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.     

超大孔径聚晶金刚石拉丝模具单向走丝电火花线切割加工工艺研究

基于试验研究,创新性地提出了采用单向走丝电火花线切割机床对超大孔径聚晶金刚石拉丝模具的孔形进行粗加工。以金刚石粒度为25μm的直径22 mm、厚度20 mm的超大孔径聚晶金刚石拉丝模具为例,进行单向走丝电火花线切割加工定径区、压缩区和安全角的工艺研究,得出了加工工艺曲线,确定了最优加工工艺参数,提高了粗加工效率,确保了良好的孔形精度。结果表明:选择脉冲宽度4μs、脉冲间隔40μs、峰值电流15 A、走丝速度10 m/min时,可获得较满意的加工效果。     

Material Removal Rate,Kerf, and Surface Roughness of Tungsten Carbide Machined with Wire Electrical Discharge Machining

In this article, the effects of varying seven different machining parameters in addition to varying the material thickness on the machining responses such as material removal rate, kerf, and surface roughness of tungsten carbide samples machined by wire electrical discharge machining (WEDM) were investigated. The design of experiments was based on a Taguchi orthogonal design with 8 control factors with three levels each, requiring a set of 27 experiments that were repeated three times. ANOVA was carried out after obtaining the responses to determine the significant factors. The work piece thickness was expected to have a major effect on the material removal rate but showed to be significant in the case of surface roughness only. Finally, optimization of the machining responses was carried out and models for the material removal rate, kerf, and surface roughness were created. The models were validated through confirmation experiments that showed significant improvements in machining performance for all investigated machining outcomes.     

因瓦合金纳米抛光材料去除机理的分子动力学模拟∗

因瓦合金作为一种独特的低膨胀材料已广泛用于航空航天等高科技领域,但目前还鲜有对其超精密加工理论和技术的研究,而纳米抛光是因瓦合金超精密加工的一种重要手段。 针对纳米抛光过程中因瓦合金的材料去除机理,基于分子动力学模拟研究抛光速度对材料去除效率、亚表面损伤和抛光表面平整度的影响。 通过对磨屑、能量、抛光力、位错运动等方面的分析揭示因瓦合金的变形损伤机制。 研究结果表明:材料去除效率随着抛光速度将达到一个临界值,当抛光速度低于 100 m/ s 时,磨削热促使位错形核,亚表面损伤厚度增加;当抛光速度高于 100 m/ s 时,应变速率急剧增大导致位错运动受限,使得亚表面损伤厚度得以降低。 为实现因瓦合金高效率和低损伤加工机制提供理论依据和技术支持。     

State of the art in wire electrical discharge machining (WEDM)

Wire electrical discharge machining (WEDM) is a specialised thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining processes. This practical technology of the WEDM process is based on the conventional EDM sparking phenomenon utilising the widely accepted non-contact technique of material removal. Since the introduction of the process, WEDM has evolved from a simple means of making tools and dies to the best alternative of producing micro-scale parts with the highest degree of dimensional accuracy and surface finish quality.Over the years, the WEDM process has remained as a competitive and economical machining option fulfilling the demanding machining requirements imposed by the short product development cycles and the growing cost pressures. However, the risk of wire breakage and bending has undermined the full potential of the process drastically reducing the efficiency and accuracy of the WEDM operation. A significant amount of research has explored the different methodologies of achieving the ultimate WEDM goals of optimising the numerous process parameters analytically with the total elimination of the wire breakages thereby also improving the overall machining reliability.This paper reviews the vast array of research work carried out from the spin-off from the EDM process to the development of the WEDM. It reports on the WEDM research involving the optimisation of the process parameters surveying the influence of the various factors affecting the machining performance and productivity. The paper also highlights the adaptive monitoring and control of the process investigating the feasibility of the different control strategies of obtaining the optimal machining conditions. A wide range of WEDM industrial applications are reported together with the development of the hybrid machining processes. The final part of the paper discusses these developments and outlines the possible trends for future WEDM research.     

Fabrication of micro-electrodes by multi-EDM grinding process

In this study, a multi-EDM grinding process is adapted to fabricate micro-electrodes. Equipments such as a wire EDM machine and a traditional CNC-EDM machine are used for machining micro-electrodes. Rod electrodes of copper with diameter 3.0 mm were cut to be 0.15 mm on wire-EDM machine at first step. EDM grinding process was used to grind micro-electrodes to fine diameter bellow 20 μm on a CNC-EDM machine at second step. For EDM grinding, rotating mechanisms are mounted on both the WEDM machine and the CNC-EDM machine. A CCD camera is provided for viewing and for on-line dimensional controlling, when micro-electrodes were cutting. Fine electrodes could be processed to a smaller size using proposed two-steps EDM grinding process. Higher L/D ratio could be also achieved by this method. The processed fine electrodes can be used for drilling micro-holes, micro-deep holes, micro-milling, micro-punching, and manufacturing of micro-nozzles.     

Thermo-mechanical analysis and optimal tension control of micro wire electrode

The tension control of the micro wire electrode is a key technology for the micro wire electro-discharge machining (WEDM). Based on the coupled thermo-mechanical analysis, both the three-dimensional temperature and the stress distribution in the micro wire are determined. As a result, the tension of the micro wire electrode during the WEDM process can be optimized in accordance with the discharge energy, which is sampled and fed back to the tension control system in real time. Then the development of an optimal tension control system characterized by the form of master–slaver structure makes it possible to keep the wire tension optimal in the process of WEDM. The results of the machining experiments show that the optimal wire tension control is effective on the improvement of the machining accuracy with the prevention of wire breakage for the micro WEDM.     

Study of specific discharge energy in WEDM and its application

The relationship between machining parameters and machining characteristics of different materials in WEDM is difficult to obtain because a large number of experiments must be conducted repeatedly. A new concept attempting to solve this problem is presented in this paper. The specific discharge energy (SDE) defining as the real energy required to remove a unit volume of material is proposed. The SDE is constant for a specific material. Experimental results reveal that the relative relationship of SDE between different materials is invariant as long as all materials are machined under the same machining conditions. It is also found that the materials having close value of SDE demonstrate very similar machining characteristics such as machining speed, discharge frequency, groove width and surface finish of the machined surface under the same machining conditions. This result can be applied for the determination of the settings of machining parameters of different materials. Furthermore, by dimensional analysis of SDE, a quantitative relationship between machining characteristics such as the material removal rate and the efficiency of material removal and machining parameters is derived.     

High efficiency slicing of low resistance silicon ingot by wire electrolytic-spark hybrid machining

As the semiconductor industry requires the cutting of silicon ingots into wafers, the slicing of large, ultra thin wafers is one of the main technologies to prevent wastage. Recently, apart from conventional inner diameter (ID) blade and multi-wire saw methods, wire electrical discharge machining (WEDM), which has no cutting force, has been introduced to this area and low resistance silicon may be sliced by WEDM. In this paper, a novel approach, based on wire electrolytic-spark slicing strategy using hybrid oil/aqueous electrolyte, combining electric discharge and anodic etching into a single process, is investigated experimentally. Some improvements, such as a new wire winding system, hybrid electrolyte and high efficiency pulse generator, have been adopted in a kind of high speed (HS)-WEDM machine. Experiments have been conducted to evaluate the machining rate, surface quality and wafer thickness of low resistance (0.5–3 Ω cm) mono-crystalline silicon. It has been demonstrated that with properly selected electrical parameters and electrolyte, a maximum machining rate of 600 mm²/min can be obtained and with a wafer thickness less than 120 μm. Furthermore, in comparison with WEDM, heat affected zone and harmful metal residues are considerably diminished, which provides significant theoretical and experimental support for future applications.     

TiNi形状记忆合金的电火花加工性能

TiNi形状记忆合金由于具有优异的超弹性和形状记忆效应等性能而被大量地应用于工业生产中。然而,形状记忆合金的传统加工相当复杂。因此,研究TiNi形状记忆合金的电火花线切割加工（WEDM）性能。采用L27正交阵列以尽量减少实验。在不同的脉冲持续时间、脉冲关断时间、伺服电压、冲洗压力和线速度条件下进行实验。为同步优化提出一种利用Taguchi设计与实用理念的多响应优化方法。通过对信噪比（S/N）的均值分析和方差分析,确定最佳参数水平。Taguchi分析表明：1μs脉冲持续时间、3.8μs脉冲关断时间、40 V伺服电压、1.8×105Pa冲洗压强和8 m/min线速度,有利于同时使材料去除率最大化和表面粗糙度最小化。TiNi形状记忆合金电火花线切割加工的优化结果表明：脉冲持续时间显著影响材料去除率和表面粗糙度。在较长的脉冲持续时间时,在加工表面可观察到放电坑、微裂纹和重铸层。