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.     

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.     

A parallel link end effector for scanning electrical discharge machining process

Because a parallel mechanism has a high-frequency response, multiple degrees of freedom (DOF), and high stiffness, it can be applied to an end effector for electrical discharge machining (EDM) with a scanning motion. A prototype has 3 DOF: two tilting angles around the x- and y-axes, and the movement in the z-direction. It consists of, a base plate, a stage, a constraint link, and three inchworm devices that act as links. The inchworm devices are connected with the stage and the base plate. The z-position and inclination of the stage are changed by adjusting the length of the inchworm devices. The electrode feeding is controlled by the combination of the steplike movement with the inchworm devices and continuous extension of piezos. The frequency response of the stage by the continuous extension of the piezos is up to 200 Hz. The positioning accuracy of the end effector is less than 30 μm in height and 0.04° in inclination. Some examples of EDM by the scanning motion are demonstrated.     

High-quality cutting of polished single-crystal silicon by wire electrical discharge machining

We discussed a method for cutting smoothly polished single-crystal silicon surfaces by wire electrical discharge machining to obtain a high-quality surface. To cut out parts with smooth surfaces from the plates by rough-cutting in water while maintaining the initial smoothness of the surfaces, several kinds of masks were applied to the polished surfaces before cutting. It was found that although the application of resin masks is effective for obtaining smooth surfaces far from the cut section, the surface smoothness near the section cut in water is less than in the case of cutting in oil. Next, finish-cutting in oil was performed to remove cracks and chips generated by rough-cutting in oil. As a result, although a few chips were generated at edges of the cut section, cracks were successfully removed by finish-cutting, so that the surface quality was successfully improved by finish-cutting in oil.     

Optimisation of the electrical discharge machining process using a GA-based neural network

In this paper, the optimisation of the EDM process parameters from the rough cutting stage to the finish cutting stage has been reported. A trained neural network was used to establish the relationship between the process parameters and machining performance. Genetic algorithms with properly defined objective functions were then adapted to the neural network to determine the optimal process parameters. Examples with specifications intentionally assigned the same values as those recorded in the database or selected arbitrarily have been fed into the developed GA-based neural network in order to verify the optimisation ability throughout the machining process. Accordingly, the optimised results indicate that the GA-based neural network can be successfully used to generate optimal process parameters from the rough cutting stage to the finish cutting stage.     

椭圆齿轮的CAD与线切割加工

利用图形交互方式进行椭圆齿轮齿形的计算机辅助设计,得到轮齿的标准渐开线齿廓,并对齿根处的过渡曲线进 行处理。以一个椭圆齿轮为例,进行设计和线切割加工,得到由图形所确定的齿轮轮廓。     

用正交试验分析中电参数对圆柱度影响

电火花加工脉冲放电的统计学研究表明电参数与加工质量间存在一定的规律性。为实现电火花加工小孔圆柱度误差的合理控制,通过大量的工艺试验研究放电参数与小孔圆柱度间的规律是十分必要的。提出了多截面直角坐标测量方法,实现了小孔圆柱度的定量评定。在此基础上,采用正交试验研究了放电参数（开路电压、电流,脉宽,脉间,抬刀周期）对小孔圆柱度的影响。结果表明：脉宽对圆柱度的影响最为显著,开路电压次之,其余三个参数的影响较弱;同时也得到了以圆柱度误差最小为评价目标的一组放电参数。     

Modelling of surface finish,electrode wear and material removal rate in electrical discharge machining of hard-to-machine alloys

Hard-to-machine alloys are commonly used for industrial applications in the aeronautical, nuclear and automotive sectors, where the materials must have excellent resistance to corrosion and oxidation, high temperature resistance and high mechanical strength. In this present study the influence of different parameters of the electrical discharge machining process on surface roughness, electrode wear and material removal rate have been studied. Regression techniques are employed to model arithmetic mean deviation Ra (μm), peak count Pc (1/cm), material removal rate MRR (mm³/min) and electrode wear EW (%). All these parameters have been studied in terms of current intensity supplied by the generator of the electrical discharge machine I (A), pulse time t_i (μs), duty cycle η and open-circuit voltage U (V). This modelling allows us to obtain mathematical data and models to predict that the most influential factor in MRR and Ra is the current intensity and in the case of EW and Pc is the pulse time.     

Electrical discharge machining of submicron holes using ultrasmall-diameter electrodes

We have carried out the electrical discharge machining (EDM) of submicron holes using ultrasmall-diameter electrodes. Two types of electrode were used: tungsten electrodes fabricated by the combination of wire electrodischarge grinding and electrochemical machining, and silicon electrodes originally designed as probes for scanning probe microscopes. The diameters of the former and latter were 1 μm or less, and less than 0.15 μm, respectively. Holes were drilled using a relaxation-type pulse generator at an open-circuit voltage of less than or equal to 20 V with the machine's stray capacitance as the only capacitance. Using tungsten electrodes, holes of less than 1 μm in diameter and more than 1 μm in depth were successfully drilled. A 1.3-μm-wide slot was also fabricated by drilling many holes with a small pitch. It was possible to drill holes of approximately 0.5 μm diameter using silicon electrodes because the electrode diameter was less than those of the tungsten electrodes. These holes have the smallest reported diameter for holes drilled by EDM, indicating the possibility of submicron- and nanoscale machining by EDM.     

The study on the atomic force microscopy base nanoscale electrical discharge machining

This study proposes an innovative atomic force microscopy (AFM) based nanoscale electrical discharge machining (AFM-based nanoEDM) system which combines an AFM with a self-produced metallic probe and a high-voltage generator to create an atmospheric environment AFM-based nanoEDM system and a deionized water (DI water) environment AFM-based nanoEDM system. This study combines wire-cut processing and electrochemical tip sharpening techniques on a 40-μm thick stainless steel sheet to produce a high conductive AFM probes, the production can withstand high voltage and large current. The tip radius of these probes is approximately 40 nm. A probe test was executed on the AFM using probes to obtain nanoscales morphology of Si wafer surface. The silicon wafer was as a specimen to carry out AFM-base nanoEDM process in atmospheric and DI water environments by AFM-based nanoEDM system. After experiments, the results show that the atmospheric and DI water environment AFM-based nanoEDM systems operate smoothly. From experimental results, it can be found that the electric discharge depth of the silicon wafer at atmospheric environments is a mere 14.54 nm. In a DI water environment, the depth of electric discharge of the silicon wafer can reach 25.4 nm. This indicates that the EDM ability of DI water environment AFM-based nanoEDM system is higher than that of atmospheric environment AFM-based nanoEDM system. After multiple nanoEDM process, the tips become blunt. After applying electrochemical tip sharpening techniques, the tip radius can return to approximately 40 nm. Therefore, AFM probes produced in this study can be reused.     

The effect of cutting parameters and cutting tools on machining performance of carbon graphite material

Abstract

The present study focuses on the effects of cutting speed, feed rate and cutting tool material on the machining performance of carbon graphite material. Polycrystalline Diamond (PCD) cutting tools are used in machining experiments and its performance is compared with the tungsten carbide (WC) and Cubic Boron Nitride (CBN) tools. Machining performance criteria such as flank and nose wear and resulting surface topography and roughness of machined parts were studied. This study illustrates that feed rate and cutting tool material play a dominant role in the progressive wear of the cutting tool. The highest feed rate and cutting speed profoundly reduce the tool wear progression. The surface roughness and topography of specimens are remarkably influenced from the tool wear. Major differences are found in the wear mechanisms of PCD and WC and CBN cutting tools.     

基于Linux的微细电火花加工数控系统的研究

为了满足微细电火花加工高精度、高灵敏度和强实时性的运动控制要求,提出了以可编程多轴控制器为下位机、PC和Linux为上位机的体系结构,进行了六轴联动微细电火花加工数控系统的软硬件设计.为了解决微细电极在线制造和补偿等技术难题,该数控系统集成了机器视觉功能,基于V4L2应用程序接口开发了图像采集程序,基于OpenCV开发了图像处理程序,通过Canny边缘检测算法,提取了微细电极的边缘轮廓,可以在线观察和测量微细电极.此外,基于Lex和YACC设计并实现了数控代码解释器.     

Contouring of polished single-crystal silicon plates by wire electrical discharge machining

We investigate the effect of cutting by wire electrical discharge machining (WEDM) on the shape accuracy of polished single-crystal silicon. Single-crystal silicon plates are polished, and then contoured in deionized water or in oil by WEDM. The shape accuracy of the polished surfaces is measured with an interferometer. As a result, the polished surfaces are deformed into convex shapes by WEDM cutting. The polished surfaces tend to become flat as the roughness of the cut sections decreases, and the flatness is independent of the type of cutting liquid. Cutting in oil is advantageous for maintaining the smoothness of polished surfaces. These findings confirm that, in the contouring process of polished single-crystal silicon blocks, smooth and high-accuracy surfaces are achieved by conducting rough- and finish-cutting WEDM processes in oil.     

A review on the use of dielectric fluids and their effects in electrical discharge machining characteristics

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. In electrical discharge machining (EDM), a process utilizing the removal phenomenon of electrical discharge in dielectric, the working fluid plays an important role affecting the material removal rate and the properties of the machined surface. Choosing the right dielectric fluid is critical for successful operations. This paper presents a literature survey on the use of dielectric fluids and also their effects in electrical discharge machining characteristics.     

Cutting of polished single-crystal silicon by wire electrical discharge machining

Smoothly polished single-crystal silicon plates were cut by wire electrical discharge machining (WEDM) in water and in oil in order to investigate the effect of WEDM on the polished surfaces. For cutting in water, polished surfaces near cut sections have chips and cracks, and are extremely rough; the rough regions are upheaved. Examinations suggest that the upheaved region is silicon dioxide and results from oxidization of the surfaces by WEDM. Moreover, the polished surfaces far from the cut section are somewhat rough. For cutting in oil, polished surfaces near a cut section are smooth and almost flat although they have chips and cracks. These findings indicate the WEDM in oil is better than that in water for cutting polished single-crystal silicon to obtain high-quality surfaces.     

基于田口法的高速切削参数优化研究与应用

应用田口法对切削速度、背吃刀量以及每齿进给量三个主要影响表面粗糙度的因素进行分析,求出各个因素不同水平的平均表面粗糙度和信噪比(S/N),得到最优切削参数。预测经最优切削参数加工得到的表面粗糙度值,最后通过确认实验验证了其正确性。     

Modeling and analysis of the effects of machining parameters on the performance characteristics in the EDM process of Al2O3+TiC mixed ceramic

Electric discharge machining (EDM) has achieved remarkable success in the manufacture of conductive ceramic materials for the modern metal industry. Mathematical models are proposed for the modeling and analysis of the effects of machining parameters on the performance characteristics in the EDM process of Al₂O₃+TiC mixed ceramic which are developed using the response surface methodology (RSM) to explain the influences of four machining parameters (the discharge current, pulse on time, duty factor and open discharge voltage) on the performance characteristics of the material removal rate (MRR), electrode wear ratio (EWR), and surface roughness (SR). The experiment plan adopts the centered central composite design (CCD). The separable influence of individual machining parameters and the interaction between these parameters are also investigated by using analysis of variance (ANOVA). This study highlights the development of mathematical models for investigating the influences of machining parameters on performance characteristics and the proposed mathematical models in this study have proven to fit and predict values of performance characteristics close to those readings recorded experimentally with a 95% confidence interval. Results show that the main two significant factors on the value of the material removal rate (MRR) are the discharge current and the duty factor. The discharge current and the pulse on time also have statistical significance on both the value of the electrode wear ratio (EWR) and the surface roughness (SR).     

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。     

Employing severe plastic deformation to the processing of electrical discharge machining electrodes

The tool electrode has a significant role in electrical discharge machining (EDM) performance, as it affects machining efficiency, surface quality and the geometrical accuracy of the machined component. This study presents a new approach for developing a pure copper electrode using severe plastic deformation (SPD) to enhance the machining characteristics during EDM. Equal channel angular pressing (ECAP) is selected because it is the most successful SPD method of processing bulk materials. Finite element analysis, microstructural assessment as well as nanoindentation tests are carried out to determine the behavior of pure copper after one and two ECAP passes. The effectiveness of EDM when using ECAP-treated electrodes is evaluated by introducing new techniques of measuring the volumetric overcut (VOC) and corner sharpness. In addition, tool wear rate (TWR), material removal rate (MRR), electrode wear ratio, surface roughness, surface crack density and the critical crack zone are studied. The results emphasize that an electrode subjected to one pass of ECAP can enhance the workpiece accuracy by decreasing the VOC and increasing corner sharpness by 13 and 66%, respectively. It is also revealed that the nanohardness enhancement following ECAP leads to lower TWR and electrode wear ratio. An investigation of the surface characteristics indicates a thinner recast layer is achieved when using one ECAP pass-treated electrode, which leads to 26% lower surface crack density.     

An experimental investigation of tool wear in electric discharge machining

In this study, the variations of geometrical tool wear characteristics – namely, edge and front wear – and machining performance outputs – namely, workpiece removal rate, tool wear rate, relative wear and workpiece surface roughness – were investigated with varying machining parameters. Experiments were conducted using steel workpieces and round copper tools with a kerosene dielectric under different dielectric flushing conditions (injection, suction and static), discharge currents and pulse durations. The experiments have shown that machining parameters and dielectric flushing conditions had a large effect on geometric tool wear characteristics and machining performance outputs. Additionally, published research on tool wear is presented in detail in this study.