【作者】 赵伟；

【导师】 方宗德；

【作者基本信息】 西北工业大学 ， 机械制造与自动化， 2003， 博士

【摘要】 电火花加工作为不同于传统加工的一种工艺方法，被广泛应用在模具行业和汽车工业等制造领域，并且发挥着不可替代的作用。然而由于电火花放电的蚀除过程是相当复杂的，所以到目前为止还没有形成统一的电火花理论，而传统理论的一些内容已难以圆满解释电火花加工过程中的全部现象。这需要我们不断的研究和实践，找出其内在规律，完善其理论基础。这不仅对完善电火花加工理论本身有着重要的意义，同时必将促进并有助于推动电火花加工工艺的发展和进步。 本文针对电火花放电通道中带电粒子的运动对两电极蚀除量的影响规律以及极性效应理论的不足，采用单脉冲放电和有限次脉冲放电等一系列实验手段并通过模型分析对电火花加工中的理论问题进行了较为系统的研究，并将主要结论在钛合金TC4的电火花加工中得到验证。本文的主要工作和结论如下： 1．进行了相同材料的针一板、棒状电极的单脉冲放电研究。单脉冲条件下的放电研究可以排除碳保护膜对电极重量变化的影响，从而定性反映每次放电阴极、阳极真实的蚀除情况。结果显示尽管在大脉宽条件下放电，正极的蚀除仍然大于负极的蚀除。并从极间能量分配角度和放电通道在两极表面振荡和跳跃等方面对放电结果进行了分析。指出碳保护膜对电极蚀除的影响在单脉冲放电时是微乎其微的。提出了连续脉冲下的放电结果可以不同于单脉冲条件下的放电结果的观点。 2．文中变换放电能量和放电次数进行了有限次脉冲放电研究。采用有限次脉冲放电这样一种介于单脉冲放电和连续放电之间的放电形式进行实验，既可以了解碳保护膜的变化对两极蚀除的影响过程，又便于对放电后的电极质量称量。 通过实验结果中阴极、阳极蚀除量随加工时间的动态变化对放电通道中电子和正离子的运动进行了综合分析。认为无论脉宽如何变化，通道中正离子对阴极的轰击作用对阴极的蚀除影响都不大，否定了在脉宽较大条件下放电正离子可以高速轰击阴极并使其蚀除量增加的观点。 3．探讨了碳保护膜的形成条件及其对电极蚀除量的动态影响过程，并首次指出碳保护膜对阳极蚀除量的补偿作用是导致长时间放电加工条 博士论文摘要件下阴极蚀除量大于阳极蚀除量的直接原因。 4.提出了一个新的观点，即不论采用正极性加工还是负极性加工，都应先进行一段时间的正极性加工。在放电开始时先进行一段时间的正极性加工这样不但有利于放电的产生，而且当去除量很小时还可以充分利用此时阳极蚀除量大于阴极蚀除量的特点提高蚀除效率。 5.对电火花放电加工进行了模型化分析，认为对阴极传递能量并影响其蚀除的粒子主要是光子，不是正离子。 6.运用本文的实验及其分析结果，在原极性效应理论的基础上，提出了一个更为完善的极性效应理论。成功的解释了正离子和电子在气体、煤油和水基工作液等不同介质中的电火花放电中对电极蚀除的影响作用，完成了在不同介质中进行电火花放电的部分理论基础的统一工作，起到了完善电火花放电加工理论基础的作用。 7.以石墨为电极对电火花加工钦合金TC4进行了验证性实验，结果表明无论脉宽大小均应采用正极性加工，因此时加工速度快。并通过扫描电镜和X射线衍射等手段对电火花加工钦合金时其表面不产生碳保护膜的主要原因进行了深入的分析。更多还原

【Abstract】 EDM, as a process different to conventional machining, is greatly used in manufacturing mould and automobile industry. None uniform theory about: EDM has been formed at present because of the complex EDM process. Some contents of former theory can’t be used to explain all phenomenons in EDM, so we must continue to research and form perfect theory of EDM, which is important to accelerate the development of EDM.In order to research the influence to the deterioration of anode and cathode by the impaction of the moving electriferous particle in electric discharge channels and the insufficiency of the polarity effect theory, a series of systematic research is taken, which include monpulse EDM experiment, limited continuous pulse experiment and model analysis. At last, the main conclusion is proved in machining TC4 by EDMUsing same material electrodes whose shape are pin-board and club-club, monpulse EDM experiment is taken. The experiment can avoid the influence of the carbon-protection-film to weight change. So the real deterioration of anode and cathode can be gotten qualitatively. The result shows that the deterioration of anode is larger than that of the cathode even under electric discharge with large pulse width. The result is analyzed carefully from oscillation and bounce of the plasma channels on the electrodes’ surface. One point that the result gained under single pulse discharge must not conform to the result gotten under continuous pulse in EDM is presented.Limited continuous pulse experiment is taken with changing the discharge energy and the discharge times. Limited continuous pulse experiment, which is between single pulse discharge and continuous pulse discharge, is not only convenient to find out the influence process of carbon-protection-film to electrodes but also easy to weigh the electrodes after discharge. With the dynamic changing of electrode’s erosion along machining time taken into account, we analyze the movement law of electron and positive ion in plasma channels. We think the impaction of positive ion in plasma channels to cathode surface is very small no matter large or short the pulse width is. The point that the positive ion can impact the cathode surface with high speed and increase the cathode erosion under large width pulse discharge can’t be confirmed.Precondition of how carbon-protection-film is formed and dynamic influence process of carbon-protection-film to electrode erosion are discussed. It is considered that the compensation of carbon-protection-film to anode erosion results in the cathode erosion bigger than that of the anode; under long time machining.A new point is presented that positive polarity machining should be taken for a period time no matter positive or negative polarity machining will be used. To take positive polarity machining for a period time not only can make discharge easy to be come into being but also can increase productively because of the anode erosion larger than that of cathode at the beginning of EDM when the asked work erosion is very small.After model analysis to EDM, we think it is photon but positive ion that sends energy by impacting cathode and influents the cathode erosion.A new polarity effect theory is presented based on our research and former polarity effect theory. Using the new theory, we succeed to explain the function of positive ion and electron in electric discharge plasma to electrode erosion in different medium such as gas, kerosene and water based medium. Uniform of EDM theory in different medium is realized. Our research improves the development of EDM theory.Experiment to prove the new theory is taken by using graphite electrode to machine TC4 in EDM. The result shows positive polarity machining should be taken no matter positive or negative polarity machining will be used because of it’s large erosion speed. Scanning electron microscope and X-Ray diffraction are used to analyze the reason of no carbon-protection-film at the surface of TC4 after EDM.更多还原