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.     

基于线框电极的电火花直孔套料加工研究

试验研究一种使用线框电极的电火花加工的新工艺———套料加工。根据正交试验原理设计了混合位级正交表来试验和分析粗加工时电加工参数对加工速度和电极损耗率的影响,以确定线框电极套料加工时最佳电规准参数。最后依据试验数据绘出了三维图形,更加直观地表达了试验的结果。     

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。     

Study of the Batch Production of Micro Parts Using the EDM Process

The micro machining of copper plates by the electrical discharge machining (EDM) process is described. Tungsten carbide was selected as the material for the electrode. Experiments were carried out on a conventional CNC-EDM machine to investigate machining of micro holes, and micro slots. The results show that micro holes, and micro slots can be successfully processed on a conventional CNC-EDM machine. To improve the productivity of micro parts using the EDM process, a batch production method of micro EDM using multi-electrodes has been studied. A new technique for preparing multi-electrodes has been developed. Results also show that the batch production of micro parts using EDM is feasible and that the batch production of micro parts using EDM process with multi-electrodes is very effective.     

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.     

弯曲孔电加工工艺的实验研究

实验研究探讨了一种使用线框电极的电火花套料加工的新工艺.根据正交试验方法来分析精加工时加工参数对加工速度、电极损耗和加工表面粗糙度的影响,以确定套料精加工时最佳的电规准参数.依据直孔套料加工参数在模具材料中加工出了圆弧弯曲孔.     

4Cr5MoVSi电火花加工试验特征规律研究

采用紫铜工具电极,在峰值电流为4-24A、脉冲宽度为25-200μs、加工电压为80-200V的电参数范围内,综合应用因子试验和正交试验方法,对难加工材料4Cr5MoVSi进行了电火花加工试验。在进行电加工基础特征规律分析的基础上,考查了电参数对加工速度、双边侧面放电间隙、电极损耗的影响,并对电火花加工机理进行了分析。研究结果表明:采用紫铜电极电火花加工4Cr5MoVSi,在本试验范围内,峰值电流Ip与脉冲宽度ti、加工电压U、脉冲间隔t0存在一定的交互作用;与其它三个因素相比,峰值电流对加工速度、电极损耗、双边侧面放电间隙的影响更显著;随脉冲宽度和加工电压的增大,电极损耗逐渐减小。     

Micro-electrodischarge machining using water as a working fluid—I: micro-hole drilling

Micro-electrodischarge machining (medm) using water as a working fluid is systematically studied to find its characteristics. As a result, the unique advantages of high removal rate, low electrode wear and consequently higher working efficiency, without formation of carbonaceous materials are found under optimum experimental conditions, as compared with the case when kerosene is used. This was achieved by the choice of suitable combinations of electrode and workpiece materials and electrode polarity. Use of a tungsten electrode with straight polarity is exceedingly good with respect to high removal rate and low electrode wear. This makes it possible to obtain a non-tapered straight micro-hole around 0.1 mm in diameter with a certain anticipative working gap. The advantageous properties of this machining method are effectively utilized to drill deep micro-holes with a ratio of depth to diameter of the order of 10–17 as in the case of 2.9 mm depth and 0.17 mm diameter, which is superior to the limits achievable with both electrodischarge drilling (edd) using kerosene and mechanical drilling with a micro-drill.     

Optimization of EDM process for multiple performance characteristics using Taguchi method and Grey relational analysis

Electrical discharge machining (EDM) is one of the most extensively used non-conventional material removal processes. The Taguchi method has been utilized to determine the optimal EDM conditions in several industrial fields. The method, however, was designed to optimize only a single performance characteristic. To remove that limitation, the Grey relational analysis theory has been used to resolve the complicated interrelationships among the multiple performance characteristics. In the present study, we attempted to find the optimal machining conditions under which the micro-hole can be formed to a minimum diameter and a maximum aspect ratio. The Taguchi method was used to determine the relations between machining parameters and process characteristics. It was found that electrode wear and the entrance and exit clearances had a significant effect on the diameter of the micro-hole when the diameter of the electrode was identical. Grey relational analysis was used to determine the optimal machining parameters, among which the input voltage and the capacitance were found to be the most significant. The obtained optimal machining conditions were an input voltage of 60V, a capacitance of 680pF, a resistance of 500Ω, the feed rate of 1.5μm/s and a spindle speed of 1500rpm. Under these conditions, a micro-hole of 40μm average diameter and 10 aspect ratio could be machined.     

Experimental study on micro EDM-drilling of Ti6Al4V using helical electrode

There is a growing interest in the machining of micro-holes with high aspect-ratio in difficult-to-machine alloys for the aerospace industry. Processes based on electro discharge machining (EDM) and developed for the manufacture of both micro-electrode and micro-hole are actually used, but most of them involve micro-EDM machines. In this work, the influence of EDM parameters on material removal rate, electrode wear, machining time and micro-hole quality when machining Ti6Al4V is studied. Due to an inefficient removal of debris when increasing hole depth, a new strategy based on the use of helical-shaped electrodes has been proposed. The influence of helix angle and flute depth with respect to process performance has been addressed. Main results include 37% reduction in machining times (hole diameter 800 μm) when using electrode helix angle of 45° and flute-depth of 50 μm, and an additional 19% with flute-depth of 150 μm. Holes of 661 μm diameter and as much as 6.81 mm depth, which yields in aspect ratio of 10:1, have successfully been machined in Ti6Al4V.     

Electrode wear and material removal rate during EDM of aluminum and mild steel using copper and brass electrodes

In the present study an analysis has been done to evaluate the electrode wear along the cross-section of an electrode compared to the same along its length during EDM of aluminum and mild steel using copper and brass electrodes. In an overall performance comparison of copper and brass electrodes, we found that electrode wear increases with an increase in both current and voltage, but wear along the cross-section of the electrode is more compared to the same along its length. This is due to easier heat transfer along the length compared to the same along the cross-section of the electrode. It was also found that the wear ratio increases with an increase in current. That means, though a higher current causes more removal of work material and the electrode, comparatively more material is removed from the electrode. The highest wear ratio was found during machining of steel using a brass electrode. The low thermal conductivity of brass electrodes causes less heat loss, and its low melting point results in fast melting of the electrode material. At the same time, low thermal conductivity of steel results in poor heat absorption, and its high melting temperature causes poor removal of work material. These factors result in the highest wear ratio during machining of steel using a brass electrode. The highest material removal rate was observed during machining of aluminum using brass electrodes. Comparatively low thermal conductivity of brass as an electrode material does not allow the absorption of much heat energy, and most of the heat is utilized in the removal of material from aluminum workpiece at a low melting point. But during machining of steel using copper electrodes, a comparatively smaller quantity of heat is absorbed by the work material due to its low thermal conductivity. As a result material removal rate becomes very low.     

电极材料对极间放电电压及加工特性影响

电火花加工技术具有良好的加工性能,在制造领域受到越来越多的关注,然而由于其加工理论滞后于实际生产,影响了其在实际生产中的进一步应用。选用五种不同配比电极材料进行电火花加工实验,测量其稳定加工时的间隙放电电压;并进行相应的加工特性实验,论证电极材料对极间放电电压和加工特性的影响。实验结果表明:在稳定加工中,极间放电电压基本保持不变,而且随着材料和开路电压的不同,极间放电电压随之变化,当选用Cu75W为电极材料时,极间放电电压达到最高值,从而影响了最终的加工特性。     

EXPERIMENTAL INVESTIGATIONS INTO THE INFLUENCE OF MAJOR OPERATING PARAMETERS DURING MICRO-ELECTRO DISCHARGE DRILLING OF CEMENTED CARBIDE

Present study investigates the influence of major operating parameters on the performance of micro-EDM drilling of cemented carbide (WC-10wt%Co) and identifies the ideal values for improved performance. The operating parameters studied were electrode polarity, gap voltage, resistance, peak current, pulse duration, pulse interval, duty ratio, electrode rotational speed and EDM speed. The performance of micro-EDM drilling process was evaluated by machining time, material removal rate (MRR), relative electrode wear ratio (RWR), spark gap, surface finish and dimensional accuracy of micro-holes. It has been found that there are two major conflicting issues in the micro-EDM of carbide. If the primary objective is to obtain better surface finish, it can be obtained by the sacrifice of high machining time, low MRR and high RWR. However, for faster micro-EDM, the surface roughness is higher and electrode wear is again much higher. It is concluded that negative electrode polarity, gap voltage of 120 V, resistance of 33 Ω, peak current of 8 A, pulse duration of 21 μs, pulse interval of 30 μs, duty cycle of 0.47, electrode rotational speed of 700 rpm and EDM speed of 10 μm/s can be considered as ideal parameters to provide improved performances during the micro-EDM of WC-Co.     

Characteristic investigation of pipe cutting technology based on electro-discharge machining

Pipe cutting technology plays an important role in the process of offshore platforms decommissioning, as many devices such as tubing, drill pipe, and casing need to be decommissioned. In this study, a novel cutting pipe technology based on electro-discharge machining (EDM) is proposed, and a cutting pipe mechanism is developed to cut the pipes for decommissioning offshore platforms. The machining principles and characteristics of the technique are described. The effects of machining parameters, including tool polarity, dielectric fluid, electrode material and width, pulse on-time, pulse off-time, peak voltage, and electrode rotation speed to machining performance, are investigated. The material removal rate (MRR) of the machined casing and tool electrode wear ratio (EWR) is obtained based on the calculation of the percentage of mass loss per machining time. The experimental results show that a better cutting performance can be obtained with negative tool polarity at the conditions of dielectric fluid of emulsion, pulse on-time of 500 μs, pulse off-time of 200 μs, peak voltage of 70 V, copper electrode width of 28 mm, and electrode rotation speed of 250 rpm is a better choice. Additionally, the cutting slots surface has been investigated by the means of SEM. The cutting slots machined by the rotary EDM are clean and smooth.     

激光微涂敷层的电火花后处理及其加工性能

分析、测量了不同加工条件下的材料去除率、相对电极损耗和电火花加工表面粗糙度,并研究了表面微裂纹和微硬度分布。实验结果表明,不同的材料具有类似的电火花加工性能,材料去除率随脉冲电流的增加而增加,峰值电流比脉冲宽度对表面粗糙度的影响更显著。研究结果对于选择合适参数进行电火花后处理具有重要意义。     

采用紫铜管绕制的线框电极电火花套型加工模具的研究

首先较详细的描述了本研究中使用的紫铜管绕制的线框电极的结构和尺寸,对试验条件和方法作了简要的说明,分析了管电极中的小孔的冲液方向对电火花套型加工效果的影响.介绍了使用的紫铜管绕制的线框电极加工模具的试验结果及其原因,最后对采用实心紫铜丝绕制的线框电极和采用紫铜管绕制的线框电极的主要加工指标作了对比分析.     

空气中微细电火花沉积与去除可逆加工技术研究

论述了一种新的电火花加工方法。它使用通用的电火花成形加工机床,利用常见的电极材料,在空气介质中,通过脉冲放电在工件表面上沉积生长电极材料,再通过反转极性和适当的轨迹控制对所生成的沉积材料进行有选择的去除加工,进而实现材料的生长与去除可逆加工。通过对电火花加工理论的研究,预测和论证了实现这一新加工方法的可能性和实现条件。通过试验成功地将钢、铜和钨三种电极材料沉积到工件上,形成直径为 100~240 mm、高度为1 000~2 500 mm的微小圆柱体。并对沉积物进行了选择去除,实现了在同一设备上的可逆电火花加工。对沉积材料的致密性、硬度及其与工件的结合强度等进行了系统的分析,表明沉积物组织致密、坚硬,可以满足功能材料的要求。     

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.     

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.     

超大深径比深小孔的工艺方法和电极研制

深径比超过1000的深小孔加工是世界难题,尤其是直径小于3mm的深小孔。在分析普通电火花深孔加工和专业电火花深小孔加工机床对超大深径比小孔加工仍存在排残屑、散热、稳定性差和导向困难等基础上,为克服上述问题而发明了一种其导向、稳定性与加工深度无关的自导向、自稳定的特殊电极,并给出了可靠的工艺实施方案方法,独特的工件倒置安装方式,表述了加工规律和试验结果。