Wire electrical discharge machining of ASP30 tool steel

Wire electrical discharge machining is a non-traditional cutting process for machining of hard and high strength materials. This study analyzed the effects of the main input parameters of wire electrical discharge machining of ASP30 steel (high alloyed Powder metallurgical [PM] high speed steel) as the workpiece on the material removal rate and surface roughness. The input parameters included spraying pressure and electric conductivity coefficient of the dielectric fluid, linear velocity of the wire and wire tension. The machined surface quality was evaluated using SEM pictures. Results indicated that increasing the spraying pressure of dielectric fluid leads to a higher material removal rate and surface roughness and that increasing the wire tension, linear velocity of wire, and electric conductivity of the dielectric fluid decreases the material removal rate and surface roughness.

     

Super-high-thickness high-speed wire electrical discharge machining

High-speed wire electrical discharge machining (WEDM-HS) of materials of super-high thickness (more than 1000 mm) is a challenging problem. First, sufficient energy is required to maintain the inter-electrode normal discharge. Next, there must be adequate inter-electrode dielectric fluid. Third, in order to generate a smooth cut surface, it is necessary to suppress the vibration of the wire electrode to reduce vibration lines on the cutting surface. To better understand these challenges, the energy and the flow of the medium between two electrodes were analyzed, allowing the establishment of a relevant model. The results indicated that for super-high-thickness machining, the pulse energy must be adequate to compensate for the energy consumed in the molybdenum wire and inter-electrode working liquid. In addition, the running speed of the wire electrode should be improved to ensure that there is a sufficiently high flow rate of the dielectric fluid. The servo control mode of the existing machine tools and dielectric fluid were improved and then a process experiment was performed. The experimental results show that the process can be carried out efficiently and stably and the workpiece surface can be cut smoothly using the improved working liquid and servo control mode.     

Influence of machining parameters on surface roughness in finish cut of WEDM

Surface roughness is significant to the finish cut of wire electrical discharge machining (WEDM). This paper describes the influence of the machining parameters (including pulse duration, discharge current, sustained pulse time, pulse interval time, polarity effect, material and dielectric) on surface roughness in the finish cut of WEDM. Experiments proved that the surface roughness can be improved by decreasing both pulse duration and discharge current. When the pulse energy per discharge is constant, short pulses and long pulses will result in the same surface roughness but dissimilar surface morphology and different material removal rates. The removal rate when a short pulse duration is used is much higher than when the pulse duration is long. Moreover, from the single discharge experiments, we found that a long pulse duration combined with a low peak value could not produce craters on the workpiece surface any more when the pulse energy was reduced to a certain value. However, the condition of short pulse duration with high peak value still could produce clear craters on the workpiece surface. This indicates that a short pulse duration combined with a high peak value can generate better surface roughness, which cannot be achieved with long pulses. In the study, it was also found that reversed polarity machining with the appropriate pulse energy can improve the machined surface roughness somewhat better compared with normal polarity in finish machining, but some copper from the wire electrode is accreted on the machined surface.     

Application of TOPSIS to Taguchi method for multi-characteristic optimization of electrical discharge machining with titanium powder mixed into dielectric fluid

Mixing powder into dielectric fluid in electrical discharge machining (PMEDM) is a very interesting technological solution in current research. This method has the highest efficiency in simultaneously improving the productivity and quality of a machined surface. In this study, material removal rate (MRR), surface roughness (SR), and the micro-hardness of a machined surface (HV) in electrical discharge machining of die steels in dielectric fluid with mixed powder were optimized simultaneously using the Taguchi–TOPSIS method. The process parameters used in the study included workpiece materials (SKD61, SKD11, SKT4), electrode materials (copper, graphite), electrode polarity, pulse-on time, pulse-off time, current, and titanium powder concentration. Some interaction pairs among the process parameters were also used to evaluate the effect on the optimal results. The results showed that MRR and HV increased and SR decreased when Ti powder was mixed into the dielectric fluid in EDM. Factors such as powder concentration, electrode material, electrode polarity, and pulse-off time were found to be significant in the optimal indicator (C*) and the S/N ratio of C*. Powder concentration was also found to be the most significant factor; its contribution to C* was 50.90%, and S/N ratio of C* was 51.46%. The interactions of the powder concentration and certain process parameters for C* were found to be largest. The optimum quality characteristics were MRR?=?38.79 mm³/min, SR?=?2.71 μm, and HV?=?771 HV. The optimal parameters were verified by experiment, and its accuracy was good (max error ≈13.38%). The finished machined surface under optimum conditions was also analyzed. The machined surface quality under optimum conditions was good. In addition, the results of the study showed the TOPSIS limitations of TOPSIS in a multi-criteria optimization problem.     

非导电工程陶瓷电火花磨削技术

开发出双电极同步伺服跟踪电火花磨削新技术,该技术突破了传统的机械磨削和电解电火花机械复合磨削方法,利用导电磨轮与紧贴非导电工程陶瓷工件表面作自动伺服进给运动的薄片辅助电极间的放电实现电火花磨削。对非导电的Al2O3工程陶瓷进行加工试验,给出加工参数如脉冲宽度、脉冲间隔、峰值电压、峰值电流、磨轮转速以及铜片电极厚度等对材料去除率和表面粗糙度的影响规律关系。试验结果表明,该种新型加工技术具有效率高、表面质量好、成本低和对环境无污染等优点。     

Optimization of wire electrical discharge machining (WEDM) process parameters using Taguchi method

Wire electrical discharge machining (WEDM) is extensively used in machining of conductive materials when precision is of prime importance. Rough cutting operation in WEDM is treated as a challenging one because improvement of more than one machining performance measures viz. metal removal rate (MRR), surface finish (SF) and cutting width (kerf) are sought to obtain a precision work. Using Taguchi’s parameter design, significant machining parameters affecting the performance measures are identified as discharge current, pulse duration, pulse frequency, wire speed, wire tension, and dielectric flow. It has been observed that a combination of factors for optimization of each performance measure is different. In this study, the relationship between control factors and responses like MRR, SF and kerf are established by means of nonlinear regression analysis, resulting in a valid mathematical model. Finally, genetic algorithm, a popular evolutionary approach, is employed to optimize the wire electrical discharge machining process with multiple objectives. The study demonstrates that the WEDM process parameters can be adjusted to achieve better metal removal rate, surface finish and cutting width simultaneously.     

Performance analysis of wire electrochemical turning process��RSM approach

Electrochemical machining (ECM) has become one of the most widely spread techniques of the non-traditional processes. The main problem of ECM is that of choosing the correct working parameters to attain a high degree of accuracy under fine surface finish conditions. Recently, electrochemical turning has gained attention as a finishing process. By feeding a shaped tool into a rotating workpiece, axially symmetric turned parts can be manufactured. In this way, large symmetric workpiece can be made with small tools. This paper discusses the feasibility of using a wire as a tool in electrochemical turning process (WECT). The present study measures the performance criteria of the WECT process through investigating the effect of working parameters, namely, applied voltage, wire feed rate, wire diameter, workpiece rotational speed, and overlap distance, on metal removal rate, surface roughness, and roundness error. The experimental results are statistically analyzed and modeled through response surface methodology. The regression model adequacies are checked using analysis of variance. Furthermore, the optimal combination of these parameters has been evaluated to maximize metal removal rate and minimize surface roughness and roundness error. The study reveals the ability of using a wire as a tool in WECT and its productivity; the shape errors can be controlled through the mentioned input parameters. The results show that the increase of wire feed rate enhances the productivity of the process and improves both surface quality and roundness error. Also, the increase of rotational speed improves both the productivity of the process and geometrical error of the produced parts.     

Determining cutting parameters in wire EDM based on workpiece surface temperature distribution

The material removal process in wire electrical discharge machining (WEDM) may result in work-piece surface damage due to the material thermal properties and the cutting parameters such as varying on-time pulses, open circuit voltage, machine cutting speed, and dielectric fluid pressure. A finite element method (FEM) program was developed to model temperature distribution in the workpiece under the conditions of different cutting parameters. The thermal parameters of low carbon steel (AISI4340) were selected to conduct this simulation. The thickness of the temperature affected layers for different cutting parameters was computed based on a critical temperature value. Through minimizing the thickness of the temperature affected layers and satisfying a certain cutting speed, a set of the cutting process parameters were determined for workpiece manufacture. On the other hand, the experimental investigation of the effects of cutting parameters on the thickness of the AISI4340 workpiece surface layers in WEDM was used to validate the simulation results. This study is helpful for developing advanced control strategies to enhance the complex contouring capabilities and machining rate while avoiding harmful surface damage.     

Research on the influence of dielectric characteristics on the EDM of titanium alloy

This study investigated the influences of dielectric characteristics, namely, electrical conductivity, oxidability, and viscosity on the electrical discharge machining (EDM) of titanium alloy. A new kind of compound dielectric with optimal processing effect was developed based on the identified effects. Comparative experiments on titanium alloy EDM in compound dielectric, distilled water, and kerosene were performed to analyze the difference in material removal rate (MRR), relative electrode wear ratio (REWR), and surface roughness (SR). The experimental results revealed that titanium alloy EDM in compound dielectric achieved the highest MRR, a lower REWR than that in kerosene, and better SR and fewer micro-cracks than that in distilled water.     

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.     

Empirical modeling and optimization of wire electrical discharge machining

Wire electrical discharge machining is a widely used process in manufacturing industries to machine complex profiles. The performance of any machining process is based on choosing the right combination of input parameters. Metal removal rate and surface roughness are the most important output parameters, which decide the performance of a machining process. The selection of optimal parameters in wire electrical discharge machining is difficult as it is a complex process and involves a large number of variables. The present work models the metal removal rate and the surface roughness in terms of the input variables using the response surface methodology and, consequently, the developed mathematical models are utilized for optimization. Since the influences of machining parameters on the metal removal rate and the surface roughness are opposite, the problem is formulated as a multiobjective optimization problem. Non-dominated sorting genetic algorithm is then applied to obtain the Pareto-optimal set of solutions.     

Performance Analysis of Wire Electrodes on Machining Ti-6Al-4V Alloy using Electrical Discharge Machining Process

High-strength materials with complex shapes can be easily machined by electrical discharge machining process. In the present study, an attempt has been made to analyze the influence of wire electrode on Kerf width and workpiece surface roughness in wire EDM process. Due to its importance in the aircrafts and automobiles, Ti-6Al-4V alloy has been chosen as the workpiece material. The various experiments have been conducted based on a Taguchi L₉ orthogonal array with various types of wire electrodes, such as conventional brass wire, zinc-coated wire and diffused coated brass wire. From the experimental results, it has been observed that diffused coated wire produced better surface finish with minimum kerf width compared to the other two wire electrodes. It has also been observed that the pulse off-time has more influent nature on machining characteristics such as surface roughness and kerf width.     

Optimization of electrical discharge machining characteristics of WC/Co composites using non-dominated sorting genetic algorithm (NSGA-II)

Electrical discharge machining (EDM) is a process for shaping hard metals and forming deep and complex shaped holes by arc erosion in all types of electro conductive materials. In the present work, the effectiveness of the EDM process with tungsten carbide and cobalt composites is evaluated in terms of the material removal rate and the surface finish quality of the workpiece produced. The objective of this research is to study the influence of operating parameters of EDM such as pulse current, pulse on time, electrode rotation and flushing pressure on material removal rate and surface roughness. The experimental results are used to develop the statistical models based on second order polynomial equations for the different process characteristics. The non-dominated sorting genetic algorithm (NSGA-II) has been used to optimize the processing conditions. A non-dominated solution set has been obtained and reported.     

Investigation on the effects of ultrasonic vibration on material removal rate and surface roughness in wire electrical discharge turning

An investigation has been made to combine ultrasonic vibration and wire electrical discharge turning. Design of a submerged, precise, flexible, and corrosion-resistant rotary spindle is introduced. The spindle was mounted on a five-axis wire electrical discharge machine to rotate the workpiece in order to generate free-form cylindrical geometries. An auxiliary device that produces ultrasonic vibration was installed between the two wire guides. The ultrasonic system consists of an ultrasonic generator, a transducer, and a wire holder. When the wire is being driven, the transducer together with the wire holder vibrates under the resonance condition. Material removal rate (MRR) indicates efficiency and cost-effectiveness of the process. Experimental results show that wire vibration induced by ultrasonic action has a significant effect on material removal rate. This study has been conducted to evaluate the influence of four design factors: power, pulse off time, spindle rotational speed, and ultrasonic vibration over material removal rate. This has been done by means of design of experiments technique. Analysis of variance was used to determine significant effective factors and also to obtain an equation based on data regression. Experimental results indicate that ultrasonic vibration and power are the most significant influencing parameters on MRR. Rotational speed and pulse off time are the next in ranking. In order to study surface roughness, R _a is measured in different machining parameters.     

激光微涂敷层的电火花后处理及其加工性能

分析、测量了不同加工条件下的材料去除率、相对电极损耗和电火花加工表面粗糙度,并研究了表面微裂纹和微硬度分布。实验结果表明,不同的材料具有类似的电火花加工性能,材料去除率随脉冲电流的增加而增加,峰值电流比脉冲宽度对表面粗糙度的影响更显著。研究结果对于选择合适参数进行电火花后处理具有重要意义。     

An experimental study on micro-EDM in low-resistivity deionized water using short voltage pulses

Deionized water has been used as dielectric fluid for micro-electrical discharge machining (micro-EDM) because it gives higher material removal rate and lower tool wear than hydrocarbon oil. Moreover, it is a relatively low-cost and eco-friendly substance. Therefore, deionized water tends to be more favorable for micro-EDM. However, it causes weak electrochemical reaction during micro-EDM due to its slight conductivity. This leads to the unanticipated additional material removal from the workpiece which affects the machining shape and quality. The study in this paper aims to suppress the electrochemical reaction in die-sinking micro-EDM using deionized water by employing short voltage pulse. Experiments were carried out to fabricate micro-holes using the developed nanosecond pulse circuit. Different pulse parameters were applied to identify the main factor affecting the electrochemical reaction rate. Machining gap was found to be thinner and workpiece surface adjacent to the rim of micro-holes were found to be free of defects caused by material dissolution when pulse duration reached a critical value. Moreover, the influence of pulse parameters on material removal rate and machined shape was also investigated. Besides, energy-dispersive X-ray spectroscopy analysis showed that the machined surface using deionized water was less affected from material migration during micro-EDM process in comparison to hydrocarbon oil.     

ELECTRIC DISCHARGE MILLING AND MECHANICAL GRINDING COMPOUND MACHINING OF SILICON CARBIDE CERAMIC

Silicon carbide (SiC) ceramics have been widely used in modern industry. However, the manufacture of SiC ceramics is not an efficient process. This paper proposes a new technology of machining SiC ceramics with electrical discharge milling and mechanical grinding compound method. The compound process employs the pulse generator used in electrical discharge machining, and uses a water-based emulsion as the machining fluid. It is able to effectively machine a large surface area on SiC ceramics with a good surface quality. In this paper, the effects of pulse duration, pulse interval, peak voltage, peak current and feed rate of the workpiece on the process performance parameters, such as material removal rate, relative electrode wear ratio and surface roughness, have been investigated. A L₂₅ orthogonal array based on Taguchi method is adopted, and the experimental data are statistically evaluated by analysis of variance and stepwise regression. The significant machining parameters, the optimal combination levels of machining parameters, and the mathematical models associated with the process performance are obtained. In addition, the workpiece surface microstructure is examined with a scanning electron microscope and an energy dispersive spectrometer.     

Parametric optimization for surface roughness, kerf and MRR in wire electrical discharge machining (WEDM) using Taguchi design of experiment

This paper reports the effect and optimization of eight control factors on material removal rate (MRR), surface roughness and kerf in wire electrical discharge machining (WEDM) process for tool steel D2. The experimentation is performed under different cutting conditions of wire feed velocity, dielectric pressure, pulse on-time, pulse off-time, open voltage, wire tension and servo voltage by varying the material thickness. Taguchi’s L18 orthogonal array is employed for experimental design. Analysis of variance (ANOVA) and signal-tonoise (S/N) ratio are used as statistical analyses to identify the significant control factors and to achieve optimum levels respectively. Additionally, linear regression and additive models are developed for surface roughness, kerf and material removal rate (MRR). Results of the confirmatory experiments are found to be in good agreement with those predicted. It has been found that pulse on-time is the most significant factor affecting the surface roughness, kerf and material removal rate.     

基于电流概率的半导体线切割往复渐进式模糊控制

在应用电火花线切割技术切割半导体材料时,工具电极与工件之间的放电状态主要有空载、正常放电和短路3种状态。由于半导体电阻率较高,正常放电状态与短路状态的电压电流特性相似,难以区别,现提出基于电流脉冲概率模糊控制策略,解决正常状态和短路状态的无法鉴别问题。利用直线电机的高频响应特性,采用模糊控制算法控制工件“进给-回退-再进给”往复渐进式向前运动,并通过实验证明了此算法可以稳定实现速度的伺服控制,有效地改善表面质量。     

A review on the use of dielectric fluids and their effects in electrical discharge machining characteristics

Electrical discharge machining (EDM) is one of the earliest non-traditional machining processes. EDM process is based on thermoelectric energy between the work piece and an electrode. In electrical discharge machining (EDM), a process utilizing the removal phenomenon of electrical discharge in dielectric, the working fluid plays an important role affecting the material removal rate and the properties of the machined surface. Choosing the right dielectric fluid is critical for successful operations. This paper presents a literature survey on the use of dielectric fluids and also their effects in electrical discharge machining characteristics.