Ultrasonic welding is increasingly used to join PVC-coated polyester fabrics in membrane structures where seam reliability is critical, particularly under cold-service conditions. This study systematically investigates the effects of welding pressure (0.5,1.5 and 2.5bar), coating thickness (0.6 and 0.8mm), seam margin (6 and 12mm), and temperature (20°C and - 20°C) on the mechanical performance and failure behavior of continuously ultrasonically welded seams. A full-factorial experimental design was employed, and seam strength (N/5cm), extension at failure, work of rupture, and seam efficiency were evaluated using load-extension analysis. Increasing welding pressure from 0.5 to 2.5bar produced a 2.5-5 fold increase in seam strength and substantially enhanced energy absorption. Increasing thickness from 0.6 to 0.8mm improved seam strength. Furthermore, at a pressure of 2.5bar, increasing the seam margin from 6 to 12mm raised the seam strength from 546.0 to 1190.4. At - 20°C, seams exhibited higher strength but reduced ductility, reflecting a stiffer and more brittle response. Fractographic analysis revealed a transition from predominantly adhesive failure at low pressure to cohesive failure at 2.5bar, consistent with improved interfacial fusion. FTIR and EDS analyses confirmed that ultrasonic welding primarily induced morphological rather than major chemical changes. Regression-based predictive models were developed and validated, demonstrating reliable strength prediction under independent processing conditions. The results provide quantitative guidance for optimizing ultrasonic welding parameters to ensure durable seam performance in PVC-coated textile structures operating under both ambient and subzero environments.

• Developed a surface-quality-based framework for assessing ultrasonic torsional welds of Al–Cu joints. • Integrated 3D surface topography, microhardness mapping, and microstructural analysis for weld evaluation. • Employed torque-controlled ultrasonic welding to precisely regulate energy input and bond formation. • Established direct correlation between surface morphology, interfacial integrity, and mechanical strength (2481 N) • Introduced a predictive, non-destructive method enabling early detection of weak zones and reliable process optimization. Reliable joining of aluminum and copper is a major challenge for creating efficient and lightweight electrical systems in cars and other new energy vehicles. This study investigates a high-tech solution using an ultrasonic torsional welding machine with precise torque control to carefully manage the joining energy. This study presents an integrated framework for assessing and predicting the quality of aluminum-copper (Al-Cu) dissimilar joints produced by an advanced torque-controlled ultrasonic torsional welding (USTW) system. We introduce the combined use of high-resolution 3D surface topography and microstructural analysis as a powerful, non-destructive method for evaluating weld integrity. The precision torque-control mechanism enabled the detailed study of how controlled energy input manifests at welded interface. Our results successfully establish a direct correlation amid specific surface topography signatures such as defined roughness parameters (Ra, Rz, Rp, Rv, Rq) and 3D volumetric uniformity. Microhardness mapping revealed a consistent and intense work-hardened bond line (peak ∼ 155 HV), confirming robust solid-state bonding. Energy-dispersive spectroscopy (EDS) verified the process efficacy in creating a clean and contaminant-free interface. Crucially, we demonstrate that by quantifying surface heterogeneity, potential weak zones can be identified before mechanical failure. Good welds showed fine-grained metal grains but poor welds showed cracks, spattered metal dots and trapped oxides during SEM analysis. During the tensile test, the strongest sample withstood 2481 N when we pulled the joints apart but the most flexible one stretched longer.

To evaluate the effectiveness of an ultrasonic welding (USW)-assisted thermoplastic obturation technique for improving root canal sealing, void reduction, and lateral canal penetration. A three-phase experimental approach was employed: (1) Customized gutta-percha points were developed, optimized to incorporate ultrasonic-responsive thermoplastic obturation cores; (2) in vitro testing was conducted using micro-computed tomography (CT) and infrared thermometry to assess lateral canal flow and thermal safety, respectively; and (3) an ultrasonic generator (28+ kHz), booster, and sonotrode were used to generate the heat required for obturation. Compared with traditional methods, the USW technique demonstrated a mean void reduction of 62% (95% CI: 58%-66%, p < 0.001), significant lateral canal penetration, and maintained temperatures safely below 45°C. No microfractures were observed in the treated teeth. The USW-assisted obturation technique facilitates and enhances root canal obturation, reduces voids, and maintains tooth structural integrity through precise energy application combined with improved flow mechanics.

Insights into microstructure evolution and interface joining mechanism in ultrasonic spot welding of Cu/Ti-6Al-4V dissimilar joints

The utilisation of composite materials has the potential to play a vital role in the development of lightweight structures for future generations of aircraft, with the objective to reduce emissions. Ultrasonic welding is a process that has been proven to exhibit advantageous qualities, including the capacity to achieve welds with a comparatively short process time. Furthermore, its capacity to function as both a static and a continuous process makes it a viable candidate for facilitating the realisation of this objective. The present study investigates the potential of a novel explicit modelling approach for the static ultrasonic welding process to more accurately represent the welding process by incorporating a more precise representation of the hammering effect. The hammering effect describes the partial loss of contact between the sonotrode and the upper adherend. The model's validation was achieved through a multifaceted approach that incorporates high-speed camera recording, encompassing digital image correlation, laser displacement sensor measurements, and static ultrasonic welding experiments. These experiments encompassed varying welding times, followed by fracture surface analysis. The findings showed that an explicit time-domain model can effectively represent the static welding process of unidirectional materials utilising a film energy director. The experimental validation demonstrated a high degree of correlation between the thermal behaviour of the welding interface and the simulation results. The study demonstrated that the neutral position of the sonotrode exhibited an increase during the initial phase of the welding process due to dynamic stresses. This phenomenon enables reduced constraint movement of the adherends and the energy director, which results in the disconnection of the sonotrode from both the upper adherend and the energy director, as well as the adherends and the anvil. The higher neutral position of the sonotrode was then implemented in an explicit simulation of the static ultrasonic welding process.

Carbon fiber-reinforced thermoplastic (CFRTP) composites are now widely used in many fields. Ultrasonic welding (UW) is a key technology for joining these materials. The control mode of UW has a great effect on the quality of the welded joints. However, there is still not enough research comparing the different welding control modes. This paper investigates the effects of the time control, energy control, and displacement control modes on the ultrasonic welding quality of carbon fiber-reinforced polycarbonate (CF/PC). A flat PC film is used as the energy director (ED). The evaluation focuses on the lap-shear strength (LSS), macro- and micro-morphology, fracture surface characteristics and power-displacement curves of the welding process. Furthermore, significant differences are observed in the temperature field evolution and joint failure modes across the different control modes and process parameters. Results indicate that the displacement control mode achieves the highest joint quality and process stability, yielding a maximum LSS of 30.6 MPa. A correlation analysis reveals that the displacement-energy relationship exhibits the strongest coupling, and the Pearson correlation coefficient r is 0.896.

Solid‐state batteries (SSBs) are widely regarded as promising next‐generation energy storage technology due to their potential for enhanced safety and higher energy density compared to conventional Li‐ion batteries. Among the various oxide solid electrolytes, garnet Li 7 La 3 Zr 2 O 12 (LLZO) is considered one of the most promising, yet the Li–LLZO solid–solid interface remains a major bottleneck. Both LLZO and the relatively stiff Li metal anode rapidly accumulate Li 2 CO 3 surface impurities and form limited contact, leading to large interfacial resistance. Here, we demonstrate that ultrasonic welding (USW) provides a rapid, mechanically driven route to establish intimate Li–LLZO contact within seconds. A preliminary ambient‐air experiment confirms the basic feasibility of the technique, while all controlled welding experiments performed in Ar yield Li/LLZO interfaces with resistances on the order of several hundred Ω cm 2 . Systematic comparison of pyramidal and flat horn geometries reveals that uniform pressure delivery is essential for stable interfacial formation, with the flat horn reducing the resistance to approximately 225 Ω cm 2 . Furthermore, introducing a sputtered Au interlayer significantly enhances mechanical conformity and wetting by compensating LLZO surface roughness and enabling Li to more effectively accommodate LLZO surface asperities. As a result, the interfacial resistance decreases to as low as 1.5 Ω cm 2 , among the lowest values reported for garnet–Li interfaces processed at room temperature. This study demonstrates USW as an effective mechanical strategy for constructing low‐resistance Li–garnet interfaces suitable for next‐generation SSBs.

Mechanistic role of a Cu interlayer in dissimilar ultrasonic welding of Ti to low-carbon steel

Towards robust ultrasonic welding of CF/PEEK composite to aluminum hybrid joints

Enhancement of ultrasonic welding of CFRTP by introducing in-situ laser-etched groove-type energy directors and structural parameter design based on energy absorption theory

The lack of reliable low-temperature joining solutions has hindered the application of SiC particle-reinforced aluminum matrix composites (SiCp/Al MMCs) in advanced packaging, such as for thermoelectric systems. This study investigates a low-temperature joining approach using a Sn-Ag-Cu-Ti filler metal assisted by ultrasound. Microstructural and thermodynamic analyses reveal a novel matrix-dissolution-dominated interfacial mechanism, distinct from conventional active soldering. Contrary to expectations, Ti does not participate directly in the interfacial reactions; instead, it plays a critical role in facilitating solder adhesion to the base material and assisting in subsequent removal of surface oxides, thus enabling pronounced dissolution of the aluminum matrix under the assistance of ultrasound. The liberated Al and Mg atoms form nanoscale amorphous reaction layers (Al 2 O 3 and MgAl 2 O 4 ) at the SiC interface, while a separate Al 2 O 3 /Ag 2 Al structure forms at the Al interface. Driven by this unique bonding mechanism, the joints achieve a remarkable shear strength of approximately 56 MPa, where failure propagates through the solder, demonstrating superior interfacial integrity. This work elucidates a novel interfacial reaction pathway and provides a viable strategy for the low-temperature integration of metal-ceramic composites in thermal management applications.

This study investigates the joint characteristics of a 60-layered copper foil stack using linear vibration ultrasonic welding for lithium-ion pouch cell applications. With increasing demand for high-capacity electric vehicle batteries, ensuring the reliability of multilayer electrode joints is essential. Experiments were conducted by varying vibrational amplitude, welding time, and clamping pressure. Weld quality was analyzed based on indentation profiles, joint strength, and failure modes. Results revealed that optimal welding energy (500-900 J) produced well-formed joints without surface cracks or tearing. Excessive welding energy (>900 J) led to material thinning and interfacial failure. The maximum T-peel peak load of 138.7 N was obtained at the 30th joining interface under 25 µm amplitude, 0.8 s welding time, and 1.5 bar clamping pressure. Interface-dependent optimum conditions were observed, reflecting thickness-direction variations in deformation and bonding within the 60-layer stack. Indentation length and depth correlated linearly with welding energy. Failure modes transitioned from no adhesion to tearing and button-pull types. The findings provide guidelines for optimizing welding parameters for high-quality multilayer foil joints in battery manufacturing.

This study presents a comparative analysis of cylindrical lithium-ion cell architectures, tracing the evolution from the conventional tabbed design (18650/21700) to the large-format 4680 cell with its tabless current collectors. This architectural shift is driven by the imperative to minimise internal ohmic resistance and enhance thermal management in high-power automotive battery applications. Forensic investigation reveals that the 4680 design replaces localised, high-resistance tab connections with a distributed, low-impedance interface, necessitating the adoption of advanced manufacturing techniques, including long ultrasonic torsional welding and highly controlled high-power density laser welding. Crucially, the welding of external aluminium busbars to the cell relies on sophisticated microstructural engineering, particularly for the challenging dissimilar Aluminium-Steel (Al-Steel) anode weld. This weld format employs a spiral laser path to limit the formation of brittle aluminium-iron (Al-Fe) intermetallic compounds (IMCs), leveraging the steel cell casing’s nickel plating to promote a more ductile Al-Fe-Ni phase for improved joint reliability. Furthermore, the 4680 cell incorporates a significantly thicker casing (≈0.54 to 0.7 mm) for enhanced mechanical strength. In conclusion, the 4680 cell achieves superior performance through robust mechanical design and advanced welding processes that prioritise microstructurally sound, low-resistance interfaces.

This study investigates the development of advanced protective gloves by applying novel 3D-printed PET-G mesh overlay structures onto three textile substrates-polyamide (PA), polyester (PES), and cotton-using ultrasonic welding and contact welding. The focus was on assessing weld quality, thickness uniformity, and functional durability. Weld morphology and bonding integrity were evaluated using X-ray microtomography (micro-CT), while bending fatigue tests assessed mechanical performance under cyclic loading. The results show that ultrasonic welding produces more uniform welds, enhancing fatigue resistance, particularly on cotton and polyamide substrates. Non-uniform welds with thicker or uneven areas, typical of contact welding, correlated with reduced mechanical durability. These findings highlight the potential of additively manufactured overlay structures for hybrid protective gloves, demonstrating that weld thickness uniformity and substrate compatibility are key factors in optimizing mechanical performance. This work extends our previous research by introducing new 3D-printed overlay architectures and provides valuable insights into the practical implementation of additively manufactured polymeric structures in PPE development.

Unveiling the impact of ultrasonic frequency pulse current assisted-MIG welding on the microstructure, mechanical properties, and corrosion behavior of 316L stainless steel

Ultrasonic Welding of Multi-layer PET-Al Composite Current Collector and Al Tab: Joining Mechanism and Resistance Analysis

Sequential ultrasonic spot welding is an interesting joining method for overlapping thermoplastic composite structures. In the framework of the EU Clean Aviation Multi-functional Fuselage Demonstrator (MFFD) and the lower shell SmarT multifunctional and INteGrated TP fuselage (STUNNING) projects, SAM XL and TU Delft Aerospace Engineering collaboratively developed and demonstrated a robot-based sequential ultrasonic spot welding process for the sub-assembly of structural frames and clips in a fuselage section demonstrator. This full-scale thermoplastic composite fuselage section demonstrator, which was recently awarded the 2025 JEC Innovation award, measures 8.0 m in length and 4.0 m in diameter. Our robot-based sequential ultrasonic spot welding technology played an important role in ensuring the joining of structural clips and frames in the stiffened fuselage skin of the demonstrator, through the use of more than 1600 spot welded joints with an average welding time of approximately 10 s per spot, thereby significantly reducing cycle times as compared to traditional joining methods such as fastening or riveting. This paper provides a comprehensive overview of the technology development process and highlights the results achieved during the sub-assembly of the demonstrator, as well as the challenges encountered.

Sensor and feature selection for cost- and time-efficient online monitoring of ultrasonic metal welding

Investigation of the weldability of 3D printed dissimilar materials (PLA Plus and PLA CF) using ultrasonic assisted friction stir spot welding

Additive manufacturing and ultrasonic welding enabled repair of carbon fiber reinforced thermoplastic polymers: Towards in-situ restoration of mechanical and functional properties