Electrical Discharge Surface Alloying of Ti and Fe Workpiece Materials Using Refractory Powder Compact Electrodes and Cu Wire

The paper reviews the use of metal powders dispersed in the dielectric fluid and refractory PM electrodes, to initiate workpiece surface modification during EDM. Experimental work details the effects of EDM parameters (up to 270 V) on the hardness/composition of the white layer following die sink machining of AISI H13 tool steel and roll texturing of 2% Cr steel using partially sintered PM electrodes. Similar data are presented following EDM scanning and wire cutting of standard TI alloy TI-6AI-4V and a y TIAI. With AISI H13, recast layers were 5-20 μm thick and up to ∼ 1350 HK_0.025. When machining TI-6AI-4V with WC/Co electrodes, recast microhardness was 600-2900 HK_0.025. Wire cutting y TIAI generated porous alloyed layers up to 115 μm thick with extensive cracks and no increase in bulk hardness.     

EDM performance of Cr/Cu-based composite electrodes

Electrode materials for electrical discharge machining (EDM) are usually graphite, copper and copper alloys because these materials have high melting temperature, and excellent electrical and thermal conductivity. The electrodes made by using powder metallurgy technology from special powders have been used to modify EDM surfaces in recent years, to improve wear and corrosion resistance. However, electrodes are normally fabricated at high temperatures and pressures, such that fabrication is expensive. This paper proposes a new method of blending the copper powders contained resin with chromium powders to form tool electrodes. Such electrodes are made at low pressure (20 MPa) and temperature (200 °C) in a hot mounting machine. The results showed that using such electrodes facilitated the formation of a modified surface layer on the work piece after EDM, with remarkable corrosion resistant properties. The optimal mixing ratio, appropriate pressure, and proper machining parameters (such as polarity, peak current, and pulse duration) were used to investigate the effect of the material removal rate (MRR), electrode wear rate (EWR), surface roughness, and thickness of the recast layer on the usability of these electrodes. According to the experimental results, a mixing ratio of Cu–0wt%Cr and a sinter pressure of 20 MPa obtained an excellent MRR. Moreover, this work also reveals that the composite electrodes obtained a higher MRR than Cu metal electrodes; the recast layer was thinner and fewer cracks were present on the machined surface. Furthermore, the Cr elements in the composite electrode migrated to the work piece, resulting in good corrosion resistance of the machined surface after EDM.     

气膜冷却孔电火花加工参数优化及重熔层厚度测量实验

气膜冷却孔加工表面粗糙度、重熔层厚度直接影响航空发动机服役寿命。兼顾叶片气膜冷却孔加工效率和重熔层厚度,研制了加工参数在线可调的窄脉宽高峰值电流脉冲电源系统,进行了气膜冷却孔电火花加工参数优化实验,寻找重熔层厚度和加工效率的显著影响因素。在此基础上,采用灰关联度分析法进行多目标优化,利用优化后的加工参数,得到了较理想的实验结果。     

Performance parameters studies in machining of AISI D2 steel with dot-textured,groove-textured & non-textured cutting tool at the flank face

Surface texturing is a method where there is a change in tribological properties due to change in surface characteristics. The present work is a comparison of the performance of dot-textured coated carbide tool with groove-textured and non-textured coated carbide tool in machining AISI D2 steel. Micro dot textures are made on the flank face using micro-electric discharge machining. Considering full factorial design, total 8 experiments are performed with cutting speed, feed and depth of cut as process parameters. For each parameter, two levels are considered. Flank wear and surface roughness are investigated to compare the function of dot-textured coated carbide tool with the groove-textured and non-textured coated carbide tool. In every condition, flank wear is less in machining with both types of textured tool in comparison to the non-textured coated carbide tool. In most of the cases, surface roughness is less for both types of textured tool than the non-textured tool. Comparing dot-textured tool over groove-textured tool, it is observed that dot-textured tool is better than the groove-textured tool in reducing flank wear and surface roughness. Analysis of white layer and micro hardness at the machined surfaces revealed that dot-texturing helps in minimizing the thickness of white layer and micro-hardness property in comparison to groove-textured and non-textured tool. Thus, dot texturing is found to be better in improving machinability than groove-textured and non-textured tool.     

45钢电火花成型表面组织结构的研究

在煤油介质中,以YT15硬质合金作为电极加工45钢.正极性加工时,在45钢表面得到显微硬度高于基体的白亮层,且其厚度和表面质量可通过改变放电参数进行调整.利用电子探针对白亮层进行了成分分析.本研究为利用电火花成型机完成表面强化加工提供了依据.     

A comparative study of surface integrity of Ti–6Al–4V alloy machined by EDM and AECG

The electrical discharge machining (EDM) process produces the recast layer with or without cracks on the surface that requires a remedial post-treatment in the manufacture of critical or highly stressed surfaces. One of the frequently used post-treatment processes is also the abrasive electrochemical grinding (AECG) and it has been widely used in the precision machining of difficult-to-cut materials due to an enhanced surface integrity and productivity. The aim of this study is to investigate improvability of surface integrity in terms of machining voltage, electrolyte flow rate and table feed rate parameters of AECG in EDMed Ti6Al4V alloy. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrograph (EDS) and surface roughness measurement were performed to study the surface characteristics of the machined samples. Experimental results indicate that the AECG process effectively improves the surface roughness and eliminates the EDM damages completely by setting suitable grinding parameters.     

Machining performance on hybrid process of abrasive jet machining and electrical discharge machining

To develop a hybrid process of abrasive jet machining (AJM) and electrical discharge machining (EDM),the effects of the hybrid process parameters on machining performance were comprehensively investigated to confirm the benefits of this hybrid process.The appropriate abrasives delivered by high speed gas media were incorporated with an EDM in gas system to construct the hybrid process of AJM and EDM,and then the high speed abrasives could impinge on the machined surface to remove the recast layer caused by EDM process to increase the efficiency of material removal and reduce the surface roughness.In this study,the benefits of the hybrid process were determined as the machining performance of hybrid process was compared with that of the EDM in gas system.The main process parameters were varied to explore their effects on material removal rate,surface roughness and surface integrities.The experimental results show that the hybrid process of AJM and EDM can enhance the machining efficiency and improve the surface quality.Consequently,the developed hybrid process can fit the requirements of modern manufacturing applications.     

低盐溶液电火花-电解复合加工微小方孔试验

综合电火花加工快速蚀除材料与电解加工溶解重铸层的优势,提出了在低电导率的NaNO3溶液中使用电极逐层往复式铣削加工微小方孔的电火花-电解复合加工方法,并研究了电解液浓度、电压和电容参数对微小方孔加工质量的影响。结果表明:电解液浓度与加工电压对微小方孔加工质量影响较大,电容影响相对较小。选用最优加工参数在100μm厚的321不锈钢片上加工微小方孔,得到的方孔加工质量好、侧壁表面无重铸层,且工具电极相对损耗仅0.05%。     

分层厚度对微细电火花铣削加工模具及热压制品表面粗糙度的影响

分层厚度直接影响微细电火花铣削加工的加工效率及表面粗糙度。为了合理规划微细电火花铣削加工的分层厚度,提高加工效率,研究了分层厚度对微细电火花加工的模具型腔及相应热压成形制品表面粗糙度的影响,同时分析了热压成形制品表面与微模具型腔表面之间的关系,以及热压前、后微模具型腔表面轮廓的变化。结果表明:当电极轨迹重叠率一定时,模具型腔底面的表面粗糙度值随着分层厚度的增加而增大;分层厚度对型腔侧壁表面粗糙度无明显影响;热压制品表面轮廓算术平均偏差小于模具型腔表面轮廓算术平均偏差;热压后的模具表面轮廓发生了变化,表面粗糙度值Ra和峰高Rpk减小,峰谷Rvk增大。     

Performance and Surface Integrity of Ti6Al4V After Sinking EDM with Special Graphite Electrodes

Titanium and its alloys have high chemical reactivity with most of the cutting tools. This makes it difficult to work with these alloys using conventional machining processes. Electrical discharge machining (EDM) emerges as an alternative technique to machining these materials. In this work, it is investigated the performance of three special grades of graphite as electrodes when ED-Machining Ti6Al4V samples under three different regimes. The main influences of electrical parameters are discussed for the samples material removal rate, volumetric relative wear and surface roughness. The samples surfaces were evaluated using SEM images, microhardness measurements, and x-ray diffraction. It was found that the best results for samples material removal rate, surface roughness, and volumetric relative wear were obtained for the graphite electrode with 10-μm particle size and negative polarity. For all samples machined by EDM and characterized by x-ray (XRD), it was identified the presence of titanium carbides. For the finish EDM regimes, the recast layer presents an increased amount of titanium carbides compared to semi-finish and rough regimes.     

PCBN刀具干湿切削淬硬钢表面完整性研究

本文以采用PCBN刀具切削淬硬轴承钢GCr15为试验，对干、湿切削两种润滑条件下，工件表面粗糙度及表面白层（一种在加工表面形成的晶相组织发生变化的结构）进行了对比研究。实验结果表明：干、湿切削都可获得较好的表面粗糙度，湿切削表面粗糙度Ra稍低；湿切削没有发现明显的白层产生，干切削白层生成较早，且白层与黑层的厚度随着刀具磨损的增加而逐渐增加。     

硅电极电火花表面改性的研究

以工业纯硅为电极,通过电火花放电对试样进行表面改性处理.电火花设备型号为EDM7125,工作液为普通煤油,电极材料含硅99.6%,工件材料为45钢和球铁.采用扫描电镜及金相显微镜对试样表面形态进行了研究,对试样表面进行了能谱分析,对试样进行了耐蚀及表层结合强度等试验.结果表明:试样加工后表面形成一层含硅超过16%的合金层.电火花加工球铁石墨基本未脱落,但石墨周围易产生或扩展显微裂纹.高硅层结合强度非常高,进行永久变形时,无剥离和裂纹产生.而且,经电火花加工过的试样耐蚀性得到极大提高.另外,电火花加工,当参数合理时,可达到粉末混入加工的目的,试样可获得好的表面质量.     

利用TiC半烧结体电极进行电火花表面处理的实验研究

研究了一种在普通电火花加工机床上实现金属工件表面处理的新方法。它使用传统电火花加工方法，通过特制的半烧结体电极在加工过程中使工件表面迅速形成一层硬质碳化物陶瓷，从而达到改善工件表面性能的目的。对这种方法的原理进行了初步的探讨，并在大量实验的基础上，通过厚度测量、表面粗糙度测量、X射线衍射分析等一列实验手段，对沉积层的生成特性进行了详细的分析。实验与分析表明，用电火花加工的方法进行金属表面沉积陶瓷层技术是一种极具潜力的表面改性方法。     

Workpiece surface roughness and integrity after WEDM of Ti-6Al-4V and Inconel 718 using minimum damage generator technology

Following a brief review of EDM and its use on advanced aerospace alloys including workpiece integrity constraints, data are presented after machining Ti-6Al-4V and Inconel 718. Roughing and finishing (multiple trim cut) strategies were employed on two high specification machines with pulse generators designed to provide minimum workpiece integrity damage. Results include productivity, 3D topographic maps of workpiece surfaces, microstructural and microhardness depth profile data. Average recast thickness was <11 μm, several trim passes showing no apparent recast or damage. Similarly, no significant change in workpiece microhardness variation was observed with cracking confined to the recast layer.     

聚晶立方氮化硼刀具刃口放电加工工艺研究

通过调整电火花加工的主要放电参数（脉冲宽度和加工电流）,对聚晶立方氮化硼（PCBN）4~进行放电加工,进而对样刀刃口表面进行x射线衍射分析,并在扫描电子显微镜下观察其表层结构及能谱分析。通过对加工后样刀表面变质层主要成分及产生原因的分析,总结了脉冲宽度和加工电流对样刀表面变质层厚度、刃口表面粗糙度影响的关系曲线,为制定精密快速放电加工PCBN刀具的工艺提供了重要依据。     

Recast layer removal after electrical discharge machining via Taguchi analysis: A feasibility study

This study explores the feasibility of removing the recast layer (RCL) using etching and mechanical grinding for Ni-based superalloy materials by means of electrical discharge machining (EDM). The EDM process is widely used for machining hard metals and performing specific tasks that cannot be achieved using conventional techniques. The sparks produced during the EDM process melt the metal's surface, which then undergo ultra rapid quenching. A layer forms on the workpiece surface defined as a recast layer after solidification. Molds and dies desire to remove the RCL even though it is hard and has good matrix adherence.This experiment is divided into three stages. The first stage acquires a thick recast layer by using EDM with a larger discharging energy. A thick recast layer is essential for verification of the EDM technique for observing the recast process. Thus, this work applies the Taguchi L₁₈ analytical method to acquire the thick recast layer. The second stage optimizes the recast layer removal technique. Therefore, the thick recast layer is intentionally made in the first stage. This work determines the second stage setting using Taguchi's recommendation. Thus, the L₉ orthogonal array sets up the etching and mechanical grinding parameters and observes the recast layer removal quantity analysis. Finally, an experiment studies the surface characteristics of Ni-based superalloys, such as composition and micro-hardness after removing the recast layer.     

Investigation of the effects of electrode orientation and fluid flow rate in near-dry EDM milling

This research investigates the effects of electrode lead and tilt angles and dielectric fluid flow rate on material removal rate, tool electrode wear ratio, and surface roughness in near-dry electrical discharge machining (EDM) milling process. Computational fluid dynamics (CFD) model is developed to predict the dielectric fluid flow rate and qualitatively compare with the experimentally measured EDM material removal rate. The optimum lead angle, which maximized material removal rate and minimized tool electrode wear ratio, was found. The decrease in the lead angle has a negative effect on the roughness of machined surface. The increase in tilt angle reduces the material removal rate and increases the tool electrode wear ratio. The change in tilt angle does not have a significant effect on the surface roughness and can be used to prevent gouging in finishing EDM milling. This study shows that the material removal rate is linearly proportional to the mass flow rate of air and kerosene mixture, the tool electrode wear ratio is inversely related to the mass flow rate of air and kerosene mixture, and the average surface roughness does not have a good correlation with the flow rate of the mixture.     

Analysis of surface topography changes in steel sheet strips during bending under tension friction test

In order to investigate the frictional behaviour and the change in surface roughness of different sheet topographies, a bending under tension friction test, BUT, was used. This test exposes the material to bulk-plastic deformation under conditions similar to those present in the drawing radius of a real tool. Each steel sheet material has been tested under different lubrication conditions. To measure the sheet surface topography a 3D stylus technique was used.For each steel strip the original surface, the area in contact with the tool and the resulting surface topography were measured. When comparing “standard” 3D surface roughness data for original and final surfaces, no correlation with friction data was obtained. However, with a special evaluation technique good correlation with oil retention volume and frictional behaviour was found for the surface in contact with the tool. By using measurements from the contact area, filtering the measured surface in two steps, firstly with a 5th degree polynom to get rid of the circular form and secondly with a ball filter to get rid of the waviness located in the topmost layer in the surface and then plotting the bearing area curve for the filtered surface on a probability paper, the real area of contact for each steel sheet surface can be determined, as well as the number of oil pockets and their mean area. The oil pockets were estimated by using a software in which areas of peaks were estimated, on a surface inverted at the level of the real area of contact.By plotting the mean area of the oil pockets versus the coefficient of friction for a sheet material with an excess amount of lubricant, a relationship is determined.     

Fatigue Life of Superalloy Haynes 188 in Hydrogen

The effects of hydrogen and surface finish on the mean low cycle fatigue life of Haynes 188 were studied. Specimens were prepared and fatigue tested with gage sections having low stress ground (LSG) and electro-discharge machined (EDM) surfaces. Fatigue tests were performed at temperatures of 25 to 650?°C with varied strain conditions, in hydrogen and helium environments. Fatigue life decreased with increasing strain range, strain ratio, temperature, and with hydrogen atmosphere. A Smith-Watson-Topper stress parameter could be used to account for variations in strain range and strain ratio, and most strongly influenced life. Hydrogen reduced fatigue life by about 5× (80%) at 25?°C, but was much less harmful at 650?°C. Standard EDM finish did not consistently reduce mean fatigue life from that of LSG finish specimens. Additional tests indicated fatigue life in hydrogen was maintained for varied EDM conditions, provided specimen roughness and maximum recast layer thickness were not excessive.     

Machinability analysis in turning tungsten–copper composite for application in EDM electrodes

Electro-discharge machining (EDM) is widely used in tooling industry, where it is applied on materials, which are too hard to be machined with conventional techniques. The tungsten–copper is broadly used as an EDM electrode for machining of die steel and tungsten carbide workpieces. As, tungsten–copper electrode is more costly than conventional electrodes, there is a need to understand the machinability aspects in turning of this material. Hence, an attempt has been made in this paper to study the effects of cutting conditions on machinability characteristics such as cutting force, feed force, depth force, machining force, power, specific cutting force, arithmetic average surface roughness and maximum peak to valley height during tungsten–copper turning with K10 carbide cutting tool. The response surface methodology (RSM) based second order mathematical models of machinability aspects are developed using the data obtained through full factorial design (FFD). The adequacy of the machinability models is tested through the analysis of variance (ANOVA). The response surface analysis reveals that a combination of higher cutting speed with low-to-medium feed rate is advantageous in reducing the forces, power and surface roughness, which in turn increases the specific cutting force.