The Research And Simulation Analysis Of The Electrical Discharge Machining Mechanism Of The Al₂O₃-TiC Engineering Ceramics

Engineering ceramics,using a variety of micron or sub-micron synthetic high-purity oxides,carbides,nitrides,borides and other inorganic non-metallic material as raw material,are made by the use of exact control technology of forming and sintering.Engineering ceramics have high hardness,high temperature resistance, corrosion resistance,wear-resistance and other excellent performances which can meet the demanding requirements of materials in the areas of spacecraft,weapons, machinery manufacturing,and other areas.There are traditional processing methods and special processing methods in machining the sintered ceramics.When traditional methods of machining being applied,generally,engineering ceramics can be processed only by diamond tools due to its high hardness.And large contact force and mechanical vibration exist in the processes,may causing fracture easily for the ceramics' brittleness.The EDM method,belonging to non-traditional machining methods,is able to process the engineering ceramics which have certain conductivity for electrical discharge machining.This method has the advantages of non-contact processing, small macro-forces and low cost on the basis of its capability to meet the needs of machining accuracy and machining quality,arousing wide concern home and abroad. Therefore,research in process and the processing technology in order to improve processing quality,machining accuracy,and to improve the processing means,to expand the processing scope has become the most popular research direction in the field of engineering ceramics' EDM.In contrast,the basic theory—processing mechanism of the engineering ceramics' EDM machining is far behind the advancement of the processing and processing technology.Therefore,this paper carry out the theoretical study on the ceramics' EDM grinding mechanism aiming at the Al₂O₃-TiC ceramics with rotary surface,apply the finite element methods and molecular dynamics method to carry out the computer simulation analysis.The simulation model of the material loss is setup and verified by processing experiment.The main contents of the paper are as follows:1.Using the CNC wire-cut electric discharge machine with the model NO. DK7725 combined with the additional rotary devices and the tracking electrode,a long cylinder work piece made by Al₂O₃-TiC ceramics with rotary surface is EDM grinded.Choose the processing parameters of the peak electric current I_P=10A, pulse width ti=16μs,spark sustaining voltage 20V,the actual discharge time te= 10μs.2.Aiming at a single discharge cycle of the discharge process,according to machining parameters,total energy of single spark pulse is calculated,and in accordance with the ratio of energy distribution,the input energy to the ceramic work piece is calculated.The radius of discharge channel is calculated in accordance with the formula of the radius of discharge channel configuration.A Gaussian form of heat flux heat input model is established according to the input energy to the ceramic work piece and the radius of discharge channel.3.In accordance with Al₂O₃ and TiC Ceramics' thermal performance parameters respectively,combined with the theoretical formula and empirical formula,the Al₂O₃-TiC ceramic composite's thermal performance parameters such as heat capacity,thermal conductivity,enthalpy,are calculated.A non-linear transient thermal analysis of a single discharge processing cycle of the Al₂O₃-TiC ceramic grinding was carried out in the finite element analysis software ANSYS based on heat transfer theory and the finite element method.The simulative molten—gasification corrosion model of the material is obtained after dealt with the results.The results showed that the depth of vaporization is about 0.68μm,depth of melting is about 0.95μm.4.In accordance with the mechanical properties parameters of Al₂O₃ ceramics and TiC ceramics,combined with the theoretical formula and empirical formula,the Al₂O₃-TiC composite ceramics' elastic modulus,thermal expansion coefficient and other thermal performance parameters are calculated.A non-linear thermal stress analysis of EDM grinding process of Al₂O₃-TiC ceramic is analyzed by the ANSYS Software's thermal—structural coupled method.5.An assumed criteria for fractured corrosion of Al₂O₃-TiC ceramics is proposed: To investigate each node's three principal stress of the thermal stress field calculation results,when a principal stress's absolute value of the three principal stresses in a node is higher than the Al₂O₃-TiC ceramics' fracture strength,the node will have a fracture phenomenon.The fracture model of the material loss is established,and the morphology of corrosion pit is obtained through this model:The pit depth is 5μm,the diameter is 22μm.6.According to the material's melting—gasification corrosion model and fracture model,a complete erosion model of Al₂O₃-TiC engineering ceramics is proposed,and the conclusion is attained:the scope of corrosion is decided by the scope of fracture in the ceramic material processing.At the same time,molecular dynamics methods is applied to simulate the material's behavior in the level of atoms, under the state of the material's temperature being above the melting point and boiling point;the macro-pressure and volume states under the transient discharge state is obtained.7.The post-discharge pit depth and diameter are measured by the use of optical microscopy and roughness measuring instrument.Pit depth and diameter have been obtained under simulation models with different breaking strength.We found that the ratio of the diameter and depth of the pits is about 4.5 in simulation model,whereas the ratio of the diameter and depth of the actual discharge pits is about 5.0,the ratios relative error is about 10%,proving that the simulation in this paper work and the assumption are reasonable.The work in this paper has important significance in improving the processing quality,the processing efficiency and controlling the accuracy.And molecular dynamics simulation can provide a new way for the future research direction, providing basis for the future study,giving us insights into the physical nature of the EDM process for further study of the mechanism of the ceramics' EDM machining.