Traditional Electrical Discharge Machining Research Articles

PERFORMANCE EVALUATION AND ECONOMIC ASSESSMENT IN ELECTRICAL DISCHARGE MACHINING OF SS316 USING GRAPHITE POWDER DISPERSED IN BIODEGRADABLE PALM OIL DIELECTRIC

In today’s rapidly evolving manufacturing industry, researchers and engineers are constantly seeking innovative methods to improve machining processes. One such area of interest is the use of electrical discharge machining (EDM) for difficult-to-machine metals like SS316. This research compares the performance and economic aspects of traditional EDM and powder-mixed EDM when machining SS316 using copper electrode. Graphite powder dispersed in biodegradable palm oil is investigated as a dielectric media with the aim of enhancing EDM performance. According to the findings, the analysis of the cutting performance of different machinability aspects revealed that using graphite powder mixed with palm oil as a dielectric in EDM outperformed conventional EDM relating to material removal, surface finish, surface hardness, electrode wear rate and hole overcut. The flushing condition and unique properties of graphite powder and palm oil, such as cooling, and thermal conductivity, contributed to the improved performance observed in EDM processes. These findings highlight the potential of graphite powder mixed with palm oil as a promising alternative dielectric in EDM, offering enhanced machining capabilities and improved surface quality. The total machining expenditure per part under PMEDM (INR 505.50) is lowered by 9.2% than expenditure under conventional EDM (INR 525). The surface microhardness of the machined component attained using graphite powder-mixed EDM is enhanced in comparison to that achieved using standard EDM due to the creation of a carbon-rich re-solidified layer.

Micro-electrical discharge machining of nitinol alloy using coated electrode and multi-energy field

ABSTRACT Nitinol alloys are widely utilized across various fields owing to their exceptional elasticity and shape memory characteristics. Their low thermal conductivity, high strength, and high toughness pose significant challenges to conventional machining technologies. To address these challenges, several non-conventional machining processes such as electrical discharge machining have been developed. This study introduces an innovative approach that combines the use of insulated coated electrodes with multi-energy field-assisted electrical discharge machining to improve the application of electrical discharge machining in machining deep microporous. We investigated the effects of the insulated electrode and multi-energy field on surface morphology, taper accuracy, diameter cutting, and the thickness of the recast layer in detail. The findings suggest that the insulated coated electrode combined with multi-energy field-assisted electrical discharge machining achieves better taper accuracy and lower diameter cutting, resulting in a smoother surface and a more uniform, thinner recast layer compared to traditional electrical discharge machining.

Experimental optimization of machining GH4145 by atomizing discharge ablation milling

Atomizing discharge ablation milling (ADAM) technology is an efficient discharge machining technology derived from the traditional electrical discharge machining (EDM) method, which can be used to efficiently machine hard-to-machine materials such as nickel-based superalloy. In this present, the performance of machining nickel-based superalloy GH4145 by ADAM and Air near-dry EDM were compared, and the experimental results showed that the material removal rate (MRR) obtained by ADAM was nearly double that of the latter. A single-factor experiment were conducted to investigate the effect of electrode rotation speed on ADAM’s processing performance. Subsequently, an orthogonal experimental method was used to design the experiment. The signal-to-noise ratio analysis method was used to systematically study the performance characteristics of ADAM, including the influence of atomization amount, oxygen pressure, discharge current, duty ratio on MRR and tool electrode relative wear rate (TWR). The results showed that discharge current was the most influential processing parameter on MRR and TWR. Finally, the optimal combination of processing process parameters that met the requirements of various processing effect evaluation indicators were obtained and the correctness of the single objective optimization results was verified through experiments.

The evaluation of machining performances and surface roughness of TZM-molybdenum superalloy processed by silicon carbide powder mixed EDM process using RSM and ANOVA

In the present era, the concept of Industry 4.0 plays a significant part in improving the efficiency, quality, and utilization of resources by automation and enabling intelligent operations in manufacturing processes. As a result, there is a requirement to develop an environment that improves efficiency as well as quality in order to accomplish net zero in manufacturing. The objective of powder mixed electric discharge machining (PMEDM) is to enhance the quality of the surface and machining efficiency of traditional electrical discharge machining. The PMEDM method was applied to TZM-molybdenum superalloy in the present investigation by incorporating silicon carbide particles into the dielectric medium. Powder concentration, peak current, pulse on time, pulse off time, and gap voltage were the considered input variables for the investigation. The impacts of the input variables on the surface of the specimen’s roughness and the rate of material removal (MRR) were examined. The experiment model was built using response surface methodology. To find out if the input factors were significant with regard to each response, an analysis of variance (ANOVA) was performed. Powder concentration, pulse current, gap voltage, and pulse on time are found to be the important input variables for both surface roughness and MRR based on ANOVA analysis.

Mathematical Models and System of Intelligent Servo for High-Efficiency Electrical Discharge Assisted Arc Milling on Difficult-to-Cut Materials

Difficult-to-cut materials, such as superalloys and titanium alloys, have been increasingly used in aerospace and other fields. However, commonly used mechanical milling methods for difficult-to-cut materials have problems, including low processing efficiency and severe tool wear. Electrical discharge assisted arc milling (EDAAM) is a novel high-efficiency machining method proposed by the authors to solve these processing problems. The machining efficiency achieved by EDAAM when processing difficult-to-cut materials is much higher than that achieved by mechanical milling and conventional electrical discharge machining (EDM) milling. However, if EDAAM adopts the traditional EDM servo control method, it will easily form deep and large discharge craters on the surface of the workpiece, which may lead to high machining errors and cause the workpiece to be scrapped. To ensure normal processing, low-energy discharge parameters that may reduce the processing efficiency have to be adopted. To address the above issues and achieve the optimal machining condition of difficult-to-cut materials, mathematical models and system of intelligent servo for EDAAM are proposed. An EDAAM discharge information dataset is obtained, and the intelligent recognition and classification method for discharge states is proposed. The EDAAM intelligent servo control system is proposed based on mathematical models created. The experimental results of superalloy Inconel 718 by EDAAM show that, compared with the nonintelligent servo control system, the intelligent servo control system can increase the material removal rate by up to ten times, reduce the relative electrode wear rate by 37%, and avoid the scrapping of the workpiece.

Research on Electrostatic Field-Induced Discharge Energy in Conventional Micro EDM.

The electrostatic field-induced electrolyte jet (E-Jet) electric discharge machining (EDM) is a newly developed micro machining method. However, the strong coupling of the electrolyte jet liquid electrode and the electrostatic induced energy prohibited it from utilization in conventional EDM process. In this study, the method with two discharge devices connecting in serials is proposed to decouple pulse energy from the E-Jet EDM process. By automatic breakdown between the E-Jet tip and the auxiliary electrode in the first device, the pulsed discharge between the solid electrode and the solid workpiece in the second device can be generated. With this method, the induced charges on the E-Jet tip can indirectly regulate the discharge between the solid electrodes, giving a new pulse discharge energy generation method for traditional micro EDM. The pulsed variation of current and voltage generated during the discharge process in conventional EDM process verified the feasibility of this decoupling approach. The influence of the distance between the jet tip and the electrode, as well as the gap between the solid electrode and the work-piece, on the pulsed energy, demonstrates that the gap servo control method is applicable. Experiments with single points and grooves indicate the machining ability of this new energy generation method.

The role of various dielectrics used in EDM process and their environmental, health, and safety issues

Electrical discharge machining (EDM) is one of the well-known newer machining processes which are used to machine ceramics, alloys, composites, and hard metals. Besides being a process with lower material removal rate (MRR), it also releases toxic vapors & fumes, and aerosols due to the thermal decomposition of the dielectrics. Moreover, disposal of these toxic and non-biodegradable dielectric wastes also poses a major challenge to the environment. This article discusses the issue of noxious fumes that are released during machining, as well as the use of alternative dielectric mediums that can be utilized in place of traditional EDM oils.

Elucidating Powder-Mixed Electric Discharge Machining Process, Applicability, Trends and Futuristic Perspectives

Since the inception of electric discharge machining (EDM), it has facilitated the production industries, for instance, die & mold, automotive, aerospace, etc., by providing an effective solution for machining hard-to-cut materials and intricate geometries. However, achieving high machining rates and a fine surface finish is an inherent issue with the traditional EDM process. The emergence of the powder mixed electric discharge machining (PMEDM) process has not only provided the opportunity for enhancing productivity and surface finish but also opened a window for its potential application in surface modification/coating of biomaterials. The process incorporates simultaneous machining and coating of bioimplants, i.e., lacking in the already available chemical and physical coating methods while requiring costly post-treatment procedures. This study comprehends the influence of powder characteristics and EDM process parameters on the performance parameters. The impact of tool electrodes and additive powders on the machined and coated surface of commonly used biomaterials. Furthermore, the study depicts the most frequently used methods for optimizing the PMEDM process, future research directions, challenges, and research trends over the past decade.

Surface integrity of Ti-6Al-4V alloy in hybrid electrical discharge machining processes

Titanium alloy is one of the difficult-to-machine materials. The final conditions of the machined surface of this alloy are influenced by electro-discharge machining. High temperatures and thermal cycles in machining operation induce undesirable alterations in the surface quality of Ti-6Al-4V. One of the ways to improve the negative effects of electrical discharge machining is to use hybrid methods. There is no comprehensive research on the effect of hybrid electrical discharge machining process on the surface integrity of the Ti-6Al-4V alloy. In this paper, hybrid electrical discharge machining techniques including ultrasonic-assisted electrical discharge machining, powder-mixed dielectric electrical discharge machining using Al2O3 nanopowders and powder-mixed dielectric combined with ultrasonic-assisted electrical discharge machining, were used for processing of this alloy. The hybrid electrical discharge machining processes were evaluated by basic specifications of surface integrity including surface cracks, heat affected area, residual stress, and corrosion resistance. It was found that in powder-mixed dielectric combined with ultrasonic-assisted electrical discharge machining process, developed microcracks were very low and this process developed a thinner heat-altered layer, compared to traditional electrical discharge machining process, which produced a thicker heat-altered layer. The findings also, demonstrated that ultrasonic waves have reduced residual stresses compared to other methods and its stress diagram was distinct in comparison with the other processes. The corrosion rate of samples machined by electrical discharge machining process was higher than other hybrid processes; in powder-mixed dielectric electrical discharge machining process, the machined samples had the highest corrosion resistance.

A highly energy-efficient milling of Inconel 718 via modulated short electric arc machining

An excellent and advanced manufacturing method named modulated short electric arc machining (M-SEAM) was proposed in this study to solve the problems of low machining efficiency and high specific energy consumption (SEC) for difficult-to-machine materials in the traditional electric discharge machining (EDM) and electric arc machining (EAM) process.The discharge channel is established by the collision between the electrode and the workpiece. The arc spreads and moves as the electrode rotates. Moreover, the energy balance equation of the modulated arc was established, which revealed that the volt-ampere characteristic is resistive when the frequency of pulse voltage tends to infinity in the steady state, the arc had a large relative thermal inertia, and two stable operating points were analyzed. M-SEAM processing was performed using graphite and Inconel 718 as electrode and workpiece materials, respectively. The results showed a maximum MRR of 49,020 mm3/min, and the relative electrode wear rate (REWR) and SEC were limited to 0.92% and 50.21 kJ/cm3, respectively. The peak current was 1940 A, and the maximum discharge time for a single arc was 328.56 ms.

A comprehensive review on metallic implant biomaterials and their subtractive manufacturing.

There is a tremendous increase in the demand for converting biomaterials into high-quality industrially manufactured human body parts, also known as medical implants. Drug delivery systems, bone plates, screws, cranial, and dental devices are the popular examples of these implants - the potential alternatives for human life survival. However, the processing techniques of an engineered implant largely determine its preciseness, surface characteristics, and interactive ability with the adjacent tissue(s) in a particular biological environment. Moreover, the high cost-effective manufacturing of an implant under tight tolerances remains a challenge. In this regard, several subtractive or additive manufacturing techniques are employed to manufacture patient-specific implants, depending primarily on the required biocompatibility, bioactivity, surface integrity, and fatigue strength. The present paper reviews numerous non-degradable and degradable metallic implant biomaterials such as stainless steel (SS), titanium (Ti)-based, cobalt (Co)-based, nickel-titanium (NiTi), and magnesium (Mg)-based alloys, followed by their processing via traditional turning, drilling, and milling including the high-speed multi-axis CNC machining, and non-traditional abrasive water jet machining (AWJM), laser beam machining (LBM), ultrasonic machining (USM), and electric discharge machining (EDM) types of subtractive manufacturing techniques. However, the review further funnels down its primary focus on Mg, NiTi, and Ti-based alloys on the basis of the increasing trend of their implant applications in the last decade due to some of their outstanding properties. In the recent years, the incorporation of cryogenic coolant-assisted traditional subtraction of biomaterials has gained researchers’ attention due to its sustainability, environment-friendly nature, performance, and superior biocompatible and functional outcomes fitting for medical applications. However, some of the latest studies reported that the medical implant manufacturing requirements could be more remarkably met using the non-traditional subtractive manufacturing approaches. Altogether, cryogenic machining among the traditional routes and EDM among the non-traditional means along with their variants, were identified as some of the most effective subtractive manufacturing techniques for achieving the dimensionally accurate and biocompatible metallic medical implants with significantly modified surfaces.

Surface Roughness in Abrasive Mixed Rotary Electrical Discharge Machining: Experimental Approach

This research study focused on the alliance of blending silicon carbide powder of size 60 µm into dielectric oil (kerosene) with electrode revolution in electrical discharge machining of D3 steel using electrode made of copper. Peak current, pulse on-time, and electrode revolution were picked as machining variables to check their influence on the surface roughness of the workpiece. The full factorial experimentation was performed with 27 experimental runs. The analysis of variance result indicated electrode revolution as the most influential variable with a percentage aid of 32.75%, followed by peak current and pulse on-time, which accounted for 28.98 and 6.09%, respectively. The decrement in surface roughness was recorded at higher electrode rotational speed. The field emission scanning electron microscopy of machined samples was performed and results showed significant improvement on surface characteristics. The surface finish improved from 12.36 µm to 10.32 µm in silicon carbide powder blended rotational electrical discharge machining over traditional electrical discharge machining. The minimum surface roughness achieved was 4.81 µm at optimal conditions.

Microcosmic mechanism of die-sinking mixed-gas atomization discharge ablation process on titanium alloy

In order to reveal the microscopic mechanism of the titanium alloy die-sinking mixed-gas atomization discharge ablation process (MA-DAP), a single-pulse discharge test was performed using a needle electrode discharge device. According to the step-like characteristic of the single discharge waveform, the micro-erosion process could be divided into four stages: preparation for oxidation ablation; oxidation occurrence and oxide layer generation; oxidation-ablation dynamic balance and oxide layer prototype formation; and oxidation-ablation termination and integral oxide layer formation. Theoretical analysis showed that the violent exothermic oxidation reaction between the oxygen medium and the high-temperature melting material introduced a large quantity of external chemical energy into the sparking region. Fast vaporization and explosion of the atomized medium after heating gave MA-DAP high particle removal power. The technological experimental results showed MA-DAP provides high material removal efficiency and strong deep-hole machining ability. The depth-to-diameter ratio of the specially shaped titanium alloy MA-DAF blind hole was 11 times that from traditional electrical discharge machining, while the cross-sectional hardness can be reduced by 45%.

Comparative Analysis of Dry-EDM and Conventional EDM in machining of Hastelloy

Dry EDM may be a modification of the traditional electrical discharge machining (EDM) process during which the liquid dielectric is replaced by a gaseous medium. High velocity gas is supplied through it into the discharge gap. The flow of high velocity gas into the gap facilitates removal of debris and prevents excessive heating of the tool and work piece at the discharge spots. it's now known that aside from being an environment–friendly process, other advantages of the dry EDM process are low tool wear, lower discharge gap, lower residual stresses, smaller white layer and smaller heat affected zone.[1]
 Keeping literature review into consideration, during this research, an effort has been made by selecting compressed gas as a dielectric medium, with Hastelloy as a work piece material and copper as a tool electrode. Conventional experiments were also performed. Experiments are performed using Taguchi DoE orthogonal array to watch and analysis the consequences of various process parameters to optimize the response variables like material removal rate (MRR) and gear wear rate (TWR).

Study on the machining characteristics of high-efficiency mixed gas atomized discharge ablation process of titanium alloy

Titanium alloy is widely used in aerospace and other industry fields because of its excellent physical and chemical properties. However, the fabrication process is still a challenge for the traditional machining processes due to the ultra hardness and chemical reactivity properties of titanium alloy. Electrical discharge machining (EDM) is a significant processing approach to machine titanium alloy regardless of hardness, while accompanied by disadvantages such as electrode wear and low machining efficiency. This paper proposed a novel mixed-gas atomization discharge ablation process (MA-DAP) method for high-efficiency machining titanium alloy with low tool wear. An atomized dielectric formed by a mixed gas, which mainly composed of oxygen and supplemented by nitrogen, and water medium was used in the machining process. The exothermic oxidation between the oxygen component in the atomized dielectric and high-temperature molten material activated by spark discharges could multiply accelerate material removal of workpiece. The explosive effect generated by the vaporization expansion of the water component in the dielectric would improve the machining quality and the processing capability of large depth-to-diameter ratio holes. To investigate the machining characteristics of the new approach, comparative experiments were conducted in terms of material removal rate, electrode relative wear rate, machining accuracy, surface morphology, and recast layer. The experimental results showed that, compared with traditional EDM, the material removal rate of MA-DAP was dramatically increased by more than an order of magnitude, and other technological indexes are greatly improved simultaneously. A deep-shaped blind hole with a depth-to-diameter ratio greater than 12 was obtained by the MA-DAP.

Rotating short arc EDM milling method under composite energy field

• A new EDM milling method with rotating short arcs under composite energy field was proposed. • A mathematical model to describe the trajectory of particles in the composite field was established. • Rotating short arc was generated by the Lorentz force, the electrical force and the high-speed rotation of electrode. • The MRR of rotating short arc machining is increased by 46 % compared with traditional EDM. • An increase in the strength of the magnetic field increases the MRR and decreases the TEWR. Electrical discharge machining (EDM) is a rapidly developing technique amongst nontraditional techniques. However, low processing efficiency significantly hinders its application in industry. This study proposes a new high-speed EDM milling method using rotating short arcs under a composite energy field. By the combined effect of the Lorentz force, electric field force, and high-speed rotation of the tool electrode, rotating short arcs are generated between the tool electrode and the workpiece, which in turn provide constant erosion of materials. The proposed method can increase the discharge energy density by converging the electric arcs through the composite energy field, and increase the energy obtained by the workpiece. By this means, it improves the material removal rate. During processing, a portion of debris is attracted by the magnetic field and adheres to the end surface of the electrode, which can protect the electrode and reduce the electrode wear rate. Compared with traditional EDM, the material removal rate of the rotating short arc milling was increased by 46 %, while the tool electrode wear rate decreased by 62 %. Furthermore, an increase in the strength of the magnetic field increases the material removal rate of the rotating short arc milling and decreases the tool electrode wear rate and surface roughness. Therefore, high-efficiency and high-quality EDM milling can be achieved by using the proposed method.

Experimental investigation for sustainable electric discharge machining with Pongamia and Jatropha as dielectric medium

ABSTRACT This research work is a feasibility analysis for the newly developed dielectric based on non-edible vegetable oil, Pongamia (Pongamia pinnata) and Jatropha (Jatropha curcas) for electrical discharge machining (EDM). The traditional EDM uses kerosene as a dielectric with poor safety and unfriendly environmental consequences. In addition to eliminating the risks from kerosene to operator and atmosphere, bio-dielectric can also enhance the machining performance of traditional sinking EDM. As input parameters peak current, gap voltage, and pulse on time were selected and one variable at a time (OVAT) strategy was used to design experimental plans to investigate the application of the newly proposed bio-dielectric. In addition, the mechanism of material removal with Pongamia and Jatropha bio-dielectric is also discussed in detail. The results obtained have shown that the performance of the proposed Pongamia and Jatropha is better than commercially available kerosene oil for MRR, lower EWR and SR, and machined specimens with better surface integrity. It is proposed that dielectric based on Pongamia and Jatropha oil may be used as a hydrocarbon-based dielectric alternative to improve the sustainability of the EDM process.

Utilizing a porous-electrode for the flushing fluid in electrical discharge machining

In traditional electrical discharge machining (EDM), abnormal machining phenomena, such as short circuits and arc drawing, are often induced by inter-electrode erosion particles. These result in low machining efficiency and poor surface quality. In this paper, a porous electrode is prepared by high-temperature sintering. The dielectric liquid flows down through the pores in the electrode and then out of its sides to flush the eroded particles rapidly out from between the electrodes, thus reducing the occurrence of these abnormal machining phenomena in EDM and improving machining efficiency. A computational fluid dynamics simulation was used to analyze and compare the flow between the electrodes and the particles flushed out by a single-channel electrode and a porous electrode. The results show that the flow field for the porous electrode is distributed, and it can effectively and quickly remove eroded particles out of the inter-electrode discharge gap. Consistent with the simulation, the experimental results show that porous-electrode EDM can achieve a higher machining efficiency than traditional EDM, and the machining speed is not affected by the machining depth. Moreover, the use of a flushing fluid can avoid the generation of carbon pillars. With the increase of the flow rate of the flushing fluid, due to the dual effects of the flushing fluid reducing the concentration of eroded particles and the flushing fluid interfering with the plasma discharge channel, the material removal rate has a double peak.

Thermophysical-Based Modeling of Material Removal in Powder Mixed Near-Dry Electric Discharge Machining

Electrical discharge machining (EDM) is a non-conventional method of machining hard materials with intricate shapes. Near-dry electric discharge machining (ND-EDM) is an advanced method of EDM which is eco-friendly and is more efficient in terms of material removal rate (MRR) than traditional EDM. In this research, an approach has been made to perform a new electrical discharge machining operation on EN-31 steel which utilizes metallic powder as an additive along with a gaseous dielectric (for example air) in ND-EDM. This advanced method of machining is known as powder mixed near-dry EDM. This study involves modeling for output process parameter—Material Removal Rate. The mathematical model was developed using the approach of Gaussian heat distribution. FEM modeling was done on ANSYS WORKBENCH 16.0 module. The experiments were performed and comparative study was done between the results obtained by modeling and experiments. The maximum experimental MRR was 7.68 mm3/min, and the error percentage between experimental, mathematical and FEM was under 30%. It was concluded that the modeling was done successfully and results obtained do comply with the methodology of the research.

Research on discharge characteristics of working mediums of electric discharge machining

Successful surface modification can be obtained by Electrical Discharge Machining (EDM). In this work the discharge characteristics in misted deionized water and near-dry powder-mixed medium was studied systematically, as well as the microstructure and properties of electrical discharge strengthened layers on TC4 alloy. It indicates that the breakdown voltage of EDM in misted deionized water medium has been reduced to about 1/3 than in air medium. In near-dry powder-mixed medium, it is reduced to about 1/9, because the discharge gap is much larger than that of other mediums. In other words, a stable discharge can be obtained by larger discharge gaps and lower pulse energy than traditional EDM surface strengthening method, which leads to more stable discharge process. Experimental researches show that dense and sound combination with matrix like, multiphase hybrid intensification and chrysanthemum petal-like microstructure of strengthened layers can be observed in the near-dry powder-mixed medium. Meanwhile, it is found that the microhardness of the strengthened layer is up to about 1200 HV, which is four times higher than the base material.