Design and Analysis of Ultrasonic Horns Operating in Multiple Vibration Modes

A number of recent studies have shown that combining different modal responses can provide opportunities to improve the vibration behaviour of the output faces of tuned ultrasonic horns to provide a more effective use of the ultrasonic energy. Investigation the benefits of combining different modal responses with a view to optimizing the energy transfer from a range of power ultrasonic devices that rely on tuned horns is essential. This research will therefore aim to investigate the use of combining and exciting different vibration modes in order to design more effective resonant horns for use in high power ultrasonics applications such as metal forming, welding, cleaning and surgical devices. The research is extended to study the possibility of design an ultrasonic transducer which can operate in multiple vibration modes by modify its geometric features. The longitudinal- torsional mode is selected first because of its wide applications in ultrasonic field. The effect of geometrical modifications of transducer's matching part is being analyzed analytically, numerically and experimentally. The suggested modifications are including cut of slots and reduce the cross sectional area so that the excited longitudinal vibrational mode can be regenerated into a longitudinal-torsional mode. The considerations of simplicity of manufacturing and exciting and the efficient of energy conversion are the main advantages of the proposed transducer. Keywords–ultrasonic transducer, design horn; resonant frequency; model and harmonic analysis DOI: 10.7176/JIEA/9-3-02 Publication date:May 31st 201

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

A study of ultrasonic metal welding

Ultrasonic metal welding (USMW) has received significant attention in the past few years, and has become more reliable and suitable for a wide range of applications. In recent years, the technique has been extensively used due to the advent of component miniaturisation and improvements in producing lightweight components. There are a number of advantages for USMW, including greater efficiency and speed, longer tool life, higher accuracy and no filler or flux needed to be used. Thus the technique can be viewed as being environmently friendly. However, the technique is not inexpensive, primarily due to the high cost of welding tools. Therefore, the design and construction of a lateral-drive USMW system which is capable of joining thin metals is presented in this thesis. The fundamental aspect of this study is the design of an integrated spot welding horn, along with other welding components such as a stationary anvil, mounting holder, welding bed, as well as the relevant fixing tools and fixtures. High precision is required in the design of the components, and in particular the welding horn. Because the horn is responsible for transferring energy to the welding zone, specimens must be prevented from sliding during the joining process, and an appropriate clamping force must be applied which will ensure acceptable bonding. Many criteria have been examined to enhance the performance of a working horn. The horn excitation frequency has been matched to the transducer frequency, ensuring that the horn will be vibrated longitudinally close to 20 kHz, thereby allowing the tuned mode to be isolated from other non-tuned modes, which guarantees uniformity of the vibration amplitude at the horn working surface, high gain factor of 4.108, and the avoidance of any stress initiated at the points between connecting components. Examining of these criteria is essential in order to optimise the excitation of the horn and to transmit the energy with minimum dissipation. The analytical studies and the finite element (FE) modelling of the welding components were successfully simulated, from which the vibrational behaviour and dynamical characteristics of the system were precisely verified using experimental modal analysis (EMA). The welding stack (the horn connected to the transducer), welding components and fixtures were then set-up on the driving machine. The device was examined prior to welding to ensure the excitation at high vibration. Many tests were successfully conducted on the welding together of aluminium and copper in a number of different configurations using the ultrasonic metal spot welding system. Weld strength and quality were shown to depend on complex relations of process parameters such as clamping force, amplitude of vibration, welding time and input power. A series of weld combinations with different thicknesses and ii variations in metal conditions were studied. The results of the lap tested specimens suggest that the bond strength is sensitive to the relationships between clamping force and vibration amplitude. Overall, the weld strength results suggest that the Al-Al welds are stronger and more consistent in terms of weldability than the Cu-Cu welds. In the welding of dissimilar metals, stronger welds are produced when the aluminium specimen is placed on top and in contact with the horn tip, rather than the copper. The thickness and surface condition of the metals such as hardness, surface roughness and oxides, are significantly affect the weld strength. In welding of Al-Cu or Cu-Al, an increase in energy and time was necessary to generate an acceptable bond. The use of stepped amplitude profiling results in a pronounced increase in the weld strength improves consistency and enhances weldability. However, horn tip/specimen adhesion and specimen marking did not occur under certain conditions. The results of the FE simulation and experimental tensile tests, for the load displacement curves profiles, allow for good estimation of the maximum load and therefore weld strength. Weld quality of aluminium and copper specimens were observed through investigation of the deformed surfaces using Nomarsky optical microscopy and scanning electron microscopy (SEM). The results illustrate that good quality welds can be achived by joining specimens, regardless of the surface condition of the metal. The SEM confirmed that no mixing occurred by melting or fusion between intimate surfaces, which indicates that USMW occurs due to adhesion and cohesion mechanisms. Furthermore, xray diffraction confirms the percentage of morphology between Al and Cu, which indicates that largest weld formations are prevalent for those specimens that are softer and lower in hardness and surface roughness, regardless of the type of tempering

Evaluation of Vibration Amplitude Stepping and Welding Performance of 20 kHz and 40 kHz Ultrasonic Power of Metal Welding

Today ultrasonic power technique is consider a mandatory technique which is always entered in many processes such as in metal and plastic welding to overcomes many issues, with aided of applying force (pressure) and supplied high frequency vibration, a solid-state weld can be generated by ultrasonic metal welding technique. That gives a technique the ability to join not only a small component, whereas also to join thicker specimens, which depends on a proper control of matching welding conditions. Therefore a welding performance can be studied and compared after designed welding horn to resonance at frequencies of 20 kHz and 40 kHz. The analyses of the designed horn are completed through use a vibration mathematical expressions, modal and harmonic analyses to ensure the weldability due to applying ultrasonic power to the working area and also to compare the performance of joint at using two resonance frequencies of 20 kHz and 40 kHz. The dimensions of the horns were determined to match the selected resonance frequencies, which the lengths were calculated as 132 mm and 66 mm respectively. The analysis of the exciting model indicates that the axial vibration modes of 19,584 Hz and 39,794 Hz are obtained in 10th mode, while the two frequency values are recorded 19,600 Hz and 39,800 Hz from the frequency response of the two horns. The weld strength between Al and Cu specimens with a thickness 0.5 mm was evaluated using a tensile test, which the analyses were obtained under using different welding pressure and varied amplitudes. The results were recorded within exciting a horn with two different resonance frequencies, show the enhancement of weld strength and quality through control of stepping amplitude, the enhancement means obtain good strength of the weld, reduce sticking horn to specimen, and lower specimen marking