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.     

放电电流对电火花线切割精加工表面粗糙度的影响规律研究

电火花线切割精加工的表面粗糙度是衡量加工性能的重要指标之一。在加工过程中，表面粗糙度会受到放电电流的影响，其中包括放电电流能量、电流脉宽及电流极性的影响。通过在低速走丝电火花线切割机上进行多次加工实验，研究分析了放电电流对线切割精加工表面粗糙度的影响规律。     

型芯零件的电火花线切割加工工艺分析

针对一典型零件外轮廓的加工,对型芯零件加工工艺路线,线切割加工时设备的选用、电极丝的准备、工作液的配制、工件的准备、编制加工程序,进行工艺对比分析和合理选择,从而使零件在电火花线切割机床上加工时能保证零件外轮廓的加工精度。这一经验总结也有助于今后加工类似零件时能达到加工要求。     

线切割断丝保护方法研究与改进

针对高速走丝电火花线切割机床的断丝问题,在总结分析信号反馈式、机械触发式、电流通断式等断丝保护方法的工作原理与优缺点的基础上,提出了一种新颖的双导轮式断丝保护方法,设计了相应的断丝保护装置与控制电路,并采用ANSYS对悬臂梁上的电极丝进行振动仿真分析,确定断丝保护装置的最优安装位置。仿真与实验证明:设计的断丝保护装置能有效降低电极丝的磨损,使其受力均衡,振动减弱,运动更加平稳;设计的控制电路具有断丝误判率低、可靠性高的优点。     

复杂直纹面加工中电极丝中心轨迹的求取算法研究

针对电火花线切割加工复杂直纹面的问题，以直纹面理论为基础，从实际加工要求出发，提出了求取电极丝中心轨迹的“广义电极丝”模型。分析了直导线直纹面电极丝中心轨迹的变化趋势，计算结果表明直接用电极丝中心轨迹两端点的连线近似表示该中心轨迹是欠妥的，为提高代码精度应对求取的电极丝中心轨迹进行同步线性化处理。     

Experimental investigation of effects of cutting parameters on surface roughness in the WEDM process

The experimental study presented in this paper aims to select the most suitable cutting and offset parameter combination for the wire electrical discharge machining process in order to get the desired surface roughness value for the machined workpieces. A series of experiments have been performed on 1040 steel material of thicknesses 30, 60 and 80 mm, and on 2379 and 2738 steel materials of thicknesses 30 and 60 mm. The test specimens have been cut by using different cutting and offset parameter combinations of the “Sodick Mark XI A500 EDW” wire electrical discharge machine in the Middle East Technical University CAD/CAM/Robotics Center. The surface roughness of the testpieces has been measured by using a surface roughness measuring device. The related tables and charts have been prepared for 1040, 2379, 2738 steel materials. The tables and charts can be practically used for WEDM parameter selection for the desired workpiece surface roughness.     

电火花线切割NC代码编译与运动轨迹仿真研究

针对目前电火花线切割数控系统NC代码编译复杂并且几乎不具备扩展性和通用性的问题,提出一种简单、清晰的线切割NC代码编译方案。基于.NET开发平台,采用C#开发语言,通过正则表达式进行词法分析,使用自定义函数进行语法分析。采用该方案能对简单平面图形、锥度切割和上下异形切割进行编译。通过.NET绘图功能显示图形,利用逐点比较插补法,对直线和圆弧进行插补,实现运动轨迹仿真。     

三维接口电火花线切割轨迹的数学放样技术研究

提出了牙嵌式三维接口线切割轨迹的数学放样方法。在AutoCAD软件环境下,建立卡环的几何模型,用三视图和画法几何方法优化线切割平面,用电脑扫描的方法测量线切割平面的位置和角度尺寸。研究表明:对于420 mm卡环,保证完全根切、不留残余根高的线切割平面P1最大偏角是35°,清根距离为3.25 mm;保证上爪强度的最大偏角是24°,清根距离为3.69 mm;线切割平面P1的偏角应在24°~35°之间。数学放样满足了加工要求。     

二次切割法在模具加工中的应用

电火花线切割加工中,影响模具加工精度与表面粗糙度的原因是多方面的。应用二次切割法,既有利于提高切割效率,又能保证加工质量,也可去除模具零件表面交接点突尖。     

数控电火花线切割加工在塑料模加工中的应用

分析了数控电火花线切割加工在塑料模加工中的应用场合,探讨了数控电火花线切割加工在塑料模加工应用中的几种特殊方法.     

大厚度工件电火花线切割加工多次切割腰鼓度成因研究

为研究往复走丝电火花线切割加工在大厚度工件多次切割时形成腰鼓度的成因,对厚度为185 mm的工件进行了多次切割实验,通过改变工作液电导率、电极丝走丝速度、修刀补偿量和电极丝直径等条件,对加工形成的腰鼓度进行了测试及分析。结果表明:大厚度切割过程中,两极之间的脉冲放电爆炸力是产生腰鼓度的主要原因,通过增加电极丝直径以提高电极丝截面惯矩,可减小因放电爆炸力对电极丝形成的挠度,从而减小腰鼓度误差值。     

电火花线切割加工工艺参数优化研究

在对国内外电火花线切割加工的研究现状及发展趋势综述基础上，针对加工工艺参数优化采用理论分析的方法进行研究。分别通过传统的统计分析法和人工神经网络对线切割加工工艺参数进行优化。统计分析法采用正交矩阵法建立了工艺指标与影响因素之间的关系模型．通过约束优化法进行参数优化：采用误差反向传递神经网络的智能方法通过时实验数据的学习来对工艺参数进行优化，结果表明神经网络方法优于传统方法。为进一步实用化奠定了基础。     

线切割加工中材料性能对加工质量的影响

分析和研究了线切割加工中材料性能对加工质量、加工工艺以及加工效果的影响,通过不同加工材料的实验数据对比分析指出了切割加工中合理选取极性效应、放电间隙的重要性,提出了合理制定加工工艺、实施加工方法以及优化加工参数的一些具体措施和解决对策。实践证明完善了切割工艺,提高了加工质量。     

Fundamental geometry analysis of wire electrical discharge machining in corner cutting

Fundamental geometry properties of wire electrical discharge machining (WEDM) process in corner cutting is studied. The concept of discharge-angle is introduced, and its mathematical expression is derived by analytical geometry. A model to estimate the metal removal rate (MRR) in geometrical cutting is developed by considering wire deflection with transformed exponential trajectory of wire centre. The computed MRR is compared with measured sparking frequency of the process since they are equivalent to each other for an iso-energy type machine. A very good agreement is obtained. Both of the discharge-angle and MRR drop drastically to a minimum value depending on the corner angle being cut as the guides arrive at the corner apex, and then recover to the same level of straight-path cutting sluggishly. Hence the observed phenomenon of increased gap-voltage and decreased sparking frequency in corner cutting can be physically interpreted. In addition, the variation of the machining load caused by the change of MRR, which was taken as unknown disturbance in the past, can be predicted and used for control purpose.     

电火花线切割加工参数对加工速度和表面粗糙度影响的研究

讨论了电火花线切割加工中影响加工速度和表面粗糙度的几个主要参数:脉冲宽度、峰值电流、脉冲间隔及工件厚度,并通过正交试验分析了加工参数对加工速度、表面粗糙度的影响关系,为科学、合理地设定电火花线切割加工参数提供了参考。     

A Taguchi and experimental investigation into the optimal processing conditions for the abrasive jet polishing of SKD61 mold steel

This study introduces an abrasive jet polishing (AJP) technique in which the pneumatic air stream carries not only abrasive particles, but also an additive of either pure water or pure water with a specified quantity of machining oil. Taguchi design experiments are performed to identify the optimal AJP parameters when applied to the polishing of electrical discharge machined SKD61 mold steel specimens. A series of experimental trials are then conducted using the optimal AJP parameters to investigate the respective effects of the additive type and the abrasive particle material and diameter in achieving a mirror-like finish of the polished surface. The Taguchi trials indicate that when polishing is performed using pure water as an additive, the optimal processing parameters are as follows: an abrasive material to additive ratio of 1:2, an impact angle of 30°, a gas pressure of 4 kg/cm², a nozzle-to-workpiece height of 10 mm, a platform rotational velocity of 200 rpm, and a platform travel speed of 150 mm/s. Applying these processing parameters, it is found that the optimal polishing effect is attained using #8000SiC abrasive particles and a 1:1 mixture of water-solvent machining oil and pure water. The experimental results show that under these conditions, the average roughness of the electrical discharge machined SKD61 surface is reduced from an original value of R_a=1.03 μm (R_max: 7.74 μm) to a final value of R_a=0.13 μm (R_max: 0.90 μm), corresponding to a surface roughness improvement of approximately 87%.     

补偿量在电火花线切割加工冲裁模中的计算与应用

介绍了数控电火花线切割加工冲裁模时基准模与非基准模补偿量的计算方法,并在此基础上得出一种快速编制非基准模加工程序的途径。     

Three-dimensional characteristics analysis of the wire-tool vibration considering spatial temperature field and electromagnetic field in WEDM

In this paper, a three-dimensional multi-physics coupling model (thermal model, electromagnetic field model and structural model) is proposed for analyzing and controlling the vibration of wire electrode in cutting thin plate process. Firstly, a three-dimensional thermal model is developed to evaluate temperature distribution of wire electrode considering heat convection and heat conduction, and the numerical solutions of wire temperature increment are performed under different process parameters. Secondly, the mechanism of electromagnetic force acting on wire tool is clarified in detail, and a spacial finite element method (FEM) program is designed to analyze the electromagnetic field considering electromagnetic induction. Then, combining thermal model with electromagnetic field model, and conventional structural model, a multi-physics coupling model is established to acquire the frequency and amplitude of wire vibration under random multiple-spark discharges. Furthermore, the simulational results of multi-physics coupling model on wire vibration show a good agreement with experimental data, and the influencing rules of processing parameters on wire vibration are also illustrated to seek the best parameter combination. Eventually, three practical methods are presented to restrain wire vibration performance, and the significant effects on suppressing the wire vibration and improving geometric accuracy have been obtained.     

Numerical study on the evolution of surface defects in wire drawing

In this study, a three-dimensional finite element analysis for multi- or single-pass wire drawing was carried out in order to evaluate the deformation behavior of various surface defects, such as longitudinal, transverse, oblique, and round, introduced during the manufacturing processes. For numerical simulations, a free surface contact treatment algorithm was employed to suppress node penetration by applying a penalty method. Simulation results were compared with the experimental data obtained by optical microscopy for multi-pass drawing samples of the medium carbon steel wire with a longitudinal round-type defect in terms of variation of the load requirement and evolution of the cross-sectional shape of the surface defect. Additional numerical studies were carried out to investigate changes of cross-sectional shapes of various surface defects depending on stress distributions in the single-pass wire drawing. It was found that the radial and circumferential stress components determined the final shape and aspect ratio of the defect. The current numerical approach can be helpful in determining a guideline to assess the acceptability of the surface quality of the drawn wire for the secondary manufacturing process based on the available data in the literature.     

Computational fluid dynamics analysis of working fluid flow and debris movement in wire EDMed kerf

In wire EDM, better exclusion of debris from the machined kerf is very important to obtain a stable machining performance. The purpose of this study is to investigate the fluid flow in the kerf and better jet flushing conditions of working fluid from the nozzles. The flow field and the debris motion in the kerf were analyzed by computational fluid dynamics (CFD) simulation, comparing with the observation by high-speed video camera. The influence of flow rate of working fluid from nozzles and the nozzle stand-off distance on flow field in the kerf and debris particle motion were discussed.