A study on the fine-finish die-sinking micro-EDM of tungsten carbide using different electrode materials

In recent years, tungsten carbide (WC) and its composites (WC–Co) are widely used in the die and mold industries due to their unique combination of hardness, strength and wear resistance. Micro-EDM is one of the most effective methods for machining these extremely difficult-to-cut materials. However, numerous applications of WC often involve intense mechanical demands at the surface. Therefore, fine-finish micro-EDM of WC is becoming an imminent and important issue. In this study, investigations have been conducted with view of obtaining fine surface finish in the micro-EDM of WC using tungsten (W), copper tungsten (CuW) and silver tungsten (AgW) electrodes. It was found that the surface characteristics are dependent mostly on the discharge energy during machining. The fine-finish micro-EDM requires minimization of the pulse energy supplied into the gap. In addition, the surface finish was found to be influenced greatly by the electrical and thermal properties of the electrode material. The performance of the electrodes for the finishing micro-EDM was evaluated based on the achieved surface roughness and surface characteristics with respect to material removal rate (MRR) and electrode wear ratio (EWR). It was found that AgW electrode produces smoother and defect-free nanosurface with the lowest R_a and R_max among the three electrodes. Besides, a minimum amount of material migrates from the AgW electrode to the WC workpiece during the finishing micro-EDM. On the other hand, CuW electrodes achieved the highest MRR followed by AgW. In the case of electrode wear, the W electrode has the lowest wear followed by CuW and AgW. Finally, considering all the performance parameters, AgW appears to be the best choice for finish die-sinking micro-EDM of WC.     

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.     

Fabrication of complex shape electrodes by localized electrochemical deposition

Localized electrochemical deposition (LECD) is a promising technology for fabrication of high-aspect ratio electrode of various materials. This technology is found to be one of the simple and inexpensive ways to fabricate electrodes for micro-EDM. This study presents a novel method to manufacture electrodes with complex cross-section using mask of non-conductive material. In this study, the mask is placed between the anode and cathode, which is immersed in mixed electrolyte of copper sulfate, 1.0 M sulfuric acid and as an additive agent 0.04 g/l of thiourea. The deposition of copper is localized on the cathode surface using a mask and applying ultra short voltage pulses between the anode and cathode. In this setup the cathode is placed above the anode and mask, so that the deposited electrode can be used directly for EDM or any application without changing tool orientation. The deposition characteristics such as size, shape, surface, and structural density according to gap between the anode and mask, applied voltage, pulse frequency and duty ratio have been investigated in this study. Finally, appropriate conditions have been found out for effective fabrication of smooth and fine-grained deposited electrodes based on the findings of the various experiments.     

Electrode Potential Measurements

The importance of electrode potential measurements in metal finishing is highlighted and the principles of such measurements are concisely reviewed. Scales for electrode potential are compared and practical determinations are considered.     

Study on thick film resistor and electrode fabricated by laser micro-cladding electronic pastes

Nowadays, electronic devices are required to be smaller, to have a high-density integration and to be of lower cost. In order to meet the developing demands, some new techniques have appeared in recent years. In this paper, a technique named laser micro-cladding electronic pastes is used to fabricate the thick film resistor and electrode units on insulator substrates without using a mask. The results demonstrate that the high-quality resistors could be fabricated by laser micro-cladding. However, the processing steps are very important since they have significant effects on the surface finish, the extent of diffusion between electrode film and resistor film, and on the reliability of the resistors. Laser micro-cladding electronic pastes may become a novel technique to fabricate high quality conductive lines (electrodes) and resistors with good properties that will come into industrial application in the future.     

微细电极的正交点电接触在线测量及组合制作工艺

为服务于微细电火花加工用微细工具电极在线制作,提出一种正交点电接触标准细棒的微细电极在线测量方法。将电极轴线与标准细棒轴线正交（垂直）布置,通过电极外径与标准细棒外径之间低压电感知的点接触方式,避免或减少标准棒尺寸误差和安装误差的影响。提出采用自穿孔成形伺服反拷法和线电极磨削法组合工艺,并结合在线测量反馈方式,实现了钨材料微细电极较高效率的在线制作,尺寸可控精度可达±1．5μm。     

整体叶轮电火花加工电极的成形电铸

电火花加工是整体叶轮的主要加工工艺方法之一,其中工具电极的制造是关键.研究了采用电铸技术制备电火花加工工具电极.由于电极结构复杂,电沉积时电场发生畸变,导致阴极表面的电场分布极不均匀,侧壁与底部结合处的电流密度远小于阴极表面其他地方的电流密度,针对这种情况,通过增加辅助阳极、屏蔽侧面等改善措施,成功制备了工具电极.     

Study on the inner surface finishing of tubing by magnetic abrasive finishing

With the development of industry manufacturing technology, fine surface finish is in high demand in a wide spectrum of industrial applications. Presently, it is required that the parts used in manufacturing semiconductors, atomic energy parts, medical instruments and aerospace components have a very precise surface roughness. Amongst them, vacuum tubes, wave guides and sanitary tubes are difficult to polish by conventional finishing methods such as lapping, because of their shapes. The surface roughness of these tubes affects the performance of the entire system, but the finishing technology for these tubes is very scant in manufacturing fields. This project was proposed by a Shanghai Far East pharmaceutial and mechanical factory. They stated that the roughness of the inner surface must be less than 0.3 μm Ra after finishing. An internal magnetic abrasive finishing (MAF) process is proposed for producing highly finished inner surfaces of tubes used in this study. The process principle and the finishing characteristics of unbounded magnetic abrasive within internal tubing finishing are described first. MAF setup was designed for finishing three kinds of materials tubing, such as Ly12 aluminum alloy, 316L stainless steel and H62 brass. Experimental results indicated that finishing parameters such as polishing speed, magnetic abrasive supply, abrasive material, magnetic abrasive manufacturing process and grain size have critical effects on the material removal rate (MRR). How the inner surface micro shape changes course during finishing of an aluminous tube is demonstrated.     

Investigating the recycling of nickel hydride battery scrap

New nickel hydride alloys have been developed to replace the cadmium-containing negative electrodes of nickel-cadmium batteries. The new, cadmium free alloys promise enhanced electrochemical properties as well as reduced environmental toxicity. Rechargeable batteries using nickel hydride electrodes are strong candidates for electric vehicle applications. The U.S. Bureau of Mines is investigating hydrometallurgical technology that separates and recovers purified metallic components present in nickel hydride battery scrap. A preliminary investigation of acid dissolution and metal recovery techniques using whole batteries and electrode rolls has shown potential options that will allow the successful recycling of much of the battery fabrication scrap.     

The use of doped polyaniline as an electrode in the galvanic anodic protection of ferrous metals in industrial acid solutions

In order to investigate the galvanic anodic protection (GAP) of ferrous metals (such as 410, 304 and 316 stainless steels) in acid solutions by doped polyaniline (PANi), separate doped PANi powder-pressed electrodes with different surface areas (the area ratio of the PANi electrode to stainless steel is between 1:1 and 1:2) have been prepared. These were coupled with ferrous metal in the following solutions: 5 M sulphuric acid, 5 M phosphoric acid and industrial phosphoric acid (containing 5 M phosphoric acid and 0.05% chloride ion) to construct a galvanic cell, in which PANi is cathode while ferrous metal is anode. The results indicate that a PANi electrode with sufficient area can provide corrosion protection to stainless steel in these acidic solutions. A pilot scale coupling experiment was carried out. The results indicate that PANi is a promising material as an electrode for the anodic protection of ferrous metals in acidic solutions in industrial situations.     

Simulation for the prediction of surface roughness in magnetic abrasive flow finishing (MAFF)

The final machining (or finishing) of precision parts with high level of surface finish and close tolerance is making the application of magnetic abrasive finishing technology increasingly important. Magnetic abrasive flow finishing (MAFF) is a new abrasive finishing process combining the features of abrasive flow finishing (AFF) and magnetic abrasive finishing (MAF). MAFF provides a high level of surface finish and close tolerances for wide range of industrial application. This paper focuses on the modeling and simulation for the prediction of surface roughness on the workpiece surface finished by MAFF process. A finite element model is developed to find the magnetic potential distribution in the magnetic abrasive brush formed during finishing action and then it is used to evaluate machining pressure, surface finish and material removal. The simulation results are compared with the experimental results available in the literature. The simulated workpiece surface roughness shows features similar in nature to the experimental results.     

EDM turning using a strip electrode

Turning by electrical discharge machining (EDM turning) is an effective method to machine hard-to-cut materials. Generally, a wire-EDM is utilized in EDM turning because it is not concerned with electrode wear. However, wire-EDM turning has a slow machining speed due to its small machining area, and the wire may break due to overheating electrodes. For these reasons, its machining speed must be limited. In this study, a strip-EDM was created in an effort to overcome the problems in the EDM-turning process. This machining method used a conductive strip as an electrode. The strip was fed continuously, like a wire-EDM; therefore electrode wear was not a concern. One advantage of the strip-EDM was that it increased the material removal rate because of its large machining area and non-breaking electrode. In the experiments, machining characteristics were investigated according to machining conditions, and practical machining was carried out via fabrication of complex shapes on a shaft workpiece.     

Detection of chemical warfare agent Nitrogen Mustard-1 based on conducting polymer phthalocyanine nanorod modified electrode

A simple method is reported for the detection of chemical warfare agent Nitrogen Mustard-1 (NM-1) by using a modified electrode which was prepared by electrochemically immobilizing copper phthalocyanine (CuPc) into polypyrrole (pPy) in presence of a cationic surfactant cetyltrimethylammonium bromide (CTAB) during the polymerization of pyrrole in an aqueous solution. The surface of the modified and bare electrodes are characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques in order to know the surface morphology and elemental composition of the modified electrodes, respectively. SEM images indicated the presence of nanorods on pPy/CuPc/CTAB sample and EDS study confirmed the nanorods as CuPc. Moreover, EDS study confirmed that the nanorods are only on the pPy matrix and not inside the pPy. FTIR results confirmed the presence of CuPc in pPy film. AC impedance spectroscopy analysis of the modified electrode with NM-1 exhibited more electron transfer resistance. The prepared modified electrode showed good electrochemical activity with NM-1 when compared to the unmodified gold electrode.     

Power metallurgy tool electrodes for electrical discharge machining

Electrodes in electrical discharge machining (EDM) can be compared with cutting tools in conventional machining. Tool performance is one of the important factors that determine the quality of the machined component. Due to the ease of manufacturing and control over the properties of electrodes, the powder metallurgy (P/M) technique has an advantage over other methods of electrode fabrication. P/M electrodes affect the micro- and macrovariables in EDM and the properties of P/M electrodes can be controlled over a wide range by adjusting the compacting and sintering conditions. The performance of P/M electrodes on various aspects of EDM operation is discussed in this paper.     

A study on the fabrication of curved surfaces using magnetorheological fluid finishing

A fabrication method of curved surfaces on silicon-based micro-structures using magnetorheological finishing is studied. Thorough explanations are made on the procedures for the evaluation and analysis of surface characteristics of a workpiece and on the fabrication method of the curved surface profile associated with the experiments using magnetorheological finishing. The effect of magnetic field around tool assembly on finished surface profiles is investigated using a finite element method (FEM). The analysis on the magnetic field is performed separately from that of the fluid flow field with the assumption that the field is weakly coupled to the working fluid at steady state with a certain geometric configuration adopted in this work. Several experiments were performed under controlled conditions and the results are demonstrated along with the physical interpretations thereof. The edge effect is turned out to be very important as the target workpiece gets smaller, which can be actively used for the fabrication of curved surfaces on millimeter-scale structures. Response surface methodology (RSM) is applied to predict the profile and roughness of the curved surface of the workpiece to be proceeded with a set of known experimental conditions. In order to use the RSM method, two control input and two response variables are chosen deliberately. Among the multi-regression models generally used in the modeling area, a second-order regression model is employed. The predicted results are verified through additional experiments performed independently.     

Technique of pulse electrochemical finishing in molds and dies

Surface finishing is one of the most important processes in mould and die making. This process is necessary not only for smoothing the surface of die or mould, but also for removing the surface layer, which has been damaged by the preceding machining process and finally improve the performances and lifetime of moulds to a large extent. It has been reported that between 30% and 40% of the total time required to manufacture a die or mold is spent on finishing operations, most of which are performed by skilled workers employing traditional techniques. At present, key problems in mould and die finishing technology can improve the finishing efficiency, consistency and quality at reduced costs. A new and high efficiency unconventional finishing technology, pulse electrochemical finishing was introduced. Experiments were done in neutral nitrate electrolytes. The influence of electrolyte composition, intereletrode gap, finishing time, flow quality, current density, compositions of steel materials and pulse parameters on the resulting surface finishing was investigated. Results indicate that pulse parameters have important influence on operations finishing and the proper selection of pulse parameters can lead to both good smoothing efficiency and surface quality at low costs.     

Electrolytic magnetic abrasive finishing

Electrolytic magnetic abrasive finishing (EMAF) is a compound finishing process, involving traditional magnetic abrasive finishing (MAF) and an electrolytic process. The aim of including the electrolytic process into the EMAF system is to produce a passive film (or oxide film), which is much easier to remove than the original metal surface during processing. Moreover, in the presence of both electric and magnetic fields, the negatively charged ions move toward the anode surface along a cycloid curve by the action of the Lorentz force. Under appropriate operating conditions, this phenomenon promotes electrolytic effects, resulting in a further increase in finishing efficiency, yielding a superior surface. This study describes the principles of the process, the finishing characteristics of surface roughness and material removal, and the associated mechanisms. Experimental results show that the EMAF process yields quite excellent finishing characteristics, better than those obtained by MAF, especially with a high electrolytic current. The process parameters such as electrolytic current, electrode gap, magnetic flux density, and rate of workpiece revolution must be appropriately fitted to obtain a superior refined surface with high efficiency.     

Ti-Cu层合电极的电解水析氢性能

目前通过使用粘接剂将催化剂粘接到基体上成为电解水析氢电极的主流制备方式,但粘接剂本身电阻较大且粘接强度低,易脱落。金属Pt是目前公认的最好的析氢金属电极,但其昂贵的价格限制了工业上大规模的使用。通过爆炸焊接技术将析气过电位低,稳定性好和强度高的钛与导电性优异的铜结合,构筑出一种自支撑钛-铜层合电极。电化学测试表明：相对于单一金属电极,钛-铜层合电极在1 mol/L KOH溶液中表现出良好的电解水析氢(HER)性能和导电性,且稳定性优异,在电流密度为10 mA·cm^-2,测试时间为20 000 s的稳定性测试中电位起伏只有0.05V。电解水析氢量测量实验结果中同样能够验证在实际工作中,钛-铜层合电极具备更优异的析氢性能。利用工作中产生的凹凸不平和富含孔洞的表面形貌暴露出更多的活性位点和电化学活性表面积,使得层合电极的HER性能在长时间工作中不会降低,还略有提高,这在电极材料有效制备且降低成本方面,具有广阔的工程应用前景。     

Monitoring of laser processing using induced current under applied electric field on laser produced-plasma

A new electrode circuit for measuring the induced current from laser plasma produced during laser material processing has been devised. The new electrode circuit has greatly increased the possible separation between the electrodes and the workable probing distance of the electrodes from the processed sample surface, namely 38 and 22 mm, respectively, sufficing the requirements of actual industrial laser material processing, avoiding direct contact of the electrodes with the big plasmas and profound sputtering. Several possible electrode configurations were investigated to accommodate the specific needs of the actual laser processing. It was shown that this technique is a very effective tool for accurately determining the moment of completion of penetration, as required in the laser piercing process. In contrast to this, the optical method currently in use cannot accurately determine the piercing completion moment due mainly to the disturbance from smoke arising at the processing point. A preliminary work using a CW CO₂ laser normally used in the actual industrial material processing was also made, resulting in a strong induced current signal corresponding to the laser pulse duration and frequency. The signal was successfully used for monitoring the penetration completion in a stainless steel plate drilling process. This reveals that this technique can be used for monitoring actual industrial material processing using high power lasers.     

Magnetic-Assistance Finishing Processes in Freeform Surfaces

A new finishing process that uses magnetic force with high efficiency to assist discharging dregs from the electrode gap during electrochemical finishing on freeform surfaces is investigated in the current study. The factors affecting electrochemical finishing and the effects of magnetic assistance are primarily discussed. The main experimental parameters are magnetic strength, distance between the two magnets, diameter of the electrode, current density, the on/off period of pulsed current, and rotational speed of the wire electrode. Providing a large magnetic field intensity or using a smaller distance between the two magnets produces a larger magnetic force and discharge efficiency, and results in a better finish. A higher current density with magnetic assistance reduces the finishing time and avoids difficulties in dreg removal. A high rotational speed of the wire electrode produces a better finish. Pulsed direct current can slightly promote the effect of electrochemical finishing, but the current density needs to be higher. Magnetic assistance during the electrochemical finishing process makes a greater contribution in a shorter time making the surface of the workpiece smooth and bright.