Ultrasonic Processing System
The ultrasonic-assisted vibration processing system mainly comprises of an oscillating circuit generator, a signal amplifying circuit, a vibrator, an amplitude amplifier (horn) and tool. According to the principle of ultrasonic vibration, the oscillating circuit generates oscillating power, and then the oscillating power, through piezoelectric material, converts alternating voltage into vibration across the thickness and amplifies the amplitude using a set of horns. This vibration is then transmitted to the tool or the target workpiece to produce vibrations to augment the traditional processing, as shown in Figure 1. A general oscillating circuit is an RLC circuit, where the capacitive reactance (XC) lags the zero reference angle for resistance by 90° and the inductive reactance (XL) is ahead of the zero reference angle for resistance by 90°. So there is 180° phase difference between XL and XC. At a frequency when the two opposite electrical impedances cancel out, the circuit is a pure electrical impedance circuit. Therefore, the output current is the maximum and the power is the maximum. This is called resonance, as shown in Figure 2.
Figure 2. Relationship between output current and frequency for oscillating circuit under the resonance condition
The purpose of the vibrator is to ultrasonically convert high-frequency complex electric energy into kinetic energy. Since Massachusetts Institute of Technology developed barium titanate (BaTiO3) in 1947, which has 39 times higher piezoelectric coefficient than quartz, it is suitable to be made into actuator. currently, it is a common choice for piezoelectric vibrators. Ultrasonic processing usually uses low-frequency vibration. To lower the working frequency range for a vibrator, a sandwich type piezoelectric vibrator is commonly used by clamping metal onto the two ends of a piece of piezoelectric ceramic. This is called composite piezoelectric vibration, for which the structure is shown in Figure 3.
Figure 3. Basic structure for piezoelectric vibrator