Electrical Discharge Grinding Research Articles

Thermal simulation of microelectrode machining process during block electrical discharge grinding

Electrical discharge machining is widely used in aerospace industries, semiconductor applications, micro-electromechanical systems, and other fields of the machining of micro-holes, micro-shafts, and micro-structures due to non-contact stress during the electrical discharge machining process. In the electrical discharge machining process, the machining precision of electrical discharge machining depends on the dimensional precision of the tool electrode, therefore, the machining process of microelectrode has attracted growing concern. In this study, a thermal model of the microelectrode machining process was proposed to simulate the formation process of microelectrode based on the temperature distribution during block electrical discharge grinding of the microelectrode process. According to the microelectrode machining process, the thermal model considers the main influential factors such as random distribution of discharge points, time-dependent discharge channel radius, Gauss heat source, phase transformation latent heat, etc. Through the thermal simulation analysis, the temperature distribution and the dynamic spark-erosion process of the microelectrode based on random repetitive spark discharges were obtained during block electrical discharge grinding of the microelectrode. Besides, it is found that the maximum temperature value and discharge crater volume of the electrode surface fluctuate and gradually decrease with the increase of discharge times. In addition, the effect of pulse width on the machining process of microelectrode was investigated by numerical simulation and block electrical discharge grinding of microelectrode experiment. The results indicated that the crater volume and the maximum temperature value on the surface of the microelectrode increased with the increase of pulse width. The formation process of microelectrode was considered a significant indicator to determine the machining precision and machining efficiency of the electrical discharge machining process.

Micro ECDM process comparison using different tool feed methods of constant gravity and spring-force

Quartz glass has been widely used in multiple frontier fields of science and technology owing to its excellent chemical and mechanical properties, such as optical communication, semiconductor, photovoltaic power, and aerospace. ECDM (electrochemical discharge machining) is a non-traditional material removal process suitable for machining non-conductive materials of high hardness and brittleness. The tool electrode feed method is a key factor affecting the ECDM process. Experimental research was carried out for comparing the conventional gravity feed method and a newly-developed spring-force feed method. Micro tool electrodes of Φ150 µm were fabricated by combining the method of TF-WEDG (tangential feed-wire electrical discharge grinding) and reverse micro EDM (electrical discharge machining). Machined microstructures of blind holes, channels, squares, and patterns were compared by the gravity feed method and the spring-force feed method respectively. The experimental results show that the spring-force feed method can improve the micro ECDM process considering the aspects of dimensional accuracy, overcuts, deteriorated edges, surface topography, and tool wear.

Influence of Different Shaping and Finishing Processes on the Surface Integrity of WC-Co Cemented Carbides

Investigation of four different surface-shaping and finishing sequences is carried out on the surface integrity of a WC-10Co hardmetal grade. The surface conditions include grinding, electrical discharge machining and grinding, followed by mechanical and dry-electrochemical polishing using the DryLyte® technology. The evaluation includes the measurement of roughness, residual stresses, the Vickers hardness, indentation fracture toughness determination and the damage induced by conical contact response. By scanning electron microscopy, a systematic and detailed examination of the residual imprints is carried out to determine the critical loads for damage initiation and development across the different surface conditions. The results indicate that the use of dry-electrochemical polishing enables the attainment of polished surfaces without any corrosive damage to the metallic binder. Moreover, it retains the mechanical attributes reminiscent of the core material, comprising 85% that were initially induced via grinding.

Research on Geometric Constraint Strategies for Controlling the Diameter of Micro-Shafts Manufactured via Wire Electric Discharge Grinding.

Micro-tools comprising difficult-to-machine materials have seen widespread application in micro-manufacturing to satisfy the demands of micro-part processing and micro-device development. Taking micro-shafts as an example, the related developmental technology, based on wire electric discharge grinding (WEDG) as the core method, is one of the key technologies used to prepare high-precision micro-shafts. To enable efficient and high-precision machining of micro-shafts with target diameters, instead of performing multiple repeated on-machine measurements and reprocessing, a geometric constraint strategy is proposed based on the previously introduced twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG). This strategy encompasses the tool setting method, tangential feed distance compensation, and an equation that establishes the relationship between tangential distance and diameter variation. These components are derived from a key points analysis of the geometric constraints. The micro-shafts with diameters of 50 µm and consistencies of ±1.5 µm are repeatedly processed. A series of micro-shafts with diameters ranging from 30 µm to 120 µm achieve geometric constraints with a diameter accuracy of ±2 µm, accompanied by the complete continuous automation of the entire process. Accordingly, it can be concluded that the geometric constraint strategy is flexible and stable and can be controlled with high precision in the TMTF-WEDG process.

Experimental Investigation of the Effects of Machining Parameters on the Performance of Form-Cutting Tools Manufactured by Wire Electrical Discharge Machining (WEDM) and Grinding Processes.

In this research, a comparison between two methods of grinding and WEDM and the chip formation of each form tool was studied through a set of designs of experiments. A multi-functional form tool with different cutting-edge shapes was designed to compare different production methods, and a grinding machine and a five-axis wire-cutting machine were made. The form tools by the wire cutting method were made with three different machining states, rough, semi-finish, and finish. The results of the experimental test showed that the chip formation of the finished surface of the wire cut tool was close to the ground tools. Additionally, the tool life in wear generation was assessed, revealing that the tool generated through the wire-cutting method with three passes exhibited superior performance compared to alternative approaches. Furthermore, employing the wire-cutting technique with high surface finishing yielded optimal outcomes for producing form-cutting tools featuring complex profiles.

Experimental study on polishing of fluid magnetic abrasives for the wire electrical discharge grinding surface of micro-shafts

Experimental study on polishing of fluid magnetic abrasives for the wire electrical discharge grinding surface of micro-shafts

A REVIEW ON ELECTRICAL DISCHARGE GRINDING: CURRENT STATUS AND FUTURE PERSPECTIVES

Electrical discharge machining (EDM) is widely applied for machining difficult-to-cut materials in mold and die industries. However, the major limitations associated with the EDM are low productivity and poor surface integrity of the machined surfaces. In recent years, several developments have been applied to overcome such limitations of EDM. Electrical discharge grinding (EDG) is a hybrid machining process that simultaneously involves the spark erosion action of EDM and the mechanical abrasion action of the grinding wheel for the material removal purpose. The rotating motion of the grinding wheel also contributes to the easy removal of debris particles, thereby improving the material removal. It is evident from the literature that the rotating motion of the grinding wheel enhances the flushing mechanism resulting in better performance of the process. This paper aims to present a comprehensive review of the research carried out in EDG, highlighting the result of the experimental, modeling, and optimization techniques applied in this area. Initially, the background of EDM and the need for hybrid EDM processes have been presented. Then, a few hybrid EDM processes have been discussed, addressing their advantages and limitations. Further, the concept of EDG and electrical discharge diamond grinding (EDDG) has been discussed, along with the classification of the EDDG process. Finally, this paper explores the current research status and future research perspective in the area of EDG and EDDG processes.

Fabrication and capillary characterization of multi-scale microgroove wicks for ultrathin phase-change heat transfer devices

Multi-scale microgroove wicks (MWs) with the features of micro fins, micropillars, and reentrant cavities were fabricated for the application in ultrathin phase-change heat transfer devices. Wire electrical discharge machining (WEDM), electrical discharge shape machining (EDSM), micro-milling, and grinding were used to fabricate MWs with the same design parameters. The structural features of the MWs were characterized by SEM and their capillary performances were evaluated through the capillary rise test. The machining methods affected the structure characteristics of MWs greatly, i.e., MW fabricated by the combination of WEDM and EDSM (MW-WE) maintained the best forming shape, while MW fabricated by micro-milling deformed severely and some micropillars even disappeared. The capillary rise tests were conducted with ethanol and acetone as the working fluid, respectively. MWs showed similar capillary performances under both working liquids. MW-WE maintained the best capillary performance while MW fabricated by micro-milling performed worst. The wicking height and capillary parameter of MW-WE achieved 60.4 mm and 1.57 μm, respectively, which were about twice and 4.62 times that of MW fabricated by micro-milling. The superior capillary performance of MW-WE was attributed to the fluent microgrooves, capillary value effect induced by reentrant cavities, and rough surfaces.

Advancements in abrasive electrical discharge grinding (AEDG): A review

A hybrid machining process that combines the working principles of conventional abrasive grinder and an electrical discharge machine, mentioned as Abrasive Electrical Discharge Grinding (AEDG) is being studied. It exploits the benefit of both the machining process Abrasive Grinding (AG) and Electrical Discharge Machining (EDM). The review understands the need of such a machining process, its working principles, basic designs and more importantly, how different process parameters affect the machining performance. In this paper, three different designs of the tool is understood. Later, based on different experimental and study reports, effects of process parameters on the machining is learned.

Dual-wafer intergrinding thinning by bipolar-discharge EDM with a capacity-coupled pulse generator considering large gap capacitance and minimization of discharge energy

The noncontact electrical discharge grinding technique has the potential to effectively grind thin, increasingly large-diameter wafers. This study proposes a bipolar electrical discharge machining (bipolar-EDM) method to realize the intergrinding of dual wafers, in which both wafers serve as the working electrode. A capacity-coupled (CC-type) pulse generator generates regular and identical bipolar discharges, ensuring symmetrical and stable removal of both wafers. Thus, both the energy efficiency and wafer thinning yield are doubled. The process characteristics are evaluated through equivalent circuit analysis and experiments, demonstrating that two thinned wafers exhibit high consistency in surface integrity and material removal rate (MRR). Moreover, the dual-wafer system causes an increase in the circuit resistance and gap capacitance, leading to a much lower discharge energy. This is beneficial for precision wafer grinding and thinning by electrical discharge machining (EDM) while keeping damage minimal. As a result, two Φ20 mm 4H–SiC wafers were thinned simultaneously with a maximum thinning rate of 3 μm/min. A mirror-like smooth surface (Ra < 80 nm) was obtained under finishing conditions, demonstrating its capability for precise wafer processing.

Experimental study on dressing concave trapezoidal diamond grinding wheel by electrical discharge grinding method

Electrical discharge grinding (EDG) method is proposed for dressing bronze bonded diamond grinding wheel for the first time. The advantage of this dressing method is that it can realize the discharge removal of non-conductive diamond abrasive particles and greatly improve the dressing efficiency. It is suitable for dressing coarse-grained complex forming grinding wheel. The material removal mechanism in EDG dressing is deeply analyzed, and a three-dimensional heat conduction model in the discharge process is established. The temperature field distribution in bronze and diamond under corresponding discharge parameters is obtained by numerical simulation, and the grinding depth is optimized based on the softening depth of diamond. The dressing scheme of quickly removing the rectangular block area first and then approaching layer by layer according to the design profile is formulated. The high-precision concave isosceles trapezoidal grinding wheel is dressed by using the optimized machining parameters. Finally, the dressing accuracy is evaluated by grinding the graphite plate. The detection results show that the dimensional errors of the upper and lower lines are all within 5 μm, the dimensional error of the height is 9 μm. The maximum error of the angle between the two waist is 0.33°. The minimum transition arc radius between waist and lower line is 202 μm. The straightness errors of the lower line and the two waist oblique lines are less than 7 μm. The profile error at the transition between waist and lower line is less than 62 μm.

Effect of spattering on formation mechanisms of metal matrix composites in laser powder bed fusion

Metal matrix composites (MMCs) with specially designed structures can be fabricated by laser powder bed fusion (LPBF) time-efficiently and cost-effectively, but reinforcements pose enormous challenges to the technique. In this work, the effect of reinforcement on the formation of MMCs in LPBF is studied by taking diamond grinding wheels (GWs) as an example. Based on the balling phenomenon observed in the LPBF process, the formation characteristics of GWs such as surface morphology, porosity, and flexural strength are investigated. The balling size is increased with an increase in the linear energy density of the laser beam due to more intense diamond spattering. The acting forces applied by the plume and ambient gas flow generated around the melt pool on a diamond grain are analyzed to investigate the generation of diamond spatter. For MMCs with coarse reinforcements, spattering is the dominant cause of the balling phenomenon due to the induced discontinuous melt tracks and uneven powder layers. Furthermore, the performance of a cup-type diamond GW fabricated by LPBF in the electrical discharge grinding (EDG) process of reaction-bond silicon carbide (RB-SiC) is evaluated by the surface and subsurface quality. The grinding process removes the resolidified layer of RB-SiC induced during the electrical discharging process and suppresses crack generation in the subsurface. The results presented in this study reveal the influence of diamond grains on the formation mechanism of GWs, which is also suitable for MMCs with coarse reinforcements.

Influence of the punch with concave cutting-edge on the blanking force in micro punching process

Micro blanking machining is a promising manufacture technology to realize mass production of micro parts efficiently. In the process of blanking, the blanking force is significant to the punch, die, and sheet workpiece. In order to investigate the influence of cutting-edge shape of the punch on the micro blanking process, a self-developed micro combined EDM and blanking machine tool is applied in this paper. A punch with concave cutting-edge is capable to be fabricated online through a series of processing based on micro EDM: 3D milling, wire electrical discharge grinding and reverse EDM copy machining techniques. Then the punch and die are accurately matched online due to the preparation of them in the same coordinate system. Micro blanking parts and punching parts with the complex cross-sectional shape is obtained by using the online fabricated punch with flat cutting-edge and concave cutting-edge respectively in the workpiece of stainless steel SUS304 foil. The characteristic of blanking force varying with time indicates that the blanking force is significantly reduced in the case of concave cutting-edge, meanwhile, both blanking parts and punching parts have the high quality.

Prediction Model of Surface Roughness in Dry Electrical Discharge Grinding of Metal Ceramics

Prediction Model of Surface Roughness in Dry Electrical Discharge Grinding of Metal Ceramics

RESEARCH OF THE CUTTING MECHANISM AT ELECTRICAL DISCHARGE GRINDING

The paper presents the results of a study of the cutting mechanism during electrical discharge grinding of hard alloys. The cutting mechanism during electrical discharge grinding was studied using mathematical modeling. By means of geometric modeling, a method of grinding cup wear was developed. The functional dependence of the diamonds use factor in the Kw wheel on the technological parameters of processing, wear and tool characteristics were determined. Analysis of the results of the study shows that an increase in efficiency at electrical discharge grinding can be achieved by reducing the wear of S, and by corresponding variation in the concentration of diamonds and technological modes of processing.

Non-contact grinding/thinning of silicon carbide wafer by pure EDM using a rotary cup wheel electrode

The significantly increased stability of third-generation semiconductors, both mechanically and chemically, presents a significant challenge to traditional wafer grinding. This study develops pure electrical discharge machining as an alternative for non-contact wafer grinding and thinning to achieve high precision and low cost. This method employs a copper-made rotary cup wheel as the tool electrode to replace the conventional diamond wheel to realize electrical discharge grinding. A prototype is built to evaluate the new process with single-crystal SiC. Aiming at ultra-precision machining, the material response of SiC to both single and consecutive discharge is elucidated. The influencing mechanism of pulse conditions on hard, brittle crystalline SiC material is demonstrated via experiments and simulation. Further, the material removal behavior, grinding stability, surface integrity, wafer shape accuracy, and process-induced subsurface damage are comprehensively investigated via single and consecutive discharge experiments under various conditions. In addition, the extreme precision that is achievable by contemporary EDM technology is explored. As a result, a 30 μm thin Φ20 mm SiC wafer with a subsurface damaged layer <1 μm was obtained, showing the potential of EDM for the processing of third-generation semiconductor wafers.

Development of Centreless Electric Discharge Grinding Machining Process and Optimization of Process Parameters

Aims &amp; Objective: Producing thin walled rotationally symmetrical parts of difficult-to-machine materials by electrical discharge machining is an evolving field of research. Poor heat transmissivity, high hot strength and in-process deflection of thin walled Inconel 600 parts puts great challenge for its processing by conventional machining methods. Methods: In this study a novel hybrid process called centreless electric discharge grinding(CEDG) is employed for machining of Inconel 600 tubes using rotating disc wheel electrode to improve process parameters. This paper details about the experimental findings of the influence of four process parameters viz. pulse on time, peak current, gap voltage, and duty cycle on the responses viz. average material removal rate (MRR) and average surface roughness(Ra). Response surface method’s (RSM) central composite design was implemented to determine the effects of parameters on responses. Analysis of variance (ANOVA) techniques were employed to establish the adequacy of the mathematical models and to analyse the significance of regression coefficients. RSM’s desirability approach was used to solve the multi-response optimization. Results: It was clearly noticed that the peak current and gap voltage were the most influential parameters to affect the MRR and surface roughness. Maximum average MRR of 473 mg per min. was achieved at pulse on time 60µs, peak current 25 amps, gap voltage 40 V, at duty cycle of 8 while minimum average surface roughness of 8.4 µm Ra was obtained at pulse on time 40µs, peak current 15 amps, gap voltage 40 V, and duty cycle 6. Conclusion: Confirmation run was conducted by adjusting the variables at optimal level within the selected range. It was concluded that optimum level of variables can be determined for optimized responses prior to conduct of experiment.

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.