Improvement in machining speed with working gap control in EDM milling

High-speed electrical discharge machining (EDM) milling is investigated with working gap control. EDM milling has a merit that does not need complex electrode fabrication; however, it is necessary to improve the removal rate in EDM milling. Rotation of the electrode improves the removal rate, but this rotation causes a periodic change in the working voltage. As a consequence, the periodic change causes a disturbance that decreases the control performance. EDM milling realizes a high machining precision by the scanning method. A small working area allows for fast scanning. If the working gap is appropriate, it becomes longer because the machined surface of the workpiece is removed. Therefore, the conventional controller remains at the steady offset and lowers the machining efficiency. The proposed controller introduces a notch filter, which eliminates the frequency component due to rotation of the electrode. It also has a feed-forward compensator to eliminate the steady offset. The controller for each machining condition is derived from a coordinate transformation and the least-squares approximation. It is confirmed that the proposed controller achieves machining speeds that are 2–6 times faster in a straight line and greater than 30% higher in the profile machining than in the conventional one.     

Study of EDM cutting of single crystal silicon carbide

Electrical discharge machining (EDM) is developing as a new alternative method for slicing single crystal silicon carbide (SiC) ingots into thin wafers. Aiming to improve the performance of EDM slicing of SiC wafers, the fundamental characteristics of EDM of SiC single crystal were experimentally investigated in this paper and compared to those of steel. Furthermore, EDM cutting of SiC ingot by utilizing copper foil electrodes was proposed and its performance was investigated. It is found that the EDM characteristics of SiC are very different from those of steel. The EDM machining rate of SiC is higher and the tool wear ratio is lower compared to those of steel, despite SiC having a higher thermal conductivity and melting point. Thermal cracks caused by the thermal shock of electrical discharges and the Joule heating effect due to the higher electrical resistivity are considered to be the main reasons for the higher material removal rate of SiC. It is concluded that the new EDM cutting method utilizing a foil electrode instead of a wire electrode has potential for slicing SiC wafers in the future.     

Multi-discharge EDM coring of single crystal SiC ingot by electrostatic induction feeding method

A new technique of EDM coring of single crystal silicon carbide (SiC) ingot was proposed in this paper. Currently single crystal SiC devices are still of high cost due to the high cost of bulk crystal SiC material and the difficulty in the fabrication process of SiC. In the manufacturing process of SiC ingot/wafer, localized cracks or defects occasionally occur due to thermal or mechanical causes resulted from fabrication processes which may waste the whole piece of material. To save the part of ingot without defects and maximize the material utilization, the authors proposed EDM coring method to cut out a no defect ingot from a larger diameter ingot which has localized defects. A special experimental setup was developed for EDM coring of SiC ingot in this study and its feasibility and machining performance were investigated. Meanwhile, in order to improve the machining rate, a novel multi-discharge EDM coring method by electrostatic induction feeding was established, which can realize multiple discharges in single pulse duration. Experimental results make it clear that EDM coring of SiC ingot can be carried out stably using the developed experimental setup. Taking advantage of the newly developed multi-discharge EDM method, both the machining speed and surface integrity can be improved.     

铝基碳化硅异形电极电火花加工技术研究

为了改善电火花深小孔加工过程中,因加工碎屑排出不畅而导致的加工速度慢、电极损耗严重等问题,制备螺旋、三沟槽和削边三种形貌的异形结构电极。在相同的加工条件下,以铝基碳化硅为实验材料,采用异形结构电极与圆柱电极分别进行不同深度下深小孔加工实验,对加工效率、电极损耗和深小孔内表面形貌三方面进行对比分析。实验结果表明:异形结构电极在深小孔的加工效率和电极损耗方面都优于圆柱电极;小孔内表面形貌方面:圆柱电极加工后的孔内表面附着碎屑较多。     

螺旋电极电解扩孔工艺研究

介绍了螺旋电极电解扩孔，该方法兼有小间隙电解加工和脉冲电流电解加工的优点，用于硬质金属材料导孔的加工是一种行之有效的新的工艺方法，文对其中原理。加工实验研究和基本工艺规律作了综述。     

Precision machining of micro tool electrodes in micro EDM for drilling array micro holes

Micro electro discharge machining (micro EDM) is suitable for machining micro holes on metal alloy materials, and the micro holes can be machined even to several microns by use of wire electro discharge grinding (WEDG) of micro electrodes. However, considering practicability of micro holes <Φ100 μm in batch processing, the controllable accuracy of holes’ diameter, the consistency accuracy of repeated machining and the processing efficiency are required to be systematically improved. On the basis of conventional WEDG method, a tangential feed WEDG (TF-WEDG) method combined with on-line measurement using a charge coupled device (CCD) was proposed for improving on-line machining accuracy of micro electrodes. In TF-WEDG, removal resolution of micro-electrode diameter (the minimum thickness to be removed from micro electrode) is greatly improved by feeding the electrode along the tangential direction of wire-guide arc, and the resolution is further improved by employing negative polarity machining. Taking advantage of the high removal resolution, the precise diameter of micro-electrode can be achieved by the tangential feed of electrode to a certain position after diameter feedback of on-line measurement. Furthermore, a hybrid process was presented by combining the TF-WEDG method and a self-drilled holes method to improve the machining efficiency of micro electrodes. A cyclic alternating process of micro-electrode repeated machining and micro holes’ drilling was implemented for array micro holes with high consistency accuracy. Micro-EDM experiments were carried out for verifying the proposed methods and processes, and the experimental results show that the repeated machining accuracy of micro electrodes was less than 2 μm and the consistency accuracy of array micro holes was ±1.1 μm.     

超声电火花复合加工速度工艺试验研究

电火花加工的最大缺点是加工速度低，为了解决这个问题，人们进行了各种试验研究。其中超声电火花复合在加工小孔中可一定程度地提高加工速度，但就其作用机理和适用范围仍存在许多争论。本次试验在D703F高速电火花小孔加工机床上附加陶瓷换能器和变幅杆，通过夹紧装置将变幅杆与工具电极相连，实现电极超声振动的电火花小孔加工。在不同的电参数（电流强度和脉冲宽度）和电极参数（电极直径）下，进行了2种加工方法下的加工速度对比试验。找到了在加工小孔时，是否采用超声电火花复合加工工艺的分界点，对其增加加工速度的现象提出了新的解释。     

分散剂在电火花小孔加工中的作用机理及试验研究

从研究水分散剂的分散机理入手,分析研究了水分散剂对电火花小孔加工的排屑、加工速度和加工质量的影响。通过电火花小孔加工中采用自来水工作液和分散剂工作液的加工效果对比,发现在电火花小孔加工的水基工作液中加入一定比例的分散剂后,不仅使电火花小孔加工的加工速度提高、电极相对损耗降低,而且有效脉冲数增加,二次放电数明显减少,工具电极作用端和被加工孔的锥度变小,加工质量提高。     

An analysis of overcut variation and coupling effects of dimensional variable in EDM process

In the electrical discharge machining (EDM) process, the overcut greatly affects the precision and accuracy of the workpiece dimensions. However, the overcut and the final workpiece dimensions are difficult to predict due to the non-linear, complex relationship among the electrode wear, the electrode diameter, electrical discharging parameters, and the machine positioning accuracy. In the present study, the variation of the side overcut and the bottom overcut, the electrode dimensions, the spark hole dimensions, and the machine positioning accuracy in the EDM process are investigated. Variance analysis is used in a batch process under different electrical discharging parameters. The experiment results show that the coupling effect between the electrode diameter and spark hole diameter is an important factor for estimating the variation of the side overcut in the EDM process. With inclusion of the coupling effects, the predicted variation of side and bottom overcut in a batch EDM process and the EDM machine positioning accuracy is shown to be in good agreement with experimental results.     

Micro-hole Maching of Copper Using the Electro-discharge Machining Process with a Tungsten Carbide Electrode Compared with a Copper Electrode

This paper describes micro-hole machining of a copper plate using the electro-discharge machining (EDM) process. Tungsten carbide was selected as the material for the electrode and compared with a copper-electrode. A precision centreless grinding process was employed to grind the electrode down to the desired diameter. A series of experiments were performed on a traditional EDM machine to investigate the effects of electrode material polarity setting and of a rotating electrode. Results have shown that electrode wear and hole enlargement are both smaller when positive polarity machining is selected; whereas electrode wear is larger and machining speed is higher when negative polarity machining is selected. High-quality micro-hole machining in copper can be achieved by the proposed method.     

微通道结构带状电极电火花加工方法研究

针对大厚度、高深宽比金属微通道结构加工的难题,提出一种带状电极电火花加工方法,利用厚度30～100 μm的带状电极,在金属基体上高效制造微通道结构。研究了带状电极电火花加工机理,建立了带状电极在加工间隙中的运动模型,分析了影响带状电极运动的主要因素,搭建了带状电极电火花加工装置,开展了微通道结构带状电极加工实验研究,获得了带状电极电火花加工基础工艺规律。利用带状电极电火花加工方法成功加工出的具有200条微通道的反应器结构和44×45微换热器阵列结构,表明带状电极电火花加工可以实现窄宽度(100 μm以下)、大厚度(35 mm以上)、高深宽比(10以上)和高精度(缝宽标准差3 μm以内)的大批量微通道结构的高效加工,相关方法和技术有望在微模具、微散热器、微反应器等领域获得推广和应用。     

Investigating and removing the re-sticky debris on tungsten carbide in electrical discharge machining

Electrical discharge machining (EDM) is an excellent method to machine tungsten carbide with high hardness and high toughness. However, debris from this material produced by EDM re-sticking on the workpiece surface remarkably affects working efficiency and dimension precision. Therefore, this study investigated the re-sticky phenomenon of tungsten carbide and how to reduce the debris re-sticking on the workpiece surface. In general, the polarity in EDM depended on the different electrical parameters of the machine input and the different materials of the tool electrode. The first item of investigation observed the re-sticky position of the debris to study the effect of different polarities during the EDM process. Next, the tool electrode was set at different conditions without rotation and with a 200 rpm rotational speed to evaluate the rotating effect in EDM. Finally, different lift distances of the electrode and different shapes of electrode with rotation were utilized to investigate the improvement for reducing debris re-sticking on the machining surface. The results showed that only negative polarity in EDM could cause the re-sticky phenomenon on tungsten carbide. On the other hand, debris would notably re-stick on any machining position when the tool electrode was not rotated in EDM. Besides, debris significantly stuck on the center of the working area with rotation of the electrode. Additionally, a larger lift distance of the tool electrode could reduce debris re-sticking on the working surface, but this process would decrease material removal rate in EDM. In the end, a special shaped design of the tool electrode resulted in the re-sticky debris completely vanishing, when the electrode width was 0.6 times the diameter of this cylindrical electrode.     

Analysis of the machining characteristics of EDM as functions of the mobilities of electrons and ions

Electrical discharge machining (EDM) is a process that can be used effectively to machine conductive metals regardless of their hardness. In the EDM process, material removal occurs because of the thermal energy of the plasma channel between the electrode and the workpiece. During EDM, the electrode as well as the workpiece is abraded by the thermal energy. Tool wear adversely affects the machining accuracy and increases tooling costs. Many previous studies have focused on mitigating the problems of tool wear by investigating various EDM parameters. In this study, the tool wear problem was investigated on the basis of the mobilities of electrons and ions in the plasma channel. The material removal volumes of both the electrode and the workpiece were compared as functions of the gap voltage. The material removal difference according to the capacitance was also investigated. The tool wear ratio was calculated under different EDM condition and an EDM conditions for reducing the tool wear ratio was suggested.     

TC4钛合金电火花小孔加工多目标优化试验研究

为提升电火花加工TC4钛合金的表面加工质量和加工效率,选取紫铜圆柱电极开展TC4钛合金电火花小孔加工试验,采用正交试验法,以电极相对损耗率、表面粗糙度、工件材料去除体积为工艺指标,分析峰值电流、维持电压、放电脉宽对工艺指标的影响重要性。采用RBF(Radial basis function)神经网络对已有试验数据进行训练,建立放电参数与工艺指标之间的数学预测模型。以该预测模型为适应度函数,将遗传算法与Skyline选择算法结合进行多目标优化仿真,得到最佳工艺指标,最后开展多目标优化验证试验。结果表明：当峰值电流为14 A、维持电压39 V/42 V、放电脉宽102μs/108μs时能够取得最优的加工结果,优化值与试验值误差较小。     

高精度硬质合金套类零件的加工方法

介绍硬质合金套类零件电解和电解磨削加工的基本原理,综合运用了以下多种新工艺:螺旋电极电解扩孔、螺旋 电极电解磨孔、中极法电解磨削外圆及端面。     

高精度镗刀微调机构

在镗床上加工或修理高精度内孔时,普遍存在刀具调整难、效率低、加工精度难以保证的问题。提出了一种高精度镗刀微调机构,该机构利用大传动比轮系传动,通过微调镗刀的径向移动量,其孔径加工精度可达1μm以下。     

Feasibility study of micro-slit EDM machining using pure water

This study addresses micro-slit EDM machining feasibility using pure water as the dielectric fluid. Experimental results revealed that pure water could be used as a dielectric fluid and adopting negative polarity EDM machining could obtain high material removal rate (MRR), low electrode wear, small slit expansion, and little machined burr, compared to positive polarity machining. In comparing kerosene versus pure water, pure water was observed to cause low carbon adherence to the electrode surface. Also discharge energy does not decrease and the discharge processes are not interrupted. Therefore, MRR was higher, and related electrode wear ratio compared to kerosene use was lower. In a continual EDM with multi-slit machining, kerosene will cause carbon element adherence, creating an initially high MRR and electrode wear, with rapid decline. However, pure water will not cause carbon element adherence on the electrode surface, so MRR and electrode wear is always stable in this process.     

On the temperature and specific energy during electrodischarge diamond grinding (EDDG)

Electrodischarge diamond grinding (EDDG) is a hybrid machining process comprising conventional grinding and electrodischarge machining (EDM) as its constituent processes. It has the potential of shaping advanced engineering materials. Temperature of the workpiece and material removal rate are chosen as responses in full factorial (3³) design with current, pulse-on time, and wheel speed as process parameters. Specific energy is a vital consideration for any machining process. EDM is known for its inefficiency. Experiments were conducted with a specially fabricated bronze disk as tool electrode to evaluate specific energy in EDM, and the results were compared with that of EDDG. It has been found that specific energy required in EDDG is less than that in EDM with a rotating disk electrode.     

Improvement of EDM efficiency with a new adaptive control strategy

In most of the commercially available EDM systems, the control parameters such as the electrode jump height and the discharge machining time between two consecutive electrode jump actions are set manually to constant values which can ensure stable machining even under the worst machining conditions. It is beneficial to keep the machining process stable, but much time is consumed in the electrode jump process. In order to improve the EDM efficiency, a new adaptive control strategy which directly and automatically regulates the electrode jump height and discharge machining time has been developed in this paper. Experimental results show that the adaptive control system can obviously improve the machining efficiency regardless of the surface area, shape, and depth of the machined dies. Meanwhile, the accuracy and surface roughness of the fabricated dies can be well retained.     

单晶硅游离磨粒线切割技术研究

游离磨料多线切割技术具有切割效率高、切口材料损耗小、表面损伤程度浅、切割噪声小等优点，能满足晶圆大直径化发展的加工需求。但游离磨料线切割技术发展历史短，目前还缺乏对游离磨料线切割过程材料的去除本征规律的充分认识和系统研究。本文介绍了游离磨料线切割方法的工作原理，综合分析了游离磨料线切割硅片的材料去除机理、切割线振动模型、切割温度及其影响因素等方面的研究结果，以期为游离磨料多线切割技术的深入研究和推广应用提供基础。