Experimental investigations into electrical discharge machining with a rotating disk electrode

In electrical discharge machining, when the provision of holes in the electrode is impracticable, flushing of the working gap poses a major problem. Use of a rotating disk electrode is proposed as a more productive and accurate technique than use of a conventional electrode. Material removal rate, tool wear rate, relative electrode wear, corner reproduction accuracy, and surface finish aspects of a rotary electrode are compared with those of a stationary one. The effective flushing of the working gap brought about by the rotation of the electrode remarkably improves material removal rate and machines surfaces with a better finish. Despite the prevalent high tool wear rate, the reproduction accuracy is least affected as the wear gets uniformly distributed over the entire circumference of the disk. Machining of a sharp corner is possible even with an aluminum electrode, whose relative electrode wear is greater than unity.     

Reducing electrode wear ratio using cryogenic cooling during electrical discharge machining

In this study, cooling effect of copper electrode on the die-sinking of electrical discharge machining of titanium alloy (Ti-6Al-4V) has been carried out. Investigation on the effect of cooling on electrode wear and surface roughness of the workpiece has been carried out. Design of experiment plan for rotatable central composite design of second order with four variables at five levels each has been employed to carry out the investigation. Current intensity (I), pulse on-time (t _on), pulse off-time (t _off), and gap voltage (v) were considered as the machining parameters, while electrode wear and surface roughness are the responses. Analysis of the influence of cooling on the responses has been carried out and presented in this study. It was possible to reduce electrode wear ratio up to 27% by electrode cooling. Surface roughness was also reduced while machining with electrode cooling.     

超声电沉积制备电火花加工铜电极的研究

电火花加工中,电极是影响加工质量和加工效率的重要因素。电沉积是制备电极材料的有效方法,为了改善沉积层质量,将超声场引入到电沉积中,采用金相显微镜、扫描电子显微镜观察电铸铜层微观形貌,并测试显微硬度和电火花耐电蚀性。结果表明,超声电沉积得到的铜铸层晶粒更加细小、均匀,致密性好;显微硬度比普通电沉积铜提高20%以上;电极相对损耗低,抗电蚀性能得到提高。     

Diameter control of microshafts in wire electrical discharge grinding

In microelectrical discharge machining (μEDM), the machining repeatability of microshafts with the same diameter is low due to the complex and stochastic nature of sparking. To improve machining repeatability, the effects of the main error sources on diameter accuracy of microshafts fabricated by wire electrical discharge grinding (WEDG) were analyzed. Strategies to minimize diameter differences between the target microshaft and the microshaft finally obtained by semifinishing and finishing were then proposed. Determining an appropriate infeed (depth of a cut) according to the desired erosion depth in the radial direction (ΔR) of microshafts was chosen as the control strategy for the semifinishing of microshafts produced by WEDG. To determine the infeed, empirical models that evaluate the relationship between the infeed and ΔR were developed through a large number of experiments. For the finishing of microshafts using WEDG, machining strategies such as zero infeed and stopping the wire electrode running, were proposed to eliminate some of the inherent errors. Finally, the empirical models developed for determining the infeed were verified by the successful fabrication of a stepped microshaft, which has small deviations from its desired diameters. By employing the developed empirical models and machining strategies, diameters of 26 out of 28 microshafts fabricated were found to lie in the range of 45?±?2 μm. The experimental results verify that the diameter control strategies are effective and can be used to improve machining repeatability.     

Study of high-efficiency electrical discharge machining-induced ablation machining of titanium alloy TC4 using a multi-function electrode

Aimed at overcoming the low efficiency of electrical discharge machining (EDM), and taking advantage of the characteristic that most metals can burn in oxygen, a new high-efficiency process is put forward: EDM-induced ablation machining (EDM-IAM) using multi-function electrode technology. EDM-IAM injects oxygen and dielectric fluid into the processing area through a dedicated channel of a multi-function electrode. The chemical energy caused by the reaction of metal and oxygen can much improve the material removal efficiency. To study the factors affecting the efficiency of the process, the ablation machining of a titanium alloy (TC4) using a multi-function electrode was carried out; analysis of the worked surface was done with scanning electron microscopy, X-ray diffraction, and discharge waveforms. The results show that the substances of the worked surface are mainly TiO, TiO_1.2, TiO₂, and smaller amounts of Ti₃O and other titanium oxides. Violent oxidation combustion reaction occurs during the ablation machining process. The processing efficiency of ablation machining can reach 347.7 mm³/min, which is 58.7 times that of normal EDM for the same processing conditions. The main reasons for the high material removal rate are the higher utilization rate of electric spark discharge energy, consumption of material by ablation, melting effect of combustion heat on the workpiece material, and forced chip removal effect by local explosion.     

Enhanced laser shutter using a hard disk drive rotary voice-coil actuator

Rotary voice-coil motors from computer hard disk drives make excellent mechanical shutters for light beams. However, the complexity of the necessary electronic driving circuit can hinder their application. A new design is presented here, using a single integrated circuit originally intended for controlling dc motors. A digital input signal switches a unipolar power supply bidirectionally through the voice coil. Short high-current pulses are generated on the transitions to ensure rapid shutter action, while a low holding current reduces the power requirement and heating of the actuator. The circuit can reverse the current to brake the shutter and reduce the impact at the end of its travel. With a focused laser beam, the shutter achieves rise times below 500 ns. A method for producing variable length pulses is also described, demonstrating durations as short as 700 ns.     

Mist-jetting electrical discharge dressing (MEDD) of nonmetal bond diamond grinding wheels using conductive coating

Diamond wheels are widely used in high-precision grinding of hard and brittle materials; unfortunately, they are difficult to true and dress. This paper addresses that problem in that it proposes an effective dressing technique—mist-jetting electrical discharge dressing (MEDD) of nonmetal bond diamond grinding wheels using conductive coating. A conductive phase is coated on the wheel surface to increase the conductivity of the nonmetal bond. Electrical discharge model was built to analyze feasibility and select optimized parameters of MEDD. Experiments were conducted to evaluate the dressing performance of MEDD in terms of surface morphology of the wheel surface, grinding force, and surface roughness of the workpiece. Experimental results show that abrasive grains on the wheel protrude are satisfied. The discharge parameters have an important influence on the dressing result. The grinding force and the surface roughness of the workpiece significantly reduced after dressing.     

Thermal simulation of machining of alumina with wire electrical discharge machining process using assisting electrode

Journal of Mechanical Science and Technology - Electrical discharge machining or Wire electrical discharge machining have proven to be an alternate mean for machining nonconducting materials to a...     

The drilling of Al2O3 using a pulsed DC supply with a rotary abrasive electrode by the electrochemical discharge process

The electrochemical discharge machining (ECDM) process has the potential to machine electrically non-conductive high-strength, high-temperature-resistant (HSHTR) ceramics, such as aluminum oxide (Al₂O₃). However, the conventional tool configurations and machining parameters show that the volume of material removed decreases with increasing machining depth and, finally, restricts the machining after a certain depth. To overcome this problem and to increase the volume of material removed during drilling operations on Al₂O₃, two different types of tool configurations, i.e., a spring-fed cylindrical hollow brass tool as a stationary electrode and a spring-fed cylindrical abrasive tool as a rotary electrode, were considered. The volume of material removed by each electrode was assessed under the influence of three parameters, namely, pulsed DC supply voltage, duty factor, and electrolyte conductivity, each at five different levels. The results revealed that the machining ability of the abrasive rotary electrode was better than the hollow stationary electrode, as it would enhance the cutting ability due to the presence of abrasive grains during machining.     

A study of electrochemical deburring using a moving electrode

The electrochemical deburring process with graphite balls was investigated using turned aluminium specimens. Three different types of electrolyte were compared for quality of deburring and metal dissolution rate. Micrographs of deburred samples were analysed to evaluate deburring quality.     

On-machine wire electrical discharge dressing (WEDD) of metal-bonded grinding wheels

Traditional multivariate control charts such as Hotelling’s χ ² and T ² control charts are designed to monitor vectors of variable quality characteristics. However, in certain situations, data are expressed in linguistic terms and, under these circumstances, variable or attribute multivariate control charts are not suitable choices for monitoring purposes. Fuzzy multivariate control charts such as fuzzy Hotelling’s T ² could be considered as efficient tools to overcome the problems of linguistic observations. The purpose of this paper is to develop a fuzzy multivariate exponentially weighted moving average (F-MEWMA) control chart. In this paper, multivariate statistical quality control and fuzzy set theory are combined to develop the proposed method. Fuzzy sets and fuzzy logic are powerful mathematical tools for modeling uncertain systems in industry, nature, and humanity. Through a numerical example, the performance of the proposed control chart was compared to the fuzzy Hotelling’s T ² control chart. Results indicate uniformly superior performance of the F-MEWMA control chart over Hotelling’s T ² control chart.     

Optimisation of the electrical discharge machining process using a GA-based neural network

In this paper, the optimisation of the EDM process parameters from the rough cutting stage to the finish cutting stage has been reported. A trained neural network was used to establish the relationship between the process parameters and machining performance. Genetic algorithms with properly defined objective functions were then adapted to the neural network to determine the optimal process parameters. Examples with specifications intentionally assigned the same values as those recorded in the database or selected arbitrarily have been fed into the developed GA-based neural network in order to verify the optimisation ability throughout the machining process. Accordingly, the optimised results indicate that the GA-based neural network can be successfully used to generate optimal process parameters from the rough cutting stage to the finish cutting stage.     

Electrical discharge abrasive drilling of hard materials using a metal matrix composite electrode

The main object of the present work was to develop an electrical discharge abrasive drilling (EDAD) methodology to remove the re-solidified layer through the grinding induced by a metal matrix composite electrode prior to the re-solidification of molten material. A metal matrix composite (Cu/SiC_p) electrode, with an electroless pretreatment of Cu coating on SiC_p to enhance bonding status between Cu and SiC_p, was made with a rotating device and this was employed to study the EDAD technology. The machinability of the mold steel HPM50 and tungsten carbide P20 was investigated by the combined technologies of EDAD. The machined surfaces of these materials were examined by scanning electron microscopy (SEM) and their surface roughness measured by a profilemeter. From the experimental results, it was found that the EDAD machining efficiency was three to seven times than that of normal EDM operation for mold steel. However, the efficiency improvement is hardly detectable for tungsten carbide. In addition, the surface roughness of both materials could be improved in comparison with that achieved after EDM.     

Material removal rate and electrode wear ratio study on the powder mixed electrical discharge machining of cobalt-bonded tungsten carbide

In this article, a material removal rate (MRR) and electrode wear ratio (EWR) study on the powder mixed electrical discharge machining (PMEDM) of cobalt-bonded tungsten carbide (WC-Co) has been carried out. This type of cemented tungsten carbide was widely used as moulding material of metal forming, forging, squeeze casting, and high pressure die casting. In the PMEDM process, the aluminum powder particle suspended in the dielectric fluid disperses and makes the discharging energy dispersion uniform; it displays multiple discharging effects within a single input pulse. This study was made only for the finishing stages and has been carried out taking into account the four processing parameters: discharge current, pulse on time, grain size, and concentration of aluminum powder particle for the machinability evaluation of MRR and EWR. The response surface methodology (RSM) has been used to plan and analyze the experiments. The experimental plan adopts the face-centered central composite design (CCD). This study highlights the development of mathematical models for investigating the influence of processing parameters on performance characteristics.     

氧化锆陶瓷材料的旋转超声加工

研究了用旋转超声加工的方法对氧化锆陶瓷材料进行磨削,探讨了旋转超声磨削的机理,并采用正交组合试验方法,进行了旋转超声磨削加工试验。通过试验探讨了工艺参数对表面粗糙度的影响,从而确定了一组最佳的磨削工艺参数。     

Application of non-dominated sorting genetic algorithm for multi-objective optimization of electrical discharge diamond face grinding process

Hybrid machining processes (HMPs), having potential for machining of difficult to machine materials but the complexity and high manufacturing cost, always need to optimize the process parameters. Our objective was to optimize the process parameters of electrical discharge diamond face grinding (EDDFG), considering the simultaneous effect of wheel speed, pulse current, pulse on-time and duty factor on material removal rate (MRR) and average surface roughness (Ra). The experiments were performed on a high speed steel (HSS) workpiece at a self developed face grinding setup on an EDM machine. All the experimental results were used to develop the mathematical model using response surface methodology (RSM). The developed model was used to generate the initial population for a genetic algorithm (GA) during optimization, non-dominated sorting genetic algorithm (NSGA-II) was used to optimize the process parameters of EDDFG process. Finally, optimal solutions obtained from pareto front are presented and compared with experimental data.     

一种采用电火花加工技术的表面改性方法

研究了一种在普通电火花加工机床上实现金属工件表面改性的新方法。它是在传统电火花加工方法的基础上,通过特制的半烧结体电极,在电火花加工过程中能够在工件表面迅速形成一层硬质碳化物陶瓷,从而达到改善工件表面性能的目的。对这种方法的原理进行了初步的探讨,并在大量实验的基础上,通过厚度测量、硬度梯度测试、X射线衍射分析等一系列实验手段,对沉积层的生成特性进行了详细的分析。最后利用本方法在普通的高速钢车刀上进行了初步应用。试验与分析表明,用电火花加工的方法进行金属表面沉积陶瓷层技术是一种极具潜力的表面改性方法。