Design of effective plate-shape electrode in ultrasonic electrochemical finishing

This research provides a process of ultrasonic aided electrochemical finishing using a low-cost electrode with high efficiency. It requires no expensive special-purpose equipment or high material removal as the conventional ECM does. It offers fast improvement of the surface roughness of the workpiece and is a new area in ECM. In the current study, the electrochemical finishing is classified into electrochemical smoothing and electrobrightening, higher electrical current is not required when an effective plate-shape electrode is used to reduce the response area. This process can be used for various turning operations including profiling, form turning, and flute and thread cutting. Through simple equipment attachment, electrochemical smoothing and electrobrightening can follow the cutting on the same machine and chuck. The controlled factors include the chemical composition and concentration of the electrolyte, the initial gap width, and the flow rate of electrolyte. The experimental parameters are the current density, rotational speed of the workpiece, on/off period of pulsed current, frequency and power level of ultrasonics, and the electrode geometry. Smaller end radius and smaller angle of declination are associated with higher current density and provides larger discharge space and better polishing effect. The electrode of inclined plane with slant discharge flute performs the best. The average effect of the ultrasonics is better than the pulsed current while the machining time needs not to be prolonged by the off-time. It was also found that electrobrightening after precise turning needs quite a short time to make the workpiece smoothing and bright, and the electrochemical smoothing saves the need for precise turning, making the total process time less than the electrobrightening.     

Continuous finishing processes using a combination of burnishing and electrochemical finishing on bore surfaces

A novel finishing tool was developed by using the two finishing processes of burnishing and electrochemical finishing. The finishing tool design included a burnishing tool and an electrode as a bore surface finish improvement, which goes beyond traditional boring by utilizing the continuous processes of burnishing and electrochemical finishing. Only a short time is required to make the bore surface smooth and bright with the use of these continuous finishing processes. The experimental results show that the large current rating is closely concerned with the fast feed rate of the finishing tool and is advantageous to the finishing processes. A small end radius or a small thickness of the electrode provides a more sufficient discharge, which is advantageous for the finish. The finishing effect is better with a high rotational speed of the finishing tool, since the dregs discharge the electrochemical machining, and burnishing becomes easier, which is also advantageous to the finishing processes. The finishing time using continuous current was not as prolonged as with the pulsed current.     

Design of continuity processes of electrochemical finishing and grinding following turning

A newly designed finishing process utilizing an effective electrode and a grinding tool to execute the continuous electrochemical finishing and grinding processes following turning is described in this paper. The proposed process can be used for a variety of turning operations. Electrochemical finishing and grinding can be performed following the finishing process on the same machine by using a simple attachment. The factors affecting electrochemical finishing, grinding performance, and electrochemical finishing are discussed. The electrode was tested with both continuous and pulsed direct current. A higher work piece rotational speed produced a better finish. Changing the electrode design from a semicircle to a wedge form with a small end radius caused the electrolytic products and heat to dissipate more rapidly and provided the best finishing. Pulsed direct current finishing was slightly better than using continuous direct current finishing. However, the use of pulsed current would increase machining time and cost. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Dr. P.S. Pa obtained his doctorate at National Tsing Hua University, Taiwan. Presently he is an Associate Professor at Graduate School of Toy and Game Design of National Taipei University of Education. His fields of interest are innovative design and manufacturing processes. His current research includes ECM process for mould and die materials, precision finishing, toy design, and electro-optical engineering.     

Design of freeform surface finish using burnishing assistance following electrochemical finishing

This study discusses the performance assessment of the continuous burnishing processes following electrochemical finishing using a design, which incorporates a finish-tool that includes an electrode and a nonconductive burnishing-tool. One can expect to make an effective evaluation on the processing features and set up the complete data for processing parameters. In the future, it is also expected to spread a freeform surface finish instead of the conventional hand or machine polishing. In the experiment, a model toy missile is taken as a workpiece. The electrode is used with the continuous and pulsed direct current application. The burnishing-tool uses ceramic material and is connected with the electrode and axial feed. It was found that the finished effect of the finish-tool with convex features is better than mat of the concave features. Pulsing direct current can slightly improve the effect of electrochemical finishing. High rotational speeds produce a better finish for workpieces. This presents an effective and low-cost finishing process that includes the design of a finish-tool, which uses burnishing assistance, and follows electrochemical finishing after traditional machining makes the freeform surface of a workpiece smooth and bright.     

<Emphasis Type="Italic">Continuous Secondary Ultrasonic Electropolishing of an SKD61 Cylindrical Part</Emphasis>

An effective ultrasonic-aided electropolishing system using low-cost electrodes for polishing cylindrical parts is developed. The process can be integrated with the primary processes of traditional turning, drawing, form rolling, or extrusion to achieve a good surface finish for moulds. Ultrasonic energy is applied to the electrolyte for residue discharge during electropolishing. Both continuous and pulsed direct current are tested in the study. The controlled factors include the chemical composition and concentration of the electrolyte, the electrolyte temperature, the flowrate of electrolyte, the initial gap width, and the rotational speed of the workpiece. The experimental parameters are the frequency and power of the ultrasonic vibration, electrical current density, pulse period, rotational speed of the electrode, the electrode feedrate, and the electrode geometry. The incorporation of ultrasonics is found to be more effective than the use of pulsed current, without sacrificing the polishing time. An average surface roughness of 0.3 μm can be obtained by this method. ID="A1"Correspondance and offprint requests to: Professor H. Hocheng, Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu, Taiwan. E-mail: hocheng@pme.nthu.edu.tw     

Design of rib plate of electrode in electrochemical smoothing and electrobrightening of large hole

This study discusses the improvement of surface finish of medium or large holes beyond traditional drilling, boring, rough turning, or extruding by electrochemical smoothing using inserted rib-plate electrodes. High electrical current is not required when the rib plate is used to reduce the engaged area for large hole. Traditionally, the hole polishing requires a sequence of complicated premachining or scarce manual skill. In the current experiment, six types of electrode are completely inserted and connected to both continuous and pulsed direct currents. The controlled factors include the chemical composition and the concentration of the electrolyte, and the diameter of the electrode. The experimental parameters are the current density, on/off period of pulsed current, rotational speed of electrode, and the electrode geometry. For the inserted electrodes, a thin rib plate with small wedge angle towards the root of the plate provides more sufficient discharge space, which is advantageous for polishing. The electrode of single plate performs better than the double-plate electrode. The electrode of a single plate with slant discharge flute performs the best polishing effect. Pulsed direct current can slightly improve the polishing effect at the expense of increased machining time and cost. It was also found that electrobrightening after reaming or precise turning uses quite a short time to make the hole bright, and the electrochemical smoothing saves the need for reaming or precise turning, making the total process time less than the electrobrightening.     

A Study on Electrochemical Micromachining for Fabrication of Microgrooves in an Air-Lubricated Hydrodynamic Bearing

A specially built electrochemical micromachining/pulsed electrochemical micromachining (EMM/PECM) cell, a electrode tool filled with non-conducting material, a electrolyte flow control system and a small and stable gap control unit, are developed to achieve accurate dimensions for spindle recesses. Two electrolytes, aqueous sodium nitrate and aqueous sodium chloride are applied in this study. The former electrolyte has better machinability than the latter because of its ability to change appropriately to the transpassive state without forming pits on the surface of the workpiece. It is easier to control the machining depth precisely by micrometer with pulse current than direct current. This paper also presents an identification method for the machining depth by the in-process analysis of the machining current and interelectrode gap size. The interelectrode gap characteristics, including pulse current, effective volumetric electrochemical equivalent and electrolyte conductivity variations, are analysed, based on the model and experiments. ID="A1"Correspondance and offprint requests to: E.-S. Lee, Department of Mechanical Engineering, Inha University, 253, Yonghyun-Dong, Nam-Gu, Incheon, 402–751, Korea. E-mail: leees@inha.ac.kr     

Electrochemical micro-drilling of deep holes by rotational cathode tools

In numerous non-conventional micro-machining, electrochemical micro-machining has merits such as high removal rate, leaving no residual stress and lower roughness on surfaces of machined products. It has been considered as a highly promising technology in micro-machining. Little research has been done on the deep-hole micro-drilling by electrochemical methods. This work utilizes a rotational system to extract insoluble sludge from a deep hole and reduce the difficulty of filling deep hole with electrolyte. As well as a rotational tool cathode, a pulsed power generator is used to support the intermittence machining to increase the precision of the workpiece. The influence of working parameters, such as pulsed on-times, applied voltages, electrolyte concentrations, pulsed frequencies, tool feeding rates, tool diameters, tool rotational rates, and hole depth, on the hole overcut and conicity in a electrochemical micro-drilling is investigated. A high quality micro-hole with a 33.35-??m overcut is drilled by a tungsten carbide pin of diameter 50???m on a 304 stainless steel plate of thickness 1,000???m. The hole aspect ratio (depth/diameter) reaches 8.6. It shows that a rotational tool can be utilized in the deep-hole electrochemical micro-drilling.     

Investigations on the effects of Nano-fluid in ECM of die steel

Formation of spikes in the electrochemically machined workpiece prevents to achieve the better performance of ElectroChemical Machining (ECM). Hence, this research work attempts to investigate the effects of Nano-fluid i.e. Nano Copper particles suspended NaCl electrolyte on the ECM of High carbon high chromium (HCHCr) die steel with a hardness of 63HRc. The influencing parameters are voltage, tool feed rate and electrolyte discharge rate with mixing levels. Seventy-two experiments have been conducted using Nano-fluid and plain NaCl electrolyte based on design of the experiment. The Nano Copper particles in the electrolyte break the gas layer at the inter electrode gap resulting in better MRR and surface roughness due to improved current density across the gap. A maximum MRR of 458.869 mm³/min and a minimum surface roughness of 1.39 μm Ra are obtained using Nano-fluid. The developed ANOVA models prove the significances of influencing factors in obtaining the better performance of ECM.     

<Emphasis Type="Bold">Effective Form Design of Electrode in Electrochemical Smoothing of Holes</Emphasis>

This study discusses electropolishing of holes using feeding electrodes as well as inserted electrodes for several common die materials. Traditionally, the hole polishing of a die requires a sequence of complicated premachining operations or scarce manual skill. In the current experiment, eight types of electrode are used and supplied with both continuous and pulsed direct current and another eight types of electrode are fed into holes using continuous direct current. The design features of the electrodes are of major interest for the effective electrochemical of holes. The controlled factors include the diameter of the electrode as well as the chemical composition and the concentration of the electrolyte. The experimental parameters are current density, current rating, electrode design, die material, rotational speed and feedrate of the electrode. For inserted electrodes, an electrode with a helical discharge flute performs better than one without a flute or with a straight flute. Pulsed direct current can improve the polishing effect at the expense of increased machining time and cost. For feeding electrodes, an electrode of a borer type performs better than one with a cycle lap on the leading edge. It was also found that electrobrightening after reaming needs only a short time to make the hole bright, and electropolishing saves the need for reaming, making the total process shorter than for electrob-rightening.     

Effect of hybrid electrochemical smoothing–roller burnishing process parameters on roundness error and micro-hardness

In this paper, a novel finishing process, which integrates the merits of electrochemical smoothing (ECS) and roller burnishing (RB) for minimizing the roundness error and increasing surface micro-hardness of cylindrical parts, is proposed. Through simple equipment attachments, electrochemical smoothing–roller burnishing (ECS–RB) can follow the turning process on the same machine. To explore the optimum combinations of the ECS–RB process parameters in an efficient and quantitative manner, the experiments were designed on the basis of the response surface methodology technique. The effect of ECS–RB parameters, namely, burnishing force, applied voltage, inter-electrode gap, and workpiece rotational speed on the roundness error and surface micro-hardness was studied. From the multi-objective optimization, the optimal combination of parameter settings are burnishing force of 350 N, applied voltage of 8.2 V, inter-electrode gap of 2.75 mm, and rotational speed of 970 rpm for achieving the required lower roundness error and higher surface micro-hardness. Surface micro-hardness considerably increases about 31.5% compared to the initial surface micro-hardness, and about 2.32 μm roundness error can be achieved using the optimum combination of process parameters. Therefore, the combination of ECS and RB is a feasible process by which it potentially reduces roundness error and surface micro-hardness of axis-symmetric parts improving their reliability and wear resistance.     

Development and investigations on a hybrid tooling concept for coaxial and concurrent application of electrochemical and laser micromachining processes

In hybrid laser-electrochemical micromachining, both laser and electrochemical process energies act along the same machining axis and thus both influence material removal by their interaction. The traditional nozzle based laser assisted jet-ECM concepts require laser to be focused on workpiece surface in an electrochemical environment and are limited in aspect ratios as the nozzle stays above the workpiece surface. In this work, a hybrid tooling concept is proposed for a novel process scheme of precision hybrid laser-electrochemical micromachining. The tool serves the function of both an ECM electrode as well as a leaky-type multimode waveguide for the laser and delivers laser homogeneously together with the electrolyte on the workpiece surface without requiring laser to be focused on the workpiece surface. A precision prototype hybrid machine-tool is developed which employs short pulsed nano-second laser and micro-second pulsed voltage source for precision micromachining. For this system, ray tracing and detailed multiphysics electrochemical micromachining process simulations are carried out to demonstrate the applicability of this hybrid tooling concept and explain the shape evolution. Successful experimental realization of coaxial and concurrent application of electrochemical and laser processes is presented. Prototype tool electrodes are fabricated and experiments are carried out on an in-house developed prototype hybrid machine tool. The results reveal that the proposed hybrid tool is successfully capable of concentrating laser and electrochemical process energies simultaneously in the same machining zone. However, with the initial design of this hybrid tool, a maximum of 30–40% of laser power is available in the machining zone. Some suggestions for further research will be presented.     

Improvement of electrochemical turning for machining complex shapes using a simple gap size sensor and a tubular shape tool

This paper presents the research and development of a new electrochemical machining technique, electrochemical turning (ECT), which can produce parts with complex shapes. In this technique, the electrolyte passes through a tubular electrode and is pumped to the workpiece. The actual dissolution is measured by using a new type of gap measuring and control sensor. In this sensor, the electrolyte between the tool and the workpiece becomes a resistance of a bridge circuit, while three other resistances are constant. Hence, if the gap size changes, the resistance of the electrolyte and consequently the voltage of the bridge change. This voltage can be used for measuring and control the gap size. Keeping the gap size in a constant value enables the machine to compare the actual and desired dimensions. A suitable ECT setup primarily consists of various components and subsystems, e.g., a mechanical machining unit, an electrical power and controlling system, an electrolyte flow system, etc. Some experiments were performed to identify the effects of voltage, gap size, and time on the material removal rate. As can be predicted, the removal rate increased with voltage and time and decreased with gap size. Also, surface roughness increased with voltage. More attempts will generate more possible applications for ECT.     

电解液防腐及其伏安特性研究

针对电化学光整加工机床及工件的腐蚀机理设计了防腐的措施，并通过试验确定了两种能较好地防止机床腐蚀的防腐剂及其浓度。同时，还研究了防腐剂对电解液导电性能的影响，确定了较优的防腐剂及其浓度。研究结果有助于电化学加工技术的推广应用。     

Accretion of titanium carbide by electrical discharge machining with powder suspended in working fluid

A surface modification method by electrical discharge machining (EDM) with a green compact electrode has been studied to make thick TiC or WC layer. Titanium alloy powder or tungsten powder is supplied from the green compact electrode and adheres on a workpiece by the heat caused by discharge. To avoid the production process of the green compact electrode, a surface modification method by EDM with powder suspended in working fluid is proposed in this paper. After considering flow of working fluid in EDM process, the use of a thin electrode and a rotating disk electrode are expected to keep powder concentration high in the gap between a workpiece and an electrode and to accrete powder material on the workpiece. The accretion machining is tried under various electrical conditions. Titanium powder is suspended in working oil like kerosene. TiC layer grows a thickness of 150 μm with a hardness of 1600 Hv on carbon steel with an electrode of 1 mm in diameter. When a disk placed near a plate rotates in viscous fluid, the disk drags the fluid into the gap between the disk and the plate. Therefore, the powder concentration in the gap between a workpiece and a rotational disk electrode can be kept high. A wider area of the accretion can be obtained by using the rotational electrode with a gear shape.     

Effect of machining parameters on surface integrity of silicon carbide ceramic using end electric discharge milling and mechanical grinding hybrid machining

A novel hybrid process that integrates end electric discharge (ED) milling and mechanical grinding is proposed. The process is able to effectively machine a large surface area on SiC ceramic with good surface quality and fine working environmental practice. The polarity, pulse on-time, and peak current are varied to explore their effects on the surface integrity, such as surface morphology, surface roughness, micro-cracks, and composition on the machined surface. The results show that positive tool polarity, short pulse on-time, and low peak current cause a fine surface finish. During the hybrid machining of SiC ceramic, the material is mainly removed by end ED milling at rough machining mode, whereas it is mainly removed by mechanical grinding at finish machining mode. Moreover, the material from the tool can transfer to the workpiece, and a combination reaction takes place during machining.     

超短脉冲电流微细电解加工技术研究

利用电化学腐蚀方法,在自制的电解加工机床上连续实现微细工具电极的制作和工件的加工,通过试验研究了超短脉冲的电压幅值和脉冲宽度对侧面加工间隙的影响。结果表明,减小脉冲宽度,降低加工电压,可以提高微细电解加工的精度。利用优化的加工参数,进行了微小孔加工、微细直写加工以及成形电极微细加工的实验。     

磁场电化学磁粒复合光整加工实验研究

开发出一种新的光整加工工艺－磁场电化学磁粒复合光整加工。研究了磁场环境下离子运动轨迹方程,分析了复合光整加工的原理并进行了相应的实验,由于洛仑兹力和电场力的综合作用,改变了离子运动轨迹,使被加工表面峰点电流密度更集中,磁场的搅拌作用,加快了电化学过程,使极间电流密度增大,蚀除速度加快,磁场电化学磁粒复合光整加工,与磁粒光整加工,电化学磁粒光整加工相比,提高了加工效率,改善了表面粗糙度。     

ON THE PERFORMANCE ANALYSIS OF FLEXIBLE MAGNETIC ABRASIVE BRUSH

Magnetic abrasive finishing (MAF) of alloy steel workpiece with unbounded magnetic abrasive particles (UMAPs) indicates that the surface finish in the range of nanometer can be achieved. Important controllable four process parameters have been identified which are as current to the electromagnet, machining gap, abrasive size (mesh number), and number of cycles. Experiments have been planned using design of experiments technique. Based upon the results of response surface methodology and analysis of variance (ANOVA), it is concluded that magnetic flux density that depends on current to the electromagnet and machining gap, is most influencing parameter followed by grain size and number of cycles. The surface roughness profile generated during the MAF process has been discussed. To understand the cutting mechanism of magnetic abrasive finishing process, scanning electron microscopy (SEM) and atomic force microscopy (AFM) of the machined surfaces have been carried out. The correlation between surface finish and material removal has also been established.     

Enhanced magnetic abrasive finishing of Ti–6Al–4V using shear thickening fluids additives

The available magnetic field assisted finishing process is considered as the critical stage for improvement of workpiece surface quality. This paper aims to investigate the key quality performance of an enhanced magnetic abrasive finishing in achieving nanolevel finish on Ti–6Al–4V workpieces with initial micrometer surface roughness values. The finishing media, combining the intelligent shear thickening fluids (STFs), carbonyl iron particles and SiC particles, is developed. Finishing experiments for Ti–6Al–4V workpieces are conducted using an established platform, aiming to investigate the effects of varying STFs concentration, working gap, feed rate and spindle rotational speed. It is observed from the experimental results that the developed finishing media is effective for surface finishing comparing to the finishing media without STFs. The surface roughness of 54 nm was achieved from the initial value of 1.17 μm, which improved by over 95%, under the experimental conditions of 0.8 mm working gap, 15000 mm/min feed rate, 900 rpm spindle rotational speed and 15 wt% STFs. Surface observations showed that a smooth surface without obvious scratches was obtained.