Investigation of process parameters of ultrasonic welding of copper using Taguchi and grey relational analysis

When working with thin layers of comparable and/or different metals, resistance welding and conventional welding each have their own set of limits that they must overcome. When the input parameters include a high-frequency vibration, proper weld duration and pressure, ultrasonic metal welding performs at its highest level of efficiency. Ultrasonic welding uses a lot of power, force and energy, and if the right input parameters aren’t chosen, the quality of the weld and its durability suffer. This study takes into account the relationships between the input process parameters of welding pressure, welding time and vibration amplitude and the output responses of power, force and energy in ultrasonic metal welding (UMW). For multilayer AL-8011 foils, the author utilized UMW has experimented with central composite design by design professionals. The response surface approach, often known as RSM, has been used to improve the process parameters to get the best possible welding connections.

Ultrasonic welding is a solid-state joining process that produces joints by the application of high-frequency vibratory energy in the work pieces held together under pressure without melting. In electronic and automotive applications, copper wires are connected to the equipment (alternator/rectifier) by a solid state joining process. For such an application ultrasonic metal welding is useful. The dominant problem faced by industry dealing with ultrasonic metal welding process is the poor weld quality and strength of the weld due to improper selection of weld parameters. In this work welding parameters like welding pressure, weld time and amplitude of the vibration are considered while producing ultrasonically welded joints of copper whose thickness is 0.2 mm. If other modes of joining are used, this size being very small, it may damage the weld. A suitable experimental design based on Taguchi’s robust design methodology was designed and executed for conducting trials. The analysis of variance (ANOVA) and signal to noise ratio analyses are employed to investigate the influence of different welding parameters on the weld strength and to obtain the optimum parameters.

Article history: Ultrasonic metal welding, unlike the conventional welding techniques, does not require an external heat source, welding rod, or filler metal. Therefore, ultrasonic metal welding is not only economical but also environment-friendly, and hence, it has been receiving much attention. In ultrasonic welding, heat is generated because of the plastic deformation and the friction between both surfaces of the welded materials. It is important to identify the heat-affected zone by measuring the temperature generated at the weld. In this study, the effects of the welding pressure, welding time, and vibration amplitude on the temperature distribution in the weld were evaluated by performing a transient thermal analysis of the heat generated during ultrasonic metal welding. The experimental results indicated that the temperature of the weld tends to increase with the welding time and vibration amplitude. However, an increase in the pressure does not affect the temperature of the weld largely.

Ultrasonic welding (USW) is a solid-state joining process in which the joint is created between the workpieces by the application of high frequency ultrasonic waves under pressure. Poor weld strength is one of the major problem experienced in the application of such weldments. It is mainly due to improper selection of process parameters. In order to achieve satisfactory weld strength optimization of welding process parameters is indeed essential. In this present context, the USW has been carried out to join dissimilar materials like A1100 aluminum alloy and CuZn37 brass plates of thickness 0.1 mm using Taguchi’s L16 orthogonal array design of experiments. The process parameters like amplitude, weld pressure and weld time have been taken into consideration. Taguchi’s S/N ratio concept has been employed to study the effect of different process parameters on the response like tensile strength; and finally, the optimum setting of process parameters has been decided in view of maximizing tensile strength. The predicted result of the optimized tensile strength has been validated by conducting a confirmatory test. This analysis shows that the high quality and efficient joints can be generated by exploring optimized setting of process parameters which is fruitful in mass production as well as off-line quality control of such a welding practice.

This paper gives a description of an experimental study on the ultrasonic welding of metals. In ultrasonic metal welding, high frequency vibrations are combined with pressure to join two materials together quickly and securely, without generating large amount of heat. Horn, a key part of ultrasonic welding machine, should be designed very accurately to get the natural frequencies and vibration mode required. In this study, a horn is designed and developed for ultrasonic welding of Cu sheets. The tensile strength of welded parts is investigated for evaluation of weldability. Experimental parameters of welding test is set as follows; welding time 0.4s ~ 3.4sec. and vibration amplitude 40%, 60%, 80% and welding pressure 1.5bar, 2.0bar, 2.5bar. Samples are Cu sheets of 0.1mm thickness. Experimental results showed that the tensile strength increase as welding parameters increase, but when welding pressure is excessive, the tensile strength decrease due to fracture of the Cu sheets caused by over-welding. These results could be successfully applied for ultrasonic metal welding in various fields of manufacturing industry.

Ultrasonic spot welding of Al-Cu sheets: A comprehensive study

Ultrasonic spot welding of aluminum-copper dissimilar metals: A study on joint strength by experimentation and machine learning techniques

This paper investigates the effects of process parameters on the joint strength and process robustness when multi-layered joints of dissimilar metals are produced by ultrasonic metal welding (UMW). Three layers of 0.3-mm aluminium sheet are welded with a single 1.0-mm copper sheet which is representative of electric vehicle battery interconnects. A process robustness study in which welding pressure, amplitude of vibration and welding time are varied to produce satisfactory welds is reported. The weld quality is evaluated by performing lap shear and T-peel tests where maximum loads are considered as the quality indicator. Response surfaces are developed to identify the relationship and sensitivity between the input process parameters and output quality indicators. A feasible weldability zone is defined for the first time by identifying the under-weld, good-weld and over-weld conditions based on load-displacement curves and corresponding failure modes. Relying on the weldability zone and response surfaces, multi-objective optimisation is performed to obtain maximum lap shear and T-peel strength which resulted in Pareto frontier or trade-off curve between both objectives. An optimal joint is selected from the Pareto front which is verified and validated by performing confirmation experiments, and further, used for T-peel strength analysis of different interfaces of the multi-layered joint. To conclude, this paper determines both the optimal weld parameters and the robust operating range.

Ultrasonic metal welding (USMW) for battery tabs must be performed with 100% reliability in battery pack manufacturing as the failure of a single weld essentially results in a battery that is inoperative or cannot deliver the required power due to the electrical short caused by the failed weld. In ultrasonic metal welding processes, high-frequency ultrasonic energy is used to generate an oscillating shear force (sonotrode force) at the interface between a sonotrode and few metal sheets to produce solid-state bonds between the sheets clamped under a normal force. These forces, which influence the power needed to produce the weld and the weld quality, strongly depend on the mechanical and structural properties of the weld parts and fixtures in addition to various welding process parameters, such as weld frequencies and amplitudes. In this work, the effect of structural vibration of the battery tab on the required sonotrode force during ultrasonic welding is studied by applying a longitudinal vibration model for the battery tab. It is found that the sonotrode force is greatly influenced by the kinetic properties, quantified by the equivalent mass, equivalent stiffness, and equivalent viscous damping, of the battery tab and cell pouch interface. This study provides a fundamental understanding of battery tab dynamics during ultrasonic welding and its effect on weld quality, and thus provides a guideline for design and welding of battery tabs from tab dynamics point of view.

Ultrasonic metal welding for battery tabs must be performed with 100% reliability in battery pack manufacturing as the failure of a single weld essentially results in a battery that is inoperative or cannot deliver the required power due to the electrical short caused by the failed weld. In ultrasonic metal welding processes, high-frequency ultrasonic energy is used to generate an oscillating shear force (sonotrode force) at the interface between a sonotrode and few metal sheets to produce solid-state bonds between the sheets clamped under a normal force. These forces, which influence the power needed to produce the weld and the weld quality, strongly depend on the mechanical and structural properties of the weld parts and fixtures in addition to various welding process parameters such as weld frequencies and amplitudes. In this work, the effect of structural vibration of the battery tab on the required sonotrode force during ultrasonic welding is studied by applying a longitudinal vibration model for the battery tab. It is found that the sonotrode force is greatly influenced by the kinetic properties, quantified by the equivalent mass and equivalent stiffness, of the battery tab and cell pouch interface. This study provides a fundamental understanding of battery tab dynamics during ultrasonic welding and its effects on weld quality, and thus provides useful guidelines for design and welding of battery tabs from tab dynamics point of view.

Microstructure investigation and optimization of process parameters of ultrasonic welding for Al–Cu dissimilar joints using design of experiment

Ultrasonic metal welding is often used as a rapid and effective technique for joining sheet metals without causing them to melt. Precise management of the welding process parameters is crucial for achieving excellent joint quality. However, modeling the behavior of the weld material and the welding process is still very challenging. This study aimed to create 3D finite element models that accurately simulate the ultrasonic metal welding process. The proposed material model integrates frictional heat and ultrasonic softening, as well as the cyclic plasticity model. A friction law incorporating a variable friction coefficient is examined to investigate surface impacts. This coefficient is influenced by contact pressure, slippage, temperature, and the number of cycles. The findings of this study demonstrate that the oscillation frequency significantly influences both the temperature fluctuation and the extent of the heat-affected zone. Increased frequencies lead to accelerated temperature fluctuations and expanded heat-affected. Furthermore, ultrasonic welding combined with preheating led to a much wider heat-affected zone than ultrasonic welding without heating. The minimum preheating temperature required for ultrasonic welding of aluminum is 150 °C. This model can predict the relative displacement between welded plates. Assessing the oscillations that arise during the ultrasonic welding process is beneficial in selecting suitable welding settings to prevent excessive heating. This aids engineers in choosing appropriate welding parameters to avoid excessive heat generation during ultrasonic welding, hence limiting the reduction in tensile strength of the weld. Consequently, it can decrease the expense of the experimental methodology.

Ultrasonic metal welding is widely used for joining multiple layers of dissimilar metals, such as aluminum/copper battery tabs welding onto copper busbars. It is therefore important to have a robust product/process design using ultrasonic metal welding that ensures consistent welds with desired quality. In this work, the effects of longitudinal and flexural vibrations of the battery tab during ultrasonic welding on the development of axial normal stresses that occasionally cause cracks near the weld area are studied by applying a one-dimensional continuous vibration model for the battery tab. Analysis results indicate that fracture could occur near the weld area, due to low cycle fatigue as a result of large dynamic stresses induced by resonant flexural vibration of the battery tab during welding. This study provides a fundamental understanding of battery tab dynamics during ultrasonic welding and its effects on weld quality, and can be used to develop guidelines for product/process design of ultrasonically welded battery tabs.

Several difficulties are faced in joining thinner sheets of similar and dissimilar materials from fusion welding processes such as resistance welding and laser welding. Ultrasonic metal welding overcomes many of these difficulties by using high frequency vibration and applied pressure to create a solid-state weld. Ultrasonic metal welding is an effective technique in joining small components, such as in wire bonding, but is also capable of joining thicker sheet, depending on the control of welding conditions. This study presents the design, characterisation and test of a lateral-drive ultrasonic metal welding device. The ultrasonic welding horn is modelled using finite element analysis and its vibration behaviour is characterised experimentally to ensure ultrasonic energy is delivered to the weld coupon. The welding stack and fixtures are then designed and mounted on a test machine to allow a series of experiments to be conducted for various welding and ultrasonic parameters. Weld strength is subsequently analysed using tensile-shear tests. Control of the vibration amplitude profile through the weld cycle is used to enhance weld strength and quality, providing an opportunity to reduce part marking. Optical microscopic examination and scanning electron microscopy (SEM) were employed to investigate the weld quality. The results show how the weld quality is particularly sensitive to the combination of clamping force and vibration amplitude of the welding tip.

Energy crisis poses a major challenge in the modern industrial scenario. A critical aspect of the shop floor work includes the welding of dissimilar metal sheets which require the right amount of energy. In order to tackle these challenges, a conservative and energy efficient method are necessary. Recently, automotive industries have been widely adopted the ultrasonic metal welding process for assembling lithium-ion battery packs and its modules. The joining of these dissimilar metals using any other conventional welding process is extremely challenging due to varying physical, chemical, thermal properties, the formation of the heat affected zone and lesser bond strength. However, ultrasonic metal welding yields better quality welds under the influence of optimal parametric conditions. In this research, the weld quality of two dissimilar materials, namely, aluminum (AA1060) with cupronickel (C71500) sheets investigated at different welding time, vibration amplitudes and welding pressures with a fixed ultrasonic frequency of 20 kHz. Experimental results show the tensile shear strength of the weld is maximum at the highest vibration amplitude with a moderate amount of weld pressure and weld time. Additionally, the joint quality and its associated microstructure at the weld region are analyzed by scanning electron microscopy (SEM) to reveal the bond strength with the interlocking feature.