INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET)

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1 INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET) International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN (Print), ISSN (Online) Volume 5, Issue 9, September (2014), pp IAEME ISSN (Print) ISSN (Online) Volume 5, Issue 9, September (2014), pp IAEME: IJARET.asp Journal Impact Factor (2014): (Calculated by GISI) IJARET I A E M E ASSIGNMENT OF WEIGHTS METHOD FOR THE OPTIMIZATION OF TiN COATED CARBIDE REAMING Siby Varghese 1, Josephkunju Paul C. 2, S. Karunanidhi 3 1 P. G. Scholar, Department of Mechanical Engineering, Mar Athanasius College of Engineering, Kothamangalam, Kerala, India 2 Professor and Head, Department of Mechanical Engineering, Mar Athanasius College of Engineering, Kothamangalam, Kerala, India 3 Scientist G and Dy. Director, Research Centre Imarat, DRDO, Hyderabad, India ABSTRACT All the engineering fields, especially in the aerospace applications and the defense field are developing and advancing in technology day by day. The manufacturing of Electro Hydraulic Servo Valve (EHSV) considered for this work is a two stage electrically operated hydraulic valve, in which the output flow is proportional to the input current. The material used for EHSV is SS 440 C. In the manufacturing of EHSV, the cylindrical bores are manufactured using the wire electric discharge machining (WEDM). The problems associated with WEDM including its high surface roughness value, high cylinricity, increased time for manufacturing cylindrical bores and high costs associated with its production can only be eliminated by replacing the existing WEDM process with suitable process which is cost effective, time saving and produce components with better quality. For this purpose TiN coated carbide reamer is the best option to overcome the above mentioned problems for the manufacturing of cylindrical bores. This study investigates the effects of various parameters such as speed, feed and allowance on the surface finish and cylindricity of the EHSV valve body. Assignment of weights method is used to find the combinations of the above mentioned parameters to get the optimum results. Keywords: Assignment of Weights, MRPI Plot, Taguchi s Design of Experiments, Tin Coated Carbide Reamer, WEDM. 31

2 ISSN (Online) Volume 5, Issue 9, September (2014), pp IAEME 1. INTRODUCTION Wire EDM is most extensively use techniques in manufacturing components with intricate shapes and profile. But this process is not suitable for manufacturing components with cylindrical bores and uniformly tapered bores, as they are time consuming and costly process. Application of advanced reamers like TiN coated carbide reamer can be used to overcome the problems related to manufacturing of cylindrical and tapered bore manufacturing of components in precision manufacturing. Technological and economical comparison, surface integrity, corner error, crater, corrosion, etc. of WEDM process where studied with the help of literatures [1], [2], [3], [4], [6], [7], [8], [9], [10]. While considering the manufacturing of EHSV, the WEDM is applied for the manufacturing of cylindrical bores in the EHSV valve body. But it is a time consuming and costly process. Also WEDM has several disadvantages as seen from several journals. So advanced process such as special purpose reaming process can be used instead of WEDM process for cylindrical bore manufacturing. Reaming is common machining process for enlarging, smoothing and accurately sizing existing holes to tight tolerances [5]. International manual [14] for special purpose tools gives a complete idea about the type of tools that suitable for different work materials. In that manual the type of reamer suitable for machining SS 440C is found as TiN coated carbide reamer. It was found that the most influencing parameter for reaming process are speed, feed, depth of cut and allowance. In this work, depth of cut is not considered as the variable parameter; as it can only be varied according to the length of spool bore. Reaming was retained for finishing, as a process capable of yielding required results when performed on inexpensive machine tools such as drill press with simple fixtures. Reaming is suitable for batch production typically of job shops, facing the challenges of meeting specifications at competitive costs. Better surface finish and bore geometry can be obtained with the help of reaming process. Apparently minor influences led to enhanced process control and substantially better results at no extra cost. Results supported selection of production parameters meeting specified quality and cost targets, as well as substantial improvements [11]. From [13] it was found that average surface roughness for reaming range between 0.8 µm and 3.2 µm, but high-accuracy reaming can produce average surface roughness as low as 0.4 µm. The quality of the reamed holes was evaluated in terms of geometrical characteristics (diameter, roundness, cylindricity and surface roughness). Roundness as well as cylindricity was verified to be smaller than the specified tolerance. Higher feed rate leads to lower and more repeatable roughness. MQL in reaming leads to high quality results in terms of hole dimensions and surface finish. [12] The feed and speed are important process parameters to control surface roughness, tool wear, material removal rate and hole diameter error. Thus it is essential to employ suitable combination of cutting speed and feed so as to reduce the variations that can affect the quality of the holes. Assignment of weights method can be used for optimizing the proposed reaming process. 2. EXPERIMENTS AND METHODS The main objective of this project work is to find out how various reaming parameters such as speed, feed and allowance influence various output characteristics such as surface finish and cylindricity while considering the manufacturing of cylindrical bores in the EHSV valve body. Figure 1 shows the different bores in EHSV valve body. 32

3 ISSN (Online) Volume 5, Issue 9, September (2014), pp IAEME Figure 1: Bores in EHSV valve body 2.1. Experimental details for proposed reaming process The experiment was conducted on vertical milling machine as shown in figure 2. The machine has speed settings up to 15,000 RPM, feed settings up to 30,000 mm/min. The experiments are conducted on stainless steel 440C. TiN coated carbide reamer is used for reaming as shown in fig. 3. Figure 2: Experimental reaming setup Figure 3: TiN coated carbide reamer The number of experiments and input levels are decided based on the design of experiments and the input parameters and their levels are presented in table 1. Table 1: Reaming Prameters Input Parameters Speed (RPM) Feed (mm/min) Allowance (mm) Level Level Level Design of Experiments To test the effect of these factors on a response variable, a suitable experiment is designed such that the necessary data for testing the significance of the effects of the factors on the response variable are collected. Identification of the response variable is the first step to be followed for the designing of experiment. Identify the factor affecting response variables, fix the number of levels of 33

4 each factor, form the skeleton of the experiment and define its components comprises the next step for designing an experiment. Taguchi L9 orthogonal array as tabulated in table 2 is selected with the help of MINITAB 16 software. Table 2: L9 Orthogonal Array Experimen P1 P2 P3 t Scheme of Experiments Based on L9 orthogonal array, experiments are conducted on Stainless steel 440C with TiN coated carbide reamer tool for different experiment levels which are shown in Table 1. Speed, feed and allowance are selected as input variable parameters. Three varying parameters with three different levels are taken for the purpose of design of experiments. Exp. No. Table 3: Scheme of experiment Speed Feed Allowance (RPM) (mm/min) (mm)

5 The levels are taken with the help of range of the variable parameters are chosen with the help of GUHRING international manual for advanced machine tools. Each test is repeated three times in order to achieve validity and accuracy. The L9 array for the experimental run is shown in table Assignment of weights method In assignment of weights method, the multi response problem is converted into a single response problem. Here we have two responses; surface finish and cylindricity. Multi Response performance Index (MRPI) can be calculated using the equation 1. Since MRPI is a weighted score, optimal levels are identified based on maximum MRPI. MRPI = W 1 R 1 + W 2 R 2 (1) Where, W 1 be the weight assigned to the first response R 1 and W 2 be the weight assigned to the first response R 2. The weights can be determined by dividing the individual responses by the response total value. Since here both the responses considered are having smaller the better characteristics, reverse normalization procedure is used. That is, for each data, 1/SR and 1/ are obtained and the corresponding W SR and W are computed using the equation 2 and RESULTS AND DISCUSSION W SR = (1/SR)/( 1/SR) (2) W = (1/ )/( 1/ ) (3) Results were obtained for surface finish and cylindricity for reaming of SS 440C experimental blocks. MINITAB 16 software is used to perform Taguchi design of experiment. Assignment odf weights method was performed to found the optimum combination of input parameters Experimental Combinations Three blocks of SS 440C where chosen for conducting experiments. In each block, 9 holes were reamed based on experimental combinations obtained. Figure 4: Experimental Blocks All the trials where repeated thrice in order to validate the experimental results. Figure 4 shows the experimental blocks chosen for this work. 35

6 Trial No. Table 4: Reaming experimental combinations Bore No. Speed (RPM) Feed (mm/min) Allowance (mm) 1 A1, B1, C A2, B2, C A3, B3, C A4, B4, C A5, B5, C A6, B6, C A7, B7, C A8, B8, C A9, B9, C Experimental Results for Different Trials The experimental results obtained by reaming experiment conducted on three blocks of SS 440C were tabulated below on table 5. The responses investigate are surface finish and cylindricity. The experiment was conducted three times, in order to achieve repeatability. The ranges for different parameters are set with reference to Guhrings international manual for special tools. Table 5: Experimental results for different trials Trial No. Surface Roughness, SR (µm) Cylinricity, (µm) SR1 SR2 SR

7 3.3. Assignment of Weights Table 6: Weight and MRPI Average SR Average 1/SR 1/ Weights SR MRPI Average values of each response were calculated. The weights and MRPI were calculated using equations 1, 2 and 3. Multi Response Performance Index (MRPI) obtained can be treated as single response problem and MRPI data is analyzed to determine the optimal level for the factors. Level totals of MRPI values are tabulated on table 7. The weights can be determined by dividing the individual responses by the response total value. Since here both the responses considered are having smaller the better characteristics, reverse normalization procedure is used. Table 7: Level Totals of MRPI FACTORS LEVELS SPEED (A) FEED (B) ALLOWANCE (C) The optimal levels are selected based on maximum MRPI are A 2, B 1 and C 2. 37

8 MRPI CHART MRPI SPEED FEED ALLOWANCE Figure 5: MRPI Chart Graphical representation showing the factor effects on mean MRPI are shown optimal combination found from effect on mean MRPI are: in figure 5. The Speed Feed Allowance = 800 RPM = 80 mm/min = 0.3 mm 3.4. Confirmation Test The confirmation test is the final step in verifying the results obtained from Taguchi s design approach. The optimal conditions are set for the significant factors and experiments are run under specified reaming conditions. The results from the confirmation experiment are compared with the predicted average based on the parameters and levels tested. The confirmation experiment is a crucial step and is highly recommended by Taguchi to verify the experimental results. The purpose of the confirmation experiment is to validate the conclusions drawn from the experiment. Confirmation experiment is conducted using the optimal levels of the significant factors. The confirmation test block is shown in fig. 6. Figure 6: Confirmation test block 38

9 Table 8: Confirmation test results Bore No. Surface Roughness, SR (µm) Cylindricity, (µm) The confirmation test is conducted on SS 440C test block with TiN coated carbide reamer with the optimum level of combinations found using grey relational analysis. The confirmation test results were tabulated in table 8. In the confirmation test, the responses for which data collected are for surface roughness and cylindricity. From the confirmation test results, it was found that while reaming with optimal conditions by assignment of weights method, the cylindricity and surface finish obtained were much better than expected results. 4. CONCLUSION From the experiments, the optimal combination was obtained as speed (800 RPM), feed (80 mm/min), and allowance (0.3mm) using assignment of weights method. This optimum combination was used to confirm the experiment. The confirmation test results validated the experiment. REFERENCES [1] F. Klocke, M. Zeis, A. Klink, D. Veselovac, 2013, Technological and economical comparison of roughing strategies via milling, sinking-edm, wire-edm and ECM for titanium and nickel based blisks, CIRP Journal of Manufacturing Science and Technology, [2] D. Welling, 2014, Results of surface integrity and fatigue study of Wire-EDM compared to broanching and grinding for demanding jet engine components made of Inconel 718, Procedia CIRP, [3] L. Li, Y.B. Guo, X.T. Wei, W. Li, 2013, Surface integrity characteristics in wire-edm of inconel 718 at different discharge energy, Procedia CIRP, [4] F. Klocke, D. Welling, J. Dieckmann, 2011, Comparison of grinding and Wire EDM concerning fatigue strength an surface integrity of machined Ti6Al4V components, Procedia Engineering, [5] S. Karunanidhi, M. Singaperumal, 2010, Design, analysis and simulation of magnetostrictive actuator and its application to high dynamic servo valve, Sensors and Actuators, [6] Fuzhu Han, Jie Zhang, Isago Soichiro, 2007, Corner error simulation of rough cutting in wire EDM, Precision Engineering, [7] D.K. Aspinwall, S.L. Soo, A.E. Berrisford, G. Walder, 2008, Workpiece Surface roughness and integrity after WEDM of Ti-6Al-4V and Inconel 718 using minimum damage generator technology, CIRP Annals Manufacturing Technology, [8] Haruki Obara, Harutoshi Satou, Masatoshi Hatano, 2004, Fundamental study on corrosion of cemented carbide during wire EDM, Journals of Material Processing Technology, [9] K.H. Ho, S.T. Newman, S. Rahimifard, R.D. Allen, 2004, State of the art in wire electric discharge machining (WEDM), International Journal of Machine Tools & Manufacture [10] B. Bojorquez, R.T. Marloth, O.S. Es-Said, 2002, Formation of a crater in the workpiece on an electric discharge machine, Engineering failure Analysis,

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