Discharge Property And Experimental Studty On EDM Of Ni-Al₂O₃Functionally Graded Materials

Metal–ceramic FGMs not only combine the high temperature resistance of ceramicswith the toughness of metals, but also make full use of the advantage of two kinds ofmaterials that are composited to minimise parametric mismatch when bonding dissimilarmaterials. Due to their special structure and superior property, metal–ceramicfunctionally graded materials (FGMs) are now used in many areas. However, it isdifficult to machine them into complex shapes by conventional machining methodsbecause of their special structure and superior property. Electrical discharge machining(EDM) as a non-contact machining method can overcome the drawbacks of conventionalmachining methods. More importantly, EDM can take full advantage of the structure ofmetal–ceramic functionally graded materials to realize the secondary process of ceramicmaterials. Thus, study on electrical discharge machining of metal-ceramic material ismeaningful in practice and application purpose.This thesis reviews the current research status of metal-ceramic functional gradientmaterials and summarizes the main machining methods. In view of the unique structureof metal-ceramic functionally gradient materials, a new method (self-induced electricaldischarge machining method, SEDM) to machine Ni–Al2O3(Metal–Ceramic)functionally graded materials is advanced based on analyzing the principle of electricaldischarge machining and auxiliary electrode method. And then the removal mechanism,the discharge property and machining process of this material by use of self-inducedelectrical discharge machining method is studied.The tests shows that Ni–Al2O3(Metal–Ceramic) functionally graded materials couldbe machined by self-induced electrical discharge machining method. Through theanalysis, the material that consists of metal layer of100%Ni?gradient layer one of70vol%Ni?gradient layer of30vol%Ni and ceramic layer of100%Al2O3has three kindsof removal mechanisms which are melt?vaporization, dislodgement of Al2O3particle andmelt?vaporization after forming conductive film of alumina. What is more, the EDXS ofworkpiece's surface shows that graphite electrode could strengthen conductive film andimprove the stabilization of electrical discharge machining.By analyzing the discharge property, it is concluded that the discharge waveform isdifferent from conductive layer to the insulating layer. Discharge waveform ofconductive layer is almost discharge waveform fully discharged, and the machiningprocess is stable. There are two kinds of alumina discharge waveform. Carbide tungstenelectrode machining appears completely discharge waveform and incomplete dischargewaveform which deteriorates the process; graphite electrode machining appears completely discharge waveform and oscillating waveform which is a new king ofwaveform and maintains the machining stability.On the basis of analyzing the material removal mechanism and discharge property,graphite electrode is more suitable for the machining process of the material through thecontrastive analysis of the tungsten electrode and graphite electrode, Lastly, Under thecondition of the graphite electrode, a depth of15mm hole with a depth-diameter ratio of5, is get by SEDM successfully.