复杂型面多轴电火花加工的电极损耗补偿

在复杂型面的多轴电火花加工中,电极损耗对加工精度具有影响显著,因此,对电极损耗进行准确补偿非常重要。通过研究得出电极表面损耗与电场强度有关,并建立了电极损耗系数与电场强度之间的关系。在此基础上,提出了考虑电极运动路径的电极损耗补偿方法,并通过加工实验证明了该方法的准确性与有效性。     

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.     

Development of Technology and Strategies for the Machining of Ceramic Components by Sinking and Milling EDM

This paper investigates the manufacturability of B₄C, SiC, Si₃N₄-TiN by milling EDM and the performance of it has been compared to conventional sinking EDM. It is shown that due to the good flushing conditions, milling EDM performs well, even for the machining of ceramic materials with a rather low electrical conductivity (B₄C, SiC). Because the used milling EDM technique removes material in a layer by layer fashion (2D-machining), a new strategy for the machining of complex 3D-shapes in ceramic material has been developed. It consists of a milling EDM pre-machining step, followed by one or more finishing sinking EDM steps. The developed strategy has been validated on an industrial example and compared to a pure sinking EDM strategy. Time reductions of more than 50% were obtained.     

Advancing EDM through Fundamental Insight into the Process

This paper aims to show the prospects of electrical discharge machining (EDM) technology by interrelating recent achievements in fundamental studies on EDM with newly developed advanced application technologies. Although gap phenomena in EDM are very complicated and hence not yet very well understood, recent improvements in computers and electronic measuring instruments are contributing to new discoveries and inventions in EDM technology. Such newly acquired insight sometimes raises questions on the validity of the established theories of EDM phenomena, and EDM processes once believed to be impossible or unrealistic are now becoming practical.     

Anomalous influence of polarity in sink EDM of titanium alloys

An anodic tool polarity is generally adopted in sink electrical discharge machining (EDM) to maximize material removal relative to tool wear. Sink EDM of Ti and Ti6Al4V is however atypical in that these materials necessitate a cathodic tool polarity. Adding to the intrigue is γ-TiAl, which machines better under the conventional anodic polarity. This research focused on clarifying the phenomena behind this interesting behavior by investigating removal mechanisms over a range of relevant process conditions. The anomaly is demonstrated to arise from the polarity-dependent nature and extent of TiC formation on the work surface, which significantly affects material removal.     

微细电火花加工电极磨损几何形状研究及仿真

通过实验研究了微细电火花加工盲孔的电极损耗,并基于Matlab软件,在二维矩阵的基础上,通过选取网格设定大小,设定工具运动情况、放电间隙、放电间隙影响因子、单个脉冲去除凹坑大小及相对电极损耗率等参数,仿真电极形状变化的全过程。该模型经后续完善后可用于预测补偿。为了验证仿真模型,对比了仿真结果与实际实验,证明该仿真方法可行。     

Machining Characteristics of EDM by Radio-frequency Plasma

An extension to the electrical discharge machining method by introduction of radio-frequency plasma is proposed. Sparking with the radio-frequency plasma can be generated in paraffin oil by simple electrical circuitry. In this paper, experimental investigations are described on the fundamental effects of the resonant frequency, type of electrode and workpiece materials on machining characteristics for high performance radio-frequency machining in paraffin oil. The results show that the removal rate and the electrode wear vary with the resonant frequency and type of electrode materials. The surface roughness can be reduced to less than 1μm Rz under suitable experimental conditions.     

Reliability of electrode wear compensation based on material removal per discharge in micro EDM milling

This paper investigates the reliability of workpiece material removal per discharge (MRD) estimation for application in electrode wear compensation based on workpiece material removal. An experimental investigation involving discharge counting and automatic on the machine measurement of removed material volume was carried out in a range of process parameters settings from fine finishing to roughing. MRD showed a decreasing trend with the progress of the machining operation, reaching stabilization after a number of machined layers. Using the information on MRD and discharge counting, a material removal simulation tool was developed and validated.     

Clarification of EDM gap phenomena using transparent electrodes

This paper describes the heat source diameter of single pulse discharge in electrical discharge machining. To observe the discharge plasma, SiC and Ga₂O₃ single crystals were used as the electrode material since they are optically transparent and electrically conductive. It was found that plasma diameter expands within a few microseconds after dielectric breakdown and the plasma diameter is much larger than the discharge crater. From the measured diameter of the crater, the heat source diameter was obtained by solving the inverse problem of heat conduction analysis, and it was found that the heat source diameter is smaller than the plasma diameter but larger than the crater diameter.     

Gap control for near-dry EDM milling with lead angle

A new gap control strategy for five-axis milling using near-dry electrical discharge machining (EDM) has been experimentally investigated. The conventional EDM control strategy only allows the retraction of the electrode in the direction of machining trajectory, which results in inefficient gap control when the electrode is not perpendicular to the workpiece. The new gap controller is capable of retracting the electrode in the direction of its orientation. This enables more efficient enlargement of the discharge gap leading to faster recovery of average gap voltage. Experimental results show a 30% increase in material removal rate while the tool electrode wear ratio and surface roughness are not affected. Furthermore, EDM efficiency is improved due to the change in the electrode retraction in its axial direction. The gain tuning of the proposed controller is also discussed. This study shows the direction of electrode retraction is important for five-axis near-dry EDM milling.     

电火花电解复合加工工作液浓度对电极损耗的影响研究

针对电火花电解复合加工的电极损耗问题,以模具钢为加工对象开展了电火花电解复合加工实验。分析了在不同极性和电极材料条件下,工作液浓度对电极相对损耗、电极形状变化规律及加工精度的影响。结果表明:合理控制工作液浓度能降低电极相对损耗及减小电极形状变化。     

Analysis and performance of slotted tools in electrical discharge drilling

Accumulation of machining debris due to inadequate gap flushing severely limits the material removal rate and impairs the quality of the machined surface in electrical discharge machining. This is particularly pronounced in electrical discharge drilling of holes with a high aspect-ratio, wherein conventional flushing techniques essentially cease to be effective. To this end, this paper proposes the application of novel tool electrodes comprising geometric features specifically designed to promote tool rotation-induced debris egress. The corresponding flow fields are modelled numerically to optimize said designs. Relative to conventional rotating cylindrical tools, removal rate enhancements on the order of 300% are demonstrated.     

Rotating Curvilinear Tools for EDM of Polygonal Shapes with Sharp Corners

Flushing of the inter-electrode gap is of critical importance in the performance of electrical discharge sinking operations. When the provision of flushing holes in the tool or the workpiece is impractical, effective flushing is best realized by inducing a relative motion between the electrodes. This paper relates to a novel application inspired by the kinematics of a Reuleaux Triangle that facilitates flushing through synchronous orbiting of a rotating curvilinear tool. This innovative scheme enables the machining of regular as well as non-regular polygonal shapes with sharp corners. Experimental results from implementing this concept on a 4-axis CNC EDM machine tool are presented.     

玻璃刻花加工中心三维刀具半径补偿技术研究

在分析玻璃刻花具体加工工艺的基础上，详细介绍了三维刀具半径补偿算法的实现。实践证明，通过配置旋转轴C轴，运用三维刀具补偿技术可以加工出复杂的花纹图案。     

电火花加工中多材质电极损耗规律的实验研究

针对电火花加工中多材质电极的损耗和形状变化,在模具钢工件上开展了电火花多材质电极加工实验研究,分析了电极材料、加工极性对多材质电极损耗的影响规律,并以黄铜-模具钢电极、紫铜-铜钨合金电极为研究对象,分析了多材质电极的形状变化规律。结果表明:长度损耗小的电极材料能辅助减小同组其他材料的电极损耗,但通常其角损耗较大;加工中多材质电极结合处形成过渡曲面,当加工进入均匀损耗阶段后,过渡曲面的圆弧半径和圆心角基本恒定不变。     

EDM drilling of ultra-high aspect ratio micro holes with insulated tools

This work presents an innovative method for the Electrical Discharge Drilling of ultra-high aspect ratio (AR > 30) micro holes. It makes use of tools insulated on the sidewall by means of a coating. The concept is to promote the process stability of micro EDM deep drilling by preventing secondary sparks. The performance of standard and customized tools is compared and reviewed against the main criteria of shape quality, tool wear and machining time. Process capabilities are also defined for a given coating. Micro holes within 0.2 mm in diameter and aspect ratio (AR) up to about 120 could be obtained within 1 h. A micro punching die is also realized by combining this strategy with micro wire EDM.     

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.     

单晶硅电火花铣削电极损耗研究

提出了一种以电火花加工技术对半导体硅材料进行铣削加工的方法,分别进行了单晶硅和45钢的电火花铣削加工,发现铣削单晶硅的电极体积相对损耗仅为0.41%,而45钢达到9.22%.针对此现象,从蚀除机理、放电间隙以及放电电流的爬坡特性方面对单晶硅放电加工特性进行了研究,并解释了其电极损耗低的原因.最后研究了不同加工规准下,单晶硅电火花铣削加工电极相对损耗的工艺规律.     

High Speed 3D Milling by Dry EDM

This paper describes the high speed EDM milling of 3D cavities using gas as the working fluid. In this new process, the molten workpiece material is removed and flushed out of the working gap with the help of high-pressure gas flow. The advantages or this technique are the remarkably small tool electrode wear and the significantly high material removal rate especially when oxygen gas is used due to the extremely strong oxidation of steel workpieces. Experiments showed that the material removal rate increases dramatically when the discharge power density on the wonting surface exceeds a certain threshold due to thermally activated chemical reaction between the gas and workpiece material. The maximum removal rate obtained was almost equal to that of high speed milling of quenched steel by a milling machine. The machining accuracy was considerably better when the gas was sucked through the pipe electrode than Jetted.     

基于切削力实现铣刀实时监测的实用性研究

根据生产实际,提出基于切削力实现铣刀实时监测的方法。在考虑切削参数一定时,建立了切削力与后刀面磨损量(VB值)的数学模型。通过提取切削力信号方差,建立了监测模块。并在对机床改造小的前提下,设计了带有力传感器的机床夹具,使监测更加简单可行。