Simulation And Experimental Study On Electrical Discharge Machining Of Ni-Al₂O₃Functionally Graded Material

Advancement in aerospace technology raises increasingly strict requirementsfor composite materials and emphasizes the development of multi-function andmulti-performance composite materials. As a combination of its two integrations,functionally graded materials （FGM） hold the properties of both metal and ceramics,which ensures its promising application potential. Scientists have made greatachievements on both design and preparation methods of FGM during the course ofnearly three decades. However, due to the fact that the composition of FGM varieswith space dimensions, it has been proved to be a traditionally difficult machiningmaterial. Confined by lack of effective secondary machining methods, furtherapplications of FGM have been hindered to certain degree.In order to solve the difficulties of FGM secondary processing, research onFGM non-conventional machining is of great necessity. Taking full advantages ofthe conductivity of metal phase to generate discharge, Electrical DischargeMachining is a prominent candidate for processing FGM.Ni-Al₂O₃graded material is widely used in both application areas such asthermal stresses relaxation material and in research areas such as FGM preparationand testing methods. This paper provides a simulational and experimental study onelectrical discharge machining of Ni-Al₂O₃functionally graded materials.To obtain a theoretical insight into the material removal mechanism of thegraded layers of FGM, finite element analysis models are established of both theheat transfer processes and the corresponding thermal stresses field during EDM. Onthe basis of the simulation study, multifold experimental researches are also carriedout to verify the material removal model of FGM containing Al₂O₃grains of largesize. For FGMs containing medium and small ceramic grain, comparativeexperimental study demonstrates the differences in material removal mechanismsbetween various grain sizes.With a clear understanding of the material removal mechanism of FGM inEDM processes, WEDM process tests reveal the impacts of inter-layer interactionson the machinability of FGM, as well as its influences on material removal rate（MRR） and post-processing surface quality indices such as surface roughness.For EDM drilling process of the Ni-Al₂O₃graded material, the relationshipbetween machining setting-up parameters such as open-circuit voltage, chargingcurrent, and discharge capacitance and material removal rate is demonstrated bycentral composite experiment design. Mathematical modeling of the response surface of the relationship between MRR and machining settings is provided. Byusing this mathematical model, a more comprehensive interpretation of themachining process is also made in this study.This paper supplies a systematic work of simulational and experimental study,as an evidence to justify the machinability of FGM, on Electrical dischargemachining of metal-ceramics functionally graded materials. By revealing itsmaterial removal mechanism and a series of distinctive phenomena in EDM process,this work is valuable to constitute a solid theoretical foundation for subsequentresearches on self-adaptive control strategy of FGM electrical dischargingmachining.