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.     

Workpiece and electrode influence on micro-EDM drilling performance

In recent years, the need for products containing micro-features has shown a pronounced and steady growth in several fields of application. For the development of micro-holed devices, one of the most important technologies is micro-EDM (Electro Discharge Machining). Micro-EDM can be considered as an ideal process to obtain burr-free micron-size features with high aspect ratios. In particular, micro-EDM is a non-contact material removal process in which rapid electric spark discharges remove the material composing the workpiece by means of melting and vaporizing phenomena. The present work deals with the fabrication of micro holes using micro-EDM technology. The investigation focuses on the influence of different electrodes and workpiece materials on the process performance, expressed in terms of tool wear ratio. In particular, the influence of four different workpiece materials (stainless steel, titanium, magnesium and brass), three electrode materials (copper, brass and tungsten carbide) and two different electrode shapes (cylindrical and tubular) was investigated. Moreover, an analysis of the geometrical characteristics of the micro holes in terms of conicity and diametrical overcut was carried out. An influence of electrode geometries, electrode material and workpiece material on the final output was found.     

Application of Taguchi-grey multi responses optimization on process parameters in electro erosion

Convention Taguchi method deals with only single response optimization problems. Since the electrical discharge machining process involved with many response parameters, Taguchi method alone cannot help to obtain optimal process parameters in such process. In the present work, an endeavor has been made to derive optimal combination of electrical process parameters in electro erosion process using grey relational analysis with Taguchi method. This multi response optimization of the electrical discharge machining process has been conducted with AISI 202 stainless steel with different tool electrodes such as copper, brass and tungsten carbide. Gap voltage, discharge current and duty factor have been used as electrical excitation parameters with different process levels. Taguchi L₂₇ orthogonal table has been assigned for conducting experiments with the consideration of interactions among the input electrical process parameters. Material removal rate, electrode wear rate and surface roughness have been selected as response parameters. From the experimental results, it has been found that the electrical conductivity of the tool electrode has the most influencing nature on the machining characteristics in EDM process. The optimal combination of the input process parameters has been obtained using Taguchi-grey relational analysis.     

工具电极耐磨性和液体组分对电流变加工的影响

实验研究了基于电流变效应即效微型砂轮研抛加工过程中具有不同耐磨性电极材料(淬火钢电极、不锈钢电极、黄铜电极、石墨电极)、不同组分电流变液对玻璃材料去除率的影响,探讨了其作用机理。结果表明:淬火钢和不锈钢锥状电极的加工效率明显高于黄铜和石墨锥状电极,即采用耐磨性好的工具电极材料具有更好的加工效果;沸石粉电流变液的材料去除率高于二氧化硅电流变液的材料去除率。其作用机理是,锥状工具电极材料的耐磨性决定了工具尖端与工件表面之间的加工间隙的保持性,电流变液组分直接影响了电流变效应的强度,从而影响了电流变效应即效微型砂轮对工件表面的研磨压力,形成了不同的材料去除率。     

Performance analysis of EDM electrode fabricated by localized electrochemical deposition for micro-machining of stainless steel

Electrical discharge machining (EDM) is an important and widely used process for the fabrication of complex three-dimensional structure of micro-tools, micro-components, and parts with micro-feature. It allows high precision, low setup cost, large freedom of design, and good surface quality. However, in order to produce different varieties of high-accuracy structures on machine, microelectrode fabrication is necessary so as to reduce the clamping error which is one of the biggest challenges in the field of micro-EDM. In this study, it has been shown that localized electrochemical deposition (LECD) is one of the simplest, inexpensive, and damage-free ways to fabricate complex-shaped electrodes for micro-EDM compared to other conventional electrode fabrication processes. In this study, electrode was fabricated with the help of a non-conductive mask which was placed between the anode and the cathode where the cathode was placed above the anode and mask and the system was immersed in a plating solution of acidified copper sulfate. The micro-EDM was carried out by the deposited electrode without changing or removing its orientation. The performance of LECD electrode was evaluated in this study by micro-holes fabrication on high melting point material such as stainless steel in terms of the material removal rate, tool relative wear ratio, and dimensional accuracy. Finally, the performance of the LECD electrode was also evaluated by a comparative study with a circular EDM electrode for fabrication of complex three-dimensional structure.     

An experimental work on using conductive powder-filled polymer composite cast material as tool electrode in EDM

This paper introduces the composite tool electrodes made of electrical conductive powder-filled polyester resin matrix material, providing promise for the electrical discharge machining (EDM) process. The dendrite-shaped copper powder, graphite powder, and their mixture were used as conductive fillers. Six different types of composite electrodes, namely, plain copper-polyester, pressed copper-polyester, furnaced copper-polyester, plain copper-graphite-polyester, pressed copper-graphite-polyester, and furnaced copper-graphite-polyester were prepared. It is found experimentally that increasing v _f improved workpiece material removal rate, tool wear rate, relative wear, and electrical conductivity of electrodes. The pressed copper-polyester electrodes were found to be promising in the ED finishing of workpieces at low machining current settings. The practical applicability of the proposed composite electrodes in the industry was also illustrated.     

Influence of reinforcement particles on the mechanism of the blasting erosion arc machining of SiC/Al composites

Electrical arc machining has shown its remarkable efficiency in processing difficult-to-cut materials, especially high-temperature alloys and metal-based composites. Despite several studies about the material removal mechanisms of the electrical arc machining of metal alloys, few of these reports relate to the mechanism of machining composites with electrical arcing. Considering that reinforcements such as SiC particles have different thermal and electrical properties with metal alloys, research on the influence of SiC reinforcement on the electrical arc machining process is important and necessary. Based on comparison experiments using 20 and 50 vol.% SiC/Al composites, this research focused on the influence of SiC particles on the machining performance and material removal mechanism of blasting erosion arc machining (BEAM), and further analyzed the influence of reinforcements on composite material removal mechanisms. Analysis revealed that the molten material expelling mechanism is also influenced by the SiC fraction difference. For the BEAM of lower SiC fraction composites, both the SiC particles and the molten aluminum are mainly pumped and ejected by the flushing dielectric. In greater SiC fraction composites, most SiC particles are directly sublimed by heat. In addition, the mechanism of BEAM in the material removal and tool wear of SiC/Al composites was discussed based on heat transfer simulation and observation. Furthermore, the results disclosed that many chemical reactions take place during machining that have an obvious influence on the tool wear rate.     

Experimental research on machining characteristics of SiC ceramic with end electric discharge milling

Silicon carbide (SiC) ceramic has been widely used in modern industry. However, the beneficial properties of SiC ceramic make machining difficult and costly by conventional machining methods. This paper proposes a new process of machining SiC ceramic using end electric discharge (ED) milling. The process is able to effectively machine a large surface area on SiC ceramic at low cost and no environmental pollution. The effects of emulsion concentration, emulsion flux, milling depth, copper electrode number, and copper electrode diameter on the process performance such as the material removal rate, electrode wear ratio, and surface roughness have been investigated. In addition, the microstructure of the machined surface is examined with a scanning electron microscope, and the material removal mechanism of SiC ceramic during end ED milling is obtained.     

QT700-2电火花加工工艺试验特征规律研究

综合应用单因素实验和正交实验对QT700-2进行电火花加工试验,在分析电火花加工QT700-2基础特征规律之上,考查了电规准对材料去除率、电极损耗等的影响规律。研究结果表明,采用紫铜电极负极性标准切入加工QT700-2时,在试验范围内,峰值电流对加工速度和电极损耗的影响最为显著;脉冲宽度在25～400μs范围内存在一个使加工速度最快的脉冲宽度ti;峰值电流虽然可以提高加工效率,但是会急剧加速电极损耗,在保证较低相对损耗比的同时提高加工效率,应首先考虑提高脉冲宽度。     

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.     

Analysis of rotary electrical discharge machining characteristics in reversal magnetic field for copper-en8 steel system

The material removal rate (MRR), along with the electrode wear rate (EWR), plays an important role in analysing machine output during electrical discharge machining. This work focuses on the improvement of machine output by introducing an induced magnetic field on the workpiece during rotary electrical discharge machining (REDM) of EN-8 steel with a rotary copper electrode. The workpiece was placed inside the induced magnetic field, wherein polarity of the magnetic field gets reversed periodically. Using Taguchi’s recommended design of experiments, we initially conducted experiments with eight input parameters at different levels . Significant parameters were identified with the help of the signal-to-noise ratio and ANOVA. Finally, another set of experiments was conducted for analysis of the process and development of empirical expressions for MRR and EWR. Experimental results established that rotary electrical discharge machining with a polarity reversal magnetic field delivers better machining output than machining in a non-magnetic field. Thus, this work benefits the EDM process by reducing the machining costs and by producing better geometrical trueness on workpieces, as MRR increased and EWR decreased.     

Surface modification using semi-sintered electrodes on electrical discharge machining

This study investigates how machining characteristics and surface modifications affect low-carbon steel (S15C) during electrical discharge machining (EDM) processes with semi-sintered electrodes. Among the machining characteristics determined, the material removal rate (MRR), surface deposit rate (SDR), and electrode wear rate (EWR) are included. Additionally, exactly how semi-sintered electrodes affect the surface modifications is also evaluated by electron probe microanalyzer (EPMA), micro hardness, and corrosion resistance tests. The experimental results confirmed that the composition of the semi-sintered electrodes is transferred onto the machined surface efficiently and effectively during the EDM process, and that the process is feasible and can easily form a modified layer on the machined surface.     

水气联合电火花加工实验研究

将自来水和压缩空气作为电介质,使用实心成形电极对钢件进行电火花加工实验,探讨其加工机理。实验证明,空气与水的配合状况对电火花效果起着决定性作用;加工中可以获得较大的加工速度(材料蚀除速率)和较低的电极相对损耗,加工后工件表面粗糙度值一般较大;水气联合电火花加工适宜于高电流大脉宽加工。     

Influence of discharge energy on machining characteristics in EDM

The machining characteristics of electrical discharge machining (EDM) directly depend on the discharge energy which is transformed into thermal energy in the discharge zone. The generated heat leads to high temperature, resulting in local melting and evaporation of workpiece material. However, the high temperature also impacts various physical and chemical properties of the tool and workpiece. This is why extensive knowledge of development and transformation of electrical energy into heat is of key importance in EDM. Based on the previous investigations, analytical dependence was established between the discharge energy parameters and the heat source characteristics in this paper. In addition, the thermal properties of the discharged energy were experimentally investigated and their influence on material removal rate, gap distance, surface roughness and recast layer was established. The experiments were conducted using copper electrode while varying discharge current and pulse duration. Analysis and experimental research conducted in this paper allow efficient selection of relevant parameters of discharge energy for the selection of most favorable EDM machining conditions.     

Performance of sinking EDM electrodes made by selective laser sintering technique

Electrical discharge machining (EDM) is a nonconventional machining process widely applied for the manufacture of intricate shapes in hard materials which are not easily machined by conventional machining processes. The production of geometrically complex EDM electrodes is difficult, time consuming, and it can account for about 50 % of the total process costs. Selective laser sintering (SLS) can be an alternative technique to produce EDM electrodes in a faster way. This work conducted an experimental study on the performance of EDM electrodes made by SLS using pure copper, bronze–nickel alloy, copper/bronze–nickel alloy, and steel alloy powders. Important EDM performance measures such as material removal rate and volumetric relative wear were investigated and discussed for finishing, semifinish, and roughing regimes. This work contributes with an insight into the production of EDM electrodes via selective laser sintering, as an alternative technique to conventional machining processes, as well as to evaluate the performance of the electrodes, and also provide directions for future research on this field.     

Error calculation for corrective machining with allowance requirements

Electroforming copper from the copper sulfate baths or the pyrophosphate baths is one of commonly used methods for manufacturing electro-discharge machining (EDM) tool electrode, in particular for the fabrication of micro- and meso-scale tool electrodes with complex cross-section, but few literature on the electrode-wear performance of electroformed copper electrode has been available until today. To better select copper tool electrode materials, the wear resistance of the macroscopic and tiny copper tool electrodes deposited from the copper sulfate baths and the pyrophosphate baths were investigated comparatively with the same micro-EDM parameters. The optimal electrodeposition parameters in which the deposited copper had the lowest electrode-wear ratio were first obtained from the two baths, respectively. And then, the wear resistance of the micro-featured copper tool electrode electroformed using the optimal deposition conditions from the two baths were evaluated comparatively. Experimental investigations showed that, both at the macro-scale level and at the micro-scale level, the copper tool electrode electroformed from the pyrophosphate baths (the smallest electrode-wear ratio was 10% for the macro-electrode and 12.8% for the micro-electrode) exhibited better wear resistance than that deposited from the copper sulfate baths (the smallest electrode-wear ratio was 11.95% for the macro-electrode and 17.3% for the micro-electrode).     

Process performance of micro-EDM drilling of stainless steel

An experimental campaign based on the execution of through micro-holes on stainless steel plates was carried out using a micro-EDM machine Sarix SX-200. The experimental campaign was carried out by varying several process parameters, namely peak current, voltage and frequency. Tubular electrodes made of two different materials (tungsten carbide and brass) were used. A study of the in progress material removal rate (MRR) and tool wear ratio (TWR) during the drilling process was performed. Some mathematical laws governing the relation between process parameters and performance indexes were defined. Two technological windows representing TWR and MRR as a function of the hole depth, for different electrode materials, were obtained.     

一种弹载电子产品储热装置的设计与试验

为满足某弹载电子产品在高温环境中工作的需求,设计了一种储热装置对该产品进行有效温控。根据该产品的工作特性和相关技术要求进行储热装置的结构设计,分别用H62黄铜、5A06铝合金和泡沫铜基石蜡相变材料制作了具有同样结构外形的储热装置。设计制作与产品热耗一致的模拟热源用于储热装置的性能试验,对3 种储热装置的储热能力、导热能力等物理性质进行对比分析。结果表明,相变材料储热装置可以满足温控需求,并在储热能力和重量上有明显优势,值得在同类型产品平台中推广和应用。     

EDM electrode manufacturing using RP combining electroless plating with electroforming

This study investigates an effective method for manufacturing electrical discharge machining (EDM) electrodes using the rapid prototyping (RP) system based on electroless plating (nickel plating) and electroforming (copper). This method was shown to finish the development of die-sinking electrical discharge machining (EDM) electrodes, shorten the electrode manufacturing process, decrease the manufacturing duration as well as the cost of electrodes. The electrode prototype was drawn with Pro/E 3D CAD, and the CAD model was then transformed into the stereo lithography (STL) file format. A Zcorp 402 3DP rapid prototyping machine was adopted to make a gypsum powder electrode prototype with a complex appearance. The gypsum material is sealed by resin permeation, enhancing its water-resistance and strength. Electroless plating was then performed to introduce electric conductivity onto the gypsum electrode surface, followed by copper electroforming of the thickness about 1 mm to obtain the EDM electrode. Furthermore, die-sinking electric discharge machining was performed. Test results indicate that no crack was found on the electrode and that the electrical discharge machining effects are promising.     

Towards the effective tool wear control in micro-EDM milling

The electrode wear in micro-electrical discharge milling (micro-EDM milling) is one of the main problems to be solved in order to improve machining accuracy. This paper presents an investigation on wear and material removal in micro-EDM milling for selected process parameter combinations typical of rough and finish machining of micro-features in steel. The experiments were performed on state-of-the-art micro-EDM equipment. Based on discharge counting and volume measurements, electrode wear per discharge and material removal per discharge were measured for several energy levels. The influence of the accuracy of volume measurements on the electrode wear per discharge and on the material removal per discharge are discussed, and the issues limiting the applicability of real time wear sensing in micro-EDM milling are presented.