Powder Mixed Electrical Discharge Machining Process Research Articles

Multi-Objective Optimization using Taguchi and Grey Relational Analysis on Machining of Ti-6Al-4V Alloy by Powder Mixed EDM Process

Powder mixed electric discharge machining (PMEDM) is hybrid manufacturing process used in various industries for machining of advanced materials with complex profiles. PMEDM enhances the machining capabilities of the EDM process by mixing the conductive powder to the dielectric fluid. In this present work experimental design is performed using Taguchi L27 orthogonal array combined with grey relational analysis is used to determine the optimal set of process parameters for multi-objective responses on machining of titanium alloy. Pulse on time, peak current, pulse off time and concentration of graphite powder mixed in the dielectric medium are taken as input process parameters to analyze on the performance measures in terms of surface roughness and material removal rate

Assessing the effects of different dielectrics on environmentally conscious powder-mixed EDM of difficult-to-machine material (WC-Co)

Electrical discharge machining (EDM) is a well-known nontraditional manufacturing process to machine the difficult-to-machine (DTM) materials which have unique hardness properties. Researchers have successfully performed hybridization to improve this process by incorporating powders into the EDM process known as powder-mixed EDM process. This process drastically improves process efficiency by increasing material removal rate, micro-hardness, as well as reducing the tool wear rate and surface roughness. EDM also has some input parameters, including pulse-on time, dielectric levels and its type, current setting, flushing pressure, and so on, which have a significant effect on EDM performance. However, despite their positive influence, investigating the effects of these parameters on environmental conditions is necessary. Most studies demonstrate the use of kerosene oil as dielectric fluid. Nevertheless, in this work, the authors highlight the findings with respect to three different dielectric fluids, including kerosene oil, EDM oil, and distilled water using one-variable-at-a-time approach for machining as well as environmental aspects. The hazard and operability analysis is employed to identify the inherent safety factors associated with powder-mixed EDM of WC-Co.

Surface modification of tool steel by electrical discharge machining with molybdenum powder mixed in dielectric fluid

Research works in electrical discharge machining (EDM) with powder suspended in dielectric fluid indicate significant gains in process stability and surface roughness improvement of EDMachined components. Powder-mixed EDM (PMEDM) process is also investigated in order to obtain a resolidified layer (recast layer), which acts as a kind of coating, having superior mechanical properties to the base material. Molybdenum (Mo), commonly used as an alloying element in steels, in solid solution or in the form of various carbides, provides high resistance to wear, corrosion, and high hardness. However, as reported in literature, there are technological gaps in the use of molybdenum as an additive powder in PMEDM process. The influences of different sizes of fine Mo powder particles (˂5 and ˂15 μm) suspended in dielectric fluid in several EDM finishing regimes and machining times were investigated regarding AISI H13 tool steel surface modification. Samples were evaluated in terms of hardness, chemical composition, and microstructure using optical microscopy, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), nanoindentation, and X-ray diffraction (XRD). Results showed an enrichment of the modified surface layer (recast layer) with Mo, in which the formation of phases of Fe-Mo and Mo x C and also the presence of Mo in solid solution were observed, resulting in a four times fold hardness increase in comparison with the metal matrix. Best results were obtained with 1-A discharge current and less than 15-μm particle size, with the formation of a Mo-enriched, 14-GPa hardness uniform modified layer, with a constant thickness of 5 μm free of pores and microcracks. Machining times did not affect the characteristics of resolidified layer (recast layer). This work provides PMEDM process referential parameters to the use of Mo as a material for providing better surface mechanical properties.

Powder Mixed Electric Discharge Machining: An Innovative Surface Modification Technique to Enhance Fatigue Performance and Bioactivity of β-Ti Implant for Orthopedics Application

The development of surface modification technique has been the subject of the studies regarding the fatigue performance and biological characterization of the modified layers. In the present research work, powder mixed electric discharge machining (PMEDM) a novel nonconventional machining technique has been proposed for surface modification of β-Ti implant for orthopedics application. The surface topography and morphology like roughness, surface cracks, and recast layer thickness of each of the machined specimens were investigated using Mitutoyo surface roughness tester and field-emission scanning electron microscopy (FE-SEM), respectively. This study aims to investigate the effect of surface characteristics of PMEDM process on the fatigue performance and bioactivity of β-Ti implants and moreover a comparative analysis is made on the fatigue performance and biological activity of specimens machined with presently used machining methods like electric discharge machining (EDM) and mechanical polishing. The high cycle fatigue (HCF) performance of polished specimens was superior and had no adverse effect of microstructure on fatigue endurance. As expected, the fatigue behavior of β-Ti implant-based alloy, after undergoing EDM treatment, is poorly observed due to the microrough surface. The fatigue performance is dependent on microstructure and surface roughness of the specimens. Subsequent PMEDM process significantly improves the fatigue endurance of β-Ti implant-based alloy specimens. PMEDMed surface with micro-, sub-micro-, and nano-structured topography exhibited excellent bioactivity and improved biocompatibility. PMEDMed surface enabled better adhesion and growth of MG-63 when compared with the polished and EDMed substrate. Furthermore, the differentiation results indicated that a combination of nanoscale featured submicrorough PMEDMed surface promotes various osteoblast differentiation activities like alkaline phosphatase (ALP) activity, osteocalcin production, the local factor osteoprotegerin, which inhibits osteoclastogenesis.

Investigating surface properties of cryogenically treated titanium alloys in powder mixed electric discharge machining

Although electrical discharge machining is a metal removal process in form of debris, efforts have been made in this article to make use of this process as a surface treatment method. Effect of different process parameters and mechanism of material deposition also studied under this study. Powder mixed electric discharge machining (PMEDM) process has been used which helps in improving the surface properties. In this study, changes in surface properties of cryogenically treated titanium alloy after PMEDM process were investigated. Experimental results showed significant improvement in micro-hardness by 94.85 %. Various studies, like scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) were carried out to study the characteristics of the machined surface. After scanning the machined surface through XRD and EDX, the transfer of various elements from electrode material and powder mixed dielectric and their chemical compounds were observed. After screening the results, peak current was observed as the highly influential parameter that affected the micro-hardness as well as surface quality of the machined surface.

Effect of impregnated powder materials on surface integrity aspects of Inconel 625 during electrical discharge machining

In recent times, nickel-based super alloys are widely utilized in aviation, processing, and marine industries owing to their supreme ability to retain the mechanical properties at elevated temperature in combination with remarkable resistance to corrosion. Some of the properties of these alloys such as low thermal conductivity, strain hardening tendency, chemical affinity, and presence of hard and abrasives phases in the microstructure render these materials very difficult-to-cut using conventional machining processes. In this work, an experimental setup was developed and integrated with the existing electrical discharge machining system for carrying out powder-mixed electrical discharge machining process for Inconel 625. The experiments were planned and conducted by varying five different variables, that is, powder concentration, peak current, pulse-on time, duty cycle, and gap voltage based on the central composite design of response surface methodology. Effects of these parameters along with powder concentration were investigated on various surface integrity aspects including surface morphology, surface roughness, surface microhardness, change in the composition of the machined surface, and residual stress. Results clearly indicated that addition of powder to dielectric has significantly improved surface integrity compared to pure dielectric. Among the powders used, silicon has resulted in highest microhardness, that is, almost 14% more than graphite. Lowest surface roughness (approximately 50% less than pure kerosene) and least residual stress were obtained using silicon powder (approximately 8% less than graphite-mixed dielectric). Relative content of nickel was reduced at the expense of Nb and Mo after addition of powders like aluminum and graphite in dielectric during electrical discharge machining.

Experimental investigations in powder mixed electric discharge machining of Ti–35Nb–7Ta–5Zrβ-titanium alloy

ABSTRACTThe present research is the first type of study in which the application of powder mixed electrical discharge machining (PMEDM) for the machining of β-phase titanium (β-Ti) alloy has been proposed. β-Ti alloys are new range of titanium alloys, which has a wide-spread application in dental, orthopedics, shape memory, and stents. The aim of the present study is to fabricate submicro- and nanoscale topography by PMEDM process to enhance the biocompatibility without affecting machining efficiency. The effect of Si powder concentration along with pulse current and duration on the surface and machining characteristics has been investigated. A significant decrease in surface crack density on the machined surface with 4 g/l Si powder concentration was observed. When β-Ti alloy was modified at 15 A pulse current, longer pulse interval with 8 g/l concentration of Si powder particles, the interconnected surface porosities with pore size 200–500 nm was observed. Moreover, at Si powder concentrations of 2 g/l and 4 g/l, the recast layer thickness is 8 µm and 2–3 µm, respectively. Elemental mapping analysis confirmed that PMEDM also generated carbides and oxides enriched surface, a favorable surface chemistry to enhance the biocompatibility of β-Ti alloy. Furthermore, PMEDM also enhances the machining performance by improving material removal rate and reducing tool wear rate.

State of the art in powder-mixed electric discharge machining: A review

Accomplishment of high machining rates along with good surface quality is a major concern in electric discharge machining process. Powder-mixed electric discharge machining in which suitable powder particles are impregnated in dielectric has gone forth as a potential solution to this problem. Nevertheless, challenges such as dielectric circulation, homogeneous blending of the powder particles in the dielectric, debris removal and quantity of the powder material required have to be addressed carefully before implementing this process on a large scale in the manufacturing industry. Extensive research in the field of electric discharge machining using powder-suspended dielectrics has started only in the recent years. In this article, a comprehensive review of the research going on in the field of powder-mixed electric discharge machining is presented. The emphasis is given on powder-mixed electric discharge machining mechanism, influence of powder characteristics and machining parameters on various responses. Some of the major application areas, variants of the basic powder-mixed electric discharge machining process and possibilities of further improvement are also discussed.

Influence of graphite powder mixed EDM on the surface integrity characteristics of Inconel 625

ABSTRACTSurface integrity in electric discharge machining (EDM) has always been a major concern in the manufacturing industry. Although, EDM with a powder suspended dielectric has shown good potential in enhancing the material removal rate and improving surface finish, influence of the same on the overall surface integrity is not very clear. The current work utilized the graphite powder and evaluated its role in combination with concentration and machining parameters, on surface roughness (Ra), surface crack density (SCD), white layer thickness, microhardness depth profile, possible phase changes, and residual stress during powder-mixed EDM (PMEDM) of Inconel 625 (a nickel-based super alloy), that is now-a-days regularly used in aerospace, chemical and marine industries. The results showed that significant reduction in surface roughness, crack density, and white layer thickness is possible with the PMEDM process. It also promoted formation of carbides and other alloy compounds which is responsible for augmentation of hardness in surface and subsurface region. The added particles also caused a decline in tensile residual stress of the machined samples.

Investigation of the Tool Wear Rate in Tungsten Powder-Mixed Electric Discharge Machining of AA6061/10%SiCp Composite

This paper presents the experimental investigation on tool wear rate (TWR) in powder-mixed electrical discharge machining (PMEDM) of aluminum 6061 alloy reinforced with 10% silicon carbide particles (AA6061/10%SiCp composite). Composite material is fabricated by mechanical stir casting process and further characterized by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Tungsten powder with concentration of 4 g/L is mixed in the dielectric fluid. To know the influence of powder suspension in dielectric fluid on TWR, comparative study is done on the basis of experiments performed using basic EDM and PMEDM process. Experiments have been designed as per central composite rotatable design (CCRD) using response surface methodology (RSM) approach. Four process parameters, namely, peak current, pulse-on time, pulse-off time, and gap voltage have been considered for TWR investigation. Individual and interactive influence of various parameters on TWR is explained with the help of analysis of variance and three-dimensional graphs. Using RSM approach, results have been further optimized. PMEDM approach provides 51.12% reduction in TWR for machining of AA6061/10%SiCp composite.

Parameter optimisation of powder mixed EDM of aluminium-based metal matrix composite using Taguchi and grey analysis

Powder-mixed electrical discharge machining (PMEDM), a non-conventional manufacturing process involves the use of a dielectric fluid mixed with abrasive powder (Al2O3), combines the benefits of mechanical and thermal interactions. The aim of this article is to use a new approach of performance evaluation to evaluate the effectiveness of optimising multiple performance characteristics of PMEDM of SiC reinforced ZA-27 metal matrix composites (MMCs). Taguchi analysis is used to plan and analyse the experiment and grey relational analysis (GRA) for multi-parameter analysis. The considered process parameter includes the four control factors namely powder concentration, % Sic in MMC, pulse current (Ip) and duty cycle (τ). The combination of L9 orthogonal array design of experiment with GRA enables to determine the optimal parameters for multiple responses. GRA is used to obtain a single performance index, grey relational grade through grey relational coefficient to optimise the PMEDM process. In addition, analysis of variance (ANOVA) for the GRC is also utilised.

Effect of Powder Mixed Electrical Discharge Machining (PMEDM) on Difficult-to-machine Materials – a Systematic Literature Review

AbstractThe last decade has witnessed an increasing interest in the novel applications of electrical discharge machining (EDM) process. Due to the continuous efforts by the researchers many innovations have been made to improve the performance of EDM process. Among various EDM variants, powder EDM is one of the successful technique, which shows the considerable improvement in the performance of EDM by increasing the MRR and surface finish as both of these responses are mainly considered by the industries. Despite the better processing results, powder mixed EDM process is used in industry at slow pace. Therefore, with a vast future scope of powder EDM in areas of machining and surface modification of difficult-to-machine materials, authors in this paper explored all the parameters and terms related with powder mixed EDM process. The main aim of the paper is to help the researchers to understand this concept thoroughly and research the process parameters further in more details to get more improvements in the process resulting in achieving desired quality levels.

Comparative study of powder mixed EDM and rotary tool EDM performance during machining of Al-SiC metal matrix composites

Electrical discharge machining (EDM) is used for machining of any electrically conductive materials irrespective of their hardness. A number of EDM process variants have been developed over the years for improving the machining performance. Powder mixed EDM (PMEDM) and rotary tool EDM (REDM) are such process variants which have improved the efficiency of the machining process. In the present study, a comparative study of the effect of various process parameters were carried out on PMEDM and REDM process. The output characteristics measured were the material removal rate (MRR) and the tool wear rate (TWR). Experimental results reveal that the MRR in PMEDM was higher as compared to conventional die-sinking EDM. However, average MRR of REDM process was about 2.5 times higher as compared to that of the PMEDM process. In PMEDM, the debris accumulation in the inter electrode gap limited the machining rate. In case of REDM, tool rotation improved the flushing efficiency.

Parametric Optimization of PMEDM Process with Chromium Powder Suspended Dielectric for Triangular Electrodes

In this article, parametric optimization for material removal rate (MRR) and surface roughness (SR) study on the powder mixed electrical discharge machining (PMEDM) of EN-8 steel has been carried out. Response surface methodology (RSM) has been used to plan and analyze the experiments. Average current, duty cycle, diameter of electrode and concentration of micro-nickel powder added into dielectric fluid of EDM were chosen as process parameters to study the PMEDM performance in terms of MRR and SR. Experiments have been performed on newly designed experimental setup developed in laboratory. Most important parameters affecting selected performance measures have been identified and effects of their variations have been observed.

Predictor Equations for Estimating Crater Dimensions in PMEDM Process Using Fem Simulation and Experimental Validation

In the present study, the powder mixed EDM (PMEDM) process was simulated using FE approach to obtain simulated temperature profiles for estimating the crater dimensions and volume removed during formation of each crater. The craters formed in PMEDM process had higher diameter and shallow depth resulting in improved MRR and better surface finish. The addition of powder increased the amount of heat available at the workpiece between 20-25% as compared to conventional EDM process. The results were subsequently validated experimentally to compare the actual measurements with the simulation output. Predictor equations for crater radius and depth incorporating the significant factors were developed and also validated with the experimental results.

Effect of process variables on microhardness, grain size and strain during machining of various die steels with powder-mixed electric-discharge machining using dummy treated experimental design

This experimental study investigates the effect of process parameters in a powder-mixed electric-discharge machining process on the microhardness of the deposited and the non-deposited region of the machined surface. The microscopic observations using a scanning electron microscopy revealed a transfer of material on to the workpiece during machining, leading to a formation of compounds resulting in improvement of its properties. The X-ray diffraction plots were used to assess the grain size and the micro-strain for each die steel material. The addition of tungsten or graphite powder affected the microhardness significantly, while aluminium or copper had no effect. The grain size was affected by the cooling rate and the powder used during machining besides process parameters, such as current and pulse-off time. The average grain size varied between 18 to 40 nm. Trials conducted with low melting point metallic powders slowed the cooling rate, resulting in finer grains. HCHCr, H13 or H11 die steel workpieces showed a higher average strain as compared with EN31.

Parametric Optimization of PMEDM Process with Chromium Powder Suspended Dielectric for Minimum Surface Roughness and Maximum MRR

In this article, parametric optimization for material removal rate (MRR) and surface roughness (SR) study on the powder mixed electrical discharge machining (PMEDM) of EN-8 steel has been carried out. Response surface methodology (RSM) has been used to plan and analyze the experiments. Average current, duty cycle, diameter of electrode and concentration of micro-nickel powder added into dielectric fluid of EDM were chosen as process parameters to study the PMEDM performance in terms of MRR and SR. Experiments have been performed on newly designed experimental setup developed in laboratory. Most important parameters affecting selected performance measures have been identified and effects of their variations have been observed.

Optimal parameter settings for rough and finish machining of die steels in powder-mixed EDM

The present study was undertaken to identify the appropriate parameter settings for rough and finish machined surface for EN31, H11, and high carbon high chromium (HCHCr) die steel materials in a powder-mixed electric discharge machining process. The effect of seven different process variables along with some of their interactions was evaluated using a dummy-treated experimental design and analysis of variance. Material removal rate (MRR), tool wear rate, and surface finish were measured after each trial and analyzed. The parameter settings for rough and finished machining operations were obtained. EN31 exhibited maximum MRR as compared to the other two materials at similar process settings. Copper (Cu) electrode with aluminum suspended in the dielectric maximized the MRR. Suspending powder in the dielectric resulted in surface modification. Graphite powder showed a lower MRR but improved the surface finish. HCHCr require higher current and pulse on settings for initiating a machining cut and works best in combination with tungsten–Cu electrode and graphite powder for improved finish. The MRR for H11 is lower than EN31 but significantly higher than HCHCr under same process conditions.

Material removal rate and electrode wear ratio study on the powder mixed electrical discharge machining of cobalt-bonded tungsten carbide

In this article, a material removal rate (MRR) and electrode wear ratio (EWR) study on the powder mixed electrical discharge machining (PMEDM) of cobalt-bonded tungsten carbide (WC-Co) has been carried out. This type of cemented tungsten carbide was widely used as moulding material of metal forming, forging, squeeze casting, and high pressure die casting. In the PMEDM process, the aluminum powder particle suspended in the dielectric fluid disperses and makes the discharging energy dispersion uniform; it displays multiple discharging effects within a single input pulse. This study was made only for the finishing stages and has been carried out taking into account the four processing parameters: discharge current, pulse on time, grain size, and concentration of aluminum powder particle for the machinability evaluation of MRR and EWR. The response surface methodology (RSM) has been used to plan and analyze the experiments. The experimental plan adopts the face-centered central composite design (CCD). This study highlights the development of mathematical models for investigating the influence of processing parameters on performance characteristics.

Simulation of Particles’ Activity in Discharge Channel of PMEDM

Powder mixed EDM can effectively improve the surface quality of a machined workpiece. In order to study the mechanism of powder mixed EDM process, particles’ activities in working conditions are simulated and corresponding experiments are done. A 3D electric fields model described by finite element method of the particles suspended in working fluid in the electric field is built, the generated field is computed and presented, and the activities of particles in the breakdown process are analyzed. The results show that this method can serve as a good way to learn the activities of particles in the breakdown of discharge.