| Ceramic-metal functionally graded materials(FGM)have attracted worldwide attention,because of their novel design concepts.They are of great application prospects in aerospace,military,automobile and other fields,because of its continuous gradual change thermodynamic properties.However,the traditional machining method for ceramic-metal FGM exists in these problems of serious tool wear and high machining cost.The ceramic-metal FGM can be machined by conventional EDM,but the machining efficiency is low and the surface quality is poor.In order to improve the machining efficiency and surface quality of work-piece.This paper takes SiC/Al FGM as an example,the thermo-electrical coupling simulation of single pulse and continuous multi-pulse discharge is carried out.The effect of solid-liquid mixing in stirred tank and the uniform suspension characteristics of powder particles were studied.The surface response method(RSM)was used to optimize the process parameters.The details are as follows:In view of the problem that the mechanism of PMEDM has not been clarified,a thermo-electrical coupling simulation model for PMEDM of ceramic-metal FGM was established,the simulation study of single pulse and continuous multi-pulse discharge thermo-electrical coupling is conducted.The effect of different process parameters on the temperature distribution of PMEDM was analyzed.The simulation results show that the shape of discharge pit changes obviously in the direction of radius,but not change obviously in the direction of the depth.Under the same processing parameter,the PMEDM produces smaller and shallower pits than the conventional EDM.The solid-liquid mixing effect of stirred tank and the uniform suspension characteristics of powder particles were simulated.The effects of groove shape,depth to diameter ratio,blade design angle,blade installation height and solid particle concentration on the flow field distribution and solid particles suspension in the stirred tank were analyzed.The design of a powder mixing stirring device is carried out,and the device structure is optimized.The results show that the optimized powder mixing device can achieve stable and reliable PMEDM,save processing cost and improve processing efficiency.Finally,the simulation results of continuous multi-pulse discharge were experimentally verified by the combination of theory and process experiments.The results show that the simulation results agree with the experimental results,the maximum error of theoretical experimental results is 5.81%and the minimum error is 4.13%.Under the conditions of 5-wt%SiC/Al FGM,powder concentration 4g/L,pulse width 175?s and pulse interval 175?s,a comparative experimental study on between conventional EDM and PMEDM was carried out.compared with the traditional EDM,the efficiency of PMEDM is improved by 16.34%,and the surface roughness is reduced by 27.28%.The process parameters were optimized.Under the condition of optimal process parameters were:pulse width 50.36?s,pulse interval 30.62?s,peak current 15.99A,flushing pressure 0.79MPa and powder concentration 1.44g/L.The material removal rate was 51.75mm3/min,the relative electrode wear rate was 1.484%,and the surface roughness was 4.224?m.The goals of high efficiency,low wear and high quality in machining ceramic-metal FGM were achieved. |
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