| Titanium alloy has been widely used in aviation, car and civilian industry because of its goodcharacteristics such as high specific strength, light quality, good inoxidability, and so on. As a result ofits low thermal coefficient, strong chemical affinity and small elasticity modulus, when processingtitanium alloy with traditional mechanical machining method, problems such as serious tool wear,difficulty in pumping out chips and rebound of machined surface will appear. Electrical dischargemachining (EDM) is a method that depends on the partial instant high temperature instead ofmechanical energy to remove materials. It’s not limited to the mechanical properties of workpiecesand proper to work on titanium alloy. Characteristics of dielectrics such as dielectricity, viscosity andoxidbillity will have direct influence on EDM of titanium alloy. This paper studied the influence ofelectrical conductivity, viscosity and oxidbillity of dielectrics on material removal rate (MRR),electrode relative wearing rate (ERWR) and surface roughness Ra of titanium alloy machined byEDM, based on which, a kind of compound dielectric of best integrative machining result has beendeveloped.The main research contents of this paper are as follows:(1) Influence of dielectric’s electrical conductivity on MRR, ERWR and Ra of titanium alloymachined by EDM has been studied. The rise of electrical conductivity makes break-over voltagedecrease and discharge gap increase, and the discharge situation becomes more stable, resulting inimproving MRR. If the discharge gap is oversize to consume more energy, MRR will go down. Thedrain current grows as the electrical conductivity raises, strengthening the electrolysis of electrode andworkpiece, and then electrode wear increases. When electrical conductivity grows, more oxygen willbe produced in water electrolysis, enhancing discharge explosion and leaving deeper discharge markson the surface, thus making Ra bigger. The electrolysis can make the surface of electrode better, infavor of improving copying precision and slowing down Ra’s growth.(2) Influence of dielectric’s oxidbility on MRR, ERWR and Ra of titanium alloy machined byEDM has been studied. Dielectric of oxidbility can react with titanium alloy of high temperature torelease huge heat, strengthening discharge explosion and making erosion particles bigger, and as aresult, improving MRR. When the erosion particles are too big to be pumped out of discharge gap,MRR will go down. Electrode is oxidized and an oxide layer forms on its surface to low the electrodewear. Oxygen released by dielectric conduces the even distribution of discharge debris in dischargegap to distribute discharge energy and get more smooth surface. (3) Influence of dielectric’s viscosity on MRR, ERWR and Ra of titanium alloy machined byEDM has been studied. The rise of viscosity strengthens dielectric’s compression on dischargechannel, improving the energy density in single discharge channel and the discharge explosion,resulting in MRR increasing, electrode wear and Ra bigger. The thermal conduction and fluidity ofdielectric become worse when the viscosity is excessive, bringing about uncompleted deionizationand serious caking problems of discharge debris, making discharge situation unstable, consequently,MRR decreases and electrode wear and Ra increase rapidly.(4) A compound dielectric for EDM of titanium alloy has been developed, which is withsynthesized discharge properties. The compound dielectric gets the highest MRR in three trios ofelectrical parameters. Due to its apparent electrolysis, electrode wear is big, but because of its highMRR, the ERWR in compound dielectric is between distilled water and kerosene. Oxygen producedin compound dielectric is much more than in distilled water because of the higher electricalcondutivity and hydrogen peroxide, therefore, better surface roughness can be got in compounddielectric. Kerosene and oxygen in compound dielectric low its cooling speed, bringing out less microcracks than in distilled water. |
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