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1、 申请上海交通大学硕士学位论文 液中喷气电火花加工机理与实验研究 液中喷气电火花加工机理与实验研究 （国家自然科学基金资助项目，项目号：50775144） 学 校： 学 校： 上海交通大学 院 系： 院 系： 机械与动力工程学院 班 级： 班 级： B0702095 学 号： 学 号： 1070209238 硕 士 生：硕 士 生： 陈焕杰 学科专业：学科专业： 航空宇航制造工程 导 师： 导 师： 康小明 副教授 上海交通大学机械与动力工程学院 2010 年 2 月 23 日 A Dissertation Submitted to Shanghai Jiao Tong University
2、for the Master Degree EXPERIMENTAL STUDY AND MECHANISM ANALYSIS ON SUBMERSED GAS-JETTING EDM Author: Chen Huanjie Specialty: Aeronautical and Astronautical Manufacturing Engineering Advisor: Associate Professor Kang Xiaoming School of Mechanical Engineering Shanghai Jiao Tong University Shanghai, P.
3、R.China February 23, 2010 第 I 页 液中喷气电火花加工机理与实验研究液中喷气电火花加工机理与实验研究 摘摘 要要 电火花加工中，放电介质对工件的材料去除率、表面质量以及电极相对损耗率有重要影响。液中电火花铣削加工时相对稳定，但电极相对损耗严重，妨碍了电火花加工性能的提高。采用煤油工作液会产生有害气体造成环境污染，采用水基工作液会附加发生电解反应。气中电火花加工时电极相对损耗很小，但由于短路率过高导致加工不稳定、材料去除率不高，还会产生烧焦气味。 液中喷气电火花加工方法就是综合利用液体、气体两种放电介质的加工性能，从空心管状电极中喷出的高速气体作为电介质，电极和工件浸
4、没在水基工作液中，气体周围的水基工作液不直接参与放电但却有助于冷却和排屑，从而改善实际放电加工的性能。 本文对液中喷气电火花加工机理进行了分析，建立了局部放电区域VOF 模型并采用 FLUENT 软件仿真计算了该区域的气体体积分数变化规律。结果表明，液中喷气电火花加工放电瞬间加工区域是处于气体包围中的。同时又进行了液中、气中、液中喷气电火花加工的机理研究对比实验，从而验证了仿真计算结果的正确性，也解释了液中喷气电火花加工与气中电火花加工相似以及出现工件碎屑熔融物粘到电极表面的原因。 本文继而进行了液中喷气电火花加工实验研究。首先对照国内外同行专家文章中的重点参数进行气中电火花加工参考性实验；接
5、着围绕四个关键因素，即脉冲宽度、脉冲间隔、峰值电流以及每层进给深度进行基于响第 II 页 应曲面的正交实验设计，并分析各因素对材料去除率和电极相对损耗率的影响以及因素之间的交互作用，从而发现各放电参数是通过组合方式来影响整体加工工艺性能。又进行了单因素加工实验，初步分析了气体压力、工件电极相对速度、电极壁厚等对材料去除率和电极相对损耗率的影响。 本文最后通过进行平面样件的铣削加工实验，对高速平动液中喷气电火花铣削加工系统进行结构分析和工艺规划，并综合评价其工艺性能。液中、气中、液中喷气电火花铣削加工实验结果证明了，高速平动液中喷气电火花铣削加工性能优于其它两种加工方法，能够保持较低电极相对损耗
6、率的同时得到较高的材料去除率，并且不产生烧焦味道气体。 本文的研究证明，高速平动液中喷气电火花铣削加工性能良好，是一种有效解决气中电火花加工短路率过高问题的方法。 关键词：关键词：液中喷气，电火花加工，放电介质，实验设计，材料去除率 第 III 页 EXPERIMENTAL STUDY AND MECHANISM ANALYSIS ON SUBMERSED GAS-JETTING EDM ABSTRACT In the process of EDM, dielectric medium has remarkable influence on material removal rate, sur
7、face quality of the workpiece and relative electrode wear ratio. The Traditional EDM can achieve stable discharging but the electrode wears dramatically, which decreases the EDM milling performance. Oil-based dielectric will generate noxious gas that pollutes the environment, while water-based diele
8、ctric will bring electrolytic reaction. EDM in gas can make less electrode wear, but its high short circuit ratio will lead to unstable process and thus low material removal rate. A kind of uncomfortable smell like burning can also be found in this process. To take the advantages of both EDM in liqu
9、id and in gas dielectric, a new method called submersed gas-jetting EDM is proposed in which the high-pressure gas blown throughout the inner hole of a tubular electrode worked as the dielectric medium, and water-based liquid around the gas helps cooling and debris evacuation but does not involve in
10、 the discharge process directly. To explore the principle of submersed gas-jetting EDM with dielectric medium, Volume of Fluid (VOF) model were used to analyze the air volume fraction of the working area between the electrode and workpiece. The results indicated that the working area is completely s
11、urrounded by the high-pressure gas and the discharge happens in the gas. In the experimental study of this method, the effects of dielectric media on minimum working gap, electrode surface and workpiece surface were analyzed, hence validated the numerical simulation results, and explained the reason
12、 that submersed gas-jetting EDM is similar with that of EDM in gas and the phenomenon of workpiece debris adhering on the electrode. 第 IV 页 To explore the law of submersed gas-jetting EDM, the preliminary experiment was conducted based on the research of counterparts all over the world, The effects
13、and interaction of four critical factors named pulse duration, pulse interval, peak current and depth of cut, on material removal rate and relative electrode wear ratio were studied with methods of orthogonal experimental design and response surface. It was found that the factors are through a combi
14、nation of ways to affect the overall EDM performance. It was also found that there are some kinds of relation between the machining abilities and gas pressure, relative speed between electrode and workpiece, wall thickness of electrode, depth of cut and so on. Through the milling machining of a plan
15、e, a new method named Submersed Gas-jetting High Speed Assist EDM Milling was finally proposed and its system structures were described. It was also discussed on the milling process planning and comprehensive machining performance. High Speed Assist Submersed Gas-jetting EDM revealed better machinin
16、g performance compared with Traditional EDM and EDM in gas. This new method not only keeps lower relative electrode wear ratio but also achieves much higher material removal rate, without burning smell. It was proved that High Speed Assist Submersed Gas-jetting EDM Milling is an effective solution to solve high short circuit ratio problem of EDM in gas, and reveals good machining performance. Keywords: EDM, Submersed gas-jetting, MRR, Dielectric medium, DOE. 第
