Probability of precision micro-machining of insulating Si3N4 ceramics by EDM

Electrical discharge machining (EDM) is used as a precision machining method for the electrically conductive hard materials with a soft electrode material. But recently we succeeded to machine on insulating material by EDM. The technology is named as an assisting electrode method. The EDMed surface is covered with the electrical conductive layer during discharge. The layer holds the electrical conductivity during discharge. For micro-EDM, the wear of tool electrode becomes lager ratio than the normal machining. So the micro-machining is extremely difficult to get the precision sample.

In this paper to obtain a fine and precise ceramics sample, some trials were carried out considering the EDM conditions, tool electrodes material and assisting electrode materials. Insulating Si₃N₄ ceramics were used for workpiece. The machining properties were estimated by the removal rate and tool wear ratio. To confirm the change of micro-machining process, the discharge waveforms were observed. The micro-machining of the Ø0.05 mm hole could be machined with the commercial sinking electrical discharge machine.     

送电距离对绝缘陶瓷电火花加工生成导电膜特性的影响

采用辅助电极法，在设定加工条件下，对绝缘陶瓷材料Si3N4进行了电火花加工实验．研究了送电距离（指金属夹具与被加工位置的最近距离）对生成导电膜的厚度、电阻等特性的影响，得出了送电距离越远，生成的导电膜越薄、电阻越大及加工速度越小的结论。     

Layer Generation Process on Work-piece in Electrical Discharge Machining

In recant years, surface modification of metals and machining of insulating ceramics by electrical discharge machining (EDM) have been successfully carried out. In surface modification by EDM with semi-sintered electrodes, worn substances in the gap region form the material source of the layer generated on the work-piece surface. In the machining of insulating ceramics by EDM, a crystallized carbon layer or carbide layer from the working oil covers the surface of the insulator. Increase in the thickness of the generated layer, however, tends to stop at a certain maximum value in both surface modification by EDM with semi-sintered electrodes and machining of insulating ceramics by EDM processes. In these machining operations, accretion and removal phenomena occur alternately. In this paper, the mechanisms of machining insulators and the accretion process are discussed considering the characteristics of the generated layers on the work-piece surface.     

绝缘性陶瓷电火花加工中生成导电膜的特性分析

采用辅助电极法，在设定加工条件下对绝缘性陶瓷材料Si3N4进行了电火花加工实验，分析了加工中生成导电膜的原因，研究了加工条件、加工深度与生成导电膜的厚度、电阻等特性的关系，指出了加工深度对生成导电膜的影响较大，且加工深度越深，生成导电膜厚度越厚、电阻越小。     

Effect of electrode material on electrical discharge machining of alumina

Technologies for machining advanced insulating ceramics are demanded in many industrial fields. Recently, several insulating ceramics, such as Si₃N₄, SiC and ZrO₂, have been successfully machined by electrical discharge machining (EDM). As unstable discharges occur during the machining of Al₂O₃ ceramics, inferior machining properties have been obtained. The formation mechanism of the electrical conductive layer on the EDMed surface is much different as compared to other ceramics. In addition to this, the electrically conductive layers are not formed sufficiently to adhere to the EDMed workpiece surface and keep a stable and continuous discharge generation on the ceramics. Graphite is widely used as electrode material in EDM. It is expected that carbon from graphite electrode implant and generate a conductive layer. Copper, graphite (Poco EDM-3) and copper-infiltrated-graphite (Poco EDM-C3) electrodes were used to compare the effects of generation of a conductive layer on alumina corresponding to EDM properties. The electrical discharge machining of 95% pure alumina shows that the EDM-C3 performs very well, giving significantly higher material removal rate (MRR) and lower electrode wear ratio than the EDM-3 and copper electrodes. The value of MRR was found to increase by 60% for EDM-3 with positive electrode polarity. As for EDM-C3, MRR was increased by 80% under the same condition. When the results were investigated with energy dispersive spectroscopy (EDS), no element of copper was observed on the conductive layer with both EDM-3 and EDM-C3. However, surface resistivity of a conductive layer created with EDM-C3 is less than with EDM-3. Surface roughness was improved to 25 μm with positive polarity of EDM-C3.     

Effect of machining fluid on the process performance of electric discharge milling of insulating Al2O3 ceramic

Wire electric discharge machining (WEDM) and electrical discharge machining (EDM) promise to be effective and economical techniques for the production of tools and parts from conducting ceramic blanks. However, the manufacturing of insulating ceramic blanks with these processes is a long and costly process. This paper presents a new process of machining insulating ceramics using electrical discharge (ED) milling. ED milling uses a thin copper sheet fed to the tool electrode along the surface of the workpiece as the assisting electrode and uses a water-based emulsion as the machining fluid. This process is able to effectively machine a large surface area on insulating ceramics. Machining fluid is a primary factor that affects the material removal rate and surface quality of the ED milling. The effects of emulsion concentration, NaNO₃ concentration, polyvinyl alcohol concentration and flow velocity of the machining fluid on the process performance have been investigated.     

石墨电极电火花加工非导电陶瓷SiO2实验研究

以导电胶涂层作为辅助电极、石墨作为工具电极,用实验的方法考察了电火花加工非导电陶瓷SiO2的可行性;证明在正极性加工条件下,石墨电极能增强导电膜生成,提高加工稳定性;并给出了脉冲宽度、加工电流等电参数对加工速度、电极损耗及表面质量等工艺指标的影响规律,得出了一些有益的结论.     

绝缘工程陶瓷的特种加工技术

针对用机械磨削方法加工绝缘工程陶瓷存在成本高、效率低和工件表面易产生微裂纹等问题，国内外学者开展了大量的研究工作，并取得了较大的研究进展。概述了绝缘工程陶瓷的激光加工、超声加工、电火花加工、等离子弧切割等特种加工技术，并对这些加工技术的原理、特点和应用状况等进行了分析评述。     

绝缘陶瓷高瞬时能量密度单脉冲放电的数值模拟

基于热传导理论建立了绝缘陶瓷高瞬时能量密度单脉冲放电的温度场模型,并对陶瓷工件、工具电极和辅助电极的温度场进行了三维数值模拟,得到了不同介质和峰值电压对陶瓷工件、工具电极和辅助电极上温度场影响规律的关系.将数值模拟与试验结果进行了对比,结果表明,所建立的绝缘陶瓷高瞬时能量密度单脉冲放电模型能较好地预测放电坑深度和体积的...     

绝缘陶瓷氮化硅高速走丝线切割加工技术研究

通过辅助电极利用高速走丝电火花线切割加工的方法对绝缘陶瓷氮化硅作了加工实验研究.介绍了辅助电极法绝缘陶瓷电火花线切割加工原理.通过调整加工电参数,研究了线切割加工氮化硅的加工特点,得出了较理想的加工参数,并对氮化硅线切割加工的去除方式作了初步研究.     

微细电火花铣削工件侧面轮廓加工研究

开展了不同分层厚度电火花铣削侧面轮廓加工研究,通过改变线性补偿值,研究不同补偿率下的电极形状与稳定铣削深度,获得了较大分层厚度下的恒定深度铣削槽;分析总结了锥形电极的形成与稳定原因和不同补偿量对电火花铣槽影响的相关规律;通过线性补偿法对圆弧形片状工件和具有一定倾角工件的侧面加工铣削,验证了实验规律.     

电火花表面改性/合金化技术研究进展

电火花表面改性/合金化不同于传统的表面处理技术,它基于电火花加工的原理,利用放电产生的高温使电极瞬间熔化,并与基体发生冶金化学反应形成涂层.涂层成分设计不同,具有耐磨、耐蚀等不同功能.涂层的厚度可控,成分和硬度分布具有梯度性.介绍了电火花表面合金化技术的特点和原理,综述了国内外的研究进展情况,分析了能量等因素对电极和工...     

A study of EDM and ECM/ECM-lapping complex machining technology

EDM (electrodischarge machining) and ECM (electrochemical machining)/ECM-lapping complex machining is investigated in this paper. First, EDM shaping and ECM finishing technology are investigated. These processes are carried out in sequence on the same machine tool with the same electrode (copper) and the same machining liquid (water). Two types of EDM and ECM complex machining are investigated. One is with a formed electrode, and the other is with simple-shape electrode scanning. The complex machining with electrode scanning is applied to produce small and various-shaped components without making a formed electrode. The EDM surface of 1 μm Ra is improved to 0.2 μm Ra by applying ECM. Second, in order to get a smoother surface, a new EDM and ECM-lapping complex machining technology is developed. The surface roughness of a machined hole is improved to 0.07 μm Ra by applying 2 min of ECM lapping. The surface finishing of a hole shape is demonstrated with the complex machining technology.     

微细电火花伺服扫描加工实验研究

进行微细电火花三维扫描加工时,由于电极损耗相对严重,导致形位公差难以保证和加工效率较低。该研究分析了电火花加工常规的电极损耗补偿方法,提出了基于放电间隙伺服控制进行电极损耗实时补偿的微细电火花三维扫描加工方法。辅助以电极电接触感知工件平面和加工原点,三维结构加工实验显示,采用间隙伺服控制进行电极损耗实时补偿有利于提高扫描加工微三维结构的形位精度和加工效率。     

A review on current research trends in electrical discharge machining (EDM)

Electrical discharge machining (EDM) is one of the earliest non-traditional machining processes. EDM process is based on thermoelectric energy between the work piece and an electrode. A pulse discharge occurs in a small gap between the work piece and the electrode and removes the unwanted material from the parent metal through melting and vaporising. The electrode and the work piece must have electrical conductivity in order to generate the spark. There are various types of products which can be produced using EDM such as dies and moulds. Parts of aerospace, automotive industry and surgical components can be finished by EDM. This paper reviews the research trends in EDM on ultrasonic vibration, dry EDM machining, EDM with powder additives, EDM in water and modeling technique in predicting EDM performances.     

基于旋转电极的方孔电火花加工新方法

提出一种方孔电火花加工新方法,利用具有勒洛三角形截面形状的工具电极在等宽方形约束孔中转动,使电极沿横截面扫过一个正方形区域,从而通过电极底面放电加工出方孔。分析了勒洛三角形电极在与其等宽的方孔中的运动方式和轨迹,设计了基于旋转电极的方孔电火花加工装置,通过实验验证了该方法的可行性。在不同的开路电压下,分别利用旋转的勒洛三角形电极和不旋转的方形电极进行方孔加工,发现旋转的勒洛三角形电极加工效率更高、电极损耗更低。     

Tool path generation for 4-axis contour EDM rough machining

Contour or CNC EDM machining of free-form surfaces requires tool paths that are different from those used in mechanical milling although in geometry both processes are described by the similar model of intersection between the rotating tool and the workpiece. In this paper, special requirements on tool paths demanded by contour EDM machining are studied and a two-phase tool path generation method for 4-axis contour EDM rough milling with a cylindrical electrode is developed. In the first phase of the method, initial tool paths for virtual 3-axis milling are generated in a commercial CAD/CAM system—Unigraphics, which provides users with plenty of options in choosing suitable tool path patterns. From these tool paths, cutter contact (CC) points between electrode and workpiece are reversely calculated. In the second phase, considering the special requirements of EDM machining, which include discharging gap compensation, electrode wear compensation, DC arcing prevention, etc., the electrode is adjusted to an optimized interference-free orientation by rotating it around the CC points obtained in the previous phase. This new orientation together with the reference point of electrode is output as new tool path. The whole algorithm has been integrated into Unigraphics, machining simulations and tests have been conducted for 4-axis contour EDM rough machining.     

电阻率对工程陶瓷电火花加工性能的影响研究

常用的工程陶瓷电阻率较高,直接采用电火花加工,性能较差。以ZnO/Al_2O_3陶瓷为例,研究了电阻率和脉冲宽度、脉冲间隔、工具极性等工艺参数对电火花加工工艺性能的影响。结果表明:采取合适的放电加工参数,在ZnO/Al2O3的电阻率达到3410Ω·cm时仍可对其进行有效的电火花加工。     

Electrical discharge machining of Ti6Al4V with a bundled electrode

The aim of this study is to investigate an efficient Ti6Al4V electrical discharge machining (EDM) process with a bundled die-sinking electrode. The feasibility of machining Ti6Al4V with a bundled electrode was studied and its effect on EDM performance was compared experimentally using a solid die-sinking electrode. The simulation results explain the high performance of the EDM process with a bundled electrode by through the use of multi-hole inner flushing to efficiently remove molten material from the inter-electrode gap and through the improved ability to apply a higher peak current. A 3-factor, 3-level experimental design was used to study the relationships between 2 machining performance parameters (material removal rate: MRR, tool wear ratio: TWR) and 3 machining parameters (fluid flow rate, peak current and pulse duration). The main effects and influences of the 2-factor interactions of these parameters on the performances of the EDM process with the bundled electrode are discussed.     

电火花摇动加工微细阵列轴和孔的试验研究

针对微细阵列轴和孔的电火花加工,提出了利用数控电火花加工机床摇动功能的摇动加工微细阵列轴和孔的方法.此法是基于电火花反拷贝加工的原理,先用丝电极在薄平板(中间电极)上按要加工的阵列轴和孔间距或数倍间距加工阵列小孔(直径0.1 mm以上),然后用加工的薄平板(中间电极)作电极,电火花摇动加工微细阵列轴(电极),最后用此微细阵列电极加工阵列孔.进行了电火花摇动加工微细阵列电极试验,得到了单电极直径为50 μm、长径比为16的3×3阵列电极,并用此电极在70 μm厚的不锈钢板上加工出单孔直径为70 μm的3×3微细阵列孔.试验结果表明,电火花摇动加工方法可实现微细阵列轴和孔的加工.