Development of High-Power Ultrasonic System Dedicated to Metal Powder Atomization

Abstract

Featured Application: The presented work considers the ultrasonic atomization as a novel approach for metal and metal alloy powder manufacturing. The article presents the results of the development works and research on the atomization process carried out using two prototype high-power ultrasonic systems. Ultrasonic systems have been designed to develop a new metal powder production process; these materials are increasingly used in modern manufacturing processes such as additive technologies or spraying and surfacing processes. The preliminary studies presented in the article were conducted for water to assess the effectiveness of both systems and to verify the theoretical and structural assumptions. In ultrasonic atomization, the ultrasonic wave causes the phenomenon of cavitation, which leads to the overcoming of the surface tension forces of the liquid and its disintegration into fine droplets. The important parameters that affect the properties of the produced droplets include, among others, the frequency of the sonotrode vibrations and the amplitude of the vibrations of the working plate. As part of the research, the paper presents the process of selecting the sonotrode geometry for two different values of the transducer’s natural frequencies (20 kHz and 70 kHz). In the design process, the finite element method was used to perform a harmonic analysis and develop the geometry of the sonotrode and the working plate. The design assumptions and the design process were presented. The modeled and then ultrasonic waveguides were verified experimentally by measuring the deflection distribution on the working plate surface using a high-precision laser displacement sensor. Then, the work ultimately resulted in conducting atomization tests of water. The obtained aerosols and the mechanism of their formation were studied using a high-speed camera. Finally, using Matlab R2020a software and image analysis scripts, it was possible to analyze the droplet size distribution generated by both systems. It was observed that 50% of the produced droplets were in the range of 35–55 μm for a 20 kHz system, while for a 70 kHz system it was 10–25 μm, which is a very satisfying distribution in terms of metal powder atomization.