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.     

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.     

Multi‐response optimization of the machining characteristics in electrical discharge machining (EDM) using span‐20 surfactant and chromium (Cr) powder mixed

Effects of Chromium (Cr) powder concentrations (C_p) and Span‐20 surfactant concentrations (C_s) on AISI D2 hardened steel were evaluated using response surface methodology (RSM) and parameter processing parameter were optimized for optimal parameter conditions using multi‐response desirability function. Responses taken involved material removal rate (MRR), electrode wear rate (EWR) and surface roughness (R_a). The experimental plan was based on the face centered, central composite design (CCD) using version 10.0 of the Design Expert software. The results identified that C_p is the most important parameter to maximize material removal rate (MRR) and minimize electrode wear rate (EWR) and surface roughness (R_a). With the topmost desirability solution, the suggested optimum parameter condition of C_p and C_s were 2.155 g/L and 10.000 g/L, respectively.     

Experimental investigation on performance of additive mixed dielectric during micro-electric discharge drilling on 316L stainless steel

This study investigates the impact of machining factors on the performance of additive mixed micro-electric discharge drilling of 316L stainless steel. The effects of three kinds of powder, powder concentration, voltage, capacitance, feed rate, and speed on tool wear rate, material removal rate, taper angle, and overcut (OC) were also investigated. The experimental results show that adding additives to the dielectric enhanced rate of material removal and reduced rate of tool wear significantly. Mixing powder with dielectric increased the length of the sparking, resulting in significant OC, and process performance also improved with the increase in amount of powder added. Further, scanning electron microscopy analysis was carried out to examine the surface characteristics and material migration properties, which confirmed that the properties of the machined surface are indeed significantly improved.     

Measurement and analysis of impact dynamics suitable for modelling pneumatic transport of metallic powder flow through a directed energy deposition nozzle

In blown powder directed energy deposition (DED) additive manufacturing powdered metal feedstock is pneumatically conveyed to the meltpool via a nozzle. DED nozzles have been the subject to a growing number of research efforts using computational fluid dynamics (CFD) with multiphase flows to study and optimize powder flow. However, many research papers published to date contain powder – nozzle impact dynamics behavior that is not realistic or not derived from experiments that resemble the powder conveyance process in the DED nozzle being studied. To provide a set of data representative of DED powder flow through a nozzle particle image velocimetry (PIV) experiments were conducted using 316L stainless steel metal powder and flat targets with varying surface roughness made of oxygen free copper, mild steel, P20 tool steel, 316L stainless steel, Inconel 718, and Ti-Al6-V4. Normal coefficients of restitution (COR) were calculated and compared to several analytical and empirical models in literature.     

Fabrication of Surface Modification Layer on Stainless Steel by Electrical Discharge Machining

A stainless steel (SUS 304) was machined by Electrical Discharge Machining (EDM) with a sialon and chromium electrode. According to the EDMed conditions, the deformed stainless steel surface turned to the coated surface with an electrode components. The following experimental factors were investigated to produce the modified surface: electrode polarity, work atmosphere, peak current, pulse duration and duty factor. In the suitable worked conditions, the modified layer had good corrosion and wear resistance.     

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.     

P. F.

Abstract

The effect of pulse duration and electrode type (copper or graphite) on the pick-up of carbon in the surface of a die steel shaped using electrodischarge machining and on surface microcracks has been studied. The present work suggests that the number and the size of surface microcracks increase with pulse duration when machining with a copper electrode, but there is some evidence to suggest that, when using a graphite electrode, the number and the length of microcracks and the average thickness of the recast layer may be greatest at intermediate (75–150μs) pulse durations. Although no definite conclusion can be drawn from the results, it is suggested that this may be because the manner of decay of the temperature field after each pulse is determined by both electrode material and pulse duration. At high current densities and long pulse durations, the length and frequency of microcracks is increased greatly at the corners of specimens machined using a graphite electrode, but this occurred to a much lesser extent when using a copper electrode – a difference that would seem to reinforce the suggestion that the characteristics of the temperature field after each pulse depend on the electrode material. It was concluded that carbon was absorbed from the dielectric (paraffin) rather than from the electrode. The amount of copper absorbed did not depend on pulse duration.

MST/1040     

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.     

Effect of tool rotation in near-dry EDM process on machining characteristics of HSS

Rotary tool near-dry electrical discharge machining (RT-ND-EDM) is a process variant of EDM, which utilizes two phase dielectric medium instead of a conventional liquid or gaseous dielectric medium. The present work, RT-ND-EDM was investigated while machining of high speed steel (AISI M2 grade) using glycerin-air dielectric medium. The effect of various input process parameters was investigated on material removal rate (MRR), surface roughness (SR), and hole overcut (HOC). The input parameters considered were tool rotation speed, current, pulse on time, liquid flow rate, and gas pressure. Experiments were designed and conducted using response surface methodology. Regression models were also developed. The results revealed that the tool rotation speed has a significant effect on MRR, SR, and HOC. FE-SEM micrographs showed that the machined surfaces obtained by RT-ND-EDM have relatively lower micro-cracks, debris accumulation and craters. Also, deep through holes were successfully drilled in 24 mm plate using RT-ND-EDM process.     

不同工艺参数对高硬度铁粉等离子弧增材熔覆的影响

目的优化马氏体不锈钢等离子弧增材熔覆工艺。方法利用等离子热源在300M表面对新型高硬度铁粉的增材熔覆工艺进行研究。基于三因素三水平熔覆工艺的正交试验,研究在大温度梯度熔覆环境下,等离子弧电流、焊枪移动速度及送粉速率对单道金属熔池的非平衡凝固组织的影响机制,综合考虑单道焊道宏观形貌、成形尺寸及稀释率,确定增材熔敷的电流、焊枪移动速度及送粉速率;在此基础上,基于多道单层及单道多层熔覆的宏观形貌及拉伸性能,确定多道多层增材熔覆的搭接率及熔覆工艺。结果在电流为140～180 A、移动速度为20～30 cm/min和送粉速率为20～30 r/min的工艺窗口内,电流对焊道的稀释率有较大影响,送粉速率次之;送粉速率对高宽比的影响最大,扫描速度次之。结论当电流大小为140 A,送粉速率为30 r/min,扫描速率为30 cm/min时,单道单层焊道的稀释率及宽高比最小,热影响区晶粒尺寸较小,叠加率为40%时,熔覆层表面平整度较高。     

Experimental studies on electrical discharge wire cutting of Ni-rich NiTi shape memory alloy

The experimental investigation explores the effect of electrical discharge wire cutting (EDWC) variable parameters such as spark gap voltage, wire tension, pulse off time, wire feed rate, and pulse on time on the surface roughness, average cutting rate, and metallographic changes of Ni_55.95Ti_44.05 shape memory alloy (SMA). The spark gap voltage, pulse off time, and pulse on time have the significant effect on the surface roughness and average cutting rate, whereas wire tension and wire feed rate have the trifling effect. Ni_55.95Ti_44.05 SMA’s surface after EDWC is characterized by many discharge craters, microcracks, voids, and white layer of resolidified molten material. The elemental composition analysis of white layer using energy-dispersive spectroscopy divulges the deposition of the foreign element from the brass wire as well as the dielectric on the surface after EDWC. The machined surface as well as the wire electrode surface consists of various compounds of Ti, Ni, Zn, and Cu which have been identified by X-ray diffraction peak analysis.     

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.     

Parametric optimization of multiwalled carbon nanotube-assisted electric discharge machining of Al-10%SiCp metal matrix composite by response surface methodology

The demand for miniaturized products having a glossy surface or nano-level surface is increasing exponentially in automobile, aerospace, biomedical, and semiconductor industries. The mirror-like surface finish has generated a need to develop advanced machining processes. The addition of powder particle into electric discharge machining (EDM) oil is considered a promising technique to achieve surface integrity at the miniaturization level. In this research, the Al–10%SiC_p metal matrix composite (MMC) has been machined after mixing the appropriate amount of multiwalled carbon nanotubes (MWCNTs) into the EDM dielectric fluid. An advanced experimental setup has been designed and fabricated in the laboratory for conducting the experiments. This proposed technology is called nano powder mixed electric discharge machining (NPMEDM). The input parameters of NPMEDM are also optimized using central composite rotatable design (CCRD) based on response surface methodology (RSM) in order to obtain the best surface finish and material removal rate (MRR). The MRR has been increased by 38.22% and surface finish has been improved by 46.06% after mixing the MWCNTs into the EDM dielectric fluid. The results indicate that the combination of parameters A5, B5, C5, and D5 might have produced maximum MRR, whereas A1, B1, C1, and D3 have produced minimum surface roughness (SR).     

Multi-objective parametric optimization of powder mixed electro-discharge machining using response surface methodology and non-dominated sorting genetic algorithm

Powder mixed electro-discharge machining (EDM) is being widely used in modern metal working industry for producing complex cavities in dies and moulds which are otherwise difficult to create by conventional machining route. It has been experimentally demonstrated that the presence of suspended particle in dielectric fluid significantly increases the surface finish and machining efficiency of EDM process. Concentration of powder (silicon) in the dielectric fluid, pulse on time, duty cycle, and peak current are taken as independent variables on which the machining performance was analysed in terms of material removal rate (MRR) and surface roughness (SR). Experiments have been conducted on an EZNC fuzzy logic Die Sinking EDM machine manufactured by Electronica Machine Tools Ltd. India. A copper electrode having diameter of 25?mm is used to cut EN 31 steel for one hour in each trial. Response surface methodology (RSM) is adopted to study the effect of independent variables on responses and develop predictive models. It is desired to obtain optimal parameter setting that aims at decreasing surface roughness along with larger material removal rate. Since the responses are conflicting in nature, it is difficult to obtain a single combination of cutting parameters satisfying both the objectives in any one solution. Therefore, it is essential to explore the optimization landscape to generate the set of dominant solutions. Non-sorted genetic algorithm (NSGA) has been adopted to optimize the responses such that a set of mutually dominant solutions are found over a wide range of machining parameters.     

Surface Roughness and Microhardness Evaluation for EDM with Cu–Mn Powder Metallurgy Tool

In the present research, composite electrode (Cu–Mn) manufactured through powder metallurgy has been used to machine hot die steel (H11) by electrical discharge machining (EDM) process with the aim of inducing manganese and carbon into the machined surface. Such alloying is expected to improve the microhardness and other surface characteristics. Best level of process parameters for better surface finish and high microhardness are found using Taguchi method. Six processing parameters are considered and their significance is investigated by analysis of variance. Techniques like energy dispersive spectroscopy, scanning electron microscopy, and X-ray diffraction are used to ascertain the surface characteristics. Surface machined at optimum process conditions for microhardness shows 93.7% improvement due to formation of cementite, ferrite and manganese carbide phases. Surface roughness having Ra value of 3.11 µm has been achieved.     

Experimental investigation on wire electric discharge machining (WEDM) of Nimonic C-263 superalloy

Nimonic C-263 superalloy offers a wide range of outstanding properties, namely, high-temperature resistance, high specific strength, high thermal fatigue, and hot corrosion resistance. The concern of the present study is mainly focused on the effect of wire electrical discharge machining (WEDM) process parameters namely, spark energy, spark frequency, and peak current on surface roughness, average cutting rate, and surface integrity aspects of Nimonic C-263 superalloy by using one-parameter-at-a-time (OPAT) approach. Surface roughness and average cutting rate were showing the increasing trend with the spark energy and peak current and reverse trend with the spark frequency. Surface integrity aspects of Nimonic C-263 such as surface topography, surface morphology, recast layer thickness, elemental composition, and phase analysis have been also considered in this study. Scanning electron microscope (SEM) micrograph of the machined surface shows the presence of micro-voids, discharge craters, micro-globules, and droplets of molten material. A recast layer of minimum thickness, with less transfer of foreign atoms (Mo, C, and O) from dielectric fluid and molybdenum wire, has been formed at lower spark energy compared to higher spark energy. The various compounds of Ni, Fe, Al, and Ti such as Fe_1.2Ni_0.8, Fe_1.5Ni_0.5, Co_0.06Fe_0.94, and Al_o.29Ni_0.27Ti_0.44 were formed on the machined surface identified through analysis of XRD peaks.     

Fatigue life prediction of additively manufactured material: Effects of surface roughness,defect size,and shape

In this paper, the effects of process‐induced voids and surface roughness on the fatigue life of an additively manufactured material are investigated using a crack closure‐based fatigue crack growth model. Among different sources of damage under cyclic loadings, fatigue because of cracks originated from voids and surface discontinuities is the most life‐limiting failure mechanism in the parts fabricated via powder‐based metal additive manufacturing (AM). Hence, having the ability to predict the fatigue behaviour of AM materials based on the void features and surface texture would be the first step towards improving the reliability of AM parts. Test results from the literature on Inconel 718 fabricated via a laser powder bed fusion (L‐PBF) method are analysed herein to model the fatigue behaviour based on the crack growth from semicircular/elliptical surface flaws. The fatigue life variations in the specimens with machined and as‐built surface finishes are captured using the characteristics of voids and surface profile, respectively. The results indicate that knowing the statistical range of defect size and shape along with a proper fatigue analysis approach provides the opportunity of predicting the scatter in the fatigue life of AM materials. In addition, maximum valley depth of the surface profile can be used as an appropriate parameter for the fatigue life prediction of AM materials in their as‐built surface condition.     

Experimental investigation of water-in-oil nanoemulsion in sinking electrical discharge machining

The most common dielectric in sinking electrical discharge machining (EDM) is kerosene. However, kerosene is inflammable; besides, it can be decomposed and release harmful gases during machining process. And, owing to its low viscosity, using kerosene in sinking EDM has low machining efficiency. Accordingly, conventional sinking EDM using kerosene as dielectric has poor safety, unfriendly environment impact, and low machining efficiency. A new water-in-oil (W/O) nanoemulsion is presented in this paper. This W/O nanoemulsion not only can eliminate the hazards from kerosene to operator and environment but also improve the machining performance of conventional sinking EDM. This research aims to experimentally investigate the machining performance of W/O nanoemulsion in comparison with kerosene in sinking EDM at relatively low discharge energy. The effects of electrode material, electrode polarity, peak current, and pulse duration on machining performance are studied. The machined surface and recast layer of workpiece are characterized as well. The experimental results demonstrate that compared with kerosene, using W/O nanoemulsion in sinking EDM can obtain a higher material removal rate (MRR), a lower relative electrode wear rate (REWR), and a machined workpiece with fewer defects and thinner recast layer.     

粉体颗粒表面的定量描述

基于离散分形布朗增量随机场 (DFBIR场 ) ,提出了一种适于微粉颗粒表面微观形貌定量分析的分形模型 ,研究了此模型的特点及其计算方法 ,提出了颗粒表面形貌的智能分形表征技术