Casting Ultrasonic Transducer Impedance Model And The Ultrasonic Power Supply Design

Because foreign countries don't provide us the high performance Al-alloy, we must have the capability of making high performance Al-alloy. Applying the ultrasonic field in the process of Al-alloy casting is an important method to promote its performance. Due to the high temperature influence the ultrasonic transducer system obviously, conventional ultrasonic power can not work long time. New ultrasonic power must be designed. In order to obtain design parameters, for example, the impedance and resonant frequency, the main study was shown as follows:1. Through the basic heat conduction theory, based on Ansys finite element simulation software, set up thermal model of ultrasonic transducer system in the condition of the casting, and using APDL of Ansys to apply the load conditions, obtained temperature field distribution of ultrasonic transducer system. The final results show that, after the system immerge into the Al-alloy melt with the temperature of 720℃within 20 minutes, the temperature of front part of tool bar varied most dramaticly, and the temperature of tool bar back part varied less dramaticly, so they should be conserned with. However temperature of front and back part of horn varied not obviously, so they can be ignored. The experimental result corresponds with this simulation result.2. Through the basic concepts of piezoelectricity, and used the equivalent circuit of piezoelectric ceramic stack and uniform section straight bar, then combined the calculated temperature field of ultrasonic transducer system, impedance model of ultrasonic transducer system in the normal temperature and in casting situation were deduced and eastablished. The material properties, size and temperature of each part of the vibration system were contacted with the model. The impedance analyse programms were writed with Matlab language, analysed the impedance in the range of 15～28 KHz with the programms in the above-mentioned situations respectively. The results show that, there are 2-stage and 3-stage vertical resonant frequencies in the two situations respectively. Due to the high temperature of aluminum alloy melt, the 1st resonant frequency decreases and the impedance of 1st resonant frequency increases obviously when the system is under the casting situation. The results corresponded with the measurement of the Agilent 4294A impedance analyzer under the two different situations.3. Combination of the impedance model derived earlier, an ultrasonic generator for Al-alloy casting was designed. The generator used TMS320F2808 as the control core, and used inverter theorem of AC-DC-AC to commutate the input 3-phase AC to square wave. Finally output high frequency voltage was generated by the matching circuit to to drive the transducer.4. The experiment was done in the working situation. It worked longer than the old power. It had the advantages of adjusting frequencies widely, and it can be used with the different kinds of ultrasonic transducer systems. The process of casting lasted successfully.