Electric discharge hole grinding in hybrid metal matrix composite

Moving toward a hybrid approach, a hybrid process, electric discharge hole grinding (EDHG) was used to machine a hybrid metal matrix composite (MMC) (Al6063/SiC/Al₂O₃/Gr). Here, holes were drilled and ground in a single step process (EDHG) using a novel tool electrode. The experiments were designed using response surface methodology (RSM). The objective of this study was to investigate the effect of electric discharge diamond hole grinding operation on the surface roughness (SR) of the hole. The input process parameters were current, duty factor, tool speed and flushing pressure. It was found that the process is very effective in producing a finished hole. A comparison of surface roughness was made between electric discharge drilling (EDD) and electric discharge diamond hole grinding, thereby showing the effectiveness of the electric discharge diamond hole grinding process. The grinding action of the process is clearly visible in the scanning electron microscopic (SEM) image. It was observed that the craters, globules of resolidified material and micro cracks, which are normally seen on surfaces machined by electric discharge machining (EDM), are completely ground off by electric discharge diamond hole grinding.     

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.     

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.     

WEDM of Mg/CRT/BN composites: Effect of materials and machining parameters

The current work presents a detailed exploration on real-time wire electric discharge machining (WEDM) experiments and grey relational analysis (GRA)–based multi-criteria optimization of material and machining characteristics for lowered surface roughness (R_a) and improvised material removal rate (MRR) of the newly developed magnesium/boron nitride/cathode ray tube (Mg/BN/CRT) hybrid metal matrix composites (MMCs). The composites were fabricated through powder metallurgy (PM) route by reinforcing silica-rich E-waste CRT panel glass powder crushed for different particle sizes (10, 30, and 50?µm) at various weight percentages (5%, 10%, and 15%) and with 2% boron nitride (BN). Taguchi-based orthogonal array procedure was utilized to formulate the experimental plan for WEDM considering reinforcement level and size, pulse on time (P_on), pulse off time (P_off), and wire feed (W_f) as the input process parameters. ANOVA results reveal that P_on and wt% of reinforcement has more effect on R_a and MRR than any other considered parameters. The developed mathematical model for R_a and MRR predicted values similar to that of experimental results. Multi-criteria optimization was done through GRA technique and the so recommended optimum parameter set furnishes higher MRR (22.34?mm³/min) and reduced R_a (2.87?µm).     

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.     

WEDM process parameter optimization of FSPed copper-BN composites

A systematic view on evaluating the machining characteristics of Wire Cut Electrical Discharge Machining (WEDM) employing Taguchi Method and Grey Relational Analysis based multiobjective optimization is provided in this research article. The outcome of various WEDM processing parameters including pulse discharge on time (Pulse_ON), pulse discharge off time (Pulse_OFF), wire feed rate (Wire_FR) along with the material characteristics of varying Boron Nitride (BN) volume fractions while machining a friction stir processed (FSPed) copper-BN surface composite was investigated. The output responses considered in this research include Material Removal Rate (MRR) and Surface roughness (R_a) that was obtained from the L27 orthogonal array based on the above said input factors. ANOVA was performed, and Pulse_ON and BN volume fraction were found most significant for MRR, while Pulse_ON and Pulse_OFF influence the most in attaining minimal R_a values. Based on the obtained experimental values for MRR and R_a, a mathematical model was developed based on the control factors and was proved to be precise in predicting the output response. An optimal combination of input control factors was finalized through grey relational analysis, and the same proved to achieve the utmost MRR (20.19?mm³/min) and nominal R_a(3.01?µs) values.     

Effects of process parameters on fatigue behavior and surface integrity of tool steel produced by electrical discharge turning

Electrical discharge machining is used in the production of countless parts with complex geometries and micro dimensions, from many elements of industrial molds to parts of motors and pumps. Also, most of these parts are cylindrical and it is always more meaningful to study their rotational fatigue behavior to predict their response during their operation. This study concentrated on the impacts of machining parameters on the surface quality and fatigue behavior of tool steel shaped by electrical discharge turning. The results based on Taguchi methodology have shown that discharge current affects R_a and R_z more, and pulse duration more affects the mean spacing of profile irregularities, S_m. As a result of the heat affected depth in the machined region, which changes in proportional with the processing parameters, the microhardness decreased from the sample surface to the core. The maximum hardness was measured at current of 12 A, pulse duration of 3 μs and pulse interval of 7 μs. According to the fatigue tests, it was found that the fatigue life decreased with the increase in R_z and S_m values. Moreover, high microhardness and thick recast layer reduced the fatigue strength of the samples with relatively smooth surface topography.     

Performance analysis of magnetorheological fluid-assisted electrical discharge machining

In this study, a newly developed method of electric discharge machining has been proposed, which uses magnetorheological (MR) fluid instead of conventional oil like kerosene. The paper aims to reveal the process parameters that affect the material removal rate (MRR) during newly developed EDM process. This hybrid machining process showed dual advantage of high-quality machined surface with improved cutting efficiency. The viscoelastic nature of MR fluid is found to give polishing effect as well as high material removal resulting in more stable processing and improved EDM performance. The experimentation has been performed to determine effect of duty cycle, discharge current, pulse on time, percentage concentration of alumina particles surface roughness, and MRR. It has been found that MRR and surface finish improved significantly. The experimental results demonstrated that the EDM process combined with MR fluid resulted in an increase in MRR and surface finish significantly under a certain limit of carbonyl iron percentage (CIPs) in MR fluid.     

Effect of nozzle angle and depth of cut on grinding titanium under cryogenic CO2

Grinding force and grinding energy are the significant factors associated with the grinding process. The higher heat at the contact zone leads to dulling grits and frequent breakage of grit particle resulting in increase of the grinding force. This problem can be met by bringing down the temperature at the contact zone. The oil-based coolant fails to eliminate the heat at the grinding zone. Hence, the approach of cryogenic coolant is required for this problem. In the present study, an experimental work has been made on the grinding Ti-6Al-4V under cryogenic carbon dioxide (CO₂) and conventional coolant condition. Grinding experiments were performed with an electroplated cubic boron nitride (CBN) wheel, with two factors such as nozzle inclination angle and depth of cut (DOC). The output response parameters considered were surface roughness (R_a), tangential force (F_t), normal force (F_n) grinding zone temperature (GT), and specific energy. The effect of CO₂ and wet coolant on the chip morphology and surface modification in grinding Ti-6Al-4V was analyzed. The experimental result indicates when cryogenic CO₂ was used as a coolant the F_t is reduced from 3 to 21% and 2 to 99% in F_n. The R_a was reduced by 333% and GT by 48% over conventional grinding.     

Optimization of material removal rate and surface roughness during electric discharge machining of ultra-fine grained Al6082 using Taguchi technique

In the current work, the statistical analysis of various electric discharge machining parameters on Al6082 ultra-fine grained aluminium alloy using Taguchi method has been presented. Repetitive corrugation and straightening (RCS) method was employed to obtain ultra-fine grained aluminium alloy. The electric discharge machining studies were carried out for test variables – pulse off time, pulse on time and current (I). The specimens were machined in dielectric medium with current range of 3 A to 9 A in step of 3 A. Machining features of the samples analysed statistically by adopting the Taguchi's - design of experiments (DOE) methodology. Impact of parameters on material removal rate (MRR) and surface roughness (SR) were examined via signal-to-noise ratio (S/N ratio, expressed in decibel, dB) as well as analysis-of-variance (ANOVA). Outcomes disclose that every selected response explicitly surface roughness (SR) and material removal rate was significantly influenced by parameters. The material removal rate was found to rise with discharge current and decrease with the duration of pulse on time and the duration of pulse off time. On the other hand, the surface roughness increased with increase in peak current and decreased with pulse on time and pulse off time especially. The machining mechanisms were examined by scanning electron microscopy.     

Experimental Investigation and Optimization of Process Parameters of Al/SiC MMCs Finished by Abrasive Flow Machining

In the era of nontraditional finishing processes, it is of upmost importance that these processes can be applied to composite materials as these have replaced traditional materials in many applications. Abrasive Flow Machining (AFM) is an advanced finishing process. Composite materials have replaced traditional materials as their properties such as light weight, high strength, and good economy are of great benefit. In the literature, work has been reported on AFM of materials such as aluminum, brass, and EN8. In the present work, composite materials with a high percentage of SiC (e.g., 20–60% SiC in Al/SiC composites) were machined using abrasive flow finishing. The Taguchi method was applied to find the effect of input parameters on material removal rate (MRR), change in surface roughness (ΔR_a), and surface topography, and L27 array was designed for experimentation. It was observed that extrusion pressure is the most significant factor in regard to MRR and ΔR_a. Optimization of response parameters (MRR and ΔR_a) was determined using the Taguchi method. Microstructure analysis was also done for workpiece materials using SEM and XRD.     

The specific cost of grinding R6M5F3 steel with various dressing methods and electric discharge actions on Kubonit wheel working surface

A comparative study of grinding R6M5F3 steel with metal-bonded Kubonit wheels in various dressing methods and with electric discharge action on the wheel working surface is carried out based on the minimum specific cost criterion. The electric discharge dressing method has been found to provide a reduction in specific grinding cost by one order of magnitude in comparison to an abrasive method. Electric discharge actions on the wheel working surface in the course of grinding result in a higher specific machining cost; therefore, it is advisable to perform grinding with periodic in-process electric discharge dressing.     

Experimental Investigations of Abrasive Mixed Electro Discharge Diamond Grinding of Nimonic 80A

This paper presents a novel hybrid machining process (HMP) called abrasive mixed electro discharge diamond grinding (AMEDDG) in which abrasive powder is mixed in dielectric fluid to perform electro discharge diamond grinding (EDDG) action on a workpiece. In-house-fabricated AMEDDG setup was used to experimentally evaluate the performance of the process during the machining of Nimonic 80A. The effects of wheel speed, powder concentration, current, and pulse-on-time (POT) were investigated on the material removal rate (MRR). The surface morphological properties of the machined workpiece were investigated based on some quality surface indicators. The experimental results show that MRR of the workpiece was influenced by wheel speed, current, and powder concentration, and optimum MRR can be achieved at a wheel speed of 1400 RPM, a powder concentration of 4 g/L, a current of 10 A, and a POT of 26 µs.     

An experimental investigation as to the effect of cutting parameters on roundness error and surface roughness in cylindrical grinding

This paper presents the results of an experimental investigation as to the effects of grinding parameters on roundness error and surface roughness in cylindrical grinding. Many variables including the wheel materials, wheel loading and dressing, workpiece metallurgy, work drive mechanisms, work holding methods, coolant types, feeds and speeds, machine stiffness and age, surface conditions, centre conditions, floor vibrations all influence the quality of ground parts. However, the composite sum of these grinding parameters creates static and dynamic forces. It is obvious that the roundness error and surface roughness are created by many parameters, but in this study, only the effects of the depth of cut, work speed and feed rate which create the grinding forces in cylindrical grinding are investigated. The grinding experiments were planned according to the principles of orthogonal arrays (OAs), developed by Taguchi, and were performed so as to understand the effects of these parameters on roundness error and surface roughness. The experimental data was analysed by using statistical tools: the percent contribution from an analysis of variance (ANOVA) and the correlation between machining parameters with roundness error (R) and also surface roughness (Ra). Roundness was found to be the most related with the cutting speed, grinding force and depth of cut, while surface roughness is related to feed rate and work speed.     

Surface damage in ZrB2-based composite ceramics induced by electro-discharge machining

Electro-conductive ZrB₂-based composite ceramics, containing SiC and B₄C, were machined with an electro-discharge machining (EDM) process. The EDMed surfaces were covered with resolidified ZrB₂ layers. Many open pores and surface cracks were observed on the surfaces. The strength degradation of the ceramics caused by machining was evaluated by three point bending tests of the partially EDMed bending specimens. The effects of pulsed current, pulse duration and duty factor on the strength and the roughness of EDMed surfaces are discussed. The strength of EDMed specimens was increased with decreases in pulse current, pulse duration and duty factor. The roughness of EDMed surfaces was decreased with decreases in pulse current, pulse duration and duty factor. The reliability of the ceramics EDMed with the appropriate conditions was as high as that of the ceramics ground with a 400 grit diamond wheel. It would be possible to use the carefully EDMed ZrB₂-based composite ceramics as structural components without any additional finishing processes.     

Experimental investigations on nanogrinding of RB-SiC wafers

Nanogrinding experiments are performed to investigate the processing characteristics and material removal mechanism of reaction-bonded silicon carbide (RB-SiC) wafers on an ultraprecision grinder using the cup wheel. #120, #600 diamond wheels are used as coarse and semifinished grinding wheels, while #2000 and #12000 diamond wheels are selected as fine and finish grinding wheels, respectively. The experimental results indicate that an ultrasmooth surface with roughness value R_a less than 3?nm and groove depth about 5?nm can be achieved using a diamond wheel whose mesh size exceeds 2000. In addition, R_a less than 1?nm and groove depth about 2?nm will be obtained with a #12000 diamond wheel. The present study reveals the feasibility of ultraprecision grinding RB-SiC materials in the ductile regime and provides technological insights into nanogrinding of hard materials with an ultrasmooth surface.     

Investigating Feasibility Through Performance Analysis of Green Dielectrics for Sustainable Electric Discharge Machining

This work represents a feasibility study for the newly proposed vegetable oil-based green dielectric fluids, biodielectric1 (BD1) and biodielectric2 (BD2) for electric discharge machining (EDM). Comparative analyses for BD1, BD2, and kerosene have been studied to assess the performance in terms of material removal rate (MRR), electrode wear rate (EWR), and relative wear ratio (RWR) for P20 + cold-worked plastic injection mold steel using electrolytic grade copper electrode. Current, gap voltage, pulse on time (T_on), and pulse off time (T_off) have been chosen as input parameters, and one variable at a time approach has been used for designing experimental plan for investigating the feasibility of the newly suggested fluids. The results obtained show that the performance of the newly suggested biodielectrics BD1 and BD2 is better than commercially used hydrocarbon-based dielectric, i.e., kerosene, for MRR and RWR. Analysis of variance results indicated that current is the most influencing parameter for MRR and EWR, while T_on is the most significant parameter for RWR. Under the influence of current, BD1 and BD2 produced 38% and 165% improvement in MRR, respectively. Moreover, BD1 and BD2 resulted 30% higher and 7% lower RWR, respectively, under the influence of T_on.     

Fuel ignition and flame front stabilization in supersonic flow using electric discharge

Recent achievements in the field of stabilization of the front of high speed combustion using electric discharge are presented. Near-surface discharge at the plane wall between electrodes installed in the plane of the wall is applied in this study. Hydrogen and ethylene directly injected from the wall to the flow with a Mach number M = 2 and an air total temperature T ₀ = 300–760 K are used as fuel. The excess fuel coefficient calculated by the total air flow rate in the channel does not exceed ER = 0.1. The value of electric power input into the discharge is W _pl/H _tot < 2% of the total flow enthalpy, while the thermal power due to combustion exceeds W _com/H _tot > 100% at a low initial gas temperature. Electric discharge is first applied to stabilize combustion under conditions of a fixed separated zone and on the plane wall of the combustion chamber. A two-stage combustion regime is demonstrated. It is shown that the application of electric discharge makes it possible to achieve complete fuel combustion η > 0.9 in a wide range of experimental parameters.     

Diamond grinding of WC-8Co hard-metal-steel 45 combined workpieces with the wheel cutting ability controlled by electrical discharge method

Optimal mechanical and electrical conditions have been defined for grinding WC-8Co hardmetal-steel 45 combined workpieces with periodic electric discharge action on the wheel working surface, which ensures an increase in removal rate and a reduction of machining unit costs in comparison to grinding with an electric-discharge dressed wheel.