Research On Technology And Mechanism Of High-speed Dry Electrical Discharge Milling Of High-strength And High-hardness Materials

High temperature nickel base alloy,titanium alloy,hard alloy,die steel and other materials due to its high strength,high hardness,corrosion resistance,wear resistance,were widely used in aerospace,automobile manufacturing,biomedical,cutting tools,and other fields.When using traditional machining method to machine this materials,the problem of serious tool wear,high machining cost and low machining efficiency are existed.Electrical discharge machining(EDM)is not affected by material strength and hardness,which is widely applied in the machining field of these materials.However,the problems of low efficiency,large energy consumption,releasing harmful gases are existed in the traditional EDM.Therefore,developing a high-efficiency,low-cost,pollution-free EDM technology for this kind of high-strength and high-hard materials is imminent.In this paper,with the high-strength and high-hard materials,the theoretical analysis and experimental investigation on the technology and mechanism of the high-speed dry electrical discharge milling were carried out,and some achievements of important theoretical and application value are obtained:A novel technology of high-speed dry electrical discharge milling of high-strength and high-hard material is presented.In this technology,the work piece materials are fast melted by the enough energy provided by thousands ampere current and millisecond pulse duration time,then are removed by the high speed air flow and high speed rotating electrode.The maximum machining efficiency 5862 mm~3/min of titanium alloy is obtained.The machining efficiency of dry EDM is improved by hundreds or thousands times.Meanwhile,the cheap graphite is used as electrode materials,and the cheap and no-polluting air is used as dielectric.This technology has the advantages of high efficiency,low cost and no pollution.A new method to research on the machining performance and material removal mechanism of EDM based on a given number of pulse discharge is presented.This method has a more research on the mechanism,and more significant guiding effect on the practical production.A method to research on the impact mechanism of the discharge process with the different machining parameters based on the geometry dimension of the recast area in the crater is presented.The energy distribution rule and material thrown rule of conventional EDM,high-speed dry EDM and high-speed liquid EDM are comparatively studied.The flow field of the machining gap has been investigated based on the air-solid two-phase flow theory.The flow of the dielectric and the movement of the machining debris in the machining gap of high-speed dry EDM are modeled.The distribution of debris at different time in the machining is obtained.The effects of the inlet gas pressure and the gas width in outside on the conditions of removing debris have been investigated.The temperature field of the single pulse discharge has been investigated based on the heat transfer theory.The temperature distribution characteristics of the titanium alloy work piece and graphite electrode are obtained with different current and different air pressure.The corresponding relation of the melting boundary of the workpiece and electrode in the depth and diameter with the current and air pressure are analyzed.Through a lot of experiments,the effects of electrode materials,machining parameters,and dielectric type on the process performance of high temperature nickel base alloy and titanium alloy have been investigated.The microstructure of the machined workpiece surface is systematically examined,and the effects of electrode materials,machining parameters,and dielectric type on the microstructure characteristics are revealed.A new and improve technology on high-speed dry EDM is presented.This method combines the advantage of high-speed dry EDM and high-speed liquid EDM,which has the advantages of high machining efficiency,good surface quality,thin heat affected zone thickness and green environmental protection.The influences of peak current,air pressure,droplet size,electrode rotation speed and droplet density on the material removal rate,surface roughness,and width of overcut in continuous machining and the material removal weight,trace length,and trace width in single pulse machining are investigated.The micro characteristics,such as recast layer,heat affected zone,micro-hardness,micro-crack and micro-void of the machined materials are examined.The flow field of the machining gap has been investigated based on the air-liquid-solid three-phase flow theory.The flow of the dielectric in the machining gap of high-speed dry EDM improved method is modeled.