【作者】 崔景芝；

【导师】 王振龙；

【作者基本信息】 哈尔滨工业大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 电火花加工的非接触加工、宏观作用力小等自身特点决定了其在微细加工领域的优势地位。经过几十年的发展以及加工工艺的不断完善,微细电火花加工不仅仅适用于微细轴、微细孔的加工,还能够进行三维微结构的加工。正因如此,微细电火花加工技术研究已成为微型机械制造领域的一个非常重要的方向,受到了国内外学者的广泛关注。但目前国内外学者对微细电火花加工技术的研究尚不系统,尤其是对微细电火花加工基础理论研究方面更显力度不足,至今还没有一套完整的理论模型来解释整个电火花加工过程。为此,本文尝试对微细加工过程中放电通道的建立过程以及通道的电磁特性;微细放电过程中电极材料的沉积、去除的微观过程;单脉冲放电电极材料蚀除量预测的热传导过程等微细电火花加工过程中的若干关键环节进行分析以及仿真模拟,并设计相应的实验来对所建立的模型进行了验证。由于电火花加工过程是在放电通道中发生、进行的,因此,放电通道的研究对于电火花加工技术研究有着重要意义。本文首先就放电通道展开研究,采用粒子模拟方法建立了放电过程的通道模型;对放电过程中等离子体通道的形成过程、以及等离子体通道的振荡特性进行了模拟研究;模拟结果清晰的反映了放电通道的发展过程,以及在此过程中,电子、离子的运动状态、带电粒子的空间分布。本文还分析了放电通道中等离子体的纵振和横振的形成机理;并且通过脉冲放电实验,证明了放电过程中放电通道的振荡波动对材料蚀除的影响,以及放电通道的电磁特性对于放电沉积过程中带电沉积粒子运动轨迹的影响。在电火花加工过程中,电极材料的物质转移是一个瞬时、微观的过程,因此采用微观模拟的手段对放电过程中电极材料的微粒运动过程进行分析模拟,将更有助于探寻电火花加工过程中电极材料形貌变化的工艺规律。为此,本文采用分子动力学方法建立了针尖电极放电的分子动力学模型,以及气中放电沉积的分子动力学模型;模拟了单脉冲放电钨针尖电极的形成过程和气中放电沉积的微观过程。在模拟过程中发现在针尖电极形成过程中存在着单个原子的气化去除和团簇原子的气化去除现象,并且就不同的放电点机制以及外加电场力进行了讨论。发现在匀强电场力作用下,针尖电极的形成过程与实验现象更加相符,并且分析了不同的电场强度以及放电点温度对于针尖电极形貌的影响。在气中放电沉积的分子动力学模拟中,得到了放电沉积过程模拟中微观参数与放电沉积参数之间的对应关系。模拟结果表明:仿真沉积过程中电场力、沉积动能与沉积速度的变化关系与实验所得到的沉积实验峰值电流和沉积速度关系十分吻合,很好的模拟了放电沉积过程中沉积粒子的微观运动过程,为进一步研究气中微细电火花沉积的工艺规律以及三维微细沉积加工奠定了一定的理论基础。从热传导角度来研究放电能量与电极材料蚀除量之间的关系,以此探寻电火花加工过程中材料的蚀除机理,一直都是电加工理论研究的热点之一。为此,本文采用有限元方法对不同热源模型下放电过程中电极材料的温度场分布进行了深入分析,得到了在格林热源载荷方式下,时变半径、定功率的热传导的解析方程;并且应用有限元仿真软件对单脉冲电火花加工过程的电极材料的温度场(变化)进行了仿真。在仿真过程中,充分考虑了电火花加工过程中的载荷以及电极材料物性参数随温度的变化特性、加工过程中的相变问题。对放电通道中的热流密度载荷的分布情况进行了深入的分析,得到了凹坑直径、深度与单脉冲脉宽、电流的对应关系。最后,本文研制了单脉冲放电实验电源,通过单脉冲放电试验对放电点热传导的有限元仿真模型的预测精度进行了检验。通过试验证明仿真模型具有85%以上的预测精度。更多还原

【Abstract】 Electrical Discharge Machining (EDM) is a non-contact machining technique with little cutting force, which establishes its advantage station in the fields of micromachining. After continual development for decades, micro Electrical Discharge Machining (micro-EDM) is not only applied for machining micro-shafts, micro-holes and micro three dimensional structures, but also shows excellent potential for machining silicon materials. Study of micro-EDM technology is of great significance in the fields of micro-machine manufacture and been regarded greatly by researchers home and abroad. However, there is not systemic research on this technology at present, especially for its basic theory problems. There is no systematical theory model to illustrate the discharge process. For this reason, a discharge model is built in this research and computer simulation technology to analyze discharge process, relevant experiments were designed to validate the accuracy of the models.Discharge channel is the surrounding where discharge process occurs, so research on discharge channel is the basis of the research of discharge machining. Thereby, a discharge channel model based on particle in cell method is built. Forming process and oscillation characters of discharge channel are simulated and analyzed. From the simulation result plots, it can be clearly observed that electrical particles movement during the discharge process and particles’distribution under balance state vividly. Mechanism of channel’s oscillation, composed of vertical oscillation and horizontal oscillation, is also demonstrated. Subsequently, influences of oscillation to electrode material erosion and influences of discharge channel’s electromagnetic characters to particles’movement locus in deposition in gas are testified by discharge experiment.Because discharge process is instantaneous and microcosmic, microcosmic method has to be applied to measure the particles’movement in electrode surface. For this reason, molecular dynamics method is applied to simulate the pinpoint electrode forming process and electrode deposition process. From the simulation plot, it is found that during tungsten microelectrode self-sharpening process, single atom removing and bulk atom cluster removing both exist. Electric field force is a key factor for microelectrode shape forming. Influences of electric field force to microelectrode self-sharpening and temperature in discharge point to microelectrode self-sharpening process are discussed.In deposition experiments in air, it is found that with discharge current increases, energy of single discharge increase, correspondingly the deposited granule’s size and deposition height both increase. However when discharge current exceeds a certain value, energy of single discharge is too excessive that deposition electrode is easy to burn, deposition height decreases, even to naught. From the simulation results it is found the same law. Simulation results show that the relation of emitting velocity to deposition height and relation of discharge electric field to deposition height of the simulation result are accordant to the trend of deposition height to discharge current in experiment. In the end it is found the critical values of discharge electric field and emitting velocity of depositing molecules of Cu. This research provides the reliable theoretical basis for further experimental study on the processing law of deposition and three dimensional deposition in air in Micro EDM.Electrode material erosion mechanism and how to measure the relationship of discharge energy and quantity of electrode erosion are the keys of research of EDM theory. In this paper, the heat conduction process in electrode is analyzed and a relatively rational model is built, in model both thermal current density load of gauss distribution and convection load are applied, material properties varying with temperature was considered, phase change is solved with enthalpy method. Analytic solution of temperature pattern of round heat sources is presented under the changing discharge channel radius with time and fixed input total power. The temperature fields of single pulse EDM are simulated by ANSYS and relation of crater shape and discharge parameters through simulation under different pulse-on time and current discharge condition is anylized. Finally, a single pulse power supply was designed and some corresponding experiments were done, the results show that the simulation results have the preferable precision of prediction, indicating a worthwhile theoretical foundation for continuous EDM simulation in further.更多还原