Optimization of the WEDM process of particle-reinforced material with multiple performance characteristics using grey relational analysis

This paper presents an effective approach for the optimization of the wire electric discharge machining (WEDM) process of Al₂O₃ particle-reinforced material (6061 alloy) with multiple performance characteristics based on the grey relational analysis. The machining information for the difficult-cutting particle-reinforced material is inadequate and complicated. The response table and response graph for each level of the machining parameters are obtained form the grey relational grade, and select the optimal levels of machining parameters. In this study, the machining parameters namely the cutting radius of working piece, the on time of discharging, the off time of discharging, the arc on time of discharging, the arc off time of discharging, the servo voltage, the wire feed and water flow are optimized with considerations of multiple performance characteristics, such as the surface removal rate and the maximum surface roughness. It is clearly shown that the above performance characteristics in the WEDM process are great improved together through this approach.     

Grey relational analysis coupled with principal component analysis for optimization design of the cutting parameters in high-speed end milling

This paper investigates optimization design of the cutting parameters for rough cutting processes in high-speed end milling on SKD61 tool steel. The major characteristics indexes for performance selected to evaluate the processes are tool life and metal removal rate, and the corresponding cutting parameters are milling type, spindle speed, feed per tooth, radial depth of cut, and axial depth of cut. In this study, the process is intrinsically with multiple performance indexes so that grey relational analysis that uses grey relational grade as performance index is specially adopted to determine the optimal combination of cutting parameters. Moreover, the principal component analysis is applied to evaluate the weighting values corresponding to various performance characteristics so that their relative importance can be properly and objectively described. The results of confirmation experiments reveal that grey relational analysis coupled with principal component analysis can effectively acquire the optimal combination of cutting parameters. Hence, this confirms that the proposed approach in this study can be an useful tool to improve the cutting performance of rough cutting processes in high-speed end milling process.     

混合铝基复合材料钻削工艺参数的优化(英文)

采用Taguchi方法和灰色关联分析对Al356/SiC-云母混合金属基复合材料的钻削工艺参数进行优化。实验采用L18正交阵列,在计算机的控制立式机床上进行。考察的钻削性能指标包括轴向力、表面粗糙度、刀具磨损和毛刺高度,对影响这些性能的钻削工艺参数进行了优化,包括轴转数、给进速度、钻头类型和云母质量分数。结果表明:给进速度和钻头类型是影响钻削过程的重要因素,通过这种方法可以有效地改进钻削工艺的性能。     

A numerical model of the EDM process considering the effect of multiple discharges

The electrical discharge machining (EDM) process is, by far, the most popular amongst the non-conventional machining processes. The technology is optimum for accurate machining of complex geometries in hard materials, as those required in the tooling industry. However, although a large number of EDM machines are sold every year, scientific knowledge of the process is still limited. The complex nature of the process involves simultaneous interaction of thermal, mechanical, chemical and electrical phenomena, which makes process modelling very difficult. In this paper a new contribution to the simulation and modelling of the EDM process is presented. Temperature fields within the workpiece generated by the superposition of multiple discharges, as it happens during an actual EDM operation, are numerically calculated using a finite difference schema. The characteristics of the discharge for a given operation, namely energy transferred onto the workpiece, diameter of the discharge channel and material removal efficiency can be estimated using inverse identification from the results of the numerical model. The model has been validated through industrial EDM tests, showing that it can efficiently predict material removal rate and surface roughness with errors below 6%.     

Machining characteristics of magnetic force-assisted EDM

The gap conditions of electrical discharge machining (EDM) would significantly affect the stability of machining progress. Thus, the machining performance would be improved by expelling debris from the machining gap fast and easily. In this investigation, magnetic force was added to a conventional EDM machine to form a novel process of magnetic force-assisted EDM. The beneficial effects of this process were evaluated. The main machining parameters such as peak current and pulse duration were chosen to determine the effects on the machining characteristics in terms of material removal rate (MRR), electrode wear rate (EWR), and surface roughness. The surface integrity was also explored by a scanning electron microscope (SEM) to evaluate the effects of the magnetic force-assisted EDM. As the experimental results suggested that the magnetic force-assisted EDM facilitated the process stability. Moreover, a pertinent EDM process with high efficiency and high quality of machined surface could be accomplished to satisfy modern industrial applications.     

Adaptive control for EDM process with a self-tuning regulator

In order to improve the performance of machines, there is a growing need to develop a highly stable servo control system for electrical discharge machining (EDM). With the perpetual push towards the untended EDM operation, an adaptive control system is and will continue to be a primary option. In this paper, a new EDM adaptive control system which directly and automatically regulates tool-down-time has been developed. Based on the real-time-estimated parameters of the EDM process model, by using minimum-variance control strategy, the process controller, a self-tuning regulator, was designed to control the machining process so that the gap states follow the specified gap state. With a properly selected specified gap states, this adaptive system improves the machining rate by, approximately, 100% and in the meantime achieves a more robust and stable machining than the normal machining without adaptive control. This adaptive control system helps to gain the expected goal of an optimal machining performance.     

基于信噪比的微小孔加工工艺参数的分析方法

加工工艺参数准确合理的分析方法是优化组合电火花微细加工中多目标工艺参数的重要前提和保证。文章利用参数设计中的信噪比方法对电火花微小孔加工过程中的工艺参数进行分析研究，得到电火花微小孔加工过程中关键参数单因子工艺指标的优化分析结果，从而达到对电火花微小孔加工工艺参数进行单因子优化设计的目的，为多目标工艺参数综合优化组合提供重要的数据支持。试验结果表明信噪比分析方法能够较好地解决电火花微细加工中的关键工艺参数优化问题，对加工效率和加工精度有一定的改善和提高。     

Machining performance on hybrid process of abrasive jet machining and electrical discharge machining

To develop a hybrid process of abrasive jet machining (AJM) and electrical discharge machining (EDM),the effects of the hybrid process parameters on machining performance were comprehensively investigated to confirm the benefits of this hybrid process.The appropriate abrasives delivered by high speed gas media were incorporated with an EDM in gas system to construct the hybrid process of AJM and EDM,and then the high speed abrasives could impinge on the machined surface to remove the recast layer caused by EDM process to increase the efficiency of material removal and reduce the surface roughness.In this study,the benefits of the hybrid process were determined as the machining performance of hybrid process was compared with that of the EDM in gas system.The main process parameters were varied to explore their effects on material removal rate,surface roughness and surface integrities.The experimental results show that the hybrid process of AJM and EDM can enhance the machining efficiency and improve the surface quality.Consequently,the developed hybrid process can fit the requirements of modern manufacturing applications.     

A plate capacitor model of the EDM process based on the field emission theory

The electrical discharge machining (EDM) process is, by far, the most popular amongst the non-conventional machining processes. The technology is optimum for accurate machining of complicated shapes in hard materials, required in the modern industry. However, although a lot of EDM machines are widely applied for many years, fundamental knowledge of the process is still limited. The complex nature of the process involves simultaneous interaction of thermal, plasma temperature and electromagnetism factors, which makes the machining process modeling very difficult. In this paper, based on the analysis of the electric discharge machining (EDM) process, a plate capacitor model is constructed to describe the discharging process in a pulse time. The whole EDM process is divided into four stages, successively as interelectrode electric-field establishment, electric discharge channel formation, stable EDM and deionization, the interaction of each stage and the distribution function of EDM energy are deduced using the field electron emission theory. For the purpose of analyzing the effect of the single factor, a set of machining through-hole experiments were carried out and investigated. The study shows that critical electric-field intensity and the effective discharging time rate play major roles on the improvement of machining efficiency; the model can explain the differences of machining efficiency using different materials of tool pole and different EDM parameters; and the theoretical results are concordant with the experimental data well.     

High Aspect Ratio and Complex Shaped Blind Micro Holes by Micro EDM

It is difficult to drill high aspect ratio through holes and complex shaped blind holes using micro EDM. The debris concentration in the narrow discharge gap causes abnormal discharges leading to excessive electrode wear and lower machining precision. In micro EDM, the electrode size is too small for internal flushing. This paper presents a new approach for effective self-flushing using planetary movement. Through micro holes with an aspect ratio of 18 have been drilled. This approach is also demonstrated by drilling blind noncircular micro holes with sharp corners and edges. The process performance characteristics are analyzed under different machining conditions.     

Optimization of Abrasive Powder Mixed EDM of Aluminum Matrix Composites with Multiple Responses Using Gray Relational Analysis

Abrasive powder-mixed electrical discharge machining (APM-EDM), a hybrid manufacturing process involving the use of a dielectric fluid mixed with abrasive powder, combines the benefits of mechanical and thermal interactions. The aim of this article is to use a new approach of performance evaluation, gray relational analysis (GRA), to evaluate the effectiveness of optimizing multiple performance characteristics of APM-EDM of 6061Al/Al₂O_3p/20p aluminum matrix composites (AMCs). The considered process parameter includes the seven control factors namely pulse current (A), pulse ON time (μs), duty cycle (%), gap voltage (V), time interval of tool lift (s), abrasive powder concentration (g/L), abrasive particle size (μm), and a noise factor, aspect ratio (shape of tool electrode). The combination of L18 (2¹ × 3⁷) orthogonal array design of experiment with GRA enables to determine the optimal parameters for multiple responses. GRA is used to obtain a single performance index, gray relational grade through gray relational coefficient to optimize the APM-EDM process with lower tool wear rate, surface roughness, and higher material removal rate. In addition, analysis of variance (ANOVA) for the GRC is also utilized.     

Improvement of Dry EDM Characteristics Using Piezoelectric Actuator

This paper describes improvement of the machining characteristics of dry electrical discharge machining (dry EDM) by controlling the discharge gap distance using a piezoelectric actuator. Dry EDM is a new process characterized by small tool electrode wear, negligible damage generated on the machined surface, and significantly high material removal rate especially when oxygen gas is used. However, the narrow discharge gap length compared with conventional EDM using oil as the dielectric working fluid results in frequent occurrence of short circuiting which lowers material removal rate. A piezoelectric actuator with high frequency response was thus introduced to help control gap length of the EDM machine. To elucidate the effects of the piezoelectric actuator, an EDM performance simulator was newly developed to evaluate the machining stability and material removal rate of dry EDM.     

Optimization of electrical discharge machining process parameters for Al6061/cenosphere composite using grey-based hybrid approach

Fly ash has congregated considerable attention as a potential reinforcement for aluminum matrix composites (AMCs) to enhance selective properties and reduce the cost of fabrication. However, poor machinability of such AMCs limits their application. The present study focuses on the preparation of cenosphere fly ash reinforced Al6061 alloys by compo casting method. X-ray diffraction analysis of the prepared AMCs exposes the presence of cenosphere particles without any formation of other intermetallic compounds. In this study, electrical discharge machining (EDM) was engaged to examine the machinability of the prepared metal matrix composite (MMCs). The measured performance characteristics for the various combinations of input process parameters were considered to be MRR, EWR and SR. Face centered central composite design (CCD) of response surface method (RSM) was employed to design the number of experimental trials required and a hybrid approach of grey-based response surface methodology (GRSM) was imposed for predicting the optimal combination of processing parameter in EDM process. Generous improvement was observed in the performance characteristics obtained by employing both the optimal setting of machining parameters. The optical 3D surface profile graphs of the ED machined surface also revealed the improvement in surface quality and texture employing the optimal processing conditions proposed by hybrid GRSM approach.     

Surface integrity and material removal mechanisms associated with the EDM of Al2O3 ceramic composite

Electric discharge machining (EDM) has been proven as an alternate process for machining complex and intricate shapes from the conductive ceramic composites. The performance and reliability of electrical discharge machined ceramic composite components are influenced by strength degradation due to EDM-induced damage. The success of electric discharge machined components in real applications relies on the understanding of material removal mechanisms and the relationship between the EDM parameters and formation of surface and subsurface damages. This paper presents a detailed investigation of machining characteristics, surface integrity and material removal mechanisms of advanced ceramic composite Al₂O₃–SiC_w–TiC with EDM. The surface and subsurface damages have also been assessed and characterized using scanning electron microscopy (SEM). The results provide valuable insight into the dependence of damage and the mechanisms of material removal on EDM conditions.     

A fuzzy pulse discriminating system for electrical discharge machining

In this paper, the use of fuzzy set theory to construct a new pulse discriminator in electrical discharge machining (EDM) is reported. The classification of various discharge pulses in EDM is based on the features of the measured gap voltage and gap current. To obtain optimal classification performance, a machine learning method based on a simulated annealing algorithm is adopted to automatically synthesize the membership functions of the fuzzy pulse discriminator. Experimental results have shown that EDM discharge pulses can be not only correctly but also quickly classified under varying cutting conditions using this approach.     

Electrical discharge machining of Ti6Al4V with a bundled electrode

The aim of this study is to investigate an efficient Ti6Al4V electrical discharge machining (EDM) process with a bundled die-sinking electrode. The feasibility of machining Ti6Al4V with a bundled electrode was studied and its effect on EDM performance was compared experimentally using a solid die-sinking electrode. The simulation results explain the high performance of the EDM process with a bundled electrode by through the use of multi-hole inner flushing to efficiently remove molten material from the inter-electrode gap and through the improved ability to apply a higher peak current. A 3-factor, 3-level experimental design was used to study the relationships between 2 machining performance parameters (material removal rate: MRR, tool wear ratio: TWR) and 3 machining parameters (fluid flow rate, peak current and pulse duration). The main effects and influences of the 2-factor interactions of these parameters on the performances of the EDM process with the bundled electrode are discussed.     

电火花加工控制技术综述

介绍了电火花加工原理及其加工过程中涉及的主要控制问题,论述了近20年来应用于电火花加工过程中的控制技术,即自适应控制、专家控制、遗传算法、模糊控制、神经网络控制、灰色控制及其相应的混合智能控制.     

A study on the effect of different vibration-assisted methods in micro-WEDM

In micro electrical discharge machining (μEDM), since the discharge energy is very low and is usually performed by a resistor-capacitor (RC) generator the discharge process is highly complex and unpredictable. In addition, due to low discharge energy the discharge is unstable and the machining efficiency is reduced as a result of poor flushing condition in a very small gap. This greatly affects the productivity and limits micro EDM applications. This paper presents development methods to improve the machining efficiency of a widely accepted non-traditional machining process, micro wire electrical discharge machining (WEDM), using non-ultrasonic vibration. It is found that when vibration is applied to the micro-WEDM process, discharge is much more effective with fewer short circuits. From experiment results, it is observed that greater improvement can be achieved when the vibration is applied to the workpiece rather than to the wire. With vibration applied to the workpiece, machining efficiency can be increased by 2.5 times greater than without vibration and 1.5 times compared to the case vibration is applied to the wire. In addition, there exists an optimum relation between vibration parameters, energy and feedrate such that EDM at a constant feedrate can further improve the machining efficiency.     

电火花加工放电介质的研究

通过对电火花加工放电通道中等离子体柱的形状和放电通道的电流、电磁特性进行分析,并对电火花加工中不同介质的加工性能进行对比和总结,提出电火花加工介质的技术研究方向应符合绿色制造和资源的可持续发展的理念。     

State of the art electrical discharge machining (EDM)

Electrical discharge machining (EDM) is a well-established machining option for manufacturing geometrically complex or hard material parts that are extremely difficult-to-machine by conventional machining processes. The non-contact machining technique has been continuously evolving from a mere tool and die making process to a micro-scale application machining alternative attracting a significant amount of research interests.In recent years, EDM researchers have explored a number of ways to improve the sparking efficiency including some unique experimental concepts that depart from the EDM traditional sparking phenomenon. Despite a range of different approaches, this new research shares the same objectives of achieving more efficient metal removal coupled with a reduction in tool wear and improved surface quality.This paper reviews the research work carried out from the inception to the development of die-sinking EDM within the past decade. It reports on the EDM research relating to improving performance measures, optimising the process variables, monitoring and control the sparking process, simplifying the electrode design and manufacture. A range of EDM applications are highlighted together with the development of hybrid machining processes. The final part of the paper discusses these developments and outlines the trends for future EDM research.