Electrical Discharge Grinding Research Articles

Research on Micro-Size Electrical Discharge Grinding Polycrystalline Cubic Boron Nitride Based on Single Pulse

Polycrystalline cubic boron nitride (PcBN) was a high temperature and high pressure composite material with high hardness. With its high wear resistance and good chemical stability, it conforms to the basic characteristics of modern advanced cutting technology of "high efficiency, high precision, high efficiency and green". Currently, it was widely used in the field of ferrous metal cutting tools. Electrical discharge grinding was one of the most effective methods for machining polycrystalline cubic boron nitride cutters. It was especially suitable for machining complex shapes and thin edge cutters. Single pulse electrical discharge grinding is the basis of continuous EDG machining and an effective method to study micro-scale electrical discharge grinding. In this study, the morphology of single pulse discharge corrosion pits and the relationship between discharge parameters and material removal rate, such as the deep-diameter ratio of the corrosion pits, the pulse width and the deep-diameter relationship of the corrosion pits, were studied with the polycrystalline cubic boron nitride composite sheet of 2 micron particle size as the test material and the independently developed single pulse discharge power supply as the device. The experimental results show that the radius and heat affected area of the discharge corrosion pit increase rapidly, then slowly, and finally gradually with the extension of pulse duration. The corrosion depth generally varies gently in the range of 0.2 ~ 0.5 micron, and the pulse duration has no obvious effect on the depth of the discharge corrosion pit. With the extension of pulse duration, the ratio of radius to depth of the corrosion pit changed in the range of 13 ~ 20, and the ratio basically declined.

SURFACE ROUGHNESS MODELING DURING ELECTRIC DISCHARGE GRINDING WITH VARIABLE POLARITY OF ELECTRODES

The article presents the probabilistic-statistical modeling of surface roughness in the process of electric discharge grinding with the variable polarity of electrodes. The correlation between electric modes of machining and indicators of the quality of the machined surface was established. A probabilistic-statistical model of part surface roughness formed during grinding is obtained, which establishes the correlation between high-altitude surface parameters and electrical machining modes. The developed model makes it possible to calculate the height parameters of the part roughness depending on the electrical modes of grinding. The height of microroughness is determined by the same machining conditions as the depth of erosion pits. It is possible to obtain low roughness if electrical machining modes are reduced.

The Performance of Polycrystalline Diamond (PCD) Tools Machined by Abrasive Grinding and Electrical Discharge Grinding (EDG) in High-Speed Turning

Polycrystalline diamond (PCD) tools are widely used in industry due to their outstanding physical properties. However, the ultra-high hardness of PCD significantly limits the machining efficiency of conventional abrasive grinding processes, which are utilized to manufacture PCD tools. In contrast, electrical discharge grinding (EDG) has significantly higher machining efficiency because of its unique material removal mechanism. In this study, the quality and performance of PCD tools machined by abrasive grinding and EDG were investigated. The performance of cutting tools consisted of different PCD materials was tested by high-speed turning of titanium alloy Ti6Al4V. Flank wear and crater wear were investigated by analyzing the worn profile, micro morphology, chemical decomposition, and cutting forces. The results showed that an adhesive-abrasive process dominated the processes of flank wear and crater wear. Tool material loss in the wear process was caused by the development of thermal cracks. The development of PCD tools’ wear made of small-sized diamond grains was a steady adhesion-abrasion process without any catastrophic damage. In contrast, a large-scale fracture happened in the wear process of PCD tools made of large-sized diamond grains. Adhesive wear was more severe on the PCD tools machined by EDG.

A study on machining performance of wire electric discharge grinding (WEDG) process during machining of tungsten alloy micro-tools

In this experimental study, tungsten alloy micro-tools of high aspect ratio are machined through wire electric discharge grinding (WEDG) method using the step machining technique on a hybrid micro-electro-discharge machine to achieve high productivity and finish. Tungsten alloy micro-tools are widely used in the fabrication of miniature products. The precise and economical machining of the tungsten material with an optimum level of accuracy and surface properties is a challenge because of its exceptional characteristics like hot hardness, high strength, low wear, and corrosion rate. The material removal rate (MRR) and surface roughness (Ra) responses are studied during machining of micro-tools, selecting the variability of applied voltage, circuit capacitance, and spindle speed during machining for a constant-aspect-ratio micro-tool. Both voltage and capacitance are found to be influencing parameters for MRR and surface roughness. Higher voltage and capacitance values tend to increase MRR and roughness values on the machined micro-tool. Further, the parametric conditions are also identified for higher MRRs and lower surface roughness (Ra) values after employing the hybrid Taguchi design of experimentation methodology. Surface topography of the machined surface studied by energy-dispersive spectroscopy (EDS) reveals the presence of pyrolytic carbon and oxygen elements. Field emission scanning electron microscopy (FESEM) images show a little waviness across the machined surface. A mathematical model is developed to evaluate the correlation among governing parameters for machining response and validated by confirmation experiments. The machining procedure can be further developed to fabricate more predominant fluted micro-tools for difficult-to-machine tungsten material.

Influence of Die Machining Operation on the Friction Condition in the Cold Forming Process

The texture of a die surface plays an important role in the tribology of metal forming processes. The surface texture is defined by surface roughness and its orientation, which is influenced by the manufacturing process. In this research, the effects of various die machining operations on the friction condition in the forming process of CK45 steel are investigated using ring compression tests. The dies are fabricated through six machining operations, including horizontal and vertical milling, electrical discharge machining, grinding, polishing, and turning. The ring specimens are compressed by parallel die plates. The effects of different parameters such as machining method, lubrication condition, and deformation percentage on the friction coefficient are investigated using design of experiments and analysis of the results. Finite element simulation is also used to obtain the calibration curves in the ring compression test. The obtained results reveal the significant effect of the die machining process on friction coefficient. In addition, the maximum and minimum friction coefficient values are associated with electrical discharge machining and grinding with polishing, respectively. Furthermore, it is found that despite the approximately same values of mean roughness (Ra ) in vertical milling, electrical discharge machining, and turning, different friction coefficients are obtained due to the dissimilar mean roughness depth (Rz ), surface hardness, and surface texture of the inserts.

Machining of cylindrical parts by wire electrical discharge grinding using thin plate guide

In order to meet the processing requirements of precise cylindrical parts on hard and difficult-to-machine materials, this paper introduces wire electrical discharge grinding (WEDG) using thin plate wire guide for cylindrical parts machining. The spindle system and the wire transport system to realize this processing method was added to a low speed wire electrical discharge machining (LS-WEDM) machine tool. In order to realize the online measurement of the machining accuracy of the cylindrical parts, an online measurement system of two-degree-of-freedom based on laser displacement sensor was built. The reasons for the incomplete removal of the machined surface were analyzed. Through the application of a new tool setting strategy and reasonable selection of processing parameters, the phenomenon of incomplete processing can be avoided. The experimental research on the effects of part rotational speed, wire feed rate, wire running speed and wire tension on roundness, surface roughness Sa, and surface morphology were carried out. Finally, example of the cylindrical parts is given to verify the machining accuracy.

In situ drilling and milling of thin sheet using microelectrical discharge machining

The present study investigates fabrication of microrod using block electrical discharge grinding process and performs in situ drilling and milling of thin sheets using the fabricated rods by the microelectrical discharge machining process. The microrods are fabricated at a wide range of discharge energy (DE) by varying voltage and capacitance, and their effect on machining time (MT), material removal rate, average diameter and standard deviation in diameter (SDD) are evaluated. To get the benefit of both higher efficiency as well as dimensional accuracy, a technique of variable energy setting is coined, wherein higher DE is applied initially to increase efficiency followed by lower DE to improve dimensional accuracy and precision. The fabricated microrods are then used as tools for in situ microelectrical discharge drilling (µED-drilling) and microelectrical discharge milling (µED-milling) on brass and titanium sheet. In µED-drilling, MT and tool wear (TW) of brass is lower as compared to titanium, whereas overcut of brass is higher than titanium. ‘To and fro’ technique is used to compensate the TW in µED-milling and to achieve dimensional accuracy. The technique is successful in achieving fairly straight microslot in brass with SDD of 17 µm as compared to titanium with SDD of 113.50 µm.

EDM GAP MODELING AT ELECTRICAL DISCHARGE GRINDING WITH CHANGE OF ELECTRIC POLARITY

The paper presents an experimental study and modeling in the Simulink graphical environment of the EDM gap at electrical discharge grinding (ED grinding) with change of electric polarit of difficult-to-machine materials. Based on the experimentally obtained oscillograms of currents and voltages in the cutting zone, an EDM gap model has been developed, which implements the nonlinear dependence of the active resistance of the electroerosion gap on its value, which makes it possible to take into account the effect of the interelectrode environment on the parameters of electric discharge pulses. Comparison of the calculated oscillograms obtained in the Simulink model with the experimental ones has shown that during ED grinding, the developed EDM gap model adequately reflects the real electrical processes occurring in the electroerosion gap.

Micro-texturing on flat and cylindrical surfaces using electric discharge micromachining

The present work discusses micro-texturing on flat and cylindrical surfaces using the electric-discharge micromachining (EDMM) process. The arrays of micro-dimples are generated on flat Ti-6Al-4V surfaces using a block–electric discharge grinding (block-EDG)–fabricated microtools of an average diameter of 148 µm and 105 µm. Large-area surface texturing on flat Ti-6Al-4V and aluminium surfaces are performed to analyse the variation in water contact angle with varying depths of dimples. Adopting the electric discharge–milling (ED-milling) strategy, micro-pillars of dimensions 242 µm × 166 µm × 50 µm are machined on flat Ti-6Al-4V surfaces. The EDMM process for non-flat surfaces, such as curved (internal and external), spherical and freeform surfaces, is receiving attention in various applications. Machining of the aforementioned surfaces using the EDMM process appears to be problematic, due to the continuous change in curvature, which results in the subsequent spark gap variation. In the present work, processing of cylindrical surfaces for micro-features generation, such as micro-dimple arrays, has been attempted. Arrays of micro-dimples are machined on copper and Ti-6Al-4V cylindrical surfaces. A precise indexing setup is fabricated to hold and index the workpiece at the desired angular positions. Unlike machining on flat surfaces, the relative dimensions of the tool and the workpiece’s curvature result in non-uniform wear at the tool’s end cross-section. Owing to this non-uniform wear of tool electrode caused by the curvature effect of the workpiece, the formation of a microscopic bump/spike is observed on the dimple’s bottom. The depth of the dimple up to which the entire bottom surface of the tool is not exposed to the sparks is defined as its critical depth. For a combination of a tool and a workpiece of diameters 500 µm and 5 mm, respectively, the critical depth of the dimple is found to be 12.53 µm. However, the critical depth increases with a decrease in workpiece diameter, provided the diameter of the tool is constant.

Experimental Investigation on CO2 Laser-Assisted Micro-Grinding Characteristics of Al2O3

Fabricating micro-scale features in ceramic materials, such as alumina (Al2O3), is challenging because of their high hardness and brittleness. Laser-assisted machining, in which a laser beam is a heat source for pre-softening the local area on a workpiece, is an effective hybrid method for machining ceramics. The study identified the effects of carbon dioxide (CO2) laser-assisted micro-grinding (LAMG) with a wire electrical discharge grinding polycrystalline diamond tool on Al2O3. Comprehensive investigations have been conducted on the effects of laser beam machining itself and the effect of machining parameters, such as laser beam power, axial depth of cut, and feed rate. The average grinding force was found to decrease by 46% in the thrust direction and 44% in the feed direction, and surface roughness decreased by 17% with LAMG. Moreover, machining at a higher feed rate was possible without tool fracture. The results indicate that the CO2 laser heating of Al2O3 has significant advantages over conventional methods regarding machinability and channel geometry. Finally, an improved LAMG process to prevent edge cracks by revising the machining conditions is proposed.

Experimental investigations on electrical discharge grinding of composite material

Electrical Discharge Grinding is a very complex hybrid machining process of electrical discharge machining and grinding which is suitable for machining of flat surface materials by generating the spark between the non-abrasive rotating round tool and workpiece. In this process, mechanical and thermal energies are liable for improving the material removal rate and reducing the surface roughness owing to successful flushing of working gap. In the present work, an attempt has been initiated to develop Electrical Discharge Grinding setup and parametric study of input parameters such as current and wheel rpm on output parameters like material removal rate and surface roughness while the grinding the Al-SiC-B4C-Mg as a hybrid composite workpiece material using copper tool electrode..During the preliminary experimentation, it shows that output parameters increase while varying the current and wheel speed.

Fabrication of micro rods by twin-mirroring-wire tangential feed micro electrical discharge grinding

In micro electrical discharge machining (micro-EDM), the precision fabrication of cylindrical micro rods is difficult to achieve with a high processing efficiency. In order to overcome this challenge, this paper proposes a new processing method, which is denoted as twin-mirroring-wire tangential feed micro electrical discharge grinding (TMTF-WEDG). The machining principle, characteristics, and realization of the new method are firstly introduced. Then, the advantages of TMTF-WEDG in terms of machining efficiency and accuracy are demonstrated. The experimental results have shown that the machining efficiency can be increased to more than 70% in comparison with conventional tangential-feed wire electrical discharge grinding. It has also been proved that a minimum removal of material corresponding to a reduction of less than 1 μm in the diameter of a micro rod can be obtained by TMTF-WEDG. This considerably helps in improving the accuracy and repeatability of the machining process. A deviation of less than 1 μm on the diameter of a micro rod has been obtained in a length range of 800 μm. The process repeatability in machining five micro rods has been established to be below 2 μm. The proposed method is therefore of great significance for improving the machining efficiency and ensuring a high precision in the shaping process of cylindrical micro rods.

Study on taper reduction of high aspect ratio micro-shafts fabricated by twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG)

• New method, named TMTF-WEDG, was proposed for manufacturing micro-shaft. • The main reasons for the taper of micro-shaft are the deformation of the micro-shaft and the wear of wire electrodes. • According to the experimental results, the parameters were selected to control the discharge energy to minimize the taper. • The feed strategy was improved to avoid the effect of wire electrode wear on taper. • High-precision micro-shaft with small diameter and large aspect ratio was successfully prepared. Efficiently fabricating large-aspect-ratio micro-shaft with small diameter and high accuracy is a significant technology in micro-manufacturing. In this paper, based on the newly proposed method, named twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG), we developed the micro-shaft fabrication system to improve the efficiency by twin-mirroring-wire and accuracy by tangential feed. Besides, the narrow slit formed by twin-mirroring-wire constrains the diameter of micro-shaft, which allows improving the repeatability of micro-shaft diameter by controlling the tangential feed distance and narrow slit width. But during the TMTF-WEDG, we found that the micro-shafts with small diameter and large-aspect-ratio tend to have processing taper. The reasons for the tapered micro-shaft are the wire electrode wear due to non-running during finishing and the deformation of micro-shaft with low stiffness due to the small diameter and large aspect ratio. The heat generated by the discharge causes the deformation and its conduction inside the micro-shaft. Discharge energy needs to be controlled during the finishing of TMTF-WEDG, which was achieved by controlling processing parameters. By studying the effects of parameters on the processing taper, optimized parameters minimized the taper of the micro-shaft. The feed strategy was improved so that the micro-shaft always discharges with new wire electrodes. In this way, we successfully fabricated a tungsten micro-shaft with a diameter of 8.5 μm and a length of 400 μm, and the diameter variation is less than 2 μm. The aspect ratio of another micro-shaft with a diameter of 39.38 μm is larger than 50, with the diameter variation within ± 2 μm. By using such micro-shaft, we performed micro-holes processing by micro-EDM on a 304 stainless steel sheet, and the accuracy of 49 micro holes was controlled within 1 μm.

Shaping Soft Robotic Microactuators by Wire Electrical Discharge Grinding.

Inflatable soft microactuators typically consist of an elastic material with an internal void that can be inflated to generate a deformation. A crucial feature of these actuators is the shape of ther inflatable void as it determines the bending motion. Due to fabrication limitations, low complex void geometries are the de facto standard, severely restricting attainable motions. This paper introduces wire electrical discharge grinding (WEDG) for shaping the inflatable void, increasing their complexity. This approach enables the creation of new deformation patterns and functionalities. The WEDG process is used to create various moulds to cast rubber microactuators. These microactuators are fabricated through a bonding-free micromoulding process, which is highly sensitive to the accuracy of the mould. The mould cavity (outside of the actuator) is defined by micromilling, whereas the mould insert (inner cavity of the actuator) is defined by WEDG. The deformation patterns are evaluated with a multi-segment linear bending model. The produced microactuators are also characterised and compared with respect to the morphology of the inner cavity. All microactuators have a cylindrical shape with a length of 8 mm and a diameter of 0.8 mm. Actuation tests at a maximum pressure of 50 kPa indicate that complex deformation patterns such as curling, differential bending or multi-points bending can be achieved.

Accuracy improvement of micro-shafts fabricated by the twin-mirroring-wire tangential feed electrical discharge grinding

Abstract The new method of micro-shaft fabrication, named twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG), is mainly characterized by the tangential feed strategy and the narrow slit formed by twin-mirroring-wire to achieve the diameter control of micro-shaft. The critical factors of micro-shafts accuracy and repeatability include processing position offset of micro-shaft, front edge position fluctuation of wire electrodes, and asymmetry of the twin-mirroring-wire electrodes, which cause the deviation of the tangential feed path and fluctuation in narrow slit width. The diameter of the micro-shaft was smaller than the theoretical value with processing position offset, which is not conducive to the control of the micro-shaft diameter. The front edge fluctuation of the wire electrodes caused the variation of the micro-shaft diameter to be around ±3 μm in the axial direction. The asymmetry of the twin-mirroring-wire electrode is the key factor affecting the tangential feed path which further affects the controlling the repeatability of the micro-shafts. New strategies were proposed, including the determination of the initial machining position achieved by tool setting, improvement of the twin-mirroring-wire system, the determination of the feed path, and improvement of feed strategy for trimming the taper of micro-shafts. The processing results show that a micro-shaft with a diameter of 45 μm and uniformity of ± 0.5 μm was successfully fabricated. For five repeated fabricated micro-shafts, the diameter repeatability was controlled within ±1 μm.

Study of the effects of important factors on the diameter accuracy of micro-shafts fabricated by TMTF-WEDG

It is very significant to improve the diameter accuracy of micro-shafts fabricated by micro-electrical discharge machining (micro-EDM) in micro-tools application. The diameter accuracy includes the uniformity of a single micro-shaft in axial direction and the repeatability of micro-shafts with the same diameter. A newly proposed method, named twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG), can realize high uniformity and repeatability of micro-shafts via tangentially feeding and constraining of a narrow slit formed by a twin-mirroring-wire on the diameter of micro-shafts, respectively. Controlling the material removal thickness in single-step machining of micro-shafts is necessary to achieve high uniformity and repeatability. This paper focuses on the effects of the several important factors on the material removal thickness of micro-shafts to reveal the effects on the diameter uniformity and repeatability, including the open voltage, capacitance, feed rate in the Z-direction, feed step in the Y-direction, and tangential feed distance. The results indicate that the lower open voltage or the smaller capacitance or higher Z-direction feed rate, the smaller the thickness of the material removed, which is advantageous for controlling the consistency and repeatability of the micro-shafts. Decreasing of Y-direction feed step from 20 to 5 μm is accompanied by a reduction in material removal thickness, and the material removal thickness of less than 0.4 μm is achieved with a smaller feed step of in the Y-direction. As the tangential feed distance S2 decreases, the material removal thickness of the micro-shafts decreases gradually. In this study, the uniformity and repeatability of brass and tungsten micro-shafts are controlled within 1 μm and 2 μm, respectively.

Fabrication of micro rotary structures by wire electrochemical grinding

Micro rotary structures have attracted increasing attention in many industrial applications. However, the fabrication of complex micro rotary structures with high strength, high hardness, and low rigidity, poses a significant challenge to traditional machining methods. To solve this difficult problem, this study proposes a novel method of fabricating complex micro rotary structures by using wire electrochemical grinding (WECG), which is an anodic dissolution process and has no machining force. WECG, a type of ECM, has some major advantages over wire electrical discharge grinding (WEDG): no electrode wear, absence of residual stress, good surface quality, low machining cost, and high machining efficiency. Firstly, this study investigated the influences of the process parameters on the dimensional accuracy of the micro grooves produced, then optimized these process parameters. A qualitative simulation of WECG was conducted to reveal the reason for the trumpet-like micro grooves fabricated by WECG. Finally, based on the optimal process parameters, several different kinds of rotary structures were successfully produced by WECG. The experimental results demonstrate that WECG is a promising method for fabricating complex rotary structures of difficult-to-cut materials at low cost and with high efficiency.

Experiments Research on Electrical Discharge Grinding Polycrystalline Diamond Tool based on Surface Quality Analysis

As the hardest material in the field of synthetic materials, polycrystalline diamond has attracted more and more attention in the field of tools, which reflects the basic characteristics of ‘high efficiency, precision and flexibility’ of modern advanced cutting technology and clean production. Electrical discharge grinding (EDG) is often used in polycrystalline diamond tools, especially in special shape, thin and fine edge cutting tools. Taking two kinds of grain size of polycrystalline diamond as the research object, taking the machining test and material test as the analysis means, this paper simply compares the surface quality of disc electrode and wire electrode machining, and studies the influence of diamond particle size, electrode polarity and electrode rotation speed on the surface quality and material removal rate of precision electrical discharge grinding polycrystalline diamond. The results show that there is no porous structure, good surface quality and no selectivity in discharge removal when using the negative polarity machining. With the increase of electrode rotation speed, the removal amount of polycrystalline diamond material increases gradually, and the surface roughness of polycrystalline diamond material decreases first, then increases. When the electrode rotation speed reaches 80 m/min, the surface roughness of the polycrystalline diamond sample reaches the minimum value, and the removal amount of polycrystalline diamond material also tends to be stable.

Fabrication of tapered micro rods using twin static wire electrical discharge grinding process

Wire electrical discharge grinding (WEDG) is an attractive alternative to traditional grinding technologies for machining tapered micro rods. However, controlling the shape and diameter of the micro rods can be challenging using conventional WEDG. A new approach of WEDG using two static brass wires (TS-WEDG) is proposed in this paper for reducing the complexity in fabricating tapered micro rods. Following this approach, tapered micro rods can be fabricated by feeding a rotating micro rod along the centreline between two inclined wires. A prototype device for TS-WEDG processing has been developed. This device allows to adjust the position of one wire, thus changing the relative angle and distance between the two wires. This way the size and taper of the micro rods can be controlled. The feasibility of the proposed TS-WEDG approach has been experimentally verified. The results have shown that TS-WEDG is a promising method for efficiently fabricating micro rods having either a positive or a negative taper.

3D Manufacturing Method for Micro Structures by Combining Galvanoplasty and EDM

For decades, micro-EDM has made a great contribution to the miniaturization of products owing to its suitableness for processing surface micro features. However, micro-EDM is usually not considered as a primary option for the manufacture of micro 3D suspended structures. Even though this could be done by making special electrodes or by generating unusual feed paths, the whole process is complex and time-consuming. To cope with these difficulties, with a combination of micro-EDM and micro galvanoplasty, a novel hybrid 3D micro-manufacturing method named manufacture integrating galvanoplasty and electrical discharge (MIGED) is proposed. With the use of MIGED, a target micro component is fabricated layer-by-layer just like 3D printing. During the fabrication process for each layer, micro galvanoplasty is applied to deposit all materials, such as copper and nickel, micro-EDM milling is used to machine the layer’s pattern and block electrical discharge grinding is used for surface planarization. To support the deposition of suspended structures, a certain sacrificial material, such as copper, is introduced and removed after all layers are formed. Feasibility of MIGED was testified on a modified EDM/ECM combined machine. To study the 3D micro-manufacturing capability, a manufacturing test for suspended bridges was carried out. Two micr an’do bridges with a size of 400μm×100μm×50μm and 400μm×100μm×100μm respectively are manufactured and dimensional accuracy is discussed.