Development and performance of a novel ultrasonic vibration plate sonotrode for grinding

Abstract

Compared with Conventional Grinding (CG), the Ultrasonic Vibration-Assisted Grinding (UVAG) is more competitive for the machining of difficult-to-cut materials. In this article, a novel ultrasonic vibration plate sonotrode that enables the special longitudinal full-wave and transverse half-wave vibration modes was proposed. The vibration characteristics of the proposed sonotrode was theoretically studied based on the apparent elasticity and Rayleigh methods, achieving a single longitudinal workpiece ultrasonic vibration with an amplitude of 7.6 μm. A superior vibration uniformity was achieved, as indicated by the coupling coefficient of 0.5. Based on the proposed method, the normal and tangential grinding forces decreased by 35 % and 39 % in comparison with the CG, and an improved machined surface was obtained in the UVAG of Ti-6Al-4V, with the following characteristics: vibration amplification of 7.6 μm; a cut depth of 0.1 mm; a workpiece feed rate of 100 mm/min; and a grinding speed of 30 m/s.

Introduction

Compared with the Conventional Grinding (CG) technology, the Ultrasonic Vibration-Assisted Grinding (UVAG) technology [[1], [2], [3], [4], [5], [6]] is more promising and competitive for machining difficult-to-cut materials [7,8], such as titanium alloys [9], nickel-based superalloys [10], ceramics [11,12], and CFRP composites [13,14] owing to the low grinding force, low grinding temperature and excellent surface integrity. In most systems, vibrations are applied to either the cutting tool or the workpiece.

Vivekananda et al. [15] designed a special ultrasonic vibration tool for the turning of 304 stainless steel using the Finite Element Method (FEM). Their experiments verified that the ultrasonic vibration-assisted turning is suitable for reducing surface roughness and cutting force. Kuo et al. [16] proposed a rotary ultrasonic milling tool similarly through FEM simulation. Teimouri et al. [17] have found an optimal processing parameter for cutting force with the cutting tool ultrasonic-assisted turning of 7075 aerospace alloy. Huuki et al. [18] applied the cutting tool ultrasonic vibration to burnish a 34CrNiMo6 steel. Zhao et al. [19] designed a new type of ultrasonic-assisted elliptical vibration wheel to grind Nano-ZrO₂ ceramics. However, the vibration uniformity and the consistency of vibration direction are poor when the ultrasonic vibration is applied to a large-sized cutting tool, thereby restricting the size of the cutting tool and further limiting the cutting speed in grinding and milling.

Compared with the cutting tool ultrasonic vibration, the workpiece ultrasonic vibration has greater application potential due to its simple structure and wide application space and has recently attracted the attention of researchers. Han et al. [20] designed a porous block sonotrode to form micro plastic. The workpiece held on the surface of the ultrasonic vibration sonotrode was driven by two separate transducers, and the vibration characteristics were altered by the holes in the sonotrode. Over 5% extrusion force was reduced with ultrasonic vibration assistance. Abdullah et al. [21] proposed a special ultrasonic vibration device for UVAG. The workpiece was directly fixed on the end of ultrasonic horn, then held on the machine tools by special clamps, which realized the longitudinal and transverse workpiece ultrasonic vibration. Zhu et al. [11,22] proposed the 1D ultrasonic vibration platforms that could realize axial ultrasonic vibration-assisted milling and the tangential ultrasonic vibration-assisted grinding. The workpiece surface roughness was improved between 25 % and 45 % with ultrasonic vibration. Tawakoli et al. [23] proposed a special ultrasonic vibration sonotrode. The multi resonance behavior was achieved using the holes on the front and side surfaces of the sonotrode. Additionally, the ultrasonic electrical discharge machining was realized by Mishra et al. [24] through workpiece ultrasonic vibration. The horn of ultrasonic transducer was inserted into the tank through a Teflon bush, and an adjustable vertical support was provided at the other end outside the tank. The maximum material removal rate increased by 36 % after the application of ultrasonic vibration.

Although all the abovementioned studies proposed many structures of ultrasonic vibration devices, the design theory and methods are rarely mentioned. In terms of design theory, Zhao et al. [19] utilized the Kelvin model to establish the dynamic model and studied the effect of thermo-mechanical load on vibration characteristics. Aoyagi et al. [25] designed an ultrasonic motor on the basis of the simplified equivalent circuit method. El-Sayed et al. [26] studied the free vibration of a multi-span pipe conveying fluid and used the transfer matrix method to assemble the system of equations that resulted from the application of the boundary conditions. For the workpiece ultrasonic vibration system design, the device design is based on the FEM as the vibration mode of sonotrode is usually complex. Thus, the relationship between the device size and vibration mode is difficult to determine.

However, the development of workpiece ultrasonic vibration is currently focused on the structure innovation, and the connection of vibration theory and the structure of ultrasonic vibration device is still insufficient. Research on vibration characteristic of ultrasonic vibration devices is inadequate. Consequently, further study of the development of workpiece ultrasonic vibration is important to improve the manufacturing quality of a workpiece, especially for grinding wheels or cutting tools with complex shapes or large sizes.

To fill the abovementioned gap, this paper proposes a special ultrasonic vibration plate sonotrode for the UVAG. The vibration characteristics of the plate sonotrode and the relationship between the plate sonotrode size and vibration mode are discussed based on the apparent elasticity and Rayleigh methods. The remainder of this article is organized as follows. Section 2 introduces the workpiece ultrasonic vibration system and working principle. Section 3 focuses on the development of the plate sonotrode on the basis of the apparent elasticity method and the Rayleigh method. Section 4 presents the vibration characteristics of the plate sonotrode. Section 5 discussed the vibration characteristics detected experimentally. Section 6 compared the grinding experiment results between CG and UVAG and discussed the verification of the superiority of the plate sonotrode designed in this article.