Showing papers on "Spot welding published in 2022"

Advances in FSW and FSSW of dissimilar Al-alloy plates

Abstract: Abstract Numerous industrial applications, particularly those in the transport industry, require the joining of dissimilar materials which offers considerable benefits in terms of low cost, design flexibility, and weight reduction for overall structures. The problems associated with conventional fusion welding processes have stimulated researchers in recent years to develop new joining methods for dissimilar materials which are particularly difficult to join. Friction stir welding (FSW) originally developed for joining difficult-to-weld Al-alloys and FSSW (a variant of FSW for spot welding) have exhibited great potential for obtaining sound joints in various dissimilar alloy systems in different configurations namely butt-, lap- and spot-welding, particularly in dissimilar Al-alloys systems with different properties, which are very difficult to weld using conventional fusion welding techniques. A major difficulty in joining dissimilar Al-alloys by FSW/FSSW lies in the discontinuity in mechanical and technological properties (such as high-temperature strength, plastic deformation capacity, viscosity, etc.) of the materials to be welded across the abutting surfaces. This discontinuity as well as inherent asymmetry in heat generation and material flow of FWS/FSSW processes causes a higher asymmetry in materials flow behavior in dissimilar welding. However, it is relatively easier to implement the FSW/FSSW process to dissimilar Al-alloys in contrast to FSW of dissimilar materials combinations with very differing properties, such as Al-alloy to Mg-alloy or Al-alloy to steel.

Machine learning with domain knowledge for predictive quality monitoring in resistance spot welding

Abstract: Abstract Digitalisation trends of Industry 4.0 and Internet of Things led to an unprecedented growth of manufacturing data. This opens new horizons for data-driven methods, such as Machine Learning (ML), in monitoring of manufacturing processes. In this work, we propose ML pipelines for quality monitoring in Resistance Spot Welding. Previous approaches mostly focused on estimating quality of welding based on data collected from laboratory or experimental settings. Then, they mostly treated welding operations as independent events while welding is a continuous process with a systematic dynamics and production cycles caused by maintenance. Besides, model interpretation based on engineering know-how, which is an important and common practice in manufacturing industry, has mostly been ignored. In this work, we address these three issues by developing a novel feature-engineering based ML approach. Our method was developed on top of real production data. It allows to analyse sequences of welding instances collected from running manufacturing lines. By capturing dependencies across sequences of welding instances, our method allows to predict quality of upcoming welding operations before they happen. Furthermore, in our work we strive to combine the view of engineering and data science by discussing characteristics of welding data that have been little discussed in the literature, by designing sophisticated feature engineering strategies with support of domain knowledge, and by interpreting the results of ML analysis intensively to provide insights for engineering. We developed 12 ML pipelines in two dimensions: settings of feature engineering and ML methods, where we considered 4 feature settings and 3 ML methods (linear regression, multi-layer perception and support vector regression). We extensively evaluated our ML pipelines on data from two running industrial production lines of 27 welding machines with promising results.

Thermal process and material flow during dissimilar double-sided friction stir spot welding of AZ31/ZK60 magnesium alloys

Abstract: A computational fluid dynamics (CFD) model for double-sided friction stir spot welding (FSSW) between AZ31 and ZK60 magnesium alloys using adjustable pins is proposed in this paper. Multiple phase flow theories are combined to track the metal interface and phase distribution using FLUENT software. The heat transfer and material flow for the 5 stages of the friction stir welding process, including the pre-heating, plunging, welding, rising and post-heating stages, are presented. For further evaluation, the calculated flow and thermal responses are compared with experimental data, which overall showed good agreement. The material between the upper and lower pins is softened after the pre-heating process and is then driven by the plunging pin to form a keyhole below the upper tool and a bulge region in the bottom of the plates. The welding interface between the pins is bowl-shaped after plunging, and grows uneven during the welding stage due to the extensive plastic material flow. The keyhole is then fully eliminated after the rising of the pins. After welding, the region between the tools is heated to a maximum temperature of 670 K and the welding interface slightly fluctuates and a phase mixing phenomenon occurs, suggesting that AZ31 and ZK60 plates are well joined by using the adjustable pins.

Machine learning with domain knowledge for predictive quality monitoring in resistance spot welding

Abstract: Abstract Digitalisation trends of Industry 4.0 and Internet of Things led to an unprecedented growth of manufacturing data. This opens new horizons for data-driven methods, such as Machine Learning (ML), in monitoring of manufacturing processes. In this work, we propose ML pipelines for quality monitoring in Resistance Spot Welding. Previous approaches mostly focused on estimating quality of welding based on data collected from laboratory or experimental settings. Then, they mostly treated welding operations as independent events while welding is a continuous process with a systematic dynamics and production cycles caused by maintenance. Besides, model interpretation based on engineering know-how, which is an important and common practice in manufacturing industry, has mostly been ignored. In this work, we address these three issues by developing a novel feature-engineering based ML approach. Our method was developed on top of real production data. It allows to analyse sequences of welding instances collected from running manufacturing lines. By capturing dependencies across sequences of welding instances, our method allows to predict quality of upcoming welding operations before they happen. Furthermore, in our work we strive to combine the view of engineering and data science by discussing characteristics of welding data that have been little discussed in the literature, by designing sophisticated feature engineering strategies with support of domain knowledge, and by interpreting the results of ML analysis intensively to provide insights for engineering. We developed 12 ML pipelines in two dimensions: settings of feature engineering and ML methods, where we considered 4 feature settings and 3 ML methods (linear regression, multi-layer perception and support vector regression). We extensively evaluated our ML pipelines on data from two running industrial production lines of 27 welding machines with promising results.

Fracture dominant in friction stir spot welded joint between 6061 aluminum alloy and galvannealed steel based on microscale tensile testing

Abstract: The macroscale mechanical properties of dissimilar joints are generally influenced by the fracture behavior of joint interface. However, little is known about the dominant factor for the joint properties related with both macroscale fracture behavior and microscale interfacial properties. Herein, microscale tensile testing of the joint interface was coupled with the macroscale fracture evaluation to elucidate the dominant factor of strength in dissimilar joints between 6061 aluminum alloy and high tensile strength galvannealed steel via friction stir spot welding (FSSW). Microstructural analyses revealed the characteristic formation of interfacial microstructure accompanied by friction and Zn discharge during the FSSW process. Microscale tensile testing was performed on the specimen on which the pre-notch was introduced to induce local fracture at the intended position on the joint interface. Results showed the presence of the weakest interface attributed to initial joining defects formed by Zn concentration at the outer area, which were consistent with the outside of the crack arresting area confirmed by macroscale evaluation. These results indicated that the joint strength of dissimilar joints between 6061 aluminum alloy and galvannealed steel is dominated by the local strength of the joining area without defects and suggested a process design for improving dissimilar joints.

Experimental investigation on the effect of spot diameter on continuous-wave laser welding of copper and aluminum thin sheets for battery manufacturing

Abstract: Welding of dissimilar materials, particularly copper and aluminum alloys, has gained considerable industrial interest in many different electric and electronic fields, such as the production of lithium-ion batteries for automotive applications. The differences in physical and chemical properties of these materials make fusion welding processes difficult to apply due to the formation of hard and brittle intermetallic compounds that impair both mechanical and electrical performance. In this paper, the effect of spot diameter on dissimilar laser autogenous lap-welding of copper and aluminum was studied. Experiments were conducted using a mid-power fiber laser source equipped with a galvo scanner and two different focal lengths to obtain two different spot diameters. The results showed that a smaller spot diameter promoted the formation of sound weld beads with better control of penetration depth, reduced mixing of the base metals and lower laser power requirements. By selecting the correct process parameters, good mechanical properties and low contact resistance could be obtained with both focal lengths. SEM-EDX analysis confirmed that a smaller spot diameter minimized the formation of copper rich phases in the weld bead.

Experimental investigation on the effect of spot diameter on continuous-wave laser welding of copper and aluminum thin sheets for battery manufacturing

Abstract: Welding of dissimilar materials, particularly copper and aluminum alloys, has gained considerable industrial interest in many different electric and electronic fields, such as the production of lithium-ion batteries for automotive applications. The differences in physical and chemical properties of these materials make fusion welding processes difficult to apply due to the formation of hard and brittle intermetallic compounds that impair both mechanical and electrical performance. In this paper, the effect of spot diameter on dissimilar laser autogenous lap-welding of copper and aluminum was studied. Experiments were conducted using a mid-power fiber laser source equipped with a galvo scanner and two different focal lengths to obtain two different spot diameters. The results showed that a smaller spot diameter promoted the formation of sound weld beads with better control of penetration depth, reduced mixing of the base metals and lower laser power requirements. By selecting the correct process parameters, good mechanical properties and low contact resistance could be obtained with both focal lengths. SEM-EDX analysis confirmed that a smaller spot diameter minimized the formation of copper rich phases in the weld bead.

Effect of post-weld tempering pulse on microstructure and mechanical properties of resistance spot welding of Q&P1180 steel

Abstract: Resistance spot welds (RSWs) of quench and partitioning (Q&P) steels exhibit poor mechanical properties due to the brittleness of the nugget microstructure. To solve this problem, the nugget microstructure in RSWs of Q&P1180 steel was modified by applying a post-weld tempering pulse with different protocols. Effects of the post-weld tempering pulse on microstructural evolution and mechanical properties of RSWs were investigated. The results indicate that a proper post-weld tempering pulse (cooling time of 1000 ms and post welding current of 4 kA) achieved a 70% improvement in the cross-tension peak load and a 6% improvement in the tensile-shear peak load. The nugget, consisting of tempered martensite and retained austenite with low hardness and high toughness, hindered the crack propagation towards the nugget during the cross-tension test and improved cross-tension property. In the tensile-shear testing, a new failure mechanism was discovered. Despite the decrease in nugget hardness, the improvement of toughness helped enlarge the effective area subjected to the shear load during the tensile-shear test, resulting in the improvement of the tensile-shear property.

Effect of post-weld tempering pulse on microstructure and mechanical properties of resistance spot welding of Q&P1180 steel

Abstract: Resistance spot welds (RSWs) of quench and partitioning (Q&P) steels exhibit poor mechanical properties due to the brittleness of the nugget microstructure. To solve this problem, the nugget microstructure in RSWs of Q&P1180 steel was modified by applying a post-weld tempering pulse with different protocols. Effects of the post-weld tempering pulse on microstructural evolution and mechanical properties of RSWs were investigated. The results indicate that a proper post-weld tempering pulse (cooling time of 1000 ms and post welding current of 4 kA) achieved a 70% improvement in the cross-tension peak load and a 6% improvement in the tensile-shear peak load. The nugget, consisting of tempered martensite and retained austenite with low hardness and high toughness, hindered the crack propagation towards the nugget during the cross-tension test and improved cross-tension property. In the tensile-shear testing, a new failure mechanism was discovered. Despite the decrease in nugget hardness, the improvement of toughness helped enlarge the effective area subjected to the shear load during the tensile-shear test, resulting in the improvement of the tensile-shear property.

Resistance spot welding of advanced high strength steel for fabrication of thin-walled automotive structural frames

Abstract: This investigation presents the process parameter optimization of resistance spot welded (RSW) advanced high strength steel (AHSS) joints using response surface methodology (RSM) for fabrication of thin-walled automotive structural frames. Resistance spot welding (RSW) is used to minimize solidification cracking, heat affected zone (HAZ) softening and distortion related problems in joining of thin advanced high strength steel (AHSS) sheets. The three factor – five level central composite design (3 × 5 - CCD) matrix pertaining to the minimum number of experiments was chosen for designing the experimental matrix. The polynomial regression analysis was employed to develop the empirical relationships between RSW parameters and performance characteristics of AHSS joints. The 3-dimensional (3D) response surfaces were developed using RSM which shows the optimal process window to enhance the strength of spot joints. The RSW joints made using welding current of 5.0 kA, electrode pressure of 4.0 MPa, and welding time of 1.50 s displayed maximum lap tensile shear fracture load (LAP-TSFL) of 21.7 kN, cross tensile shear fracture load (CROSS-TSFL) of 17.65 kN, and nugget zone hardness (NZH) of 589 HV 0.5 respectively. The results of ANOVA indicates that welding current, electrode pressure and welding time significantly influences the LAP-TSFL, CROSS-TSFL and NZH of joints respectively. The superior TSFL and NZH of joints made using optimized RSW parameters is attributed to the evolution of needle/lath martensite in nugget zone .

Interfacial bonding mechanism and fracture behavior in ultrasonic spot welding of copper sheets

Abstract: Cu/Cu joints were fabricated using ultrasonic spot welding. Weld attributes and microstructure, welding interface temperature, effective thickness, bond density, grain size and hardness transition zone were investigated to understand the interfacial bonding mechanism, fracture behavior and mechanical properties. For the Cu/Cu joint fabricated at the welding time of 0.8 s, the gradient of the grain size along the direction from the welding line towards the base metal could be observed. The microstructure with nano-sized grains at the welding line was induced by dynamic recrystallization. Under this condition, the grain boundaries moved across the interfaces, resulting in the formation of the metallurgical bonding at the Cu/Cu interface. The mixed fracture characteristics occurred on the fracture surface.

Dissimilar laser spot welding of aluminum alloy to steel in keyhole mode

Abstract: Laser spot welding was used for the dissimilar joining of aluminum alloy to steel in the keyhole mode. The results showed that the defocusing amount and laser power had significant influence on the weld formation. The aluminum alloy was prone to the formation of welding defects, such as porosity and cracks in the fusion zone, which resulted in an extremely instable welding process and poor joint strength. In order to improve the weld quality, a copper heat sink was placed under the aluminum alloy, which effectively absorbed the heat of the aluminum alloy and reduced the previous reported welding defects. The influence of laser power, defocusing amount, welding time, and shielding gas on the joint characteristics was also investigated. The microstructure analysis showed that a conelike fusion zone and sparsely distributed Fe-Al intermetallic compounds were formed. Hence, a combination of metallurgical bonding and mechanical interlocking was achieved in the laser keyhole spot welds, enhancing the joint mechanical properties. The joint strength of the laser keyhole spot welds reached 620 N/mm, which was comparable to that obtained in resistance spot welds.

Role of Fe2Al5 in fracture of novel dissimilar aluminum-steel resistance spot welds using multi-ring domed electrodes

Abstract: In a comparative study of resistance spot welded (RSW) 1.2 mm AA6022 joined to 2.0 mm high strength low alloy (HSLA) steel and 1.2 mm AA6022 joined to 2.0 mm low carbon steel (LCS) it was found that quasi-static tensile tests and mini shear tests exhibited similar intermetallic compound (IMC) strength but different load capacity, i.e., nominal shear strength in tensile shear tests. This phenomenon was related to the Fe2Al5 structure and properties at the Al-steel interface which were unique for each stack-up. The thicker Fe2Al5 layer in 1.2 mm AA6022-2.0 mm LCS was comprised of fewer but larger grains which contributed to a larger difference between the Young's modulus of FeAl3 and Fe2Al5 than in 1.2 mm AA6022-2.0 mm HSLA. The Fe2Al5 in the AA6022-LCS stack-up was more brittle and rigid with greater nanohardness values and smaller variation in elastic modulus that may have contributed to lower overall joint strength with large variation. In addition, AA6022-LCS welds produced with non-optimized and optimized weld schedules produced different IMC shear strengths which was attributed to the different mismatch in Young modulus values that accentuated the differences in shear stresses at the FeAl3/Fe2Al5 interface.

Role of Fe2Al5 in fracture of novel dissimilar aluminum-steel resistance spot welds using multi-ring domed electrodes

Abstract: In a comparative study of resistance spot welded (RSW) 1.2 mm AA6022 joined to 2.0 mm high strength low alloy (HSLA) steel and 1.2 mm AA6022 joined to 2.0 mm low carbon steel (LCS) it was found that quasi-static tensile tests and mini shear tests exhibited similar intermetallic compound (IMC) strength but different load capacity, i.e., nominal shear strength in tensile shear tests. This phenomenon was related to the Fe2Al5 structure and properties at the Al-steel interface which were unique for each stack-up. The thicker Fe2Al5 layer in 1.2 mm AA6022-2.0 mm LCS was comprised of fewer but larger grains which contributed to a larger difference between the Young's modulus of FeAl3 and Fe2Al5 than in 1.2 mm AA6022-2.0 mm HSLA. The Fe2Al5 in the AA6022-LCS stack-up was more brittle and rigid with greater nanohardness values and smaller variation in elastic modulus that may have contributed to lower overall joint strength with large variation. In addition, AA6022-LCS welds produced with non-optimized and optimized weld schedules produced different IMC shear strengths which was attributed to the different mismatch in Young modulus values that accentuated the differences in shear stresses at the FeAl3/Fe2Al5 interface.

Microstructural and Mechanical Properties of AZ31B to AA6061 Dissimilar Joints Fabricated by Refill Friction Stir Spot Welding

Abstract: Dissimilar friction stir spot welds (FSSW) between the magnesium and aluminum alloys are joined, using a novel approach called refill friction stir spot welding. The present work aims to evaluate the macrostructural and mechanical properties of refill friction stir spot welded AZ31B and AA 6061-T6 alloys in two combinations, i.e., identical Mg-to-Mg and dissimilar Mg-to-Al joints, and the results are compared with the results obtained in conventional friction stir spot welding. The hardness profiles of the similar welds had the appearance of a W-shape, and the Thermo mechanically affected zone and heat-affected zone of both methods had lower hardness values than the rest of the weld. Along with the interface between the aluminum and magnesium sheets, a thin intermetallic compound layer of Al12Mg17 has been identified, which has led to an increase in hardness. The static shear strength of both similar and dissimilar refill spot friction welds was much greater than that of traditional spot friction welds. In both similar and dissimilar spot friction welds, two distinct failure scenarios are discovered.

Investigation on shearing strength of resistance spot-welded joints of dissimilar steel plates with varying welding current and time

Abstract: The present research investigated the effects of welding current and welding time on the shearing strength of resistance spot-welded joints of low carbon steel and stainless steel plates. The macro characteristics, microstructure and micro-hardness of welded joints were also examined. It was found that the welded joints produced with a welding current of 10 kA and welding time of 80 ms showed the highest shearing strength. The diameter of welded joints and nuggets increased with increasing welding current and welding time. For evaluation of the microstructure, different regions including the nugget, coarse heat-affected zone, fine heat-affected zone and base materials were observed within the welded joints. Also, the nugget and coarse heat-affected zone showed higher hardness than the fine heat-affected zone and base materials due to the presence of martensite. The findings obtained in this research are applicable in the development of resistance spot welding processes for joining dissimilar steel plates.

Friction Stir Spot Welding of Different Thickness Sheets of Aluminum Alloy AA6082-T6

Abstract: Friction stir spot welding (FSSW) is one of the important variants of the friction stir welding (FSW) process. FSSW has been developed mainly for automotive applications where the different thickness sheets spot welding is essential. In the present work, different thin thickness sheets (1 mm and 2 mm) of AA6082-T6 were welded using FSSW at a constant dwell time of 3 s and different rotation speeds of 400, 600, 800, and 1000 rpm. The FSSW heat input was calculated, and the temperature cycle experience during the FSSW process was recorded. Both starting materials and produced FSSW joints were investigated by macro- and microstructural investigation, a hardness test, and a tensile shear test, and the fractured surfaces were examined using a scanning electron microscope (SEM). The macro examination showed that defect-free spot joints were produced at a wide range of rotation speeds (400–1000 rpm). The microstructural results in terms of grain refining of the stir zone (SZ) of the joints show good support for the mechanical properties of FSSW joints. It was found that the best welding condition was 600 rpm for achieving different thin sheet thicknesses spot joints with the SZ hardness of 95 ± 2 HV0.5 and a tensile shear load of 4300 ± 30 N.

Effective Range of FSSW Parameters for High Load-Carrying Capacity of Dissimilar Steel A283M-C/Brass CuZn40 Joints

Abstract: In the current study, a 2 mm thick low-carbon steel sheet (A283M—Grade C) was joined with a brass sheet (CuZn40) of 1 mm thickness using friction stir spot welding (FSSW). Different welding parameters including rotational speeds of 1000, 1250, and 1500 rpm, and dwell times of 5, 10, 20, and 30 s were applied to explore the effective range of parameters to have FSSW joints with high load-carrying capacity. The joint quality of the friction stir spot-welded (FSSWed) dissimilar materials was evaluated via visual examination, tensile lap shear test, hardness test, and macro- and microstructural investigation using SEM. Moreover, EDS analysis was applied to examine the mixing at the interfaces of the dissimilar materials. Heat input calculation for the FSSW of steel–brass was found to be linearly proportional with the number of revolutions per spot joint, with maximum heat input obtained of 11 kJ at the number of revolutions of 500. The temperature measurement during FSSW showed agreement with the heat input dependence on the number of revolution. However, at the same revolutions of 500, it was found that the higher rotation speed of 1500 rpm resulted in higher temperature of 583 °C compared to 535 °C at rotation speed of 1000 rpm. This implies the significant effect for the rotation speed in the increase of temperature. The macro investigations of the friction stir spot-welded joints transverse sections showed sound joints at the different investigated parameters with significant joint ligament between the steel and brass. FSSW of steel/brass joints with a number of revolutions ranging between 250 to 500 revolutions per spot at appropriate tool speed range (1000–1500 rpm) produces joints with high load-carrying capacity from 4 kN to 7.5 kN. The hardness showed an increase in the carbon steel (lower sheet) with maximum of 248 HV and an increase of brass hardness at mixed interface between brass and steel with significant reduction in the stir zone hardness. Microstructural investigation of the joint zone showed mechanical mixing between steel and brass with the steel extruded from the lower sheet into the upper brass sheet.

Advances in simulation and experimental study on intermetallic formation and thermomechanical evolution of Al–Cu composite with Zn interlayer: Effect of spot pass and shoulder diameter during the pinless friction stir spot welding process

Abstract: In this study, the pinless friction stir spot welding of aluminum–copper composite with Zn interlayer was analyzed under experimental measurement and finite element method. The role of shoulder diameter, 16, 18, and 20 mm, and the number of spot pass, one to three pass, on microstructure, mechanical properties, and thermal history of weld samples were investigated. Based on the obtained results, there is a good agreement between numerical data and experimental analyses. It was shown that the heat source, due to plastic deformation and friction, increased as the shoulder diameter was increased, whereas the stress distribution in the weld samples was reduced. In addition, the thickness of the Zn interlayer at the joint interface changes when shoulder size increases from 16 to 20 mm, due to high temperature and intermixing between materials. From the microstructure analysis, the grain size in the joint zone gradually decreases as the spot pass increases from 1 to 3. It was concluded that the shoulder diameter of 16 mm with three spot passes showed the best result of 7.45 kN. Depending on X-ray diffraction analyses of the fracture surfaces, three primarily intermetallic phases including the Al2Cu, CuZn5, and CuZn2 were determined in the weld interfaces. Based on finite element method analysis, the axial compressive stresses showed the lowest profile as the shoulder diameter of the tool is 16 mm. Finally, the ductile fracture was detected as the main fracture mechanism for the joint sample with optimal joining conditions.