International Journal of Mechanical and Production Engineering Research and Development (IJMPERD) ISSN 2249-6890 Vol. 3, Issue 2, Jun 2013, 57-62 ÂŠ TJPRC Pvt. Ltd.
EFFECT OF WEDM MACHINING PARAMETERS ON OUTPUT CHARACTERISTICS S.A. SONAWANE1 & M.L. KULKARNI2 1
Department of Mechanical Engineering, SKN Sinhgad College of Engineering, Korti, Pandharpur, Maharashtra, India 2
Maharashtra Academy of Engineering, Alandi, Pune, Maharashtra, India
ABSTRACT Wire Electrical discharge machining [WEDM] is an electro-thermal machining process. It can machine any material irrespective of its hardness, brittleness or toughness with utmost accuracy. As there is no contact between wire and the work piece mechanical stresses are not induced during machining. In WEDM many machining parameters are involved. A small change in the control parameters affects the process performance namely material removal rate, surface finish, cutting speed, dimensional deviation and geometrical accuracy. In this paper an investigation of the effect of machining parameters namely pulse-on time, pulse-off time, peak current, wire feed rate, wire tension and servo voltage on cutting rate and surface finish is presented. Experimental results showed that with increase in the pulse-on time, peak current and wire feed rate, cutting rate increases and surface finish decreases. Also, the empirical model developed for cutting rate and surface finish is validated and has showed good agreement with experimental results.
KEYWORDS: WEDM, Cutting Rate, Surface Finish INTRODUCTION Wire electrical discharge machining is a non-conventional machining process widely used in aerospace, automotive, tool and die industries. In WEDM a thin wire of size 0.05-0.3 mm in diameter may be used as a tool kept in tension using a mechanical tensioning device. Thus, reducing the tendency to produce inaccurate parts. A small gap of the order of 0.025-0.05 mm is maintained between the wire and the work piece . Material removal mechanism in WEDM is mainly due to melting and vaporization and takes place by a series of rapid, repetitive and discrete spark discharges between wire and work piece in presence of dielectric fluid. The dielectric fluid used may be deionized water, oil or hydrocarbon fluids. Miller et. al. analysed the effect of spark on time duration (Ton) and spark on time ratio (Ton/T) on MRR and surface integrity of four types of advanced materials viz. porous metal foams, metal bond diamond grinding wheels, sintered Nd-Fe-B magnets and carbon carbon bipolar plates. Han et. al.  carried out experiments on alloy steel to study the effect of pulse duration, discharge current, sustained pulse time, pulse interval time, polarity effect and conductivity of the dielectric on surface roughness during finish cutting of WEDM. Kanlayasiri and Boonmung  investigated machining of DC53 die steel by varying the process parameters such as pulse on time, pulse off time, pulsepeak current and wire tension to investigate their effects on surface roughness. Tsai et. al.  presented an investigation about the effect of heterogeneous second phase i.e. quantity, area fraction and diameter of spheroidal graphite particles to evaluate machinability of the ferritic SG cast irons in the WEDM process. Bamberg and Rakwal  investigated machinability of gallium-doped p-type germanium to analyze the effect of machining parameters such as spark voltage, capacitance, wire type and wire diameter slicing rate, surface roughness and surface contamination. Klink et. al.  studied surface integrity of powder metallurgical tool steel ASP2023 while machining in the oil and water dielectric. In this study, experiments were conducted to analyze the effect of cutting parameters such as pulse-on time, pulse-off time, peak
S.A. Sonawane & M.L. Kulkarni
current, wire tension, wire feed rate, and servo voltage on cutting rate and surface finish during WEDM machining process. Empirical model is developed with the help of regression analysis method.
EXPERIMENTATION The experiments were performed on an Electronica supercut WEDM machine. Different settings of process parameters pulse on time, pulse off time, peak current, wire tension, wire feed rate and servo voltage were used in the experiments. AISI D3 die steel of size 40mm x 40mm x 10mm was used as work piece material. Coated brass wire (CuZn50) of 0.25 mm diameter was used as tool electrode. The chemical composition of material given by the energydispersive spectrometer (EDS) in percentage of mass is as follows: C= 2.1, Si= 0.25, Mn= 0.35, Cr= 12, Mo= 0.6, V= 0.7. The value of flushing pressure was fixed at 1 unit (15 kg/cm 2) and the value of servo feed was kept at 2100 units. Conductivity of the dielectric was maintained at 20 µS/cm at 22°C. Surface finish was measured with the help of Mitutoyo’s surface finish tester (S J 201). The cut-off length was 0.8 mm. During surface finish measurement, total three measurements were taken on each specimen at different locations. The final value was taken as average of these measurements.
RESULTS AND ANALYSIS Effect of Pulse-on time As shown in figure 1 and 2, with increase in pulse on time, discharge energy increases which creates larger and deeper craters on the work piece surface. As a result cutting rate increases and surface finish reduces.
Figure 1: Effect of Pulse-on Time on Surface Finish
Figure 2: Effect of Pulse-on Time on Cutting Rate
Effect of Pulse-off Time As pulse off time increases, number of discharges within a given period decreases. Thus, decreasing the spark energy which will create small craters on the work piece surface. Due to this effect cutting rate and decreases and surface finish improves as shown in figure 3 and 4.
Figure 3: Effect of Pulse-off Time on Surface Finish
Figure 4: Effect of Pulse-off Time on Cutting Rate
Effect of WEDM Machining Parameters on Output Characteristics
Effect of Peak Current Figure 5 and 6 indicates that, the higher the peak current, larger the discharge energy. This results in increase of cutting rate and decrease in the value surface accuracy. In other words, effects of peak current and pulse-on time settings on the output characteristics are similar.
Figure 5: Effect of Peak Current on Surface Finish
Figure 6: Effect of Pulse-off Time on Cutting Rate
Effect of Wire Feed Rate As WEDM is a thermal erosion process, in which material removal takes place both from the work piece and wire. At low feed rate, more amount of material is removed from the wire resulting in the decrease in diameter of the wire. As a result spark energy decreases which will remove small amount of material from the work piece surface. Thus, cutting rate decreases and surface finish increases at low feed rate as shown in figure 7 and 8.
Figure 7: Effect of Wire Feed Rate on Cutting Rate
Figure 8: Effect of Wire Feed Rate on Surface Finish
Effect of Wire tension With increase in wire tension, wire phenomenon reduces which results in uniform distribution of spark density along the length of the wire. Because of this uniform amount of material will be removed from the work piece surface. It is observed from fig. 9 and 10 that, effect of wire tension is negligible on cutting performance.
Figure 9: Effect of Wire Tension Surface Finish
Figure 10 Effect of Wire Tension on Cutting Rate
S.A. Sonawane & M.L. Kulkarni
Effect of Servo voltage As the servo voltage increases, ignition delay time increases. This results in decrease in the discharge cycles within a given period which leads to decrease in the spark energy. As a result small craters are produced on the work piece surface which leads to decrease in the cutting rate and improvement in the surface finish as indicated in the fig. 11 and 12.
Figure 11: Effect of Servo Voltage on Surface Finish
Figure 12: Effect of Servo Voltage on Cutting Rate
EMPIRICAL MODELING With the help of data obtained through experimentation multiple linear regression analysis was carried out and following correlations was obtained for cutting rate and surface finish: Cutting rate = - 7.40 + 0.115 X1 - 0.154 X2 + 0.00825 X3 + 0.226 X4 + 0.120 X5 - 0.0241X6 Surface finish = - 10.9 + 0.127 X1 - 0.0465 X2 + 0.00399 X3 + 0.0835 X4 + 0.0743 X5 - 0.0323 X6 Where X1 = Pulse-on time, X2 = Pulse-off time, X3 = Peak Current, X4 = Wire feed rate, X5 = Wire tension, X6 = Servo voltage. Further, the model is validated through experimentation and it is found that results of regression analysis and results of experiments are in good agreement. Table 1 shows the comparison of results between regression analysis and experimentation. Table 1: Comparison of Results between Regression Analysis and Experimentation for Cutting Rate and Surface Finish Sr. No.
Cutting Rate mm/min Regression Experimentation
% Age Error
Surface Finish, µm Regression Experimentation
CONCLUSIONS From the results of the experimentation following conclusions are drawn:
As pulse-on time, peak current and wire feed rate increases, cutting rate increases and surface finish becomes poorer.
As pulse-off time and servo voltage increases, cutting rate decreases and surface finish improves.
Wire tension has less effect on cutting rate and surface finish as compared to other cutting parameters.
Effect of WEDM Machining Parameters on Output Characteristics
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Han, F. et. al. (2007). Influence of machining parameters on surface roughness in finish cut of WEDM. International Journal of Advanced Manufacturing Technology, 34, 538-546.
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Tsai, T.C. et. al. (2008). The effect of heterogeneous second phase on the machinability evaluation of spheroidal graphite cast irons in the WEDM Process. Materials and Design, 29, 1762-1767.
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