【作者】 付秀琢；

【导师】 张勤河；

【作者基本信息】 山东大学 ， 机械设计及理论， 2012， 博士

【摘要】 微细电火花加工是一种非接触式的、宏观切削力很小的加工过程,大大减轻了工具与工件之间的力学负担,并且微细电火花加工可控性好、能加工任何强度和硬度的导电材料,使其在微细轴、微小孔及微三维结构等微细制造方面具有独特的技术优势和广阔的应用前景。但微细电火花加工过程也存在因放电能量及放电间隙微小而导致的放电状态不稳定、加工效率低、电极损耗大的缺点,严重制约着该技术在微细加工领域的广泛应用。因此,迫切需要研究开发高效率、高稳定性、低电极损耗的新型微细电火花加工技术,以适应微细制造领域的发展需要。本文查阅了大量的微细电火花加工的相关文献资料,系统分析了当前微细电火花加工技术研究现状及未来发展趋势。在此基础上,基于压电陶瓷的逆压电效应提出了一种新型微细电火花加工方法——压电自适应微细电火花加工。该加工方法通过压电致动器将放电间隙调节装置与放电能量发生装置有机集成在一起,实现了加工过程中放电问隙与放电状态的自适应调节。该方法原理及结构简单,控制方便,能有效提高微细电火花的加工效率、降低其电极损耗,为高深径比的微小孔及异型孔的加工提供了很好的解决方案,是一种有着广阔前景的微细电火花加工技术。压电自适应微细电火花加工的加工原理、加工过程及加工特性与常规电火花加工相比有一定的特殊性,为了进一步揭示其本质,本文对压电自适应微细电火花的加工机理进行了深入研究。通过单脉冲放电凹坑的分析,建立了压电自适应微细电火花单脉冲放电凹坑直径的回归模型,并在此基础上建立了压电自适应微细电火花微小孔加工的材料去除率模型。分别从介质击穿、放电通道形成、放电能量的转换与分配、电蚀产物的抛出、介质消电离等方面对压电自适应微细电火花的放电机理进行了深入研究。研究结果表明在压电自适应微细电火花加工过程中电蚀产物的抛出主要是由热爆炸力、磁流体动力等综合作用的结果；压电自适应微细电火花加工能够实现短路自消除,提高了系统的控制效率,降低系统对微细电火花伺服控制的灵敏度要求；工件与电极之间的周期性自适应伸缩运动能够在一定程度上促进电蚀产物的抛出及工作液的消电离,改善放电环境,从而提高放电状态的稳定性,并且能够增加工具电极与工件之间的火花放电频率,进而提高加工效率。本文针对压电自适应微细电火花的独特特点,设计并研制了一套压电自适应微细电火花加工系统。该系统由机械与电气两大部分组成。机械部分主要由花岗岩基座、宏微伺服系统、精密旋转主轴、微细电极的在线反拷及检测系统等部分组成。电气部分主要包括微能脉冲电源、电路检测与反馈回路、接触感知回路等组成部分。伺服控制系统是微细电火花加工系统中不可或缺的组成部分,性能优良的伺服控制系统是实现微细电火花加工过程稳定进行的可靠保证。本文研究的伺服控制系统采用压电致动器与直流伺服电机驱动的滚珠丝杠宏微结合的方式,既能实现较大行程的进给,又能实现很高的进给分辨率和定位精度。在加工过程中压电致动器利用其高频特性根据放电状态对放电间隙进行自适应调节,使放电间隙始终保持在最佳范围之内,保证电火花高效稳定加工。微细电极的在线制作与检测是制约微细电火花加工技术发展的瓶颈。本文在分析各种电极在线制作的优缺点的基础上,采用切向反拷法实现电极的在线制作。并充分利用机床本身的接触感知功能及数控系统来实现电极直径的在线精确测量。较高的材料去除率、较低的电极损耗及良好的表面质量一直是微细电火花加工追求的目标。本文围绕微小孔电火花加工过程中各项工艺目标的实现途径,基于正交试验利用信噪比分析法研究了开路电压、电容值、限流电阻、主轴转速、初始进给速度等加工参数对加工时间、电极损耗、表面粗糙度等各项工艺目标的影响规律,并在此基础上对单目标工艺参数进行了优化。研究结果表明对工艺目标的要求不同,所得到的工艺参数的优化组合也有所不同,甚至有时是相互矛盾的。针对这一问题本文引入了灰关联分析法。在正交试验的基础上,利用信噪比分析法对试验结果进行分析,然后利用灰关联度对计算结果进行优化分析,将多目标工艺参数的优化问题转化为单目标灰关联度的工艺参数的优化,得到压电自适应微细电火花微小孔加工的多项工艺目标下的参数优化组合。验证试验结果表明,基于信噪比及灰关联度的优化方法可以在一定程度上提高加工效率、加工表面质量,降低工具电极损耗。系统的试验研究是评价所研制的微细电火花加工系统性能的最佳方法,本文最后针对所研制的压电自适应微细电火花加工系统进行了加工实验研究。验证了该系统加工微细轴、微小孔及简单微三维结构的能力,充分说明了本加工系统的广泛实用性。更多还原

【Abstract】 Micro-electrical discharge machining (micro-EDM) is a non-contact machining process; the macro cutting force is small, which eliminates the mechanical stresses between workpiece and electrode. And micro-EDM can machine any hardness conductive materials even nonconductive materials; it has great advantages and broad applications in micro machining fields for fabricating micro axis, micro holes and micro three-dimensional structures. Micro discharge energy and micro discharge gap cause the un-stable discharge state during micro-EDM process, which leads to the low machining efficiency and high electrode wear ratio. Such shortcomings restrict the application of micro-EDM in micro machining fields. Thus, new micro EDM techniques with high efficiency, high stabibility and low electrode wear are urgent need to be developed.On the basis of great lots of relevant literatures and data, micro-EDM techniques are reviewed to point out the latest research and future development tendency, a new piezoelectric self-adaptive micro-EDM(PSMEDM), based on inverse piezoelectric effect, was developed in this paper. The discharge gap regulation fitting and discharge energy fitting are integrated by piezoelectric actuator, realizing the self-regulation of discharge gap depending on the discharge state. The working principle and structures are simple. The system can improve the machining efficiency and reduce the electrode wear and provides a good method for fabricating high-aspect-ratio micro holes and allotypic holes, the technique has a broad prospect.The working principle, process and characteristics of PSMEDM are different from the conventional discharge machining. In order to comprehend the machining nature, the physical mechanism of PSMEDM was researched in this paper. Based on the single discharge crater, the diameter regression model of single discharge crater was set up, and the model of MRR was deduced. The mechanism of PSMEDM was further studied from the aspects of the breakdown of the dielectric, the spread of the discharging channel, the conversion and distribution of the discharging energy, the removal of the machining debris, the deionization as well as the integrated effect of the impulsive discharges. The results indicate that the removal of the machining debris during PSMEDM is concurrent results of the thermal expansion and magnetic fluid dynamic force. The PSMEDM can realize self-elimination of short circuits, which can improve the control efficiency and decrease the response requirements of servo control system. And the self-adaptive adjustable motion of the electrode during machining process is favor of removing of machining debris and deionization of working fluid, improving the discharge environment and stability of discharge state, and the discharge frequency is increased, the material removal rate is improved.Based on the analysis of special characteristics about PSMEDM, a set of PSMEDM system is designed and developed. The system includes mechanical part and electrical part. The mechanical part consists of granite basement, macro and micro servo system, precise rotary spindle, in-process fabrication and detection of micro electrode. The electrical part consists of micro generator, detecting circuit for discharge process and contact sensing circuit.The servo control system is an important part in micro-EDM system. An excellent servo control system stabilizes the machining process. A combined device with piezoelectric ceramic and DC servo motor has been developed as a servo system in this study. The PSMEDM system not only can realize EDM with long trip but also has high resolution and positioning accuracy. The piezoelectric actuator regulates the discharge gap depending on the discharge state, and insures the discharge gap retain within the best range.The fabrication and measurement in process of micro electrode is a bottleneck problem which restricts the development of micro-EDM technology at long time. After analyzing the merits and drawbacks of a variety of fabrication methods of micro-electrode, the block electrical discharge grinding with tangent feeding was adopted to fabricate micro-electrode in process. The measurement of electrode in process is completed through the combination of the contact perception function and numerical control function in this machine system.Higher MRR. lower EWR and better surface quality are the goals that micro-EDM pursues. Based on orthogonal experiment, S/N analysis method was adopted to investigate the effects of parameters such as open voltage, capacitance, resistance, rotate speed, and initial speed, upon the individual performance characteristic. Through the arrangement of such kind of experiment, a full knowledge of the implementations on each of the performance characteristics like machine time, electrode wear and surface roughness can be obtained. Further the parameters for single performance characteristic are optimized. It is found that different optimization objective results in a quite different combination of process parameters, and sometimes even lead to a quite poor performance for the other characteristic. In such cases, the theory of grey relational analysis was used in this study. S/N analysis method was adopted to dispose the experiment data, then the grey relational analysis was used to evaluate the performance with multiple characteristics; that is, the optimization of the parameter settings with multiple performance characteristics can be transformed into the maximization of the grey relational grades and the biggest grade for each parameter dictates the best arrangement of parameters corresponding to it. Thus, the optimization with multiple performance characteristics for PSMEDM system can be gained. And the validating experiment results dictate that this method can improve the machine efficiency and surface quality, decrease the electrode wear.Experimental researches are the best methods to evaluate the micro-EDM system. The performance of this PSMEDM system has been evaluated through micro EDM tests in this study. The performance of machining the micro-shafts, micro-holes and micro3D structures is validated. The experiments show its excellent machining performance and wide practicability of the machining system.更多还原