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For the production of e-mobility components such as cable harnesses, battery cells, power electronics, etc., ultrasonic metal welding is well-established process of choice. These electrical applications require high quality for every single connection; single points of failure and no possibility of repair after installation or commissioning are state of the art. At present, the prevailing binding mechanisms and their sensitivity to the numerous process influencing variables like base material hardness, surface, and cleanliness are still the subject of research. In order to ensure sufficient quality despite the lack of process understanding, random destructive testing is carried out during ongoing production. The welding systems’ internal monitoring methods are currently not sufficient to make a prediction of the joint quality achieved. To determine process phases and extract features regarding the joint formation, the observation of process vibrations at the horn, anvil, and the components using laser-doppler-vibrometry, laser triangulation sensors or other suitable external measurement technology is common. These methods require external accessibility to the measurement position, not given in the industrial production environment. In this study, measurements of the high-frequency power signal of the welding system are conducted, and several machine learning models for quality prediction are set up. To ensure the robustness, several disturbances, e.g., changing material hardness and cleanliness, are taken into account. Thus, it will be evaluated to what extent an industrially suitable quality monitoring can be implemented by means of electrical measuring technology and how much more accurate such an external measuring system is compared to the possibilities already available in the welding system.

UV bonding technology’s biggest limitation is the need of a transparent joining part to be able to cure the adhesive with an external light source. This is to be solved with ribbon fabrics made with polymer optical fibres (POF) which guide the UV light into the adhesive bond. On the basis of previously published experiments, a set of POF fabrics with different thread densities and weft materials is evaluated optically regarding the emitted UV light intensity and mechanically regarding the shear strength of the adhesive bonds. A factorial experiment plan indicates that higher tensile lap-shear strength comes with lower weft fineness and higher weft density. The maximum shear strength achieved was 8.3 MPa with potential room for improvement due to non-cohesive failure, relatively high weft densities and a comparatively low powered UV light source.

Copyright of Joining Plastics / Fügen von Kunststoffen is the property of DVS Media GmbH and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Joining Plastics / Fügen von Kunststoffen is the property of DVS Media GmbH and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fiber-reinforced plastics (FRP) are widely used in the automotive industry due to their lightweight construction potential. Especially, injection-molded components are very popular because of their short cycle times. Unfortunately, this manufacturing process results in some disadvantages for delayed adhesive bonding. On the one hand, such thermoplastics have a very low surface energy (Polyamide 6 (PA6) 36 mJ/m), on the other hand residues of release agents on the surface hinder adhesion between product and adhesive. These disadvantages have to be overcome by the right surface pre-treatment process. Currently, a solvent-containing process is usually used for this purpose. If necessary, the use of primer is common. In the presented paper, the pre-treatment process of an injection-molded component made of polyamide 6 reinforced with glass short-fibers is presented. First, material-specific properties are measured. The influence of laser pre-treatment at 355 nm and 1064 nm wavelength is investigated. Measurements of surface free energy and surface roughness are conducted. The bonding strength is validated by peel test and tensile shear tests. The shear strength was doubled by laser pre-treatment at a medium energy level, partially cohesive failure of the adhesive was achieved. Both investigated wavelengths led to a great improvement of bonding strength at suitable parameters.

Considering the aerospace sector, the use of adhesively bonded joints is constantly increasing over the last decades. Due to its lightweight and capability of joining various materials with different coefficient of thermal expansion, this joining technique offers many benefits over conventional methods like rivets, screws and welding. On the other hand, structural adhesives consists of polymer chains that can be severely affected by the environment. An example of such an environmental effect is the interaction of the polymer chains of the adhesive with ionizing radiation in space. Nevertheless in the literature, the influence of ionizing radiation on the mechanical properties of epoxides is covered but not well understood. The present work describes a method of determining the stiffness of an adhesively bonded single lap joint (SLJ) using closed form solution equations. This analytical approach is compared with a numerical model. The mechanical properties of the adhesive in both models is degraded due to irradiation, based on experiments conducted by the European Organization for Nuclear Research (CERN). The results show that the degradation of the mechanical properties of the adhesive layer has a significant influence on the joint stiffness. This effect increases with growing adhesive layer thickness. Comparing the results with a finite element model, it is shown that the developed calculation scheme overestimates the stiffness of the SLJ. This is caused by the neglection of bending stresses within the adherends.

Resistance spot welding (RSW) is an economic, robust welding process, which is easy to automate and widely used in automotive industry. In this work, the resistance spot weldability of die-cast aluminum alloys EN AC-AlSi7MnMg, EN AC-AlSi9Mn and EN AC-AlSi10MnMg-T6/T7 to wrought aluminum alloy EN AW-AlSi1MnMg-T6 is investigated when applying the standard welding profile as recommended in VDA 238-401 considering main challenges in welding aluminum die castings, for example, porosity and inhomogenities. Weldability is best for EN AC-AlSi10MnMg-T6/T7, but the results show limited applicability of VDA 238-401 in general, especially for high total sheet thicknesses, because of invalid electrode force favouring spatter formation and weld spot irregularites. Still, all spot welds between die castings and 2 mm wrought aluminum sheets reach the recommended shear tension forces for spot diameter dwof 5·vt (2 mm: 5.95 kN; 3 mm: 8.96 kN; according to DIN EN ISO 18595), although being afflicted with solidification porosity and liquation cracking. Gas porosity is not observed and solidification porosity is only found to be significant for weld spot failure when being located close to the joining level, which is observed at welding depths of approximately 50% into the wrought aluminum sheet. Here, a failure path across the nugget is found. Weld porosity apart from the joining level is less significant and failure path is found along the fusion line between nugget and wrought aluminum. Instead, hardness difference between nugget and HAZ is the main reason for weld spot failure. Although the applied welding current profile is not suited best for RSW of mixed joints between aluminium die castings and wrought aluminium alloys, the results confirm its potential, for example, a significantly reduced gas porosity compared to applied fusion welding processes.

Metal foils are being widely used, from the chemical or electronics sector to household appliances. The joining of these foils by adhesive bonding is often the preferred method due to discolouring and warping under the thermal stresses of other joining methods, such as welding. However, long curing times are a disadvantage of adhesive bonding compared to welding. The use of electromagnetic induction is a promising solution for accelerated curing. This work investigates induction heating for accelerated curing of 1-C epoxy adhesives for bonding of thin nickel foils. Process parameters for rapid curing of the adhesives were determined based on reaction kinetics using differential scanning calorimetry measurements. According to those results peel test specimens were fabricated, and the peel resistance was evaluated using a 90° peel load.

This paper describes the use of resistance projection welding of lap joints between tinned copper terminals with flat aluminum conductors. With the exception of resistance brazing, resistance welding, which has been established for many decades, is currently not used for joining dissimilar metal joints made of copper and aluminum. The use of this technology could potentially result in particularly cost-effective joints that are easily scalable to different sizes of terminals. For the necessary current density during the welding process, a mechanically embossed welding projection in the copper conductor surface is required. During the welding process, the projection moves into the softer aluminum material without being deformed. The projection expresses part of the brittle liquid intermetallic compounds produced. Shear tensile tests, electrical conductivity measurements and micrographs are used to assess the technical properties of the joint. The presented results show that the created intermetallic joint has good electrical and mechanical properties despite pronounced intermetallic AlCu layers.

•Monitoring of ultrasonic metal welding process using industrial measuring equipment.•Sensor fusion and automated data pre-processing.•Random forest based shear strength prediction.•Robust model suitable for different material parameters.

UV-light hardening adhesives provide many advantages as fast curing and good handling compared to PUR-based adhesives. But currently their use is limited as they may only be used if at least one adherent is transparent. The authors proved that the use of UV-light hardening adhesive systems on non-transparent adherents is possible using POF for UV-light initiation in the adhesive gap. Therefore the POF is integrated to the adhesive gap and remains there after curing is completed. The UV light is guided through the POF and initiates the joining process, which may reduce the processing time to below 3 minutes. [ABSTRACT FROM AUTHOR]

Fiber-reinforced plastics (FRP) are increasingly used in modern industry. They offer numerous advantages in comparison to traditional materials. However, they cannot meet all requirements, which is why it is necessary to join FRP to a metallic base structure in most cases. Existing joining techniques cannot fulfill the demands of a fiber-fair joining technique that does not damage the fibers and can transfer applied forces into underlying laminate layers on the one hand but also provides a ductile failure behavior that is detectable with an integrated sensor on the other hand. An innovative, modified arc welding process offers a way to create small-scale pin structures that work as micro shear connectors without damaging the fibers of the composite, but ensure a multi-step failure behavior. This particular failure behavior enables the use of an integrated sensor system, which monitors the joint.

7000 series aluminum alloys have particularly high strength, if compared to other aluminum alloys or even to some high strength steels. Currently, this alloy is considered on the next developments of automotive structures, as an enabler of improved mechanical and safety properties, associated with weight reduction, supporting the industry to fulfill fuel economy and greenhouse gases emissions regulations. Due to the proneness to hot cracking and welding embrittlement, the joining of 7000 series sheets is limited to mechanical methods, such as self-piercing rivets.