06 NAMRCKaodry Wire EDM

7/29/2019 06 NAMRCKaodry Wire EDM

1/8

DRY WIRE ELECTRICAL DISCHARGE MACHININGOF THIN WORKPIECE

C.C. Kao, Jia Tao, Sangwon Lee, and Albert J. ShihMechanical EngineeringUniversity of MichiganAnn Arbor, MI 48109

KEYWORDS

Dry EDM, thin workpiece, MRR.

ABSTRACT

This study investigates the dry wire electricaldischarge machining (EDM) on thin workpieces.Dry EDM experiments were conducted in air,which was used as the dielectric fluid. Effects ofspark cycle (T), spark on-time (Ton), air flow rate,workpiece thickness, and type of work-materialwere studied under wet and dry EDM conditions.The material removal rate (MRR) was low in dryEDM and could be slightly improved by the useof air flow. The increase in workpiece thicknessand work-material melting temperature had anadverse effect on the MRR. The reduction ofMRR in dry EDM can be related to the rate andpercentage of spark, arc, and short pulses. Thisstudy also observed the deposition of debris in

the groove cut by dry wire EDM. For a thickworkpiece, the groove was totally blocked.

INTRODUCTION

Dry EDM is a novel machining process thatuses gas as dielectric fluid. This process wasfirst presented by Kunieda et al. [1997] using a

rotating copper tube as the electrode for dry die-sink EDM. Dry EDM using air or oxygen flowingout from a tubular electrode was investigated.Experimental results showed that using oxygenas the dielectric fluid in dry EDM could achievehigher material removal rate (MRR) than that inwet EDM. The electrode wear rate was very low,which indicated the feasibility of using dry EDMfor precision machining.

Kunieda and his colleagues have furtheradvanced the dry EDM process to wire EDM[Kunieda, 2001; Wang, 2004] and three-dimensional EDM milling [Kunieda, 2003; Yu,2004]. The gap between electrode andworkpiece is narrow in dry EDM. The narrowgap, sometimes close to zero [Kunieda, 2001],causes frequent short circuit and low MRR.Compared to water- and oil-based EDMdielectric fluids, gas has much lower viscosity.Therefore, dry EDM has lower energy density

per pulse, which results in a lower MRR[Kunieda, 2001; Li, 2004]. To reduce theprobability of short circuit and improve the MRRin dry EDM, a piezoelectric actuator was applied[Kunieda, 2004].

In this study, the dry wire EDM cutting ofworkpiece with small thickness was investigated.

A set of experiments was conducted on several

Transactions of NAMRI/SME 253 Volume 34, 2006


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types of materials, including brass, aluminumalloy, carbon steel, and graphite bipolar plate toexplore the feasibility of dry wire EDM. Thesematerials have distinctly different meltingtemperatures, electrical conductivity, andmachinability in dry EDM. It was observed thatthree key factors significantly influencing themachinability in dry EDM were the workpiecethickness, melting temperature, and heatcapacity. A conventional wire EDM machine canbe used for dry wire EDM of thin workpiece withlow melting temperature. For thin workpiece,the debris can be efficiently removed by the air

jet in dry EDM. The workpiece with low meltingtemperature allows low energy input withoutbreaking the wire electrode. Dry wire EDMexperiments were conducted in this study toquantify effects of the spark cycle, spark on-time,air flow rate, thickness, and type of work-material on the MRR.

The wire EDM process monitoring [Rajurkar1993; Ho, 2003, 2004] was applied to analyzethe phenomena of dry wire EDM. By evaluatingthe measured gap voltage and current withrespect to preset threshold values [Dauw, 1983],the spark, arc, and short EDM pulses can beidentified. Measurement of the gap voltage andcurrent and identification of types of pulse (open,spark, arc, and short) were conducted in thisresearch for both wet and dry EDM processes.Under identical process parameters, the rate ofeach pulse type in wet and dry EDM were

calculated and compared.

In this paper, the dry EDM experimental setupand procedures are first presented. Theexperimentally measured MRR in dry EDM arereported and effects of work-material type andthickness are discussed. The rate of spark, arc,and short pulses for various dry EDM setups arecompared. Finally, the groove width anddeposition of debris are examined.

EXPERIMENTAL SETUP AND PROCEDURES

Wire EDM machine setup

The EDM experiments were conducted on aBrother HS-5100 wire EDM machine. A copperwire electrode of 0.254 mm diameter was used.Three cutting conditions were studied: wet, drywithout air flow, and dry with air flow in theelectrode-workpiece gap region. For wet EDMexperiments, the workpiece was submerged indeionized water. Jets of water were applied at

about 1 liter/min flow rate from both top andbottom to flush away the debris generated in thedischarge gap between workpiece and wireelectrode. No water was used in dry EDMexperiments, which were conducted either instationary air or using an optional air jet, asshown in FIGURE 1(A). The air jet was deliveredat 0.17 MPa pressure via a 2 mm inner diameterplastic tube oriented with 45 angle to wire at 10mm away for debris flushing.

(A) (B)

FIGURE 1. DRY WIRE EDM SETUP AND CUTTINGOF 1.27 MM THICK AL 6061: (A) THE ORIENTATIONOF TUBE FOR AIR FLOW AND (B) DRY EDMWITHOUT AIR FLOW.

For all wet and dry EDM experiments, the axialdirection wire feed speed was set at 12 mm/s,the tension force of wire was 18 N, the servovoltage was 45 V, and the open voltage betweenthe wire electrode and workpiece was about 72V. Brass and Al 6061 were selected as thework-materials. Baseline dry wire EDMexperiments were conducted on the 0.2 mmthick brass and 1.27 mm thick Al 6061. FIGURE

1(B) shows the dry EDM of the 1.27 mm thick Alplate without the air flow. An odor of burningcould be smelled during the dry EDM process.This environmental issue, not addressed in thisstudy, needs to be resolved before theapplication of dry EDM in production.

Experimental procedures

In this study, wire EDM experiments wereconducted to investigate: 1. MRR, 2. rate ofspark, arc, and short EDM pulses, and 3. groove

width and debris deposition.

MRR. Spark cycle T, spark on-time durationTon, air flow rate, workpiece thickness, and typeof work-material are five process variablesselected. Effects of these variables on MRR indry EDM were investigated and compared withthat of wet EDM. A method to study effects ofTand Ton using envelopes of MRR has been

Air tube



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developed by Miller et al. [2004,2005]. Thismethod was applied to identify characteristics ofdry EDM in this study. Envelopes of feasible Tand Ton for wet and dry EDM with and without airflow on the 0.2 mm thick brass and 1.27 mmthick Al 6061 workpiece were generatedexperimentally. For a given T

on, Twas varied to

find the maximum achievable wire feed rate,which was converted to MRR, in each testsetting. When Twas increased to an upper limit,the short circuit occurred. At the other extreme,when Twas decreased to a lower limit, the wirebreakage occurred. For brass, Ton was set at 2,6, 14, and 18 s for wet EDM and 3, 10, 14, and18 s for dry EDM. For Al, Ton was set at 4, 10,14, and 18 s for both wet and dry EDMconditions. Very low Ton, such as 2 s, was notachievable in some EDM conditions. Byconnecting the upper and lower limits of eachTon, the short circuit and wire breakage

boundary lines of the envelope were obtained.In addition, specific machine limits of themaximum T (1000 s) and minimum T (6 s)exist. To investigate effects of workpiecethickness and material in dry EDM, additionalexperiments were conducted at T= 250 s andTon = 14 s.

Rate and percentage of spark, arc, andshort pulses. An Agilent Infiniium 54833Adigital oscilloscope was used to measure thegap voltage and current in the EDM process.

The sampling rate of data acquisition was set at1 MHz. Every 2 s, a 30 ms time period (30,000data points) of voltage and current data wererecorded. At least six sets of 30 ms data weregathered after the steady-state MRR had beenachieved in the EDM process. The data formedseveral pulse trains which were used for furtheranalysis of the pulse rate in each EDM setup.Three types of pulses (spark, arc, and short), asshown in FIGURE 2, were identified in the pulsetrain.

To automatically determine the type andnumber of pulses with a computer, Dauw et al.[1983] developed an algorithm using presetthreshold voltage values and rates of voltagechange. A more elaborate pulse identificationalgorithm, which includes using the measuredcurrent data, is proposed in this study. For aspark pulse, the voltage has to be higher than athreshold value, designated as Vh, and thecurrent at discharge needs to be larger thananother threshold value, designated as Ih. The

Vh and Ih used in this study, as marked in theFIGURE 2(A), are equal to 68 V and 20 A,respectively. For an arc pulse, as shown inFIGURE 2(B), both the voltage and current riseand drop quickly. The peak voltage is not ashigh as that in spark. To distinguish spark andarc, another threshold voltage, V

l, as marked in

FIGURE 2(A), is used. An arc pulse is definedwhen the voltage is between Vh and Vl and thecurrent is larger than Ih. In this study, Vl = 20 V.For a short pulse, the voltage is low and currentis high, although not as high as that in arc andspark pulses. As shown in FIGURE 2(C), whenthe voltage is below Vl and current is above Ih,this pulse is designated as a short. A Matlabprogram was developed to identify each pulsefrom measured voltage and current data.

-10

10

30

50

70

90

110

Current(A)

10 ms

Arc Short

-140

-100

-60

-20

20

60

100

Voltage(V)

Spark

Vh

Vl Votage

Current

10 ms 10 ms

(A) (B) (C)

Ih

Votage Votage

Current Current

FIGURE 2. CHARACTERIZATION OF EDM

PULSES: (A) SPARK, (B) ARC, AND (C) SHORT.

Of all EDM pulses, the rates of spark, arc, andshort pulses are three indices that determine thestatus or efficiency of the dry EDM process. Agood EDM setup has low rates of short and arcpulses and a high rate of spark pulses.

Groove width and debris deposition. Thegroove width and debris deposition of differentEDM conditions were measured using an opticalmicroscope at 100X.

MATERIAL REMOVAL RATE IN DRY WIREEDM

FIGURES 3 and 4 show the experimentallymeasured MRR for brass and Al 6061. DryEDM process has a lower MRR than wet EDM.



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Brass

FIGURE 3 shows envelopes of MRR for wetEDM, dry EDM with airflow, and dry EDMwithout airflow for cutting 0.2 mm thick brass.

Brass

0

3

6

9

12

15

0 200 400 600 800 1000

Spark cycle, T (s)

Materialremovalrate(mm

3/min)

Ton = 18 s Ton = 14 s

Ton = 6 s Ton = 2 sWire breakage T upper limit

T lower limit Short circuit

Wet EDM

A A

0.2 mm

C

(A)

Brass

0

1

2

3

4

5

0 200 400 600 800 1000

Spark cycle, T (s)

Materialremovalrate(mm3

/min)

Ton = 18 s Ton = 14 s Ton = 18 s Ton = 14 s


Wire breakage Short circuit Wire breakage Short circuit

T upper limit

Dry EDM with air flow Dry EDM without air flow

A A0.2 mm

E

D

F

(B)

FIGURE 3. ENVELOPS OF TON AND T ON MRRFOR WIRE EDM CUTTING OF 0.2 MM THICKBRASS: (A) WET AND (B) DRY WITH ANDWITHOUT AIR FLOW.

Boundary lines of the envelopes are firstidentified. The upper boundary line is the 18 smachine limit ofTon. The left boundary line, inwet EDM (FIGURE 3(A)), is constrained by wirebreakage and lower limit ofT(6 s); and, in dryEDM (FIGURE 3(B)), is determined by the wirebreakage only. The bottoms of the envelopesare bounded by the lowest possible Ton (2 s forwet and 3 s for dry EDM) and the short circuitlimit, which is marked by the dashed line. Theright boundary is the upper limit ofT(1000 s).

The maximum MRR in wet, dry EDM withairflow, and dry EDM without airflow are 14, 3.8,

and 2.8 mm3/min, respectively. The low MRR in

dry EDM is consistent with the observation ofWang and Kunieda [2004]. This is caused bythe low viscosity of air, which results in a smallerexplosive force and less material removal foreach spark.

Low spark cycle Tin wet EDM generates morefrequent spark pulses and higher MRR, asillustrated in FIGURE 3(A). Dry EDM does notexhibit the same trend. The MRR drops when Treaches a threshold value. ForTon = 18, 14, and10 s, such threshold values are about 250, 125,and 75 s, respectively. The decrease of MRRat low T in dry EDM is due to the difficulty ofexpelling debris in the EDM region. The higherrate of debris generation at low Tcauses morefrequent short pulses, which significantly reducethe MRR. For example, without air flow in dryEDM with Ton = 18 s, the MRR drops to only

0.3 mm3/min, marked by the circle F in FIGURE3(B), when T = 60 s. In dry EDM, theaccumulation of debris in the gap between wireand workpiece results in frequent short circuitingand very low MRR. By introducing air flow intodry EDM to assist the debris removal, the MRRis increased by about 30% at Ton = 18 s and T= 250 s, as shown in FIGURE 3(B).

In wet EDM, high MRR can be achieved at lowT. The problem changes from frequent shortcircuiting to wire breakage due to high energyinput. The wire breakage boundary line is on

the left side of the envelope. In dry EDM, due tothe reduction of MRR at low T, the wirebreakage boundary line shrinks significantly.

Al 6061

FIGURE 4 shows envelopes of MRR for wetand dry EDM of Al 6061. The workpiece is 1.27mm thick, compared to the 0.2 mm thick brass inFIGURE 3. Like in FIGURE 3, the upperboundary line is the machine limit (Ton = 18 s).The left boundary line is constrained by wire

breakage. The bottoms of the envelopes arebounded by the lowest possible Ton (4 s) andthe short circuit limit, marked by dashed lines.The right boundary line is the machine upperlimit ofT(=1000 s).

In wet EDM, a low spark cycle T alsogenerates higher MRR. Unlike in FIGURE 3,only when Ton = 18 s, the MRR of Al 6061 indry EDM show significant drop at low T. This is



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also caused by the frequent short circuitingassociated with a large volume of debrisgeneration.

Al 6061

0

5

10

15

20

25

0 200 400 600 800 1000

Spark cycle, T (s)


3/min)

Ton = 18 s Ton = 14 s

Ton = 10 s Ton = 4 s

Wire breakage Short circuit

B B

Wet EDM

1.27 mm

G

(A)

Al 6061

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 200 400 600 800 1000Spark cycle, T (s)


3/min)



Wire breakage Short circuit Wire breakage Short circuit

T upper limit

Dry EDM with air flow Dry EDM without air flow

B B1.27 mm

H

I

(B)

FIGURE 4. ENVELOPES OF TON AND T ON MRRFOR WIRE EDM CUTTING OF 1.27 MM THICK AL6061: (A) WET AND (B) DRY WITH AND WITHOUT

AIR FLOW.

The threshold value ofTfrom which the MRRstarts dropping is about 250 s. With no air flowin dry EDM when Ton = 18 s, a slight change ofT from 250 to 225 s reduces the MRR from0.78 to 0.44 mm

3/min. The air flow can help

remove the debris and increase the MRR byabout 5 to 30% in dry EDM, as shown in

FIGURE 4(B). In wet EDM, the 22 mm3/minmaximum MRR of Al 6061 is higher than that ofbrass (14 mm

3/min). This is due to the lower

melting temperature and heat capacity of Al6061.

Dry EDM for Al 6061 has a very low MRR.The maximum MRR in wet, dry EDM with airflow, and dry EDM without airflow are 22, 1.0,and 0.68 mm

3/min, respectively. The maximum

MRR achieved in dry EDM with air flow, markedas line BB in FIGURES 4(A) and 4(B), is lessthan 5% of that in wet EDM. In comparison, forthe 0.2 mm brass in FIGURE 3, the maximumMRR in dry EDM is about 28% of that in wetEDM. The significant difference is most likelydue to the thicker Al 6061 workpiece.

Effect of workpiece thickness on MRR

The thickness of workpiece, t, has a significanteffect on the efficiency of debris removal andMRR in wire EDM. FIGURE 5 shows the MRRof wet and dry EDM without air flow of Al 6061 atseven levels oft, ranging from 0.2 to 1.27 mm.

ln(MRR) = -1.38 t + 2.28

ln(MRR) = -2.84 t +2.33

0.1

1.0

10.0

0 0.5 1 1.5

Workpiece thickness, t (mm)


3

/min)

Wet EDM Dry EDM without air flow

Al 6061

FIGURE 5. EFFECT OF THICKNESS ON MRR OFAL 6061 FOR WET AND DRY EDM.

All EDM tests were under the same T= 250 sand Ton = 14 s. The MRR (in logarithmic scale)vs. tfollows the trend of straight line for both wetand dry EDM conditions. This indicates theexponential decay of MRR versus the workpiecethickness. The slope of these two lines is thedecay rate. The dry EDM condition has a morenegative slope, i.e., a higher decay rate of MRR.When t= 0.2 mm, the dry EDM processes stillhave good MRR, about 6.5 mm

3/min, which is

about 80% of the 8 mm3/min in wet EDM. But

when tis increased to 1.27 mm, the MRR in dryEDM is reduced to only 0.5 mm

3/min, which is

only about 25% of that in wet EDM. Thefrequent occurrence of short and arc pulses dueto the agglomeration of debris is the likely cause.

Effect of type of work-material on MRR

FIGURE 6 shows the experimental results ofMRR for three types of work-material, Al 6061,brass, and AISI 1020 carbon steel, all with the



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same workpiece thickness t= 1.27 mm, T= 250s and Ton = 14 s for wet and dry, with andwithout air flow, EDM conditions. The wet EDMhas higher MRR than that of dry EDM withairflow. The air flow in dry EDM alwaysimproves the MRR.

0.0

0.5

1.0

1.5

2.0

2.5

Wet Dry with air

flow

Dry without air

flow


3/min)

Al 6061

Brass

AISI 1020 Steel

FIGURE 6. EFFECT OF TYPE OF MATERIAL ONMRR (WORKPIECE 1.27 MM THICK).

The correlation between the thermal propertiesof the work-material and MRR is consistent: theEDM of Al 6061 has higher MRR than brass,and brass has higher MRR than AISI 1020 steel.The heat capacity and melting temperature of Al6061, brass, and AISI 1020 carbon steel are2.42, 3.20, and 3.81 J/cm

3-K and 652, 955, and

1510C, respectively [Davis, 1994, 2001; Holt,1996]. Compared to brass and AISI 1020 steel,

under all three EDM conditions, Al 6061 has thelowest melting temperature and takes the leastenergy to reach its melting temperature per unitvolume of workpiece. Therefore, the EDM of Al6061 has the highest MRR, as shown by thesquare symbol in FIGURE 6. For wet EDM, theMRR for Al 6061 and brass are about the same,2.3 mm

3/min. For dry EDM, the MRR of brass is

only 20% of that of Al 6061. The lack of highenergy density in dry EDM is the likely cause ofsuch a phenomenon.

PROCESS MONITORING RESULTSPulse rate and pulse percentage

The rates of the spark, arc, and short pulses,as shown in FIGURE 7, represent theeffectiveness of EDM processes. Fourrepresentative EDM setups are presented.

(a) 0.2 mm thick brass at 5 mm/min wire feedrate, which is much lower than the maximumwire feed rate.

(b) 0.2 mm thick brass at maximum wire feedrate: 64, 38, and 28 mm/min for the wet, drywith air flow, and dry without air flow EDMconditions.

(c) 1.27 mm thick brass at maximum wire feedrate: 5.0, 0.55, and 0.42 mm/min for the wet,dry with air flow, and dry without air flowEDM conditions.

(d) 1.27 mm thick Al 6061 at maximum wirefeed rate: 5.3, 1.7, and 1.2 mm/min for thewet, dry with air flow, and dry without air flowEDM conditions.

0

500

1000

1500

Spark Arc Short

Wet Dry with air flow Dry without air flow

0

60

120

180

Spark Arc Short

Pulserate(pulses/s)

0

500

1000

1500

2000

Spark Arc Short

Pulse

rate(pulses/s)

Spark Arc Short

(A) (B)

(C)

5 mm/min feed rate

Maximum feed rate (mm/min)

Wet: 5.0

Dry with air flow: 0.55

Dry without air flow: 0.42


Wet: 64 (C in FIG. 3(a))

Dry with air flow: 38 (D in FIG. 3(b))

Dry without air flow: 28 (E in FIG. 3(b))


Wet: 5.3 (G in FIG. 4(a))

Dry with air flow: 1.7 (H in FIG. 4(b))

Dry without air flow: 1.2 (I in FIG. 4(b))

(D)

Brass0.2 mm

Brass0.2 mm

Brass

1.27 mm

Al 6061

1.27 mm

FIGURE 7. RATE OF SPARK, ARC, AND SHORTPULSES IN WET AND DRY WITH AND WITHOUT

AIR FLOW EDM CONDITIONS: (A) 0.2 MM BRASS,5 MM/MIN FEED RATE, (B) 0.2 MM BRASS, MAX.FEED RATE, (C) 1.27 MM BRASS, MAX. FEEDRATE, AND (D) 1.27 MM AL 6061, MAX. FEEDRATE.

Under the low MRR with the wire feed ratemuch lower than the maximum possible value,as shown in FIGURE 7(A), the pulse rate is low:below 180 pulses/s for spark, below 20 pulses/sfor arc, and essentially no short pulse. The dataillustrates that, at wire feed rate below themaximum possible value, the EDM pulsecondition is stable. For the same workpiece (0.2mm thick brass), under the maximum MRRcondition, the wire feed rate and MRR can be



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increased significantly. As shown in FIGURE7(B), the rate of spark pulses has a significant

jump to 1330, 730, and 600 pulses/s for the wet,dry with air flow, and dry without air flow EDMcondition, respectively. The rate of arc pulsesalso increases to about 250370 pulses/s underboth wet and dry EDM conditions. The sideeffect of more aggressive removal of work-material is more frequent short pulses, whichincreased to about 140 pulses/s.

The effect of increasing brass workpiecethickness from 0.2 mm to 1.27 mm on EDMpulses is illustrated by comparing FIGURE 7(C)and FIGURE 7(B). As shown in FIGURE 7(C),the rate of spark pulses increases to about 1870pulses/s for wet EDM and 980 pulses/s for dryEDM. The rate of arc pulses remains about thesame for wet EDM but increases to over 540pulses/s for dry EDM. The rate of short pulses

has the most significant change, particularly fordry without air flow, which increases to 890pulses/s. The dry EDM with air flow also has650 short pulses per second. This shows theeffect of a thick workpiece: more frequent shortpulses, which significantly reduce the wire feedrate and result in lower MRR.

DEBRIS DEPOSITION AND GROOVE WIDTH

The top view and width of three grooves in wetand dry EDM of the 0.2 mm thick brass under

maximum MRR are shown in FIGURE 8.

FIGURE 8. OPTICAL MICROGRAPHS OF WIREEDM GROOVES FOR 0.2 MM THICK BRASS(USING 0.254 MM DIAMETER WIRE ELECTRODE).

The floating debris has been reported byKunieda et al. [2001,2004]. In wet EDM, thewidth of the machined groove is wider than the0.254 mm diameter wire. Difference of thegroove width and wire diameter, denoted as w,

is twice the gap distance between the wireelectrode and workpiece during EDM. For wetEDM, the groove width is about 0.26 mm. Fordry EDM with and without air flow, the width ofgroove is about the same, 0.21 mm, and w isequal to 0.04 mm.

A better illustration of the severity of debrisdeposition after dry EDM is shown in FIGURE 9for 1.27 mm brass workpiece. Under themaximum MRR, the groove is totally clogged (w= 0.254 mm). The air flow at 0.17 MPapressure does not help to prevent the cloggingof the groove in dry EDM. On the top view, onlya hole of the wire is left at the end of wire EDMcut groove. Clogging is concentrated on the topof the groove, as shown in the cross-sectionview. The width of the groove can still berecognized near the bottom of the cross-sectionof the groove. For dry EDM with air flow, the

groove width is 0.29 mm. Without airflow in dryEDM, the groove width slightly reduces to 0.28mm. In comparison, wet EDM generates muchwider groove, 0.34 mm, as shown in FIGURE9(A). The w for wet EDM is about 0.09 mm,which is consistent with the gap width observedin most wire EDM processes.

TOPVIEW

CROSS-

SECTIONVIEW

(A) (B) (C)

FIGURE 9. OPTICAL MICROGRAPHS ON THEGROOVES AND DEPOSITION OF DEBRISGENERATED BY CUTTING 1.27 MM BRASS: (A)WET EDM, (B) DRY EDM WITH AIR FLOW, AND (C)DRY EDM WITHOUT AIR FLOW.

CONCLUDING REMARKSIn this study, the dry wire EDM of thin

workpiece was proven to be possible. Effects ofspark cycle (T) and spark on-time (Ton), air flowrate, workpiece thickness, and work-materialtype on the MRR for dry wire EDM of thin

Wet

Dry withair flow

Dry withoutair flow

0.26 mm 0.21 mm 0.21 mm

0.34 mm 0.29 mm 0.28 mm



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workpiece were investigated. An EDM processmonitoring system was set up to identify thespark, arc, and short EDM pulses. The rates ofspark, arc, and short pulses were compared anddiscussed under the wet, dry with air flow, anddry without air flow EDM conditions.

Experimental results showed that not all thinwork-materials could be machined using dryEDM. For example, thin porous carbon foamand carbon bipolar plate [Miller, 2004] havefailed to be machined using the dry EDMprocess. The high melting temperature ofcarbon is the likely cause. The research in dryEDM is continuing to improve the precision,MRR, and environment issues. The use of amist of deionzied water has been investigated toreduce the smoke and fumes generated duringdry EDM and help collecting the debris in solidparticulate form.

ACKNOWLEDGMENTS

This research is sponsored by the NISTAdvanced Technology Program. Discussionswith John MacGregor of Ann Arbor Machine aregreatly appreciated.

REFERENCES

Dauw, D.F., R. Snoeys, and W. Dekeyser,(1983), Advanced Pulse Discriminating System

for EDM Process Analysis and Control, Annalsof the CIRP, Vol. 32, pp. 541-549.

Davis, J.R. (Ed.), (1994), Aluminum andAluminum Alloys, ASM International.

Davis, J.R. (Ed.), (2001), Copper and CopperAlloys, ASM International.

Ho, K.H., and S.T. Newman, (2003), State ofthe Art Electrical Discharge Machining (EDM),International Journal of Machine Tools andManufacture, Vol. 43, pp. 1287-1300.

Ho, K.H., S.T. Newman, S. Rahimifard, and R.D.Allen, (2004), State of the Art in Wire ElectricalDischarge Machining (WEDM), InternationalJournal of Machine Tools and Manufacture, Vol.44, pp. 1247-1259.

Holt, J.M., H. Mindlin, and C.Y. Ho, (1996),Structural Alloys Handbook, CINDAS/PurdueUniversity.

Li, L., Z. Wang, and W. Zhao, (2004),Mechanism Analysis of Electrical DischargeMachining in Gas, Journal of Harbin Institute ofTechnology, Vol. 36, pp. 359-362 (in Chinese).

Kunieda, M. and S. Furuoya, (1991),Improvement of EDM Efficiency by SupplyingOxygen Gas into Gap,Annals of the CIRP, Vol.40, pp. 215-218.

Kunieda, M., and M. Yoshida, (1997), ElectricalDischarge Machining in Gas, Annals of theCIRP, Vol. 46, pp. 143-146.

Kunieda, M., and C. Furudate, (2001), HighPrecision Finish Cutting by Dry WEDM, Annalsof the CIRP, Vol. 50, pp. 121-124.

Kunieda, M., Y. Miyoshi, T. Takaya, N. Nakajima,Z.B. Yu, and M. Yoshida, (2003), High Speed

3D Milling by Dry EDM,Annals of the CIRP, Vol.52, pp. 147-150.

Kunieda, M., T. Takaya, and S. Nakano, (2004),Improvement of Dry EDM Characteristics UsingPiezoelectric Actuator,Annals of the CIRP, Vol.53, pp. 183-186.

Miller, S.F., A.J. Shih, and J. Qu, (2004),Investigation of the Spark Cycle on MaterialRemoval Rate in Wire Electrical DischargeMachining of Advanced Materials, InternationalJournal of Machine Tools and Manufacture, Vol.

44, pp. 391-400.

Miller, S.F., C. Kao, A.J. Shih, and J. Qu, (2005),Investigation of Wire Electrical DischargeMachining of Thin Cross-Sections and CompliantMechanisms, International Journal of MachineTools and Manufacture, Vol. 45, pp. 1717-1725.

Rajurkar, K. P., and Wang, W. M., (1993)Thermal Modeling and On-line Monitoring ofWire-EDM," Journal of Materials ProcessingTechnology, Vol. 38, pp. 417-430.

Wang, T., and M. Kunieda, (2004), Dry EDM forFinish Cut, Key Engineering Materials, Vol.259-260, pp. 562566.

Yu, Z.B., T. Jun, and M. Kunieda, (2004), DryElectrical Discharge Machining of CementedCarbide, Journal of Materials Technology, Vol.149 pp. 353-357.


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06 NAMRCKaodry Wire EDM