Joining Technology Research Articles

A mechanical interlocking joint between sheet metal and carbon fibre reinforced polymers through punching

The joint between different lightweight materials plays a significant role in multi-material design of structural components for the automotive industry, aiming to reduce the vehicle’s weight without compromising performance or safety. Yet, conventional mechanical joining technologies between metals and Carbon Fibre Reinforced Polymers (CFRP) result in either a hole being drilled in the composite material, leading to damages which reduce the load bearing capacity, or the weight of the part being increased due to the incorporation of fasteners. At the same time, alternative mechanical joining methodologies involve complex and costly processing, hindering their industrial application. This work presents a new, simple, cost-efficient and non-weight penalizing mechanical joining technology between a metal sheet and fibre reinforced polymer prepregs consisting of a single-step punching process. In this process, the metallic sheet is completely perforated, while the prepreg is not. The punch pushes the carbon fibres through the metallic hole, with no, or minimal fibre breakage, generating a mechanical interlock. The shear strength and the absorbed energy of the co-cured joint increase with the incorporation of the mechanical interlocking joint.

Weldability assessment of Al-SS dissimilar joints produced by ultrasonic spot welding route

Multiple materials are often used in the construction of modern vehicles to make them lighter and more affordable. Steel and aluminium alloys are the great building materials for these composite structures. Ultrasonic metal welding is an efficient solid-state joining technology that requires less energy and time than conventional welding methods while also eliminating the potential problems of distortion and shrinkage. In this research, stainless steel (UNS S30400) and aluminium (AA1100) sheets are ultrasonically welded with various surface treatments, including normally cleaned, electrolytically polished, and lubricated surfaces. The studies are carried out at various weld energies while maintaining constant vibrational amplitude and weld pressure parameters. The maximum lap shear and T-peel strength values are obtained as 621 N and 230 N at 2550 J of weld energy for the lubricated surface condition. According to the temperature profile, when weld energy grows, the weld interface temperature rises as well, reaching a maximum of 460 ˚C. It offers the perfect setting for the plastic flow phenomena to build strong bonds. The effects of natural aging and softening on the weld zone at each joint surface are studied through the microhardness test. Scanning electron microscopy and energy-dispersive X-ray spectroscopy investigations are also used to analyse fracture surfaces with various interface morphologies and characteristics.

The Influence of MSR-B Mg Alloy Surface Preparation on Bonding Properties.

Nowadays, industrial adhesives are replacing conventional bonding methods in many industries, including the automotive, aviation, and power industries, among others. The continuous development of joining technology has promoted adhesive bonding as one of the basic methods of joining metal materials. This article presents the influence of surface preparation of magnesium alloys on the strength properties of a single-lap adhesive joint using a one-component epoxy adhesive. The samples were subjected to shear strength tests and metallographic observations. The lowest properties of the adhesive joint were obtained on samples degreased with isopropyl alcohol. The lack of surface treatment before joining led to destruction by adhesive and mixed mechanisms. Higher properties were obtained for samples ground with sandpaper. The depressions created as a result of grinding increased the contact area of the adhesive with the magnesium alloys. The highest properties were noticed for samples after sandblasting. This proved that the development of the surface layer and the formation of larger grooves increased both the shear strength and the resistance of the adhesive bonding to fracture toughness. It was found that the method of surface preparation had a significant influence on the resulting failure mechanism, and the adhesive bonding of the casting of magnesium alloy QE22 can be used successfully.

Joining Technologies for Aluminium Castings—A Review

Aluminium castings have been widely used in many industries, including automotive, aerospace, telecommunication, construction, consumer products, etc., due to their lightweight, good electric and thermal conductivity, and electromagnetic interference/radio frequency interference (EMI/RFI) shielding properties. The main applications of aluminium castings are in automotive industry. For lighweighting purposes, more and more aluminium castings are used in the automotive vehicle structures to reduce weight, improve fuel efficiency, and reduce greenhouse gas emissions. However, due to the features of cast aluminium, such as porosity, poor surface quality, a tendency toward hot cracking, and low ductility, joining these materials is problematic. In this paper, the joining technologies for aluminium castings and the related issues, mainly cracking and porosity, are reviewed. The current state-of-the-art of joining technologies is summarized, and areas for future research are recommended.

A new method of joining stainless steels using Ni micro-plating bonding and the mechanical properties of the joint

Stainless steel is applied in a wide range of fields as a material with high heat and corrosion resistance. Welding, brazing, and solid-phase bonding are the most common joining techniques for stainless steel. Conventional joining methods have issues such as local thermal distortion of the joining area and the need for high-temperature heat treatment at 800–1000 °C. In this paper, we investigated a new joining technique for stainless steel. With the aim of establishing a new joining technology for stainless steel, we joined stainless steel using the Ni Micro-Plating Bonding method (NMPB) and evaluated the shear stress and the tensile stress of the joints. The joining process is performed at about 55 °C, followed by heat treatment at a relatively low temperature of 300 °C or higher. Shear and tensile tests were conducted on the NMPB joined SUS304, and the results showed that the shear stress was 114 MPa and the tensile stress was 77 MPa without annealing. After heat treatment at 300–400 °C for 1.5h, the shear stress of 200 MPa and the tensile stress of 240 MPa were obtained. In addition, the heat treatment at 600–800 °C for 1.5h resulted in the shear stress of 230 MPa and the tensile stress of 400 MPa. The plating crystallographic structure before heat treatment showed preferential orientation to <001>, but after heat treatment, recrystallization progressed beyond the boundary interface at 400 °C or higher, and a non-oriented crystalline was observed.

Influence of Mean Stress on Lifetime Prediction of Adhesive Bonds

AbstractThe importance of adhesive bonds in the field of joining technology is increasing due to their advantageous properties. One of these attributes is the possibility to reduce the weight compared to welded joints in group of components. For a safe design, the knowledge of the lifetime of these components is essential. Various methods are used for the prediction of the lifetime under cyclic loading. On the one hand there are test‐based methods, on the other hand simulation‐based approaches. Test‐based ones are often time‐consuming and cost‐intensive. In addition, a change in boundary conditions requires new tests. Using a simulation‐based method, it is possible to analyse new boundary conditions rapidly. The following contribution shows a damage model approach that is able to predict the lifetime of an adhesive bond with high accuracy, by taking into account the main influencing factors. First, various lifetime influencing factors are presented. Afterwards, the model approach is extended in regard to the consideration of the important mean stress influence. Finally, the model approach is validated by the comparison of the model‐based lifetime prediction to the one from test data under multiaxial loading.

Interfacial evolution behavior and mechanical properties of Ti/steel joint via ultrasonic seam assisted resistance spot welding with Cu interlayer

Ultrasonic seam assisted resistance spot welding, as a new joining technology, was proposed for welding TC4 titanium alloy and Q235 mild steel with Cu interlayer (abbreviated as US-RSW-Cu), in which, the Cu interlayer was consolidated on the Q235 mild steel by ultrasonic seam welding (USW) in advance, which was subsequently connected with TC4 by the traditional standard resistance spot welding (RSW) in the following experiments. To investigate the effect of pre-USW on the interface microstructure and mechanical properties, the final joints were compared with the other joints by the traditional RSW without interlayer directly (abbreviated as RSW-D), and with a single Cu interlayer (abbreviated as RSW-Cu). The results depicted that the welding nugget in RSW-D and the flat interfacial structure in RSW-Cu were replaced by the inhomogenous interfacial structure in US-RSW-Cu due to the pre-metallurgical bonding between Cu interlayer and steel by USW, which also effectively decreased the welding defects. The Ti-Cu intermetallic compounds (IMCs) were generated at the final joints via US-RSW-Cu instead of most Ti-Fe IMCs, which improved significantly the joint properties and reduced the nanoindentation hardness at the joint interface. The final shearing force of welding joints by this method was the highest and reached 12,380 N, which was 2.68 times with original joint strength via a single RSW-D. The reaction layer near the Ti side via US-RSW-Cu contained abundant Fe atoms, forming Ti-Cu and TiFe2 IMCs at this position. The final welded specimen fractured at the interfacial reaction layer near the Ti side due to the generation of TiFe2 IMC. The XRD results also proved the generation of the abovementioned Ti-Cu and Ti-Fe IMCs.

Evaluation of Riveting Force Influence on the Quality of Riveted Joint of Aluminium Alloy EN AW - 6016

Joining technologies are very important aspects of production process in the automotive. Especially regarding the use of newly developed types of materials (e.g. ultra high-strength steels or aluminium alloys), in addition to welding technology, e.g. riveting or adhesive bonding technologies are used. Submitted article evaluates the effect of the riveting force on the final quality of riveted joint when joining aluminium alloy EN AW-6016 (thickness 2 mm). The actual evaluation of the riveted joint was carried out using a shear test, measuring the hardness HV01 and deformation analysis of specimen using non-contact optical scanning (ATOS III Triple Scan system).

Research on the joining of aluminum alloy and high-strength steel by dieless clinched-adhesive processes

Aluminum and high-strength steel are the best choices for modern cars due to their excellent ratio of strength to weight. As application support, the clinched-adhesive process for aluminum alloys and high-strength steels is also attracting increasingly attention. In this paper, a novel dieless clinched-adhesive process was proposed, which greatly improves the joint strength. It also has unique advantages such as low alignment requirements and low joint bulge due to the use of dieless clinched mould. In the background of automotive light weighting, this joining technology has great prospects for development and application due to its many advantages. Meanwhile, the geometric and mechanical characteristics of various material types of clinched-adhesive joints and clinched joints were analyzed. The key geometric parameters, static strength, and absorbed energy of the joints were obtained. Besides, the microscopic/macroscopic failure mechanisms of joints were investigated. The results showed that the shear strength and energy absorption of the clinched-adhesive joints were much higher than the clinched joints. The highest shear strength of 8159.7 N was obtained for the AL5052-AL5052 material combination, which was 298.3% enhanced compared with the clinched joints. The enhancement of the joint strength was mainly caused by the adhesive. Additionally, the macroscopic failure modes of clinched-adhesive joints and clinched joints with the same material combination are identical, but there are some differences in the microscopic failure mechanisms.

Modelling and Optimization of Continual Laser Joining Processes for Silicon Aluminum Alloy in Microwave Devices

Due to its higher energy and smaller heating area, laser joining technology is widely used in aluminum alloy welding and other industrial fields, which meets the solder sealing requirements for electronic packaging. According to experiments, cracks were prone to occur at the corners and spot-welding positions near the weld. In this paper, the depth and width of the melt pool were measured experimentally, and the results were used to calibrate and validate the heat source model. An empirical relationship between heat source parameters and melt pool morphology is presented. The heat source model of laser deep penetration welding was established under the same experimental conditions. And the results were in agreement with the experimental results. The finite element method was used to numerically simulate the welding process of a 50%SiAl shell and a 27%SiAl cover plate. The effects of different spot-welding sequences and numbers on the residual stress and cracking possibility of laser welded samples were analyzed. The results show that under sequential spot-welding, when the amount of spot-welding is increased, the stress peak value decreases. Compared with sequential spot welding and side-by-side spot welding, the spot-welding sequence of diagonal points first, and then side-by-side spot welding, can effectively reduce the residual stress. This research enables us to provide some guidelines in terms of studying the reliability issues of microwave devices.

Fiber orientation in continuous fiber-reinforced thermoplastics/metal hybrid joining via multi-pin arrays

Abstract Continuous fiber-reinforced thermoplastics (CFRTs) can in combination with high-strength metals offer characteristics that cannot be achieved with mono-material parts. One possible example is the combination of locally high-temperature resistance in the metal component with superior weight-related mechanical properties due to the CFRT component. This approach requires a reliable and durable joining technology, which considers the material-specific properties and allows to exploit the full potential of CFRT/metal hybrid parts. A promising approach in the field of CFRT/metal joining is the use of metallic pins, which can be embedded in the locally heated CFRT component to create a form-fitting joint. In the current state of the art, primarily single-pins are investigated and characterized: especially the distinct fiber orientation in the direct pin pressing process is only described for single-pin joints. Behind this background, the present study aims at creating an understanding of the fiber orientation mechanism for multi-pin arrays. Therefore, in the scope of this study, unidirectional reinforced glass fiber/polypropylene samples are joined via direct pin pressing and infrared heating with different 1D and 2D multi-pins arrays with different pin-diameters, spacing and pin distributions. The resulting joint morphology is consequently analyzed using micro-computer-tomography. Based on the performed investigations, a model for the fiber displacement mechanism is proposed, and the first recommendations for the design of fiber-friendly multi-pin joints with unidirectional reinforcements are given. It showed that especially pin-spacing in fiber orientation in dependency of the pin diameter is critical for a fully reconsolidated joint quality, and it is suggested that a pin-offset in the fiber direction is beneficial for a fiber-friendly joining process.

Exothermic Reactions in AlNi Foils Produced by Rolling Powders

The possibility of manufacturing multilayer reaction foils of the Al-Ni system by rolling a powder mixture is considered. The sequence and temperatures of phase transformations during heating was established by the differential thermal analysis and X-ray phase analysis. The formation of the intermetallic compounds in the foils fabricated via rolling just mixed powder occurs only when a liquid phase appears (660°C). However, the foils fabricated from mechanically activated powders exhibit significant exothermic effect at temperature of 320°C unnecessarily for a liquid phase formation and can be proposed as a multilayer reactional foils for local heating in the technology of joining of various materials.

Influence of steel yielding and resin toughness on debonding of wrapped composite joints

The concept of an innovative bonded joining technology where welding is not required is presented as an alternative to traditional welded connection for steel circular hollow section (CHS). Wrapped composite joints have potential to greatly improve fatigue endurance when applied in multi-membered truss structures, e.g. offshore jackets for wind turbines. This paper focuses on characterization of influence of chemical bonding resistance, fracture toughness of resins, and steel yielding on debonding of wrapped composite joints. Uniaxial splice joints (A-joints) are made with GFRP composite material wrapped around steel sections, and tested under static tensile loading conditions until failure. Different chemical bonding properties by application of bonding primer, different types of polymer resins and steel grade are used during the wrapping procedure. Debonding on the bonded interface are identified by surface strain measurements through 3D digital image correlation (DIC) technique. Testing results indicate that steel yielding limits full utilization of the resistance of the bonded interface. Wrapped composite A-joints with high-strength steel exhibits 75% larger ultimate load where yielding is prevented. Larger fracture toughness of toughened vinyl-ester resin contributes to 30% larger displacement of the joints at failure compared to regular vinyl-ester and polyester resins.

Synergistic strengthening in interlocking metasurfaces

Interlocking metasurfaces (ILMs) are a new class of structural metamaterials consisting of autogenous latching features. ILMs offer non-permanent joints that are an alternative to fasteners, welds, or adhesives. The mechanical properties of ILMs, including strength and stiffness, are governed by both the shape of the individual latching unit cells and the interaction between unit cells. These cross-cell interactions provide a synergistic effect that distinguish ILMs from ordinary isolated latching features: specifically, as the number of interacting unit cells increase, the strength of the ILM also increases. Remarkably, in the present study, ILMs demonstrated interfacial tensile strengths that were as much as four times stronger, and stiffer, than the equivalent isolated latching components. Computational analysis and experimental measurements confirmed the cross-cell interactions associated with ILMs. Both finite element analysis and digital image correlation strain field mapping reveal that unit cells near the edge of the ILM have different load-limiting deformation and failure mechanisms than those away from the edge: unconstrained edge unit cells bend out of the way, thus allowing the interlocking features to move past one another whereas interior unit cells do not. Due to their synergistic strengthening, ILMs show promise as a novel joining technology.

Development of a numerical simulation model for self-piercing riveting of additive manufactured AlSi10Mg

Laser additive manufacturing processes are used for the production of highly complex geometric structures due to their high geometric freedom. Additive manufacturing processes, in particular powder-based selective laser melting, are used to produce metallic additive manufactured components for the automotive and aerospace industries. Different materials are often joined together to realize sustainable lightweight construction. The production of such mixed construction joints is often realized using mechanical joining technology (e.g. self-piercing riveting). However, there is currently very little experience with the mechanical joining of metallic additive manufacturing components. Furthermore, there is insufficient knowledge about the effects that occur during the mechanical joining of additive manufacturing components. In this article, a method is presented to investigate the joinability of additively manufactured components with conventionally manufactured components using a numerical simulation of the self-piercing riveting process. For this purpose, the additive manufacturing materials are characterized experimentally, the simulation model is configured, and the joining process with additive manufacturing materials is represented in the numerical simulation. Furthermore, the influence of the building direction on the mechanical properties is shown using miniature tensile specimens. Besides the configuration of the simulation model, the influence of heat treatment on the self-piercing riveting process is presented.

An Overview of Resistance Element Welding with Focus on Mechanical and Microstructure Joint and Optimization in Automotive Metal Joints

As lightweight automotive structures improve fuel efficiency and reduce carbon dioxide emission, they have garnered extensive attention. Vehicle mass reduction, which is a key problem for next generation eco-friendly vehicles, can significantly increase mileage. Hence, industries have committed to replace conventional materials with lightweight materials, such as advanced high strength steel. Additionally, automotive industries are hindered by challenges in the field of joining technology. A novel welding technology called resistance element welding (REW), which is an appropriate thermal-based joining method, was developed recently for joining hybrid materials with other structural steel grades. In this study, the state of the art joining and the process characteristics for dissimilar metal joints have been presented because related studies show limited investigation in this area. Following by the state of them, the principal and welding quality of REW, experimentally and numerically, are reported to give comprehensive information on the current practices and research interest related to technologies. Finally, extensive work was concentrated on portional joining optimization techniques to improve different materials.

Influence of single or multi-factor coupling of temperature, humidity and load on the aging failure of adhesively bonded CFRP / aluminum alloy composite joints for automobile applications

Applying materials such as CFRP (Carbon Fiber Reinforced Plastics) and aluminum alloys to automobiles is an effective way to accomplish lightweight design, thereby bringing energy conservation and emission reduction. Bonding structure is the key joining technology for dissimilar materials, but it will degrade during the automotive service by environmental temperature, humidity and load. Scholars mainly carry out accelerated aging tests by increasing the temperature or humidity, but it is hard to compare the degree of influence of temperature, humidity and load owing to the aging environments and adhesive materials are various and different. In this study, to comprehensively compare the effects of various aging environments coupled with load that may be experienced during the service life of an automobile on the aging failure of composite bonded joints, seven typical aging environments were selected, namely room temperature (RT), high temperature (HT), low temperature (LT), high/low temperature cycle (TC), immersed in water at room temperature (IRT), high temperature and high humidity (HTHH), and hygrothermal cycles (HC). Aging environments were coupled with static load to form single or multi-factor aging conditions of temperature, humidity and load. Accelerated aging tests were conducted to analyze the failure strength, failure mode and SEM microscopic fracture surface of bonded joints made of aluminum alloy and CFRP. The degree of influence of single or multi-factor coupling of temperature, humidity and load on the aging failure of bonded joints was analyzed by visual analysis and ANOVA (Analysis of Variance). The results show that single temperature, humidity or load had limited effects on the degradation of the failure strength of butt joints, while coupling effects of multiple factors are more obvious. When the aging environment was coupled with the load, the aging environment played a major role, and the load accelerated the aging rate without changing the decreasing trend caused by the aging environment. Both the adhesive and CFRP underwent different degrees of aging, the effect of load on the degree of aging of the adhesive was significantly greater than the CFRP, but the effect of aging environment on the degree of aging of adhesive and CFRP was related to the aging time. Normally, aging environment, aging time and load had significant effects on the failure strength, and the degree of influence decreased successively. As for the selection of the accelerated aging environments for the car, HC and TC environments should be preferred and the influence of load should be taken into consideration in accelerated aging tests.

Mechanical performance and failure behavior of screw-bonded joints of aluminum sheets and cross-laminated birch veneer plates

Integrating wood-based lightweight components into advanced multi-material car bodies requires capable and reliable technologies for joining or bonding of dissimilar materials. Therefore, the present experimental study investigates hybrid lap joints of 1.5 mm-thick sheets of EN AW-6016-T4 aluminum alloy and 9 mm- or 13 mm-thick plates of cross-laminated 1 mm-thick birch veneers. Two self-cutting screws and single-component polyurethane-based adhesive were used for each joint. The mechanical performance and the fracture behavior were tested under both quasi-static and cyclic shear-tensile loadings. At each load condition fracture of the joint occurred, but neither fracture of the aluminum alloy sheet nor fracture of the veneer plate were observed. Debonding of the aluminum alloy sheet from the birch veneer plate was identified as critical failure mechanism. The adhesive provided the main contribution to both the static strength and the fatigue performance of the joints. However, the energy absorption of the joint was mainly determined by the pull-out resistance of the screws, which was dependent on the thickness of the veneer plate. To optimize the strength-to-weight ratio of the joint and to exploit the load-bearing potential of the materials, the focus should be placed on the improvement of the bonding conditions or on the adaptation of the sheet/plate thicknesses.

Characterization of Vapor Capillary Geometry in Laser Beam Welding of Copper with 515 nm and 1030 nm Laser Beam Sources by Means of In Situ Synchrotron X-ray Imaging

Laser welding of copper is being used with increasing demand for contacting applications in electric components such as batteries, power electronics, and electric drives. With its local, non-contact energy input and high automation capability enabling reproducible weld quality, this joining technology represents a key enabler of future mobility systems. However, a major challenge in process design is the combination of energy efficiency and precise process guidance in terms of weld seam depth and defect prevention (i.e., spatter and melt ejections) due to the high electrical and thermal conductivity of copper. High-power lasers in the near infrared wavelength range (𝜆 ≈ 1 μm) and excellent beam quality provide an established joining solution for this purpose; nevertheless, the low absorptivity (≤5%) advocates novel beam sources at visible wavelengths due to altered absorptivity (40% at 515 nm) characteristics as an improved tool. In order to understand the influence of laser wavelength and process parameters on the vapor capillary geometry, in situ synchrotron investigations on Cu-ETP with 515 nm and 1030 nm laser sources with the same spot diameter are compared. The material phase contrast analysis was successfully used to distinguish keyhole and melt pool phase boundaries during the welding process. A significantly different sensitivity of the keyhole depth in relation to the feed rate was found, which is increased for the infrared laser. This behavior could be attributed to the increased effect of multiple reflections at 1030 nm.

The influence of adhesive materials on the transverse vibrations of single lap joints: an experimental study

ABSTRACT In the past decades, an increasing trend towards the structural combination of lightweight materials and traditional metals has been observed. For these multi-material interfaces, traditional joining technologies such as bolting and welding have to be re-thought and adhesive bonds can be a valid alternative. The substitution of the joints has an impact on the stiffness, damping, and mass distribution of the entire assembly and should be taken into account while designing for NVH, durability, and performance. The aim of this work is to experimentally compare the effect of bolts and adhesive bonding on the vibrational response of the assembly, in terms of modal frequency, shape, and damping. Plate-to-plate single lap joints are tested under transverse vibration. In particular, we compare one M4 bolted connection and three adhesive connections, respectively, realized with stiff epoxy, flexible foam tape, and toughened acrylic. Results show that, in a low-mid frequency region between 0 and 250 Hz, the substitution of bolts with adhesives has a limited influence on mode shapes but can lead up to a 6-fold increase of the modal damping values and 10% increase of the modal frequencies.