ORIGINAL ARTICLE Influence of external loading on the resonant frequency shift of ultrasonic assisted turning: numerical and experimental analysis H. Puga 1 & J. Grilo 1 & F. J. Oliveira 2 & R. F. Silva 2 & A. V. Girão 2 Received: 2 May 2018 /Accepted: 20 November 2018 # Springer-Verlag London Ltd., part of Springer Nature 2018 Abstract In this paper, a numerical and an experimental approach are established to study the influence of the machining parameters on the resonance frequency shift of ultrasonic assisted turning. The numerical model incorporates the mechanical and electrical effect on the simulation mode shape and resonance frequency of entire ultrasonic equipment. It is numerically shown that the machining parameters’ variability promotes a resonance frequency shifting, and the depth of cut is suggested to have more effect than the feed rate. Experimental results demonstrated that for the same cutting speed and different depth of cut and feed, the frequency value shifts thus compromise the surface quality. With the frequency adjustment promoted by MMM system, surface roughness improves 10 and 14%, when the feed is increased from 0.045 to 0.18 mm/rev, respectively, for a depth of cut of 1.5 mm. Keywords Ultrasonic assisted turning . Finite element analysis . Resonance frequency . Surface roughness 1 Introduction As the demand for advanced materials continues to rise, so does the interest in process technologies which can reliably manufacture them. The chemical composition and mechanical properties of these materials often lead to poor machinability as a result of their inherent hardness and anisotropic proper- ties, which in turn generates excessive tool wear and cutting forces [1]. Over the years, authors have adopted various non- conventional techniques to circumvent the stated issue such as cryogenic turning [2], hot turning [3], ultrasonic assisted turn- ing [4], among others [5]. The use of ultrasonic technology in the manufacturing sec- tor has a considerable established position in the academic research do to its machining capabilities and advantages (see reviews [6, 7]). It can be characterized as a superimposition of ultrasonic vibration onto a tool of conventional process such as turning [8], milling [9], drilling [10], and other machining techniques [6, 7], in which the motion is applied directly to the cutting tip. Ultrasonic assisted turning (UAT) introduces the intermittent cutting characteristic to the traditional process, separating the tool insert from the workpiece through micro-scaled high-fre- quency vibration, which in turn dissipates the stress and heat resultant from cutting [11]. This method yields a far greater stability and surface finish as well as lower loads and tool wear [12, 13]. The inherent periodic cutting mechanism attains an appreciable reduction in residual stress and tool wear [14–16]. Despite the process advantages, authors [17, 18] have shown that several factors and parameters influence the end results and only a selection of vibration and cutting parameters can achieve tool-workpiece separation [11]. Notwithstanding the fact that there are substantial theoretical findings regarding the effects of the turning and vibration parameters [19, 20], these do not characterize the resonant behavior of the UAT tool. Usually ultrasonic components are modeled to work at a pre-determined frequency according to the process. On that regard, computer-aided engineering (CAE) tools are used to optimize the set horn and the cutting tool (insert), simulating a modal and harmonic analysis as well as their turning process [21]. Other authors, such as Teimouri et al. [22], have chosen to design their components through analytical equations and would later optimize their algorithm or machining parameters according to the obtained empirical results. * H. Puga puga@dem.uminho.pt 1 Centre for Micro-Electro Mechanical Systems, Department of Mechanical Engineering, University of Minho, Campus of Azurém, 4800-058 Guimarães, Portugal 2 CICECO, Department of Materials & Ceramic Engineering, University of Aveiro, 3810-193 Aveiro, Portugal The International Journal of Advanced Manufacturing Technology https://doi.org/10.1007/s00170-018-3122-3