IJIRST窶的nternational Journal for Innovative Research in Science & Technology| Vol. 1, Issue 1, June 2014| ISSN(online): 2349-6010
Investigation On Material Removal And Tool Wear Rates Of Tib2 Ceramic In Electrical Discharge Machining C. Sekar PG scholar Department Of Mechanical Engineering K.S.RangasamyCollege of Technology, Tiruchengode, India
Abstract Ceramic composites are considered as the next generation of advanced materials due to their high hardness, excellent chemical and mechanical stability under a broad range of temperature, and high specific stiffness. However, these materials are difficult to machine in conventional machining because of their high strength and complexity in shapes. Electric discharge machining (EDM) has been proven as an alternate process for machining complex and intricate shapes from the conductive ceramic composites. In present study, process parameters namely current (I), pulse on time (ton), and pulse off time (toff) are optimized with the considerations of multi responses such as Material Removal Rate, Electrode wear Rate. The experiments were conducted according to an L9 orthogonal array. The parameters are optimized using Taguchi method. Keywords: Electric discharge machining (EDM), TiB2 ceramic, Performance characteristics MRR, EWR, Taguchi L9 orthogonal array. _________________________________________________________________________________________________________ I.
INTRODUCTION
A. Literature review Silicon nitride based ceramic composites have been recognized as promising engineering materials because of their outstanding mechanical and thermal properties such as high strength at high temperature, oxidation resistance, thermal shock resistance, wear and creep resistance, etc. Therefore this material is especially used for high temperature applications in mechanical and aerospace engineering[1-3]. However, it is difficult to machine these materials in conventional machining methods. It limits their applications. To avoid these problems, Non-traditional techniques such as Ultrasonic Machining (USM), Laser Beam Machining (LBM) and Electrical Discharge Machining (EDM) can be used[4,5]. Out of these, EDM is extensively used in machining hard, high strength, complex geometry shape and temperature resistant materials in a contactless manner. The material is melted and evaporated by the heat between tool electrode and workpiece[5-8]. B. Principle of EDM Electric discharge machining is a controlled metal removing technique whereby an electric spark is used to cut the work piece, which takes a shape opposite to that of the cutting tool or electrode. The electrode is made from electrically conductive material. The electrode, made to the shape of the cavity required, and the work piece are both submerged in a dielectric fluid. Dielectric fluid should be nonconductor of electricity. A servo mechanism maintains a gap of about 0.01 to 0.02mm between the electrode & the workpiece, preventing them from coming into contact with each other. A direct current of low voltage & high amperage is delivered to the electrode at the rate of approximately 50 KHz. These electrical energy impulses vaporize the oil at this point. This permits the spark to jump the gap between the electrode and the work piece
Fig.1: EDM Setup All rights reserved by www.ijirst.org
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Investigation On Material Removal And Tool Wear Rates Of Tib2 Ceramic In Electrical Discharge Machining (IJIRST/ Volume 01 / Issue 01 / 0013)
through the dielectric fluid. Intense heat is created in the localized area of the spark impact, the metal melts and a small particle of molten metal is expelled from the surface of the work piece. The dielectric fluid which is constantly being circulated carries away the eroded particles of metal during the off cycle of the pulse and also assists in dissipating the heat caused by the spark. C. Taguchi Method Taguchi methods are the most recent additions to the toolkit of design, process and manufacturing engineers, and quality assurance experts. In contrast to statistical process control, which attempts to control the factors that adversely affect the quality of production, Taguchi methods focus on design – the development of superior performance designs (of products and manufacturing processes) to deliver quality[9,10]. II. EXPERIMENTAL WORK A. Materials The material used for this work is TiB2 ceramic disc of size 60mm x 3mm. The material is hardened to a hardness of 58 HRC. The electrode used is electrolytic copper (99.97% pure) of 8930 kgm -3 density with a melting point of 10830C. These electrodes are cylindrical in shape with a nominal diameter of 6 mm. B. Design of Experiments In L9 (33) array 9 rows represent the 9 experiment to be conducted with 3 columns at, 3 levels of the corresponding factor. The matrix form of these arrays is shown in Table 1, where 1, 2, 3 in the table represents the level of each parameters. Table 1: Taguchi L9 Orthogonal array Design Matrix
Exp. No E1 E2 E3 E4 E5 E6 E7 E8 E9
Parameter 1 1 1 1 2 2 2 3 3 3
Parameter 2 1 2 3 1 2 3 1 2 3
Parameter 3 1 2 3 2 3 1 3 1 2
Table 2: Level values of Input parameters
Sr. No
Parameters
1 2 3
Current (A) Pulse on Time (µsec) Pulse off Time (µsec)
1 15 40 2
Levels 2 3 20 25 60 80 3 4
Table 3. Experimental results
Exp. No E1 E2 E3 E4 E5 E6 E7 E8 E9
MRR (gm/min) 0.0661 0.0803 0.1024 0.0812 0.1094 0.1 0.0649 0.0948 0.1014
EWR (gm/min) 0.000931 0.004217 0.005944 0.001171 0.003333 0.006528 0.000376 0.002233 0.003175
III. RESULT AND DISCUSSION A. Effect of Input parameters on MRR The response table for signal to noise ratio for MRR is shown in Table 4. For MRR, the calculation of S/N ratio follows “Larger the Better “model. The graphical comparison is shown in Figure 2. Therefore, Pulse on Time (µsec) has the maximum effect on MRR followed by Current (A) and Pulse off Time (µsec).
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Investigation On Material Removal And Tool Wear Rates Of Tib2 Ceramic In Electrical Discharge Machining (IJIRST/ Volume 01 / Issue 01 / 0013)
Main Effects Plot (data means) for SN ratios Current
Pulse on Time
-20
Mean of SN ratios
-21 -22 -23 15
20 Pulse off Time
25
2
3
4
40
60
80
-20 -21 -22 -23
Signal-to-noise: Larger is better
Fig.2: Main effects plot for SN ratios Table 4: Response Table for Signal to Noise Ratios
Level 1 2 3 Delta Rank
Current -21.77 -20.34 -21.37 1.42 2
Pulse on Time -23.05 -20.53 -19.89 3.16 1
Pulse off Time -21.35 -21.2 -20.92 0.43 3
B. Effect of Input parameters on EWR The response table for signal to noise ratio for EWR is shown in Table 5. For EWR, the calculation of S/N ratio follows “Smaller the Better“ model. The graphical comparison is shown in Figure 3. Therefore, Pulse on Time (µsec) has the maximum effect on MRR followed by Current (A) and Pulse off Time (µsec). Main Effects Plot (data means) for SN ratios Current
65
Pulse on Time
60
Mean of SN ratios
55 50 45 15
20
25
40
60
80
Pulse off Time
65 60 55 50 45 2
3
4
Signal-to-noise: Smaller is better
Fig.3 Main effects plot for SN ratios Table 5. Response Table for Signal to Noise Rations
Level 1 2 3 Delta Rank
Current 50.88 50.63 57.16 6.54 2
Pulse on Time 62.58 50.02 46.06 16.52 1
Pulse off Time 52.45 52.03 54.19 2.15 3
IV. CONCLUSIONS The material removal rate (MRR) mainly affected by pulse on time. Pulse off time has less effect on it. The electrode wear rate (EWR) is mainly influenced by pulse on time. The effect of pulse off time is less on EWR and has least effect on it. Optimum parameters of input factors are as follows; Pulse on time (40micro seconds), Current (15A), Pulse off time (4 micro seconds). REFERENCE
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Investigation On Material Removal And Tool Wear Rates Of Tib2 Ceramic In Electrical Discharge Machining (IJIRST/ Volume 01 / Issue 01 / 0013) I. Puertas, C.J. Luis, L. Alvarez, (2008) “Analysis of the influence of EDM parameters on surface quality, MRR and EW of WC-Co”, Public university of Navarre (Spain). [2] B. H. Yan, H. C. Tsai, F.Y. Huang, (2005) “The effect in EDM of a dielectric of a urea solution in water on modifying the surface of titanium” Procedia Engineering, vol. 45, pp. 194–200. [3] S. L. Chen, B.H. Yan, F.Y. Huang, (1999) “Influence of kerosene and distilled water as dielectrics on the electric discharge machining characteristics of Ti– 6A1–4V” Journal of Materials Processing Technology, vol. 87, pp. 107-111 [4] C.J. Luis, I. Puretas, G. Villa, (2005) “Material removal rate & electrode Wear study on the EDM of silicon Carbide”, Journal of Materials Processing Technology, vol. 164, pp 889-896. [5] A.A.Khan, (2007) “Electrode wear & Material removal rate during EDM of aluminum & mild steel using copper & brass electrodes”, Springer-verlag London Limited [6] P.M. George, B.K. Raghunath, L.M. Manocha, Ashish M Warrier, (2009) “EDM machining of Carbon-Carbon composite- a Taguchi approach”, Research Journal of Material Sciences, vol. 8(2), 256-267 [7] Ali Ozgedik, Can Cogan, (2003) “An Experimental investigation of tool wear in electric discharge machining”, International Journal of Advanced Manufacturing Technology, vol. 17, pp. 1217-1225. [8] K.H. Ho, S.T. Newman (2003) “State of the art electrical discharge machining (EDM)”, International journal of Machine Tools & Manufacture, vol. 43, 1287-1300. [9] Y.S. Wong, L.C. Lim, L.C. Lee, (1995) “Effects of flushing on Electro discharge machined surface”. Journal of material processing technology. Vol. 48, pp. 299-305. [10] Yih-Fong Tzeng Fu-chen chen, (2007) “Multiobjective optimization of high speed EDM process using a taguchi fuzzy based approach”, Materials and Design, vol. 28, pp. 1159–1168. [1]
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