Vibration Assisted Machining: Theory, Modelling and Applications
2. Review of Vibration Systems
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A well-designed vibration system is quite important in vibration-assisted machining. A typical vibration system consists of vibration sources (actuators), a vibration transmission/ amplification mechanism, and a control system. Generally, the actuators and transmission/amplification mechanisms were selected to be complementary. Given that certain demands such as required vibration frequency and amplitude range are proposed in the design phase, the optimal overall device structure to match those demands is determined first. Then, the key structural parameters are optimized using the finite element analysis (FEA) method, and the corresponding dynamic and static characteristics can be obtained. As a result, these key values in turn influence the choice of the vibration actuators. According to the system’s operating frequencies, these proposed vibration devices can be divided to two groups: the nonresonant mode and the resonant mode. In a nonresonant vibration system, the vibration actuators usually vibrate below its first natural frequency. In order to increase the stability and reduce the dynamic error in the vibration stage, flexure hinge structures are widely used because of their superior dynamic response, low friction, and ease of control. For a resonant system, a sonotrode (also called a horn or concentrator) vibrates at its natural frequency, transferring and amplifying a given vibration froma vibration source, which is usually amagnetostrictive or piezoelectric transducer. This system can achieve a higher operating frequency and greater energy efficiency compared with a nonresonant system. However, its vibration trajectory cannot be controlled precisely owing to the nature of resonant vibrations and the phase lag between excitation and the mechanical response. Compared with resonant systems, nonresonant systems tend to achieve higher vibration accuracy, and it is easier to achieve closed loop control of the vibration trajectories under low-frequency conditions.