DISCHARGE CHANNEL GROWTH IN MICRO EDM OF HIGH FREQUENCY PULSE

The influences of intense magnetic pinch effect caused by electromagnetic field with high frequency on discharge channel expansion and plasma configuration change are discussed. The change of Lorentz force exerting on charged particles in discharge channel is calculated under the electromagnetic field with high frequency. Through the theoretical analysis and experimental study, the forming process of discharge channel is conjectured. And it is considered that the changes of discharge channel, such as the decrease of diameter and increase of energy density, coming from the intense magnetic pinch effect in high frequency electromagnetic field, are the main reasons for a series of special phenomena on the machined surface in micro EDM.

纳米颗粒活性剂混粉EDM特性研究

为了进一步提高EDM效率和表面质量,提出了纳米颗粒活性剂混粉EDM方法。基于Marangoni效应分析了活性剂对EDM材料去除的增强机制,并开展实验研究了纳米活性剂对钛合金EDM特性的影响。结果表明:当开路电压为100 V时,相对于混有Al_(2)O_(3)和ZrO_(2)纳米颗粒的工作液,在混有TiO_(2)纳米颗粒工作液中进行EDM可得到最高的材料去除率。采用混有纳米颗粒表面活性剂的工作液进行EDM可得到更低的工具损耗率、更高的微孔锥形度以及更低的表面粗糙度。通过在去离子水工作液中混入TiO_(2)纳米颗粒,可将EDM的表面粗糙度Ra降低50%。因此,在EDM工作液中加入活性剂纳米颗粒有助于提高加工性能。

脉冲参数主动匹配式micro-EDM脉冲电源

为了提高微细电火花加工(micro-EDM)效率,设计了一种脉冲参数主动匹配式micro-EDM脉冲电源.采用等能量加工的方法,对不同的脉冲匹配参数进行加工效率对比实验,设计了脉冲参数主动匹配式脉冲电源的结构、功能和控制策略,并进行了加工实验验证.结果表明:选定合适的脉宽和脉间参数,使极间电容单次充电和单次放电,可获得最高的加工效率;该电源脉冲参数可根据极间电压和极间电容的大小自动调整;进行微小孔加工,加工连续性较好,加工效率和加工质量较高.利用该电源可进行微细加工,加工效率较传统电源有显著的提升,并能保证较高的加工质量.

主动匹配式micro-EDM脉冲电源设计与实验

为了提高微细电火花加工(micro-EDM)效率,设计了一种脉冲参数主动匹配式micro-EDM脉冲电源。采用主动匹配式脉冲发生电路实现脉冲参数根据极间电容充放电情况自动匹配,通过实验,对电源的加工效率、加工质量和低电压加工情况进行了分析。结果表明:采用该电源可以实现在单个脉冲周期内,极间电容单次充电、单次放电;与常规晶体管脉冲电源比较,该电源可以提高加工效率,加工表面变质层无裂纹、凹坑均匀、加工质量较高;可以实现24 V低电压加工,加工后的微孔圆度和精度较高。该电源具有提高微细电火花加工效率,保证较高加工质量的作用。

Study on manufacturing freeform surface parts in micro EDM based on skin effect theory

Micro fabrication of freeform surface parts made of hard and brittle materials is always a tough job in micro machining field. This paper tries to fabricate freeform surface feature by using smooth surface of tool electrode after tool wear in micro EDM. According to the skin effect theory, the tool end shape in the stage of uniform wear can be changed by adjusting the frequency of discharge pulse. The electrical energy distributing rule of tool electrode section in RC circuit has been investigated under the influence of skin effect, and the law of spark location change has been summarized. The experimental studies demonstrate that different shapes of tool ends can be achieved by varying the pulse frequencies of discharge power supply. Additionally, a micro part of freeform surface feature with high precision and good surface quality has been successfully obtained by micro EDM through adopting the smooth surface after tool wear.

Influence of high frequency pulse on electrode wear in micro-EDM

An electromagnetic coupling mathematical model is established by finite element method and is verified by the contrastive experiments of copper matrix Ni-TiN cylindrical coating electrode,copper electrode and Cu50 W electrode.The wear mechanism of Ni-TiN/Cu composite electrode in the case of high-frequency pulse current is studied,and the influence of the fluctuation frequency of discharge current on electrode wear in micro-EDM is found out.Compared with the electrode made from homogeneous material,the high frequency electromagnetic properties of Ni-TiN composite layer can be used effectively to inhibit the effect of high frequency pulse on the electrode and improve the distribution trend of current density.

High-efficiency Approach for Fabricating MTE Rotor by Micro-EDM and Micro-extrusion

Micro-gas turbine engine（MTE） rotor is an important indicator of its property, therefore, the manufacturing technology of the microminiature rotor has become a hot area of research at home and abroad. At present, the main manufacturing technologies of the MTE rotor are directed forming fabrication technologies. However, these technologies have a series of problems, such as complex processing technology high manufacturing cost, and low processing efficiency, and so on. This paper takes advantage of micro electric discharge machining（micro-EDM） in the field of microminiature molds manufacturing, organizes many processing technologies of micro-EDM reasonably to improve processing accuracy, presents an integrated micro-EDM technology and its process flow to fabricate MTE rotor die, and conducts a series of experiments to verify efficiency of this integrated micro-EDM. The experiments results show that the MTE rotor die has sharp outline and ensure the good consistency of MTE rotor blades. Meanwhile, the MTE rotor die is applied to micro extrusion equipment, and technologies of micro-EDM and micro forming machining are combined based on the idea of the molds manufacturing, so the MTE rotor with higher aspect ratio and better consistency of blades can be manufactured efficiently. This research presents an integrated micro-EDM technology and its process flow, which promotes the practical process of MTE effectively.

Micro-EDM Milling of Complex 3D Structure with Fix-Length Compensation Method

A human face with complex 3D structure is machined with a modified fix-length compensation method in this paper.The fast development of MEMS (Micro Electromechanical Systems) has strongly enhanced the application of new harder work materials.As a low cost,flexible,good repeatable machining process with negligible process forces,micro-EDM milling is well suited for freeform metallic micro structures.A major problem in micro-EDM milling of complex 3D structure is the electrode wear.A new CAM system based on the UG software platform is developed in order to get good accuracy and higher efficiency.A correction coefficient is introduced and deduced for the modified fix-length compensation method.Using this method a human face with complex 3D stricter is machined successfully by micro-EDM milling.

灰色关联分析和熵权法的μ-EDM多目标参数优化

针对微孔的入口、出口和形状加工精度指标要求,提出灰色关联分析(Grey Relational Analysis,GRA)法和熵权法相结合的微细电火花加工多目标参数优化方法。运用熵权法,对三个加工精度指标进行分析,并得到对应的权重。通过设计正交试验并对H62黄铜进行加工试验,计算出试验结果序列的各指标的灰色关联系数。采用熵权法和GRA法综合评价模型,得出各试验序列的灰色关联度,并对其进行均值分析,实现了多目标优化向单目标优化的转变。研究结果表明,优化后工艺参数的实验结果与灰色关联度最大的H-22组试验结果相比,其入口过切量EnOV、出口过切量ExOV及锥度TA分别降低了8.97%、4.11%、8.33%,微孔的加工精度得以提高。

磁场辅助场致射流微细放电加工研究

场致射流放电加工方法利用高压电场诱导形成的微细射流与工件间放电来蚀除材料。虽无电极损耗,但微细射流的柔性较大且易受外界干扰,导致放电分散性和随机性较强,因此难以对其进行精准控制。为此,设计了一种四极性磁场施加装置,通过磁场对离子束的约束作用控制射流,并分析了磁场的作用机理,研究了磁场约束对场致射流放电加工的蚀坑宽度、深度及表面粗糙度的影响规律。结果表明,随着磁感应强度的增大,放电蚀坑的最大深度和表面粗糙度值都减小;磁场散焦方向上蚀坑的宽度增加,而聚焦方向上蚀坑的宽度减小,同时放电时的极间距离也减小。经试验验证,所提出的磁场辅助场致射流放电加工方法适用于具有沟槽类型特征的部件加工。

Experimental Research on Effects of Process Parameters on Servo Scanning 3D Micro Electrical Discharge Machining

Servo scanning 3D micro electrical discharge machining (3D SSMEDM) is a novel and effective method in fabricating complex 3D micro structures with high aspect ratio on conducting materials. In 3D SSMEDM process, the axial wear of tool electrode can be compensated automatically by servo-keeping discharge gap, instead of the traditional methods that depend on experiential models or intermittent compensation. However, the effects of process parameters on 3D SSMEDM have not been reported up until now. In this study, the emphasis is laid on the effects of pulse duration, peak current, machining polarity, track style, track overlap, and scanning velocity on the 3D SSMEDM performances of machining efficiency, processing status, and surface accuracy. A series of experiments were carried out by machining a micro-rectangle cavity (900 μm×600 μm) on doped silicon. The experimental results were obtained as follows. Peak current plays a main role in machining efficiency and surface accuracy. Pulse duration affects obviously the stability of discharge state. The material removal rate of cathode processing is about 3/5 of that of anode processing. Compared with direction-parallel path, contour-parallel path is better in counteracting the lateral wear of tool electrode end. Scanning velocity should be selected moderately to avoid electric arc and short. Track overlap should be slightly less than the radius of tool electrode. In addition, a typical 3D micro structure of eye shape was machined based on the optimized process parameters. These results are beneficial to improve machining stability, accuracy, and efficiency in 3D SSMEDM.

基于集成正交实验与CNN方法的微细电火花微孔加工精度

针对改善微细电火花微孔加工精度问题,提出一种集成正交试验与卷积神经网络的方法。首先,利用正交试验研究进给速度、主轴转速、脉冲占空比和脉冲频率4个因素对微细电火花加工H62黄铜微孔入口过切(En-OV)、出口过切(ExOV)和锥度(TA)的影响规律及其最优加工工艺参数。然后,采用基于PyTorch框架的卷积神经网络对试验结果进行预测。结果表明:对于微孔加工入口过切,各因素按影响程度由高到低依次为脉冲占空比、脉冲频率、进给速度和主轴转速;对于微孔加工出口过切,各因素按影响程度由高到低依次为进给速度、主轴转速、脉冲占空比和脉冲频率;对于微孔加工锥度,各因素按影响程度由高到低依次为进给速度、脉冲占空比、主轴转速和脉冲频率。综合考虑并分析各因素之间关系,通过验证实验得到微孔加工精度最优组合参数:进给速度为0.02mm/s、主轴转速为1000r/min、脉冲占空比为60%、脉冲频率为3000Hz。微孔加工入口过切、出口过切和锥度的预测值与试验真实值吻合程度较高,两者相对误差均小于12%。基于PyTorch框架的卷积神经网络(CNN)具有较高的预测准确性,满足实际生产加工需求,为微细电火花微孔加工精度预测研究提供了新方法,也为实际生产加工指导提供了依据。

微细EDM技术加工微齿轮的研究

本文通过用微细电火花（ＥＤＭ）方法加工模数为０．０６的微齿轮研究，阐述了微细ＥＤＭ方法加工微齿轮的原理、方法和关键技术。

斜率与变统计周期微细电火花脉冲识别系统

针对电压阈值法不能很好统计开路时长和改变放电电压时需要调节电压阈值等问题。提出一种基于斜率比值和变统计周期的脉冲识别方法,该方法使检测装置直接用于微细电火花粗磨、精磨两种不同开路电压的加工情形中,不需要调节电压阈值且能有效的统计开路时长,从而提高检测效率和精度。首先使用NI采集卡和LabVIEW软件开发脉冲识别系统,该系统可对间隙电压进行显示、连续存储以及对文件进行拆分,接着对斜率比值法和变统计周期法进行理论分析并编写脉冲识别与统计程序,最后进行放电状态检测的实验验证。结果表明:该方法能够识别不同脉冲且适用于不同放电电压情形,程序结果与实际结果较吻合,证明了该方法的有效性和实用性。

低速WEDM制备的微织构螺旋微铣刀的铣削实验研究

基于五轴低速走丝电火花线切割机床与回转机构相结合的加工方法,制备了后刀面具有微织构的螺旋微铣刀.建立了微织构螺旋微铣刀微刃单元的切削力理论模型,并开展微织构微铣刀与常规微铣刀的对比实验研究.结果表明:微织构螺旋微铣刀的切削力相对于常规刀具降低了30%~40%,相同加工条件下,微织构螺旋微铣刀所加工的表面粗糙度降低至0.745μm,而常规微铣刀所加工的表面粗糙度为1.130μm.

微细电火花加工中的放电能量分布研究

微细电火花加工技术已经广泛应用于精密制造领域,然而由于尺度效应的存在,其加工机理特别复杂,对于放电蚀除过程中的放电能量分布尚未明确。开展了微细电火花单脉冲放电实验,并考虑到熔化潜热和汽化潜热的影响,对传统的电热模型进行了修正,基于微细电火花的放电持续时间,计算了分布到工件中的能量分布比。结果发现,由于放电初期有相当一部分的放电能消耗于放电通道的形成,所以传入工件中的能量分数随着放电持续时间的增加而增大,在放电持续时间0.63~20.5μs时,分布到工件上的放电能量分数为7.1%~16.3%。伴随着放电持续时间的持续增加放电等离子体通道半径将会一定程度增大,放电等离子体通道半径随放电持续时间的变化范围是5.9~23.2μm。

Scale Effects and a Method for Similarity Evaluation in Micro Electrical Discharge Machining

Electrical discharge machining（EDM） is a promising non-traditional micro machining technology that offers a vast array of applications in the manufacturing industry. However, scale effects occur when machining at the micro-scale, which can make it difficult to predict and optimize the machining performances of micro EDM. A new concept of ＂scale effects＂ in micro EDM is proposed, the scale effects can reveal the difference in machining performances between micro EDM and conventional macro EDM. Similarity theory is presented to evaluate the scale effects in micro EDM. Single factor experiments are conducted and the experimental results are analyzed by discussing the similarity difference and similarity precision. The results show that the output results of scale effects in micro EDM do not change linearly with discharge parameters. The values of similarity precision of machining time significantly increase when scaling-down the capacitance or open-circuit voltage. It is indicated that the lower the scale of the discharge parameter, the greater the deviation of non-geometrical similarity degree over geometrical similarity degree, which means that the micro EDM system with lower discharge energy experiences more scale effects. The largest similarity difference is 5.34 while the largest similarity precision can be as high as 114.03. It is suggested that the similarity precision is more effective in reflecting the scale effects and their fluctuation than similarity difference. Consequently, similarity theory is suitable for evaluating the scale effects in micro EDM. This proposed research offers engineering values for optimizing the machining parameters and improving the machining performances of micro EDM.

高品质大深径比微孔电火花加工研究现状

针对大深径比深微孔加工面临单一维度下大深径比高导致的排屑难等问题,综述了利用电火花技术加工深微孔的方法及演变。从工具电极的结构设计、运动规划和能场辅助方式等常用方法论述了目前电火花加工深微孔现状,同时介绍了提升深微孔加工表面质量的主要方法,最后探讨了当前电火花加工深微孔面临的瓶颈及未来发展趋势。

基于SLA成形的EDM电极加工工艺

介绍基于立体光成形(SLA)EDM电极的加工工艺。该工艺将CAD、SAL壳形铸造与真空离心铸造相结合,特别 适宜具有微形复杂形状EDM电极的单件、小批量生产,并使传统分散、多工序的EDM电极加工工艺实现了集成化和自 动化。

Fabrication of Micro Structures by Ultrashort Voltage Pulse Electrical Discharge Machining

The machining of small holes and array holes has been a difficult problem in machining field. Tiny hole is widely used in mechanical field, for instance, fuel injection nozzles, spinneret holes for synthetic fibers and wire drawing dies. This paper investigated the application of EDM (electrical discharge machining) to the fabrication of micro structures. There are obvious limitations in the process of micro-electrical discharge machining, such as electrode wear, unstable discharge condition and low machining efficiency. The effects of EDM parameters were investigated, such as voltage, pulse frequency, and frequency of ultrasonic vibration applied to electrode. Micro holes were machined with Pt electrode made by focused-ion-beam chemical vapor deposition (FIB-CVD) and Cu electrode made by wire-electrode cutting. The comparison experiments between EDM and ECM (electrochemical machining) indicated that the processing of ECM has serious stray current corrosion and poor machining precision. Moreover, the workpiece vibration was firstly proposed to be utilized in the micro-electrical discharge machining. It can be concluded that maximum machine could be obtained under the amplitude ratio of 76%, which was an appropriate parameter.