Research On FPGA-based Pulse Power Supply Of Edm And Its Gap State Detection System

Electrical Discharge Machining is an important branch of special machining.Non-contact machining determines that EDM has advantages that traditional machining does not have.Therefore,it is widely used in many fields involving national economy and people's livelihood.As a supplier of energy for EDM machining,pulse power supply directly affects the results of EDM machining.And whether EDM can be performed stably and efficiently,the gap discharge state detection technology of EDM plays a decisive role.This paper summarizes the development trend of pulse power supply of EDM and gap discharge state detection methods by studying its current status of domestic and foreign researches,and has developed excellent performance pulse power supply of EDM and its gap discharge state detection device on the basis of previous research.A set of independent pulse power supply of EDM and its gap discharge state detection system is developed,which using FPGA as the control core,in this paper.This independent pulse power supply uses FPGA as the pulse generator and a MOSFET half-bridge circuit as the main circuit.The MOSFETs of the upper and lower arms of the main circuit are alternately turned on driven by a dedicated drive circuit.Pulse power supply can output high frequency and high voltage rectangular pulse.The characteristics of voltage,current and waveform parameters of five discharge states including open circuit,electric spark discharge,transient arc discharge,stable arc discharge,and short circuit are summarized by studying the changes of voltage and current in different states during EDM discharge.The gap discharge state detection device uses the voltage and current of the five discharge states as identification elements.The hardware detection circuit and FPGA control board are combined to perform online detection of the discharge status of each pulse,and determine the status of EDM in a period of time.The FPGA samples and analyzes the data detected from the hardware circuit to determine the discharge status of each pulse,and calculate the ratio of the number of pulses in the open circuit state,the number of pulses in the spark discharge state,the number of pulses in the arc discharge state and short circuit state to the total number of pulses within 1s.When the ratio of the number of open-circuit pulses to the total number of pulses is greater than 90%,FPGA judges that the EDM process is in a partial open circuit state during this period,and then reduces the discharge gap by the computer;When the ratio of the number of discharge pulses to the total number of pulses is greater than 90%,FPGA judges that the EDM process is in the normal discharge state during this period,and there is no need to adjust the discharge gap;When the ratio of the number of arc discharge pulses and short-circuit pulses to the total number of pulses is greater than 90%,FPGA judges that the EDM process is in a partial short circuit state during this period,and the computer will appropriately increase the gap distance between the tool electrode and the workpiece.It has been verified by experiments that pulse power supply can output the rectangular pulses with frequency up to 500 KHz,pulse width and pulse interval as low as 1?s,and with adjustable voltage and current.Finally,EDM experiments with different peak currents and different pulse frequencies were designed to further verify the performance of the developed power system.The parameters such as the surface quality of the workpiece cavity,actual machining depth and machining time after the experiment were analyzed.It was verified that the power supply system could be applied to EDM in practice.The results showed that the whole device was stable in working condition and good in performance.