【作者】 魏臣隽；

【导师】 胡德金； 倪军；

【作者基本信息】 上海交通大学 ， 机械制造及自动化， 2011， 博士

【摘要】 微电子机械系统(MEMs)己在通信、汽车、生物医学、可再生能源、航空航天、智能武器等领域发挥了重要的作用。玻璃等MEMs绝缘硬脆材料具有高硬夏、高脆性、耐磨损、耐腐蚀、绝缘、透明以及生物相容性等优良属性，然而它们的微加工却十分困难。电解电火花加工(EcDM)是一种针对玻璃、石英、陶瓷等绝缘硬脆材料的微加工方法。它加工效率高、柔性好、成本低，但在精夏、深夏等方面还未达到大规模工业应用的要求。为此，本文提出一系列基于电解电火花效应的绝缘材料微加工技术。本文首先探讨了电解电火花效应的特性和机理。其次围绕电解电火花效应，建立了电解电火花加工的数学模型。最后提出并试验研究了电解电火花热辅助机械加工、电解电火花振动冲击加工和用于微磨削加工的电解电火花砂轮修整的工艺和机理。在电解电火花效应的特性和机理的研究中，揭示了电解电火花效应的静态电压一电流特性，指出是否达到临界电压直接决定电解电火花效应的发生。着重观察了放电区间的动态特性，发现放电频率和脉冲峰值电流符合泊松分布。针对气层的形成机理，建立了气泡层和气层的电学模型，引入渗流理论解释气泡层向气层转化的机制。在电解电火花加工数学建模的研究中，首先建立模型假设，阐述加工机理，之后推导出模型公式，再用有限元方法仿真得到单火花放电下的材料去除量。通过试验获取模型参数并验证模型的有效性，模型预测结果与试验结果基本吻合。开展了基于模型的电解电火花加工工艺和机理研究，发现在低电压时的材料去除方式主要是化学腐蚀，随着电压的升高热蚀去除的比例增大。本模型的特点包括：利用高斯热源代替矩形热源更能准确地描述单火花热源、用当量熔点作为材料去除准则能把复杂的热一化学耦合问题简化为热传导问题、用指数衰减函数来描述加工域效应。在电解电火花热辅助机械加工的研究中，首先阐述了加工原理，再用数学语言描述了热辅助加工过程。随后将新方法与普通电解电火花加工的效果进行对比，试验结果表明，电解电火花热辅助机械加工提高了放电域的加工效率，减小了尺寸误差和圆夏误差。研究了工艺参数对加工结果的影响，发现加工效率随电压的增大而升高，但加工精夏随之下降。在达到临界深夏之前，加工效率随工具电极转速的升高而升高。使用扫描电镜观察了加工后工件表面，证明材料去除机理是热辅助机械加工、热辅助化学加工和热熔化的共同作用，其中热辅助机械加工是主要的材料去除方式。在电解电火花振动冲击加工的研究中，首先阐述了加工原理，然后将新方法与普通电解电火花加工的效果进行对比，试验结果表明，电解电火花振动冲击加工能提高加工深夏和流体力学域的加工效率。研究了工艺参数对加工结果的影响，发现加工深夏随振动幅值线性增大。在15—150 Hz范围内，加工深夏略有增加；然而在150—500Hz的过程中，加工深夏由30¨o um跃升到550 um。使用扫描电镜观察了加工后工件表面，证明材料去除机理是热辅助机械加工、热辅助化学加工和热熔化的共同作用。在加工深夏较大时，主要材料去除方式为机械冲击。在电解电火花砂轮修整的研究中，将电解电火花效应应用到微磨削加工中的辅助砂轮修磨工艺中，利用了电解电火花加工中的电极损耗来修整砂轮。首先阐述了加工原理，然后对修整过程进行理论分析。分析得出，修整机理是火花产生的局部高温将材料熔化和电化学腐蚀。通过对微磨削砂轮修整前后砂轮表面形貌、法向磨削力以及工件表面粗糙夏的对比发现，修整后砂轮上的磨粒明显暴露出来，且磨粒没有受到破坏；法向磨削力和工件表面粗糙度都降低了50％。研究了工艺参数对修整效果的影响，发现电压和电解液浓夏是控制修整效果的关键参数，最佳条件是32 v的电压和30％的电解液浓夏。更多还原

【Abstract】 Micro-electromechanical systems (MEMS) have been playing an important role in electronics, automotives, biomedical, renewable energy, aviation and smart weapons. Non-conductive hard brittle MEMS materials such as glass have many favorable properties such as high hardness, high brittleness, wear resistance, chemical inertness, electrical insulation, optical transparency and bio-compatibility. However, they are hard to process in micromachining. Electrochemical discharge machining (ECDM) is a micromachining process for non-conductive materials like glass, quartz and some ceramics. It is featured by high efficiency, high flexibility and low cost. Nevertheless, it has not been put to large-scale industrial applications due to its low machining accuracy and machinable depth. To solve the problems, we propose a series of micromachining techniques for insulating hard brittle materials based on electrochemical discharge effect. In this dissertation, the physics and chemistry of electrochemical discharge effect was discussed; secondly, a new mathematical model for ECDM was developed; finally, experimental investigations were carried out on thermo-assisted mechanical machining using electrochemical discharge effect, electrochemical discharge vibration and shock machining and electrochemical discharge grinding wheel dressing to understand the processes and mechanisms.In the study of physics and chemistry of electrochemical discharge effect, the static voltage–current characteristics were discovered, and it was pointed out that the onset of the effect is determined by the critical voltage. Dynamic characteristics in discharge regime was emphasized, it was found that discharge frequency and peak current follow Poisson distributions. Regarding gas film formation mechanism, an electrical model of the bubble layer and gas film were set up, and percolation theory was employed to explain the transformation mechanism from bubble layer to gas film.In the study of mathematical modeling for ECDM, the model was formulated through mathematical deduction after establishing appropriate assumptions and machining mechanism. Secondly, finite element method was used to calculate the material removal subjected to a single spark. Thirdly, experiments were conducted to obtain the critical parameters and validate the model; the model predictions were basically consistent with the experimental results. The effects of process parameters and machining mechanism were studied using the model, and it was found out that the material removal mechanism at low applied voltages is mainly chemical dissolution, and the contribution of thermal erosion increases with the increase of applied voltage. The features of this model include the rectangular distribution replaced with Gaussian distribution to model the heat source induced by one spark for high accuracy, the use of equivalent temperature as the material removal criterion to transform the complex coupled thermo-chemical problem to a simple heat conduction problem, and the exponential decay function used to model the regime effect.In the study of thermo-assisted mechanical machining using electrochemical discharge effect, the machining principle was introduced; the thermo-assisted machining process was described using mathematical language. This method was compared with conventional ECDM; the experimental results showed that thermo-assisted mechanical machining using electrochemical discharge effect increases machining efficiency in discharge regime, and reduce the dimensional error as well as roundness error. The effects of process parameters were investigated. It was found out that the machining efficiency increases with the applied voltage although the machining accuracy decreases. The machining efficiency increases with the tool rotation rate before it reaches a critical depth. The machined surface was examined using a scanning electron microscope (SEM); it was proved that the machining mechanism is a hybrid effect of thermo-assisted mechanical machining, thermo-assisted chemical machining and thermal erosion. Among them, thermo-assisted mechanical machining is predominant.In the study of electrochemical discharge vibration and shock machining, the machining principle was introduced. This method was compared with conventional ECDM; the experimental results showed that electrochemical discharge vibration and shock machining increases the machining efficiency in hydrodynamic regime. The effects of process parameters were investigated. It was demonstrated that the machining efficiency increases linearly with the vibration amplitude. The machined depth slowly increases in the range of 15–150 Hz; however, it increases from 300μm to 550μm in the range of 150–500 Hz. The machined surface was examined using a scanning electron microscope (SEM); it was proved that the machining mechanism is a hybrid effect of thermo-assisted mechanical machining, thermo-assisted chemical machining and thermal erosion. Thermo-assisted mechanical machining is predominant at high machining depths. In the study of electrochemical discharge dressing (ECDD), electrochemical discharge effect is applied to auxiliary grinding wheel conditioning in micro-grinding, and the dressing takes advantage of the tool wear in ECDM. The principle of ECDD was introduced, and the dressing process was analyzed. The analysis results showed that the dressing mechanism is the high local temperature caused by the sparks and electrochemical erosion. Through the comparison of grinding face morphology, grinding force and workpiece surface roughness before and after dressing, it was shown that the abrasives were exposed without damage after dressing; normal grinding force and surface roughness of the workpiece were reduced by 50%. The effect of process parameters was investigated, and it was discovered that the applied voltage and electrolyte concentration are two key parameters in the process. The optimal condition was founded to be the applied voltage of 32 V and electrolyte concentration of 30 wt. %.更多还原