空气中微细电火花沉积与去除可逆加工技术研究

论述了一种新的电火花加工方法。它使用通用的电火花成形加工机床,利用常见的电极材料,在空气介质中,通过脉冲放电在工件表面上沉积生长电极材料,再通过反转极性和适当的轨迹控制对所生成的沉积材料进行有选择的去除加工,进而实现材料的生长与去除可逆加工。通过对电火花加工理论的研究,预测和论证了实现这一新加工方法的可能性和实现条件。通过试验成功地将钢、铜和钨三种电极材料沉积到工件上,形成直径为 100~240 mm、高度为1 000~2 500 mm的微小圆柱体。并对沉积物进行了选择去除,实现了在同一设备上的可逆电火花加工。对沉积材料的致密性、硬度及其与工件的结合强度等进行了系统的分析,表明沉积物组织致密、坚硬,可以满足功能材料的要求。     

Process modeling of hybrid machining system consisted of electro discharge machining and end milling

This paper presents a novel hybrid machining process (HMP) that combines cutting action with machining using discharge pulses. Working conditions for a machine tool capable of combining micro-electro discharge machining (EDM) with milling is still an ill-defined problem relying on heuristics because there is insufficient knowledge of the discharge mechanism and the effects of machining parameters. The proposed HMP that combines micro-EDM and milling processes was applied to a steel alloy (AISI 1045) as the workpiece and end mill tungsten carbide as the tool electrode. Test results obtained from a number of experiments showed that the developed HMP yields reasonable machining time and surface roughness. Significant controlling variables for the machining response were identified and ranked using the Taguchi method. Furthermore, the response surface method was used to develop an empirical model based on the correlation between input variables and output responses.     

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.     

Tool fabrication system for micro/nano milling—function analysis and design of a six-axis Wire EDM machine

The dies or molds used for the fabrication of micro products usually are made of ultra-hard materials such as tungsten carbide or silicon carbide and have sophisticated three-dimensional geometries. Such kind of dies or molds can only be fabricated by milling operations instead of grinding processes with ultra-hard milling tools made of PCD or CBN. Electrical discharge machining (EDM) is a good choice for the fabrication of such ultra-hard tools. In this paper, a function analysis and design of a six-axis Wire EDM (WEDM) machine is introduced. Based on the typical micro/nano cutting tool geometry features, a mathematical model between the cutting tool and the electrode wire is built. Then, the mathematical model is analyzed and it turns out that six axes are needed for cutting such complicated tool geometries. According to the WEDM features, first the axes are allocated to the workpiece side and the electrode wire side. The workpiece is assigned three linear motions and one rotary motion around its center line and the wire has two rotary motions. Second, the axis sequences are defined. At last, the best concept of the mechanical structure for the six-axis WEDM machine is selected.     

Accretion of titanium carbide by electrical discharge machining with powder suspended in working fluid

A surface modification method by electrical discharge machining (EDM) with a green compact electrode has been studied to make thick TiC or WC layer. Titanium alloy powder or tungsten powder is supplied from the green compact electrode and adheres on a workpiece by the heat caused by discharge. To avoid the production process of the green compact electrode, a surface modification method by EDM with powder suspended in working fluid is proposed in this paper. After considering flow of working fluid in EDM process, the use of a thin electrode and a rotating disk electrode are expected to keep powder concentration high in the gap between a workpiece and an electrode and to accrete powder material on the workpiece. The accretion machining is tried under various electrical conditions. Titanium powder is suspended in working oil like kerosene. TiC layer grows a thickness of 150 μm with a hardness of 1600 Hv on carbon steel with an electrode of 1 mm in diameter. When a disk placed near a plate rotates in viscous fluid, the disk drags the fluid into the gap between the disk and the plate. Therefore, the powder concentration in the gap between a workpiece and a rotational disk electrode can be kept high. A wider area of the accretion can be obtained by using the rotational electrode with a gear shape.     

Analysis of the machining characteristics of EDM as functions of the mobilities of electrons and ions

Electrical discharge machining (EDM) is a process that can be used effectively to machine conductive metals regardless of their hardness. In the EDM process, material removal occurs because of the thermal energy of the plasma channel between the electrode and the workpiece. During EDM, the electrode as well as the workpiece is abraded by the thermal energy. Tool wear adversely affects the machining accuracy and increases tooling costs. Many previous studies have focused on mitigating the problems of tool wear by investigating various EDM parameters. In this study, the tool wear problem was investigated on the basis of the mobilities of electrons and ions in the plasma channel. The material removal volumes of both the electrode and the workpiece were compared as functions of the gap voltage. The material removal difference according to the capacitance was also investigated. The tool wear ratio was calculated under different EDM condition and an EDM conditions for reducing the tool wear ratio was suggested.     

MICRO ELECTRICAL DISCHARGE MACHINING DEPOSITION IN AIR

A new deposition method is described using micro electrical discharge machining (EDM) to deposit tool electrode material on workpiece in air. The basic principles of micro electrical discharge deposition (EDD) are analyzed and the realized conditions are predicted. With an ordinary EDM shaping machine, brass as the electrode, high-speed steel as the workpiece, a lot of experiments are carried out on micro EDD systematically and thoroughly. The effects of major processing parameters, such as the discharge current, discharge duration, pulse interval and working medium, are obtained. As a result, a micro cylinder with 0.19 mm in diameter and 7.35 mm in height is deposited. By exchanging the polarities of the electrode and workpiece the micro cylinder can be removed selectively. So the reversible machining of deposition and removal is achieved, which breaks through the constraint of traditional EDM. Measurements show that the deposited material is compact and close to workpiece base, whose components depend on the tool electrode material.     

混粉电火花加工中极性效应的研究

为研究极性效应对混粉电火花加工的影响规律．采用钢对钢加工、铜对钢加工两种电极组合在添加硅粉的煤油工作液及普通煤油工作液中进行实验，并更换不同的极性，考察了两极材料的去除率和表面粗糙度，结果表明负极总能得到更高的材料去除率，而正极总能得到更低的表面粗糙度值。此现象可从两极表面能量密度差异的角度予以解释。     

Micro-hole Maching of Copper Using the Electro-discharge Machining Process with a Tungsten Carbide Electrode Compared with a Copper Electrode

This paper describes micro-hole machining of a copper plate using the electro-discharge machining (EDM) process. Tungsten carbide was selected as the material for the electrode and compared with a copper-electrode. A precision centreless grinding process was employed to grind the electrode down to the desired diameter. A series of experiments were performed on a traditional EDM machine to investigate the effects of electrode material polarity setting and of a rotating electrode. Results have shown that electrode wear and hole enlargement are both smaller when positive polarity machining is selected; whereas electrode wear is larger and machining speed is higher when negative polarity machining is selected. High-quality micro-hole machining in copper can be achieved by the proposed method.     

Analysis of energy distribution during electric discharge machining of tungsten carbide

Abstract

During electrical discharge machining (EDM) process, electrical energy is used for the machining of the components. Energy distribution in electrical discharge machining process is the distribution of input energy supplied during machining to various components. In order to improve the technological performance during EDM process, it is essential to understand the distribution of input energy in the entire system. An experimental study on the effect of EDM energy distribution parameter for tungsten carbide is presented. The copper tungsten electrode has been used for the study. Experiments have been performed in specially designed dielectric insulated tank. To minimise the energy wastage, workpiece as well as the electrode was covered with Teflon. Current and pulse duration have been selected as variable parameters. The objective of this study is to analyse the amount of electrical energy used for machining effectively. The detail of this study has been presented in this paper.     

Improvement in machining speed with working gap control in EDM milling

High-speed electrical discharge machining (EDM) milling is investigated with working gap control. EDM milling has a merit that does not need complex electrode fabrication; however, it is necessary to improve the removal rate in EDM milling. Rotation of the electrode improves the removal rate, but this rotation causes a periodic change in the working voltage. As a consequence, the periodic change causes a disturbance that decreases the control performance. EDM milling realizes a high machining precision by the scanning method. A small working area allows for fast scanning. If the working gap is appropriate, it becomes longer because the machined surface of the workpiece is removed. Therefore, the conventional controller remains at the steady offset and lowers the machining efficiency. The proposed controller introduces a notch filter, which eliminates the frequency component due to rotation of the electrode. It also has a feed-forward compensator to eliminate the steady offset. The controller for each machining condition is derived from a coordinate transformation and the least-squares approximation. It is confirmed that the proposed controller achieves machining speeds that are 2–6 times faster in a straight line and greater than 30% higher in the profile machining than in the conventional one.     

大深径比微小孔快速电火花加工系统研究

电火花加工因具有宏观作用力小、可控性好等优点,被广泛应用于微小孔加工领域,但对于快速加工大深径比微小孔仍存在散热困难、排屑不畅、电极损耗大及加工过程不易控制等技术难点。为此,在分析电火花加工机理及加工特点的基础上,研发了一台用于快速加工大深径比微小孔的电火花机床。该设备通过采用立式布局,应用电极旋转、工件振动的旋振式机构,实现在加工过程中快速散热和排屑;通过采取工业控制计算机搭载数据采集卡和运动控制器的方式,实现了加工过程的检测控制功能一体化。针对电火花加工过程中放电信号严重畸变以及放电状态不稳定导致加工状态难检测的问题,提出了两级模糊逐级映射放电状态检测方法,同时为了实现机床的快速响应和精确控制,设计了双闭环加工控制系统。实验表明,该机床适合于大深径比微小孔的快速加工,且性能稳定,可靠性高。     

Analysis of rotary electrical discharge machining characteristics in reversal magnetic field for copper-en8 steel system

The material removal rate (MRR), along with the electrode wear rate (EWR), plays an important role in analysing machine output during electrical discharge machining. This work focuses on the improvement of machine output by introducing an induced magnetic field on the workpiece during rotary electrical discharge machining (REDM) of EN-8 steel with a rotary copper electrode. The workpiece was placed inside the induced magnetic field, wherein polarity of the magnetic field gets reversed periodically. Using Taguchi’s recommended design of experiments, we initially conducted experiments with eight input parameters at different levels . Significant parameters were identified with the help of the signal-to-noise ratio and ANOVA. Finally, another set of experiments was conducted for analysis of the process and development of empirical expressions for MRR and EWR. Experimental results established that rotary electrical discharge machining with a polarity reversal magnetic field delivers better machining output than machining in a non-magnetic field. Thus, this work benefits the EDM process by reducing the machining costs and by producing better geometrical trueness on workpieces, as MRR increased and EWR decreased.     

Effect of ultrasonic-assisted EDM on the surface integrity of cemented tungsten carbide (WC-Co)

This paper studies the effects of tool electrode ultrasonic vibration on some surface integrity properties of cemented tungsten carbide (WC-10%Co) in the electrical discharge machining (EDM) process. Surface integrity concerns surface alterations associated with a manufacturing process, including surface topography, surface metallurgy, and changes of the mechanical and physical properties of the material as well as residual stresses. Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) capabilities, optical microscopy, micro-hardness testing and white light interferometric microscopywere employed to study the surface integrity. This paper studies the topography of the machined surface, the size and amount of cracks on the surface layer, hardness variation in the depth and the composition of the defective layer, when machining with and without ultrasonic vibration of the copper electrode under different machining conditions. SEM, micro-hardness testing results together with surface topography investigation showed ultrasonic-assisted EDM applicability in improving surface integrity.     

Experimental Investigation on Electrical Discharge Drilling of Ti-6Al-4V Alloy

This article describes the experimental investigation related to creation of holes in aerospace titanium alloy workpiece using static electrode machining and electrical discharge drilling (EDD) process. Special attachment for holding and rotating the tool electrode was developed and installed on electrical discharge machining (EDM) machine by replacing the original conventional tool holder provided on die sinking EDM. The effect of input parameters such as gap current, pulse on-time, duty factor and RPM of tool electrode on output parameters for average hole circularity (C_a) and average surface roughness (R_a) have been studied. It is observed that the effect of rotating electrode machining has considerable influence on the output parameters over stationary electrode machining. The micro-graphs and photographs of few selected samples were taken by SEM and metallurgical microscope, which also commensurate with the findings of the study.     

Electrical discharge grinding of polycrystalline diamond – Effect of wheel rotation

Electrical Discharge Grinding (EDG) is an advanced machining process that becomes popular in manufacturing of Polycrystalline Diamond (PCD) tools. This research investigated the effects of wheel rotation as well as debris flow direction on the quality of PCD tools based on a series of EDG experiments. Experimental results showed the debris that flowed toward the cutting edge could significantly affect the edge sharpness and symmetry of the tool, which were critical for the smaller edge apex angle. Evidence of spark concentration caused by the debris accumulation phenomenon were found through microscopic analysis on the eroded surfaces. This research also revealed the unexplained phenomenon associated with the undercut that normally formed beneath the PCD cutting edge after erosion. By examining PCD samples using scanning electron microscopy (SEM) and Raman spectroscopy, the formation of the heat-affected layer caused by the high-temperature erosion process in the EDG was analyzed. Results also proved that the surface finish of tungsten carbide (WC) and notch width of the PCD tools, particularly on the tungsten carbide WC/PCD interface, should not be taken as the index to measure PCD tool quality.     

电火花摆碾加工的原理及装置设计

用传统电火花加工硬质合金刀片时,需要事先制作成形电极,加工成本高且加工质量较差,因此提出一种新的加工方法—电火花摆碾加工。电火花摆碾加工通过控制普通电极的旋转和摆动来加工出特定形状的锥形孔,具有加工效率高、加工质量好、节省成形电极制作时间和成本等优点。为进行初步试验,在现有加工设备基础上设计了一套电火花摆碾加工装置,包括电极自转摆角装置、工件回转装置以及控制系统三个部分。设计的夹具可实现三角刀片的自动定心及快速装夹。     

Characteristic investigation of pipe cutting technology based on electro-discharge machining

Pipe cutting technology plays an important role in the process of offshore platforms decommissioning, as many devices such as tubing, drill pipe, and casing need to be decommissioned. In this study, a novel cutting pipe technology based on electro-discharge machining (EDM) is proposed, and a cutting pipe mechanism is developed to cut the pipes for decommissioning offshore platforms. The machining principles and characteristics of the technique are described. The effects of machining parameters, including tool polarity, dielectric fluid, electrode material and width, pulse on-time, pulse off-time, peak voltage, and electrode rotation speed to machining performance, are investigated. The material removal rate (MRR) of the machined casing and tool electrode wear ratio (EWR) is obtained based on the calculation of the percentage of mass loss per machining time. The experimental results show that a better cutting performance can be obtained with negative tool polarity at the conditions of dielectric fluid of emulsion, pulse on-time of 500 μs, pulse off-time of 200 μs, peak voltage of 70 V, copper electrode width of 28 mm, and electrode rotation speed of 250 rpm is a better choice. Additionally, the cutting slots surface has been investigated by the means of SEM. The cutting slots machined by the rotary EDM are clean and smooth.     

Investigation of emulsion for die sinking EDM

Machining fluid is a primary factor that affects the material removal rate, surface quality, and electrode wear of electrical discharge machining (EDM). Kerosene is the most commonly used working fluid in die sinking EDM, but it shows low ignition temperature and high volatility; if the improper operations are undertaken, it can cause conflagration. Using distilled water or pure water as the machining fluid in EDM, no fire hazard occurs, and the working environment is well; however, using distilled water or pure water as the machining fluid in EDM, the material removal rate of machining large surface is low, and the machine tool is easily eroded. Emulsion-1 and emulsion-2 used as working fluid in die sinking EDM are developed. The compositions of emulsion-1 and emulsion-2 are introduced. In comparison with kerosene, emulsion-1 and emulsion-2 used in EDM show high material removal rate, low surface roughness, high discharge gap, and good working environment. The electrode wear ratio in emulsion-1 is lower than that in kerosene. The electrode wear ratio in emulsion-2 is higher than that in kerosene. The effects of composition and concentration of emulsifier on the emulsion property and EDM performance have been investigated. The comparative tests of EDM performance with kerosene, emulsion-1, and emulsion-2 have been done.     

Performance assessment of microwave treated WC insert while turning AISI 1040 steel

This study attributed to post treatment of tungsten carbide (WC) inserts using microwave irradiation. Tungsten carbide inserts were subjected to microwave radiation (2.45 GHz) to enhance its performance in terms of reduction in tool wear rate, cutting force surface roughness and improvement in tool life. Performance of tungsten carbide insert is very much affected by machine operating parameters i.e. speed, feed and depth of cut. An attempt has been made to investigate the effects of machining parameters on microwave treated tool inserts. This paper describes the comparative study of machining performance of untreated and microwave treated WC tool inserts used for turning of AISI 1040 steel. Machining performance has been evaluated in terms of flank wear, cutting force, surface roughness, tool wear mechanisms. Critical examinations of tool wear mechanisms and improvements in metallurgical properties such as microstructural change, phase activation of WC grains were identified using scanning electron microscope (SEM). Results obtained from the turning using the microwave treated tool inserts showed a significant reduction tool wear thereby enhancing the surface quality of workpiece.