Research On High Frequency Pulse Power Supply Of Dry Edm

Dry-EDM has the characteristics of friendly processing environment,low tool electrode wear,thin white layer and heat affected layer,and large diameter of discharge crater,which is considered by the industry as a new EDM technology in the future.Based on the above advantages and the analysis of the rapid expansion of the discharge channel and the concentration of energy density at the initial stage of the formation of the discharge channel,this paper proposed that the high-frequency narrow-pulse width power supply is suitable for the precision machining of the EDM in gas,and studied the high-frequency pulse power supply of dry-EDM.Since the physical and chemical characteristics of gas medium are different from liquid medium,the design of power supply system should match the discharge characteristics of gas gap.Therefore,this paper firstly studied the characteristics of gas discharge gap as power supply load,and proposed the power supply design requirements according to the analysis of discharge waveform,and accomplished the development of dry-EDM pulse power supply.This research is helpful to gain insights into the EDM performance of gas medium under narrow pulse width and promoted the research of EDM mechanism and the improvement of EDM performance.The contents researched in this paper are as follows:Firstly,based on the gas discharge theory and the experimental results of dry-EDM,an equivalent circuit model of gas spark discharge was innovatively established by using the circuit simulation software LTspice.The relationship between processing conditions and discharge waveforms was theoretically established.The model was used for simulate the influence of different parameters on discharge waveform under rectangular pulse and RC power supply.The suitable range of machining parameters and the influence of different power supply modes on discharge were obtained.The existence of minimum maintenance current was found and its important role in maintaining discharge was analyzed.This part of research provides the theoretical basis for the design of the structure and parameters of the high-frequency pulse power supply.According to the characteristics of dry EDM and the results of simulation analysis,the design specifications and design scheme of pulse power supply were determined.In order to meet the design requirements of high-frequency pulse,a new switching device SiC MOSFET with high withstand voltage,high current and low heat generation at high frequency was selected,and the design of its corresponding drive circuit was completed.The discharge waveforms of different power supply topologies were simulated by the established gas spark discharge model.Based on the analysis results,the topologies of main circuits of the transistor-type pulse power supply and the controllable RC pulse power supply were determined.In addition,the short circuit detection circuit was designed to reduce the effect of the short state on EDM.Finally,the high-frequency pulse power supply was debugged and the functional verification of the power supply was carried out.The processing experiments were carried out with the pulse power supply,and the simulation results of the power supply topology were further verified.The influence of power supply parameters on the material remove rate of dry-EDM was investigated by using the high-frequency pulse power supply,and it was found that the narrow pulse width has higher material remove rate and lower surface roughness,which verified that the high frequency pulse machining can be applied to finish machining.Experimental results of the influence of the non-electrical factors,such as spindle electrode rotation speed,electrode shape and spindle servo speed,showed that combining of the high-frequency pulse processing characteristics as well as improving the servo system and other non-electrical factors can further improve the processing efficiency of dry EDM.