Joining Process Research Articles

Influence of Sheet Covers on Filling Behavior in Electrochemical Joining of Additively Manufactured Components

This paper focuses on the electrochemical joining of additively manufactured components using simulation-based and experimental methods. The study investigates the influence of cover screens on the filling behavior of the joining zone. Experimental methods involving additive manufacturing and electroplating are combined with simulation models to provide a realistic representation of the joining process. The results show a good agreement between the simulated and experimental findings, indicating the applicability of the simulation model. The parameter study reveals that higher cover factors result in a decrease in the excess material ratio, indicating reduced material deposition outside the joining zone. The filling time required to completely fill the joining zone is influenced by both the cover size and the opening angle of the joining zone. The optimal parameter combinations depend on whether the filling time or the excess material volume is to be minimized. Cavity formation within the joining zone was identified as a critical factor affecting the completeness of the filling. The study provides insights into the influence of cover screens on the electrochemical joining process and offers guidance for optimizing the design of the joining zone.

New Input Factors for Machine Learning Approaches to Predict the Weld Quality of Ultrasonically Welded Thermoplastic Composite Materials

Thermoplastic composites (TCs) enjoy high popularity in the field of engineering. Due to this popularity, there is a growing need to assemble this material with the help of fast and efficient joining processes. One joining process, which has seen increased use, is the process of ultrasonic welding. To make reliable statements about the quality of the joined material, some kind of quality assurance has to be made. In terms of ultrasonic spot welding, there are already some documented approaches for observing or predicting the joining quality, but some of these most promising parameters for quality assurance are difficult to measure in the process of continuous ultrasonic welding. This is why new parameters are investigated for their potential to improve the prediction of ultrasonic-welded TCs’ quality. Thermography and sound emission data have been found to have a correlation with the produced weld quality and are fed into different machine learning algorithms. Despite the relatively small dataset, trained algorithms reach binary classification rates of over 90%, indicating that the newly discovered parameters show the potential to improve the quality assurance of ultrasonic-welded TCs in the future. This improvement may enable the establishment of the ultrasonic welding of TCs in manufacturing.

Influence of the application of ultrasound on the microstructure of cemented carbide/steel joints brazed with Ag49ZnCuMnNi

The poor wettability of cemented carbides by molten metals as well as the different material properties compared to steel makes thermal joining process challenging. In this regard, innovative ultrasonic-assisted induction brazing is capable of joining the materials quickly, cost-effectively and without using environmentally hazardous fluxes. Instead, the oxide scales are broken up within the joining process due to ultrasonic-induced cavitation in the molten filler alloy and hence promote the wetting. However, since the use of ultrasound in brazing steel/cemented carbide joints is still insufficiently investigated, there is still a need to explore the fundamental influences of ultrasound on the brazing process. In this work, the effect of ultrasound on the microstructure of the brazed joints and the diffusion depth of different elements were analysed. The two ultrasonic parameters activation time and amplitude were varied during the experiments. Acicular or dendritic structures that have formed in the braze metal without ultrasonic stimulation were transformed into globular structures, when ultrasound was applied. In addition, a non-eutectic silver-rich phase formed, which was not observed in joints manufactured without the use of ultrasound. Furthermore, the use of ultrasound led to increased diffusion between the base material and the filler material as well as the dissolution and distribution of oxides in the edge regions of the brazing joints.

NUMERICAL INVESTIGATIONS ON COMBINED EFFECT OF WELDING RESIDUAL STRESS AND AXIAL COMPRESSIVE LOAD ON BUCKLING CAPACITY OF THIN LOW CARBON STEEL PLATES

Arc welding is the most commonly used metal joining process and its broad range of applications from large structural fabrications such as bridges to delicate satellite and aerospace components. Welding Residual Stress (WRS) and cracks developed during welding, reduce the quality of welds. Aerospace structures are normally fabricated using thin metal sheets to reduce mass and are always susceptible to buckling. Many researchers have published WRS numerical models and experimental validations, but the impact of WRS on the buckling of thin low carbon steel plates is yet to be studied. The main objective of this study is to analyse the influence of external compressive load and tendon force generated by welding residual stress on buckling strength of the TIG welded low-carbon steel plates. Linear buckling of welded plates under the combined effect of external compressive load and WRS generated due to various weld lengths were numerically modelled and its critical buckling loads are computed. The numerical simulation findings show that the critical buckling strength decreases by 80% when the weld length to plate width ratio (w/wl) is equal to unity and it reduces to minimum when the w/wl ratio is 0.5. After w/wl ratio is 0.5, buckling strength increases and this behavior is caused by the stress field interaction that arises from both the applied axial compressive load and the WRS on the plate.

Effect of friction stir welding parameters on microstructure and mechanical properties of the dissimilar alloys of AZ91D and AA7075

Friction stir welding is an efficient joining process for light metal alloys, offering benefits such as high joint efficiency and reduced grain sizes. This work is to investigate the process parameters that can improve the welding quality and reduce the brittle intermetallic compounds, including Al3Mg2 (β) and Al12Mg17 (γ) in the welded region. It was perceived that the process parameters influenced the morphological characteristics and input heat, thereby affecting the materialization of intermetallic compounds. The primary diffraction peaks of both Al and Mg were present in all the joints. Two specific intermetallic phases, Al3Mg2 and Al12Mg17, were formed as a result of the diffusion of Al and Mg atoms during welding. These intermetallic compounds were found in all the joints. The Al12Mg17 phase, when mixed with the Mg phase, tended to migrate towards the weld surface where the AZ91D plate was positioned. This migration might lead to constitutional liquation, which refers to the melting of specific phases during solidification, resulting in the materialization of eutectic microstructures. The highest ultimate tensile strength (UTS) value of 116.64 MPa was achieved with a rotational tool speed of 800 r/min and a traverse speed of 20 mm/min. On the other hand, the lowest UTS value of 68.32 MPa was observed with a rotational tool speed of 400 r/min and a traverse speed (TS) of 20 mm/min. It was noted that lower UTS values were associated with the materialization of dense layers of intermetallic compounds (Al12Mg17 and Mg + Al12Mg17) in the stir zone when using lower rotational tool speed and TS. It suggests that improper processing parameters can lead to the materialization of intermetallic compound in the stir zone, which subsequently decreases the mechanical properties of the weldments.

Thermogravimetric analysis (TGA) and determination of activation energies of waste paper products

Tetra Pak® paper and PE (polyethylene) wastes were evaluated to obtain a new composite material with awareness of environmental responsibility. Fillers and coupling agents were used for this joining process. Calcite (CaCO3), boric acid (H3BO3), SPT (Sodium Perborate Tetrahydrate / NaBO3.4H2O), titanate, MAPE (maleic anhydride grafted polyethylene, and vinyltriethoxysilane (C8H18O) composites were produced in 30 × 30 cm plates. A total of 30 samples were prepared as 5 mg flour for thermogravimetric analysis (TGA). Samples were observed in a thermal analyzer at 10, 15, or 20 °C/min heating rate in nitrogen atmosphere. Graphs were obtained as a result of TGA, and the activation energies were calculated using these graphs. The activation energy was calculated using the Flynn-Wall-Ozawa method. The determined activation energies of the composites were close to each other for each temperature group. In the samples using calcite and vinyltriethoxysilane, relatively higher activation energies were observed in comparison to the samples with boric acid and MAPE.

Double-Sided Self-Pierce Riveting: Electro-Mechanical Analysis of Dissimilar Al-Cu Half-Lap Butt Joints

Double-sided self-pierce riveting (DSSPR) can be utilized as an alternative to self-pierce riveting (SPR) to produce butt joints through half-lap joints in dissimilar materials. The mechanical joining process makes use of tubular rivets with simple geometry that are here employed to join two sheets made from aluminium (Al) and copper (Cu). This research work analyses the influence of the stainless-steel rivet on both the electrical and mechanical performance of the joint. The electrical resistance variation of the joined assembly is measured at different temperatures and compared with conventional fastened joints made from the same material combination. The mechanical performance of the aluminium–copper connections is evaluated by means of shear tests and compared to the original fastened Al-Cu joint. An experimental approach is utilized to analyse the combined influence of different mechanical and electrical parameters to assess the performance of DSSPR in electrical applications.

Microstructural and numerical variation of friction spot welded AA7075 couples

Abstract Friction stir spot welding (FSSW), which is one of the joining methods, is an interesting solid state joining process. In this experimental study, the joining of AA7075, which is the one of the Al-based alloys, with the FSSW method was conducted. Firstly, the microstructural inspections were performed by helping an optical microscope. Second, a numerical simulation study was performed using SolidWorks and ANSYS software. Therefore, these data were evaluated with modeling for understanding the events in zone of FSSW center. Thus, it could be contributed to understand the complex thermo-mechanical joining process period. The present simulation primarily aims to explain the effect of a set of process such as parameters and tool geometry on the workpiece couples. Johnson–Cook damage criteria model was selected to obtain the stress distribution on the workpiece couples consisting of AA7075. The model also showed that temperature and stress did not exhibit much appreciable change on flow with the change of the tip profile. As a result, it was found that tool rotation speed and tool plunge depth are highly effective on both microstructure and numerical modeling properties, apart from the tool geometry, which is one of the welding parameters.

Investigations on the Influences of the Thermomechanical Manufacturing of Aluminium Auxiliary Joining Elements

The demands on joining technology are constantly increasing due to the consistent lightweight construction and the associated increasing material mix. To meet these requirements, the adaptability of the joining processes must be improved to be able to process different material combinations and to react to challenges caused by deviations in the process chain. One example of a highly adaptable process due to the two-step process sequence is thermomechanical joining with Friction Spun Joint Connectors (FSJCs) that can be individually adapted to the joint. In this paper, the potentials of the adaption in the two-stage joining process with aluminium auxiliary joining elements are investigated. To this end, it is first investigated whether a thermomechanical forming process can be used to achieve a uniform and controlled manufacturing regarding the process variable of the temperature as well as the geometry of the FSJC. Based on the successful proof of the high and good repeatability in the FSJC manufacturing, possibilities, and potentials for the targeted influencing of the process and FSJC geometry are shown, based on an extensive variation of the process input variables (delivery condition and thus mechanical properties of the raw parts as well as the process parameters of rotational speed and feed rate). Here it can be shown that above all, the feed rate of the final forming process has the strongest influence on the process and thus also offers the strongest possibilities for influencing it.

Adhesion properties of the hybrid system made of laser-structured aluminium EN AW 6082 and CFRP by co-bonding-pressing process

ABSTRACT A parameter investigation for manufacturing a hybrid system through the prepreg pressing process was carried out within the scope of this work to achieve optimal adhesion properties. The hybrid specimen comprises an aluminium sheet of alloy EN AW 6082 in T6 condition and a thermoset Carbon Fibre Reinforced Plastics prepreg. The prepreg pressing process allows the curing reaction of epoxy resin and the joining process to occur simultaneously to avoid an additional bonding process step. The surface of the aluminium sheet was pretreated in advance using a pulsed Nd:YAG laser to enhance the bonding properties. In the first step, the shear edge tests investigated the adhesion properties achieved with different consolidation (temperature, time and pressure) and laser parameters. Then, 3-point bending tests were carried out to investigate the influence of the consolidation parameters on the mechanical properties of the Carbon Fibre Reinforced Plastics-laminate. In this way, the optimal parameter sets for manufacturing hybrid structures were determined.

A novel mechanical joining method for sheet-tube structures by annular ring compression

Joining by forming has lately received great attention for connection between sheets and tubes due to its high joining efficiency, simple operation, and excellent joining strength. However, protrusion or indentation often occurs adjacent to the joints and, in some cases, the sheet warps, seriously affecting the performance of the connector. To overcome this problem, we propose a novel joining by forming process by compressing an accessory ring to produce the annular squeezing of the sheet, thus forming high-quality joints with smooth surfaces. A numerical-experimental analysis was adopted to identify the influence of the ring width and height on the joint cross-section, effective strain, tube thickness, and flow velocity. To assess the performance of the enhanced joint, its mechanical properties, microstructure, and failure modes were also analyzed. The results showed that the ring width and height have a significant effect on joint strength. Compared with the original joining process without the ring, the joint utilizing a wider ring can obtain higher pull-out loads (58.9% higher) to detach the sheet from the tube, while no sheet warpage happens for excessive local deformation. The utilization of larger and higher rings also motivates the increase of the pull-out strength. In some cases, tube plastic instability can be triggered during the pull-out tests, thus avoiding the full detachment of the components and contributing to the safety of the mechanical joint. Compared with the non-deformation zone, the grains in the deformation zone of the sheet are compressed and become elongated, and there are inclined separation bands between the two regions. This paper provides a new and efficient method for manufacturing sheet-tube structures with high joining strength.

Improving the interfacial bonding strength and suppressing shrinkage porosity of 6061Al/GFRTP hot-pressing joints via interfacial modification

The application of metal-plastic hybrid structures is of great significance for structural lightweight. The metal surface treatment is critical for metal-plastic joints. In this study, nanosecond laser was used to construct different microscale grooves on 6061 aluminum alloy (6061Al) surface to realize stable joints with glass fiber reinforced thermoplastic composites (GFRTP) by hot-pressing joining. The impacts of nanosecond laser processing on interfacial bonding of 6061Al/GFRTP were studied using analytical methods and finite element simulations. The results showed that the mechanical interlocking effectively improved the strength of connections. Moreover, the laser texturing patterns had different effects on promoting the wettability of metal surface and improving the heat conduction path. During the hot-pressing joining process, the poor wettability of molten GFRTP on untextured metal surface and different solidification rates at various molten positions led to the formation of shrinkage, which reduced the bonding area and induced stress concentration. When the pitch distance of textured grooves was 0.3 mm, the porosity was reduced to 1.15 %, and the corresponding maximum bonding strength was 9.78 MPa.

An ontology-based knowledge framework for selection of joining process in plastic assembly

Selection of assembly process is one of the important stage of product development which need to tackle at the earlier stage product realization. Selecting the most appropriate joining process needs various assembly joint information (liaison) which includes both the geometric and non-geometric information. To capture, represent, and reuse this information across domains is a highly knowledge-intensive process that necessitates the use of an active artificial intelligence (AI) tool. In this research, an AI tool called ontology-based knowledge framework is used to assist with identifying the best plastic assembly process to effectively support designers and process planners. The methodology for selecting a joining process and developing a knowledge-based framework is described, together with industrial application of the suggested approach is proposed. To express many key concepts like liaison, process, requirement for variant product etc., a joining process selection (JPS) ontology is created. To get the necessary knowledge for process selection that integrates several instances and knowledge rules, ontology mapping of joining method selection concepts is done using Semantic Web Rule Language (SWRL). The suggested method uses rule-based reasoning to automatically infer the best joining methods. Finally, industrial application of the suggested framework is proposed to assess the applicability of this approach.

Initial Study on Press Welding With Indium Applied to High-Temperature Superconducting DC Feeder Cables

High-temperature superconducting (HTS) DC feeder cable has been proposed for reducing energy loss in railway systems. The feeder cables are required to be installed during the night using a quickly-fabricable low-resistive joint. A soldering technique has been widely used for connecting HTS round-shaped cables in transmission or feeder cable systems. In this study, we proposed applying press welding with indium at room temperature (cold pressure welding) or with heat treatment at 90–120 °C as an alternative candidate for the cable-to-cable joint. First, we examined the necessity of the pre-joint process, polishing the HTS tape, and pickling indium foil with 10% HCl as well as the joining temperature. The examination was performed using tape-to-tape joints with copper-alloy-laminated Bi-2223 tapes. The joint resistance and mechanical strength for railway application were satisfied even by a joint fabricated at room temperature skipping the above two pre-joint processes. Then, we fabricated straight and spiral joints of the model cable made of copper-alloy-laminated Bi-2223 tapes with various joining processes and spiral pitches. The joint resistivity for the model cable joint was less influenced by the joining process and spiral pitch and it was comparable to that of a single tape-to-tape joint. As a conclusion, press welding with indium with a simplified process, joining at room temperature, and skipping some of pre-joint processes can be applied to quick and simple joint fabrication of HTS DC feeder cable.

A multi-criterion optimization of mechanical properties and sustainability performance in friction stir welding of 6061-T6 AA

Nowadays, the transportation industry is curious about fabricating lightweight vehicles under a sustainable manufacturing process to minimize fuel consumption costs and environmental footprints. Assessing the sustainability performance metrics of the friction stir welding (FSW) process reduces the sawing costs and environmental impacts. However, the evaluation and assessment of the sustainability performance metrics integrated with the mechanical properties of the weld joint have not been sufficiently studied. Thus, this study investigates the multi-criterion process parameter optimization of friction stir welding (FSW) to attain an optimum parameter to enhance the mechanical properties of the weld joint and decrease energy consumption and carbon dioxide emission. Experimentations are conducted using a vertical CNC milling machine on a 5 mm 6061-T6 AA material with a butt joint orientation. Tool rotational speed, traverse speed, and tool profile were used as processing parameters. Response of the study, such as transient temperature and energy consumption, was measured during the joining process, whereas hardness, tensile strength, and CO2 emission were examined post-processing. The multi-criterion optimization was done using the Taguchi-based grey relational analysis method. In addition, the transient temperature was predicted by an auto-regressive moving average (ARIMA) and Ansys simulation. The finding showed that higher rotational and minimum welding speeds had imparted a sound weld. Besides, the analysis of variance results showed that welding speed has a significant parameter at a 95% confidence interval. The proposed ARIMA model's result showed that the transient temperature prediction accuracy reached 99.922%, and the error percentage between the FEA simulation and experimental work reached 2.067%.

A method for the reproducible and accurate determination of electrical resistances based on multi-layer joints in lithium-ion batteries

The transition from fossil fuels to renewable energy sources is significantly influenced by the development of energy storage systems such as batteries. One of the crucial steps in the production of lithium-ion batteries is the electrical connection of the individual electrodes by weld seams. Various joining processes, such as laser beam welding or ultrasonic metal welding, are used for this purpose. An important quality feature of the connections is a low electrical joint resistance, which is essential for reducing cell-internal energy losses and avoiding thermal inhomogeneities in the cells.The aim of this work was to determine the electrical resistance of the joint between a stack of foils and an arrester tab. For this purpose, a measuring method was developed and applied to different sample configurations. The influence of different probe tips on the measurement results was compared using single current collector foils and arrester tabs. The measurement of the electrical resistance was possible in the considered range with a maximum relative uncertainty of 2.38%. Using the presented approach made it possible to evaluate the influence of the seam trajectory on the electrical resistance for cell-internal contacting. In addition, the measuring method is suitable for comparing different welding strategies and, thus, for designing the cell-internal joining processes regarding the resulting electrical joint resistances.

Mathematical modelling to predict bead geometry in MIG welded aluminium 6101 plates

MIG (Metal Inert Gas) welding is a popular metal joining process due to its ability to weld a wide variety of metals. The mechanical properties of a weld are governed by the weld geometry parameters, namely the height of reinforcement, the width of the bead and penetration depth. The input welding parameters like wire feed rate, voltage, welding speed etc. in turn decide the above bead geometry parameters. The present research work aims at developing mathematical models connecting these input parameters to the bead geometry parameters for MIG welded aluminium 6101 plates. The mathematical models were generated by the central composite rotatable design technique. The developed models’ adequacy was verified by ANOVA (Analysis of variance) and RSM (Response Surface Methodology) was used to analyze the results graphically.

Tensile, microhardness and microstructural characteristics of friction stir welded/processed AA7075 alloy: A review

The aircraftand automobile industries have a great demand for aluminium alloys such as AA7075 due to their excellent features. However, it is difficult to join AA7075 using electric arc welding process. Therefore, a novel green welding process namely, friction stir welding (FSW), could be employed for fabricating the joints without any defects. FSW, is a proven solid state joining process capable to join several key engineering materials such as aluminium, magnesium, copper, titanium, and several steel grades. In this review study, the FSW characteristics of a well-known aircraft alloy AA7075 is presented systematically. Weld/processed characteristics such as microhardness, ultimate tensile strength, and microstructural are discussed. It is observed that, FSW process could yield better joints without any defects unlike in traditional welding processes. By proper selection of tool and process parameters will result in improvement of weld efficiency of AA7075 alloy. Fine grained microstructure resulting in better hardness and strength of AA7075 joints. However, there is lack of studies that needs to be carried out on integration of the digital tools such as artificial intelligence (AI) and machine learning (ML) is necessary to reduce FSW time.

Mechanical and Microstructure Characterisation of the Hypoeutectic Cast Aluminium Alloy AlSi10Mg Manufactured by the Twin-Roll Casting Process

Multi-material designs (MMD) are more frequently used in the automotive industry. Hereby, the combination of different materials, metal sheets, or cast components, is mechanically joined, often by forming joining processes. The cast components mostly used are high-strength, age-hardenable aluminium alloys of the Al–Si system. Here, the low ductility of the AlSi alloys constitutes a challenge because their brittle nature causes cracks during the joining process. However, by using suitable solidification conditions, it is possible to achieve a microstructure with improved mechanical and joining properties. For this study, we used the twin-roll casting process (TRC) with water-cooled rollers to manufacture the hypoeutectic AlSi10Mg for the first time. Hereby, high solidification rates are realisable, which introduces a microstructure that is about four times finer than in the sand casting process. In particular, it is shown that a fine microstructure close to the modification with Na or Sr is achieved by the high solidification rate in the TRC process without using these elements. Based on this, the mechanical properties increase, and especially the ductility is enhanced. Subsequent joining investigations validate the positive influence of a high solidification rate since cracks in joints can be avoided. Finally, a microstructure-property-joint suitability correlation is presented.

Low-resistance joints for YBCO-coated conductors with Ag nanoparticle paste

Due to the limited available piece length of YBCO-coated conductors (i.e. tapes or wires) and the different requirements for magnetic field, joints are inevitable for manufacturing high-temperature superconducting magnets. In this study, a sintering nano-silver (Ag) process was developed and used to connect YBCO tapes stabilized by anAg layer with low-temperature and short-time sintering of Ag nanoparticle (NP) paste. The thermodynamic characteristics of Ag NP paste were explored using a TG/DSC setup. The effects of sintering temperature, mechanical pressure and lapped length on microstructures and electrical properties of joints were comprehensively investigated. It is found that the pre-volatilization of low-boiling-point solvent in the paste is beneficial to improve the densification of sintered structure, thus contributing to increasing the critical current I c of the joint. With increasing sintering temperature, the I c of the joint will be close to that of the virgin tape, and the joint resistance experiences small fluctuations, but joint connectivity is enhanced. As the temperature reaches 205 °C, I c decreases to 84% of the virgin tape, and joint resistance increases obviously. In addition, the axial tension strength at room temperature is improved with the increase in mechanical pressure, while the resistance does not demonstrate distinct variation. Considering the electromechanical properties, the optimal joining process is determined as sintering at 180 °C and 30 MPa for 10 min. The joint with this technology possesses a closely connected interface and a well-sintered nano-Ag microstructure with pores. By further extending the lapped length, a YBCO joint resistivity as low as ∼10.56 nΩ cm2 is obtained, which is around a quarter of that of the soldering joint, and the process is much easier than that of the Ag diffusion joint.