【摘要】：電火花加工作為特種加工的重要組成部分,憑借其無宏觀切削力、可加工異形型腔、材料適應(yīng)范圍廣等優(yōu)點,在航空航天、能源動力、模具制造等領(lǐng)域得到了長足的發(fā)展。在電火花加工的過程中,工具電極是加工效果的關(guān)鍵決定因素。不同材料的電極對加工效率、電極損耗、工件表面粗糙度等都有較大的影響。石墨電極具有放電效率高、損耗小、重量輕、膨脹率極低、易加工修整、不易拉弧放電等優(yōu)點,在電火花加工領(lǐng)域受到廣泛應(yīng)用。探究石墨電極電火花加工機理與工藝規(guī)律,是提高電火花加工效率、減小電極損耗、改善工件表面質(zhì)量的關(guān)鍵,也是電火花行業(yè)的追求目標(biāo)。本文為探尋石墨電極電火花高效率低損耗加工的機理與最佳參數(shù),進行了深入的理論分析與大量的實驗研究。首先為探究電火花加工的微觀過程與原理,進行了基于單脈沖放電實驗的石墨電極電火花加工溫度場仿真。根據(jù)單脈沖放電實驗結(jié)果,對放電過程中的能量分配進行總結(jié)分析,擬合出放電通道半徑。結(jié)合目前電火花領(lǐng)域主流的高斯熱源模型建立起石墨電極電火花單脈沖放電的熱傳導(dǎo)模型。在該模型的基礎(chǔ)上進行溫度場有限元仿真,得到溫度場仿真模型并進行實驗驗證,利用該仿真模型對加工效率與電極損耗進行了預(yù)測與驗證。為探索各加工參數(shù)對石墨電極電火花加工效果的影響,進行了單因素實驗研究。進行實驗方案設(shè)計與實驗誤差排除,分別研究了電極極性、脈沖占空比、脈沖寬度、峰值電流與伺服參考電壓等因素對加工效率、電極損耗、表面粗糙度的影響規(guī)律,結(jié)合溫度場仿真模型對實驗現(xiàn)象與成因進行理論分析,給出了實際加工過程中參數(shù)選取的建議。在總結(jié)單因素實驗結(jié)果的基礎(chǔ)上,開展石墨電極電火花加工中心復(fù)合實驗,建立加工效率與電極損耗的回歸方程并進行了實驗驗證。通過多目標(biāo)優(yōu)化求解出高效率低損耗加工的最佳參數(shù)。對實驗過程中出現(xiàn)的電極負損耗現(xiàn)象進行了探究。通過觀察石墨電極表面微觀結(jié)構(gòu)、分析積碳層的組成成分,發(fā)現(xiàn)電極表面生成了類金剛石物質(zhì),利用仿真確定了其保護作用。通過表面形貌與實驗測量推斷出電極表面積碳不定期生長與脫落的現(xiàn)象。
[Abstract]:As an important part of special machining, EDM has made great progress in the fields of aerospace, energy power, mould manufacturing and so on, because of its advantages such as no macroscopic cutting force, machining special-shaped cavity and wide range of materials. In the process of EDM, tool electrode is the key determinant of machining effect. The electrode of different materials has great influence on machining efficiency, electrode loss, workpiece surface roughness and so on. Graphite electrode is widely used in the field of EDM because of its advantages such as high discharge efficiency, low loss, light weight, low expansion rate, easy to be machined and trimmed, and not easy to pull arc discharge. It is the key to improve the efficiency of EDM, reduce the electrode loss and improve the surface quality of the workpiece to explore the mechanism and process law of EDM with graphite electrode, and is also the pursuit goal of EDM industry. In order to find out the mechanism and optimum parameters of graphite electrode EDM with high efficiency and low loss, the theoretical analysis and a large number of experimental studies have been carried out in this paper. In order to explore the micro process and principle of EDM, the temperature field of EDM based on single pulse discharge experiment was simulated. According to the experimental results of monopulse discharge, the energy distribution during discharge is summarized and analyzed, and the discharge channel radius is fitted. The heat conduction model of single pulse discharge of graphite electrode EDM is established by combining Gao Si heat source model which is the mainstream in the field of EDM at present. Based on this model, the temperature field is simulated by finite element method, and the simulation model of temperature field is obtained and verified by experiments. The machining efficiency and electrode loss are predicted and verified by the simulation model. In order to explore the effect of machining parameters on the effect of graphite electrode EDM, a single factor experiment was carried out. The effects of electrode polarity, pulse duty cycle, pulse width, peak current and servo reference voltage on machining efficiency, electrode loss and surface roughness were studied. Based on the simulation model of temperature field, the experimental phenomenon and cause of formation are analyzed theoretically, and some suggestions on the selection of parameters in the process of practical processing are given. On the basis of summing up the results of single factor experiments, the composite experiment of graphite electrode EDM center was carried out, and the regression equation of machining efficiency and electrode loss was established and verified by experiments. The optimum parameters of high efficiency and low loss machining are solved by multi-objective optimization. The phenomenon of negative electrode loss in the process of experiment was investigated. By observing the microstructure of graphite electrode surface and analyzing the composition of carbon deposition layer, it was found that diamond-like carbon was formed on the electrode surface, and its protective effect was determined by simulation. The phenomenon of irregular growth and falling off of carbon deposition on the electrode surface was inferred by surface morphology and experimental measurement.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG661

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