality groups according to ISO 13919–1. The welds were characterized regarding their hardness and weld microstructure. Residual stress was determined by means of X-ray diffraction, and tensile tests as well as fatigue tests were conducted. The fatigue tests were evaluated by the nominal stress approach, the critical distance approach, and the stress averaging approach and correlated to weld quality measures. Resulting from this, fatigue resistance of laser welded butt welds with gap can be estimated by the FAT160 design S–N curve. The stress evaluation parameters for the determination of k eff -values ( ρ* = 0.4 mm, a = 0.1 mm) were confirmed.

The role of thermal contribution in the design of AA2024 friction stir welded butt and lap joints: mechanical properties and energy demand

Abstract: Although in recent times the use of solid-state welding processes as friction stir welding (FSW) has become increasingly widespread, for some joint morphologies, as lap joints, there are still significantly less data available on both process parameters optimization and energy consumption. In the present paper, the authors investigated the possibility of enhancing the joint quality in two different configurations, i.e. lap and butt joints, taking into account specific thermal contribution (STC) conferred to the weld. Strength, micro-hardness and microstructure were evaluated on the produced AA2024 aluminum alloys butt and lap joints. The surface response method (RSM) was used to investigate the effects of the main process parameters and to identify optimal technological parameters in terms of joint resistance, while the specific energy consumption (SEC) of the entire process was acquired with the aim to provide design guidelines taking into account, at the same time, mechanical performance and environmental impact. It was found that the same optimal range of revolutionary pitch can be identified for both the configurations. Additionally, maximizing welding speed, for a given revolutionary pitch, contributes to significantly reduce the environmental impact of the process with no detrimental effect on the joint performance.

Analysis of the Welding Process of Steel Pistons of Internal Combustion Engines

Abstract: The aim of the article is to analyze the friction welding process of steel pistons, due to the small amount of scientific literature on this subject. First, it is necessary to present the design features of steel pistons and their advantages and disadvantages. Then the article analyses it presenst the types of friction welding processes used in the production of pistons of internal combustion engines with the analysis of their differences. It present two basic methods of welding in the production of steel pistons, i.e. friction butt welding and low pressure friction welding. Finally, a proper analysis of the friction welding processes of steel pistons of internal combustion engines is presented. At the end, the conclusions of the analysis are presented and proposals for improving the process are made.

Stress and distortion of the 10 mm thick plate EH40 and 316L different butt joints in 10 kW laser welding

Abstract: Residual stress has a negative influence on the service life of different welded joints between high-strength steel and stainless steel, especially in corrosive environment, it is very easy to cause fracture failure of welded joints. In this study, three types of medium-thick plate butt joints in single-pass full penetration laser welding, including EH40 & 316L, EH40 & EH40 and 316L & 316L butt joints, were deeply studied and verified by thermo-elastoplastic finite element method and experiments. The peak exponentially increasing double cone heat source model was used to calculate the transient temperature field. The relevant data of longitudinal, transverse residual stresses and angular distortion in three cases were extracted for comparative analysis. At the same time, the influence of the same material and different materials on the evolution mechanism of nodes stress in the weld was also discussed. It had been found that the geometric profile average error between the simulation and experiment in three cases was less than 0.5%. The stress state changes of the weld and its vicinity nodes in EH40 & 316L butt joint were faster than EH40 & EH40 and 316L & 316L butt joints. Compared with the welded joints of the same material, the welded joints of EH40 and 316L in the weld and its vicinity were remarkable differences in transverse residual stress, equivalent residual stress and angular distortion. The transverse residual stress gradient value of the EH40 side in EH40 & 316L was almost twice that of EH40 & EH40. The mismatch material properties of EH40 & 316L aggravated the generation of transverse tensile residual stress on the EH40 side. The results obtained in the current study were beneficial to the assessment of the integrity in the butt joints and the control of potential risks.

Ultra-Narrow Gap Fiber Laser Conduction Welding Technology for 304 Stainless Steel Thick Plates and the Mechanical Properties of Welding Joints

Abstract: The application of thick metal plates is increasing, and the welding problem is becoming more and more prominent. Narrow gap laser welding is one of the important methods, and it is also a research hotspot. The stainless steel thick plates were welded using the ultra-narrow gap fiber laser conduction welding with filler wire. Results show that the ranges of technological parameters for the achievement of the weld seam with no defects are smaller when the gap width is comparatively larger. Using the optimized technological parameters, the butt welding with no defects on the 3 mm gap between two 304 stainless steel plates with 60 mm thickness was achieved through the filling 20 times. This welding method of 304 metal with large thickness is rare in the literature. The tensile strength of the welding joint can be up to 87% of that of the base metal, and the micro-hardness and yield strength of the joint are comparable with those of the base metal.

Predicting laser penetration welding states of high-speed railway Al butt-lap joint based on EEDM-SVM

Abstract: The Al butt-lap joints are widely applied in China Railway High-speed (CRH) trains body joints. However, the gaps caused by the thermal deformation in Al butt-lap joints lead to the lack penetration or over penetration. To predict the penetration state of laser welds in Al butt-lap joints with different gaps, this work investigated the correlation between the plasma plume morphology and penetration state monitored by high-speed imaging system and the vertical gap and horizontal gap were utilized as intermediary. The ensemble experience mode decomposition (EEMD) was used to obtain the frequency features of plasma plume morphology. A support vector machine (SVM) model combined with EEMD was then established to classify the different penetration state, which adopted the original signals at time-domain and the mode decomposition signals at frequency-domain as input. The EEMD-SVM accuracy of 97.98% was the highest among the EMD-SVM of 86.44% and the SVM of 58.15%. The EEMD-SVM obtained both high Accuracy and Recall when the quantity of positive and negative samples were utmost different. The classification of the EEMD-SVM model was the most superior among the EMD-SVM model and SVM model. This proposed method provided a novel and accurate approach to perform process monitoring and penetration defects detection during laser welding of butt-lap joints.

Effect of process parameters on performances of TWIP steel/Al alloy dissimilar metals butt joints by laser offset welding

Abstract: In this paper, butt joints of twinning-induced plasticity (TWIP) steel and aluminum alloy dissimilar metals were carried out by the laser offset welding method, and the amount of the aluminum alloy that melted was controlled by adjusting the offset distance of the laser beam spot. The aim of this study was to regulate the influence of the intermetallic compounds (IMCs) layer thickness, crystal structure and crack defects on the tensile strength of the welded joint. The tensile strength of the welded joint was obviously improved by adjusting the welding process parameters without adding any alloying elements. The results demonstrated that the crack initiated at the junction between the aluminum base metal and the weld seam and propagated along with the interface. The increase in the recrystallized fraction was beneficial to improve the tensile strength of the joint. The tensile strength of welded joints with more low-angle grain boundaries was lower. The smaller the thickness of the IMCs layer was, the higher the welded joint strength was. The optimized welding process parameters were as follows: d = 0.2 mm, P = 900 W, V = 15 mm/s and △ f = −2 mm in the present study, and the tensile strength of the joint reached 155 MPa. This study provides a theoretical basis for solving the welding cracking problem of steel/aluminum heterojunctions without additional interlayer material and so as to improve the strength of the steel/aluminum laser welded joint.

Microstructure and Mechanical Properties of Joints Depending on the Process Used

Abstract: Today, numerous design solutions require joining thin-walled sheets or profiles as the traditional methods of welding with a consumable electrode in gas shielding, most often used in production processes, do not work well. The reason for this is that a large amount of heat is supplied to the joint, causing numerous welding deformations, defects, and incompatibilities. Moreover, the visual aspect of the connections made more and more often plays an equally crucial role. Therefore, it is important to look for solutions and compare different joining processes in order to achieve production criteria. The paper compares the properties of a 1.5 mm thick steel sheet joined by the manual and robotic MAG 135 and 138 welding process, manual and robotic laser welding, CMT welding with the use of solid or flux-cored wire, and butt welding. The macro- and microstructure, as well as the microhardness distribution of individual regions of the joints, were analyzed depending on the type of joining technology used. Furthermore, the mechanical properties of individual zones of joints were investigated with the use of a digital image correlation system. On the basis of the obtained test results, it was found that the joints made by the processes of manual laser welding and butt welding were characterized by a very regular weld shape, the smallest joint width, and greater grain refinement compared to other analyzed processes. Moreover, this method was characterized by the narrowest zone of hardness increase, only 3 mm, compared to, e.g., a joint made in the process of robotic welding CMT, for which this zone was more than twice as wide. Furthermore, the heat-affected zone for the joints made in this way, in relation to the welds produced by the MAG 135/138 method, was, respectively, 2 and 2.7 times smaller.

Residual Stress Redistribution Analysis in the Repair Welding of AA6082-T6 Aluminum Alloy Joints: Experiment and Simulation

Abstract: Residual stress has a three-dimensional scale effect (length, depth, and width) in the process of repair welding, which has a detrimental impact on the service of the aluminum alloy welded structures in high-speed trains. This paper aims to systematically analyze the effects of the repair welding dimension on the residual stress redistribution and obtain the optimal repair welding principles. A combination of blind-hole drilling method and stress linearization in BS7910 was adopted to investigate residual stress redistribution under various repair welding dimensions. The results indicate that repair welding dimension was in accordance with the principle of “SNL (shallow, narrow and long)” and the optimal repair length, depth, and width of butt joints in this study were 15t, 0.25t, and t, respectively (t is the plate thickness of butt joints).

Microstructural Observations of an AA6082-T6 Hybrid Metal Extrusion & Bonding (HYB) Butt Weld

Abstract: Hybrid Metal Extrusion & Bonding (HYB) is a relatively new solid-state welding method that distinguishes from the more traditional ones by utilising filler material addition to obtain joining. Regarding the mechanical properties, previous research has shown that HYB has the capability to outperform comparable fusion welds and match that of comparable Frictions Stir Welds. The present work is concerned with the microstructural characterisation of a 4 mm thick AA6082-T6 HYB butt weld, with main emphasis on the region of the joint Thermo-Mechanical Affected Base Material (TMA-BM). A sample extracted from the joint was examined using different experimental techniques, including optical microscopy, EBSD, EDX and hardness measurements. The formation of sharp interfaces or porosity between the base and the filler material was observed and interpreted. Grain refinements of the base material were witnessed and the main causes of this phenomenon were discussed, along with softening behaviour experienced in the TMA-BM of the weld. The implications of this work are relevant as they unveil important microstructural aspects that characterise this type of joint, as well as provide important directions for future research investigations.

Development of a portable laser peening device and its effect on the fatigue properties of HT780 butt-welded joints

Abstract: • A miniaturized laser peening device using a thumb-sized Nd:YAG microchip laser was developed. • The device introduced compressive residual stress into HT780 high-strength steel to a depth of 0.1 mm. • The fatigue strength of HT780 butt-welded joints increased by 50 MPa with this device. Laser peening (LP) is a well-established technique for introducing compressive residual stress (RS) near the surface of metal components, to improve their high-cycle fatigue properties. The authors have developed a compact LP device with a thumb-sized Nd:YAG microchip laser mounted on a collaborative robot arm. The device was applied to 9-mm-thick HT780 high-strength steel plate samples with irradiated pulse energies of 7.5−8.0 mJ, spot sizes of 0.42−0.58 mm and pulse densities of 100−1,600 pulses/mm 2 . X-ray diffraction showed that the maximum compressive RS was over 500 MPa near the surface, and the LP effect reached a depth of approximately 0.1 mm from the surface. Butt-welded HT780 samples were laser-peened with a pulse energy of 7.7 mJ, spot size of 0.49 mm and pulse density of 800 pulses/mm 2 . Then, the samples were subjected to a uniaxial fatigue test with a stress ratio of 0.1. The results showed that the fatigue strength at 10 7 cycles was improved by at least 50 MPa, comparable to the improvement attained by LP in a previous study with a pulse energy of 200 mJ from a conventional Nd:YAG laser.

Fatigue and Ultimate Strength Assessment of Post Weld Treated Strenx® 1100 Plus Butt Welds

Abstract: The demand of stronger and lighter structures is rapidly growing. Today’s applications vary over a large range of industries where the requirements are different for different products which requires application driven research of the 3rd generation Advance High-Strength Steels (AHSS). These are high-strength steels that are tailor-made to get desired mechanical properties. One AHSS manufactured by SSAB is their Strenx® 1100Plus steel that is specially designed to get excellent welding properties. In the current study the fatigue life improvement was investigated when using post weld treatments, TIG dressing and HFMI (High Frequency Mechanical Impact), for butt welded joints in Strenx® 1100Plus. Fatigue testing and assessment was carried out, using nominal stress and effective notch stress approaches, and the results were compared with fatigue strength recommendations for similar joints and steel grades given by the International institute of Welding (IIW). It is concluded that one additional FAT class increase could be observed in comparison to what is recommended by IIW for both types of post weld treatment methods.