Research On High Efficient Machining Technolog Of Electrical Discharge Milling

In the aerospace industry,a great deal of thin-wall parts has been applied in order to reduce the whole weight of the equipment,which is benefit to reduce lunching costs.In order to gurantee the strength,stiffness and stability of those parts which will be used in extreme environment,most of those thin-wall parts are made by titanium alloys and nickel-based superalloys,which have an excellent mechanical property and conclude as difficult-to-cut materials.In those materials machining,the weight ratio between finished parts and blanks is normally lower than 20%,most of materials need to be removed from matrix.The main machining methods for those materials are lathing and milling,owing to the outstanding mechanical propery of those materials,low machining efficient and serious cutters wearing problems in the machining have not been solved until now.In order to solve those machining problems in difficult-to-cut materials machining,electrical discharge milling(ED-milling)was proposed to improve the machining efficient and ruduce tooling costs.By applying acoustic emission(AE)technique,the AE wave that emitted by pressure change of gas bubble during discharge process was collected.The materials removal difference in different working medium was studied by analyzed the AE signals.It was found that intense pressure change was only detected at the breakdown moment in air and oil discharge process.While adopting water emulsion as working medium,intense pressure changes were detected at the discharge breakdown and end moment respectly,which was benefit to materials removal process.By distinguish material melting and removing process,the material melting and removing process in spark discharge were investigated.By comparing its' AE difference,the difference between spark discharge and arc discharge was analyzed,and the conditions for material removal in arc discharge was discussed.Based on large current pulse power supply,discharge detecting system and servol control system,the ED-milling equipment was designed on a mechanical milling setup.Arc discharge was employed for material removal,and servo control strategy was designed based on discharge voltage,which improved the stability of machining process.The polarity effect in discharge process was analyzed based on discharge energy distribution.The role of electrode rotating motion and high pressure flushing in material removal process was studied by experiments.In order to improve the flushing effect and debris removal efficient in the discharge gap,the dielectric flow field in ED-milling machining was studied by theoretical analysis and simulation.The dielectric was divided into effective dielectric and auxilary dielectric based on its outlet area,and the proportion of effective dielectric in flow field was studied.The influence of cutting depth and electrode diameter on dielectric flushing effect was analyzed.A seperating electrode with central inlet and outer ring inlets was proposed,which improved flushing effect and reduced electrode manufacturing costs.Temperature model for discharge process was established,and it was found that high dielectric flow velocity would reduce the material molten thickness.In order to guarantee the dimensional accuracy of machined workpiece,electrode wearing process and its compensation was studied.The superiority of graphite electrode was verified by tests.The influence of process parameters on tool electrode wearing ratio(TWR)was analyzed by experiments,and it was found that cutting depth played an important in electrode wearing.Electrode side wearing was compensated by adjusting track overlap rate.For axial direction wearing,different compensation strategies were designed for various machining conditions respectively.The proposed compensation strategy based on electrode length measuring by discharge timer combined with wearing prediction has an outstanding performance in guaranting machining accuracy.The influence of process parameters on MRR,surface roughness and heat affected layer thickness were studied by experiments,the influence of discharge process on surface quality was also examed.Compared with sinking ED-milling and mechanical milling,ED-milling is more appropriate to use in high efficient rough machining of difficult-to-cut materials.Mechanical milling was adopted for finish machining,and ED-milling rough machining and mechanical milling finish machining can be done in one machine tool.The application of this technology in difficult-to-cut materials machining can improve the machining efficient and reduce machining costs without influence the quality of the product.