Feasibility study of micro-slit EDM machining using pure water

This study addresses micro-slit EDM machining feasibility using pure water as the dielectric fluid. Experimental results revealed that pure water could be used as a dielectric fluid and adopting negative polarity EDM machining could obtain high material removal rate (MRR), low electrode wear, small slit expansion, and little machined burr, compared to positive polarity machining. In comparing kerosene versus pure water, pure water was observed to cause low carbon adherence to the electrode surface. Also discharge energy does not decrease and the discharge processes are not interrupted. Therefore, MRR was higher, and related electrode wear ratio compared to kerosene use was lower. In a continual EDM with multi-slit machining, kerosene will cause carbon element adherence, creating an initially high MRR and electrode wear, with rapid decline. However, pure water will not cause carbon element adherence on the electrode surface, so MRR and electrode wear is always stable in this process.     

Modelling of surface finish and material removal rate in rough honing

In the present work influence of different parameters of the rough honing process on surface roughness and material removal rate were studied. Specifically, second order mathematical models are presented for mean average roughness Ra (μm), maximum peak-to-valley roughness Rt (μm) and material removal rate Qm (cm min⁻¹), obtained by means of regression analysis.     

An experimental investigation of tool wear in electric discharge machining

In this study, the variations of geometrical tool wear characteristics – namely, edge and front wear – and machining performance outputs – namely, workpiece removal rate, tool wear rate, relative wear and workpiece surface roughness – were investigated with varying machining parameters. Experiments were conducted using steel workpieces and round copper tools with a kerosene dielectric under different dielectric flushing conditions (injection, suction and static), discharge currents and pulse durations. The experiments have shown that machining parameters and dielectric flushing conditions had a large effect on geometric tool wear characteristics and machining performance outputs. Additionally, published research on tool wear is presented in detail in this study.     

Experimental and numerical investigations of material removal process in electrochemical discharge machining of glass in discharge regime

Electrochemical discharge machining (ECDM) can be applied as a non-traditional processing technology for machining non-conductive materials such as glass and ceramics, based on the phenomena of evoked electrochemical discharges around the tool electrode. The material removal mechanism of ECDM is noticeably complex and difficult to experimentally characterize. In this paper, finite element models were proposed to predict the material removal in the ECDM discharge regime. First, the single-pulse discharge on a tapered electrode was modeled. It was found that about 30.5% of the discharge energy is transferred to the workpiece. The continuous discharge on a cylindrical electrode was thereafter modeled according to this phenomenon, in which the removal of a layer of the workpiece material starts from the projected contour of the edge of the electrode end and extends inward during the ECDM processing. The effective discharge ratio for material removal was calculated to be 10.1%. The drilling depths of holes at different applied voltages were predicted by the proposed finite element method. It was found that the predicted values were consistent with the experimental results.     

Optimisation of the electrical discharge machining process using a GA-based neural network

In this paper, the optimisation of the EDM process parameters from the rough cutting stage to the finish cutting stage has been reported. A trained neural network was used to establish the relationship between the process parameters and machining performance. Genetic algorithms with properly defined objective functions were then adapted to the neural network to determine the optimal process parameters. Examples with specifications intentionally assigned the same values as those recorded in the database or selected arbitrarily have been fed into the developed GA-based neural network in order to verify the optimisation ability throughout the machining process. Accordingly, the optimised results indicate that the GA-based neural network can be successfully used to generate optimal process parameters from the rough cutting stage to the finish cutting stage.     

Novel methods for high-speed observation of material removal and molten pool movement in EDM

This paper proposes two new methods to observe discharge phenomena without interference from the plasma in electrical discharge machining. The first method uses a bandpass filter with a bandwidth of 800–820 nm and laser illumination with a wavelength of 800–820 nm. The second method also uses a bandpass filter with a bandwidth of 800–820 nm; however, in this method, the tungsten material is used not only as the tool electrode but also as the illumination source. First, the discharge process was observed using traditional methods to investigate the influence of the plasma on the observation of the discharge process. Then, the process of removing molten material from both the tool electrode and workpiece, as well as molten pool movement, was observed using the first method proposed in this paper. The material removed from the tool electrode was scattered upward along the end profile of the tool electrode, while the material removed from the workpiece was distributed along the horizontal direction. To explain these phenomena, the flow distribution in the gap was qualitatively analyzed using a fluid simulation. Finally, the discharge process was also observed using the second method proposed in this paper. A tungsten tool electrode can emit light with a wavelength of 800–820 nm, which shines on the observed region during the discharge process. The observation results verified the phenomenon of multiple explosions of the molten pool during the discharge process. Moreover, it was found that the material removed by the explosion of the molten pool was scattered in different directions and hardly influenced by the flow distribution in the gap.     

Three-dimensional shaping by dot-matrix electrical discharge machining

This paper deals with a new prototyping method called dot-matrix electrical discharge machining (EDM) with scanning motion. The machining process by the dot-matrix method is similar to printing motion with a dot-impact printer. This method can be applied not only to EDM but also electrochemical machining and forming. A prototype of the machining unit for the dot-matrix method has six feeding devices for thin wire electrodes. The electrodes of 300 μm in diameter are arranged with the pitches of 760 μm. To obtain a smooth surface, a planetary motion in the x-y-plane is added to the feeding of the machining unit in the z-direction, the same area is machined repeatedly, or the machining unit is moved with fine feed. By compensating for the wear of the electrode during the scanning EDM, various shapes with the accuracy of micrometers order can be obtained without a formed tool electrode.     

Investigation of pad wear in CMP with swing-arm conditioning and uniformity of material removal

Chemical mechanical polishing (CMP) process plays the role of planarizing and smoothing the uneven layers after the material deposition process in the semiconductor industry. In this process, pad conditioning using a diamond disk is inevitable to attain a high material removal rate (MRR) and to ensure the stability of the process. Pad conditioning is performed for providing uniform surface roughness and opening up the glazed surfaces of the polishing pad. However, the uneven pad wear resulting from pad conditioning leads to changes in the uniformity of MRR and productivity of the device. In this study, we investigate the pad wear profile after swing-arm conditioning of the pad, based on measurements performed using a pad measurement system (PMS). Conditioning experiments are conducted with seven cases of profiles of the conditioner's duration time (PCDT). In all the cases, “W”-shaped pad profiles are generated through swing-arm conditioning. It is observed that a concave-shaped PCDT results in the lowest value of maximum pad wear rate. The average depth of pad wear (h_avg) is mainly related to the MRR, and the maximum depth of pad wear (h_max) and the horizontal distance from the wafer center to the position (e) where the maximum pad wear occurs affect the within-wafer non-uniformity (WIWNU). A concave-shaped PCDT results in longer life of the polishing pad by minimizing the variation in pad wear. This paper can provide a technical assistance in selecting the conditioning recipe and improving the lifetime of the polishing pad in the CMP process.     

Effects of Powder Characteristics on Electrodischarge Machining Efficiency

This paper presents the effects of various powder characteristics on the efficiency of electrodischarge machining (EDM) SKD-11. The additives examined include aluminium (Al), chromium (Cr), copper (Cu), and silicon carbide (SiC) powders that have significant differences in their thermophysical properties. The machining mechanism with the addition of the foreign particles, the tool wear rate (TWR), and the material removal rate (MRR) have been investigated. It was found experimentally that the particle concentration, the particle size, the particle density, the electrical resistivity, and the thermal conductivity of powders were important characteristics that significantly affected the machining performance in the EDM process. Proper addition of powders to the dielectric fluid increased the MRR and, thus, decreased the TWR. Under the same particle concentration experiments, the smallest suspended particle size led to the greatest MRR and, thus, the lowest TWR. Of the additives investigated, chromium powder produced the greatest MRR and the lowest TWR, whereas the process without foreign particles has the converse effects. The addition of copper powder to the dielectric fluid was found to make almost no difference to the pure kerosene EDM system.     

Influence of electrical discharge machining parameters on cutting parameters of carbon fiber-reinforced plastic

Today the use of high-strength carbon fiber-reinforced plastics (CFRP) composite as a material for many engineering applications is showing an increasing demand in the industry. These composites are replacing the traditional use of steel because they offer many advantages such as very light weight, high strength, and high stiffness associated with good corrosion-resistant properties. Unfortunately, there is little technological knowledge on the electrical discharge machining (EDM) process of high-strength composite materials, especially about the CFRP. In this work, a study has made into the possibility of using EDM process as a means of machining CFRP composite. Various cutting conditions such as peak current, pulse-on time, pulse-off time and open-circuit voltage were selected to perform electrical discharge machining. The effect of electrode rotation was also studied. Optimum cutting conditions and machine settings for EDM were chosen for machining CFRP composites.     

A comparative study on the wear resistance of electrical discharge machined surfaces

The properties of the surface were affected by many factors such as the pulse parameters, tool electrode material, and dielectric liquid in electrical discharge machining. Austenitic, dual-phase, and ferritic steel work materials were electrical discharge machined using graphite and copper tool electrodes in hydrocarbon- based oil and water dielectric liquids. Then the surfaces were analyzed regarding sliding friction wear responses on a comparative basis. The results revealed that the surface wear responses are sensitive to the type of the tool electrode material when machining in water dielectric liquid. However, the use of hydrocarbon-based dielectric liquid substantiality suppresses the influence of tool electrode on surface wear response due to excessive carbon release from the cracked dielectric. The machined surface topographical features were also affected due to the used electrical parameters regarding crater size, globular attachments, and microcracks that led significant alterations in sliding friction response. Primarily, weakly bounded globular attachments on the machined surface were dislodged at the initial stages of the friction tests and led higher sliding distances to the steady friction conditions. Finally, the results were compared with the subsurface microstructural properties to comprehend the wear responses.     

Electrical discharge machining of the AISI D6 tool steel: Prediction and modeling of the material removal rate and tool wear ratio

In this investigation, response surface method was used to predict and optimize the material removal rate and tool wear ratio during electrical discharge machining of AISI D6 tool steel. Pulse on time, pulse current, and voltage were considered as input process parameters. Furthermore, the analysis of variance was employed for checking the developed model results. The results revealed that higher values of pulse on time resulted in higher values of material removal rate and lower amounts of tool wear ratio. In addition, increasing the pulse current caused to higher amounts of both material removal rate and tool wear ratio. Moreover, the higher the input voltage, the lower the both material removal rate and tool wear ratio. The optimal condition to obtain a maximum of material removal rate and a minimum of tool wear rate was 40 μs, 14 A and 150 V, respectively for the pulse on time, pulse current and input voltage.     

Effect on crystalline structure of AISI M2 steel using tungsten–thorium electrode through MRR,EWR, and surface finish

To investigate on the crystalline structure of AISI M2 steel by using tungsten–thorium electrode in electrical discharge machining (EDM) process was studied. Furthermore, the investigation were carried out for finding the value of material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) of tool steel material depending upon three variable input process parameters. On the basis of weight loss, the value of MRR and EWR were calculated at optimized process parameter. Subsequently, surface topography of the processed material were examined through different characterization techniques like scanning electron microscopy (SEM), Optical surface profiler (OSP) and Atomic force microscopy (AFM), respectively. In XRD study, broadening of the peak was observed which confirmed the change in material properties due to the homogeneous dispersion of the particles inside the matrix. Lowest surface roughness and MRR of 0.001208 mg/min was obtained. Minimum surface roughness was obtained 1.12 μm and 2.18427 nm by OSP and AFM study, respectively. Also, minimum EWR was found as 0.013986 mg/min.     

Electrical discharge machining of submicron holes using ultrasmall-diameter electrodes

We have carried out the electrical discharge machining (EDM) of submicron holes using ultrasmall-diameter electrodes. Two types of electrode were used: tungsten electrodes fabricated by the combination of wire electrodischarge grinding and electrochemical machining, and silicon electrodes originally designed as probes for scanning probe microscopes. The diameters of the former and latter were 1 μm or less, and less than 0.15 μm, respectively. Holes were drilled using a relaxation-type pulse generator at an open-circuit voltage of less than or equal to 20 V with the machine's stray capacitance as the only capacitance. Using tungsten electrodes, holes of less than 1 μm in diameter and more than 1 μm in depth were successfully drilled. A 1.3-μm-wide slot was also fabricated by drilling many holes with a small pitch. It was possible to drill holes of approximately 0.5 μm diameter using silicon electrodes because the electrode diameter was less than those of the tungsten electrodes. These holes have the smallest reported diameter for holes drilled by EDM, indicating the possibility of submicron- and nanoscale machining by EDM.     

Employing severe plastic deformation to the processing of electrical discharge machining electrodes

The tool electrode has a significant role in electrical discharge machining (EDM) performance, as it affects machining efficiency, surface quality and the geometrical accuracy of the machined component. This study presents a new approach for developing a pure copper electrode using severe plastic deformation (SPD) to enhance the machining characteristics during EDM. Equal channel angular pressing (ECAP) is selected because it is the most successful SPD method of processing bulk materials. Finite element analysis, microstructural assessment as well as nanoindentation tests are carried out to determine the behavior of pure copper after one and two ECAP passes. The effectiveness of EDM when using ECAP-treated electrodes is evaluated by introducing new techniques of measuring the volumetric overcut (VOC) and corner sharpness. In addition, tool wear rate (TWR), material removal rate (MRR), electrode wear ratio, surface roughness, surface crack density and the critical crack zone are studied. The results emphasize that an electrode subjected to one pass of ECAP can enhance the workpiece accuracy by decreasing the VOC and increasing corner sharpness by 13 and 66%, respectively. It is also revealed that the nanohardness enhancement following ECAP leads to lower TWR and electrode wear ratio. An investigation of the surface characteristics indicates a thinner recast layer is achieved when using one ECAP pass-treated electrode, which leads to 26% lower surface crack density.     

A review on the use of dielectric fluids and their effects in electrical discharge machining characteristics

Electrical discharge machining (EDM) is one of the earliest non-traditional machining processes. EDM process is based on thermoelectric energy between the work piece and an electrode. In electrical discharge machining (EDM), a process utilizing the removal phenomenon of electrical discharge in dielectric, the working fluid plays an important role affecting the material removal rate and the properties of the machined surface. Choosing the right dielectric fluid is critical for successful operations. This paper presents a literature survey on the use of dielectric fluids and also their effects in electrical discharge machining characteristics.     

用正交试验分析中电参数对圆柱度影响

电火花加工脉冲放电的统计学研究表明电参数与加工质量间存在一定的规律性。为实现电火花加工小孔圆柱度误差的合理控制,通过大量的工艺试验研究放电参数与小孔圆柱度间的规律是十分必要的。提出了多截面直角坐标测量方法,实现了小孔圆柱度的定量评定。在此基础上,采用正交试验研究了放电参数（开路电压、电流,脉宽,脉间,抬刀周期）对小孔圆柱度的影响。结果表明：脉宽对圆柱度的影响最为显著,开路电压次之,其余三个参数的影响较弱;同时也得到了以圆柱度误差最小为评价目标的一组放电参数。     

A parallel link end effector for scanning electrical discharge machining process

Because a parallel mechanism has a high-frequency response, multiple degrees of freedom (DOF), and high stiffness, it can be applied to an end effector for electrical discharge machining (EDM) with a scanning motion. A prototype has 3 DOF: two tilting angles around the x- and y-axes, and the movement in the z-direction. It consists of, a base plate, a stage, a constraint link, and three inchworm devices that act as links. The inchworm devices are connected with the stage and the base plate. The z-position and inclination of the stage are changed by adjusting the length of the inchworm devices. The electrode feeding is controlled by the combination of the steplike movement with the inchworm devices and continuous extension of piezos. The frequency response of the stage by the continuous extension of the piezos is up to 200 Hz. The positioning accuracy of the end effector is less than 30 μm in height and 0.04° in inclination. Some examples of EDM by the scanning motion are demonstrated.     

An investigation of tube and rod electrode wear in micro EDM drilling

This paper studies the influence of various factors contributing to micro electrode wear during electrical discharge machining (EDM) drilling with micro rod and micro tube electrodes. In this paper, a simple method for calculating volumetric wear ratios is proposed based only on geometrical information obtained from the process. The objective of the research is to investigate the wear behaviour of electrodes and the suitability of electrode wear compensation methods. Electrode shape deformation and random variation of the volumetric wear are studied as the main factors affecting the applicability of wear compensation methods and as an indicator of the accuracy achievable with the micro EDM process.     

Cutting forces,tool wear and surface finish in high speed diamond machining

We have investigated the cutting forces, the tool wear and the surface finish obtained in high speed diamond turning and milling of OFHC copper, brass CuZn39Pb3, aluminum AlMg5, and electroless nickel. In face turning experiments with constant material removal rate the cutting forces were recorded as a function of cutting speed between v_c = 150 m/min and 4500 m/min revealing a transition to adiabatic shearing which is supported by FEM simulations of the cutting process. Fly-cutting experiments carried out at low (v_c = 380 m/min) and at high cutting speed (v_c = 3800 m/min) showed that the rate of abrasive wear of the cutting edge is significantly higher at ordinary cutting speed than at high cutting speed in contrast to the experience made in conventional machining. Furthermore, it was found that the rate of chemically induced tool wear in diamond milling of steel is decreasing with decreasing tool engagement time per revolution. High speed diamond machining may also yield an improved surface roughness which was confirmed by comparing the step heights at grain boundaries obtained in diamond milling of OFHC copper and brass CuZn39Pb3 at low (v_c = 100 m/min) and high cutting speed (v_c = 2000 m/min). Thus, high speed diamond machining offers several advantages, let alone a major reduction of machining time.