电铸工艺对工具电极材料抗电蚀性能的影响研究

提升基于准LIGA工艺制作的微细电火花加工工具电极材料的耐电蚀能力,是准LIGAMicroEDM组合加工高深宽比三维微结构可靠实现的重要研究内容。论述了该组合加工的技术优势及其工艺路线,理论分析了电铸电极材料电蚀性的影响因素,试验研究了电沉积工艺参数和操作条件如添加剂种类及其添加量、电流密度、温度等对电铸铜工具电极电蚀能力的影响。结果表明,组合添加适量明胶和Cl-,在适当的电流密度和温度等工作条件下,电铸出的铜工具电极在微细电火花加工中表现出超强的耐电蚀能力,重量相对损耗为0.3%。     

电火花成型加工工具电极损耗的研究

在电火花成形加工过程中,工具电极的损耗是影响工件几何形状精度的主要因素之一。从工具电极的制作工艺着手,利用电铸制造工具电极,并在铸液中加入不同的添加剂,进行电极放电损耗试验。试验结果表明,在适当温度和电流密度条件下,加入Cl^-和某苯基添加剂电铸形成铜工具电极的耐电蚀能力比不加添加剂的有明显提高。     

涡轮叶片冷却孔电火花加工管电极的铜电铸层制备及其抗电蚀性

以降低高温镍基合金涡轮叶片冷却孔电火花加工电极损耗率为目标,基于精密电铸工艺,优化了铸液工艺参数,在添加纳米La₂O₃条件下制备了铜管电极的铜电铸层,并将其与未添加La₂O₃所制备的铜电铸层进行了材料性能对比分析。以Inconel 718镍基合金叶片冷却孔为加工对象,利用所制备的带有纯铜电铸层的管电极进行了抗电蚀性能对比研究。试验结果表明：铸液中La₂O₃的添加量为1.2g/L时,铜电铸层晶粒最细,晶粒平均直径为15.9μm,表面粗糙度降至0.140μm,显微硬度可达98.2HV;用其制成的铜管电极损耗率较普通紫铜管电极和未添加纳米La₂O₃的铜管电极损耗率分别降低了13.29%和7.26%。     

Influence of flushing on performance of EDM with bunched electrode

The existing applications of electrical discharge machining (EDM) for bulk material removal are restricted by their comparatively low material removal rates. The bunched-electrode EDM proposed in this study, using the powerful multi-hole inner flushing, is an effective way of being released from this restriction. This paper investigates the mechanism by which flushing (flushing modes and flushing parameters) influences machining performance indices, i.e., material removal rate and tool wear rate, using experiments and simulations. Based on an investigation conducted, compared with traditional solid electrode with mono-hole inner flushing, a bunched electrode with multi-hole inner flushing endures higher peak current and results in larger material removal rate and higher relative tool wear ratio because of a more effective flushing process. By properly choosing inlet velocity and electrode effective-area ratio, a higher material removal rate is achieved and relative tool wear ratio is kept at a lower level.     

A study on the wear resistance characteristics of pulse electroforming Ni–P alloy coatings as plated

In this study, attempt has been initiated to investigate the wear resistance of Ni–P alloy coatings manufactured by pulse current (PC) electroforming technology. The wear tests of such plated coatings were carried out at ambient temperature and without lubricants. The parameters of the electroforming experiments include peak current density, duty cycle and pulse frequency. The results of this investigation showed that the internal stress of the PC-deposited Ni–P coating is much lower than that of direct current (DC) deposited Ni–P coating. The analytical results indicate that increasing of the phosphorus content in the layer reduces the hardness of the Ni–P electroformed coatings, and it gradually leads to transformation of the coatings structure from micro-crystalline to nano-crystalline/X-ray amorphous. Wear trace morphology shows that the wear mechanism of Ni–P coatings herein is related to hardness. As the hardness increases, the worn morphology of the coatings changes from with scratches and abrasions to that with the steel debris adhered on the coatings. The wear resistance of Ni–P alloy electroformed layers increases with the hardness of the coatings. The hardness primarily affects the wear resistance of the Ni–P as plated coatings, and the optimum wear resistance of Ni–P coatings can reach 11 times that of Ni coatings.     

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.     

Black layer affects the thermal conductivity of the surface of copper–tungsten electrode

The aim of this article is to show that the black layer composition varies with an interaction of electrical discharge machining (EDM) input parameters, which affects the electrode wear ratio (EWR), using the Taguchi methodology. An orthogonal array that provides a countermeasure to interactions was used. The analysis seeks the optimal levels of the EDM input parameters that produce an improvement in the EWR. The additive model was used with the optimum levels of the parameters to predict the EWR values. The outcome analysis shows a poor confirmation, meaning that there is an interaction of EDM input parameters affecting the EWR values. Thus, the present investigation reveals that black layer affects the electrode wear ratio due to a change in the thermal conductivity of the surface of copper–tungsten electrode.     

铜-石墨复合电极材料制备及抗电蚀性能分析

通过复合电铸技术,在耐电蚀性强的铜主体中引入抗电蚀性能优异的石墨微粉,制备了铜-石墨复合电极材料,探讨了复合电沉积条件与石墨含量的关系,用扫描电子显微镜分析了复合铸层的形貌特点,测定了表面粗糙度和显微硬度,试验研究了复合电极材料的抗电蚀能力。结果表明,在一定工艺条件下制备的铜-石墨复合电极材料表现出较优异的抗电蚀性能。     

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.     

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.     

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.     

An Investigation into Improving Worn Electrode Reliability in the Electrical Discharge Machining Process

In this paper, the use of a strength–stress interference model to study electrode reliability during wear in electrical discharge machining has been reported. In order to improve the electrode reliability, the Taguchi method, which is a powerful tool for parameter design of performance characteristics is used to determine machining parameters for minimum electrode wear ratio in electrical discharge machining operations. Through this study, not only is the electrode reliability improved, but also the machining parameters that significantly affect the electrode wear ratio in electrical discharge machining operations are obtained. Experimental results are provided to verify this approach.     

A comparative study on the wear resistance of electrical discharge machined surfaces

The properties of the surface were affected by many factors such as the pulse parameters, tool electrode material, and dielectric liquid in electrical discharge machining. Austenitic, dual-phase, and ferritic steel work materials were electrical discharge machined using graphite and copper tool electrodes in hydrocarbon- based oil and water dielectric liquids. Then the surfaces were analyzed regarding sliding friction wear responses on a comparative basis. The results revealed that the surface wear responses are sensitive to the type of the tool electrode material when machining in water dielectric liquid. However, the use of hydrocarbon-based dielectric liquid substantiality suppresses the influence of tool electrode on surface wear response due to excessive carbon release from the cracked dielectric. The machined surface topographical features were also affected due to the used electrical parameters regarding crater size, globular attachments, and microcracks that led significant alterations in sliding friction response. Primarily, weakly bounded globular attachments on the machined surface were dislodged at the initial stages of the friction tests and led higher sliding distances to the steady friction conditions. Finally, the results were compared with the subsurface microstructural properties to comprehend the wear responses.     

脉冲电流对稀土电铸铜性能的影响

电铸是一种电沉积金属的工艺,有极高的复制精度和可重复性,适用于制造外观形状精密复杂的金属零件。本文分析了采用脉冲电源、稀土硫酸铜电铸液制备一定厚度的电铸铜时,脉冲电流密度和稀土添加剂对电铸层性能的影响规律,以及对铜金属基体晶粒显著细化作用,并分析了其影响机制。     

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.     

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.     

SURFACING ELECTRODE WITH CRACKING RESISTANCE AND WEARABILITY

A new surfacing electrode is developed with cracking resistance and wearability based on high microhardness of TiC and VC, carbides of Ti and V are formed in deposited metal by means of high temperature arc metallurgic reaction. The results show the hardness of surfacing metal increases with the increase of ferrotitanium (Fe-Ti), ferrovanadium (Fe-V) and graphite in the coat. However, when graphite reaches the volume fraction of 11%, the hardness reaches its peak value, and when beyond 11%, the hardness falls off. As Fe-Ti, Fe-V and graphite increase, the cracking resistance of deposited metal and usability of electrode declines. Carbides are dispersedly distributed in the matrix structure. The matrix microstructure of deposited metal is lath martensite. Carbides present irregular block. When using the researched surfacing electrode to continue weld with non-preheated, no seeable crack or only a few micro-cracks can be observed in the surface of deposited metal. The hardness is above 60 HRC. The wear res     

The parameters evaluation and optimization of polycrystalline diamond micro-electrodischarge machining assisted by electrode tool vibration

The objective of this research is to evaluate and optimize machining parameter of tool electrode vibration on micro-electric discharge machining of polycrystalline diamond. The machining parameters evaluated are charge voltage, capacitance, and vibration of the tool electrode. An orthogonal array, signal-to-noise ratio, and analysis of variance are employed to analyze the effect of these machining parameters. The results show that by application of vibration on tool electrode in machining of polycrystalline diamond, it has significant effect up to 66.48% in increasing material removal rate without increasing surface roughness and tool electrode wear. Using Taguchi method for design of experiment, other significant effects on surface quality and tool electrode wear are also investigated. The results also show that surface roughness is mostly affected by the amount of capacitance (52.24%), and the tool electrode wear is also affected by the amount of capacitance (92.82%).     

刮板输送机仿生条纹型中部槽耐磨性试验研究

为了提高刮板输送机中部槽的耐磨性,以扇贝壳及穿山甲鳞片的非光滑条纹结构为仿生原型设计了仿生中板。以磨损深度为响应值,基于单因素法和响应面法进行磨损分析,探究耐磨仿生的最优结构参数,结果表明：显著性影响由大到小依次为宽度、宽高比、节距,条纹宽高比与条纹宽度的交互作用最为明显;在特定工况（煤颗粒粒度6~8 mm、载荷20 N、刮板链链速0.65 m/s）下,条纹型结构的最优耐磨参数组合为：宽高比4.94,宽度1.81 mm,节距6.33 mm。对最优参数组合下的条纹中板与光滑中板的耐磨性进行仿真和试验对比,结果表明：最优耐磨参数组合下的条纹中板具有良好的耐磨性能,与光滑中板相比,磨损质量减小78.54%。分析其耐磨机理发现,条纹凸体对煤散料的流动具有分流和导向作用,缓解了中板表面的受力,使磨损深度减小。     

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.