Development Of Regression Model For Al6061+ Sic Tool And Optimization Of Process Parameters On Electro Discharge Machining

Proper selection of manufacturing conditions is one of the most important aspects to take into consideration in the majority of manufacturing processes and, particularly, in processes related to Electrical Discharge Machining (EDM). These are the conditions that determine important characteristics such as material removal rate, Electrode Wear. In the present work experiments are conducted on EDM using Al6061+SiC (with 3%,6%,9% composition of SiC in Al 6061 Alloy ),Copper and Brass materials as electrodes and EN8 steel as work material. Discharge current (IP), pulse on time (TON), pulse off time (TOFF) are selected as inout process parameters, Metal Removal Rate (MR), Tool Wear Rate (TWR) as response. Taguchi design of experiment is used to find the influence of process parameters on response and a mathematical model is developed. Percentage contribution of each factor is determined.


INTRODUCTION
Electrical Discharge Machining (EDM) process involves a controlled erosion of electrically conductive materials by initiation of rapid and repetitive spark discharge between electrode tool and work piece, separated by a small gap of about 0.01 to 0.05mm known a spark gap. This is either flooded or immersed under dielectric fluid. The controlled pulsing of direct current produces the spark discharge between the work piece and tool. Each spark produces enough heat to melt and vaporize a tiny volume of the work piece material leaving a small crater on its surface. The energy contained in each spark is discrete and it can be controlled so that material removal rate, surface finish and tolerance can be produced. EDM is most widely used machining process among the non-traditional machining methods. It is successfully employed for producing intricate and irregular shape profiles common in tool rooms.

LITERATURE REVIEW
The Following Literature Review is observed in the investigation on EDM.  Sushil Kumar Choudharyetal.[ [1]in their study on "Current Advanced Research Development of Electric Discharge Machining (EDM): A Review" carried out the work on shaping hard metals and forming deep complex shaped holes by arc erosion in all kinds of electroconductivematerials.  K.H. Ho, S.T. Newman [2],in their study on "State of the art electrical discharge machining (EDM)",discuss about the die making process to a micro-scale application machining.  Rao, P. Srinivasa et al. [3] have studied that have an effect on by means of design four factors such as current, servo control, duty cycle and open circuit voltage over the outputs on the MRR, TWR, SR and hardness on the die-sinker EDM process of machining AISI 304 SS.  S. H. Tomadiet al. [4] analyzed that impact of machining settings of the tungsten carbide on the outputs such as TWR, MRR and Surface finish. To find errors between the predicted values and to experimental runs in terms of machining characteristics. They were found out copper tungsten tool use for better surface finishing of work piece. They were using full factorial DoE, to optimization and discovered out with greater pulse off time lesser tool wear of the tungsten carbide and with current, voltage and pulse on time increment with tool wear increased.  Zhao Wanshenget al. [5] have studied about surface machining process by EDM. Shows the consists of a series of discharge craters, and explain that there is no screw-like trail left on the hole's inside wall that would be formed by ordinary drilling. This can change the field of distribution condition when fluid or gas flows through the small hole. As there is no macroscopic force, it is easy to machine a half hole by using EDM.  UlasÇaydaset al. [6] analyzed that the EW and WLT in die-sinking EDM process were modeled and analyzed through response surface methodology (RSM  [7] have studied in micro EDM, they defined about the discharge gap that is very small, and the dimensions of the electrode is just too small to use internal and/or outside flushing to dispose of debris. In their paper, a new method the usage of planetary movement of the electrode is proposed to lessen the particles concentration and enhance precision. The planetary movement of electrode provides extra area for particles elimination. Therefore, the material removal rate increases and the electrode wear reduce. This method has been confirmed through machining of micro holes with excessive element ratio and blind noncircular micro holes.  G. Appa Rao et al. [8] have studied the effect of normal heat treatment on the microstructure and mechanical properties of hot isostatically pressed superalloyinconel 718. In this, Inconel 718 was analyzed processed through powder metallurgy (P/M) hot isostatic pressing (HIP) route. In this study, they have led to better study of the property and structure relationships in HIP + heat treated analysis on alloy 718 and suggest that the standard heat treatment approved for wrought IN 718 is not convenient for HIPed alloy and has to be modified to realize optimum properties.   The stress rupture life and ductility of the alloy have also made better marginally after heat treatment and has got the minimum expected life for wrought heat treated IN 718, however, the rupture ductility was found to be much less than the specified value. This suggest that the recommended heat treatment for wrought alloy is not suitable for HIP processed alloy and has to be modified to realize optimum properties.  Kuldeep Ojha, R.KGarg,K.K.Singh(2010) [19] in their study on " MRR improvement in Sinking Electrical Discharge Machining" have researched on the development resulting in improvement in material removal rate.  Arun Kumar M.B and R.P.Swamy [20] in their study on "Evaluation of mechanical properties of Al6061, Flyash and E-Glass fiber reinforced Hybrid metal matrix"(May-2011) It has been observed that the addition of flyash significantly improves ultimate tensile strength along with compressive strength and hardness properties as compared to that of reinforced matrix.  AshwaniKharola [21] in " Analysis of Various machining parameters of EDM on Hard Steel using copper and Aluminium electrodes" (March 2015) have studied the process parameters on EDM using Copper, Aluminium electrodes and EN8 work material."  J. Laxman and Dr.K.Gururaj [22] in their journal "Modeling and Analysis of EDM process parameters using Taguchi technique and Fuzzy based modeling" (2014) Experiment were designed by Taguchi's technique and conducted by taking three levels of the peak current, pulse on time, pulse off time and tool life time on Titanium super alloy.  J.Jeevamalar and S. Ramabalan [23] in their article "Die sinking process parameters" have given a detailed explanation of Die sinker EDM, MRR, TWR, SR,Taguchi method.  C. Mathalai Sundaram, R.Sivasubramanian, M.Sivakumar [24] in their study on " An Experimental Investigation on Machining Parameters of Electrical Discharge Machining of OHNS Steel" have studied the EDM process performance and the machining conditions with Copper and Aluminium tool electrode and its effects on the process output parameters viz, material removal rate and tool wear rate and percentage wear rate.  VedPrakashPandey, MrR.N.Mall [25] in their study on "Analyis of material removal rate of AlSi 304 SS in EDM process" have studied the effect of various process parameters.  MehulG.Mehta, Nikul.K.Patel [26] in their study on "Temperature and thermal stress analysis of EDM" (Jan-2014), have presented a basic review on the different parameters and the various methods applied to estimate the temperature distribution and thermal stress analysis.  BholaJha, K.Ram and Mohan Rao [27] in their study on "An overview of technology and research in electrode design and manufacturing in sinking electrical discharge machining" (Dec-2011), have reported a review on the research related to EDM electrode deign and its manufacturing for improving and optimizing performances.

OBJECTIVES & METHODOLOGY
The objecvtive of the current work is to develop Mathematical model for the input and out parameters considered . Design of experiments is adopted in order to run minimum number of experimental trials. Experiments are carried out as per the design matrix. Adequacy of model is tested by fisher test at 5% significance level. Student's t-test is done for each regression coefficient to check the significance. The final mathematical model is formed by removing non significant coefficients. Analysis of Variance (ANOVA) is done to find out the percentage contribution of each factor to the Metal Removal Rate and Tool Wear Rate.

Design Of Experiments -Taguchi Method
Taguchi has envisaged a new method of conducting the design of experiments which are based on well defined guidelines. This method uses a special set of arrays called orthogonal arrays. These standard arrays stipulate the way of conducting minimal number of experiments which could give the full information of all the factors that affects the performanceparameters. There are many standard orthogonal arrays available, each of the arrays is meant for a specific number of independent design variables and levels. The L9 orthogonal array is meant for understanding the effect of 4 independent factors each having 3 factor level values. This array assumes that there is no interaction between any two factors. While in many cases, no interaction model assumption is   6 8 10 The EDM process variables (factors) are identified to develop the mathematical model to predict the MRR and Tool Wear . These include pulse on time (T ON ), pulse off time (T OFF ) and pulse current (Ip), Voltage (V) . The first order model is assumed with two and three four interactions which can be expressed as

EDM PROCESS CHARACTERISTICS
Metal removal rate is calculated from weight difference of work piece before and after the performance trail.

EXPERIMENTATION COPPER AND
L9 orthogonal array ( Table 2).The polarization on the electrode be located as negative whereas that of work piece be located as positive. The dielectric liquid recycled was EDM oil having specific gravity 0.763. Fig  Machined components.

OPPER AND BRASS TOOLS
The experimentation is carried out on SYCNC PC L9 orthogonal array ( Table 2).The polarization on the electrode be located as negative whereas that of work piece be located as positive. The dielectric liquid recycled was EDM oil having specific gravity 0.763. Fig -1 s Machined components.

XPERIMENTATION (MACHINING OF RASS TOOLS )
The experimentation is carried out on SYCNC PC L9 orthogonal array ( Table 2).The polarization on the electrode be located as negative whereas that of work piece be located as positive. The dielectric liquid recycled was EDM oil having specific 1 shows the Experimental setup, Fig  Machined components.

ACHINING OF EN8
The experimentation is carried out on SYCNC PC L9 orthogonal array ( Table 2).The polarization on the electrode be located as negative whereas that of work piece be located as positive. The dielectric liquid recycled was EDM oil having specific hows the Experimental setup, Fig   Fig 3:Experimentation on EN8 with Al6061+SiC(3%,6%,9%),Copper and Brass tools

EN8 ON EDM
The experimentation is carried out on SYCNC PC L9 orthogonal array ( Table 2).The polarization on the electrode be located as negative whereas that of work piece be located as positive. The dielectric liquid recycled was EDM oil having specific hows the Experimental setup, Fig   Al6061+SiC(3%,6%,9%),Copper and Brass tools

EDM WITH
The experimentation is carried out on SYCNC PC-60 Electrical Discharge Machine as per L9 orthogonal array ( Table 2).The polarization on the electrode be located as negative whereas that of work piece be located as positive. The dielectric liquid recycled was EDM oil having specific hows the Experimental setup, Fig-2 shows the Various Tools, Fig   Fig 2. Tools used for Experimentation Al6061+SiC(3%,6%,9%),Copper and Brass tools

ITH AL6061+SIC
Electrical Discharge Machine as per L9 orthogonal array ( Table 2).The polarization on the electrode be located as negative whereas that of work piece be located as positive. The dielectric liquid recycled was EDM oil having specific 2 shows the Various Tools, Fig   Fig 2. Tools used for Experimentation Al6061+SiC(3%,6%,9%),Copper and Brass tools C (3%,6%,9%), Electrical Discharge Machine as per L9 orthogonal array ( Table 2).The polarization on the electrode be located as negative whereas that of work piece be located as positive. The dielectric liquid recycled was EDM oil having specific 2 shows the Various Tools, Fig-3 shows Electrical Discharge Machine as per L9 orthogonal array ( Table 2).The polarization on the electrode be located as negative whereas that of work piece be located as positive. The dielectric liquid recycled was EDM oil having specific 3 shows

Fig-5 MRR Vs Inp
Tool Wear Rate TWR is calculated machining to the product of machining period and density of the tool materials.

MRR Vs Inp
Tool Wear Rate TWR is calculated machining to the product of machining period and density of the tool materials.   as the proportion of the change of weight of the electrode tool before and after machining to the product of machining period and density of the tool materials.

Cost Analysis
The following table gives the information about the unit cost of Electrode Material. It is seen from the table that Copper material has highest cost and Al6061 alloy with 3%SiC has Lowest cost.  Fig-7 Cost of Electrode Material

RESULTS & CONCLUSIONS
The experiments were carried out by Taguchi methodology. The results obtained were recorded and the metal removal rate was calculated and the regression model in linear form is developed.
The following conclusions are drafted from the work carried out.  Al6061+ SiC (with SiC of 3%) tool has a maximum metal removal rate of 7.2 g/hour for a combination of input variables Pulse on time: 500μs, Current: 8A, Voltage: 40V, Pulse off time: 100μs.  Al6061+ SiC (with SiC of 6%) tool has a maximum metal removal rate of 5.4 g/hour for a combination of input variables Pulse on time: 900μs, Current: 10A, Voltage: 45V, Pulse off time: 100μs.  Al6061+ SiC (with SiC of 9%) tool had a maximum metal removal rate of 3.6 g/hour for a combination of input variables Pulse on time: 900μs, Current: 10A, Voltage: 45V, Pulse off time: 100μs.  Copper Tool had a maximum metal removal rate of 9.9 g/hour for a combination of input variables Pulse on time: 900μs, Current: 10A, Voltage: 45V, Pulse off time: 100μs