Investigation on Deformation Behavior in the Surface of Metal Foil with Ultrasonic Vibration-Assisted Micro-Forging.

Zidong Yin,Ming Yang

doi:10.3390/ma15051907

Abstract

Excitation of the acoustic field, leading to the Blaha effect, significantly affects the plasticity of a material. In the micro-forming field, the so-called impact effect is found to generate a larger amount of dislocation and produce greater plastic deformation than acoustic softening. In this study, the mechanism of deformation in the surface of the material with ultrasonic vibration assistance was investigated and compared with that in the bulk. Forging tests using a newly developed ultrasonic vibrator were carried out on pure Cu foils with various process conditions. The longitudinal vibration frequency of the ultrasonic transducer was 60 ± 2 kHz, and the vibration amplitude was in an adjustable range of 0~6 μm. Forging tests were carried out at different amplitudes. The result shows that acoustic softening and the impact effect could be separated by an oscilloscope in the micro-forging system. The difference in deformation on the surface asperity caused by acoustic softening and the impact effect is discussed. Compared to acoustic softening, which has a limited effect on the deformation of the surface asperity, the impact effect could create more plastic deformation on the surface asperity. Therefore, the reduction in the surface roughness would increase after the impact effect occurs. In addition, to confirm the mechanism of acoustic softening and the impact effect, the microstructural evolution of specimens, at the surface scale and inner scale, was investigated by electron backscatter diffraction (EBSD). It was found that acoustic softening could create more grain refinement, and with the amplitude increasing, the impact effect would oppositely cause the surface grains to grow. In this study, the mechanism of how the impact effect and acoustic softening affect the deformation behavior of the surface asperity was investigated.

Highlights

Due to the increasing demand for micro technical products, such as micro-electromechanical systems (MEMS), the process of micro-forming has been widely used to produce miniature metallic parts
If the created deformation by the punch stays at the valley position, it is not sufficient to cause plastic deformation; the elastic spring back would cause the material of the surface to recover its original state following the punch, when it moves from the valley position to the peak position and finishes a period of vibration
A novel micro-forging test, which can separate acoustic softening from the impact effect efficiently, was used, and copper chips were applied to surface finishing by ultrasonic vibration at different amplitudes

Summary

Introduction

Due to the increasing demand for micro technical products, such as micro-electromechanical systems (MEMS), the process of micro-forming has been widely used to produce miniature metallic parts Some problems such as the so-called size effect will be caused by scaling down the ratio of roughness until its dimensions decrease, increased forming stress [1,2], and lower forming accuracy in the process behavior [3]. Weidong Zhai and li Yanle (2019) studied the ultrasonic-assisted incremental sheet forming process, and the result showed that the forming force was considerably reduced, and the bearing capacity could be improved. Both of these effects were more obvious at the step-down size or in a thin material sheet [6]. The result showed that the flow stress was decreased by ultrasonic vibration with different geometry sizes, and more significantly when the size was scaled down [7]

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Results

Conclusion