An investigation of ultrasonic-assisted electrical discharge machining in gas

This study focuses on using ultrasonic to improve the efficiency in electrical discharge machining (EDM) in gas medium. The new method is referred to as ultrasonic-assisted electrical discharge machining (UEDM). In the process of UEDM in gas, the tool electrode is a thin-walled pipe, the high-pressure gas medium is applied from inside, and the ultrasonic actuation is applied onto the workpiece. In our experiment, the workpiece material is AISI 1045 steel and the electrode material is copper. The experiment results indicate that (a) the Material Removal Rate (MRR) is increased with respect to the increase of the open voltage, the pulse duration, the amplitude of ultrasonic actuation, the discharge current, and the decrease of the wall thickness of electrode pipe; and (b) the surface roughness is increased with respect to the increase of the open voltage, the pulse duration, and the discharge current. Based on experimental results, a theoretical model to estimate the MRR and the surface roughness is developed.     

Workpiece surface modification using electrical discharge machining

Electrical discharge machining (EDM) is a widely used process in the mould / die and aerospace industries. Following a brief summary of the process, the paper reviews published work on the deliberate surface alloying of various workpiece materials using EDM. Details are given of operations involving powder metallurgy (PM) tool electrodes and the use of powders suspended in the dielectric fluid, typically aluminium, nickel, titanium, etc. Following this, experimental results are presented on the surface alloying of AISI H13 hot work tool steel during a die sink operation using partially sintered WC / Co electrodes operating in a hydrocarbon oil dielectric. An L8 fractional factorial Taguchi experiment was used to identify the effect of key operating factors on output measures (electrode wear, workpiece surface hardness, etc.). With respect to microhardness, the percentage contribution ratios (PCR) for peak current, electrode polarity and pulse on time were ˜24, 20 and 19%, respectively. Typically, changes in surface metallurgy were measured up to a depth of ˜30 μm (with a higher than normal voltage of ˜270 V) and an increase in the surface hardness of the recast layer from ˜620 HK_0.025 up to ˜1350 HK_0.025.     

Study on the characteristics of electrical discharge machining using dielectric with surfactant

This research mainly explores the influence of surfactant on the characteristics of electrical discharge machining (EDM) process on mold steel (SKD61). In this study, particle agglomeration is reduced after surfactant molecules cover the surface of debris and carbon dregs in kerosene solution. Debris is evenly dispersed in dielectric to improve the effects of carbon accumulation and dreg discharge, and reduce the unstable concentrated discharge. The EDM parameters, such as peak current, pulse duration, open voltage and gap voltage are studied in this paper. The experimental results show that after the addition of Span 20 (30 g/L) to dielectric, the conductivity of dielectric is increased. The machining efficiency is thus increased due to a shorter relay time of electrical discharge. When proper working parameters are chosen, the material removal rate is improved by as high as 40–80%. Although the improvement of surface roughness is not obvious, the surface roughness is not deteriorated since the material removal rate is great.     

Sink electrical discharge machining of hydrophobic surfaces

The phenomenon of hydrophobicity observed in such surfaces as lotus leaves is typically manifest by hierarchical structures on low-energy surfaces. Sustained interest in fabricating hydrophobic surfaces has resulted in a myriad of processes, which are but limited by their largely referring to soft materials and/or involving multiple process steps. The present work explored the application of electrical discharge machining (EDM) for the single-step manufacture of durable, metallic hydrophobic surfaces. Simple sink EDM in a hydrocarbon dielectric, with no special process kinematic or tooling requirements, is demonstrated to rapidly generate surfaces that are intrinsically water repellent, with contact angles approaching 150°.     

线切割加工质量的分析及改善措施

线切割加工在模具制造业中常用于加工精密、微细的模具零件。通过介绍线切割的加工原理,研究了线切割加工过程容易产生的加工质量缺陷,分析了加工面变形与开裂、变质层及表面粗糙度产生的原因,提出了进一步提高工件表面质量的改善措施和方法。实践中可以通过合理选材、优化电参数、选择正确的加工路线等方面综合分析和控制线切割加工,在保证生产率的前提下,改善和提高线切割加工质量。     

加工间隙对电火花加工质量影响的分析

在电火花加工中要降低各种干扰因素的影响,确保加工质量和稳定的加工过程,放电间隙的一致性是非常重要的一个技术指标。详细分析了影响放电间隙状态变化的因素,提出了维持放电间隙大小一致性的相应措施,对进一步改善电火花加工质量具有一定的参考价值。     

Applications of acoustic mapping in electrical discharge machining

The spatial distribution of discharges in electrical discharge machining (EDM) comprises valuable process information, which is not accurately obtained from electrical signals that are utilized extensively for process monitoring and control. This research hence explored the application of acoustic emission (AE) to map the discharges, in consideration of the acoustic time lag. In particular, the work refers to realistic process conditions, wherein AE from successive discharges cause repeated signal interference, which is detrimental to reliable time lag estimation. The applications of this capability for the respective identification of electrode length and workpiece height in fast-hole EDM and wire EDM are presented.     

Machining performance on hybrid process of abrasive jet machining and electrical discharge machining

To develop a hybrid process of abrasive jet machining (AJM) and electrical discharge machining (EDM),the effects of the hybrid process parameters on machining performance were comprehensively investigated to confirm the benefits of this hybrid process.The appropriate abrasives delivered by high speed gas media were incorporated with an EDM in gas system to construct the hybrid process of AJM and EDM,and then the high speed abrasives could impinge on the machined surface to remove the recast layer caused by EDM process to increase the efficiency of material removal and reduce the surface roughness.In this study,the benefits of the hybrid process were determined as the machining performance of hybrid process was compared with that of the EDM in gas system.The main process parameters were varied to explore their effects on material removal rate,surface roughness and surface integrities.The experimental results show that the hybrid process of AJM and EDM can enhance the machining efficiency and improve the surface quality.Consequently,the developed hybrid process can fit the requirements of modern manufacturing applications.     

Study on a new kind of combined machining technology of ultrasonic machining and electrical discharge machining

An analysis on the mechanisms of ultrasonic machining and electrical discharge machining has been carried out, and a technology, which combines the advantages of both of them, has been proposed in this paper. It can be used to machine all conductive hard and brittle materials with high efficiency and surface integrity. The mechanism of this combined technology has been studied by the authors. The experimental results show that the efficiency of it is over three times greater than that of ultrasonic machining, and the surface integrity is not significantly different.     

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.     

Sub-nanosecond monitoring of micro-hole electrical discharge machining pulses and modeling of discharge ringing

Monitoring the gap voltage and current in micro-hole electrical discharge machining (EDM) using high-speed data acquisition with 0.5 ns sampling period is conducted. The spark and arc pulses at three stages, namely electrode dressing, drilling, and penetration, of the micro-hole EDM are recorded. The EDM process parameters are setup to use negative polarity to blunt the electrode tip and positive polarity for micro-hole drilling and penetration. A new phenomenon of pre-discharging current is discovered. In the first 20–30 ns of spark and arc pulses, the current starts to rise while the voltage remains the same. Effects of EDM process parameters, including the open voltage, electrode diameter, and polarity, on the rate of spark and arc pulses and electrode feed rate are investigated. A model based on the RLC circuit is developed to study the ringing effect at the end of a discharge. The intrinsic parasitic capacitance and resistance of a RLC circuit are calculated from the decaying voltage signal and compared under two sets of experiments with varying wire electrode diameter and gap voltage to validate the ringing model. The calculation and experimental results validate the proposed RLC model for ringing phenomenon. The model shows the electrode diameter has negligible effect on ringing and high open voltage increases the parasitic resistance and damping in ringing. The monitoring technique and ringing model developed in this research can assist in the selection and optimization of micro-hole EDM process parameters.     

An algorithm for surface design and tool path generation in wire-cut electrical discharge machining

This paper proposes a CAD/CAM mathematical foundation to design ruled surfaces for wire-cut electrical discharge machining (EDM). This method combines the boundary planes concept, the coordinate representation of lines, control lines and design function to generate free form ruled surfaces. The tool motion and offset surface can also be generated simply by the same approach for computer numerical control (CNC) wire-cut EDM. The algorithm, being different from conventional methods, can present a surface or tool path concisely and uniquely. A numerical example is given to illustrate the proposed approach.     

Development of a process signature for electrical discharge machining

Electrical discharge machining (EDM) is a versatile unconventional machining process allowing high precision manufacturing. Due to the thermal main active principle, the process-induced heat affected rim zone always needs to be particularly considered regarding its characteristics as the resulting surface integrity has to fulfill the needed functional properties for advanced applications. Today, no deterministic model is available especially for the residual stress prediction. As consequence, current process design is based on experience and heuristic optimization. The paper therefore mechanistically links the material modification and the process-induced load. Inversion of the according process signature component finally allows model-based process design.     

Simulation model of debris and bubble movement in consecutive-pulse discharge of electrical discharge machining

Debris concentration and bubble volume fraction in the bottom gap between the electrode and workpiece affect the state of consecutive-pulse discharge and the efficiency of electrical discharge machining (EDM). Thus, the mechanisms of debris and bubble movement during consecutive-pulse discharge should be elucidated. However, these mechanisms have not been fully understood because of debris and bubble movement in the machining gap are difficult to simulate and observe. This study proposes a three-dimensional model of flow field with liquid, gas, and solid phases for machining gap in EDM. The mechanisms of debris and bubble movement in the machining gap during consecutive-pulse discharge were analyzed through the model. Debris and bubble movement in consecutive-pulse discharge was observed through experiments. The results showed that the proposed simulation model is feasible. The bubble expansion is the main way that the bubbles exclude from machining gap. Much debris moves outside the machining gap following the excluded bubbles, which is the main way that the debris excludes from machining gap. The bubble expansion becomes strong with the increase of the discharge current and pulse-on time.     

Effect of metal coating on machinability of high purity germanium using wire electrical discharge machining

This paper reports on the research of wire electrical discharge machining (WEDM) as a cutting process for n-type high purity germanium (HP Ge). WEDM requires sufficient electrical conductivity of the work piece for discharges to occur. Owing to the very high material resistivity of HP Ge (32.8 Ω cm), the electrical conduction is too low for WEDM to be efficient. To temporarily enhance the conduction, metals (aluminum and nickel) were deposited on the HP Ge on 1 or 2 sides with various thicknesses (1.0, 2.0, and 3.0 μm) using sputter deposition. This shortens the path of conduction between the HP Ge and the WEDM ground and also serves to trigger the discharges. Machining experiments were performed to determine the correlation between the slicing rate and locally enhanced HP Ge through various discharge energies (potential voltage: 150, 200, 250 and 300 V and capacitance: 1, 3.3, 5.5, 9.9 and 21.4 nF). From the results, the obtained maximum slicing rate is 7.7 mm²/min for Al coating (2 sides, 1.0 μm thickness) at high energy (300 V, 21.4 nF), which is improved as much as 27 times over uncoated HP Ge. The fastest cutting without creating subsurface microcracks was measured as 1.12 mm²/min performed at 150 V and 9.9 nF. Additional slicing experiments at reverse polarity (positive wire and negative work piece, uncommon polarity for WEDM) were performed at 150 V and various capacitances. The experiment proved that there were rectifying contacts at the metal coating surface. It was found that under identical EDM settings, a faster slicing rate also showed a reduction in kerf size due to less lateral discharge energy. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were used to investigate microcracks and to analyze surface impurities.     

Effect of electrode material on electrical discharge machining of alumina

Technologies for machining advanced insulating ceramics are demanded in many industrial fields. Recently, several insulating ceramics, such as Si₃N₄, SiC and ZrO₂, have been successfully machined by electrical discharge machining (EDM). As unstable discharges occur during the machining of Al₂O₃ ceramics, inferior machining properties have been obtained. The formation mechanism of the electrical conductive layer on the EDMed surface is much different as compared to other ceramics. In addition to this, the electrically conductive layers are not formed sufficiently to adhere to the EDMed workpiece surface and keep a stable and continuous discharge generation on the ceramics. Graphite is widely used as electrode material in EDM. It is expected that carbon from graphite electrode implant and generate a conductive layer. Copper, graphite (Poco EDM-3) and copper-infiltrated-graphite (Poco EDM-C3) electrodes were used to compare the effects of generation of a conductive layer on alumina corresponding to EDM properties. The electrical discharge machining of 95% pure alumina shows that the EDM-C3 performs very well, giving significantly higher material removal rate (MRR) and lower electrode wear ratio than the EDM-3 and copper electrodes. The value of MRR was found to increase by 60% for EDM-3 with positive electrode polarity. As for EDM-C3, MRR was increased by 80% under the same condition. When the results were investigated with energy dispersive spectroscopy (EDS), no element of copper was observed on the conductive layer with both EDM-3 and EDM-C3. However, surface resistivity of a conductive layer created with EDM-C3 is less than with EDM-3. Surface roughness was improved to 25 μm with positive polarity of EDM-C3.     

气中放电加工电极夹具的研制

介绍了一种气中放电加工电极夹具的结构及工作原理，阐述了设计要点，给出了设计过程和应用实例。该电极夹具克服了一般电极夹具不能旋转、不能密封的缺点，实际应用效果良好。     

Influence of silicon powder-mixed dielectric on conventional electrical discharge machining

Electrical discharge machining (EDM) is a technological process with a large industrial implementation. Its use is particularly intense when very complex shapes on hard materials with a high geometrical and dimensional accuracy are required. However, the technological capability of the process has limited its application when the specification of the part surface quality imposes polished and mirror-like characteristics. The addition of powder particles in suspension in the dielectric modifies some process variables and creates the conditions to achieve a high surface quality in large areas. This paper presents a new research work aiming to study the performance improvement of conventional EDM when used with a powder-mixed dielectric. A silicon powder was used and the improvement is assessed through quality surface indicators and process time measurements, over a set of different processing areas. The results show the positive influence of the silicon powder in the reduction of the operating time, required to achieve a specific surface quality, and in the decrease of the surface roughness, allowing the generation of mirror-like surfaces.     

Study of electrical discharge machining technology for slicing silicon ingots

Silicon slicing technology is an undergoing process and its performance improvements meet the ever-challenging and versatile demands. A new attempt to apply the WEDM strategy to slice the semiconductor materials is studied. The barriers from unusual material characteristics are to be conquered to make this idea realizable. The existing WEDM technology is utilized to slice the heavy-doped silicon ingot and its feasibility is examined. The machining rate and surface roughness are measured under various current on times and servo voltages in both the water immersed and water flushing WEDM machines. If small current on time is collocated with proper off time and lower gap voltage sensitivity under automatic feed mode, the stable area machining rate of around 76 mm²/min can be attained, and the R_a value is 3.6 μm or so which is acceptable if the following polishing procedure is considered. The thickness of defects to be polished can be predicted from the SEM photographs of the cross-sections of the sliced wafers. If the wire diameter is 0.25 mm and the wafer thickness is 1 mm, the portion of material loss including the kerf and the amount to be polished is under 26%.