Spot Welding Technique Research Articles

Fatigue Strength of Rivet Resistance Spot Welding Technique in Comparison with Self-Piercing Riveting for Multi-material Body-in-White Structure

Cost-efficient multi-material design requires suitable joining techniques, ideally with low investment cost by re-using existing assembling lines. The recently developed resistance rivet spot welding (RRSW) technique combines mechanical joining with spot welding and enables cost-efficient joining of aluminum (Al) to steel for multi-material body-in-white structures. Here, the static and fatigue strengths of different hybrid Al-steel specimens made by RRSW were measured and compared to other state-of-the-art joining techniques, such as self-piercing riveting (SPR) and RSW. The static strength of RRSW matched or exceeded that of SPR regardless of the sheet thickness, whereas the fatigue strength of the RRSW joints showed a strong dependency on the thickness of the steel sheets. For thinner steel sheets, the fatigue of the RRSW-joined metal sheets was lower in comparison with SPR. Fatigue cracks were initiated in thin steel sheets around the weld nugget. By contrast, for thicker steel sheets, the fatigue strength of RRSW matched or exceeded that of SPR. With a thicker material combination of 1.5 mm steel and 1.0 mm Al, fatigue cracks occurred only in the Al sheet in both SPR and RRSW. For suitable steel sheet thickness, RRSW is thus a durable technique to join steel and Al.

A Comprehensive Review on Optimal Welding Conditions for Friction Stir Welding of Thermoplastic Polymers and Their Composites.

Friction stir welding (FSW) and friction stir spot welding (FSSW) techniques are becoming widely popular joining techniques because of their increasing potential applications in automotive, aerospace, and other structural industries. These techniques have not only successfully joined similar and dissimilar metal and polymer parts but have also successfully developed polymer-metallic hybrid joints. This study classifies the literature available on the FSW and FSSW of thermoplastic polymers and polymer composites on the basis of joining materials (similar or dissimilar), joint configurations, tooling conditions, medium conditions, and study types. It provides a state-of-the-art and detailed review of the experimental studies available on the FSW and FSSW between similar thermoplastics. The mechanical properties of FSW (butt- and lap-joint configurations) and FSSW weld joints depend on various factors. These factors include the welding process parameters (tool rotational speed, tool traverse speed, tool tilt angle, etc.), base material, tool geometry (pin and shoulder size, pin profile, etc.) and tool material, and medium conditions (submerged, non-submerged, heat-assisted tooling, cooling-assisted tooling). Because of the dependence on many factors, it is difficult to optimize the welding conditions to obtain a high-quality weld joint with superior mechanical properties. The general guidelines are established by reviewing the available literature. These guidelines, if followed, will help to achieve high-quality weld joints with least defects and superior mechanical properties. Apart from parametric-based studies, the statistical-based studies (e.g., analysis of variance (ANOVA)-based studies) are covered, which helps with the determination of the influential parameters that affect the FSW and FSSW weld joint strength. Also, the optimal ranges of the most influential process parameters for different thermoplastic materials are established. The current work on the development of general guidelines and determination of influential parameters and their operating ranges from published literature can help with designing smart future experimental studies for obtaining the global optimum welding conditions. The gaps in the available literature and recommendations for future studies are also discussed.

Enhancing weld attributes in ultrasonic spot welding of carbon fibre-reinforced thermoplastic composites: Effect of sonotrode configurations and process control

Ultrasonic welding is a versatile welding technique for the assembly of thermoplastic composite structures. The research in this paper aims at improving the manufacturing efficiency and the weld attributes, featured by welded area, weld strength and failure mechanisms, of ultrasonic spot welded joints by adopting proper sonotrodes combined with process control techniques. To achieve this goal, the research was carried out in two steps. In the first part, single-spot ultrasonic welding was performed by using sonotrodes with various diameters. The influence of the sonotrode sizes on the welding processes and weld attributes of the as-manufactured welded joints was investigated. Based on the information gathered from the first part, a novel simultaneous spot welding technique to produce two welded spots within a single step was subsequently proposed. The results in both parts indicated that the increase of the sonotrode size could significantly improve the welding efficiency. The weld attributes were also effectively enhanced by adopting proper welding force.

Role of Intercritical Annealing in Enhancing the Cross-Tension Property of Resistance Spot-Welded Medium Mn Steel

Among the third-generation advanced high-strength steels, medium Mn steels are one of the most promising candidates in the modern automotive industry. However, their application is challenged by the weldability and corresponding poor mechanical property. In this study, the resistance spot welding (RSW) technique was used to join 7Mn steels. A post-weld heat treatment containing intercritical annealing was followed to tune the nugget microstructure. In this case, the trapped C and Mn during RSW can fully diffuse, diminishing the grain boundary embrittlement. Meanwhile, the austenite reversion transformation occurs in the joint, facilitating the formation of a mixed microstructure consisting of ferrite and austenite. With these efforts, the cross-tension strength (CTS) of the RSW 7Mn steel can reach as high as 11.6 kN with outstanding plastic deformation, giving rise to a button pullout fracture mode. This study provides an accessible approach to tailor the microstructure and final CTS of RSW joints of the medium Mn steel, which can guide the optimization of the RSW process.

On the fatigue and fracture behavior of keyhole-free friction stir spot welded joints in an aluminum alloy

The target of this research study was to evaluate the shear-tensile and fatigue behavior of aluminum 6061 alloy welds, in two different heat treatment conditions, joined by the recently developed intermediate layer friction stir spot welding (FSSW) technique. The keyhole, which is the disadvantage of the conventional FSSW process, was avoided using an additional intermediate layer (IL) accompanied by a simple tooling. Shear-tensile experiments demonstrated acceptable mechanical performance of IL-FSSW joints in comparison with that obtained using alternative methods. Fatigue behavior of the joints revealed a dependency to pre-processing temper especially at high cyclic load levels with improved life for the aged condition. Observations on the failure regions under shear-tensile experiments exhibited plug type and shear-plug type fracture modes for the aged and annealed conditions, respectively. In contrast, the fracture mode showed variation with respect to the load level but not to the type of temper during cyclic loading.

Pin plunging reinforced refill friction stir spot welding of Alclad 2219 to 7075 alloy

Abstract A Pin-plunging reinforced refill friction stir spot welding (P-RFSSW) technique was introduced in this study in order to solve the problem of the central void defect and the alclad residues in the weld center associated with conventional refill friction stir spot welding (C-RFSSW) of dissimilar alclad aluminum alloys. The P-RFSSW process is based on promoting the plastic deformation in the weld center owing to the addition of an initial pin plunge stage. The microstructure and mechanical properties of the C-RFSSW and P-RFSSW joints were compared. Results have shown that the P-RFSSW process could eliminate the central void defect and promote the metallurgical bonding and intermixing in the weld. Weld strength was improved when using P-RFSSW compared with the C-RFSSW process, which was attributed to the specific downward extended hook defect into the stronger, thicker 7 series aluminum alloy.

COMPARISON BETWEEN LASER ADDITIVE MANUFACTURING AND LASER SPOT WELDING OF TITANIUM GRADE 2

The microstructure and hardness of the melted area in a titanium grade 2 sample processed by Laser Spot Welding were compared to those processed by Selective Laser Melting. The results show that the materials obtained with the two processes have very similar characteristics. On the basis of what had been observed, it can be inferred that the Laser Spot Welding technique could be a low-cost way to verify the possibility of obtaining the desired properties with new alloys processed by Selective Laser Melting.

Resistance Spot Welded Al 1100 Alloy with Carbonaceous Interlayers

Weld and surface properties of Al 1100 alloy by incorporating graphene nanoparticles, different varieties of graphite and CNTs interlayer has been studied here. The incorporation of different carbonaceous interlayers was achieved by drop casting and alloy plates were joined together by resistance spot welding technique. A single optimum welding current and time parameter was chosen by trial and error method. Lap shear tests were carried out to find the peak load bearing strengths of the alloy plates processed at the constant welding current and time conditions and a comparison of the weld strength is made. Highest load bearing capacity was exhibited by the base material as compared to that of carbonaceous nanoparticles. Microstructural characterization was done by optical microscopy and SEM. XRD was carried out to find the formation of any intermetallics or phases during the processing. Fractography was studied to analyze the underlying fracture mechanism. Micro-hardness of the Al samples processed with different carbonaceous reinforcements was found out and the maximum hardness was exhibited by the finer sized carbon nanoparticles. A comparative study is being made between the various carbonaceous nanoparticles employed here.

Influence of Refill Friction Stir Spot Welding Technique on the Mechanical Properties and Microstructure of Aluminum AA5052 and AA6061-T3

This paper presents the effects of using the refill friction stir spot welding (RFSSW) technique on the mechanical properties and microstructure of aluminum AA5052 and AA6061-T3. Specimens were first prepared from AA5052 sheet of thickness 2 mm and AA6061-T3 of 1.6 mm, for chemical analysis and mechanical tests. Workpieces were then stir spot welded by RFSSW at four rotational speeds (2000, 2500, 3000 and 4000 rpm) using two tool pin diameters (5 and 7 mm) to carry out the tensile shear tests. Microhardness testing was conducted at the best conditions along the cross-section of the welded specimens, as well as microstructure examination. The results of the tensile shear tests manifested that, for AA5052 and AA6061-T3 at the tool rotational speeds 2000 rpm and 3000 rpm, respectively, using a tool pin of 7 mm the ultimate tensile shear force was slightly higher than at other speeds in both diameters of tool pin (5 and 7 mm). However, the microhardness results displayed a W-shape at the best conditions. Finally, the microstructure inspection revealed the morphology of the major zones of the weld joint.

Tailoring micro resistance spot welding parameters for joining nickel tab to inner aluminium casing in a cylindrical lithium ion cell and its influence on the electrochemical performance

In an automotive battery, a large number of individual cells are electrically connected to meet the energy and power requirement. The choice of suitable welding techniques is critical in terms of mechanical strength and electrical contact resistance of the joint. Although soldering, ultrasonic welding and laser welding are the common joining techniques used in lithium-ion cell fabrication, application of resistance spot welding in the manufacturing of lithium-ion battery for electric vehicles is rather limited due to the difficulties in forming large weld nuggets and electrode sticking to the material. In this work, micro resistance spot welding of nickel anode tab to the one side open inner aluminium casing is carried out in an in-house fabricated cylindrical lithium-ion cell. The welding parameters for high electrical conductive nickel-to-aluminium are optimized using the Taguchi design of experiments. The weld joints are assessed by microstructural, mechanical properties and contact resistance characterization. The optimum weld joint shows a well-defined nugget with a shear strength of 338.4 MPa and the electrical contact resistance of 0.052 mΩ. The cell shows high current rate capability and 2 °C increase in the cell temperature at 2C rate. This work paves the way for the application of spot welding technique for tab welding in one side open casing for the manufacturing of lithium-ion cell.

Microstructure of Mg96Zn2Y2 alloy joint formed by resistance spot welding

Mg96Zn2Y2 alloy sheets were welded by employing a resistance spot welding technique. The microstructures of the joint were observed and analyzed using scanning electron microscopy and transmission electron microscopy to investigate the difference between it and those of the base material. The joint comprises a base metal zone, heat-affected zone, fusion zone, and nugget. In the heat-affected zone, the dissolution of secondary phases occurred locally. In the fusion zone, the α-Mg grains were coarsened; and the secondary phase was transformed into a network distribution. In the nugget, the α-Mg grains were approximately 30 μm in diameter; and most of the secondary phase possessed a long-period stacking-ordered structure of 18 periods rhombohedral lattice. The results reveal that the number of secondary phases and Mg3Zn3Y2 compounds formed in the nugget were smaller than those observed in the base metal.

Joining Strategy Analysis of Structural Dynamic in Top Hat Plate of Dissimilar Materials

Structural dynamic can be described as a study regarding analysis of model under exertion of dynamic loading. Joining in structure such as riveting, welding and soldering were strongly effects the structural dynamic properties. The aim of this paper is to conduct various joining strategy analysis in finite element software by using top hat plate structure in car as a model and result is compared with experimental data. Normal mode analysis with free-free boundary condition is applied. Resistance spot welding (RSW) technique is selected to weld flange part in top hat plate between dissimilar materials which is mild steel 1010 and stainless steel 304 with specified parameters applied. Modal testing via impact hammer test is carried out at the welded top hat plate for experimental analysis purpose. Correlation in between FEA and EMA results need to be conducted. By selecting identified parameters to execute model updating on the structure using sensitivity analysis method, the discrepancies in natural frequencies were reduced between FEA and EMA. CWELD element was chosen to represent weld model for spot weld joints due to its accurate prediction of frequencies and mode shapes compare to other weld modelling. As a closure, connection in structure parts play significant role in structural dynamics and model updating is one of successful method to lessen the discrepancies between FEA and EMA.

Nondestructive evaluation of resistance spot-welded Al-steel joints

Abstract

Effect of Different Friction Stir Spot Welding Techniques on the Mechanical Properties and Microstructure of Aluminum AA2024-T3

This paper presents a comparison of using different techniques for stir spot welding of Aluminum 2024-T3, which are refill friction stir spot welding (RFSSW), edited (RFSSW-pin) and conventional friction stir spot welding (FSSW), depending on the obtained tensile shear strength property. Specimens were prepared from AA2024-T3 sheet for chemical analysis and mechanical tests. Workpieces were stir spot welded utilizing the above mentioned techniques at four rotational speeds (2000, 2500, 3000 and 4000 rpm) using tool pin diameters (5 and 7 mm) for conducting the tensile shear tests. The microhardness along the cross section of the welded specimens was conducted at the best conditions as well as the microstructure examination. The comparison results revealed that at the rotational speeds (2000 and 4000 rpm) in both cases of tool pin (5 and 7 mm), the ultimate tensile shear force was slightly higher than that for other speeds. However, the ultimate tensile shear force was found higher at 3000 rpm speed with a tool pin 7 mm. The microhardness results manifested a W-shape at the best conditions. Finally, the microstructure examination depicted the morphology of the main zones of the weld joint.

Experimental and Numerical Investigations of Thin-Walled Stringer-Stiffened Panels Welded with RFSSW Technology under Uniaxial Compression.

Many aircraft structures are thin walled and stringer-stiffened, and therefore, prone to a loss of stability. This paper deals with accurate and validated stability analysis of the model of aircraft skin under compressive loading. Both experimental and numerical analyzes are conducted. Two different methods of joining panel elements are considered. In the first case, the panel is fabricated using rivets. In the second variant, the refill friction stir spot welding technique is used. Both types of panels are loaded in axial compression in a uniaxial tensile testing machine. The geometrically and physically nonlinear finite element analyzes of the panels were carried out in ABAQUS/Standard. The Digital Image Correlation measurement system ARAMIS has been utilized to monitor the buckling behavior and failure mode in the skin-stringer interface of the stiffened panels. The results of experiments and the digital image correlation system are presented and compared to the numerical simulations.

Projection friction stir spot welding: a pathway to produce strong keyhole-free welds

ABSTRACTThis paper introduces a novel facile method, called projection friction stir spot welding, to produce a keyhole-free friction stir welds based on a pinless tool method involving using a specially designed projection on the surface of the backing anvil. The projection plays two key roles contributing to the bonding mechanism and the joint strength: (i) encouraging the material flow perpendicular to the joint interface and (ii) bending the joint interface at the edge of the projection. The process enables pathway to produce keyhole-free welds with superior mechanical performance in steel sheets compared to the other spot welding techniques.

Determination of Fracture Modes in Novel Aluminum-Steel Dissimilar Resistance Spot Welds

With increasing demands to improve vehicle fuel economy, multi-material body structures are increasingly utilized in the automotive industry for structural lightweighting purposes. These multi-material structures pose challenges in dissimilar material joining, particularly aluminum to steel. General Motors (GM) developed a new resistance spot welding technique using a multi-ring domed electrode and multiple solidification weld schedules to address these challenges. In aluminum-steel resistance spot welds (RSWs), an iron-aluminum intermetallic compound (IMC) layer is formed at the interface and its strength affects tensile shear specimen fracture modes, i.e. interfacial versus pull out fracture. Based upon the experimental heat affected zone (HAZ) and IMC shear strengths using a new mini-shear test specimen, it was observed that it was not suitable to use the critical weld nugget diameter of 4√t recommended by the American Welding Society (AWS) to determine the fracture modes of these unique aluminum-steel spot welds. In the present study, a new formula considering the shear strength of intermetallic layer in aluminum to steel RSWs is derived to calculate a critical aluminum-steel weld nugget diameter based upon experimental results. The calculated critical weld nugget diameters were then compared with experimental results to predict fracture modes for aluminum-steel stack-ups with different sheet thicknesses.

Ultrasonic spot welding of dissimilar 2024Al alloy and SiCp/2009Al composite

Dissimilar welding of 2024Al alloy to SiC/2009Al composite was conducted via solid-state ultrasonic spot welding technique. Defect-free sound spot welds were successfully achieved. SiCp particles were observed to migrate from the composite side to 2024Al side along with the interfacial interlocking during the intense high-frequency rubbing, which increased with increasing welding energy. The microhardness across the ultrasonic spot welded similar and dissimilar joints remained nearly constant. The tensile lap shear failure load increased with increasing welding energy, and satisfied the requirements of AWS standard D17.2 for spot welding. In addition to room temperature tensile lap shear tests, all the similar and dissimilar joints were subjected to tensile tests at varying temperatures and their respective results were discussed.

Comparative Study of Spot Welding and Firiction Stir Spot Welding of Al 2024-T3

This investigation is performed to compare the resistance spot welding (RSW) of aluminum alloy (2024-T3) with friction stir spot welding (FSSW) techniques. In this work, parameters of both resistance spot welding (RSW) and friction stir spot welding (FSSW) techniques were optimized and the optimum welding variables for both techniques were obtained. For FSSW, the tensile shear strength increased with increasing probe length, tool rotational speed and tool holding time. Tensile shear force value of RSW is about 66% of that of FSSW. This is explained by the coarse dendritic structure in resistance spot welding compared to the plastically deformed stir zone and heat affected zone in FSSW. The ratio of nugget shear strength of RSW and FSSW to base metal is about 71% and 149% respectively. The maximum hardness was obtained in stir zone at the surface of the tool. Very fine grain size of about 4 microns was obtained in stir zone followed by elongated and rotated grains in TMAZ where dynamic recrystallization did not occur.

Flat friction stir spot welding of three 6061-T6 aluminum sheets

Three 6061-T6 aluminum sheets with a thickness of 1 mm for each were subjected to the flat friction stir spot welding technique, which contains two steps of welding process. In step 1, a specially designed back plate with a pre-drilled dent was used in order to form a protuberance on the bottom side of the joint. In step 2, the keyhole and the protuberance were removed by using a probe-less rotating tool and a smooth back plate. The optimized welding condition for the three sheet spot welding was 700 kg/550 rpm/2 s in step 1 and 1000 kg/600 rpm/2 s in step 2. Two sheet/sheet interfaces were formed in the bowl-like stir zone. The stir zone showed a grain size varied from 4.2 to 8.6 μm, much smaller than the 17.6 μm of the base metal. Three different tensile test modes were used to evaluate the failure behavior of the joints. The interface between the top and middle sheet showed a longer bonding length of 11.5 mm and a higher fracture load of about 6438 N. While the interface between the middle and the bottom sheet showed a bonding length of 5.2 mm and a fracture load of about 4450 N. The step 2 joints showed plug-type failure mode during the shear tensile tests.