Advancement in electrochemical micro-machining

Electrochemical micro-machining (EMM) appears to be very promising as a future micro-machining technique, since in many areas of applications it offers several advantages, which include higher machining rate, better precision and control, and a wide range of materials that can be machined. In this paper, a review is presented on current research, development and industrial practice in micro-ECM. This paper highlights the influence of various predominant factors of EMM such as controlled material removal, machining accuracy, power supply, design and development of microtool, role of inter-electrode gap and electrolyte, etc. EMM can be effectively used for high precision machining operations, that is, for accuracies of the order of ±1 μm on 50 μm. Some industrial applications of EMM have also been reported. Further research into EMM will open up many challenging opportunities of improvement towards greater machining accuracy, new materials machining and generation of complex shapes for effective utilization of ECM in the micro-machining domain.     

Experimental investigation on the influence of electrochemical machining parameters on machining rate and accuracy in micromachining domain

Non-conventional machining is increasing in importance due to some of the specific advantages which can be exploited during micromachining operation. Electrochemical micromachining (EMM) appears to be a promising technique, since in many areas of application, it offers several special advantages that include higher machining rate, better precision and control, and a wider range of materials that can be machined. A better understanding of high rate anodic dissolution is urgently required for EMM to become a widely employed manufacturing process in the micro-manufacturing domain. An attempt has been made to develop an EMM experimental set-up for carrying out in depth research for achieving a satisfactory control of the EMM process parameters to meet the micromachining requirements. Keeping in view these requirements, sets of experiments have been carried out to investigate the influence of some of the predominant electrochemical process parameters such as machining voltage, electrolyte concentration, pulse on time and frequency of pulsed power supply on the material removal rate (MRR) and accuracy to fulfil the effective utilization of electrochemical machining system for micromachining. A machining voltage range of 6 to 10 V gives an appreciable amount of MRR at moderate accuracy. According to the present investigation, the most effective zone of pulse on time and electrolyte concentration can be considered as 10–15 ms and 15–20 g/l, respectively, which gives an appreciable amount of MRR as well as lesser overcut. From the SEM micrographs of the machined jobs, it may be observed that a lower value of electrolyte concentration with higher machining voltage and moderate value of pulse on time will produce a more accurate shape with less overcut at moderate MRR. Micro-sparks occurring during micromachining operation causes uncontrolled material removal which results in improper shape and low accuracy. The present experimental investigation and analysis fulfils various requirements of micromachining and the effective utilization of ECM in the micromachining domain will be further strengthened.     

Experimental investigation into electrochemical micromachining (EMM) process

Due to several advantages and wider range of applications, electrochemical micromachining (EMM) is considered to be one of the most effective advanced future micromachining techniques. A suitable EMM setup mainly consists of various components and sub-systems, e.g. mechanical machining unit, micro-tooling system, electrical power and controlling system and controlled electrolyte flow system etc. have been developed successfully to control electrochemical machining (ECM) parameters to meet the micromachining requirements. Investigation indicates most effective zone of predominant process parameters such as machining voltage and electrolyte concentration, which give the appreciable amount of material removal rate (MRR) with less overcut. The experimental results and analysis on EMM will open up more application possibilities for EMM.     

Impact of the shape of electrode-tool on radical overcut of micro-hole in electrochemical micromachining

To make use of the full capability of electrochemical micro-machining (EMM), a meticulous research is needed to improve the material removal, surface quality and accuracy by optimizing various EMM process parameters. Keeping this in view, an indigenous development of an EMM machine set-up has been considered to carry out a systematic research for achieving a satisfactory control on the EMM process parameters to meet the micromachining requirements. In this study an EMM machine has been developed and experiments were conducted to study the influence of some of the major process parameters such as the machining voltage, electrolyte concentrations, the pulse-on-time and the machining current on the machining rate and accuracy. The effect of the shape of the tool electrode tips on EMM has been investigated experimentally with 304 stainless steel sheets. The machining rate and the overcut are significantly influenced by the shape of the tool electrode tip.     

Influence of vibration on micro-tool fabrication by electrochemical machining

Recent trend in societies is to have micro products in limited space. Efficient micromachining technologies are essential to fabricate micro products which in turn will be helpful in saving material, energy and enhancing functionality. For micromachining, micro tool is very much essential. This paper is aimed at finding the most suitable and quickest method of micro tool fabrication by electrochemical machining. Tungsten micro tools were fabricated at different machining conditions to know the influences of voltage, frequency of tool vibration, amplitude of vibration of tungsten tool, concentrations of electrolyte and dipping length of tool inside the electrolyte. Fabrication of uniform diameter of micro tool is possible at each applied voltage starting at 2 V to higher volt utilizing vibration with appropriate amplitude. Good quality micro tools with different shapes can be fabricated by controlling a proper diffusion layer thickness within a very short time introducing the vibrations of micro tool. Finally, the fabricated micro tools were applied for machining precise micro holes and micro channel using electrochemical micromachining (EMM).     

振动辅助电弧铣削加工技术实验研究

通过对电弧加工技术、电弧铣削加工技术及其机理的总结,提出了振动辅助电弧铣削加工技术。利用自行研制的实验装置,对有、无叠加振动的铣削加工放电波形进行了分析,研究了振动频率对加工速度、电极损耗的影响。结果表明:在较高频率与较大振幅的条件下,通过叠加振动可提高电弧铣削过程的稳定性,并提升加工速度,降低电极相对损耗,进而改善加工精度。振动所起的良好作用是由于叠加振动能促进放电并减少短路。     

钛合金与镍基高温合金薄片振动辅助电火花加工工艺参数优化研究

在航空发动机叶片的电解加工过程中,由于存在加工间隙,导致加工后的叶片边缘存在尺寸与形状误差。采用电火花加工并辅以振动对叶片边缘进行粗、精加工修整,考虑到电火花加工参数与工件材料加工特性存在不确定性,通过正交试验探究了粗加工的峰值电流、脉冲宽度、振幅和振动频率对材料去除率、工具电极相对体积损耗率的影响。采用横截面尺寸为29 mm×0.5 mm的钛合金和镍基高温合金薄板作为工件进行长度2 mm的切断实验,通过极差分析法和方差分析法获得加工最优参数,并得出镍基高温合金、钛合金材料去除率最高分别达12.99、13.13 mm3/min,为后续利用成形电极对叶片边缘进行精密修整提供可参考的有效电加工参数。     

振动辅助液中喷气电火花加工性能研究

提出了振动辅助液中喷气电火花加工方法。该方法通过工件机械振动改善了极间的放电状态,降低了短路率。通过实验研究了机械振动的频率和振幅对液中喷气电火花加工性能的影响,研究了振动辅助作用下电加工参数、气体压力、工具电极转速对加工性能的影响。结果表明,工件的机械振动可有效提高液中喷气电火花加工的材料去除率,改善加工表面质量,而电极损耗几乎为零。     

Finite element prediction of material removal rate due to electro-chemical spark machining

Electro-chemical spark machining (ECSM) is an innovative hybrid machining process, which combines the features of the electro-chemical machining (ECM) and electrodischarge machining (EDM). Unlike ECM and EDM, ECSM is capable of machining electrically non-conducting materials. This paper attempts to develop a thermal model for the calculation of material removal rate (MRR) during ECSM. First, temperature distribution within zone of influence of single spark is obtained with the application of finite element method (FEM). The nodal temperatures are further post processed for estimating MRR. The developed FEM based thermal model is found to be in the range of accuracy with the experimental results. Further the parametric studies are carried out for different parameters like electrolyte concentration, duty factor and energy partition. The increase in MRR is found to increase with increase in electrolyte concentration due to ECSM of soda lime glass workpiece material. Also, the change in the value of MRR for soda lime glass with concentration is found to be more than that of alumina. MRR is found to increase with increase in duty factor and energy partition for both soda lime glass and alumina workpiece material.     

超声振动辅助气中放电加工实验分析

超声振动辅助气中放电加工技术避免了常用的煤油等工作液作为介质带来的环境污染问题，具有工作环境清洁、适用范围广、加工效率高、工具电极简单等优点。实验研究了电压、脉冲宽度、峰值电流、超声振幅及气体介质压力等参数对加工效率、工件表面粗糙度及电极损耗的影响．并对试验结果进行了分析。     

A comparative experimental study of machining characteristics in vibratory, rotary and vibro-rotary electro-discharge machining

This paper compares the effects of high- and low-frequency forced axial vibration of the electrode, rotation of the electrode, and combinations of these methods in respect of material removal rate (MRR), tool wear rate and surface roughness in die sinking electro-discharge machining (EDM) with a flat electrode (planing mode).

The results of the combined states of rotation and vibration at high and low frequency (vibro-rotary EDM) are compared in order to establish which combinations are most appropriate to different machining regimes (finishing, semi-finishing and roughing). It is found that the combination of high-frequency vibration and rotation of the electrode is effective in attaining a high MRR at a specified surface roughness (R_a). This case is modelled by stepwise linear regression. The significant parameters are found by analysis of variance (ANOVA) and the optimum machining parameter settings are obtained using overlay contour plots. The advantages of vibration and rotation are seen to combine in this new process when employed for die sinking EDM with a flat electrode.     

A study on the machining of high-aspect ratio micro-structures using micro-EDM

Micro-electro-discharge machining (micro-EDM or μ-EDM) has been gaining popularity as a new alternative method to fabricate micro-structures. The main advantages of the micro-EDM method are its low set-up cost, high accuracy and large design freedom. Compared to etching or deposition techniques, micro-EDM has the advantage of being able to fabricate complex three-dimensional shapes with high-aspect ratio. However, there are many operating parameters that affect the micro-EDM process. The fabrication of micro-electrodes on the machine is also an important process to remove the clamping error to maintain high accuracy in the machined micro-structures.

In this paper, the machining of micro-structures is divided into two basic processes. One is the on-machine fabrication of the micro-electrodes with high-aspect ratio, and the other is the EDM of the workpiece in micrometer range. An optical sensor has been developed to measure and control the dimension of the thin electrode during the tool fabrication process. Different methods have been investigated to fabricate a thin electrode into the desired dimension without deflection. The performance of the micro-EDM process is evaluated in terms of the material removal rate (MRR), tool wear ratio (TWR), and the stability of the machining. Influences of the various operating parameters of the micro-EDM process, such as the operating voltage, gap control algorithm, and resistance and capacitance values in the R–C spark control circuit, are discussed.     

High-speed dry electrical discharge machining

A novel high-speed dry electrical discharge machining (EDM) method was proposed in this study. Using this method, the material can be rapidly melted by extremely high discharge energy and flushed out of the discharge gap by high-pressure and high-speed air flow. The material removal rate (MRR) of dry EDM was significantly improved by the proposed method. The MRR of dry EDM is usually in tens mm³/min, whereas the MRR of the proposed method can be as high as 5162 mm³/min, which improves the MRR by 2nd to 3rd order of magnitude. Investigation was conducted systemically. The influences of work piece polarity, discharge current, pulse duration time, gas pressure, and electrode rotation speed on machining performance were studied. The machining mechanism of this method was thoroughly analyzed. Moreover, the re-solidified layer, surface morphology, elementary composition, and phase of AISI 304 stainless steel for high-speed dry EDM were also investigated. Theoretical and technical foundations were laid for the industry application of dry EDM.     

A Study on Process Parameters of Ultrasonic Assisted Micro EDM Based on Taguchi Method

Experimental investigation of ultrasonic assisted micro electro discharge machining was performed by introducing ultrasonic vibration to workpiece. The Taguchi experimental design has been applied to investigate the optimal combinations of process parameters to maximize the material removal rate and minimize the tool wear. Analysis of variance (ANOVA) was performed and signal-to-noise (S/N) ratio was determined to know the level of importance of the machining parameters. Based on ANOVA, ultrasonic vibration at 60% of the peak power with capacitance of 3300 PF was found to be significant for best MRR. The machining time plays a significant role in the tool wear. The results were confirmed experimentally at 95% confidence interval.     

On Electro Discharge Machining of Inconel 718 with Hollow Tool

Inconel 718 is a nickel-based alloy designed for high yield, tensile, and creep-rupture properties. This alloy has been widely used in jet engines and high-speed airframe parts in aeronautic application. In this study, electric discharge machining (EDM) process was used for machining commercially available Inconel 718. A copper electrode with 99.9% purity having tubular cross section was employed to machine holes of 20?mm height and 12?mm diameter on Inconel 718 workpieces. Experiments were planned using response surface methodology (RSM). Effects of five major process parameters??pulse current, duty factor, sensitivity control, gap control, and flushing pressure on the process responses??material removal rate (MRR) and surface roughness (SR) have been discussed. Mathematical models for MRR and SR have been developed using analysis of variance. Influences of process parameters on tool wear and tool geometry have been presented with the help of scanning electron microscope (SEM) micrographs. Analysis shows significant interaction effect of pulse current and duty factor on MRR yielding a wide range from 14.4 to 22.6?mm³/min, while pulse current remains the most contributing factor with approximate changes in the MRR and SR of 48 and 37%, respectively, corresponding to the extreme values considered. Interactions of duty factor and flushing pressure yield a minimum surface roughness of 6.2???m. The thickness of the sputtered layer and the crack length were found to be functions of pulse current. The hollow tool gets worn out on both the outer and the inner edges owing to spark erosion as well as abrasion due to flow of debris.     

A new method for monitoring micro-electric discharge machining processes

Micro-electric discharge machining (μ-EDM) is a very complex phenomenon in terms of its material removal characteristics since it is affected by many complications such as adhesion, short-circuiting and cavitations. This paper presents a new method for monitoring μ-EDM processes by counting discharge pulses and it presents a fundamental study of a prognosis approach for calculating the total energy of discharge pulses. For different machining types (shape-up and flat-head) and machining conditions (mandrel rotation and tool electrode vibration), the results obtained using this new monitoring method with the prognosis approach show good agreement between the discharge pulses number and the total energy of discharge pulses to the material removal and tool electrode wear characteristic in μ-EDM processes. On applying tool electrode vibration, the machining time becomes shorter, because it removes adhesion. The effect of tool electrode vibration in order to remove adhesion can be monitored with good results. In order to achieve high accuracy, the tool wear compensation factor has been successfully calculated, since the amount of tool electrode wear is different in each machining type and condition. Consequently, a deeper understanding of the μ-EDM process has been achieved.     

A finite element analysis for the characteristics of temperature and stress in micro-machining considering the size effect

In this paper, a finite element method for predicting the temperature and the stress distributions in micro-machining is presented. The work material is oxygen-free-high-conductivity copper (OFHC copper) and its flow stress is taken as a function of strain, strain rate and temperature in order to reflect realistic behavior in machining process. From the simulation, a lot of information on the micro-machining process can be obtained; cutting force, cutting temperature, chip shape, distributions of temperature and stress, etc. The calculated cutting force is found to agree with the experiment result with the consideration of friction characteristics on the chip–tool contact surface. Because of considering the tool edge radius, this cutting model using the finite element method can analyze micro-machining with a very small depth of cut, almost the same size of tool edge radius, and can observe the ‘size effect' characteristic. Also, the effects of temperature and friction on micro-machining are investigated.     

Sensor-based modeling of slurry chemistry effects on the material removal rate (MRR) in copper-CMP process

Material removal rate (MRR) and surface quality in copper-chemical mechanical planarization (Cu-CMP) process are highly sensitive to slurry chemistry parameters, namely, pH, and concentrations of complexing, corrosion inhibiting, and oxidizing agents. Capturing the effects of these slurry parameters on MRR and surface quality in real time through the use of sensor signals is key to ensuring an efficient Cu-CMP process. In this paper, vibration sensor signals collected from the Cu-CMP experiments are used to capture the variations in various slurry parameters as well as their influence on the MRR. Two sensors, namely, a wired accelerometer (Kistler Model 8728A500, sampling at 5 kHz) and a single channel wireless accelerometer (Tmote Sky sensor node, sampling at 500 Hz) are mounted at two distinct locations on a LapMaster-12 bench-top polishing machine. Various statistical features related to time and frequency domain characteristics of the sensor signals are extracted. It was found that principal component regression models relating these features to MRR are significantly more accurate than the conventional statistical regression models that use process parameters (slurry chemistry settings) only to estimate MRR.     

不同电极材料的短电弧铣削加工效率研究

短电弧铣削加工是一种新型的放电加工,它进一步提高了放电加工效率。论述了短电弧加工材料去除机制、去离子原则和热现象,分析了余热对材料去除率(MRR)的影响。研究了短电弧铣削加工效率的主要指标——MRR,在不同工具、工件电极的材料组合下,分析峰值电流、脉冲时间、脉冲间隔、进给速度、气压等工艺因素对MRR的影响规律。实验表明:不同电极材料组合的MRR存在差异;在大多数放电条件下,石墨电极和45碳钢工件获得较高的MRR,而紫铜电极和镍基高温合金GH4169工件获得较低的MRR。     

An automatic spindle speed selection strategy to obtain stability in high-speed milling

Chatter vibration problems arise during machining. This paper aims to produce a strategy that can detect the emergence of chatter so that subsequently, in accordance with the lobe on the stability diagram where the process is located, the proper strategy may be determined, either by taking the machine to a stable spindle speed or causing continuous variation in spindle speed. The effectiveness of this strategy is contrasted for a number of different cases, using both simulation and experimental testing. The context targeted by the strategy is a high-speed mill roughing operation for cases of vibration arising on the headstock/cutting tool unit, when high material removal rates (MRR) must be maintained. Industrial implementation of the strategy and the chatter detection and diagnosis algorithm is carried out using a portable digital assistant (PDA).