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Journal of Materials Processing Technology 184 (2007) 32–41

Technology and research developments in powder mixedelectric discharge machining (PMEDM)

H.K. Kansal a,∗, Sehijpal Singh b, Pradeep Kumar c

a Department of Mechanical Engineering, SLIET, Longowal 148106, District Sangrur, Punjab, Indiab Department of Mechanical & Production Engineering, G.N.D.E.C., Ludhiana, 147001 Punjab, India

c Department of Mechanical and Industrial Engineering, I.I.T. Roorkee, 247667, India

Received 28 July 2005; received in revised form 11 October 2006; accepted 31 October 2006

bstract

Powder mixed electric discharge machining (PMEDM) is one of the recent innovations for the enhancement of capabilities of EDM process. InMEDM, the electrically conductive powder is mixed in the dielectric of EDM, which reduces the insulating strength of the dielectric fluid and

ncreases the spark gap between the tool and workpiece. As a result, the process becomes more stable, thereby, improving the material removal rate

MRR) and surface finish. Moreover, the surface develops high resistance to corrosion and abrasion. This paper presents a tutorial introduction,omprehensive history and review of research work carried out in the area of PMEDM. The machining mechanism, current issues, applicationsnd observations are also discussed. 2006 Elsevier B.V. All rights reserved.

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eywords: Electric discharge machining; Surface roughness; Material removal

. Introduction

Among all the non-conventional machining methods, electricischarge machining (EDM) is one of the most popular machin-ng methods for the manufacturing of press tools and variousies. This process enables machining of any material, whichs electrical conductive, irrespective of its hardness, shape andtrength [1]. Even highly delicate sections and weak materialsan be machined without any fear of distortion because there iso direct contact between the tool and the workpiece.

Since the invention of EDM in the 1940s, many efforts haveeen made to improve the machining performance and stabilityf EDM process. Process stability is the key factor for turningnatural material removal process into a controllable machin-

ng process [2]. Due to continuous process improvement, many

DM machines have become so stable that these can be operatedround the clock if monitored by an adaptive control system. Theemands for high machining precision with low surface rough-

∗ Corresponding author. Tel.: +91 1672 284962(O)/280038(R);ax: +91 1672 284860/280057/280072.

E-mail addresses: shaarut@yahoo.com (H.K. Kansal),ehijgnec@yahoo.co.in (S. Singh), kumarfme@iitr.ernet.in (P. Kumar).

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924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.jmatprotec.2006.10.046

Tool wear rate

ess at relatively high machining rates arise in die, mold and toolanufacturing industries [2]. To fulfill this requirement, a rela-

ively new advancement in the direction of process capabilities ishe addition of powder in the dielectric fluid of EDM [3–5]. Thisew hybrid material removal process is called powder mixedDM (PMEDM). The results show that the PMEDM can dis-

inctly improve the surface finish and surface quality to obtainear mirror like surfaces at relatively high machining rate [5–7].oreover, the surface produced by PMEDM has high resistance

o corrosion and abrasion [8,9]. In this process, a suitable mate-ial in fine powder form is mixed into the dielectric fluid of EDM.he added powder improves the breakdown characteristics of theielectric fluid, i.e. the insulating strength of the dielectric fluidecreases and consequently, the spark gap distance between thelectrode and workpiece [3,4,7] increases. Enlarged spark gapistance makes the flushing of debris uniform. As a result, therocess becomes more stable thereby improving machining ratend surface finish.

PMEDM also termed as ‘Additive EDM’ was originallynvented during late seventies as a revolutionary technique

or achieving mirror like finish relatively at high machiningates on already machined components (using conventionalethods) [10,11]. Numbers of researchers have conducted the

xperiments to investigate the effects of addition of powder

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nto dielectric fluid on the performance of EDM. While goinghrough the available literature on this process, a need is felto summarize all the results and conclusions made by differ-nt researchers. Therefore, this paper is an attempt to provide aeview of the various research activities carried out in the pastecade involving the PMEDM process.

In this paper, the fundamental principle and major techno-ogical developments into the PMEDM process are described.lthough the machining mechanism of PMEDM is not still

learly understood, the widely accepted principle of the pro-ess is presented here. The historical perspective of PMEDMrocess and its applications are discussed in the next section.he final part of the paper discusses the current problems and

uture direction for the PMEDM research.

. Technology of powder mixed EDM

This section provides the basic machining mechanism ofMEDM.

PMEDM has a different machining mechanism from the con-entional EDM [3]. In this process, a suitable material in theowder form is mixed into the dielectric fluid either in the sameank or in a separate tank. For better circulation of the powder

ixed dielectric, a stirring system is employed. For constant

euse of powder in the dielectric fluid, a modified circulationystem (Fig. 1) is used.

The experimental setup consists of a transparent bath likeontainer, called machining tank. It is placed in the work tank of

aipo

Fig. 1. Schematic of PMED

able 1hermo physical properties of various additives [7]

owder Density (g cm−1) Thermal conductivity (W cm−1 ◦C−1) Electric

l 2.70 2.38 2.45r 7.16 0.67 2.60u 8.96 4.16 1.59iC 3.21 1.0–5.0 1 × 109

cessing Technology 184 (2007) 32–41 33

DM and the machining is performed in this container. To holdhe workpiece, a workpiece fixture assembly is placed in it. The

achining tank is filled up with dielectric fluid (kerosene oil).o avoid particle settling, a stirring system was incorporated. Amall dielectric circulation pump was installed for proper circu-ation of the powder mixed dielectric fluid into the discharge gap.he pump and the stirrer assembly are placed in the same tank

n which machining is performed. The distance between powderixed dielectric suction point and nozzle outlet is kept as short

s possible (10 in.) in order to ensure the complete suspensionf powder in the discharge gap. Magnetic forces were used toeparate the debris from the dielectric fluid. For this purpose,wo permanent magnets are placed at the bottom of machiningank.

The various powders that can be added into the dielectric fluidre aluminum, chromium, graphite, silicon, copper or siliconarbide, etc. Their thermo physical properties are tabulated inable 1 [7].

The spark gap is filled up with powder particles. When aoltage of 80–320 V is applied between the electrode and theorkpiece facing each other with a gap of 25–50 �m [12], an

lectric field in the range of 105–107 V/m is created. The powderarticles get energized and behave in a zigzag fashion (Fig. 2).hese charged particles are accelerated by the electric field and

ct as conductors. The conductive particles promote breakdownn the gap and increase the spark gap between tool and the work-iece. Under the sparking area, the particles come close to eachther and arrange themselves in the form of chain like struc-

M experimental setup.

al resistivity (�� cm) Melting point (◦C) Specific heat (Cal g−1 ◦C−1)

660 0.2151875 0.111083 0.0922987 0.18

34 H.K. Kansal et al. / Journal of Materials Pr

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apfluid. The machining was performed at low discharge current(0.5–1 A) for short discharge time (<3 �s) with negative polarity.The fine and corrosion resistant surfaces of roughness less than2 �m were produced. However, this performance can only be

Fig. 2. Principle of powder mixed EDM.

ures between both the electrodes. The interlocking betweenhe different powder particles occurs in the direction of flowf current. The chain formation helps in bridging the dischargeap between both the electrodes. Due to bridging effect, thensulating strength of the dielectric fluid decreases. The easyhort circuit takes place, which causes early explosion in theap. As a result, a ‘series discharge’ starts under the electroderea. The faster sparking within a discharge takes place causingaster erosion from the workpiece surface and hence the materialemoval rate (MRR) increases. At the same time, the added pow-er modifies the plasma channel. The plasma channel becomesnlarged and widened [3]. The sparking is uniformly distributedmong the powder particles, hence electric density of the sparkecreases. Due to uniform distribution of sparking among theowder particles, shallow craters are produced on the workpieceurface. This results in improvement in surface finish.

. Evaluation of PMEDM performance

The various machining characteristics used to evaluate theerformance of PMEDM are: MRR, tool wear rate (TWR), rel-tive wear ratio (WR) and surface roughness (SR). The MRRs expressed as the weight of material removed from workpiecever a period of machining time in minutes.

RR (mm3/ min) = Workpiece weight loss (g)×1000

density (g/cm3)×machining time (min)(1)

he TWR is calculated by using the weight loss from the toolivided by the time of machining.

WR (mm3/min) = Tool weight loss (g)×1000

density (g/cm3)×machining time (min)(2)

he relative wear ratio of the workpiece and tool is expresseds:

WR = Tool wear rate

Material removal rate× 100 (3)

The SR of the workpiece can be expressed in different waysike, arithmetic average (Ra), average peak to valley height (RZ),

r peak roughness (RP), etc. Generally, the SR is measured inerms of arithmetic mean (Ra) which according to the ISO 4987:999 is defined as the arithmetic average roughness of the devi-tions of the roughness profile from the central line along the

FW

ocessing Technology 184 (2007) 32–41

easurement. It is shown as:

a = 1

L

∫ L

0|h(x) dx| (4)

here h(x) is the value of the roughness profile and ‘L’ is thevaluation length.

. Historical perspective of PMEDM

.1. Experimental investigations of PMEDM

The authors have tried to arrange the literature in the area ofMEDM as it has been reported.

Erden and Bilgin [10] reported the experimental and the-retical investigations to determine the effect of impurities inielectric fluid of EDM in 1980. Copper, aluminum, iron and car-on in powder form were mixed into the commercial keroseneil as artificial impurities and machining was performed onrass–steel and copper–steel pairs. It was found that the addedowder improves the breakdown characteristics of the dielectricuid. It was further observed that the machining rate increasesith increase in the concentration of the added powder. The

ncrease in machining rates was obtained due to the decrease inime lags at high impurity concentrations. It was further observedhat the machining becomes unstable at excessive powder con-entration due to occurrence of short circuits. Surface quality andhe gap size were also improved by the impurity concentrations.hereafter, Jeswani [11] investigated the effect of the additionf fine graphite powder into kerosene oil. It was reported thaty addition of 4 g/l of fine graphite powder increased the inter-pace for electric discharge initiation and lowered the breakdownoltage. The machining process stability was improved thataused around 60% increase in MRR and 28% reduction in WRFig. 3).

Mohri et al. [6,13,14] studied the effects of silicon powderddition on machining rate and surface finish in EDM. Siliconowder of 10–30 �m size was uniformly mixed in the dielectric

ig. 3. Effect of graphite powder addition into kerosene on MRR, TWR andR [11].

s Processing Technology 184 (2007) 32–41 35

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H.K. Kansal et al. / Journal of Material

chieved only at controlled machining conditions (even distribu-ion of additives into dielectric, short discharge time, etc.). It wasurther reported by Narumiya et al. [5] that under specific work-ng conditions, aluminum (Al) and graphite (Gr) powders yieldetter surface finish than the silicon (Si) powder. The best resultsRa less than 2 �m) are obtained for aluminum and graphite pow-er particles having diameter less than 15 �m and concentrationanges from 2 to 15 g/l.

Kobayashi et al. [15] investigated the effects of suspendedowder in dielectric fluid on MRR and SR. It was reportedhat the surface finish of SKD-61 material gets improved withhe use of silicon powder. Yan and Chen [16–18] studied theffect of suspended aluminum and silicon carbide powders onDM of SKD11 and Ti–6Al–4V. It was observed that the MRR

mproves considerably whereas the SR increases. Ming and He19] reported that the additives (conductive and inorganic oxidearticles) increase the MRR, decrease the TWR and improve theurface quality of the workpiece quite effectively, especially inid-finish machining and finish machining phases. The high

dditive concentration (above 30 g/l) causes powder-settlingroblem. A new dielectric circulation system was reported toolve this problem. They also proposed the mechanisms of theachining. Yu et al. examined the effects of aluminum powder

n EDM of tungsten carbide [20]. The aluminum powder allowsoth higher discharge gap and MRR.

Uno and Okada [8] investigated the effect of silicon powderixing on the surface generation mechanism. The EDM with sil-

con powder mixed fluid produced glossier surfaces as comparedo those produced by conventional EDM with kerosene fluid. Itas argued that EDM with silicon powder mixed fluid led to

maller undulation of a crater because the impact force actingn the workpiece is smaller. This results in the stable machiningithout short circuit between the electrode and the workpiece. In

nother study, Uno et al. [9] observed that nickel powder mixed

orking fluid modifies the surface of aluminum bronze compo-ents. The nickel powder was purposely used to deposit a layern EDMed surface to make the surface abrasion resistant. Theffect of nickel powder on surface abrasion is shown in Fig. 4

Fig. 4. Effect of nickel powder on surface abrasion [9].

t(

bp

Fig. 5. TIC generation mechanism [21].

hich indicates that the deposited layer thickness increases withhe increase in concentration of nickel powder.

Wong et al. [7] studied the “near-mirror-finish” phenomenonn EDM using fine powder (silicon, graphite, molybdenum, alu-

inum and silicon carbide) mixed dielectric. It was shown thathere is great influence of the powder and workpiece propertiesn MRR, TWR and SR. Aluminum powder has been reportedo give mirror finish on SKH-51 workpiece but failed to pro-uce mirror like finish on surface of SKH-54 material. Theemi-conductive silicon and carbon powders were seen to beffective in producing about very fine finish conditions. It wasurther observed that the appropriate settings of electrode polar-ty, pulse parameters and powder characteristics have significantnfluence on the mirror-finish condition. The negative electrodeolarity (i.e. with the tool as the negative electrode) is neces-ary to achieve the mirror-finish condition. A new method fororming hard layer containing titanium carbide by EDM witharbon powder mixed fluid using titanium electrode is proposedy Okada et al. [21]. Experimental analysis shows that a thicknd smooth TiC layer is formed on the machined surface. Thehenomenon of deposition of TiC layer on the surface of work-iece is shown in Fig. 5. The hardness and wear resistance ofhe coated layer is found much higher than that of base material

Figs. 6 and 7).

Furutani et al. [12] reported the accretion of titanium car-ide by EDM with powder suspended working fluid. Titaniumowder of size <36 �m and concentration of 50 g/l was mixed

Fig. 6. Effect of nickel powder addition on surface hardness [21].

36 H.K. Kansal et al. / Journal of Materials Processing Technology 184 (2007) 32–41

F

iptppn1aibtmmggSdtu(mTap

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phibifsiteythe increased gap distance caused the extension of slit expansionduring machining as shown in Fig. 13. As shown in Fig. 14, thehighest removal depth was achieved at the optimal concentrationof Al (5 g/l) and SiC (25 g/l).

ig. 7. Effect of carbon powder mixed into dielectric on wear resistance [21].

nto EDF-K (Mitsubishi oil). A gap voltage of 320 V and longulse interval with negative polarity was set for a smooth andhick layer of accretion (please see Fig. 8 that depicts a range ofulse duration and discharge current in which the accretion isossible). TiC layer grows a thickness of 150 �m with a hard-ess of 1600 Hv on surface of carbon steel with an electrode ofmm diameter. Wang et al. [22] investigated the effect of Alnd Cr powder mixture in kerosene. It was found that machin-ng parameters (pulse duration, discharge current, polarity, gapetween tool and workpiece, nature and concentration of addi-ives in the dielectric fluid) have remarkable influence on the

achining characteristics. The results indicate that Al and Crixture in kerosene fluid reduces the isolation and increases the

ap between the electrode and workpiece. With this, the processets stabilized and considerably enhanced the MRR (Fig. 9).mall size particle would have higher suspension effect in theielectric fluid due to their higher concentration. As a result,here is higher probability of bridging the gap and producingniform discharge dispersion resulting in good surface finishFig. 10). Rapid accretion of a thin electrode material and rapidanufacturing of a thin electrode was proposed by Mohri [23].hey reported that tungsten could be accreted in an instant ontoworkpiece with a thin tungsten electrode through its explosion

rocess.

Chow et al. [24] studied the EDM process by adding SiCnd aluminum powders into kerosene for the micro-slit machin-ng of titanium alloy. The addition of both SiC and aluminum

Fig. 8. Range of pulse duration and discharge current for accretion [12]. F

Fig. 9. Effect of addition of various powders on MRR [22].

owder to the kerosene enhanced the gap distance resulting inigher debris removal rate and material removal depth as shownn Figs. 11 and 12. Furthermore, a bridging effect is createdy the added powder and facilitates the dispersion of dischargento several increments. Thus, several discharge trajectories areormed within a single input impulse and several dischargingpots are created and hence increase the MRR and surface fin-sh. However, the addition of the powder to the kerosene disturbshe adherence of carbon nuclides attached to the surface of thelectrodes and increases the TWR. It was also observed that SiCields better material removal depth than aluminum powder and

ig. 10. Effect of addition of various powders on surface roughness [22].

H.K. Kansal et al. / Journal of Materials Processing Technology 184 (2007) 32–41 37

Fig. 11. Effect of addition of powder into dielectric fluid of EDM on gap distance[24].

Fa

1vCssaMc

Fig. 14. Material removal depth vs. pulse duration [24].

and lowest TWR. It was further observed that Cu powder hasnegligible effect on EDM due to its higher density.

A deposition method of lubricant layer during finishing EDM

ig. 12. Variation of material removal depth with concentration of differentdded powders [24].

The effect of various powder characteristics on EDM of SKD-1 material was recently reported by Tzeng and Lee [4]. Thearious additives mixed in the working fluid include Al, Cr,u and SiC. It was found that the concentration, size, den-

ity, electrical resistivity and thermal conductivity of powdersignificantly affected the machining performance. Addition of

ppropriate amount of powders to the dielectric fluid increasedRR (Fig. 15) and decreased TWR (Fig. 16). For a fixed con-

entration, the smallest size of the particle led to highest MRR

Fig. 13. Different added powders cause expansion of slits [24].

p

Fig. 15. Effect of pulse on time on MRR at different current [4].

rocess to produce parts for ultra high vacuum such as space

Fig. 16. Effect of pulse on time on TWR at different current [4].

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nvironment was proposed by Furutani and Shiraki [25]. A solidubricant, molybdenum disulphide powder was mixed into theielectric fluid to deposit a lubricant layer on carbon steel andtainless steel under the electrical conditions of high open volt-ge, low discharge current, a short pulse duration and mediumulse interval. The surface produced by PMEDM showed lowerriction coefficient than that machined by traditional EDM.

Like the other machining method, PMEDM can be dividednto two phases, finish machining and rough machining [3].umber of authors have reported their research on finish machin-

ng phase [5–9,11–14,22,23], but research on rough machininghase has been reported only by Zhao et al. [3]. It was observedhat the PMEDM has a different machining mechanism fromonventional EDM. They performed experimental research onhe machining efficiency and SR of PMEDM in rough machin-ng phase. Their results show that PMEDM process can clearlymprove machining efficiency and SR by selecting proper dis-harge parameters.

The PMEDM also helps in modifying the surface propertiesf the workpiece as explored by Simao [26]. Taguchi methodas used to identify the effect of key operating factors (open

ircuit voltage, peak current, pulse on time, electrode polaritynd capacitance) on output measures (electrode wear, work-iece surface hardness, etc.). It was reported that with the usef partially sintered electrodes made from WC/Co, a uniformlloyed/modified surface layer with relatively few micro-cracksnd an average thickness of up to 30 �m was formed. A simplepproach for robust design of high speed EDM was proposedy Tzeng and Chen [27]. For process optimization, the idealunction of an EDM system along with Taguchi method wasroposed. It was further investigated that the ideal function haslinear relationship between the input signal (intended dimen-

ion) and the output response (product dimension). The variousontrol factors (powder concentration, pulse on time, duty cycle,eak current, etc.) were optimized. Based on the experimentalesults, it was concluded that the most important factors affect-ng the EDM process robustness are pulse on time, duty cyclend peak current.

Very recently, Pecas and Henriques [28] investigated thenfluence of silicon powder mixed dielectric on conventionalDM. The surface quality is assessed through quality surface

ndicators and process time measurements over a set of differentrocessing areas. The results show that by addition of 2 g/l sili-on powder, the operating time and SR decreases. The averageR depends upon machining area and machining time. The SRaries from 0.09 to 0.57 �m for the area range of 1–64 cm2.

.2. Process mechanism of PMEDM

Many researches [2–5,8–12,19,21,27,29] have observed theehavior of powders added into the working fluid to analyze howhe debris in the gap affects the occurrence of discharge. Despitehe promising results, the key issue of machining mechanism of

MEDM is not still clearly understood. The role of the powderarticles in the discharge mechanism seems to be complicated.he absence of the particles results in arcing whereas the pres-nce of too much powder may cause unstable and inefficient

4

n

ocessing Technology 184 (2007) 32–41

DM operation. A stable machining process demands evenlyistributed discharge locations, which depend mainly upon pow-er concentration and its distribution, bubbles, deionization ofielectric fluid and surface irregularities of the workpiece [4].owever, the powder in the discharge gap may be regarded as

he most important factor for process stability as it has a signifi-ant influence on the factors like discharge transitivity, gap size,reakdown strength and deionization of dielectric fluid [2,5–6].t is required to investigate and co-relate the influence of theseactors for the control of PMEDM process.

Schumacher [30] suspended the powders into dielectric fluido improve the surface properties. The powder particle facilitateshe ignition process by creating a higher discharge probabilitynd lowering the breakdown strength of the insulating dielectricuid. He also reported the effect of material composition onurface roughness.

The movement of the debris in the discharge gap of EDMrocess was studied by Kunieda and Yanatori [29]. They madehe calculations of debris particle motion caused by the elec-rostatic forces in the narrow discharge gap filled by dielectricuid. The debris particles move towards one electrode and return

o the other repeatedly due to the electrophoresis. The velocityf the particles is so high that when a pulse voltage is applied,umerous chains of particles bridge the gap in a very short timeeriod. During this discharge duration, in the vicinity of the dis-harge spot, chains are broken due to the explosive expansion ofbubble of vapour from the dielectric liquid and its dissociatedases. But far from this discharge spot, most of the chains remainustained, and when the next pulse voltage is applied, dischargeccurs after a delay time at another closest spot. It was furtheround that the discharge delay time (also called activation time)s necessary for debris particles to form bridges between bothhe electrodes.

Luo [2] confirmed the role of debris in EDM by conductingxperiments on precision EDM. It was observed that the debrisn the discharge gap plays a very dominant role in realizing theischarge movement. It was reported that machining stabilitynd discharge transitivity during EDM is improved by the evenistribution of gap debris (please see Fig. 17).

The role of the added powder particles into the dielectricuid of EDM was also studied by Zhao et al. [3]. They observed

hat the presence of conducting micropowders in the dischargeap causes electric field aberration. Under the presence of gapoltage, a plenty of positive and negative charges gather on tohe powder particles. The points, which are nearer to the top orottom, have higher electric charge density. The discharge break-own gets initiated at these points when the electric field densityurpasses the breakdown resistant capability (Fig. 18). As aesult, the discharge passage becomes enlarged and widened.

ith this, the redistribution of electric charges takes place and aeries discharge starts between the tool and workpiece causingncrease in MRR and surface finish.

.3. Modeling of PMEDM process

Regarding the mathematical modeling of PMEDM process,o research has been reported till date. The efforts by the present

H.K. Kansal et al. / Journal of Materials Processing Technology 184 (2007) 32–41 39

Fig. 17. Effect of debris in discharge tra

apb

5

b

5

ipatm

i([hdugri

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5

Fig. 18. Schematic diagram of “series discharge” in PMEDM [3].

uthors are going on to develop a numerical model of PMEDMrocess based on finite element method (FEM). The results wille shown in the follow-up publications.

. PMEDM applications

The various applications of powder mixed EDM which haveeen reported in the literature are discussed in this section.

.1. Micro-EDM

The use of light, thin, compact and sophisticated mechan-cal elements has recently become a global trend. Number of

roducts such as micro-engines, micro-pumps, micro-robotsnd other micro-mechanical equipments have been developedo fulfill the requirements of market. The production of these

icroelements with traditional methods is restricted due to var-

bi(

nsfer in a spark gap of EDM [2].

ous complications. The micro-slit machining of titanium alloyTi–6Al–4V) using PMEDM has been reported by Chow et al.24]. The multiple slits microstructure (micro-heat scatter fin)as been fabricated under the different process discharge con-itions. The deposition of lubricant layer on equipment used inltra high vacuum such as space, accretion and fabrication ofrinding wheel by depositing very fine abrasive grains has beeneported [12,28,31,32]. The applications of PMEDM techniquen microelectro mechanical systems are highly promising.

.2. Machining of insulating materials

The machining characteristics of insulating Si3N4 ceram-cs by mixing the various powders into the dielectric fluidere studied by Tani et al. [33]. It was reported that MRR

ncreased considerably while the surface finish was not suffi-iently improved by using the powder suspended dielectric fluid.n order to improve surface finish, the powder suspended dielec-ric fluid was used under the limited pulse duration. As a result,he MRR was comparable to grinding and the surface finish wasmproved down to 4 �m. Rozenek et al. [31] compared machin-ng characteristics by using kerosene dielectric and mixture ofeionised water with different abrasive powders at different con-entrations on hard material. It was reported that the addition ofowder in the dielectric enhances both MRR and TWR.

.3. Mirror finish

Powders suspended into the dielectric fluid of EDM can alsoe used to improve the surface characteristics. Near mirror finishs reported to be obtained after suspending the metallic powdersgraphite and silicon) into the dielectric fluid of EDM [7]. Dif-

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erent powders were mixed into kerosene oil to understand thenfluence of powder and workpiece properties. Aluminum pow-er reported to give mirror finish on SKH-51 workpieces whilet fails to produce gloss finish on SKH-54 material. The sili-on and carbon powders seem to be effective in producing veryne finish conditions. Further, it was noted that it is very impor-

ant to have the correct combination of powder and workpieceaterials.

. Current problems in PMEDM

Number of issues need to be addressed in future for imple-entation of this modified process of machining. Few of them

re discussed here.Many researchers have shown that powder suspended EDM

achining can distinctly improve the SR and surface qualityn the finish machining phase and obtain nearly mirror sur-ace effects. Despite the promising results, PMEDM processs used in industry at very slow pace. One of the key reasons ishat many fundamental issues of this new development, includ-ng the machining mechanism are still not well understood.he complexity of this process, particularly in context with

hermo physical properties of the suspended particles deservesthorough investigation. Secondly, the difficulty in operation

f dielectric interchange, the high amounts of powder con-umption, the environmental requirements of fluid disposal andts higher initial cost (two to three times higher than the oneequired for a conventional EDM system) have restricted its fre-uent use [32]. The optimization of powder characteristics (type,hape, size concentration, etc.) also urgently needs a thoroughtudy. The other problems associated with the PMEDM are:1) cost effectiveness/working life of powders, (2) concentra-ion of the working fluid, (3) circulation of mixture of additivesnd working fluid, (4) filtration of additives from debris, (5)gglomeration and (6) arcing. Moreover, very little research haseen reported on the application of PMEDM in rough machininghase [3].

. Conclusions

This paper presents a detailed summary of research resultseported in the area of powder mixed EDM. It can be con-luded from this review that PMEDM holds a bright promisen application of EDM, particularly with regard to process pro-uctivity and surface quality of workpiece. As such, extensivetudy is required to understand mechanics of machining andther aspects of PMEDM.

cknowledgements

The authors would like to acknowledge the support of M/Slectronica Machine Tools Ltd., Pune, India. We are thankful

o Mr. Kulwinder Singh, Sr. Tech., Tool Room, Department of

echanical Engineering, SLIET. We are also grateful to Prof.

.L. Bali, Department of Mechanical Engineering, LIET, Jaland-ar and Er. Baljit Singh, PSEB, India for their support anduidance.

[

ocessing Technology 184 (2007) 32–41

eferences

[1] O.A. Abu Zeid, On the effect of electro-discharge machining parameterson the fatigue life of AISI D6 tool steel, J. Mater. Process. Technol. 68 (1)(1997) 27–32.

[2] Y.F. Luo, The dependence of interspace discharge transitivity upon the gapdebris in precision electro-discharge machining, J. Mater. Process. Technol.68 (1997) 127–131.

[3] W.S. Zhao, Q.G. Meng, Z.L. Wang, The application of research on powdermixed EDM in rough machining, J. Mater. Process. Technol. 129 (2002)30–33.

[4] Y.F. Tzeng, C.Y. Lee, Effects of powder characteristics on electro dis-charge machining efficiency, Int. J. Adv. Manuf. Technol. 17 (2001) 586–592.

[5] H. Narumiya, N. Mohri, N. Saito, H. Otake, Y. Tsnekawa, T. Takawashi,K. Kobayashi, EDM by powder suspended working fluid, in: Proceedingsof 9th ISEM, 1989, pp. 5–8.

[6] N. Mohri, N. Saito, M.A. Higashi, A new process of finish machining onfree surface by EDM methods, Annals CIRP 40 (1) (1991) 207–210.

[7] Y.S. Wong, L.C. Lim, I. Rahuman, W.M. Tee, Near-mirror-finish phe-nomenon in EDM using powder-mixed dielectric, Int. J. Adv. Manuf.Technol. 79 (1998) 30–40.

[8] Y. Uno, A. Okada, Surface generation mechanism in electrical dischargemachining with silicon powder mixed fluid, Int. J. Elec. Mach. 2 (1997)13–18.

[9] Y. Uno, A. Okada, Y. Hayashi, Y. Tabuchi, Surface integrity in EDM ofaluminum bronze with nickel powder mixed fluid, J. Jpn. Soc. Elec. Mach.Eng. 32 (70) (1998) 24–31 (in Japanese).

10] A. Erden, S. Bilgin, Role of impurities in electric discharge machining,in: Proceedings of 21st International Machine Tool Design and ResearchConference, Macmillan, London, 1980, pp. 345–350.

11] M.L. Jeswani, Effects of the addition of graphite powder to kerosene usedas the dielectric fluid in electrical discharge machining, Wear 70 (1981)133–139.

12] K. Furutani, A. Saneto, H. Takezawa, N. Mohri, H. Miyake, Accretion oftitanium carbide by electrical discharge machining with powder suspendedin working fluid, Precis. Eng. 25 (2001) 138–144.

13] N. Mohri, J. Tsukamoto, M. Fujino, Mirror-like finishing by EDM, in:Proceedings of the 25th International Symposium on Machine Tool Designand Research, UK, 1985, pp. 329–336.

14] N. Mohri, J. Tsukamoto, M. Fujino, Surface modification by EDM—aninnovation in EDM with semi-conductive electrodes, in: Proceedings ofWinter Annual Meet ASME, vol. 34, 1988, pp. 21–30.

15] K. Kobayashi, T. Magara, Y. Ozaki, T. Yatomi, The present and futuredevelopments of electrical discharge machining, in: Proceedings of 2ndInternational Conference on Die and Mould Technology, Singapore, 1992,pp. 35–47.

16] B.H. Yan, S.L. Chen, Effects of dielectric with suspended aluminum powderon EDM, J. Chin. Soc. Mech. Eng. 14 (3) (1993) 307–312.

17] B.H. Yan, S.L. Chen, Characteristics of SKD11 by complex process of elec-tric discharge machining using liquid suspended with aluminum powder,J. Jpn. Inst. Light Met. 58 (9) (1994) 1067–1072.

18] B.H. Yan, S.L. Chen, Effect of ultrasonic vibration on electrical dischargemachining characteristics of Ti–6Al–4V alloy, J. Jpn. Inst. Light Met. 44(5) (1994) 281–285.

19] Q.Y. Ming, L.Y. He, Powder-suspension dielectric fluid for EDM, J. Mater.Process. Technol. 52 (1995) 44–54.

20] C.P. Yu, W.C. Chen, S.W. Chang, C.C. Chang, Effects of the concentrationof suspended aluminum powder in dielectric fluid on EDM of carbide oftungsten’s, in: Proceedings of the 13th Conference of Chinese Society ofMechanical Engineers, Taiwan, 1996, pp. 445–450.

21] A. Okada, Y. Uno, K. Hirao, Formation of hard layer by EDM with car-bon powder mixed fluid using titanium electrode, in: Proceedings of 5th

International Conference on Progress of Machining Technology, 2000, pp.464–469.

22] C.H. Wang, Y.C. Lin, B.H. Yan, F.Y. Huang, Effect of characteristics ofadded powder on electric discharge machining, J. Jpn. Inst. Light Met. 42(12) (2001) 2597–2604.

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H.K. Kansal et al. / Journal of Material

23] N. Mohri, et al., A new process of additive and removal machining by EDMwith a thin electrode, Annals CIRP 40 (1) (2000) 123–126.

24] Han-Ming Chow, Biing-Hwa Yan*, Fuang-Yuan Huang, Jung-CherngHung, Study of added powder in kerosene for the micro-slit machiningof titanium alloy using electro-discharge machining, J. Mater. Process.Technol. 101 (2000) 95–103.

25] K. Furutani, K. Shiraki, Deposition of lubricant layer during finishingprocess by electrical discharge machining with molybdenum disulphidepowder suspended in working fluid, in: JSME/ASME International Con-ference on Materials and Processing, 2002, pp. 468–473.

26] J. Simao, et al., Work piece surface modification using electrical dischargemachining, Int. J. Mach. Tools Manuf. 43 (2003) 121–128.

27] Yih-fong Tzeng, Fu-chen Chen, A simple approach for robust design ofhigh-speed electrical-discharge machining technology, Int. J. Adv. Manuf.Technol. 43 (2003) 217–227.

[

[

cessing Technology 184 (2007) 32–41 41

28] P. Pecas, E.A. Henriques, Influence of silicon powder mixed dielectric onconventional electrical discharge machining, Int. J. Mach. Tools Manuf. 43(2003) 1465–1471.

29] M. Kunieda, K. Yanatori, Study on debris movement in EDM gap, Int. J.Elec. Mach. 2 (1997) 43–49.

30] B.M. Schumacher, About the role of debris in the gap during electricaldischarge machining, Annals CIRP 39 (1) (1990) 197–199.

31] M. Rozenek, J. Kozak, L. Dabrowski, Study of electrical discharge machin-ing using powder suspended working media, in: 12th ISEM Bilbao, 2001,pp. 351–357.

32] P. Pecas, E.A. Henriques, Emerging technologies in penetration EDM, OMolde 55 (2002) 26–36.

33] T. Tani, F. Fukazawa, N. Mohri, M. Okada, Machining phenomena in EDMof insulating ceramics using powder suspended working oil, in: 12th ISEMBilbao, 2001, pp. 388–392.