Research On Micro-hole Process And Penetration Detection Technology Of High Tungsten Alloy By EDM

High tungsten alloy has been widely used in aerospace industry due to its high strength and high temperature resistance.Many parts have micro-holes inside for cooling and ventilation,which would be processed with difficulty by using traditional methods,while the electrical discharge machining(EDM),with many advantages,provides an effective processing method.However,EDM also has problems,such as large electrode loss,low processing efficiency and poor machining effect,etc.Therefore,the machining process and penetration detection technology of copper-tungsten alloy with a tungsten content of 90%(CuW90)are studied.A series of basic researches on CuW90 micro-hole processed using a 0.5 mm diameter tube electrode by EDM are carried out by combining single factor experiment with orthogonal experiment.Firstly,the experimental parameters such as power capacitance,electric current,servo reference voltage,servo speed and duty cycle are studied by single factor experiments,and the reasons for the differences of electrode wear and processing time between using various working fluid are analyzed.Then orthogonal experiments are carried out on these 5 parameters by L16(45)orthogonal table.Finally,the optimum parameters combination of the micro-hole machining is obtained with the target of electrode loss and processing time,and the comprehensive optimization range reaches 73%.In terms of the special structure of CuW90,its physical model is analyzed and compared.The theoretical values of performance parameters,such as density,specific heat capacity,thermal conductivity and thermal expansion coefficient,are also calculated,and the reason of large electrode loss in EDM is analyzed theoretically.The rotating inner flushing machining gap flow field is simulated and analyzed.The distributions of velocity and pressure during different processing stage are compared according to the structure characteristics of diverse working fluid flow,and the causes of column residual are discussed.The machining characteristics of different depths are studied theoretically,and the reasons for the change of electrode shape when using different working fluid are explained.In order to realize the blind hole machining of difficult-to-machine material,the neural network method is used to predict the machining rate with different parameters.The corresponding relationship between the effective discharge times and the material removal amount during micro-hole machining is analyzed.A detection circuit based on average voltage detection method is built,and the collected voltage is judged by STM32F103ZET6 chip.Through the direct drive of the digital tube,the real-time display of the machining depth is realized,and the average error of the processed blind hole is 3.9%.Based on the unique change trend of the voltage waveform before and after the penetration of the tube electrode,the hole processing with minimum exit distance of 0.7 mm was achieved.Theoretical analysis and verification on the influence of column residual before and after penetration are carried out,and the reliability of the penetration detection criterion is proved eventually.