Study Of Laminated Electrode Applied In Blasting Erosion Arc Machining

Since more and more new materials are being widely used in aerospace and astronautics areas,traditional machining process,including cutting and milling,is faced with challenge and problem.This is because these material are all difficult-to-cut,such as Nickel based alloy,metal matrix composite,and Titanium alloy.As the technology development of high-thrust and heavy-lift rockets,the machining of large size shrouded turbine blisk needs to meet the requirements of high efficiency and low cost.Blasting Erosion Arc Machining(BEAM)is a novel high efficient arc machining technology.It inherits the advantage of Electrical Discharge Machining(EDM),which is independent of the hardness of workpiece material,and BEAM has a much higher material removal rate(MRR)than that of EDM.It makes full use of the high power density of electrical arc,so that it can rough machine the difficult-to-cut alloys very efficiently.There are two electrode types in BEAM including die-sinking and rotating electrodes,according different machining objects and demands.The rotating electrode is mainly used for arc milling machining for open cavities.Typical die-sinking electrodes,e.g.bundled electrode and solid electrode,mostly perform arc die-sinking for specific shapes in open space.However,these two kinds of electrodes are not capable of machining shrouded turbine blisks.In order to solve the problem,this paper proposed the laminated electrode combined with BEAM process.By applying this type of multi-layer laminated electrode,it’s possible to perform die-sinking BEAM machining of closed flow passage in a shrouded blisk.It can reach a high MRR of 6,988 mm~3/min with 400 A peak current,which indicates that it has great potential in real application of rough machining area.The key mechanism of BEAM is hydrodynamic force arc breaking.It means that continuous fluid flushing is an essential working condition during BEAM process.The purpose of laminated electrode is that we can design the inner flow grooves as curve shapes according to the electrode outline.Then the design theory of laminated electrode is proposed and discussed in detail.After acquiring the outline profile of solid die-sinking electrode,we slice it into several layers,and design the flushing inlet hole,fluid chamber and flow grooves outlet inside the electrode.Makino Graphite Machine center and WEDM machine are chosen as tooling method for fabricating laminated electrode.The CAM process for electrode is finished successfully.Furthermore,the modeling and simulation is done in COMSOL Multiphysics software to study the flow field inside the laminated electrode.Under certain inlet flow speed and outlet flow pressure,we can get the velocity and pressure volume map of the flow field.It’s obvious to see that the flow speed is increased from 5 m/s at the inlet to 21.2 m/s at the outlet.The design is reasonable to guarantee the hydrodynamic force arc breaking mechanism and realize stable blasting erosion arc machining.In the end,BEAM experiment by laminated electrode was performed to investigate the feasibility and machining performance of this process.An experiment platform was built.To investigate the effect of peak current,pulse duration and flushing pressure,a 3-factor 2-level full factorial experiment was designed and performed to study the machining performance.The data indicated the main effect and interaction effect on MRR and TWR of the 3 factors.The equations were given as valuable data reference for further practical application and machining performance optimization.After that,the experiment with combined negative and positive electrode was implemented.A blisk flow passage could be machined successfully by laminated electrode applied in BEAM.It’s practical to apply this process into real application for rough machining.The MRR,TWR(tool wear ratio)and metallography were studied and analyzed.High efficiency and good surface quality has been achieved.