592 Dynamics of Machines and Mechanisms, Industrial Research. Table 1: Process Parameters & corresponding levels.

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1 Applied Mechanics and Materials Submitted: ISSN: , Vols , pp Revised: doi: / Accepted: Trans Tech Publications, Switzerland Online: OPTIMIZATION OF CUTTING PARAMETERS IN WIRECUT EDM OF D2 DIE STEEL USING GRAVITATIONAL SEARCH ALGORITHM M. Durairaj 1, a, S.Elanthirayan 2,b *, K.Aanand 2,c and J.Poornachandran 2,d 1 Senior Assistant Professor, Department of Mechanical Engineering, Tagore Engineering College, Chennai 127, India. 2 U. G. Student, Department of Mechanical Engineering, Tagore Engineering College, Chennai 127, India. a durairajtagore@gmail.com, b s.elanthirayan93@gmail.com, c aana.ndk@live.com, d poornasrm01@gmail.com Keywords: WEDM, Taguchi s L-9 orthogonal array, Surface roughness, Kerf width, Gravitational Search Algorithm, D2 die steel and Zinc coated wire. Abstract Wire cut Electrical Discharge Machining is one of the important manufacturing process which is used to obtain desired shape using electrical discharge (or) by continuous sparking. This paper deals with wire cut EDM of D2 die steel using Zinc coated wire tool. Two conflicting objectives, surface roughness and kerf width, are simultaneously optimized. Experimentation was planned based on Taguchi s L-9 orthogonal array. All the experiments has been conducted under different machining conditions of gap voltage, pulse ON time, and pulse OFF time. Wire feed, wire speed, resistance, wire tension, dielectric fluid pressure and cutting length are taken as fixed parameters. In this paper Gravitational Search Algorithm (GSA) is employed for optimising surface roughness and kerf width. Introduction Wire cut EDM is a spark erosion machining process. Due to the inherent properties of this process, easily machining the complex parts and precision components. Wire EDM works by creating an electrical discharge between the tool and the work piece [1]. As the spark jumps across the gap, material is removed from the work piece. Experiments are conducted using tool as Zinc coated wire of 0.25mm diameter and D2 die steel is used as the work material for the present experiment. The surface roughness (R a ) and kerf width (K f ) were measured for nine combinations of experiments. Gravitational Search Algorithm (GSA) is proposed to obtain the optimal parameters in wire cut EDM. Experimental Design The experiments were conducted in Wire Cut Electrical Discharge Machine. Zinc coated wire of 0.25mm diameter is used as the tool to cut D2 die steel.this experimental design involves the selection of suitable levels for the machining parameters i.e. Pulse on Time, Pulse-off Time, wire feed, Gap voltage [1]. The selected L9 orthogonal array using the Taguchi's design of experiments for carrying out the Machining operation is tabulated in the table 1. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-11/05/16,04:04:42)

2 592 Dynamics of Machines and Mechanisms, Industrial Research Table 1: Process Parameters & corresponding levels. Process Parameter Unit Level 1 Level 2 Level 3 Gap Voltage Volts Pulse-on Time (T ON ) µs Pulse-off Time (T OFF ) µs Experimental results According to the Taguchi s L-9 orthogonal Array [2] which is used to identify the optimum parameter combination for obtaining minimum surface roughness and minimum Kerf Width [3]. The values of R a and K f is tabulated in the Table 2, it is used to calculate the fitness function. Table 2: Output for the Machining Parameter Ex. No T ON (µs) T OFF (µs) Gap Voltage (V) R a (µm) K f (mm) Mathematical modelling From the collected data, a statistical model for the output parameters has developed. The analytical model for the output parameters has been developed by modelling (the relationship between the output parameters and the machining conditions) [3]. The general equation of fitness function is given below. f = K X T ON a b X GV c (1) Where f is the Output Parameter, T ON is the pulse on time, T OFF is the pulse off time, GV is gap voltage and a, b, c are exponents and K is constant of proportionality. Surface roughness and kerf width The non-linear regression model for R a and k f was developed using SPSS Software with the data from the experiments conducted. R a = X T ON X GV (2) K f = X T ON X GV (3) In this present research, above two fitness functions are used in order to get the optimum results in both surface roughness and kerf width.

3 Applied Mechanics and Materials Vols Gravitational Search Algorithm Gravitational search algorithm is mainly based on Newton s Law of Gravity. It states that the gravitational force between two particles is directly proportional to the product of their masses and inversely proportional to the square of the distance between the two particles [4]. It gives the results which are obtained by various applications in an effective manner. To find the optimal solution for the stability phenomena, this paper adapts an above mentioned heuristic algorithm. The position of the mass corresponds to a solution of the problem, its gravitational and inertial masses are determined by using a fitness function. Otherwise, by correctly adjusting the gravitational and inertial masses, each mass presents a solution and the algorithm is directed. By lapse of time, we expect that the masses be attracted by the heaviest mass. This mass will present an optimal solution in the search space. The flow process of GSA is shown in fig.1 Initialize the agents (position) Update the SPSS data with current agents Evaluate the fitness Function for each agent Update the G, best and worst of the population Calculate M and a for each agent Update velocity and position for each agents No Check the Convergence criterion Yes Print the Optimal values of variables and its Objective Function Updating of Velocity and Position Fig 1: Flow diagram of GSA The next velocity can be updated by summing the current velocity and its acceleration. Similarly, the position can be updated by adding its previous position and its velocity [5]. (4) (5)

4 594 Dynamics of Machines and Mechanisms, Industrial Research Where, rand k - Random number between the intervals [0-1]. Random numbers are used to give a randomized characteristic to the search. Result and Discussion In this paper, the Gravitational Search Algorithm is used to optimize the parameters to get the optimum results for surface roughness and kerf width. The Mat lab is used to solve the problem. The result obtained from GSA is shown in the table 3 & 4. Table 3: Optimum value for R a NOTATION PARAMETER RESULT R a (Best) Surface Roughness µm T ON (Best) Pulse ON Time µs T OFF (Best) Pulse OFF Time µs GV(Best) Gap Voltage V Table 4: Optimum value for K f NOTATION PARAMETER RESULT K f (Best) Kerf Width mm T ON (Best) Pulse ON Time µs T OFF (Best) Pulse OFF Time µs GV(Best) Gap Voltage V Conclusion The experimental data of D2 die steel has been investigated by using wire EDM and the technique of Gravitational Search Algorithm was used to optimize the process parameters. The optimum input parametric combination obtained for getting minimum Surface roughness and minimum kerf width are V and V of Gap voltage, µs and µs of Pulse on Time and µs and µs of Pulse off Time. From this input parametric combinations, the surface roughness and the kerf width have been found as µm and mm. References [1] M. Durairaj, S. Gowri, M. H. Gauthamkumar, M. Ashok kumar, and R. Aishwarya, Optimization of Wire Cut Electrical Discharge Machining of Inconel 800 using Grey Relational Analysis, Advanced Materials Research Vol. 576 (2012) pp [2] Navjot Singh, Parlad Kumar and Khushdeep Goyal, Effect of two different cryogenic treated wires in wire electrical discharge machining of AISI D3 die steel, Journal of Mechanical Engineering, Vol. ME 43, No. 2, December [3] M. Durairaj, S. Gowri, D. Sudharsun and N. Swamynathan, Application of Genetic Algorithm in the optimization of cutting parameters in Wirecut EDM using Stainless Steel AISI 304, IJMEMS, 6(2) July-December 2013, pp [4] Esmat Rashedi, Hossein Nezamabadi-pour, Saeid Saryazdi, GSA: A Gravitational Search Algorithm, Information Sciences 179 (2009) [5] Taisir Eldos, Rose Al Qasim, On the Performance of the Gravitational Search Algorithm, (IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 4, No. 8, 2013.

5 Dynamics of Machines and Mechanisms, Industrial Research / Optimization of Cutting Parameters in Wirecut EDM of D2 Die Steel Using Gravitational Search Algorithm /