Effect of deep cryotreated tungsten carbide electrode and SiC powder on EDM performance of AISI 304

Abstract

Powder mixed electric discharge machining (PMEDM) is a further advancement of conventional EDM process in which electrically conductive powder is suspended in the dielectric fluid to enhance the material removal rate (MRR) along with the surface quality. Cryotreatment is introduced in this process for improving the cutting tool properties as well as tool life. In this investigation, EDM is performed for the machining of AISI 304 stainless steel using cryotreated double tempered tungsten carbide electrode when SiC powder is suspended in the kerosene dielectric. The influence of process parameters viz. pulse on time, peak current, duty cycle, gap voltage and powder concentration on tool wear rate (TWR), surface roughness (R_a), and MRR has been studied. Metallographic analysis was carried out for the machined surfaces. By the addition of powder concentration and cryotreated double tempered electrode, significant improvement in the machining efficiency has been found out. When cryotreated electrode used MRR, TWR and R_a decreased by 12%, 24% and 13.3%, respectively and when SiC powder used MRR increased by 23.2%, TWR and R_a decreased by about 25% and 14.2%, respectively.     

Electrical Discharge Machining (EDM) Characteristics Associated with Electrical Discharge Energy on Machining of Cemented Tungsten Carbide

In this investigation, cemented tungsten carbides graded K10 and P10 were machined by electrical discharge machining (EDM) using an electrolytic copper electrode. The machining parameters of EDM were varied to explore the effects of electrical discharge energy on the machining characteristics, such as material removal rate (MRR), electrode wear rate (EWR), and surface roughness. Moreover, the effects of the electrical discharge energy on heat-affected layers, surface cracks and machining debris were also determined. The experimental results show that the MRR increased with the density of the electrical discharge energy; the EWR and diameter of the machining debris were also related to the density of the electrical discharge energy. When the amount of electrical discharge energy was set to a high level, serious surface cracks on the machined surface of the cemented tungsten carbides caused by EDM were evident.     

Effect of Powder Mixed Dielectric on Material Removal and Surface Modification in Microelectric Discharge Machining of Ti-6Al-4V

Microelectric discharge milling is one of the variants of microelectric discharge machining process which acquire the attention of researchers due to its unique ability to produce microchannels and three-dimensional structures in difficult-to-machine materials like titanium. In the present work, an experimental investigation has been performed in order to study the effect of SiC microparticle suspended dielectric on machining Ti-6Al-4V with tungsten carbide electrode. The effects of major electric discharge milling process parameters—voltage, capacitance, and powder concentration in dielectric—on responses—viz., material removal rate (MRR) and tool wear rate (TWR)—were studied. Experiments were designed and performed based on response surface methodology (RSM)-Box–Behnken statistical design and the significance of in put parameters were identified with the help of analysis of variance. From the results, it is recommended to use powder concentration of 5 g/L, capacitance of 0.1 µF, and voltage of 115 V for achieving high material removal and low tool wear rate. Finally, the studies were conducted to analyze the surface modification and the quality of machined surface.     

Surface and porous recast layer analysis in µ-EDM of MWCNT-Al2O3 composites

Machining of ceramic materials has been a major challenge owing to high hardness and brittleness. The reinforcement of a conducting filler allows permissible machining in electrical discharge machining (EDM) process. The current effort analyses the impact of multi-walled carbon nanotubes (MWCNT) of concentrations of 2.5 and 5 vol. %, as conducting filler towards machinability of alumina composites in µ-EDM process. The influence of tool materials and its rotation are closely analyzed. A successful machining process is observed in both the two composites, with a higher material removal rate (MRR) in 5 vol. % MWCNTs. When the tool starts to rotate at 750 rpm, an increment of around 60–65% is observed in MRR for both the two composites. Similarly, the surface roughness (R_a) decreases by a factor of 20?25%. The brass tool is observed to yield better machining capabilities due to the frequent initiation of sparks. A highly porous machined surface is observed in both the two composites. This scenario depicts the spalling effect as more dominant than melting-evaporation effect. The extent of porous recast layer on the drilled edges is found to reduce with increasing the speed of tool rotation.     

Multiobjective optimization and analysis of copper–titanium diboride electrode in EDM of monel 400™ alloy

Electrical discharge machining (EDM) is one of the most accepted machining processes in the precision manufacturing industry. In EDM process, finding an alternative tool material is the demand in modern manufacturing industry. Therefore, an attempt had been made to fabricate copper–titanium diboride powder metallurgy electrode to test in EDM on monel 400? material. The experiments are planned using center composite second-order rotatable design and the model is developed by response surface methodology. The machining characteristics have analyzed using the developed model. In this study, four input parameters such as titanium diboride percentage, pulse current, pulse on time, and flushing pressure are selected to evaluate the material removal rate (MRR) and tool wear rate (TWR). The adequacy of the developed regression model has tested through analysis of variance test. The desirability-based multiobjective optimization is used to find the optimal process parameter which has given maximum MRR and minimum TWR. The optimum process parameters obtained were titanium diboride of 16%, pulse current of 6 A, flushing pressure of 1 Mpa, and pulse on time of 35?µs. The validity of the response surface model is further verified by conducting confirmation experiments.     

Influences of Process Parameters on MRR Improvement in Simple and Powder-Mixed EDM of AA6061/10%SiC Composite

In the present work, aluminum alloy 6061/10%SiC composite is machined using numerical controlled Z-axis (ZNC) electrical discharge machining (EDM) process. Improvement in material removal rate (MRR) is explored using tungsten powder suspended dielectric fluid in EDM process (powder-mixed electrical discharge machining (PMEDM)). Peak current, pulse on time, pulse off time, and gap voltage are studied as process parameters. Mathematical relation between process parameters and MRR is established on basis of response surface methodology. The results obtained are further compared with MRR achieved from machining using simple EDM. The existence of tungsten particles in kerosene resulted in 48.43% improvement in MRR. The influence of tungsten powder-mixed dielectric fluid on machined surface is analyzed using scanning electron microscope and energy dispersive spectroscopy (EDS). The results revealed improvement in surface finish and reduction in recast layer thickness with PMEDM. EDS analysis reported presence of tungsten and carbon in recast layer deposited on machined surface.     

Ultrasonic Assisted Electrical Discharge Machining of Ti–6Al–4V Alloy

In this research, an attempt was made to investigate the influence of copper tool vibration with ultrasonic frequency on output parameters in the electrical discharge machining of Ti–6Al–4V. The selected input parameters for the experiment comprise of ultrasonic vibrations of tool, current and pulse duration and the outputs are tool wear ratio (TWR), material removal rate (MRR), and stability of machining process and surface integrity of a workpiece, including surface roughness, thickness of recast layer, and formation of micro cracks. Scanning electron microscope and X-Ray diffraction were employed to examine the surface integrity of the workpiece. The results revealed that tool vibration with ultrasonic frequency enhances MRR via increasing normal discharges and decreasing arc discharges and open circuit pulses. Also, by using ultrasonic vibrations in finishing regimes, the density of cracks and TWR decrease while in roughing regimes, the thickness of recast layer, density of cracks, and TWR increase.     

Effects of electrode materials on performance measures of electrical discharge micro-machining

The main objective of this study is to investigate the effects of various electrode materials and their influences on electrical discharge micro-machining performance attributes. The performance attributes are determined in terms of tool wear rate (TWR), material removal rate (MRR), taper angle, overcut, and surface roughness by drilling micro-holes on SS 316?L material. It is noticed that, for high discharge energy the MRR, TWR, taper angle, and overcut are more and also when the thermal conductivity, boiling point, and melting point of the electrode material are high, the TWR is low. The surface finish is good at low discharge energy and low spindle speed. If the tool electrode is rotating at minimum speed during machining, a centrifugal effect is created on the dielectric so that debris at the inter-electrode gap is evacuated efficiently. If the tool is stationary, then the machining conditions are unstable due to improper flushing of debris.     

Powder Mixed Dielectric: An Approach for Improved Process Performance in EDM

The present study reports the outcome of experiments conducted to investigate the effect of parameters on improvement in the material removal rate (MRR), reduction in the tool wear rate (TWR), and overcut size for commonly used die steels. To overcome some of the shortcomings of electric discharge machining (EDM), an approach of powder mixing in dielectric fluids is adopted to investigate the influence of process parameters. The addition of powders in dielectric improves MRR and lowers TWR significantly. Powder concentration, current, and pulse-on time are three significant factors affecting MRR, TWR, and overcut size. An increase in powder concentration improves the process performance, but is limited by the possibility of arcing at higher concentration. Use of the powder resulted in increased effective spark length causing larger overcut. The problem is acute in trials conducted at high pulse-on duration with high powder concentration that leads to a ragged surface at cut edges. Furthermore, electrode tools with smaller tip included angle resulted in larger profile deviation at the machined surface as compared to trials conducted using tools with higher included angle. Surface morphological changes, grain size, microstrain, and material migration were investigated using SEM, XRD, and EDS analysis and a significant improvement in properties of the machined surface was observed.     

Influence of various metal powder mixed dielectric on micro-EDM characteristics of Ti-6Al-4V

Ti-6Al-4V, an advanced engineering material is difficult-to-machine using conventional machining process due to its high strength. It has properties like low weight ratio, outstanding corrosion resistance along with high level of reliable performance in micro components. Micro-electro-discharge machining (Micro-EDM), a popular nontraditional machining process has been identified as the most appropriate machining process for such material. In this paper, the effect of various conducting powders such as copper, nickel and cobalt with different concentrations are mixed with deionized water dielectric, on various responses such as material removal rate (MRR), tool wear rate (TWR), overcut (OC) and taper has been presented. Also, principal component analysis (PCA) has been applied to select the optimal parametric combination of micro-EDM process to achieve optimal values of MRR, TWR, OC and taper during micro-through hole machining. The optimal process parametric setting obtained from the proposed approach is peak current (I_p) of 1.5 A and cobalt (Co) powder concentration of 4 g/L so as to obtain the desired responses. It is also observed from the SEM image that the machined profile and surface topography obtained through the multi-objective optimal parametric combination based on PCA is quite satisfactory and can be applied to achieve geometrically more accurate micro-through holes on Ti-6Al-4V.     

Experimental Investigations into the Effects of Microelectric-Discharge Milling Process Parameters on Processing Ti–6Al–4V

Microelectric-discharge milling is acquiring more importance in micromanufacturing because of its unique ability to produce three-dimensional microcavities with high aspect ratio in electrically conductive advanced materials regardless of its mechanical properties. The present study investigates the effects of major microelectric-discharge milling process variables [voltage (V), capacitance (C), electrode rotational speed (ERS), and feed rate (FR)] on Ti–6Al–4V. The output performance measures were identified as material removal rate (MRR) and tool wear rate (TWR) to assess the machinability of Ti–6Al–4V. Experiments were designed and carried out based on response surface methodology-Box-Behnken statistical design. The most influencing parameters for responses (MRR, TWR) were found to be capacitance and FR. At a capacitance of 0.4 µF and FR of 18 mm/min, maximum MRR of 0.9756 mg/h, and TWR of 0.6342 mg/h were observed. Similarly at 0.01 µF and 6 mm/min, minimum MRR of 0.2308 mg/h, and TWR of 0.1259 mg/h were obtained.     

Wire electrical discharge machining characteristics of AA6061/cenosphere as-cast aluminum matrix composites

Machining of metal matrix composites (MMCs) reinforced with low-density waste byproduct particulates using nonconventional processes is relatively new in the field of material science. However, more attention has been paid for investigations on nontraditional machining of such MMCs currently as the conventional machining may generate additional complexity. This study investigates the wire electro-discharge machining behavior of compo-casted cenosphere-reinforced AA6061 alloys. Cu₆₀Zn₄₀-coated copper wire was used as electrode material. The investigation demonstrates that melting and vaporization are the dominant machining mechanisms. The weight fraction of cenosphere was observed to be the most substantial process variables affecting the cutting rate, on-time, and the wire speed of tool were the next in the order of importance. The presence of nonconductive cenosphere particles along with thermal degradation of the aluminum matrix composites leads to degrading processed machined surface quality. The issues related to wire breakage and poor quality of the machined surface, surface finish, and dimensional accuracy are described in detail.     

Effects of an Electrode Material on a Novel Compound Machining of Inconel718

Compound machining (CM) compounded by arc machining and electrical discharge machining (EDM) milling is a new and fast processing method used to machine so-called “difficult-to-machine” materials. This method has an exciting maximum material removal rate that reaches 11,218 mm³/min with the relative electrode wear rate (REWR) of 1.54% when machining Inconel718. The electrode material is an important factor that affects the processing cost and quality of CM. Traditionally used electrode materials in arc machining and EDM, including pure tungsten (W), cerium tungsten (WCe20), copper (Cu), tungsten copper alloy (W80), and graphite (C), were used as electrode materials to process Inconel718. Experimental results show that tubular C is the best electrode material for CM. When tubular C is unavailable, WCe20 is the suitable electrode material for rough machining and W is a better choice in finish machining. Cu electrode is unsuitable for CM because of its low melting point. Results of this work provide guidance for selecting electrode materials for the industry application of efficient CM.     

Optimization of EDM Parameters on Machining Si3N4–TiN Composite for Improving Circularity,Cylindricity, and Perpendicularity

The dominance of the spark eroding process in complex ceramic components has promoted a significant growth analysis in the ceramic composites domain in modern manufacturing industries. The latest developments in ceramic components are concentrated on both the enhancement of the mechanical properties and the machinability of complex 3D parts while using spark EDM. The current (I), pulse on time (T_on), pulse off time (T_off), and dielectric flushing pressure (DP) are considered sparking parameters for the machining of a Si₃N₄–TiN ceramic composite. These composites find their application in high-temperature environments, viz. metal forming, extrusion dies, turbine blade, and non-ferrous molten metal handling components. Taguchi's orthogonal array (OA), L₁₈, has been used to design the experiments. The optimal machining inputs are determined by the grey relational grade (GRG), which is attained from the grey relation analysis (GRA) for various response characteristics, such as the material removal rate (MRR), tool wear rate (TWR), circularity (CIR), cylindricity (CYL), and perpendicularity (PER). The significant parameters are identified via an analysis of variance (ANOVA). Finally, the optimized process parameters resulting in a higher MRR, lower TWR, lower form tolerance, and decreased orientation tolerance are verified through a confirmation test demonstrating that sparking process responses can be effectively improved.     

Experimental investigations into the performance of EDM using argon gas-assisted perforated electrodes

In the present work, a parametric study of EDM process using Argon-Gas-Assisted EDM (AGAEDM) with rotary tool during machining of high chromium high carbon diesteel has been performed. The pulse on time, tool rotation, discharge current, duty cycle, and gas pressure were selected as process factors. The effects of process factors were investigated on responses viz. surface roughness (SR), material removal rate (MRR), and electrode wear ratio (EWR). A comparison between solid tool, air-assisted tool, and argon-assisted tool has also been presented. It was found that EWR and SR were less during AGAEDM process as compared to rotary EDM(REDM) with solid tool and air-assisted EDM (AAEDM) with rotary tool under same process parameters. However, MRR was found to be higher in AAEDM process. The regression analysis and analysis of variance have been done to develop and find the adequacy of the developed models of MRR, EWR, and SR. It was observed that surface integrity of workpiece machined by AGAEDM was better than workpiece machined by AAEDM and conventional REDM process.     

Machining of a hybrid–metal matrix composite using an erosion–abrasion-based compound wheel in electrical discharge grinding

Machining of the composites made of matrix and reinforcement is always difficult for manufacturing industries due to their unusual properties. Among various existing traditional and non-traditional machining processes, erosion-based machining process i.e., Electrical Discharge Grinding (EDG) and the abrasion-based process i.e., Diamond Grinding (DG) have been shown their potential to machine such difficult-to-machine materials. The aims of the present study are to analyze the performances of the erosion–abrasion-based compound wheel during machining of the hybrid–metal matrix composite made of Aluminum–Silicon Carbide–Boron Carbide (Al/SiC/B₄C) by the stir casting method. The performances of the compound wheel have been tested on the EDM machine in the face grinding mode. The role of pulse current, pulse on-time, pulse off-time, wheel RPM, and abrasive grit number have been analyzed on the material removal rate (MRR) and average surface roughness (Ra). The experimental results showed that the machining with compound wheel gives higher MRR with better surface finish as compared to the uniform wheel. It has also been observed that MRR and Ra are highly affected by the pulse current, pulse on-time, and wheel RPM.     

Optimization of Process Parameters to Improve Form and Orientation Tolerances in EDM of MoSi2-SiC Composites

In this research, an investigation and experimental work were carried out on electric discharge machining (EDM) of intermetallic base MoSi₂-SiC ceramic composite with copper electrode. It is extremely difficult to machine MoSi₂-SiC composite using conventional machining techniques. However, it can be easily machined by executing spark EDM parameters to induce the correct optimum result. These composites find their application in high-temperature environments, viz. fuel turbo pump rotors, inlet nozzles, combustion chambers, injectors, nozzle throats, and nozzle extensions. The sparking parameters, namely current (I), pulse on time (T_on), pulse off time (T_off), spark gap (SG), and dielectric pressure (DP), were investigated by L₁₈ orthogonal array. The optimal process parameters were determined by the grey relational grade (GRG) obtained through the grey relational analysis (GRA) for multiple performance characteristics, viz. material removal rate (MRR), electrode wear rate (EWR), circularity (CIR), cylindricity (CYL), and perpendicularity (PER). The significant process parameters were obtained by analysis of variance (ANOVA) based on GRG, which showed current, pulse on time, and DP. The results were finally established using a confirmatory experiment, which showed the spark eroding process could effectively be improved.     

Electrical Discharge Machining of Functionally Graded 15-35 Vol% SiCp/Al Composites

A functionally Graded 15-35 volume% silicon carbide particulate (SiC_p) reinforced Al359 metal matrix composite (SiC_p/Al MMC) was drilled by electrical discharge machining (EDM) to assess the machinability and workpiece quality. The machining conditions were identified for both the machining performance and workpiece quality of the EDM process, including some aspects of material removal mechanisms, material removal rate (MRR), electrode tool wear, and subsequent drilled hole quality including surface texture and roundness by using surface profilometry, coordinate measuring machine (CMM), and scanning electron microscopy (SEM). It was observed that the material removal rate increases with increasing peak current and pulse-on-time up to the optimal points and drops drastically thereafter. Higher peak current and/or pulse-on-time result in both the greater tool wear and the larger average diameter error. As the percentage of the SiC particles increases, MRR was increased and electrode wear was found to be decreased. At the EDM machined subsurface layer, the fragmented and melted SiC particles were observed under the SEM and EDX-ray examination.     

Performance evaluation of cryogenically assisted electric discharge machining (CEDM) process

The performance of cryogenically assisted electric discharge machining (CEDM) process has been evaluated in the presented research paper. The machining of cryogenically treated (CT) and cryogenically untreated (CUT) AISI D2 tool steel work specimens using cryogenically cooled (CC), CT, and CUT copper electrodes have been performed. The effects of various parameters, namely, workpiece condition, tool condition, nozzle flushing, peak current, duty cycle, pulse duration, and gap voltage, have been studied on the performance indicators, viz. the material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR). The best parametric combinations have been suggested to obtain the desired quality characteristics. The interaction effects among various parameters have also been presented. An increase of approximately 18% in MRR and a reduction of 26% and 11% in TWR and SR, respectively, were observed, during the machining through CEDM in contrast to EDM. The confirmatory experiments suggested that experimental values were in permissible agreement with the predicted values for all the performance measures. Finally, the comparison of the CEDM with that of EDM process, in the light of SEM graphs, has been presented.     

Constrained multi-objective optimization of EDM process parameters using kriging model and particle swarm algorithm

This paper investigates the highly nonlinear relationship between process parameters and machining responses, including material removal rate (MRR), surface roughness (SR), and electrode wear rate (EWR) of electric discharge machining (EDM) using Kriging model. Subsequently, an emerging multi-objective optimization algorithm called particle swarm is used to determine the best machining conditions that not only maximize the machining speed but also minimize the EWR with a constraint of the SR. The experiment was carried out with P20 steel on a CNC EDM machine using copper electrode. The research result shows that the MRR increases sharply when increasing the discharge current just like other researches pointed out. However, the relationship between EWR and current is complicated. EWR appears the minimum value when the current is around 30?A. The speed of change of MRR per unit of EWR is the highest when the SR is around 14.5?µm. The combination of Kriging regression model and particle swarm optimization is considered as an intelligent process modeling and optimization of EDM machining. The proper selection of process parameters helps the EDM operator to reduce the machining time and cost.