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30120130405009

  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 71 INFLUENCE RANKING OF PROCESS PARAMETERS IN ELECTRIC DISCHARGE MACHINING OF TITANIUM GRADE 5 ALLOY USING BRASS ELECTRODE Saravanan P Sivam1&2 , Dr. Antony Michael Raj2 & Dr. Satish Kumar S3 1 (Engineering Department / Nizwa College of Technology, Nizwa, Sultanate of Oman) 2 (Mechanical Department / SRM University, Chennai, India) 3 (Production Engineering Department /Velammal Engineering College, Chennai, India) ABSTRACT Titanium alloys have received great attention because of its high tensile strength, high toughness, light weight, extraordinary corrosion resistance, having high hardness at extreme temperatures and its great weld ability. For these reasons and the electrochemical incompatibility of aluminium with the composite materials used in the aerospace industry, titanium alloys are considered to be the replacement for aluminium in space applications. Electric discharge machining (EDM) process, which is suitable for machining titanium alloy has the electrical parameters with its tool shape and size affects the machining adversely. This paper explains about an experiment conducted to investigate the effect of these electrical parameters like discharge current, pulse on time and pulse off time along with tool shapes such as square, circular and triangle shapes on material removal rate (MRR), tool wear rate (TWR), surface roughness and angle of deviation between entry and exit of the holes made in titanium grade five alloy work piece when brass is used as the electrode. Jet flushing was used in this experiment. At conclusion this paper ranks the influence of studied parameters over important responses. Taguchi technique was used to design the experiment with L27 orthogonal array and analysis of means(ANOM) technique was used to rank the influence. Keywords: Entry Exit Deviation, Influence Ranking, MRR, Surface Roughness, Titanium EDM, Tool Geometry, TWR. I. INTRODUCTION Electrical discharge machining (EDM) is one of the most extensively used non-conventional machining processes. Its uniqueness to machine electrically conductive parts regardless of hardness has been its distinctive advantage. In addition, the absence of physical contact between the electrode and the work piece in EDM eliminating mechanical stresses and other related problems during INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 4, Issue 5, September - October (2013), pp. 71-80 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 72 machining and it is a reproductive shaping process in which the form of the electrode is mirrored in the work piece[1]. This process is being used to machine very high hardness, conductive materials such as titanium and its alloys. The high strength, low weight and outstanding corrosion resistance and weld ability[2] possessed by titanium and its alloys have led to a wide and diversified range of successful applications in aerospace, automobile, chemical plant, power generation, oil and gas extraction, surgical instruments and other major industries. However, the susceptibility of titanium alloys to work hardening during machining impairs their machinability. Thus machining of titanium alloys has been a topic of interest for industrial production and scientific research worldwide. Again, the property like strong alloying tendency or chemical reactivity of Ti-6Al-4V with most tool materials, which causes rapid destruction of the cutting tool with galling, welding and smearing at the interacting surface, leads to excessive chipping and premature tool failure and poor surface finish[3]. So EDM like non-conventional machining process gained interest in machining titanium. The good properties of titanium and the electrochemical incompatibility of aluminum with the composite materials used in the aerospace industry with which it forms a galvanic couple, titanium alloys are considered to be the replacement for aluminum in space applications[4]. The most common among thirty eight grades of titanium alloys and having very wide industrial applications is the titanium grade 5 alloys[5] which are otherwise called Ti6Al4V alloy. II. EXPERIMENT DETAILS [6] The work piece material used for this study was a commercially available titanium grade 5 alloy sheet which was cut to the dimension 100x50x3mm using wire cut EDM. 3 such sheets were cut from a large sheet to avoid any variation in properties. Brass was used as a tool electrode material because of its suitability [7]. Three geometrical shapes such as square(8x8mm), circular(8mm diameter) and equilateral triangle shapes(8mm) were used. While circular shape was obtained by conventional turning the other two were obtained by milling process. In each geometry, many electrodes were produced and nine were selected with their dimensions checked for consistency. In total four experimental parameters were considered. Among that three are electrical parameters which are pulse current, pulse on time and pulse off time and the fourth one is tool geometry and its area of cross section. Table 1 gives details about the parameters and its three level values. Electrical parameter levels were decided based on the work already done by Ahmet Hascalik & Ulas Caydas [8] in their study on surface properties of EDM machined Ti6Al4V. They found optimum results lies within this range of values. TABLE I EXPERIMENTAL PARAMETERS Parameters Level1 Level 2 Level 3 Pulse Current (A) 15 20 25 Pulse on time(µs) 50 100 200 Pulse off time(µs) 50 100 200 Geometry ( area in mm2 ) Triangle (27.7) Circle (50.26) Square (64)
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 73 Taguchi’s orthogonal array model was used to design the experiment to reduce the number of replications in the experiment. The orthogonal array chosen was L27 with interaction between parameters where each row corresponds to a particular experiment (treatment combination) and each column identifies settings of design parameters. In the first run, for example, the three design variables are set at their lower level (level 1). Table 2 shows the experiment model with coded parameters where 1 indicates level 1 value, 2 indicates level 2 values and 3 indicates level 3 values of experimental parameters. TABLE 2 TAUGUCHI EXPERIMENT MODEL (L27 ARRAY WITH INTERACTION BETWEEN FACTORS) Exp. No Pulse Current Pulse on time Pulse off time Geometry 1 1 1 1 3 2 1 1 2 1 3 1 1 3 2 4 1 2 1 1 5 1 2 2 2 6 1 2 3 3 7 1 3 1 2 8 1 3 2 3 9 1 3 3 1 10 2 1 1 1 11 2 1 2 2 12 2 1 3 3 13 2 2 1 2 14 2 2 2 3 15 2 2 3 1 16 2 3 1 3 17 2 3 2 1 18 2 3 3 2 19 3 1 1 2 20 3 1 2 3 21 3 1 3 1 22 3 2 1 3 23 3 2 2 1 24 3 2 3 2 25 3 3 1 1 26 3 3 2 2 27 3 3 3 3 The experiments were performed in a ‘V5030’ EDM machine, manufactured by Electronica Corporation of India. Dielectric fluid used was kerosene with side flushing at a pressure of 0.6MPa. The work piece top and bottom faces were ground to a surface finish using a surface grinding machine before conducting the experiments. The initial weights of the work piece and the tool were weighed using a electronic balance. During the experiment the work piece was held on the machine table using a specially designed fixture with which the work piece was gas welded. The work piece
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 74 and tool were connected to positive and negative terminals of power supply, respectively. At the end of each experiment, the work piece and tool were removed, washed, dried and weighed on an electronic balance. The machining time was determined using a digital stop-watch. New brass tool electrode was used in every experiment. Nine experiments with different geometries (3 each) in a random order were performed on each one of three work pieces. Fig. 1 shows the completed work piece with some brass electrodes. Figure 1 Work piece with electrodes After every hole was made the MRR in cubic millimeters per minute was calculated using the equation (1) [6] MRR = MRW / (ρw x t) (1) Where MRW is the metal removal weight in grams, ρw is the density of the work piece in gram per cubic millimeter and t is the machining time in minutes. Metal removal weight was calculated by finding the difference of weight of the work piece before and after a hole was made[6]. Similarly after every hole was made the TWR in cubic millimeters per minute was calculated using the equation (2) TWR = TWW / (ρt x t) (2) Where TWW is the tool wear weight in grams, ρt is the density of the tool in gram per cubic millimeter and t is the machining time in minutes. Tool wear weight was calculated by finding the difference of weight of the Brass tool before and after a hole was made. Surface roughness was measured using a surface roughness gauge and the values obtained by allowing a ball on the plunger of the gauge to touch the inner surface of the hole made on the work piece. After setting the gauge to zero, it showed the surface roughness value in terms of µm. The deviation between entrance and exit (EED), otherwise known as taper angle was measured using a co-ordinate measuring machine (CMM). The CMM was used to calculate the length and width of the hole at the entrance and then to calculate the length and width of the hole at the exit. For a circular hole, it was used to calculate the diameter at the entrance and then, the diameter at the exit. The taper between these two dimensions were calculated after drafting them, in
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 75 ‘Solid Works’ software, the taper angle was observed in degrees. Lesser the deviation between the entrance and exit of a hole better is the machining process. While recording the data, to reduce the gauge error, whenever measurements were taken using a gauge like weight measurement, coordinate measurement and surface roughness measurement, three measurements were taken and averaged. The results data of the experiment is given in Table 3. TABLE 3 RESULTS DATA Exp. No MRR (mm3 /min) TWR (mm3 /min) SR (µm) EED (º) 1 0.849346 0.238417 4.04096 1.02527 2 0.926048 0.231563 3.32928 0.865872 3 0.455003 0.152276 1.80096 0.360528 4 0.969758 0.236379 3.49312 0.773472 5 1.009213 0.221744 2.708352 0.617652 6 0.658673 0.48165 2.72016 0.44709 7 1.237598 0.260462 3.81312 0.75768 8 1.39128 0.30344 3.00288 0.415464 9 1.110978 0.27254 2.386944 0.14616 10 0.87528 0.50115 4.02336 1.53468 11 1.02696 0.54093 3.86784 1.07541 12 0.54936 0.46683 2.36016 0.70812 13 1.181928 0.604461 4.666464 1.398474 14 1.23984 0.56316 3.48048 1.09956 15 0.76272 0.198959 2.32832 0.363048 16 1.35504 0.58188 4.6152 0.94542 17 1.51632 0.59241 3.71088 0.82299 18 1.03488 0.53976 2.35296 0.37695 19 0.975893 0.85995 4.8336 1.400562 20 1.144935 0.854217 4.2368 1.359369 21 0.67716 0.773546 3.1584 0.961101 22 1.195178 0.863636 5.2416 1.490607 23 1.36125 0.911138 4.0032 1.039761 24 0.863775 0.826781 2.9888 0.739197 25 1.480545 0.927108 4.84 1.217781 26 1.6434 0.945126 4.6608 1.101861 27 1.154588 0.853398 2.7264 0.377154 The experiment results were processed using Minitab software. Taguchi analysis based on analysis of means (ANOM) & analysis of variance (ANOVA) was used to find out the process parameters influence over the machining responses. P values of ANOVA and adjusted R2 values were used to find out the goodness of the model. For all responses, adjusted R2 values were more than 95% . So the experiment model was found to be good and produced highly reliable results.
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 76 III. RESULTS The results are explained here with two type of figures. One type of figure (Main effects plot) is showing the increasing or decreasing trend of responses with respect to different factor levels. The other type of figure (Influence Graphs) is providing the delta values of influence of factors with respect to a response and their ranking inside the brackets besides the factor. A. Factors Effect on MRR, Delta Values & Influence Ranking Results showed that pulse current and tool cross sectional area are directly proportional to MRR. As the increase in these two factor values increased the MRR as shown in fig 3. Whereas pulse on time at around 100µs resulted the maximum MRR. After that increase in pulse on time has negative influence over MRR. Pulse off time is influencing very little the MRR which confirms the earlier findings[3][9]. Fig 4 shows the delta values of the influence of various factors over MRR. As per that pulse on time is the rank one factor having maximum influence and is closely followed by tool cross sectional area at second rank. Current is at third rank and pulse off time the least ranked having negligible influence comparatively. MeanofMeans 252015 1.4 1.2 1.0 0.8 20010050 20010050 1.4 1.2 1.0 0.8 64.0050.2627.70 Current Pulse on time Pulse off time Geometry Main Effects Plot (data means) for Means Figure 3 Factors effect on MRR Figure 4 Factors Extent of Influence and Ranking in MRR
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 77 B. Factors Effect on TWR, Delta Values & Influence Ranking Pulse current is the single most important factor that has direct relationship with TWR as shown in fig 5. Where as other fators are showing similar tendencies as in the case of MRR. Pulse off time is again proving in significant. Fig 6, shows the influence values and ranking of factors as per the influence. The single most influential factor here is pulse current which is followed at distance by pulse on time and tool cross sectional area. MeanofMeans 252015 0.8 0.6 0.4 0.2 20010050 20010050 0.8 0.6 0.4 0.2 64.0050.2627.70 Current Pulse on time Pulse off time Geometry Main Effects Plot (data means) for Means Figure 5 Factors effect on TWR Figure 6 Factors Extent of Influence and Ranking in TWR C. Factors Effect on SR, Delta Values & Influence Ranking As shown in fig 7, current when increases, increasing the surface roughness value where as increase in pulse on time value reduces the surface roughness value in a very fast rate. As shown in fig 8, pulse on time is the rank 1 factor influencing the surface roughness favorably and is followed by current at distance in rank 2. Increase in pulse off time reduces the surface roughness. Its rank of influence is 3. The area of cross section of the tool do not show any influence over the surface roughness as the graph is almost a horizontal line.
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 78 MeanofMeans 252015 4.5 4.0 3.5 3.0 2.5 20010050 20010050 4.5 4.0 3.5 3.0 2.5 64.0050.2627.70 Current Pulse on time Pulse off time Geometry Main Effects Plot (data means) for Means Figure 7 Factors effect on SR Figure 8 Factors Extent of Influence and Ranking in SR D. Factors Effect On EED, Delta Values & Influence Ranking In case of EED, as shown in fig 9, only increase in current increases the deviation which is un wanted. Where as pulse on time, pulse off time and area of cross section of tool when increased reducing the deviation between entry and exit. In influence ranking, pulse on time is at rank 1, followed by tool cross section at rank 2, current at rank 3 and pulse off time at rank 4 as shown in fig 10. MeanofMeans 252015 1.2 1.0 0.8 0.6 0.4 20010050 20010050 1.2 1.0 0.8 0.6 0.4 64.0050.2627.70 Current Pulse on time Pulse off time Geometry Main Effects Plot (data means) for Means Figure 9 Factors effect on EED
  9. 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 79 Figure 10 Factors Extent of Influence and Ranking in EED IV. CONCLUSIONS In general the results are conforming the findings of [6][10]11]. • Results proves that the single most important factor that affects all the responses with considerable ranking is the pulse on time. • The second important factor is the pulse current. Except MRR all other responses are negatively affected by increasing current value. • Tool cross section is the third important factor. However it does not have any influence over the surface roughness. • Pulse off time is the least influential factor as it does not have any significant influence on the responses except on EED. REFERENCES [1] W. Konig, D.F. Dauw, G. Levy, U. Panten, EDM—future steps towards the machining of ceramics, Ann. CIRP 37 (2) (1988) 623–631. [2] ASM hand book, Properties and Selection: Nonferrous alloys and Special Purpose Materials, 1993,2. [3] Armendia M., Garay, A., Iriarte, L. M. and Arrazola, P.J. Comparison of the machinability of Ti6Al4V and TIMETAL®54M using uncoated WC-Co tools. J. Mater. Process. Tecnol., 2010, 210, 197-203. [4] Lutjering, G. and Williams, J. C. Titanium. Springer, 2007. [5] Rahman, M. M., Ashikur Rahman Khan, Md., Kadirgama, K., Noor, M.M. and Rosli Bakar, A. Modeling of material removal on machining of Ti-6Al-4V through EDM using brass tungsten electrode and positive polarity. World Academy of Science, Engin. & Technology, 2010, 71, 576-581. [6] Saravanan P Sivam, Antony L MichaelRaj, Satish Kumar S, Varahamoorthy R and Dinakaran D. Effects of electrical parameters, its interaction and tool geometry in electric discharge machining of titanium grade 5 alloy with graphite tool. Proc. IMechE Part B: J. Engineering Manufacture, January 2013 vol. 227 no. 1 119-131. [7] Roger Kern. Sinker electrode material selection. EDM today,2008,July/August issue. [8] Ahmet Hascalik and Ulas Caydas. Electrical discharge machining of titanium alloy (Ti-6Al- 4V).Applied Surface Science, 2007, 253,9007-9016. [9] Lee, S. H. and Li, X. P. Study of the effect of machining parameters on the machining characteristics in EDM of tungsten carbide. J. Mater. Process. Technol., 2001, 115, 344-358.
  10. 10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 80 [10] Pradhan,B.B., and Bhattacharyya, B. Modeling of Micro-EDM during machining of Titanium Alloy , Ti-6Al-4V using RSM and ANN Algorithm. Proc. IMechE Part B: J. Engineering Manufacture, 2009, 223, No. 6, 683-693. [11] Saravanan P Sivam. Influence ranking of process parameters in electric discharge machining of titanium grade 5 alloy using graphite tool elctrode. NCT 3rd Symposium Proceedings 2012, p17-18. [12] Brij Bhushan Tyagi, Mohd.Parvez, Rupesh Chalisgaonkar and Nitin Sharma, “Optimization of Process Parameters of Wire Electrical Discharge Machining of Aisi 316l”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 317 - 327, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [13] Er.Ravinder Khanna and Er.Sumit Garg, “Experimental Investigation of Machining Parameters of Electric Discharge Machine on Tungsten Carbide (K-10)”, International Journal of Production Technology and Management (IJPTM), Volume 4, Issue 1, 2013, pp. 39 - 45, ISSN Print: 0976- 6383, ISSN Online: 0976 – 6391. [14] Mane S.G. and Hargude N.V., “An Overview of Experimental Investigation of Near Dry Electrical Discharge Machining Process”, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 3, Issue 2, 2012, pp. 22 - 36, ISSN Print: 0976-6480, ISSN Online: 0976-6499.

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