High rising speed discharge current pulse for EDM generated by inductive boosting voltage circuit

This paper introduces a newly developed EDM pulse generator whose high open voltage for discharge is generated by induced electromotive force using a power supply of only 5 V. The pulse generator can generate short duration and high discharge current pulses. The rising time of discharge current pulses to 5 A can be made shorter than 50 ns with a pulse duration of 200 ns or shorter. The results proved that such discharge current pulse shapes increase material removal volume per discharge and that the higher boosting open voltage facilitates the machining of high resistivity materials.     

Integrated model for assessment of electromagnetic force field due to arc welding

Abstract

Computation of the electromagnetic force over a wide range of consumable arc welding parameters is difficult with available models because of the need for experimentally evaluated electrode extension for every individual set of parameters. This becomes more complicated in case of submerged are welding, because the welding arc remains buried beneath flux. This study presents a new approach of integrating mechanistic model of electrode extension with the computational model of electromagnetic force, wherein the apparent electrode extension is obtained by solving the electrode melting rate equation. The proposed approach is demonstrated through a case on submerged arc welding. The effect of current, voltage, electrode diameter, contact tip to workpiece distance and polarity, on the electromagnetic force, is determined and analysed. This investigation shows that detrimental effects of welding electromagnetic force can be restricted without compromising productivity because after initial rapid increase, no considerable change in melting rate is caused by the force under consideration.     

小孔分流法电火花加工的分流状态研究

介绍一种小孔电火花分流加工新方法,建立小孔的电火花分流加工的分流模型,检测研究加工过程分流状态,得出每个分电极通过的电流按基尔霍夫定律减小,从而分流放电电流和减小放电蚀除体积.在研究条件范围内,进一步对分流法电火花加工过程的分流状态检测,得到多个分电极同时形成放电火花,说明了分流法加工分流作用.研究结果表明,利用电火花机床稳定加工参数,进行等面积分流电火花加工,将加工出比原机床稳定加工临界尺寸更小的小孔,为微小孔电火花加工分流状态的研究和应用提供试验依据.     

大深径比微细孔超声辅助电火花加工技术研究

微细电火花加工中电极损耗较大,在加工大深径比微细孔时,工具电极和工件之间的狭窄间隙内流体阻力较大,气泡及加工屑不易排出,易产生频繁的非正常放电,导致电极损耗进一步增大.针对大深径比微细孔加工的这一难题,提出采用电极摇动同时在工件上加载超声波振动的新方法,成功地在3.5 mm厚的不锈钢板上加工出平均直径为120 μm的通...     

Geometric modeling of the linear motor driven electrical discharge machining (EDM) die-sinking process

Based on Z-map method, in this paper the development of a geometric model for the linear motor equipped EDM die-sinking process is described. Firstly discussed are the advantages and benefits of the introduction of the linear motor into EDM die-sinker. The current model has been employed to calculate the minimum gap distance for sparks to occur and to analyze the possibility of spark generation between the workpiece and electrode surfaces. Also calculated is the crater formed by a single spark. The final machined surface topography is predicted. The influence of peak current and discharge duration on the average surface roughness is simulated. The experiment has been conducted to study the effects of machining conditions as well as to verify the effectiveness of the developed geometric model.     

Near dry electrical discharge machining

This study investigates the near dry electrical discharge machining (EDM) process. Near dry EDM uses liquid–gas mixture as the two phase dielectric fluid and has the benefit to tailor the concentration of liquid and properties of dielectric medium to meet desired performance targets. A dispenser for minimum quantity lubrication (MQL) is utilized to supply a minute amount of liquid droplets at a controlled rate to the gap between the workpiece and electrode. Wire EDM cutting and EDM drilling are investigated under the wet, dry, and near dry conditions. The mixture of water and air is the dielectric fluid used for near dry EDM in this study. Near dry EDM shows advantages over the dry EDM in higher material removal rate (MRR), sharper cutting edge, and less debris deposition. Compared to wet EDM, near dry EDM has higher material removal rate at low discharge energy and generates a smaller gap distance. However, near dry EDM places a higher thermal load on the electrode, which leads to wire breakage in wire EDM and increases electrode wear in EDM drilling. A mathematical model, assuming that the gap distance consists of the discharge distance and material removal depth, was developed to quantitatively correlate the water–air mixture's dielectric strength and viscosity to the gap distance.     

The use of the orthogonal array with grey relational analysis to optimize the electrical discharge machining process with multiple performance characteristics

In this paper a new approach for the optimization of the electrical discharge machining (EDM) process with multiple performance characteristics based on the orthogonal array with the grey relational analysis has been studied. A grey relational grade obtained from the grey relational analysis is used to solve the EDM process with the multiple performance characteristics. Optimal machining parameters can then be determined by the grey relational grade as the performance index. In this study, the machining parameters, namely workpiece polarity, pulse on time, duty factor, open discharge voltage, discharge current, and dielectric fluid are optimized with considerations of multiple performance characteristics including material removal rate, surface roughness, and electrode wear ratio. Experimental results have shown that machining performance in the EDM process can be improved effectively through this approach.     

Geometry prediction of EDM-drilled holes and tool electrode shapes of micro-EDM process using simulation

EDM is an efficient machining process for the fabrication of a micro-metal hole with various advantages resulting from its characteristics of non-contact and thermal process. However, this process has a serious problem caused by the tool wear, which significantly deteriorates the machining accuracy. In this paper, a geometric simulation model of EDM drilling process with cylindrical tool is proposed to predict the geometries of tool and drilled hole. The geometries of tool and workpiece are represented by two-dimensional matrix. For accurate prediction of their geometries, the tool motion, the sparking gap width, the spark frequency, the crater made by a single spark, and the tool wear ratio are considered as simulation parameters. To verify the simulation model the prediction results are compared with the actual experimental ones. Consequently, it is shown that the geometry prediction results match the experimental ones well within the error of 13%. Developed model can be used in offline compensation of tool wear in the fabrication of a blind hole. For the purpose of this, a compensation scheme based on the developed model is introduced, it is then demonstrated that the scheme is successfully applied to an actual micro-hole machining.     

Effects of pulse parameters on arc characteristics and weld penetration in hybrid pulse VP-GTAW of aluminum alloy

A novel ultrafast-convert hybrid pulse variable polarity gas tungsten arc welding process(HPVP-GTAW)is developed.High frequency pulse square-wave current which has a frequency of more than 20 kHz is exactly integrated in the positive polarity current duration.The effects of pulse current parameters on arc characteristics and weld penetration have been studied during the HPVP-GTAW process using Al-5.8 Mg alloy plates.The arc characteristics studied by arc voltage and its profile,weld penetration noted by the ratio of weld depth to width have been found to be influenced significantly by the pulse current.The experimental results show that the HPVP-GTAW process can improve the arc profile predominantly and obtain the higher weld penetration with lower heat input.The observation may help in understanding the weld characteristics with respect to variation in the pulse current parameters which may be beneficial in using the novel HPVP-GTAW process to produce the better weld quality of aluminum alloy plates.     

Evaluations of spark distribution and wire vibration in wire EDM by high-speed observation

In fine wire EDM using thin wire electrode, uniform distribution of spark location is necessary to achieve stable machining performance. However, it is difficult to precisely evaluate the distribution of spark location by the conventional branched electric current method when the workpiece is thin. A new evaluation method by using a high-speed video camera is proposed. The locations of spark are measured by analyzing the recorded images. Then the effects of machining parameters, such as servo voltage, pulse interval time, wire running speed and others on the distribution of spark location are investigated. The possibility of evaluating the wire vibration is also discussed.     

工艺参数对电火花电弧高效复合加工性能的影响研究

电火花电弧复合加工解决了电火花加工效率低的问题,与电火花加工相比,其加工效率提高了数倍,针对某些材料,其加工效率甚至超过了传统机械加工,但也存在自动化程度低、电极损耗严重等缺陷。利用电火花电弧复合加工技术进行了大量实验,并以此为基础,分析了不同加工参数下的工件性能,得到在不同峰值电流、脉宽、电极主轴转速等参数下的工件加工效率、表面粗糙度及相对电极损耗率的变化规律,以期得出针对不同加工目的的最优工作参数。     

Efficiency improvement in electrical discharge machining (EDM) of constant section cavity based on experimental study and numerical calculations

Electrode jump motion is applied to most of the electrical discharge machining (EDM) machine to remove debris from machining gap. The time consumption of one consecutive-pulse discharge process between two adjacent electrode jump motions is named electrode machining time. If the two parameters can be timely adjusted to the optimal values during machining, the efficiency will be obviously improved. However, the complicated flow field of the machining gap that contains kerosene, debris, and bubbles makes it difficult to determine the optimal values of electrode machining time and jump height. This research proposes a strategy to solve this problem. By detecting the voltage and current signals between electrode and workpiece, the normal discharge frequency and abnormal discharge ratio were calculated to determine the optimal electrode machining time. Then, the optimal electrode jump height was calculated through a model which simulates the gap flow field in EDM. Experimental results show that the proposing strategy evidently improves the EDM efficiency.     

High aspect ratio micro-hole drilling aided with ultrasonic vibration and planetary movement of electrode by micro-EDM

When a micro-hole is drilled deeply by EDM, the viscous resistance in the narrow discharge gap causes difficulty in the removal of debris and bubbles from the working area, leading to frequent occurrences of abnormal discharges and resulting in extensive electrode wear. This paper presents a new method of drilling high aspect ratio micro-holes by EDM, in which the planetary movement of an electrode, with enhancement from ultrasonic vibration, provides an unevenly distributed gap for the debris and bubbles to escape from the discharge zone easily. Micro-holes with aspect ratio of 29 have been drilled.     

微细倒锥孔在线加工参数调控的电火花加工工艺

基于微细孔电火花加工中观测到的“腰鼓”现象,进行了微细倒锥孔的在线加工参数调控电火花加工工艺的研究.实验研究了开路电压、进给深度、变压深度、放电电容等加工参数对微孔加工孔形的影响.通过对工艺参数的优化选择,加工得到出入口直径平均相差18.6 μm、锥度为1.16°的倒锥孔,可用于柴油发动机倒锥喷孔的加工.进一步实验了工...     

VPTIG焊接电流参数对电弧形态及焊缝质量的影响

采用高速录像系统、记忆示波器同步实时采集变极性氩弧（VFFIG）焊接电流、电弧形态信息,比较分析了VFFIG焊接电流频率、直流电极接负（DCEN）时间和直流电极接正（DCEP）时间、DCEN及DCEP电流幅值5个参数对电弧形态及焊缝质量的影响。结果表明,通过调节以上5个参数,可以控制电弧形态、电弧力及焊接热输入,从而控制熔深及焊缝正反面成形;控制焊缝两侧清理区宽度;减少钨极烧损。采用平板对接低频脉冲调制铝合金VFFIG焊接工艺,单道焊熔深可达6min,焊缝成形良好、质量可靠。     

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.     

Investigation of wire electrical discharge machining of thin cross-sections and compliant mechanisms

The wire electrical discharge machining (EDM) of cross-section with minimum thickness and compliant mechanisms is studied. Effects of EDM process parameters, particularly the spark cycle time and spark on-time on thin cross-section cutting of Nd–Fe–B magnetic material, carbon bipolar plate, and titanium are investigated. An envelope of feasible wire EDM process parameters is generated for the commercially pure titanium. The application of such envelope to select suitable EDM process parameters for micro feature generation is demonstrated. Scanning electron microscopy (SEM) analysis of EDM surface, subsurface, and debris are presented. SEM observations lead to a hypothesis based on the thermal and electrostatic stress induced fracture to explain the limiting factor for wire EDM cutting of thin-sections. Applications of the thin cross-section EDM cutting for manufacture of compliant mechanisms are discussed.     

Compound machining of titanium alloy by super high speed EDM milling and arc machining

A novel compound machining of titanium alloy (Ti6Al4V) by super high speed electrical discharge machining (EDM) milling and arc machining was proposed in this paper. The power supply consisted of a pulse generator and a DC power source which were isolated from each other. A rotating pipe graphite electrode was connected to the negative pole of the power supply. The plasma channel was able to deionize, and maximum material removal rate (MRR) reached 21,494 mm³/min with a relative electrode wear ratio (REWR) of 1.7% because of high current and efficient flushing. Compared with traditional EDM, the compound machining achieved a significantly higher MRR but a similar REWR. To investigate the characteristics of the compound machining, the effects of electrode polarity, peak voltage, peak current, and flushing pressure on the performance of the process, including its MRR, REWR, and radius of overcut (ROC), were determined. In addition, scanning electron microscopy, X-ray diffraction, and microhardness analysis were conducted. Result shows that the proposed method can machine difficult-to-machine materials efficiently.     

A study on micro-hole machining of polycrystalline diamond by micro-electrical discharge machining

Polycrystalline diamond (PCD), with its superior wear and corrosion resistance, is an ideal material for micro-hole parts in the field of microfabrication. This study investigated the micro-hole machining performance for PCDs by micro-electrical discharge machining (micro-EDM). A series of experiments were carried out to investigate the proper machining polarity and the impacts of micro-EDM parameters on machining performance. Experimental results indicate that negative polarity machining is suitable for micro-EDM of PCDs because of the protection brought over by the adhesion sticking to the electrode. An appropriate volume of adhesion on the tool electrode can help to increase the material removal rate (MRR) and reduce the relative tool wear ratio (TWR). By contrast, an excessive volume of adhesion can lead the machining into a vicious circle in which micro-holes are drilled with overlarge diameters. An optimal set of machining conditions was chosen among the investigated ranges of nominal capacitance and electrode rotation speed. An exemplary PCD through-hole, machined under the chosen optimal machining conditions, shows satisfactory machining results.     

变极性脉冲MIG焊的控制

研究变极性脉冲MIC焊的主要目的是控制形成浅焯缝,高效焊接铝合金薄板变极性脉冲MIG蚌的控制系统由逆史控制系统和单片机控制系统构成。控制系统协调控制电弧极性、电弧稳定性、焊丝熔化及熔滴过渡、电弧电压等焊接参数,获得稳定的焊接过程。变极性脉冲MIG焊在电弧EP极性时,利用脉冲电流熔化焊丝、形成熔滴过渡,电弧EN极性时电弧沿焊丝端上爬,EN极性电孤促进焊丝熔化、减小电弧对熔池的加热作用,减小焊缝熔深,焊接薄板时其有独特优势。