Design And Experimental Study On On - Line Measurement And Control System Of Ultrasonic Compound Electric Machining

Ultrasonic machining is an effective technology to process hard and brittle materials due to its insusceptibility to hardness and conductivity. While for materials with a good combination of high hardness and toughness, the processing efficiency of ultrasonic machining is relatively lower and the tool head tend to wear obviously. Besides, the discharge and electrochemical machining is irrelevant to the mechanical properties of the machined metal material and the wear of the tool head. By combining ultrasonic, discharge and electrolysis together, the effect of original machining process can be strengthened and the processing efficiency increases at the same time. Therefore, the quality of the work piece is significantly improved. It is found that a stable state of ultrasonic compound electric machining is hard to obtain due to the variation of load change in ultrasonic vibration system, transducer heating, tool head wear and other reasons. Such phenomenon is extremely obvious when the processing depth and area increases. Therefore, the following main contents are presented in this thesis.The main factors affecting ultrasonic compound electro machining are firstly analyzed in this study. A stable state of compound processing is guaranteed by ultrasonic vibration, in which the frequency and amplitude are the most important factors. The gap has a significant effect on the discharge and electrolysis machining. Normally the smaller the machining gap, the higher the precision will be. And the machining gap is closely related to the ultrasonic vibration amplitude, pulsed voltage and conductivity in ultrasonic composite electrical processing.The on-line measuring device of ultrasonic compound electro machining contains ultrasonic vibration device, high-frequency pulse power supply, magnetic levitation workbench, synchronous chopper power, signal detection and control units. The exponential amplitude transformer and stepped amplitude transformer are designed and the up to 100 kHz frequency pulse power supply is customized, and choice of a variety of high-speed. Also a wide range of high-precision sensors for online testing process parameters are chosen. The accuracy of the core detector laser displacement sensor measurement is up to 0.01 μm and the maximum sampling frequency of 392 kHz The signals measured by sensor are delivered to the computer by Advantech PCI-1706U synchronous data acquisition card. The adjustment of ultrasonic power supply voltage is realized by using digital potentiometers to replace mechanical potentiometers in ultrasonic power in order to control the digital potentiometer output resistance ruled by the communication between the STM32 microcontroller and the computer. By using RS232 input command communication with serial port laser displacement sensor, the parameters setting is achieved and the environmental impact of measuring zero-surface drift is eliminated by timing auto zero. Based on virtual instrument technology and Lab VIEW platform, data acquisition, processing, storage and monitoring of the machining status parameters are realized by programming a ultrasonic compound electro machining measurement and control system. A serial communication program is developed by using VISA function And the automatically adjusting module of voltage and laser displacement tolerance comparison sensor is designed to adjust the ultrasonic excitation voltage and changing HI, LO value based on the vibration amplitude in the machining processing.The ultrasonic compound electro machining system is debugged and improved. Also the micro-tool electrode is designed and produced. By comparison of experiment results of the cemented carbide YT15 and YG8, stainless steel, and piezoelectric ceramic material, the interplay among these main parameters and the influences on processing efficiency and machining precision are discussed. The relationship between temperature and conductivity is tested and analyzed by using 3% and 5% mass fraction of sodium nitrite. The relationship of ultrasound excitation voltage and amplitude is testedinthe ultrasonic vibration system which consists of exponential amplitude transformer and stepped amplitude transformer. The formula of ultrasonic amplitude and ultrasonic excitation voltage is obtained by using the method of least squares linear fit of the experimental data. The stability of manual adjustment and automatic controlled ultrasonic machining are compared by using metal and nonmetal materials in the single ultrasound machining processing experiment. The influences of pulse power supply voltage and frequency on the efficiency and accuracy of ultrasonic compound electro machining are investigated. By choosing minuteness electrode in synchronization ultrasonic compound electro machining test, the obtained results show that the improved compound machining system tends to be more stable and the machining efficiency increases significantly at the same time.