MULTI-PARAMETRIC OPTIMIZATION OF EDM PARAMETERS FOR HEXAGONAL PROFILE CU ELECTRODE TO MEASURE FORM TOLERANCE ON NI-BASED SUPER ALLOY

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1 International Journal of Mechanical and Production Engineering Research and Development (IJMPERD) ISSN (P): ; ISSN (E): Vol. 8, Issue 2, Apr 2018, TJPRC Pvt. Ltd MULTI-PARAMETRIC OPTIMIZATION OF EDM PARAMETERS FOR HEXAGONAL PROFILE CU ELECTRODE TO MEASURE FORM TOLERANCE ON NI-BASED SUPER ALLOY SUBRAMANI. P & S. DHANABALAN Department of Mechanical Engineering, M. Kumarasamy College of Engineering, Karur, Tamilnadu, India ABSTRACT This research aims to examine the form tolerances, namely angularity and flatness to improve the productivity and Material Removal Rate (MRR) with a high surface finish of Ni-based super alloy. EDM is a spark erosion process, in which, the removal of material takes place due to erosion caused by electric sparks. This process is utilized for machining of conductive and difficult-to machine material, irrespective of hardness. In this experimental work, the multi-parametric optimization has been utilized for the EDM of Inconel-718 using hexagonal profile tool electrode made up of Copper. The peak current, pulse on Time (T on ) and pulse of time (T off ) were selected as process constraints to conduct experimental trials. The MRR, EWR, machining time and form tolerances were considered as output responses. The experimental outcomes were optimized by multi-parametric method Gray relational analysis coupled with Taguchi method. The optimized parameters by multi-parametric optimization method showed the considerable improvement in the process and will facilitate the EDM industries to improve the productivity with close tolerance. KEYWORDS: Electic Discharge Machining, Hexagonal Profile Electrode, MRR, Coordinate Measurement, Form Tolerance & Multi-Parametric Optimization Original Article Received: Feb 17, 2018; Accepted: Mar 07, 2018; Published: Mar 19, 2018; Paper Id: IJMPERDAPR INTRODUCTION Electric Discharge Machining (EDM) is practically versatile, applicable in precision manufacturing industries to manufacture precise and close tolerance parts with higher accuracy. When a suitable voltage is supplied across the cathode (tool) and anode (work piece), an electrostatic field of high strength is established, which cause emission of an electron from the tool. The emitted electrons get accelerated towards work piece and collide with the dielectric fields molecules, breaking them into electrons and ions. The produced electrons accelerate and dislodge. As a result, a spark is produced between anode and cathode and a very high temperature is developed on the electrode. The high temperature causes melting and vaporization of the material. The block diagram of EDM is shown in figure 1. [1.3] Nickel- based super alloys are extensively used in high precision components, because of its excellent properties. [2] However, based on the properties, Inconel-718 is a well identified difficult-to-machine super alloy material. As an attempt to use the EDM process effectively, some researchers reported the effect of EDM parameters in meso (diameter in the range from 1mm to 10 mm) drilling of Ni-based super alloy. The authors resulted that MRR is affected by peak current and duty factor, whereas SR is affected by peak current and pulse on time. [2-6, 12] editor@tjprc.org

2 934 Subramani. P & S. Dhanabalan Figure 1: Schematic of Electric Discharge Machining (EDM) Tolerance may be described and measured as the deviation between the maximal and minimal limits and the total measure that a particular dimension is allowed to deviate. Tolerances are specified generally by two methods; unilateral tolerance and the bilateral tolerance. Unilateral tolerance allows the variance for a nominal measure in one direction only, whereas the bilateral tolerance allows the dimensional variation in both the directions from the specified value. Flatness is the status or quality of a surface or an Inferred median plane having all of its ingredients in one plane. It is one of the forms of tolerance, and it never uses a datum reference. Angularity is used for the tolerancing in all the angles of surfaces, center plane or axis of datum plane other than parallel and perpendicular. In case of angularity, the tolerance on the specified basic angle is given in mm or inches rather than degrees. Stanislaw Adamczak et al (2003) investigated the importance of cylindricity measurement by using reference method. Adamczak (2006) presented the principle of reference method and also presented the method of comparing the cylindrical profile. [1] Kao et al (2007) measured and analyzed the cylindricity, diameter, roundness and taper for EDM micro-holes by using the CMM. [3] Venkaiah & Srinagalakshmi (2011) investigated the evolution of squareness using computational geometric approach and Coordinate Measuring machine. Slawomir et al (2012) reported the effect of the shape accuracy of holes manufactured by EDM process and the influence of process parameters. [14] Therefore, the importance of form tolerance in manufacture components was discussed. From the literature survey, it is ascertained that no plausible works were reported to measure form tolerances such as angularity and flatness on an Inconel-718 Ni-based super alloy using a hexagonal shaped copper tool in EDM process. Therefore, this experimental analysis and optimization work is undertaken to optimize the form tolerances in EDM by Grey relational method coupled with Taguchi method. EXPERIMENTAL PLAN Design-of-experiments (DoE) needs cautions scheduling, practical layout of the trials, Taguchi has identical procedures for every DoE application steps and the DoE can dramatically decrease the amount of trials. [9] Thus, the three parameters such as current (I p ), pulse on time (T on ) and pulse off time (T off ) had been selected for the governing parameter, and each parametric quantity had three levels denoted by level-1, level-2 and level-3, as designated in the Table 1. Table 1: Allocated Values of EDM Parameters and their Levels Parameter Units Level-1 Level-2 Level-3 A Peak current (I p ) Amps B Pulse on time (T on ) µs C Pulse off time (T off ) µs Impact Factor (JCC): NAAS Rating: 3.11

3 Multi-Parametric Optimization of EDM Parameters for Hexagonal Profile 935 CU Electrode to Measure form Tolerance on NI-based Super Alloy (I) DESIGN OF HEXAGONAL SHAPE COPPER ELECTRODE To measure the form tolerance of the hexagonal profiled deep hole, the first step was to design the hexagonal shape tool. The copper electrodes were prepared with the help of CNC milling Machine Model DMC 64 V linear with higher accuracy. The shape of the tool used for machining hexagonal shape hole is shown in the figure 2 (a) and 2 (b). Figure 2: Dimension of Hexagonal Shape Copper Tool Electrode (II) EXPERIMENTAL SET-UP AND DOE (DESIGN OF EXPERIMENT) Bruker SI turbo Analyzer and Hardness Tester HT-7 were used to measure the chemical composition and the hardness values of Inconel-718 plate. As per DoE, the experiments were performed on 15 amps rated die-sinking SPARONIX-EDM. The EDM set-up is shown in figure 3. Figure 3: Experimental Set-up of Die Sinking SPARKONIX-EDM The Inconel-718 work piece was used in the form of a 4 mm thick plate. The work piece and the electrodes were linked up with +ve and ve polarity in the D.C. power source, respectively. Side flushing die-electric kerosene along with an intensity of 0.2 kg/cm 2 was used for all the experimental work. The weight of the electrodes and work piece was measured before and after machining for every trial run with digital weight-balance (up to gram accuracy). The formula used to evaluate the material removal rate (MRR) is given below: Weight of work material removal MRR = (g/min) (1) Time The formula used to calculate the Electrode Wear Rate (EWR) is given below: Weight of electrode material removal EWR = (g/min) (2) Time editor@tjprc.org

4 936 Subramani. P & S. Dhanabalan Each trial was evaluated thrice and the mean values were obtained. The form tolerances namely angularity and flatness were measured by using a TESA Micro-Hite 3D Co-ordinate Measuring Machine (CMM). FORM TOLERANCE ANALYSIS AND MULTI-PARAMETRIC OPTIMIZATION The aim of this experimental analysis is to increase the MRR and to minimize the value of form tolerances, namely angularity and flatness. In the present experimentation work, L 18 Orthogonal Array (OA) was chosen. This OA has 18 parametric combinations [15] therefore; the total numbers of 18 experiments were conducted to measure the interactions between the various factors. The parameter combinations using the L 18 OA are shown in Table 2. Table 2: DOE matrix of L 18 Orthogonal Array (OA) Sl. No Current (X1) T on (X2) T off (X3) For accurate measurements minimum three values were taken for each specimen and the mean value was selected. The mean values of the MRR, EWR. Machining time and form tolerances such as the angle and flatness are shown in the Table 3. Table 3: Measured values for output responses, as per DOE Sl. No MRR EWR Machining Time Angle Flatness (sec.) Impact Factor (JCC): NAAS Rating: 3.11

5 Multi-Parametric Optimization of EDM Parameters for Hexagonal Profile 937 CU Electrode to Measure form Tolerance on NI-based Super Alloy Table 3: Contd., (I) MULTI-PARAMETRIC OPTIMIZATION USING THE GREY RELATIONAL METHOD The steps used for multi-parametric optimization using the Grey relational analysis are discussed below; a) Normalization of the all experimental results of MRR, EWR, Machining Time and form tolerances such as the angle and flatness: Linear normalization of experimental values is performed in the range of 0 and 1. The normalized values for output responses were calculated by using the standard formula: ( ) = ( )( (! " )(# "! " ) (3) Where, y ij = i th experiment results in j th experiment. (b) Calculation for the Grey Relational Coefficients Grey relational coefficients are evaluated to express the relation between the ideal and factual experimental consequences. The standard formula used for the computation of Grey relational coefficients is given below: δ $ = # "# % " " %&' " % " " %,0 < + < 1 (4) % " " %&' " " % " % Where, xᵒi = ideal normalized result Table 4: Calculated Values for Grey Relational Grade Sl. No Current (X1) T on (X2) T off (X3) Grey relational Grade editor@tjprc.org

6 938 Subramani. P & S. Dhanabalan (c) Calculation for the Grey Relational Grade Grey relational grades are evaluated by the average of Grey relational coefficient using the formula given below: α $ = -. δ $ /- (5) Where, α j = Grey relational grade m = No. of execution grade characteristics Table 6: Grey Relational Grade Response Table Parameters Level-1 Level-2 Level-3 A B C Average Grey relational Grade= (d) Calculation of the optimum levels: optimum levels are calculated to find the significant parameter. (e) Selection of the optimal levels of process parameters by taking the highest values of levels for each parameter from the optimum level table. The Response table is clearly indicating the level values for process parameters. The highest value of process parameters for each parameter showed the best optimized value. (f) Confirmation of experiment and verification of the optimized process parameters. (II) CONFIRMATION OF EXPERIMENT After obtaining the optimized values of process parameters, the last step is to confirm the experimentation. Table 7: Confirmation of Experiment Predicted Value Experimentation Level A 3 B 3 C 2 A 3 B 3 C 1 MRR (g/min.) EWR Machining Time Angle Flatness Grade Improvement in Grey relational grade: The estimated Grey relational grade can be calculated from the following given relation: 5 α0 = 1 +3 (α α ) /- (6) Where, α m = Total mean of the Grey relational grade at optimum level q = No. of process parameters. Impact Factor (JCC): NAAS Rating: 3.11

7 Multi-Parametric Optimization of EDM Parameters for Hexagonal Profile 939 CU Electrode to Measure form Tolerance on NI-based Super Alloy RESULTS AND CONCLUSIONS The optimized parameters for the response of MRR, EWR, machining time and form tolerances in EDM process are: 12 Amps of Peak current (I p ), 600 µs Pulse on time (T on ) & 10 µs Pulse off time (T off ). The EDM process parameters for super-alloy namely Inconel-718 has been optimized by Grey relational method coupled with Taguchi method. The optimal solution had been calculated for MRR, EWR, Machining time and form tolerances namely angle and flatness. An attempt had also been made to attain maximum and minimum evaluation of MRR and form tolerances, respectively. The attained optimum outcomes had also been examined through a real experiment and established to be satisfactory. The experimental results showed the considerable advancement in the process. The experimental results will REFERENCES facilitate the EDM industries to improve the productivity, performances and MRR (MRR) with closer tolerances. 1. Adamczak, S, Janecki, D &Stępien, K (2006), The Comparison of cylindricity profiles using normalized cross-correlation function, Measurement Science Review, vol. 6, pp K.Azad, M. S, & A. B. Puri (2012), Simultaneous optimization of multiple performance characteristics in the micro-edm drilling of titanium alloy, The International Journal of Advanced Manufacturing Technology 61, no. 9-12: Kao, J.Y, Tsao, C.C, Wang, S.S, & Hsu, C.Y (2010), Optimization of the EDM parameters on machining Ti-6Al-4V with multiple quality characteristics, Int. J. Adv Manuf. Technol., Vol 47, pp Lin, JL, & Lin, CL 2005, The use of Grey-Fuzzy logic for the optimization of the manufacturing processes, Journal of Material Processing Technology, vol. 160, pp KuntalMaji, Dilip Kumar Pratihar (2011), Modelling of EDM process using Conventional Regression Analysis and Genetic Algorithms, J. of Materi. Eng. And Perform, 20: , DOI /s Saravana Kumar, K, Pratheesh Kumar, MR &ShalikDawood, AK 2012, Optimization of CNC turning process parameters on Inconel 718 using Genetic Algorithm, Engineering Science and Technology, vol. 2, no Jemielniak, Krzysztof (2009), Rough turning of Inconel 718, Advances in Manufacturing, Science and Technology 33, no. 3: Rahman, M., Seah, W.K.H., &Teo, T.Y (1997), The machinability of Inconel 718, Journal of Material Processing Technology, Vol 63, pp Sandeep Kumar, Onkar Singh Bhatia Experimental Analysis and optimization of cylindrical grinding process parameters on Surface Roughness of En15AM steel, Int. Journal of Engineering Research and Applications ISSN: , Vol. 5, Issue 7, (Part - 2) July2015, pp Narender Singh, P, Raghukandan, K &Pai, BC 2004, Optimization by Grey relational analysis of EDM parameters on machining Al 10%SiCP composites, Journal of material processing technology, vol , pp editor@tjprc.org

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