基于分割电极的电容耦合多点放电高速电火花加工新方法研究

EDM comes with a major problem of poor removal rate. This is due to the fact that EDM can only be carried out intermittently by using a pulse generator and moreover, in the conventional EDM only one discharge occurs in single pulse, resulting in the discontinuity of the discharge process in the microscope view. Generally, the removal rate can be improved by shortening the pulse interval, however, when the pulse interval is shortened below a certain length, the plasma cannot be extinguished fully during the pulse interval, resulting in concentrated discharge and unstable machining process. But, the machining speed can hopefully be improved several times by generating discharges at multiple points for each pulse. In this study, based on the divided and electrically insulated tool electrodes, multiple parallel discharge circuits can be formed though capacitive coupling, and the multi-spark discharge can be obtained in each pulse which could improve the machining speed in large scale. This research mainly focuses the following points. First, the aim of this study is to clarify the charge and discharge process and its steady-state and transient characteristics in the multi-spark EDM through capacitive coupling by the circuit simulation, and observe the discharge location distribution and the gap discharge state in the multi-spark EDM to reveal the mechanism of the multi-spark EDM. Second, the divided tool electrodes and its installing means will be studied deeply. Furthermore, the influence of the number and structure of the divided tool electrodes on the machining performance of the multi-spark EDM will also be analyzed. Next, the detection and evaluation method of the gap discharge state and the servo feed control in the multi-spark EDM are investigated to achieve the high-efficiency and stable multi-spark EDM technology. Then, the machining characteristics and processing laws of the multi-spark EDM will be clarified through the experimental studies. Last, based on the study of the above fundamental theories and key technologies, the high-speed EDM machining in the large area mirror finishing and complex cavity will be implemented and expected to achieved. The research achievement of this project will provide theoretical basis and technical support for significantly improving the machining speed of EDM and enlarge its application area.

电火花加工存在加工速度慢的问题，这是由于电火花加工须使用脉冲电源，放电间断性发生，且每个脉冲周期内通常只发生一点放电，蚀除过程存在微观不连续性。缩短放电停歇时间可改善加工速度，但过短又会导致放电集中、加工不稳定。而如果能实现单脉冲周期内的多点放电，则有望将加工速度提高数倍以上。本项目使用多个相互绝缘的分割电极，利用电容耦合形成多个并行放电回路，实现单脉冲周期内多点放电,从而可大幅度提高加工速度。通过建模仿真明确电容耦合多点放电加工的充电\放电过程及其稳态\瞬态特性，通过实验观测多点放电位置分布和放电状态，揭示多点放电作用机制；对分割电极及装夹进行设计研究，明确其对多点放电的影响；研究多点放电状态检测和伺服进给控制技术，实现高效稳定的多点放电加工；明确多点放电加工特性和工艺规律；实现大面积镜面和复杂型腔的高速电火花加工。本研究为大幅度提高电火花加工速度提供理论依据和技术支持，拓展其应用领域。

电火花加工速度慢的问题是限制其进一步应用的瓶颈问题。导致该问题的根本原因之一是由于电火花加工须使用脉冲电源，放电间断性发生，且每个脉冲周期内通常只发生一点放电，蚀除过程存在微观不连续性。缩短放电停歇时间可改善加工速度，但过短又会导致放电集中、加工不稳定。如果能实现单脉冲周期内的多点放电，则有望将加工速度提高数倍以上。本项目基于电容耦合原理，提出基于分割电极的多点放电高速电火花加工方法，通过对电容耦合多点放电回路的充/放电过程及其稳态/瞬态特性的仿真，揭示了该方法的多点放电作用机制及影响因素，为优化电路结构和参数组合提供了理论依据。研究了多点放电极间放电状态检测方法、极间放电状态评价方法及伺服控制策略，实现了电容耦合多点放电的共同伺服控制和分别伺服控制，实现了高效稳定的多点放电加工。通过系统的实验研究明确了多点放电特性的影响因素和加工特性的工艺规律，研究表明该方法具有独特的放电能量决定机制，放电能量调节简单，多点放电稳定，在一定范围内加工速度随分割电极个数和脉冲电源频率的增加而增加；通过改进给电方式、改进伺服进给方法、优化电路参数、增加分割电极个数和提高脉冲电源频率等方法显著提高了加工速度，在一定对比条件下，加工速度最高提高了7倍。基于多电极成功地实现了阵列孔和复杂型腔的高速加工。由于该方法可以完全避免回路中分布电容的不利影响，因此本项目还进行了基于电容耦合的大面积电火花精加工方法研究，在Φ100mm的加工表面上成功获得了Ra0.3的表面粗糙度，为大面积电火花精加工提供了新的有效方法。本研究还针对放电蚀除过程和放电蚀除机理进行了分子动力学模拟研究、热流体耦合模拟研究和高速摄像观测研究，从原子水平揭示了放电蚀除的原动力，从材料本身的热学性质和流体动力学性质揭示了放电蚀除的热流耦合的实质，模拟与观测研究结合首次揭示了多种材料放电蚀除机理，为进一步改进电源及提出新工艺和新方法提供了重要的理论依据。