High Power Ultrasonic Welding Research Articles

Interfacial reactions and joint performances of high-power ultrasonic welding of aluminum to steel

Aluminum and steel dissimilar sound joints were fabricated using a 4.0 kW high-power ultrasonic welder. The microstructure and mechanical properties of the joint resulting from high-power ultrasonic welding were investigated. To further understand the formation mechanism of the joint, macro and micro plastic deformation were also examined using the finite element method. As the welding duration increased to 0.4 s, the conversion of electrical power to heat flow at the interface also increased, with approximately 56% of the electrical power being transformed into the heat flow of the welding interface. The material flowed from the center of the welding interface and accumulated at the edge, resulting in a welding area measuring 9 mm × 7 mm, significantly larger than the sonotrode tip area. The plastic strain in the welding zone reached 3.7, with the aluminum side exhibiting higher plastic strain than the steel side, facilitating Fe atom diffusion towards aluminum. The intermetallic compound (IMC) primarily consisted of FeAl3 and Fe2Al5. The joint strength increased significantly as the thickness of the IMC increased. However, when the IMC thickness exceeded 1.7 μm, the joint strength decreased. Through interfacial metallurgical reactions and intense mechanical interlock, joints with a lap-shear strength of 62.7 MPa were achieved. The fracture mode of the joint was a ductile-brittle hybrid fracture.

Texture and intermetallic compounds of the Cu/Al dissimilar joints by high power ultrasonic welding

The welded joints of copper (Cu) to aluminum (Al) were increasingly being used for electric vehicle battery applications. To better understanding the interface connection mechanism of the Cu/Al joints produced by high power ultrasonic welding (HUSW), the texture and intermetallic compounds of Cu/Al HUSW joints were systematically investigated. The grain morphology and size of pure copper along welding interface had little change with the increasing welding time, whereas the microstructure of aluminum alloy changed from elongated grains to equiaxed grains and the grain size increased rapidly at the welding time from 0.3 s to 0.5 s. The texture intensity of both copper and aluminum alloy decreased at first owing to ultrasonic softening and then increased due to the shear work hardening. The texture type of the copper had little change, whereas the gaussian texture {110}〈110〉 and the cubic rotation texture{001}〈110〉 were formed in aluminum alloy owing to the occurrence of recrystallization driven by the severe shear deformation. The formation mechanism and accelerated growth behavior of intermetallic compounds at the welding interface during HUSW were discussed based on the atom rapid diffusion and the effective thermal formation model.

Development and Analysis of Ultrasonic Welding Process Using FEM Approach for Aluminum and Copper

Ultrasonic welding is a process that uses mechanical vibrations using ultrasonic frequencies. The vibrations are produced by an ultrasonic sonotrode, which is used for joining two thin materials, especially in electronic industries (for applications in battery-making industries). Typically, ultrasonic welding is based on the parameters (frequency range, input pressure/load of the sonotrode, by varying the coefficient of friction between two metal sheets, the thickness of a sheet) while performing the joining process. In this work, the FEA Model-based study is used for analyzing the ultrasonic welding using “Von-Misses stress theory concepts”. The effects of various thickness of the sheet, normal force, coefficient of friction (at different welding conditions) are analyzed while performing the welding process. The temperature variation is studied while using aluminum and copper as thin sheets. This study can be used in the electronic industries for high power ultrasonic welding process, especially using aluminum and copper materials in the form of electrodes, sheets.

Analysis of Welding Interface and Joint Properties of High Power Ultrasonic Welding of Aluminum Alloy

Analysis of Welding Interface and Joint Properties of High Power Ultrasonic Welding of Aluminum Alloy

Effects of welding pressure on high-power ultrasonic spot welding of Cu/Al dissimilar metals

Although high-power ultrasonic welding (HPUSW) can provide better welding results about highly conductive materials, the welding mechanism is not well understood. In this study, the effects of welding pressure on dynamic process and joint characteristics (strength and fracture) of HPUSW were investigated. High pressure produces lower vibration amplitude of the upper and bottom specimens. Under excessive pressure, the vibration amplitude of sonotrode is significantly reduced, as compared to that under lower pressure during the initial welding period. The distribution of plastic strain follows the principle of crack growth and expansion. Excessive pressure results in the extrusion of trace elements from base material to the interface, which affects the process of interfacial diffusion. The maximum welding strength is obtained as the depth of penetration of sonotrode reaches its maximum value without the production of cracks. The results obtained in this work provide guidelines for optimizing the ultrasonic welding parameters.

Microstructure and Mechanical Properties of Resistance Heat-Assisted High-Power Ultrasonic Dissimilar Welded Cu/Al Joint

The Cu/Al dissimilar joint, welded by high-power ultrasonic welding technology, is still facing challenges despite the significant research attention it has attracted. In this work, the microstructure and mechanical properties of resistance heat-assisted high-power ultrasonic welding of Cu/Al are investigated, in order to obtain high-quality joints. The intermetallic compound (IMC) at the interface of hybrid welding is primarily composed of Al2Cu, and the additional resistance of heat reduces the thickness of this brittle IMC layer. The average shear stress for the joint prepared by hybrid welding is ~97 MPa, which is higher compared to the joint strength without resistance heat (90 MPa). Moreover, the duration of the hybrid welding process is shorter. Finally, the fracture of the hybrid weld is found to be a brittle–ductile hybrid mode.

Modelling intermetallic phase growth during high-power ultrasonic welding of copper and aluminum

An analytical model was developed to understand the rapid growth mechanism of intermetallic compounds (IMC) interlayer in high-power ultrasonic welding process. The analytic solution was derived for the relationships among welding time, interface temperature and vacancy concentration. The effectiveness of this model was tested by comparing the predicted thickness with the experimental value for high-power ultrasonic welding of copper and aluminium at various amplitudes. The consistency of the comparison demonstrates the accuracy of the model has been improved by considering the dynamic change process of vacancy concentration. Besides, the effects of vibration amplitude and resistance heat on the increasing of the intermetallic thickness have been investigated independently. The results show that the additional heat source could significantly promote the process of ultrasonic welding.

Modeling of high-power ultrasonic welding of Cu/Al joint

Ultrasonic metal welding is still an indistinct but useful manufacturing technology. A three-dimensional finite element model was developed to investigate this dynamic welding, including temperature rise, material deformation, and growth of intermetallic compounds. Heat generation at the upper and bottom interfaces, material softening, and high convection boundary conditions was considered. The results show that sonotrode tip teeth penetration starts earlier and increases rapidly, reaching the maximum, but anvil tip penetration starts later and increases slowly. The plastic deformation area of welding zone increases exponentially. Plastic strain is mainly generated in the welding zone, and the total plastic strain of welding zone is approximately proportional to the displacement of sonotrode tip. The thickness of intermetallic layer was dominated by ultrasonic action rather than interface temperature. The model was validated by comparing the predicted temperature, sonotrode displacement, and profile of weld cross section with the experimental results, exhibiting a good agreement.

Grain structure, texture and mechanical property evolution of automotive aluminium sheet during high power ultrasonic welding

High power ultrasonic spot welding (HPUSW) is a joining technique which is performed within less than a second and provides a more energy-efficient alternative to friction stir spot welding (FSSW), which is considered a longer cycle manufacturing process for joining automotive alloys. To date, only a few reports exist on the deformation mechanisms that take place during high power ultrasonic spot welding. In this work, dynamic recrystallization and grain growth were examined using electron backscatter diffraction (EBSD). HPUSW causes extensive deformation within the weld zone where the temperature increases to 440°C. An ultra-fine grain structure was observed in a thin band of flat weld interface within a short welding time of 0.10s. With increasing welding time the interface was displaced and ‘folds’ or ‘crests’ appeared together with shear bands. The weld interface progressively changed from flat to sinusoidal and eventually to a convoluted wave-like pattern when the tool fully penetrated the workpiece, having a wavelength of ~1mm after 0.40s. Finally, the microstructure and texture varied significantly depending on the location within the weld. Although the texture near the weld interface was relatively weak, a shift was observed with increasing welding time from an initially Cube-dominated texture to one where the typical β-fibre Brass component prevailed.

Modeling of the Thermal Field in Dissimilar Alloy Ultrasonic Welding

This paper describes a finite element model for predicting the temperature field in high power ultrasonic welding aluminum AA6111 to two dissimilar alloys, magnesium AZ31, and low carbon steel DC04. Experimental thermocouple and other evidence are used to infer the magnitude and distribution of the heat input to the workpiece, as a function of time, for each of the material combinations welded. The resulting temperature histories are used to predict the growth of intermetallic phases at the interface in Al-Mg welds. The microstructural model successfully predicts the thickness of the intermetallic layer, but the sensitivity of the results to temperature is demonstrated.

Microstructure evolution and mechanical properties of Cu–Al joints by ultrasonic welding

Dissimilar joints of copper to aluminium were produced by high power ultrasonic welding (USW). The interfacial reaction between copper and 6061 aluminium alloy as a function of welding time was studied. The intermetallic compound (IMC) layer is mainly composed of CuAl2 and Cu9Al4. The thickness of the IMC layer increases with the welding time. For a relatively long welding time (0·7 s) in USW, the dendritic solidification microstructure was observed in local regions, owing to the occurrence of the eutectic reaction, α-Al+θ→L, in the welding process. The lap shear load (or strength) of the joints first increases and then decreases with increasing welding time, and the failure of the joints occurred dominantly at the interface. This is mainly attributed to the development of IMC layer at the interface.

Automatic Frequency-Tracking Control for Ultrasound Welding System

A new frequency-tracking control method to catch the optimal working frequency for the high power ultrasonic welding system is proposed. In a high power ultrasonic resonant system, the induced high temperature will change the working frequency. Therefore, the proposed control method to track the optimal working frequency becomes very attractive and important. This control method is practically implemented by a FPGA chip which basically includes two logic circuits. One logic circuit is to find the optimal working frequency automatically and the other one is to adjust the working frequency by detecting the working current simultaneously. Experimental results exhibit the new method can effectively control and track frequency for high power ultrasonic welding system.

Ultrasonic Welding Driver with Class-E Inverter Design

A robust circuit design using matching technology to design the ultrasonic welding transducer driver with zero voltage switching is proposed. The feedback output voltage is used to control the oscillator frequency to achieve the self-tracking function. Experimental results exhibit that the Class-E inverter circuit can be effectively and stably applied on the high power ultrasonic welding system.

New frequency-tracking control method for ultrasound welding system by the FPGA Chip

A new control method to catch the optimal working frequency (or driving frequency) for the high power ultrasonic welding system has been developed. During the high power operation, an ultrasonic resonant will induce high temperature and then change the working frequency. Therefore, a control method with a FPGA chip to track the optimal working frequency becomes very attractive and it has been practically implemented in this study. Generally, the FPGA chip includes two logic circuits, i.e. a logic circuit which manages the finding of optimal working frequency and the other one is to adjust the working frequency by detecting the working current simultaneously. Experimental results exhibit that the new method can effectively control and track frequency in the high power ultrasonic welding system. Due to this kind of study based on the FPGA design, it will enhance us the understanding of the physical realization in the ultrasound welding system. Key words: Ultrasonic welding system, FPGA.