Tinku Sharma 99
IJRIT International Journal of Research in Information Technology, Volume 1, Issue 7, July, 2013, Pg. 99-109
International Journal of Research in Information Technology (IJRIT)
www.ijrit.com
ISSN 2001-5569Study the Effect of Wire-EDM Parameters on MRR & Surface Roughness for Machining D2
Steel
1
Tinku Sharma,
2Vikas soni,
3Ravinder kumar
1 Student of M.Tech.in PDM College of Engineering Bahadurgarh
Abstract
Wire Electrical Discharge Machining (WEDM) is extensively used in machining of materials when precision is of major factor.
Selection of optimum machining parameter combinations for obtaining higher accuracy is a challenging task in WEDM due to the presence of large number of process variables and complex stochastic process mechanisms. In this paper an attempt was made to study the influence of various machining parameters Pulse on, Pulse off, Bed speed and Current on metal removal Rate (MRR) and surface roughness. This study investigated the effects of machining parameters on surface roughness and MRR of wire EDM D2 die steel. Die steel is the alloy composite steel with high hardness typically used in die maker. The investigated machining parameters were Voltage Open, pulse-off time and pulse-peak current. Two level factorial design techniques were used to design the experiment and find out the parameters affecting the surface roughness and MRR. Results from the analysis show that pulse- peak current is significant variables to the surface roughness of wire-EDM die steel. The surface roughness of the test specimen increases when pulse-peak current increase.
Keyword: Wire Electrical Discharge Machining (WEDM), Process Parameters, MRR and D2 Steel.
1. Introduction
Wire Electrical Discharge Machining (WEDM) is a nontraditional, thermoelectric process which erodes material from the work piece by a series of discrete sparks between a work and tool, with de-ionized water as the dielectric medium, produce complex two and three dimensional shapes according to a numerically controlled (NC) path. The schematic representation of the WEDM cutting process is shown in Figure-1.
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Figure 1: Principle of WEDM
Principle of WEDM WEDM is a specialized thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining process. At present, WEDM is a widespread technique used in industry for high-precision machining of all types of conductive materials.
2. Literature Review
The engineer and technologists know the process of EDM for over five decades now, but accelerated developments in this area have occurred only during the last few years. WEDM is a special case of EDM. Extensive research in this field has led to better understanding of the phenomenon of metal erosion, temperature distribution, thermal-electric coupled Finite element Method(FEM) Modeling, heat transfer modeling, crater size, duty factor, surface roughness, tool wear rate, energy distribution and material removal rate. WEDM is an essential operation in several manufacturing processes in some industries, which gives importance to variety, precision and accuracy.
Several researchers have attempted to improve the performance characteristics namely the surface roughness, cutting speed, dimensional accuracy and material removal rate. But the full potential utilization of this process is not completely solved because of its complex and stochastic nature and more number of variables involved in this operation.
In this chapter the author reviews the published literature relevant to the topic of the dissertation under following heads:-
1 material removal mechanism 2 surface integrity in Electro-Erosion
So many research papers and articles are survey on Wire EDM those are related to know the effect of process parameter on performance of process. The materials investigated on WEDM are most of HSS, other Tool material, Hot Die material, Cold Die material, Nickel alloys and Titanium alloys which are hard compare to other material.
These materials are AISI M2, AISI D3, AISI D5, AISI H11, AISI 4140, SKD 11, En 16, En 19, En 31, En 32, 1040, 2379, 2738, Inconel, Ti alloys, Al alloys, 7131 cemented, Tungsten Carbide (WC) etc. Different author use different combination of process parameter. They analyze the experimental data by plotting Interaction graphs, Residual plots for accuracy and Response curves.
3 Problem Statements:
3.1 objectives
1 To investigate the effect of Ton and Toff on MRR and SR.
2 To find out the effect of peak current (Ip) on MRR and SR.
3 To find out the effect of servo voltage (SV), wire feed (WF), wire electrode material on MRR and SR.
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3.2 During experimentation following variables taking in to consideration:
3.2.1 Peak current 3.2.2 Pulse- ON time 3.2.3 Pulse-Off time 3.2.4 Wire Speed
3.2.5 Wire Tension 3.2.6 Wire Feed
3.2.7 Servo Voltage
3.2.8 Flushing pressure 3.2.9 Servo Feed
Out of which SF(2080) and WT(10) are kept constant.
4. Experimental Set-Up
4.1 Machine Tool
The experiments were carried out on a wire-cut EDM machine (ELEKTRA SPRINTCUT 734) of Electronica Machine Tools Ltd. The WEDM machine tool (Figure 4.1) has the following specifications:
Design : Fixed column, moving table Table size : 440 x 650 mm
Max. work-piece height : 200 mm Max. work-piece weight : 500 kg Main table traverse (X, Y) : 300, 400 mm Auxiliary table traverse (u, v ) : 80, 80 mm Wire electrode diameter : 0.25 mm
Generator : ELPULS-40 A DLX Interpolation : Linear & Circular
Least command input (X, Y, u, v) : 0.0005mm
Input Power supply : 3 phase, AC 415 V, 50 Hz Connected load : 10 KVA
Average power consumption : 6 to 7 KVA
Figure.4.1. Pictorial View Of WEDM Machine Tool
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The D-2 die steel plate of 125mm x 100mm x 25mm size is mounted on the ELECTRONICA SPRINTCUT WEDM machine tool (Figure 4.1) and specimens of 5mmx5mmx24mm size are cut. A set of cut specimens is shown in Figures 4.2.
Figure.4.2. Cut Specimens
5. Result Analysis and Discussion
5.1 Effect of WEDM parameters on CS (MRR) and SR
Copper coated brass wire was used to produce 3.5×3.5×25mm cuts in the D2 die steel plate. Experiments were carried out at constant value of wire tension 10N, dielectric flow rate (distilled water) of 10 liters per minute and servo feed (SF) of 2080V. Cutting speed was measured in mm/min which was displayed on computer screen of the machine control unit and surface roughness was measured from in micro-mm from surface roughness tester.
5.2 Effect of peak current
The effect of peak current on cutting speed and surface roughness of D2 die steel with wire EDM is shown in figs.5.1-5.2, under different conditions of pulse-on time (105µs, 110µs, 115µs). The other fixed parameters were pulse-off time 30µs, servo voltage 30V, wire feed 7m/min. It is clear from figure that at low pulse duration (110µs) the cutting speed is low and nearly constant. This is because of low discharge energy is produced b/w the working gap due to insufficient heating of work-piece and low pulse duration. At high pulse duration (110µs, 115µs) there is rise in cutting speed as we increase the peak current. this is due to sufficient availability of discharge energy and heating of the work-piece material. The small increase in cutting speed at high value of peak current and pulse duration is related to inferior discharge due to insufficient cooling of the work material.
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Figure: 5.1 effect of peak current on cutting speed.
The optimal material removal rate for D2 die steel took place at a peak current intensity of 85A as we can see from the figure. The cutting speed remains constant up to value of peak current 70A with different value of pulse duration. This is due to insufficient heating of the work-piece material.
Figure:5.2 effect of peak current on surface roughness.
The effect of peak current on surface roughness is shown in figure 5.2. The surface roughness of D2 die steel increases with increase in peak current and pulse duration. The surface roughness is function of two parameters, peak current and pulse-on time, both of which are function of power supply. A rough surface is produced at high peak current and/or pulse-on time. The reverse is also true. From fig. 6.2 we can also see that at low value of peak current the value of surface roughness is also low. Thus a finer surface texture will be produced at low value of peak current and/or pulse duration and vice versa.
5.2 Effect of pulse-on time
The effect of pulse-on time (pulse duration) on cutting speed and surface roughness is shown in Figure 5.3.- 5.4 under different value of peak current Ip (60A, 100A, 120A) at a pulse interval(Toff) of 30µs, SV 30V, wire feed 7rev./min, a brass coated copper wire as a tool electrode and D2 die steel as a work-piece material.
Figure 5.3 shows the results of cutting speed of D2 die steel material during its machining. From result we found that cutting speed increase with increase in pulse duration at all value of peak current. Thus cutting speed is a function of pulse duration but at low value of peak current(Ip=60) the cutting speed is low due to the insufficient heating of the material and also after pulse duration(Tonn=110) the rise in cutting speed is low because of insufficient clearing of debris from the gap due to insufficient pulse interval.
0 0.5 1 1.5 2
60 70 80 90 100 120
M R R ,m m /m in .
Ton=105 Ton=110 Ton=115
Ip, Ampere
0 2 4
60 80 100
S R , (m icr o m e te r)
peak current, Ip, Ampere
Ton=105 Ton=110
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Figure 5.3: effect of pulse-on time on cutting speed.
The cutting speed increase sharply with increase in pulse duration up to 115µs at high value of peak current due to sufficient melting and vaporization of the work-piece material and also increase in debris removal rate from the machined area. At high pulse duration i.e. after 115µs there is small rise in cutting speed or decrease in cutting speed as we can see from fig. 5.3. Figure 5.4 shows the effect of pulse-on time on surface roughness for different settings of Ip (60A, 100A, 120A). The other parameters were kept constant.
Figure5.4: effect of pulse-on time on surface roughness.
Experimental results show that surface roughness increase with increase in pulse duration at different setting of peak current but we found that surface roughness at low value of pulse duration and high value of peak current is less than the at high value of pulse duration and low value of peak current. This is due to because at low pulse duration materials remove mainly by gasifying and forms craters with ejecting morphology due to high value of peak current and heat flux in the ionized channel, which causes the temperature of the work-piece to be raised and to be easily exceed the boiling point. On the other hand a long pulse duration removes material mainly by melting and forms craters with melting morphology due to low value of peak current and heat flux in the ionized channel, which prevents the temperature of the work-piece from reaching a high value.
5.3 Effect of pulse-off time
Figure 5.5-5.6 show the effect of pulse-off time on cutting speed and surface roughness of D2 die steel material corresponding to values of Ton ( 105µs, 110µs, 115µs). the other parameters were kept Figure5.5: effect of pulse-off time on cutting speed constant under the conditions of peak current Ip 100A, SV 30V and WF 7. The effect of pulse- off time on cutting speed is shown in fig.5 5. As shown in fig. the cutting speed decreases when pulse-off time is increased. This is due to as with long pulse-off time the dielectric fluid produces the cooling effect on wire electrode and work material and hence decreases the cutting speed.
0 0.5 1 1.5 2 2.5
105 110 115 120
M R R , m m /m in .
Ton, µs
Ip=60 Ip=100 Ip=120
0 1 2 3 4
105 110 115 120
S R ,m icr o m e te r
Ton, µs
Ip=60 Ip=100 Ip=120
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Figure5.5: effect of pulse-off time on cutting speed
Figure 5.6 shows the effect of pulse-off time on surface roughness. The surface roughness changed little even though the pulse-off time changed corresponding to a small value of pulse-on time. Mainly surface roughness improves with increase in pulse-off time.
Figure5.6: Effect of pulse-off time on surface roughness.
The surface roughness is high at low value of pulse- Off time, this is due to because with a too short pulse- off time there is not enough time to clear the melted small particles from the gap b/w the tool electrode and work- piece and also not enough time for de-ionization of the dielectric: arcing occur and the surface becomes rougher. As we can see from the fig. surface roughness decrease up to pulse-off time 40µs and then increase with increase in pulse-off time. This is because more energy is required to establish the plasma channel and therefor there is higher electrode wear and higher surface toughness. We obtain the fine surface at pulse-off time 40µs with this machine taking D2 die steel as a work-piece material.
5.4 Effect of pulse- off time with peak current
The effect of pulse-off time on cutting speed is depicted in fig.5.7 with different value of peak current (Ip 60A, 80A, 100A and 120A) keeping other variables fixed at Ton 110µs, SV 30V and WF 7m/min.
0 0.5 1 1.5
30 40 50
M R R , m m /m in .
Toff, µs
Ip=60 Ip=80 Ip=100 Ip=120 0
0.5 1 1.5 2
30 40 50
M R R , m m /m in .
Toff, µs
TON=105 TON=110 TON=115
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Figure.5.7. Effect of pulse-off time on cutting speed with Ip.
Fig.5.7 shows that cutting speed decreases with increase in pulse-off time with different value of peak current. This is due to at same value of peak current the cooling effect on work-piece material increases with increase in pulse-off time and this also leads insufficient heating of the work-piece material.
5.5 Effect of servo voltage
The effect of servo voltage on cutting speed and surface roughness is depicted in Figure 5.8-5.9 with different pulse duration (Ton 110µs and 115µs) keeping other variables fixed at Toff 30µs, Ip 100A and WF 7 m/min.
Figure.5.8: Effect of servo voltage on cutting speed
Experimental results show that the cutting speed increase with increase in servo voltage and then it starts to decrease. This is due to increase in servo voltage result in higher discharge energy per spark because of large ionization of dielectric b/w working gap. Consequently, the cutting speed (MRR) increases. Effect of servo voltage on surface roughness is depicted in fig.5.9. Experimental results show that surface roughness at low value of pulse duration with increase in servo voltage first increases up to 30V and then decrease with increase in servo voltage. At
Figure.5.9. Effect of servo voltage on surface roughness.
high value of pulse duration the surface roughness continuously decrease with increase in servo voltage. This is due to because at low pulse duration the discharge energy is low so melted particles cannot flow out of the machining zone and impinge on the work-piece material and surface roughness increase but with increase in more servo voltage more energy is produced which leads to uniform melting and melted particles flushed out b/w the working gap.
0 0.5 1 1.5 2
20 30 40 50 60
M R R , m icr o m e te r
sv, v
Ton=110 Ton=115
0 1 2 3 4
20 30 40 50 60
S R . m icr o m e te r
SV, V
Ton=110 Ton=115
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Figure.5.10. Effect of wire feed rate on cutting speed.
5.6 Effect of wire feed rate
The effect of wire feed rate on cutting speed and surface roughness is shown in Figure 5.10-5.11. With different pulse duration (Ton 115µs and Ton 125µs) keeping other variables fixed at Toff 30µs, Ip 100A and SV 30V. From fig.5.10 we found that there is very small increase in cutting speed or nearly constant cutting speed with increase in wire feed rate. The maximum material removal rate is obtained at wire feed rate of 7mm/min. Cutting speed increases with increase in wire feed rate because there is less dissipation to the surrounding and hence more heat generated at spark gap, leading to higher material removal rate. For further increase in feed rate the cutting speed decrease due to the un-flushed debris b/w the working gap or unwanted melted particles b/w the working gap which form an electrically conductive path b/w the tool electrode and work-piece, causing unwanted spark b/w the tool electrode and work-piece. Thus only a portion of energy is used in work material removal which reduces the cutting speed. This is in agreement with work carried out by Kodalagara Puttanarasaiah Somashekhar et. al (2010).
Figure 5.11 shows that surface roughness decreases with increase in wire feed at different value of pulse on time. As we know with increase in wire feed rate area of work-piece electrode is small in comparison with the wire electrode and most heat is generated on the work-piece electrode. So that uniform melting of
Figure.5.11. Effect of wire feed rate on surface roughness.
the work-piece and vapourised or melted material flush away by the dielectric fluid sufficiently. As a result finish surface is produced by the machining which is in agreement with the work carried out by the C.A.Huang, et. Al (2003).
0 1 2 3
5 7 10
M R R , m m /m in
.WF, mm/min.
Ton=115 Ton=125
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6.7 Effect of wire material electrode
Figure.5.12. Effect of electrode material on cutting speed.
Effect of electrode materials on cutting sped is shown in fig. 12. High cutting speed is obtained with zinc coated electrode material. This is due to zinc coated wire is composed of a copper or brass core coated with zinc layer of suitable thickness. This outer coated layer of electrode material is characterized by a lower melting temperature in relation to core material. when a pulse is applied the wire coating is overheated and then evaporated.
Therefore a heat sink effect on the wire and thus a cooling of the core material is obtained. This heat sink phenomenon results in the improvement of the efficiency of the WEDM process by reducing wire temperature and therefore allowing a more intense thermal flow, leading to an increase of the cutting speed. Also due to the coating evaporation the gap size increases leading to better dielectric flushing and debris removal. That’s why we obtain high cutting speed with zinc coated wire electrode in comparison to brass wire.
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0 1 2 3 4
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Ton,µs
zinc wire
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