Continuous Ultrasonic Welding Research Articles

The Use of Thermal Data for Quality Assurance in the Process of Continuous Ultrasonic Welding of Thermoplastic Composite Materials

Continuous ultrasonic welding (CUW) is a manufacturing process used to join thermoplastic composite materials using high-frequency ultrasonic vibrations. Under pressure and vibration, the welding material heats up, melts and the welding partners are joined while they are cooling down. The development of CUW is getting raised attention over the last decade since the use of thermoplastic composites (TCs) in the production industry and especially the aerospace sector demands for economic and fast joining techniques. In order to establish this welding technique in the industry it is necessary to develop methods which enable to do quality assurance on the produced welding seams. In the experiments described in this paper the potential of thermal measurements for the quality assurance of the ultrasonic welding of TCs is investigated. Different thermal systems are evaluated and it is described how the data of the most promising technique is further processed and fed to an artificial intelligence (AI) algorithm. The here trained networks are created to predict lab-shear-strength values and reach mean absolute error scores of below 1 MPa. The described investigations hint that thermography seem to be a valuable resource to make more reliable quality assurance in the process of CUW of TCs and therefore might help to establish the use of this welding technology further in the industry.

Development of an inline non-destructive monitoring method for ultrasonically welded seams during a continuous joining process

The welding manufacturing process is increasingly being used as an alternative joining method to sewing for functional textiles including for medical and protective wear, high-performance reinforcement textiles for fiber-reinforced plastics, film materials, and smart textiles. Ultrasonic (US) welding technology is a universally applicable cost-effective joining method for thermoplastic membranes. A key issue with the quality of the welded seam is that many of the faults are not visible on the membrane surface. The traditional quality control of the seam cannot be performed because it is done by destructive testing methods. Therefore 100% assurance of compliance of product safety produced at a production scale is not possible. The objective of the study is to develop a nondestructive (NDT) inline testing method for the quality control of welded seams during the continuous ultrasonic welding process. Currently, the quality control of Ultrasonic (US) welded seams is performed based on sample destructive standard tests, where the quality control of complete welded seams is not ensured. The air-coupled US sensors are used to detect imperfections in the welded seam. A variety of membrane materials with base fabric made of polyester and coated with PVC coating were tested during this research. A superimposed type of seam was produced longitudinally by PVC-coated textiles with smooth surfaced anvil wheels and was welded using a welding width of 10 mm. These coated materials were provided by industrial partners and are used in diverse technical textile applications. A process-integrated NDT test method was developed. The imperfections in welded seams were identified during a continuous US welding procedure with the help of air-coupled ultrasonic sensors by developing an inline test method. A prototype to realize inline monitoring during continuous ultrasonic welding was developed and tested. Faults of different widths were artificially produced during welding. The inline monitoring of welded seams with faults was successfully performed and analyzed. The developed process can further pave the way for the development of inline monitoring of welding seams with US sensors for textile membranes joined with a continuous US welding technology.

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.

Uncovering the peel strength performance of multi-layer ultrasonic weld seams in PVC-coated hybrid textiles for weather protection

Ultrasonic welding is a fast and efficient solid-state welding process widely used in various industries. This study focuses on optimizing seam quality and peel strength in multi-layered hybrid textile materials using continuous ultrasonic welding. The influence of welding process parameters (pressure force, power, and speed) on multi-layered peel strength is examined. Three-by-three experimental designs for two and three-layer weld seams with 6 and 12 mm welding widths were developed and applied using superimposed seam type. The impact of varied factors on multi-layered peel strength was analyzed statistically and explored their corresponding tendencies in the relationships. Numerical optimization and analytical models were used to determine parametric levels for achieving desired peel strength. The results show that peel strength is affected by welding parameters, with variations observed based on layer, width, and speed. Increasing speed reduces peel strength, while higher power and pressure force enhance peel strength up to a certain point. However, excessive power and pressure forces can cause material deformation and reduce peel strength. The study also found a strong correlation between power and peel strength, emphasizing the importance of energy input during welding. Power and speed are identified as significant determinants of peel strength, with their combined influence playing a crucial role. The optimal peel strength (34.86 N/12 mm) is achieved at a welding speed of 2.11 m/min, power of 118.18 W, and pressure force of 343.94 N for a three-layer weld seam with a 12 mm welding width. Nonlinear quadratic analytical models are developed to predict multi-layered peel strength, and their results align closely with the actual points. Overall, this research provides valuable insights into optimizing seam quality and peel strength for multi-layered hybrid textile materials, benefiting weather protection applications and advancing bonding techniques in ultrasonic welding.

On the use of a rounded sonotrode for the welding of thermoplastic composites

Continuous ultrasonic welding is an attractive welding technique for thermoplastic composite structures. In this process, a metallic sonotrode connected to a piezoelectric transducer and to a press moves along the parts to be welded applying ultrasonic vibrations and a static welding force on the welding overlap. Thus far, the research carried out on this topic makes use of sonotrodes featuring a flat contact surface with the parts to be welded, which limits the use of the process to the welding of overlaps with no curvature in the welding direction. With the final aim of assessing whether this process can also be applied to curved structures, this paper explores the feasibility of using a rounded sonotrode for continuous ultrasonic welding of thermoplastic composites. The main conclusions drawn from the results obtained in this research is that it is indeed possible to continuously weld thermoplastic composite panels with a rounded sonotrode and that high-quality welds can be obtained from such a process. Furthermore, the use of a rounded sonotrode has the positive effect of lowering the temperatures at the welding interface as well as the temperatures within the adherends. On the other hand, the use of such sonotrode leads to a decreased, although still competitive, welding speed and, potentially, an increased welding force, thereby setting boundary conditions that need to be considered for each specific application.

Investigation of Actual Phenomena and Auxiliary Ultrasonic Welding Parameters on Seam Strength of PVC-Coated Hybrid Textiles

Abstract A study of polyvinylchloride-coated woven polyester fabric welding potential was conducted using continuous ultrasonic welding machines. The effect of cooling air, anvil wheel status, anvil wheel width, material surface contact, and welding gap on seam strength was studied. Three main welding parameters with different levels were selected based on 5 and 10 mm welding widths using old and new anvil wheels with and without cooling air. A lapped type of seam was applied under full factorial design. A microstructure was captured to examine the formation of welding joints, and seam tensile properties were determined. Comparative analysis of comparable welding parameters was analyzed for a gap against pressure and amplitude against power. The actual weld phenomenon was also analyzed based on the recorded machine parameters. The results showed that auxiliary parameters had a significant effect on seam strength. A microscopic image of a welded seam indicated that cooling air reduced the number and size of holes produced. Weld seam with controlled pressure or power provided higher seam strength than that of the controlled gap or amplitude. The actual phenomenon of welding parameters was important to evaluate weld seam quality, whereby the obtained results indicated good quality at lower power and pressure.

Improving the quality of continuous ultrasonically welded thermoplastic composite joints by adding a consolidator to the welding setup

Continuous ultrasonic welding is a promising high-speed and energy-efficient joining technique for thermoplastic composite structures. However, in the current state-of-the-art research on the topic numerous deconsolidation voids could be identified at the welding interface, which results in a strength knock-down. The aim of this study is, therefore, to improve the quality of continuous ultrasonically welded joints by adding a consolidation shoe to the welding setup. To determine the required consolidation pressure, the size of the shoe, and its distance from the sonotrode a stepwise approach was followed based on the static ultrasonic welding process. The closest consolidation distance, best representing the static welding conditions, did not improve the weld quality as significant porosity was still found in the weld line and in the adherends. However, for the furthest consolidation distance high-quality continuous welds were obtained with almost no porosity and a high strength.

Effect of ultrasonic welding process parameters on seam strength of PVC-coated hybrid textiles for weather protection

Using a lapped seam, PVC-coated hybrid textiles with uniform thickness were bonded by continuous ultrasonic welding and conventional joining method with the help of hot air tape welding technique for weather protection purposes. Three fundamental sewing parameters at two distinct levels and three primary welding parameters at three levels based on 6 and 12 mm welding widths were used. To consider the effect of welding and sewing parameters on seam strength, full factorial designs of experiments were designed, fabricated, and tested. The thermal behavior and possibility of chemical conversion in the welding zone under the influence of ultrasonic vibrations were examined. Variation in width of heat-affected zone of weld seam was measured. The seam strength of ultrasonic weld seam compared with that of conventional seams, and superior seam strength yielding parametric levels were assessed. The parametric influence of both joining techniques on seam quality and their tendencies in the relationship were analyzed statistically. The weld seam strength (1256.392 and 2116.93 N/50 mm) was optimized numerically and identified its trend with the variation of the weld seam. The discovered relationship led to the conclusion that the variation in the weld seam can be used to estimate the tensile strength of the weld seam through the developed effective numerical model as a non-destructive testing method, and its outcome was successful as a destructive testing method. The result shows that the ultrasonic weld seam provided a higher tensile strength ( > 75%) than the conventional seam for both evaluated welding widths and obtained statistically significant results.

A Study on Through-the-Thickness Heating in Continuous Ultrasonic Welding of Thermoplastic Composites.

Continuous ultrasonic welding is a promising technique for joining thermoplastic composites structures together. The aim of this study was to gain further insight into what causes higher through-the-thickness heating in continuous ultrasonic welding of thermoplastic composites as compared to the static process. Thermocouples were used to measure temperature evolutions at the welding interface and within the adherends. To understand the mechanisms causing the observed temperature behaviours, the results were compared to temperature measurements from an equivalent static welding process and to the predictions from a simplified heat transfer model. Despite the significantly higher temperatures measured at the welding interface for the continuous process, viscoelastic bulk heat generation and not thermal conduction from the interface was identified as the main cause of higher through-the-thickness heating in the top adherend. Interestingly the top adherend seemed to absorb most of the vibrational energy in the continuous process as opposed to a more balanced energy share between the top and bottom adherend in the static process. Finally, the higher temperatures at the welding interface in continuous ultrasonic welding were attributed to pre-heating of the energy director due to the vibrations being transmitted downstream of the sonotrode, to reduced squeeze-flow of energy director due to the larger adherend size, and to heat flux originating downstream as the welding process continues.

Sonotrodes for Ultrasonic Welding of Titanium/CFRP-Joints—Materials Selection and Design

Ultrasonic welding of titanium alloy Ti6Al4V to carbon fibre reinforced polymer (CFRP) at 20 kHz frequency requires suitable welding tools, so called sonotrodes. The basic function of ultrasonic welding sonotrodes is to oscillate with displacement amplitudes typically up to 50 µm at frequencies close to the eigenfrequency of the oscillation unit. Material properties, the geometry of the sonotrode, and the sonotrode tip topography together determine the longevity of the sonotrode. Durable sonotrodes for ultrasonic welding of high-strength joining partners, e.g., titanium alloys, have not been investigated so far. In this paper, finite element simulations were used to establish a suitable design assuring the oscillation of a longitudinal eigenmode at the operation frequency of the welding machine and to calculate local mechanical stresses. The primary aim of this work is to design a sonotrode that can be used to join high-strength materials such as Ti6Al4V by ultrasonic welding considering the longevity of the welding tools and high-strength joints. Material, sonotrode geometry, and sonotrode tip topography were designed and investigated experimentally to identify the most promising sonotrode design for continuous ultrasonic welding of Ti6AlV4 and CFRP. Eigenfrequency and modal shape were measured in order to examine the reliability of the calculations and to compare the performance of all investigated sonotrodes.

Quality Prediction of Continuous Ultrasonic Welded Seams of High-Performance Thermoplastic Composites by means of Artificial Intelligence

Thermoplastic composites (TCs) are a famous choice when it comes to high performance designs for industrial applications. Since the growing demand on the use of this material, it is important to be able to evaluate suitable processing technologies. One of those technologies is continuous ultrasonic welding (CUSW) which creates continuous joints, also called seams, between two or more TCs parts. In CUSW mechanical oscillations are applied to the material and result in melting and connecting of the welding parts.The approach to predict joint strength (qualities) of continuous ultrasonic welded TCs by training different neural networks is investigated in this study. Quality class prediction around 72 % accuracy is achieved with a fully connected neural network. Concluding, quality prediction of welded TCs with the help of artificial intelligence seems to be a suitable approach for quality observation but more research could lead to more reliable neural networks for industrial applications.

On differences and similarities between static and continuous ultrasonic welding of thermoplastic composites

Continuous ultrasonic welding is a promising high-speed and energy-efficient joining method for thermoplastic composite structures. Our aim was to identify and understand differences between the static and continuous ultrasonic welding process for thermoplastic composites. In particular, melting of the interface, consumed power and energy density, temperature evolution at the weld interface, and optimum welding conditions for both types of processes were investigated. This was done for three combinations of welding force and vibrational amplitude, parameters which are known to have a significant effect in both welding processes. Our results showed that for the continuous process the amount of non-welded area under the sonotrode remains constant, while for the static process the amount of non-welded area gradually decreases to zero. Additionally, the optimum vibration times and welding speeds in both processes are similar.

Effects of Different Roller Profiles on the Microstructure and Peel Strength of the Ultrasonic Welding Joints of Nonwoven Fabrics

Nonwoven fabrics are widely used in the textile manufacturing industry due to their advanced characteristics, such as their soft, water-repellent, recycle, ecological, and resilient functions. Nowadays, one of the innovated technologies applied to bond nonwoven fabrics is the ultrasonic welding method, due to the advantages afforded by its clean, fast, and reliable approach. In this work, isotactic polypropylene (PP) nonwoven fabrics were bonded by a continuous ultrasonic welding process. In order to consider the influence of the roller on the formation of welding joints and their mechanical properties, different roller profiles were designed, fabricated, and tested. Eight types of roller profiles corresponding to No. 1–No. 8 in the experiments were divided into four groups. After bonding, the microstructure in a typical case (i.e., No. 1) was captured by scanning electron microscopy (SEM) to examine the formation of the welding joints. Additionally, the load and the peel strength of the welding joints of all eight roller profiles were analyzed. The results showed that no welding defects, such as cracks or blowholes, were visible in the melted zone. The load depended on the area ratio(s) of the welding area (S0) to the cycling area (S1). Furthermore, it was found out that the peel strength of the welding joints with brick structures were higher than the peel strength in the case of solid line structures.

Continuous ultrasonic welding of thermoplastic composites: Enhancing the weld uniformity by changing the energy director

Continuous ultrasonic welding is a high-speed joining method for thermoplastic composites. Currently, a thin film energy director is used to focus the heat generation at the interface. However, areas of intact energy director remain in the welded seam, which significantly lowers the weld strength, and result in a non-uniformly welded seam. To improve the weld uniformity of continuous ultrasonically welded joints, we changed to a more compliant energy director. A woven polymer mesh energy director was found to give a significant improvement in weld quality. The mesh was flattened in between the composite adherends during the welding process. This flattening promoted a good contact between the energy director and the adherends, fully wetting the adherend surfaces, resulting in a more uniformly welded seam without areas of intact energy director.

Zero-flow: a novel approach to continuous ultrasonic welding of CF/PPS thermoplastic composite plates

Continuous ultrasonic welding of plastic films, fabrics, and even thermoplastic composite prepreg tape is a common industrial practice. However, continuous ultrasonic welding of stiff thermoplastic composite plates is challenging due to squeeze flow of resin at the welding interface, and significant local deformation of the welding stack, that are generally needed to achieve strong welds. This paper presents a novel approach to continuous ultrasonic welding of thermoplastic composite plates based on zero-flow welding. The proposed technique can create strong welds before any squeeze flow takes place at the interface. It is enabled by the use of very thin flat energy directors, owing to simultaneous melting of both energy director and adherends’ matrix. The results prove the feasibility and indicate the potential for high-strength welds between thermoplastic composite plates at very high speed.

Research on the seam performance of waterproof clothing based on continuous ultrasonic welding technology

Purpose An improved waterproof seam production technology (ultrasonic welding-thermo adhesive tape sealing (USW-TATS)) was developed in this study. The technology will improve the waterproof performance of seam which has problem resulted from needle holes and thread like seam leaking and excess shrinkage. Design/methodology/approach Threadless seams were produced by ultrasonic welding (USW) with coated and lamination fabric to replace the traditional sewing process in Sewing-thermo adhesive tape sealing (S-TATS). The process efficiency was evaluated by Methods-Time Measurement (MTM). Seam performance including hydrostatic pressure, shrinkage and tear force was compared among three technologies (USW, USW-TATS and S-TATS). The effect of ultrasonic welding parameters (amplitude, roller pressure and roller speed) on the USW-TATS seam performance was investigated.SEM analysis was carried out to examine the condition and morphology of the joints cross section. Findings It was found that waterproof performance and dimensional stability of USW-TATS seam were superior to that of S-TATS seam. Tear force and hydrostatic pressure increased firstly and then decreased with the increasing of USW parameters in UAW-TATS process. Binary regression relationships were found between the USW parameters and tear force or hydrostatic pressure. Shrinkage decreased with the increasing of roller pressure and speed. Practical implications Research results can be applied to predict seam performance of waterproof clothing, reduce equipment parameters setting time and enhance product quality in industry. Originality/value A threadless production technology (USW-TATS) was proposed to improve waterproof performance and dimensional stability of outdoor clothing seams.

Thermal modeling during continuous ultrasonic welding

In this study, a thermal model during continuous ultrasonic welding of thin foils has been developed. The heat generation during the process, stick/slip state, and effect of elastic/plastic strains are included in the formulation. The physics is simplified to a one-dimensional transient heat transfer analysis, the governing equation is nondimensionalized, and important parameters are identified. A fourth-order Runge--Kutta numerical scheme is used to predict the transient temperature as a function of material, constitutive, and process parameters. Comparison with experimental results is provided to justify the assumptions introduced in the model. Different heat generation terms are introduced and their contribution to overall heat generation is presented.