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Research On The Discharge Characteristics Of Powder Near Dry Electrical Discharge Strengthening Technology Of TC4Alloy

Posted on:2016-03-04Degree:MasterType:Thesis
Country:ChinaCandidate:X J HuFull Text:PDF
GTID:2181330452966508Subject:Mechanical Manufacturing and Automation
Abstract/Summary:PDF Full Text Request
Titanium alloy as a kind of important structural materials is widely used in the field ofaerospace, automobile industry and other fields, but its low hardness and poor wear resistancedefects, make its application restricted. In order to solve these problems, the surface of titaniumalloy need to be modified. The traditional strengthening technology (chemical surfacecarburizing heat treatment or nitrogen, laser deposition, micro-arc oxidation, ion implantation)processing cycle is long, and the component of strengthening layer is difficult to control. EDMsurface strengthening technology can be a good solution to the above problems. The currentresearch on the EDM surface strengthening technology, mainly concentrates on a single medium(gas or liquid), experiment and temperature field simulation. EDM surface strengthening insingle medium has some shortcomings, such as poor uniformity, thinner strengthening layer, etc.,and the experimental study and the temperature field simulation cannot directly reveal the sparkdischarge mechanism.On the basis of traditional EDM technology, this paper introduces a powder mixed near dryEDM surface strengthening technology, and reveals the discharge mechanism in electro sparksurface strengthening process, based on the principle of breakdown of discharge medium. Firstof all, establish the mathematical model of spark discharge based on the dielectric breakdownNPW and WZ model. Then simulate the electric spark discharge path in different media by usingMatlab7.11. Because of the limitation of NPW and WZ model, discharge path by simulation inthree-dimensional space. Use the finite element method, simulation of temperature field indifferent medium. Studies show that, the electric spark discharge in different working medium,the fractal dimension of discharge path is also different, and the highest temperature ofworkpiece surface is different. Fractal dimension of the size of the characterization of thedistribution of the electric spark discharge with single pulse energy, the smaller the fractaldimension, the more concentrated the energy distribution, the smaller the radius of plasmachannel, discharge energy conversion of formation of the heat source area is smaller, the higherthe temperature, can lead to excessive loss of reinforcement material of the gasification,strengthening layer is thin. On the other hand, we can get better strengthening layer organization.The simulation results show that the mixed powder dry medium in the fractal dimension, thetemperature of strengthening layer is lowest, the lowest minimum discharge energy coefficient,energy distribution is more uniform and discharge channels in the low energy density, and theexperimental results are identical with each other. The use of electric spark discharge shaping machine for powder mixed near dry electricspark surface strengthening TC4titanium alloy experiments, research the different dischargemedium, the influence of different discharge parameters (peak current, pulse width, pulseinterval)on the strengthening effect. The results show that strengthening layer microstructuremorphology has a better perform while the powder mixed near dry as the working medium, peakcurrent between (6.6-8.2)A, pulse width between (50-100)μs,and pulse interval between(80-100)μs.
Keywords/Search Tags:mix powder dry medium, TC4titanium alloy, electric spark discharge surfacestrengthening, discharge characteristics
PDF Full Text Request
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