Application of multi-criteria decision making methods for selection of micro-EDM process parameters

Ti-6Al-4V super alloy is an important engineering material with good strength to weight ratio and a wide range of applications in a number of engineering fields because of its excellent physical and mechanical properties.This work determines optimum process parameters such as pulse on time,peak current,gap voltage and flushing pressure,which influence the micro-electro discharge machining(EDM) process during machining of Ti-6A1-4V using combined methods of response surface methodology(RSM) and fuzzy-technique for order preference by similarity to ideal solution(TOPSIS).Central composite design(CCD) is used in the experimental investigation.A decision making model is developed to identify the optimum process parameters in the microEDM process,which influences several machining criterions such as material removal rate(MRR),tool wear rate(TWR),overcut(OC) and taper.Triangular fuzzy numbers are used to determine the weighting factor for each process criterion.Further a fuzzy-TOPSIS method is used to select the most desirable factor level combinations.The proposed technique can be used to select optimal process parameters from various sets of combinations of process parameters in a micro-EDM process.     

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.     

EDM of Ti-6Al-4V: Electrode and polarity selection for minimum tool wear rate and overcut

Titanium and its alloys especially Ti-6Al-4V are being widely used numerous application areas. In addition to have iconic properties, Ti-6Al-4V is considered as challenging material in machining perspective that is why it has captured global research focus. In this research, electric discharge machining of Ti-6Al-4V has been carried out by employing four different types of electrode materials (graphite, aluminum, copper, and brass) assigned with two alternate polarities (positive and negative). Selection of the most appropriate tool material and electrode polarity is the important aspect needed to be explored for this alloy. In addition to polarity, discharge current, and pulse time ratio have been considered as process variables owing to have their direct influence in electric discharge machining. Taguchi L9 array has been employed for each of the four electrodes with positive polarity and similarly L9 with negative polarity. Thus, a total number of 72 experiments have been conducted. Tool wear rate and overcut (OC) around the machined surfaces are the response characteristics to be investigated in order to achieve minimum amounts of both of these two responses. Selection of the most suitable tool with common tool polarity has been carried out meeting the decision criteria of minimum tool wear and minimum OC.     

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.     

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.     

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.     

Multi-attribute decision-making of cryogenically cooled micro-EDM drilling process parameters using TOPSIS method

The geometrical characteristics of the micro-holes along with the performance measures are matter of critical concern in micro-electrical discharge machining (μEDM) process. This paper presents the multi-attribute decision-making of cryogenically cooled micro-EDM (CμEDM) drilling process. Current (I_p), pulse on duration (T_on), pulse off duration (T_off), and gap voltage (V_g) were the input process parameters preferred to optimize the multiple responses of geometrical characterization including taper angle (TA), overcut (OC), circularity at the entry and exit (C_ent and C_exit), and performance measures including material removal rate (MRR), tool wear rate (TWR), and average roughness (R_a). The Taguchi-based L₂₇ orthogonal array (OA) is used to carry out the experimental runs, and technique for order of preference by similarity ideal solution (TOPSIS) approach is used for the identification of optimal parameters on AISI 304 stainless steel. The optimized result achieved from this approach suggests improved TA, OC, C_ent, C_exit, MRR, and lower TWR, surface roughness (SR) with the combinations of CμEDM drilling process such as I_p of 15 A, T_on of 10?µs, T_off of 30?µs, and V_g of 30?V. Analysis of variance (ANOVA) was conducted to identify the major influencing parameter.     

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.     

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.     

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.     

Performance of Additive Mixed Kerosene–Servotherm in Electrical Discharge Machining of Monel 400™

In general, kerosene and commercial grade EDM oils are conventional dielectric fluids in electrical discharge machining (EDM), despite their poor performance measures being major drawbacks. The aim of this study was to develop a dielectric fluid offering good performance measures in the EDM process, by determining the appropriate proportion of kerosene–servotherm and analyzing its performance with and without the additive concentration in EDM of monel 400?. Sixteen samples of kerosene–servotherm of varying proportions were used in this study. The optimum proportion of kerosene–servotherm was found to be 75:25, which resulted in the highest material removal rate (MRR) as compared with tool wear rate (TWR), and surface finish was found to be poorer than when using kerosene alone. In addition, 1 l of kerosene–servotherm concentrated with 6 g of graphite powder (one micron) exhibited substantial improvement in MRR, surface finish, and TWR compared with conventional dielectric fluids. Therefore kerosene–servotherm (75:25) concentrated with 6 g/l of graphite powder can be accepted as a potential dielectric fluid offering high MRR along with enhanced surface finish in EDM.     

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.     

Microstructural Analysis and Multiresponse Optimization During ECM of Inconel 825 Using Hybrid Approach

In the current study, electrochemical machining of Inconel 825, a Ni-based super alloy, was carried out using tungsten as a tool electrode material and NaCl as electrolyte. The present investigation attaches particular emphasis on explaining the mechanism of material removal of Ni-based super alloys in the ECM process. The influence of various ECM parameters such as voltage (V), concentration (C), and tool feed (F) has been investigated on the evolution of the surface morphology of Inconel 825 after ECM. Different performance measures in ECM such as material removal rate (MRR), surface roughness (SR), and radial overcut (ROC) have been measured. Grey relational analysis that uses grey relational grade as performance index has been adopted to simultaneously optimize multiple performance characteristics and determine optimal combination of ECM parameters. Moreover, principal component analysis is utilized to determine the weighting values corresponding to various output responses so that their relative importance can be adequately expressed. Optimal condition was found to be V = 16 V, C = 45 g/L, and F = 0.3 mm/min. Confirmation test was further performed to authenticate the approach applied for determining the optimal conditions that resulted in MRR of 20.867 mm³/min, SR of 0.156 µm, and ROC of 0.0697 mm, which were superior to those corresponding to all previous experimental runs.     

Parametric Evaluation on Near-Dry Electric Discharge Machining

Near-dry electric discharge machining (EDM) is an eco-friendly process. It does not produce toxic fumes and consequent health hazards. The near-dry EDM generally utilizes a mixture of two phase (liquid and air) dielectric for machining. This investigation reports the influence of four processing parameters, viz. current, flushing pressure, duty factor, and lift on three responses. The responses measured were material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR). The work material chosen was high speed steel (HSS). Mathematical models have been proposed herein for evaluation of the effect of processing parameters in near-dry EDM. These models were developed using response surface methodology (RSM). The experimental results reveal that the process parameters taken into consideration were significant for MRR. The TWR was negligible in near-dry EDM. This process gives a finer surface finish with thinner recast layer even at higher discharge energies as compared to conventional EDM.     

Examinations concerning the electric discharge machining of AZ91/5B4CP composites utilizing distinctive electrode materials

In this study, investigation has been conducted in the focus of obtaining better surface finish in the electro discharge machining (EDM) of AZ91/5B₄C_p magnesium composites using distinctive sort of anode viz. copper, tungsten–copper, brass, aluminum and 20Gr/AA6061 (GRAL-20) composites. The process parameters, pulse on time and current were performed to research the machining qualities through material removal rate (MRR) and tool wear rate (TWR). The machined composites were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The formation of black spots was observed on machining with copper–tungsten and these black spots were not found when GRAL-20 was used as electrode. Machined with GRAL-20 electrode leads to the increase in spark gap, hence adequate flushing occurs; it eliminates re-melted layers on machined surface results in better surface roughness value. The results revealed that GRAL-20 electrodes posses better MRR followed by copper electrode whereas tungsten–copper exhibits better TWR followed by GRAL-20 electrode.     

退火热处理对等径角挤压回收Ti-6Al-4V合金微观结构和显微硬度的影响

采用等径角挤压法回收Ti-6Al-4V合金切屑,并研究了回收样品和退火处理样品的微观结构和显微硬度。结果表明:在回收样品中,切屑之间的边界依然存在,而由于剧烈塑性变形,超细晶结构和较强的纤维织构得以形成。退火处理后,切屑边界部分消失,超细晶组织部分再结晶;而与此同时,退火处理样品展现出更宽泛的织构,再结晶晶粒并不存在择优取向。值得注意的是,退火处理样品的显微硬度较回收样品略有升高。     

Experimental Analysis of Al–TiC Sintered Nanocomposite on EDM Process Parameters Using ANOVA

The size minimization of titanium carbide (TiC) particles was done by high-energy mechanical milling. Later Al and TiC powders were mixed to frame cylindrical preforms with 95% density using a die set. The cylindrical preform was sintered in a muffle furnace (575°C) and subsequently cooled. Characterization was done using scanning electron microscope (SEM), field emission scanning electron microscope, and energy-dispersive spectrum. An electrical discharge machining (EDM) and L9 orthogonal array was used to perform the experiments. The present investigation was carried out to optimize parameters such as current, pulse-on time, and gap voltage on metal removal rate (MRR) and tool wear rate (TWR) during EDM of as-sintered Al–5% reinforced with ≤200 nm and 2 µm TiC particle reinforcement. The rationality of the experimental plan and the effect of electrode wear ratio based on TiC particle addition were analyzed using analysis of variance (ANOVA) with consideration to MRR and TWR. The recast layer evolution during EDM process was assessed by SEM analysis.     

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.     

Machinability of titanium alloy through electric discharge machining

Titanium alloy (Ti-6Al-4V), being considered as hard-to-machine material, offers many challenges especially during conventional machining. Electric discharge machining could be a good option if it offers a good match between material removal rate and surface finish of the machined feature. The issue of appropriate selection of electrode material for good machining of Ti-6Al-4V is not yet comprehensively explored which is the core focus of this study. Moreover, the effect of pulse time ratio is thoroughly examined which is not specifically studied before. Discharge current and pulse time ratio are considered as the input variables, whereas the material removal rate and surface roughness are selected as performance measures of machinability. Copper, aluminum, brass and graphite are employed to evaluate the machining behavior. Experimental results revealed that aluminum electrode provides the lowest surface roughness, whereas the maximum material removal rate is achieved using graphite electrode. However, graphite electrode can offer high material removal rate with low surface roughness by initially employing negative tool polarity for rough machining and then positive tool polarity for fine machining.     

On machining of hard and brittle materials using rotary tool micro-ultrasonic drilling process

The present paper reports on a recently developed rotary tool micro-ultrasonic drilling (RT-MUSD) process. The RT-MUSD process was utilized for machining of micro-holes in zirconia, silicon and glasswork materials. The effects of work material properties on the performance characteristics (material removal rate (MRR), depth of hole and hole overcut) of RT-MUSD process were investigated by varying the power rating, rotation speed, abrasive size and slurry concentration. Additionally, machined micro-holes and tool surface were analyzed considering microscopic images. The experimental results revealed that the MRR and depth of hole increased by increasing the power rating. An increase in rotation speed up to 300 rpm, abrasive size up to #1200 mesh and concentration up to 20% increased the MRR, depth of hole and decreased hole overcut. The maximum machining rate and hole overcut were observed during machining of silicon followed by glass and zirconia. The fracture toughness and hardness of the work material affected the MRR and tool wear, respectively. Pure brittle fracture mode of material removal was observed in all the work materials during RT-MUSD process. Eventually, the RT-MUSD process was optimized using desirability approach and a micro-hole of depth 4355 µm was achieved using optimal parameter settings.