Optimization of Dry Machining Parameters for High-Purity Graphite in End-Milling Process

The machining factors affecting the tool wear and surface finish produced in the end milling process are generally the cutting speed, the feed rate, the depth of cut, etc. This paper describes a study that identifies the influence of the machining parameters on the groove width and the surface roughness average for the end-milling of high-purity graphite under dry machining conditions. The experiments are based on an orthogonal arrays and grey relational analysis method is then applied to determine an optimal machining parameter setting. The dimensional accuracy of the groove width and the surface roughness average are selected as the quality targets. In this study, the feed rate is the most significant controlled factors for the machining process according to the weighted sum grade of the Δ and the R_a.     

Effect of Cryogenic Cooling of Tool Electrode on Machining Titanium Alloy (Ti–6Al–4V) during EDM

The discharge characteristics and discharge gap of machining Ti–6Al–4V titanium alloy by cryogenically cooled tool electrode electrical discharge machining (EDM) in distilled water were investigated in this study using the monopulse discharge method. The influence of the cryogenically cooled tool electrode on the discharge gap and the initial maintaining voltage between the electrode and workpiece were analyzed under various temperatures. Test results showed the initial maintaining voltage of the cryogenically cooled tool electrode EDM was lower than that of conventional EDM. The discharge gap of the cryogenically cooled tool electrode EDM was also smaller than that of conventional EDM, which improved the copying accuracy of die-sinking EDM. A comparative experiment of machining Ti–6Al–4V titanium alloy was carried out by using cryogenically cooled tool electrode EDM and conventional EDM, lower electrode wear, higher material removal ratio, and higher corner size machining accuracy was obtained by using cryogenically cooled tool electrode EDM.     

Machining Characteristics and Optimization of Machining Parameters of SKH 57 High-Speed Steel Using Electrical-Discharge Machining Based on Taguchi Method

The effects of the machining parameters in electrical-discharge machining (EDM) on the machining characteristics of SKH 57 high-speed steel were investigated. A well-designed experimental scheme was used to reduce the total number of experiments. Parts of the experiment were conducted with the L18 orthogonal array based on the Taguchi method. Moreover, the signal-to-noise ratios associated with the observed values in the experiments were determined by ANOVA and F-test. The significant parameters that critically influenced the machining characteristics were examined, and the optimal combination levels of machining parameters for material removal rate, electrode wear rate, and surface roughness were determined.     

Study of the Effect of Machining Parameters on the Machining Characteristics in Electrical Discharge Machining of Fe-Mn-Al Alloy

In this work we investigated the electrical discharge machining (EDM) of a Fe-Mn-Al alloy. The surface phenomena caused by EDM were studied in terms of machining parameters. An empirical model of the Fe-Mn-Al alloy was also proposed based on the experimental data. Experimental results indicate that the higher the discharge energy, the faster the machining time. This treatment introduces machining damage in the resolidified surface layer and worsens the surface roughness. The optimum pulse-on duration on the basis of the electrode wear ratio for the copper electrode was about 200 μs. The increase of crater depth with the applied pulsed current and pulse-on duration appears minimal under a small input energy.     

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.     

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.     

Machining Characteristics of Inconel 718 by Sinking-EDM and Wire-EDM

Inconel 718 superalloy has wide applications in several industries due to its excellent mechanical properties. However, it is very difficult to machine using conventional cutting and grinding because of its high strength at elevated temperatures. Electrical discharge machining (EDM) is an alternative competitive process to machine Inconel alloys by electrical erosion. However, machinability and surface characteristics of EDMed Inconel surfaces are poorly understood. This study focuses on the machining characteristics of Inconel 718 by Wire-EDM and Sinking-EDM with a new Cu-SiC electrode, respectively. Material removal efficiency, surface roughness, surface topography, surface alloying, and electrode wear have been characterized. It is found that the high toughness of Inconel 718 would be the major contributing factor to the absence of microcracks on the EDMed surface. The new fabricated Cu-SiC electrode for Sinking-EDM has better performance in terms of material removal rate (MRR), surface roughness, and electrode wear. The higher melting temperature and fine microstructure of SiC contribute to the lower electrode wear of the new Cu-SiC electrode than the traditional Cu electrode.     

Investigation into the Effect of Voltage Excitation of Pre-Ignition Spark Pulse on the Electro-Discharge Machining (EDM) Process

Studying the variation of the electro-discharge machining (EDM) process outputs due to the change in shape of the generated pulse is one research aspect in the EDM process. In this study, the effects of voltage excitation of the pre-ignition spark pulse on the process outputs material removal rate (MRR), electrode wear ratio (EWR), and surface roughness (Ra) have been investigated. Experiments were designed using design of experiments (DOE), and the results were analyzed using analysis of variance (ANOVA). Based on the results, it has become clear that applying voltage excitation of the pulse produces effective pulses, which in turn lessens EWR, increases MRR, and improves surface quality. Hence, the suitability of this method has been verified for EDM.     

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.     

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.     

The effect of the stress ratio on fatigue crack growth in a 3% NaCl solution

Corrosion fatigue crack growth tests have been carried out at various stress ratios for a low alloy steel SNCM 2 and type 304 stainless steel.

Measurements of the effective stress intensity factor range ratio U were performed to explain the effect of stress ratio R.

The corrosive environment decreased da/dN at R = 0.1, 0.4 and little affected da/dN at R = 0.9 for SNCM 2 and increased da/dN at all R ratios for SUS 304.

It was confirmed that there exists a threshold stress intensity factor ΔK_thCF in 3% NaCl solution for both materials tested.

The corrosive environment decreased ΔK_thCF for all conditions tested except at R = 0.1 and 0.4 for SNCM 2, where ΔK_thCF-values were nearly equal to ΔK_th-values in air. ΔK_thCF/ΔK_th was 0.6 at R = 0.9 for SNCM 2 and 0.8, 0.5 and 0.7 at R = 0.1, 0.7 and 0.9 for SUS 304, respectively.

It was shown that the complicated effect of stress ratios on crack growth for SNCM 2 can be explained using effective stress intensity factor ΔK_eff.     

Machining of Green Si3N4 Polymer Bonded Ceramic Materials

This research examined the machinability of Si₃N₄, based polymer bonded ceramic green bodies. They were clearly machinable. Surface roughness was comparable to milled steel. The machining forces were lower than those reported for other ceramics and composites. Higher percentages of polymer produced stronger, more machinable green bodies. The areas of greatest concern were: tool wear, distribution of polymer throughout the body, and choice of polymer, for good wettability. Feasible parameters for blank fabrication were determined. Optimal parameters for both blank fabrication and machining are still to be determined. Polymer bonded ceramic bodies may also have their own utility; however applications with these materials will require further investigations.     

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.     

A review on conventional and nonconventional machining of SiC particle-reinforced aluminium matrix composites

Among the various types of metal matrix composites, SiC particle-reinforced aluminum matrix composites (SiC_p/Al) are finding increasing applications in many industrial fields such as aerospace, automotive, and electronics. However, SiC_p/Al composites are considered as difficult-to-cut materials due to the hard ceramic reinforcement, which causes severe machinability degradation by increasing cutting tool wear, cutting force, etc. To improve the machinability of SiC_p/Al composites, many techniques including conventional and nonconventional machining processes have been employed. The purpose of this study is to evaluate the machining performance of SiC p/Al composites using conventional machining, i.e., turning, milling, drilling, and grinding, and using nonconventional machining, namely electrical discharge machining (EDM), powder mixed EDM, wire EDM, electrochemical machining, and newly developed high-efficiency machining technologies, e.g., blasting erosion arc machining. This research not only presents an overview of the machining aspects of SiC_p/Al composites using various processing technologies but also establishes optimization parameters as reference of industry applications.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00313-2     

Machining of Engineering Ceramics by Ultrasonic Vibration Assisted EDM Method

Ultrasonic vibration assisted EDM was performed by using an ultrasonic machine tool with a d.c. power supply, with its positive and negative poles connected to the workpiece and the tool electrode, respectively. The pulse discharge is produced by the relative motion between the tool electrode and the workpiece. In the working process of this combined technology, ultrasonic machining and EDM are complementary techniques. Experimental results show that the material removal rate is a little more than just the sum of ultrasonic machining and EDM, while surface roughness is about the same as that for ultrasonic machining.     

ELECTRO-DISCHARGE MACHINING OF TRANSFORMATION TOUGHENED ZrO - NbC CERAMIC COMPOSITE

Electroconductive transformation toughened ZrO₂ and NbC ceramic composite was machined with an electro-discharge machining (EDM) method. Effects of EDM conditions on roughness of machined surfaces were examined. Surface damage caused during machining was evaluated with flexural strength of machined specimens. Fracture surfaces of EDMed bending specimens were observed by scanning electron microscopy (SEM).

It was observed that the strength of EDMed members was decreased with increases in pulse current, pulse duration and duty factor. Pulse duration and pulse current had a great influence on the roughness of machined surfaces. When the pulse duration was large enough, noticeable delaraination in the surface layer occurred. The highest flexural strength of an EDMed specimen attained was about 1 GPa. The X-ray diffraction patterns of surface layers were changed by machining.     

绝缘陶瓷材料电火花加工技术的研究进展

陶瓷材料特性鲜明，有着广阔的应用前景。辅助电极法电火花加工绝缘陶瓷是一种新兴的加工工艺，介绍了陶瓷材料电火花加工技术的基本原理及研究进展。     

Machining and surface finishing of brittle solids

Ceramic materials are finished primarily by abrasive machining processes such as grinding, lapping, and polishing. In grinding, the abrasives typically are bonded in a grinding wheel and brought into contact with the ceramic surface at relatively high sliding speeds. In lapping and polishing, the ceramic is pressed against a polishing block with the abrasives suspended in between them in the form of a slurry. The material removal process here resembles three-body wear. In all these processes, the mechanical action of the abrasive can be thought of as the repeated application of relatively sharp sliding indenters to the ceramic surface. Under these conditions, a small number of mechanisms dominate the material removal process. These are brittle fracture due to crack systems oriented both parallel (lateral) and perpendicular (radial/median) to the free surface, ductile cutting with the formation of thin ribbon-like chips, and chemically assisted wear in the presence of a reactant that is enhanced by the mechanical action (tribochemical reaction). The relative role of each of these mechanisms in a particular finishing process can be related to the load applied to an abrasive particle, the sliding speed of the particle, and the presence of a chemical reactant. These wear mechanisms also cause damage to the near ceramic surface in the form of microcracking, residual stress, plastic deformation, and surface roughness which together determine the strength and performance of the finished component. A complete understanding of the wear mechanisms leading to material removal would allow for the design of efficient machining processes for producing ceramic surfaces of high quality. The research was supported in part by the National Science Foundation through grants MSS 9057082, Jorn Larsen-Basse, Program Director and DDM 9057916, Bruce Kramer, Program Director.     

Optimization of Electrical Discharge Machining Characteristics of SiCp/LM25 Al Composites Using Goal Programming

In the present study an effort has been made to optimize the machining conditions for electric discharge machining of LM25 Al (7 Si, 0.33 Mg, 0.3 Mn, 0.5 Fe, 0.1 Cu, 0.1 Ni,.2 Ti) reinforced with green bonded SiC particles with approximate size of 25 mum. Polynomial models were developed for the various EDM characteristics such as metal removal rate, tool wear rate and surface roughness in terms of the process parameters such as volume fraction of SK, current and pulse time. The models were used to optimize the EDM characteristics using nonlinear goal programming.     

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.