Study of the Effect of Machining Parameters on the Machining Characteristics in Electrical Discharge Machining of Fe-Mn-Al Alloy

In this work we investigated the electrical discharge machining (EDM) of a Fe-Mn-Al alloy. The surface phenomena caused by EDM were studied in terms of machining parameters. An empirical model of the Fe-Mn-Al alloy was also proposed based on the experimental data. Experimental results indicate that the higher the discharge energy, the faster the machining time. This treatment introduces machining damage in the resolidified surface layer and worsens the surface roughness. The optimum pulse-on duration on the basis of the electrode wear ratio for the copper electrode was about 200 μs. The increase of crater depth with the applied pulsed current and pulse-on duration appears minimal under a small input energy.     

非混粉电火花镜面加工及表面质量检测

采用解析法和有限元分析方法,分析了各因素对电火花加工表面质量的影响,提出了一种在电火花放电加工过程中逐级改变加工电规准,并依次加大电极的摇动量进行镜面加工的方法.提出应用白光干涉方法测量镜面加工工件表面质量的微观形貌,具有非接触、高精度等特点,垂直分辨力达到纳米级.实验表明在非混粉加工液中,不更换电极且被加工工件为45#钢的情况下,利用白光干涉测量法检测出电火花镜面加工的工件表面粗糙度Ra为0.02μm,满足电火花镜面加工精度的要求.     

Electrical Discharge Machining of Functionally Graded 15-35 Vol% SiCp/Al Composites

A functionally Graded 15-35 volume% silicon carbide particulate (SiC_p) reinforced Al359 metal matrix composite (SiC_p/Al MMC) was drilled by electrical discharge machining (EDM) to assess the machinability and workpiece quality. The machining conditions were identified for both the machining performance and workpiece quality of the EDM process, including some aspects of material removal mechanisms, material removal rate (MRR), electrode tool wear, and subsequent drilled hole quality including surface texture and roundness by using surface profilometry, coordinate measuring machine (CMM), and scanning electron microscopy (SEM). It was observed that the material removal rate increases with increasing peak current and pulse-on-time up to the optimal points and drops drastically thereafter. Higher peak current and/or pulse-on-time result in both the greater tool wear and the larger average diameter error. As the percentage of the SiC particles increases, MRR was increased and electrode wear was found to be decreased. At the EDM machined subsurface layer, the fragmented and melted SiC particles were observed under the SEM and EDX-ray examination.     

掺B金刚石膜的电火花抛光实验研究

通过化学气沉积过程中掺B,制备的金刚石膜电阻率下降10-19,导致金刚石膜整体导电,可采用电火花抛光。用扫描电镜和Raman分析了金刚石膜电加工表面的形貌和成分。金刚石膜的电火花抛光是多种效应综合作用的结果,即金刚石膜熔化、汽化、碳的氧化和蒸发、爆炸抛出、界面的化学反应以及金刚石的石墨化。通过实验研究了电加工参数对表面粗糙度和加工速度的影响,通过回归分析得到电火花抛光表面粗糙度和加工速度的经验公式,其相关系数的平方分别为0.91和0.99,表明拟合精度高。试验结果表明,放电电流和脉冲宽度对加工面的表面粗糙度和加工速度影响很大。放电电流为5 A、脉冲宽度为380μs时,抛光后表面粗糙度Ra<1μm。     

电泳沉积制备羟基磷灰石/生物玻璃梯度涂层的研究

本文研究了羟基磷灰石颗粒、生物玻璃颗粒在醋酸介质中的电泳沉积规律 ,利用它们不同的沉积规律设计了羟基磷灰石 /生物玻璃梯度沉积装置。用电子探针分析了涂层横截面元素分布 ,表明所设计的装置可实现羟基磷灰石和生物玻璃的梯度涂层     

Electrical Discharge Machining (EDM) Characteristics Associated with Electrical Discharge Energy on Machining of Cemented Tungsten Carbide

In this investigation, cemented tungsten carbides graded K10 and P10 were machined by electrical discharge machining (EDM) using an electrolytic copper electrode. The machining parameters of EDM were varied to explore the effects of electrical discharge energy on the machining characteristics, such as material removal rate (MRR), electrode wear rate (EWR), and surface roughness. Moreover, the effects of the electrical discharge energy on heat-affected layers, surface cracks and machining debris were also determined. The experimental results show that the MRR increased with the density of the electrical discharge energy; the EWR and diameter of the machining debris were also related to the density of the electrical discharge energy. When the amount of electrical discharge energy was set to a high level, serious surface cracks on the machined surface of the cemented tungsten carbides caused by EDM were evident.     

Powder Mixed Dielectric: An Approach for Improved Process Performance in EDM

The present study reports the outcome of experiments conducted to investigate the effect of parameters on improvement in the material removal rate (MRR), reduction in the tool wear rate (TWR), and overcut size for commonly used die steels. To overcome some of the shortcomings of electric discharge machining (EDM), an approach of powder mixing in dielectric fluids is adopted to investigate the influence of process parameters. The addition of powders in dielectric improves MRR and lowers TWR significantly. Powder concentration, current, and pulse-on time are three significant factors affecting MRR, TWR, and overcut size. An increase in powder concentration improves the process performance, but is limited by the possibility of arcing at higher concentration. Use of the powder resulted in increased effective spark length causing larger overcut. The problem is acute in trials conducted at high pulse-on duration with high powder concentration that leads to a ragged surface at cut edges. Furthermore, electrode tools with smaller tip included angle resulted in larger profile deviation at the machined surface as compared to trials conducted using tools with higher included angle. Surface morphological changes, grain size, microstrain, and material migration were investigated using SEM, XRD, and EDS analysis and a significant improvement in properties of the machined surface was observed.     

空气介质微细电火花沉积加工微结构机理

对微细电火花沉积加工中沉积所得不同微细结构的成形机理进行了研究．在电火花成形机床上,通过合理选择工艺参数,用黄铜电极在高速钢工件表面稳定沉积出外径约0．20mm、线径约0．09mm的微螺旋结构和直径约0．20mm微圆柱体．通过有限元法对工具电极放电点的瞬态温度场进行了模拟,分析结果表明,不同的放电能量密度影响材料的蚀除形式,继而影响蚀除电极材料在放电通道中的运动,最终影响微细结构的成形过程．对沉积材料微观组织结构分析表明,沉积材料与基体结合层为冶金结合方式,结合紧密,并由于凝固过程极大的冷却速率,使沉积材料在凝固过程中发生了晶粒细化现象．     

An Experimental Study on Electrical Discharge Machining of Manganese-Zinc Ferrite Magnetic Material

The objective of this research is to investigate the machining characteristics of manganese-zinc (Mn-Zn) ferrite magnetic material using electrical-discharge machining (EDM). The material removal rate, the surface topography, the surface roughness, the recast layer, and the chemical composition of the machined surface were studied in terms of EDM processing variables. Experimental results indicate that the morphology of debris revealed the mechanism of material removal. The surface microgeometry characteristics are not always uniform and homogenous and the EDM process produces much damage on the machined surface. The material removal rate, the surface roughness, and the recast layer are proportional to the applied discharge energy.     

Effect of Powder Mixed Dielectric on Material Removal and Surface Modification in Microelectric Discharge Machining of Ti-6Al-4V

Microelectric discharge milling is one of the variants of microelectric discharge machining process which acquire the attention of researchers due to its unique ability to produce microchannels and three-dimensional structures in difficult-to-machine materials like titanium. In the present work, an experimental investigation has been performed in order to study the effect of SiC microparticle suspended dielectric on machining Ti-6Al-4V with tungsten carbide electrode. The effects of major electric discharge milling process parameters—voltage, capacitance, and powder concentration in dielectric—on responses—viz., material removal rate (MRR) and tool wear rate (TWR)—were studied. Experiments were designed and performed based on response surface methodology (RSM)-Box–Behnken statistical design and the significance of in put parameters were identified with the help of analysis of variance. From the results, it is recommended to use powder concentration of 5 g/L, capacitance of 0.1 µF, and voltage of 115 V for achieving high material removal and low tool wear rate. Finally, the studies were conducted to analyze the surface modification and the quality of machined surface.     

Tribological Properties of Mo-N Hard Coatings on Ti6Al4V by Double Glow Discharge Technique

Mo-N hard coatings on Ti6Al4V were formed using double glow discharge technique. The fundamental coating properties, such as the phase, hardness and elastic modulus were investigated. The tribological performances of the coatings in dry wear condition were studied by means of ball-on-disc wear machine. The experimental results showed that the thickness of the Mo-N hard coating was about 10 µm. The coating was single fcc γ-Mo2N phase with (200) preferred orientation. The hardness and the elastic modulus of the coating was 13.80 GPa and 261.65 GPa respectively. The surface treatment enhanced the hardness and elastic modulus of the surface of Ti6Al4V base greatly. With GCr15 slider ball, the friction coefficient of the Mo-N hard coating was in the range of 0.56~0.65 at the steady state. Though the coating did not show friction reducing effect, it improved the wear resistance of Ti6Al4V greatly.     

Modeling and Analysis of Machinability Evaluation in the Wire Electrical Discharge Machining (WEDM) Process of Aluminum Oxide-Based Ceramic

The wire electrical discharge machining (WEDM) allowed success in the manufacture of the hard, fragile, and materials difficult to cut, especially for electroconductive ceramic materials. In this study, the mathematical models of material removal rate (MRR) and surface roughness (SR) used for the machinability evaluation in the WEDM process of aluminum oxide-based ceramic material (Al₂O₃ + TiC) have been carried out. The experimental plan adopts the face centered central composite design (CCD). The mathematical models using the response surface methodology (RSM) are developed so as to investigate the influences of four machining parameters, including the peak current, pulse on time, duty factor, and wire speed, on the performance characteristics of MRR and SR. It has been proved that the proposed mathematical models in this study would fit and predict values of the performance characteristics, which would be close to the readings recorded in experiment with a 95% confidence level. The significant parameters that critically affect the performance characteristics are examined.     

Ti6Al4V粉末及其制品的研究进展

采用粉末冶金方法生产钛合金制品,材料的利用率几乎可达100%,而且产品性能好,是低成本制造高质量钛合金零部件的重要途径。综述了国内外Ti6Al4V粉末及其粉末冶金制品的制备技术及应用概况,指出低氧球形高质量粉末的制备是钛合金粉末的发展方向,气体雾化是制备优质钛合金粉末的主要工业化生产方法,介绍了传统的粉末冶金方法及近年来新开发的粉末冶金新技术的应用情况。制备工艺的改善,加上民用领域产品需求量的大幅度增加,势必极大程度地推动粉末冶金Ti6Al4V的研究与应用。     

Thermal Treatment Optimization of Electrodeposited Hydroxyapatite Coatings on Ti6Al4V Substrate

Thermal behavior of electrodeposited hydroxyapatite (HAP) coating on a titanium alloy (Ti6Al4V) is investigated in order to optimize the heat treatment conditions for this prosthetic material. The synthesized coatings are annealed in air atmosphere at 400, 600, 800, and 1000 °C, and then characterized by X‐ray diffraction (XRD) and selected area electron diffraction (SAED) for structure and phases analysis. Scanning and transmission electron microscopy associated to energy dispersive X‐ray microanalysis (SEM‐EDXS and STEM) are used for morphology and composition analysis. The results show that when the electrodeposited coating is annealed at temperatures greater than 600 °C, a well‐crystallized HAP is obtained with a notable change of its morphology. However, at these temperatures the surface of Ti6Al4V alloy (uncoated zones of the implant) is deteriorated by the formation of a thick surface oxide layer. Therefore, we limit the heat treatment temperature for the electrodeposited coatings on a Ti6Al4V alloy at 550 °C. At this optimized temperature it is demonstrated that the link between the coating and the substrate is improved and the crystallinity of the coating is controlled which make it well bioactive.     

Electrical discharge machining of ZrO2 toughened WC composites

The interrelationships between the dispersion of the ZrO₂ phase and the electrical discharge machining (EDM) behaviour of WC based composites with 0, 5 or 10 vol% of ZrO₂ are investigated. Special attention was given to the homogeneity of the ultrafine WC – nanometric ZrO₂ powder based composites which were fully densified by means of pulsed electric current sintering (PECS). X-ray photoelectron spectroscopy (XPS) measurements revealed the presence of a nanometric WO₃ layer on the EDM surface, confirming oxidation as the major material removal mechanism (MRM). The surface roughness after the final EDM finishing regime was strongly influenced by the composite homogeneity and could be reduced down to 0.15 μm (R_a) on agglomerate-free composites. Residual stress measurements indicated that EDM did not introduce a significant amount of surface stresses, especially not after the final finishing regime. XRD measurements of EDM surfaces however indicated surface depletion of ZrO₂ by the formation of ZrC and W₂C during spark erosion.     

Ti6Al4V表面激光熔覆纯Cr粉热力学分析

为研究在激光作用下元素之间的扩散及作用机理,采用激光熔覆方法在Ti6Al4V表面熔覆纯Cr粉,利用热力学相图分析软件Thermo-Calc对Cr-Ti-Al-V四元体系进行平衡相图计算分析,利用DICTRA软件模拟合金体系的元素在Ti6Al4V基体中扩散分布情况。X射线衍射图谱表明熔覆层主要由α-Ti、Laves相Cr2Ti及亚稳态Cr1.97Ti1.07组成;扫描电镜实验结果显示熔覆层主要由片状、树枝状及细小针状组织组成。熔覆层元素体系中主要为Cr、Ti元素在不断相互扩散,Al元素扩散缓慢,V含量基本没有变化,整个体系中主要参与反应的是Cr与Ti元素。