Ultrasonic Spot Welding Process Research Articles

Correlation of surface and interfacial temperature during differential ultrasonic spot welding

Ultrasonic spot welding (USW) has become an attractive joining method for thermoplastic polymers (TP) and thermoplastic matrix composites (TPMC). In the USW process, the material to be joined is subjected to mechanical vibrations of high frequency, causing intermolecular and surface friction which heat and melt the material at the joint interface. The interface resolidifies, resulting in a joint between two materials. In USW, it is necessary to focus the mechanical vibrations at the required weld location. A common method to accomplish this is to incorporate an energy director (ED) at the interface between materials to melt preferentially. However, incorporating EDs complicates the manufacturing process, particularly for large constant thickness polymer sheets. In this work, differential ultrasonic spot welding (DUS) is used which employs a flat horn and anvil of different diameters to initiate frictional heating between laminates at the desired joint location. This work investigates the effectiveness of DUS compared to a more traditional USW setup. Additionally, by measuring temperature at both the surface and the interface during DUS using infrared imaging and a thermocouple (TC), respectively, the driving factors behind the thermal profile of the welding process are examined. The goal of coupling the thermal profile to physical attributes of the DUS process is to eventually determine if variability present in the thermal profile may be tied to well-known joint area and strength variabilities.

Prediction of Weld Strength in Power Ultrasonic Spot Welding Process Using Artificial Neural Network (ANN) and Back Propagation method

In this presented work, an Artificial Neural Network (ANN) connected with the backpropagation method was employed to predict the strength of joining materials that were carried out by using an ultrasonic spot welding process. The models created in this study were investigated, and their process parameters were analyzed. These parameters were classified and set as input variables like applying pressure, time of duration weld and trigger of vibrating amplitude. In contrast, the weld strength of joining dissimilar materials (Al-Cu) is set as output parameters. The identification from the process parameters is obtained using several experiments and finite element analyses based on prediction. The results of actual and numerical are accurate and reliable; however, their complexity has a significant effect due to being sensitivity to the condition variation of welding processes. Therefore, an efficient technique like an artificial neural network coupled with the backpropagation method is required to use the experiments as input data in the simulation of the ultrasonic welding process, finding the adequacy of the modeling process in the prediction of weld strength and to confirm the performance of using mathematical methods. The results of the selecting non-linear models show a noticeable potency when using ANN with a backpropagation method in providing high accuracy compared with other results obtained by conventional models.

Prediction of Weld Strength in Power Ultrasonic Spot Welding Process Using Artificial Neural Network (ANN) and Back Propagation Method

In this presented work, the employment of artificial neural network (ANN) connected with back propagation method was performed to predict the strength of joining materials that carried out by using ultrasonic spot welding process. The models which created in this study were investigated and their process parameters were analysed. These parameters were classified and set as input variables like for example applying pressure, time of duration weld and trigger of vibrating amplitude while weld strength of joining dissimilar materials (Al-Cu) is set as output parameters. The identification from the process parameters are obtained using number of experiments and finite element analyses based prediction. The results of actual and numerical are accurate and reliability, however its complexity has significant effect due to sensitive to the condition variation of welding processes. Therefore, the needed for an efficient technique like artificial neural network coupled with back propagation method is required to use the experiments as an input data in simulation of ultrasonic welding process, finding the adequacy of modeling process in prediction of weld strength and to confirm the performance of using mathematical methods. The results of the selecting non-linear models show a noticeable potency when using ANN with back propagation method in providing high accuracy compared with other results obtained by conventional models.

Prediction of the Interface Deformation of Ultrasonic Spot Welding of Multilayer Metal Foils Considering Energy Gradient

Abstract The ultrasonic spot welding (USW) is widely used in the joining of multilayer Cu or Al tabs in the lithium-ion battery. Due to the high-frequency vibration of the sonotrode and various deformation in each interface, the friction behavior is complex which makes it difficult to simulate the welding process of multilayer specimens. In this paper, an efficient and accurate finite element model (FEM) was proposed via introducing the interface heat flux to equivalent the heat generation by the friction. The total heat flux was determined by the heat transfer analysis and the proportion of each interface was determined based on the analysis of the friction behavior. Then, the FEM was validated by comparing the simulated temperature and deformation with experimental results. Finally, the FEM was applied to simulate the USW process of four, five, and ten layers of copper and aluminum foils in order to characterize the gradient of the ultrasonic energy. It was found that the heat generation concentrated in middle interfaces was 65% of the total in the welding of four-layer copper foils. The heat generation was mainly related to the welding parameters and the proportion was related to the size of tips and the structure of specimens. The plastic strain varied in specimens because of the gradient of the input energy. It was most obvious in the welding of 10-layer aluminum foils that the maximum equivalent plastic strain (PEEQ) in the fifth interface was 92.9% smaller than the top interface.

Mechanical and Microstructural Characterization of Ultrasonic Welded NiTiCu Shape Memory Alloy Wires to Silver-Coated Copper Ferrules

The aim of this study was to investigate the mechanical behavior, and the microstructure of NiTiCu shape memory alloy wires joined with silver-coated copper ferrules via ultrasonic spot welding. Therefore, the electrical resistance was measured during tensile testing, and the joints were analyzed by scanning electron microscopy. Energy-dispersive X-ray spectroscopy has determined the compounds of the developed welding zones. Furthermore, the influence of the ultrasonic welding on the transition temperatures of the NiTiCu wires was examined via differential scanning calorimetry. Tensile tests have shown that the ultimate tensile strengths of the joints reached almost 100% of that of the base material. An additional heat treatment rebuilt the typical shape memory alloy behavior after the ultrasonic welding process detwinned the martensitic wires. In addition, the B19′ structure of the welding zone and the ultrasonic spot-welding process did not affect the transition temperatures of the shape memory alloy.

A study on thermo-mechanical analysis of ultrasonically welded dissimilar alloys for automotive application

Abstract Ultrasonic spot welding (USW) method has the capability to produce highly efficient solid-state bonds in lightweight alloys with minimum power consumption. Unlike fusion welding techniques, this technique utilizes less energy and produces superb joint quality with refined grain structures and minimal intermetallic compounds (IMCs). This method has been receiving attention progressively in the material joining field because of its advantages like environmentally friendly, shorter weld time, and involvement of low temperature. Thus, these properties make this process suitable for welding of malleable thin metal sheets. During the USW process, it is noticed that the effect of intensive material contact increases when the weld progresses, and it leads to the frictional heating and plastic deformation phenomena. Subsequently, it results in the change of mechanical and microstructural characteristics at the weld zone. To reduce the forming load and static stress distribution from the welded samples, it is necessary to analyze the thermo-mechanical properties of ultrasonically welded joints. In the current study, various aspects of ultrasonic energy on material deformation and temperature variations are investigated using the finite element analysis (FEA). As a result, several types of features are noticed in the weld region with different forming morphologies. To further explore the effect of weld process parameters on the weld interface of this dynamic process, the strength and fracture in USW are also studied.

Microstructure and Mechanical Properties of an Ultrasonic Spot-Welded Aluminum-to-Aluminum Joint: Response to Interlayer Thickness.

To enhance the mechanical strength of an ultrasonic spot-welded Al/Al joint, an Al 2219 particle interlayer was placed between the two Al sheets during the ultrasonic spot welding process. The effects of the interlayer thickness on the microstructure and mechanical performances of the joints were systematically investigated. The results showed that, the optimum thickness of the Al 2219 particle interlayer was 10 μm, which was beneficial to enhance the weld interface temperature up to 402 °C. The bonding interface of Al/Al 2219 with a wave-like shape was sound, and no significant diffusion layer occurred. The peak lap shear tensile strength (~84.8 MPa) was obtained, which was 36% higher than that (~67.3 MPa) for the joint without the Al 2219 particle interlayer. The strengthening mechanism is caused by the increase of plastic deformation and contact areas in the weld interface.

A Control Method for the Ultrasonic Spot Welding of Fiber-Reinforced Thermoplastic Laminates through the Weld-Power Time Derivative

It was found that the ultrasonic spot welding may serve as an efficient method to join relative large thin-walled parts made of fiber-reinforced thermoplastics. In this study, a new control method for the ultrasonic spot-welding process was investigated. It was found that, when welding fiber-reinforced thermoplastic laminates without energy directors, overheating and decomposition of the polymer at the weld spot occurred. The occurrence of the overheating took place at unpredictable times during welding. It was observed that the time trace of the consumed power curve by the welder follows a similar pattern as the time trace of the temperature in the weld spot center. Based on this observation, a control system was developed. The time derivative of the welder power was monitored in real time and, as soon as it exceeded a critical value, the ultrasonic vibration amplitude was actively adjusted through a microcontroller. The controlling of the ultrasonic welding process forced the temperature in the weld spot to remain in an adequate range throughout the welding duration for the polymer diffusion to occur. The results of the controlled welding process were evaluated by means of weld temperature measurements, computed tomography scans, and microscopic analysis of the weld spot fracture surfaces.

Microstructural Characterization and Mechanical Behavior of NiTi Shape Memory Alloys Ultrasonic Joints Using Cu Interlayer.

NiTi shape memory alloys (SMAs) are a class of functional materials which can be significantly deformed and recover their original shape via a reversible martensitic phase transformation. Developing effective joining techniques can expand the application of SMAs in the medical and engineering fields. In this study, ultrasonic spot welding (USW), a solid-state joining technique, was used to join NiTi sheets using a Cu interlayer in between the two joining sheets. The influence of USW process on the microstructural characteristics and mechanical behavior of the NiTi joints was investigated. Compared with conventional fusion welding techniques, no intermetallic compounds formed in the joints, which is extreme importance for this particular class of alloys. The joining mechanisms involve a combination of shear plastic deformation, mechanical interlocking and formation of micro-welds. A better bonding interface was obtained with higher welding energy levels, which contributed to a higher tensile load. An interfacial fracture mode occurred and the fracture surfaces exhibited both brittle and ductile-like characteristics with the existence of tear ridges and dimples. The fracture initiated at the weak region of the joint border and then propagated through it, leading to tearing of Cu foil at the fracture interface.

Dynamic recovery and recrystallization mechanisms during ultrasonic spot welding of Al-Cu-Mg alloy

The 2024-T3 Al alloy substrate and 2014-O Al alloy sheet have been well welded by ultrasonic spot welding (USW). Microstructure and texture of the original and welded samples have also been investigated via scanning electron microscope (SEM), Electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The results show that dynamic recovery (DRV) formed lamellar structure with shear texture of {111} 〈110〉 and Rotated Cube {001} 〈110〉 components in the sheet of the welded sample, while dynamic recrystallization (DRX) developed heterogeneous fine/ultrafine equiaxed grains with a sharp recrystallization texture {311} 〈136〉 component in the interface zone of the welded sample. Furthermore, we systematically explored the DRV and DRX mechanisms controlling microstructure and texture evolution during the USW process. We also observed and discussed the fragmentation and dissolution of the Al-Cu-Mg alloys precipitates during the USW process.

Analysis of interface solid-state reaction on dissimilar ultrasonic spot welding of Al-Mg alloys

The solid-state joining nature of the ultrasonic spot welding (USW) process has been proven useful in the fields where joining applications involve dissimilar lightweight materials. This study focused on the USW of challenging dissimilar aluminum (Al)-magnesium (Mg) alloys to gain a better understanding of the dominant factors of joint performance with particular emphasis on proper lap-joint positioning. Weld qualities of dissimilar ultrasonic spot welds, classified through a series of experiments, were determined. Process parameters effects, such as failure load and fracture morphologies, showed distinctions between two dissimilar welds based on lap-joint position. Characteristic distinctions between welding process parameters and material combinations (lap-positioning) were found. Incomplete deformation zones were found during USW of Mg/Al combination, yet they were noticeable and almost the same size as the horn diameter. It can be found that proper lap-positioning of the top part of the specimen is important for efficient utilization of the USW process.

Weldability assessment of Mg alloy (AZ31B) sheets by an ultrasonic spot welding method

A series of ultrasonic spot welding experiments with similar Mg alloy (AZ31B) were performed to determine the process parameters and their effect on weld quality, including weld strength and fracture morphologies. Two dominant welding parameters including vibration amplitude and welding time were evaluated independently to obtain good weld quality. A horn and an anvil tip surfaces were designed with pyramidal patterns to prevent slippage of lap-structured Mg alloy sheets among tool tips during ultrasonic spot welding process. The lap joint thinning was significant at higher vibration amplitudes and longer welding times and resulted in the variation of fracture types at the weld interface. Lap-shear tests on the ultrasonic spot welded Mg alloy lap joints yielded two fracture types: shear and pullout fracture. Metallographic examinations of the fracture surfaces provided insights on the fracture characteristics of the ultrasonic spot welded Mg alloys. Variations in the fracture morphologies were the results of the actual weld nugget development and closely related to weld quality. Higher weld strength was obtained at a low welding energy range of 100–140J.

Simulating microstructure evolution of battery tabs during ultrasonic welding

Ultrasonic welding offers ability to weld thin layers of malleable metals at low temperature and low power consumption. During ultrasonic welding, intensive material interactions occur due to the severe plastic deformation (SPD) and frictional heat generation, which leads to the microstructural change. Different grain microstructures have been observed after different ultrasonic welding conditions. Theory of the microstructural evolution was for the first time hypothesized as three regimes, namely SPD, dynamic recrystallization (DRX) and grain growth according to the material thermomechanical loading conditions. A novel metallo-thermo-mechanically coupled model was developed to model the temperature-dependent mechanical deformation and microstructural evolution during the ultrasonic spot welding process. The numerical analysis was carried out with a three-dimensional (3D) finite element model using DEFORM 11.0. The material constitutive model considered cyclic plasticity, thermal softening and acoustic softening. Dynamic recrystallization and grain growth kinetics laws were applied to simulate the microstructural evolution under different welding time durations. The simulation results demonstrated that the essential characteristics of the deformation field and microstructure evolution during ultrasonic welding were well captured by the metallo-thermo-mechanically coupled model. The numerical framework developed in this study has been shown to be a powerful tool to optimize the ultrasonic welding process for its mechanical properties and microstructures.

Simulating Microstructure Evolution of Ultrasonic Welding of Battery Tabs

Ultrasonic welding offers ability to weld thin layers of malleable metals at low temperature and low power consumption. During ultrasonic welding, intensive material interactions occur due to the severe plastic deformation (SPD) and frictional heat generation, which leads to the microstructural change. Different grain microstructures have been observed after different ultrasonic welding conditions. Theory of the microstructural evolution was for the first time hypothesized as three regimes, namely SPD, dynamic recrystallization (DRX) and grain growth according to the material thermomechanical loading conditions. A novel metallo-thermo-mechanically coupled model was developed to model the temperature-dependent mechanical deformation and microstructural evolution during the ultrasonic spot welding process. The numerical analysis was carried out with a three-dimensional (3D) finite element model using DEFORM 11.0. The material constitutive model considered cyclic plasticity, thermal softening and acoustic softening. Dynamic recrystallization and grain growth kinetics laws were applied to simulate the microstructural evolution under different welding time durations. The simulation results demonstrated that the essential characteristics of the deformation field and microstructure evolution during ultrasonic welding were well captured by the metallo-thermo-mechanically coupled model. The numerical framework developed in this study has been shown to be a powerful tool to optimize the ultrasonic welding process for its mechanical properties and microstructures.

Parametric study in similar ultrasonic spot welding of A5052-H32 alloy sheets

Ultrasonic spot welding (USW) is a solid-state joining process highly applicable to lightweight alloy materials with high diffusivity rates in the melt state. To improve the understanding of the USW process and to enhance the weld strength in similar Al alloy welding, this work focused on a parametric study using some process parameters such as vibration amplitude and welding time. Experiments were conducted using lateral-drive USW machine operating in time control mode. Weld quality of USWed joint was analyzed based on the weld strength obtained by lap-shear tests and the fracture pattern subsequently characterized. Mixed fracture pattern of shear and pull-out exhibited a higher lap-shear failure load, while solely shear and pull-out was a distinct fracture pattern in lower lap-shear failure load. Shorter welding time was needed for higher vibration amplitude to generate enough temperature and to prevent over welding. Joint microstructures revealed that longer welding time produced over welding which gave short but intensified weld interface waviness, resulting to a shorter fracture path. The horn and anvil tip surface patterns influenced on the variation in temperature rise measured at the weld part and the extent of part marking/sticking. The temperature rise measured on the weld surface was useful to determine over welding condition. Weldability map of USWed Al alloy sheets could be constructed from the results of weld strength and fracture type, and an effective welding energy input was determined from welding process parameters combination.

Thermo-mechanical analysis of frictional heating in ultrasonic spot welding of aluminium plates

The thermo-mechanical analysis of an ultrasonic spot welding process was performed using developed finite element models. Temperature–time histories of aluminium specimens during welding were successfully obtained from the analysis and validated by physical tests. It was shown that the effect of frictional heating on the plastic deformation of aluminium during ultrasonic spot welding was significant and should be included in the analysis of the welding process in order to achieve good correlation with the physical phenomenon.

Mechanical Analysis of Ultrasonic Bonding for Rapid Prototyping

Ultrasonic bonding of thin foils has been recently introduced to rapid prototyping of complex-shaped and/or internally structured layered parts. This article provides the mechanical analysis of an elementary ultrasonic spot welding process of a metal foil on a previously deposited substrate. A 2-D, quasi-static/dynamic, elasto-plastic numerical model of the stress/strain field is developed by finite element analysis. Its frictional boundary conditions at the foil/substrate interface are described via a simpler plain stress, static analytical formulation, and identified experimentally by strain measurements on the substrate surface, adjacently to the ultrasonic probe. The calibrated computational simulation is validated in the laboratory and applied in studying the elastic stress concentrations, plastic deformation initiation and propagation patterns, the slippage at the interface surface and the dynamic effects of ultrasonic loading on the bonding process. This mechanical model is suitable for analysis of multi-joint ultrasonic rapid prototyping and its applications in fabrication of multi-material, functional internal structures with embedded components.