Experimental Investigation on Electrical Discharge Drilling of Ti-6Al-4V Alloy

This article describes the experimental investigation related to creation of holes in aerospace titanium alloy workpiece using static electrode machining and electrical discharge drilling (EDD) process. Special attachment for holding and rotating the tool electrode was developed and installed on electrical discharge machining (EDM) machine by replacing the original conventional tool holder provided on die sinking EDM. The effect of input parameters such as gap current, pulse on-time, duty factor and RPM of tool electrode on output parameters for average hole circularity (C_a) and average surface roughness (R_a) have been studied. It is observed that the effect of rotating electrode machining has considerable influence on the output parameters over stationary electrode machining. The micro-graphs and photographs of few selected samples were taken by SEM and metallurgical microscope, which also commensurate with the findings of the study.     

节能式电火花加工脉冲电源的系统设计

在对比传统电阻限流独立式电火花加工脉冲电源和节能式脉冲电源电路结构和控制策略的基础上，提出了节能式电火花加工脉冲电源的系统设计方案，并且通过工艺试验，在检验节能式电火花加工脉冲电源加工工艺性能的同时，也考察了其系统设计的方案可行性和加工稳定性。     

空气中微细电火花沉积的工艺规律研究

论述了一种新的电火花加工方法，它通过合理选择工艺条件在空气中将金属材料放电沉积在工件上。对电火花沉积加工的基本原理进行了分析，预测了实现条件，使用通用的电火花成形加工机床和常见的电极材料黄铜，在空气介质中，通过大量实验对微细电火花沉积进行了系统研究，得出各工艺参数的影响规律。在高速钢工件表面沉积出直径为0．19mm、高度为7.35mm的微小圆柱体。对沉积材料的测试表明，沉积材料致密，与基体结合紧密，成分取决于工具电极材料，同时基体硬度得到提高。     

MICRO ELECTRICAL DISCHARGE MACHINING DEPOSITION IN AIR

A new deposition method is described using micro electrical discharge machining (EDM) to deposit tool electrode material on workpiece in air. The basic principles of micro electrical discharge deposition (EDD) are analyzed and the realized conditions are predicted. With an ordinary EDM shaping machine, brass as the electrode, high-speed steel as the workpiece, a lot of experiments are carried out on micro EDD systematically and thoroughly. The effects of major processing parameters, such as the discharge current, discharge duration, pulse interval and working medium, are obtained. As a result, a micro cylinder with 0.19 mm in diameter and 7.35 mm in height is deposited. By exchanging the polarities of the electrode and workpiece the micro cylinder can be removed selectively. So the reversible machining of deposition and removal is achieved, which breaks through the constraint of traditional EDM. Measurements show that the deposited material is compact and close to workpiece base, whose components depend on the tool electrode material.     

Characteristics of MEDM for micro-holes with respect to circuit elements

Micro electrical discharge machining (MEDM) is a promising technology for fabricating micro-parts on a variety of materials. An RC circuit is suitable for MEDM because it produces low pulse width and relatively high peak current. However, it is not well understood how circuit elements affect machining characteristics of MEDM. In this paper, the effects of circuit elements on MEDM of micro-holes and the relation between characteristic variables of process and machining characteristics was investigated. Since the discharge inductance causes an increase in electrode wear and machining time, it should be minimized in MEDM. From this study, it should be less than a few μH. The machining time also increases with increasing the charging resistance. If the charging resistance is less than a few hundreds Ω, however, continuous arc discharge occurs and the machining speed is markedly reduced.     

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.     

复合运丝型电火花线切割加工参数分析与研究

提出了一种新型电火花线切割机床,即电极丝作往复直线运动的同时还绕自身轴线高速旋转的复合运丝型线切割机床。介绍了该类机床与其他线切割机床加工的基本工艺指标。通过与高速走丝电火花线切割机床比较实验,分析了脉冲宽度、脉冲间隔、脉冲峰值电流等电参数对加工工艺指标的影响,实验表明这种独特的复合运丝方式在降低表面粗糙度、提高加工精度等方面较传统运丝方式具有较大的优越性,且机床结构较为简单,对于各种工艺参数和电参数具有更加广泛的适用性,具有进一步研究和推广价值。     

Three-dimensional shaping by dot-matrix electrical discharge machining

This paper deals with a new prototyping method called dot-matrix electrical discharge machining (EDM) with scanning motion. The machining process by the dot-matrix method is similar to printing motion with a dot-impact printer. This method can be applied not only to EDM but also electrochemical machining and forming. A prototype of the machining unit for the dot-matrix method has six feeding devices for thin wire electrodes. The electrodes of 300 μm in diameter are arranged with the pitches of 760 μm. To obtain a smooth surface, a planetary motion in the x-y-plane is added to the feeding of the machining unit in the z-direction, the same area is machined repeatedly, or the machining unit is moved with fine feed. By compensating for the wear of the electrode during the scanning EDM, various shapes with the accuracy of micrometers order can be obtained without a formed tool electrode.     

进电方式对高阻半导体硅放电加工影响研究

进行了高阻半导体硅的放电铣削加工实验,通过检测脉冲放电电压和电流波形,对固定、旋转、随动三种进电方式下的加工情况进行了对比。结果表明：固定进电方式下,由于进电点会逐步生成不导电的钝化膜,接触电阻不断增大,回路中的总电阻不断增大,放电峰值电流逐步减小,最终导致无法加工;旋转进电方式下,由于进电电极与加工区域距离增大,导致放电回路中的体电阻不断增大,放电峰值电流也会逐步减小;随动进电方式下,放电回路中进电电极会不断刮除产生的钝化膜且极间距离维持不变,因此接触电阻和体电阻能保持始终稳定,放电加工稳定性较好。
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气中微细电火花线切割加工实验研究

气中微细电火花线切割加工用气体作加工介质,可加工难切削材料、复杂零件,具有低应力、无毛刺等特点。研究了气中微细电火花线切割加工中开路电压、极间电容、气压以及相对进给速度对试件切槽宽度和表面粗糙度的影响。实验结果显示：气压、相对进给速度和极间电容对切槽宽度和表面粗糙度有明显影响,开路电压的变化对加工结果产生有限影响。     

半导体硅电极多通道放电机理研究

为了实现电火花加工同一时刻形成多个放电通道蚀除工件,克服现有放电加工理论中同一时刻仅有一个放电通道蚀除工件的限制,提出了采用半导体材料作为电极进行放电加工的新方法。首先,通过试验证明以半导体硅为电极加工金属可以形成多通道放电;其次,建立了半导体电极单通道放电等效电路模型,发现半导体电极在放电加工时不是一个等势体,并进行了电势差分布试验,验证了多通道放电形成的原因是远离放电点处的电势较高,可以同时形成击穿产生放电;最后,进行了半导体硅电极单脉冲放电试验及成型加工试验。试验结果显示,半导体硅电极通过1次脉冲放电同时形成多个放电通道,有效地分散放电能量,相较于金属电极,每个放电坑的直径和深度都显著减小。在相同放电参数下,对比钢电极,用硅电极进行电火花加工的表面粗糙度值下降71.7%。     

基于线电极的电火花铣削加工及其脉冲能量控制

介绍了基于线电极电火花铣削加工的产生背景及其基本原理,分析了在该加工中对单个脉冲放电能量进行控制的必要性,研制出了通过控制放电持续时间来控制脉冲能量的能量控制型脉冲电源,并给出了其放电脉冲波形。     

超声振动改善气体介质电火花加工的机理研究

提出了超声振动-气体介质电火花复合加工技术,在简述其加工原理的基础上分析了超声振动在改善气体介质电火花加工中的作用,以及相关的理论机理。实验结果表明,附加超声振动能改善放电间隙状态,减少短路、拉弧现象,提高了材料的去除率。进行了超声振动-气体介质电火花加工单脉冲实验设计。     

Influence of electrical discharge machining parameters on cutting parameters of carbon fiber-reinforced plastic

Today the use of high-strength carbon fiber-reinforced plastics (CFRP) composite as a material for many engineering applications is showing an increasing demand in the industry. These composites are replacing the traditional use of steel because they offer many advantages such as very light weight, high strength, and high stiffness associated with good corrosion-resistant properties. Unfortunately, there is little technological knowledge on the electrical discharge machining (EDM) process of high-strength composite materials, especially about the CFRP. In this work, a study has made into the possibility of using EDM process as a means of machining CFRP composite. Various cutting conditions such as peak current, pulse-on time, pulse-off time and open-circuit voltage were selected to perform electrical discharge machining. The effect of electrode rotation was also studied. Optimum cutting conditions and machine settings for EDM were chosen for machining CFRP composites.     

Accretion of titanium carbide by electrical discharge machining with powder suspended in working fluid

A surface modification method by electrical discharge machining (EDM) with a green compact electrode has been studied to make thick TiC or WC layer. Titanium alloy powder or tungsten powder is supplied from the green compact electrode and adheres on a workpiece by the heat caused by discharge. To avoid the production process of the green compact electrode, a surface modification method by EDM with powder suspended in working fluid is proposed in this paper. After considering flow of working fluid in EDM process, the use of a thin electrode and a rotating disk electrode are expected to keep powder concentration high in the gap between a workpiece and an electrode and to accrete powder material on the workpiece. The accretion machining is tried under various electrical conditions. Titanium powder is suspended in working oil like kerosene. TiC layer grows a thickness of 150 μm with a hardness of 1600 Hv on carbon steel with an electrode of 1 mm in diameter. When a disk placed near a plate rotates in viscous fluid, the disk drags the fluid into the gap between the disk and the plate. Therefore, the powder concentration in the gap between a workpiece and a rotational disk electrode can be kept high. A wider area of the accretion can be obtained by using the rotational electrode with a gear shape.     

电流型电火花加工脉冲电源的研究

分析了传统独立电火花加工脉冲电源和逆变式电火花加工脉冲电源的不足,论述了电源型电火花加工脉冲电源的工作原理,大量的样机和独立式脉冲电源的对比工艺试验表明,电流型脉冲电源不仅满足了电火花加工多项性能指标的要求,而且达到了高效节能的效果。     

Novel methods for high-speed observation of material removal and molten pool movement in EDM

This paper proposes two new methods to observe discharge phenomena without interference from the plasma in electrical discharge machining. The first method uses a bandpass filter with a bandwidth of 800–820 nm and laser illumination with a wavelength of 800–820 nm. The second method also uses a bandpass filter with a bandwidth of 800–820 nm; however, in this method, the tungsten material is used not only as the tool electrode but also as the illumination source. First, the discharge process was observed using traditional methods to investigate the influence of the plasma on the observation of the discharge process. Then, the process of removing molten material from both the tool electrode and workpiece, as well as molten pool movement, was observed using the first method proposed in this paper. The material removed from the tool electrode was scattered upward along the end profile of the tool electrode, while the material removed from the workpiece was distributed along the horizontal direction. To explain these phenomena, the flow distribution in the gap was qualitatively analyzed using a fluid simulation. Finally, the discharge process was also observed using the second method proposed in this paper. A tungsten tool electrode can emit light with a wavelength of 800–820 nm, which shines on the observed region during the discharge process. The observation results verified the phenomenon of multiple explosions of the molten pool during the discharge process. Moreover, it was found that the material removed by the explosion of the molten pool was scattered in different directions and hardly influenced by the flow distribution in the gap.     

Experimental investigations into electrical discharge machining with a rotating disk electrode

In electrical discharge machining, when the provision of holes in the electrode is impracticable, flushing of the working gap poses a major problem. Use of a rotating disk electrode is proposed as a more productive and accurate technique than use of a conventional electrode. Material removal rate, tool wear rate, relative electrode wear, corner reproduction accuracy, and surface finish aspects of a rotary electrode are compared with those of a stationary one. The effective flushing of the working gap brought about by the rotation of the electrode remarkably improves material removal rate and machines surfaces with a better finish. Despite the prevalent high tool wear rate, the reproduction accuracy is least affected as the wear gets uniformly distributed over the entire circumference of the disk. Machining of a sharp corner is possible even with an aluminum electrode, whose relative electrode wear is greater than unity.     

ELECTRIC DISCHARGE MILLING AND MECHANICAL GRINDING COMPOUND MACHINING OF SILICON CARBIDE CERAMIC

Silicon carbide (SiC) ceramics have been widely used in modern industry. However, the manufacture of SiC ceramics is not an efficient process. This paper proposes a new technology of machining SiC ceramics with electrical discharge milling and mechanical grinding compound method. The compound process employs the pulse generator used in electrical discharge machining, and uses a water-based emulsion as the machining fluid. It is able to effectively machine a large surface area on SiC ceramics with a good surface quality. In this paper, the effects of pulse duration, pulse interval, peak voltage, peak current and feed rate of the workpiece on the process performance parameters, such as material removal rate, relative electrode wear ratio and surface roughness, have been investigated. A L₂₅ orthogonal array based on Taguchi method is adopted, and the experimental data are statistically evaluated by analysis of variance and stepwise regression. The significant machining parameters, the optimal combination levels of machining parameters, and the mathematical models associated with the process performance are obtained. In addition, the workpiece surface microstructure is examined with a scanning electron microscope and an energy dispersive spectrometer.     

电火花加工单脉冲放电通道直径扩展规律研究

电火花加工的加工表面是由一系列的脉冲放电凹坑叠加而成的,因此研究单脉冲放电通道直径的扩展规律,对研究电火花加工的工艺规律以及加工表面质量预测等具有非常重要的意义。研究脉冲放电通道的形成与扩展机理,讨论电压、极值电流、脉宽等放电参数对放电通道直径扩展的影响,并根据理论推导建立了单脉冲放电通道直径扩展的数学模型。以煤油作为电介质工作液开展了单脉冲放电试验,使用超景深显微镜对单脉冲放电凹坑的直径进行了测量,并把测量得到的单脉冲放电直径数据代入建立的数学模型进行回归求解。回归公式的计算值与试验测量得到的单脉冲直径数据吻合度较高。