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Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications
           (IJERA)                   ISSN: 2248-9622            www.ijera.com
                  Vol. 2, Issue 5, September- October 2012, pp.1986-1993
   Process Parameters Optimization Of Micro Electric Discharge
            Machining Process Using Genetic Algorithm
                              Ruben Phipon* and B.B.Pradhan
                                   Department of Mechanical Engineering,
                                   Sikkim Manipal Institute of Technology,
                                     P.O. Majitar 737136, Sikkim, India.

ABSTRACT
         Micro Electric Discharge Machining              suitable optimization technique to search for correct
(micro EDM) is a non-traditional machining               parameter values for the desired responses.
process which can be used for drilling micro             Hung et al. [1] while using a helical micro-tool
holes in high strength to weight ratio materials         electrode with Micro-EDM combined with
like Titanium super alloy. However, the process          ultrasonic vibration found that it can substantially
control parameters of the machine have to be set         reduce the EDM gap, variation between entrance
at an optimal setting in order to achieve the            and exit and machining time, especially during deep
desired responses. This present research study           micro-hole drilling. Jeong et al. [2] proposed a
deals with the single and multiobjective                 geometric simulation model of EDM drilling
optimization of micro EDM process using                  process with cylindrical tool to predict the
Genetic Algorithm. Mathematical models using             geometries of tool and drilled hole matrix. The
Response Surface Methodology (RSM) is used to            developed model can be used in offline
correlate the response and the parameters. The           compensation of tool wear in the fabrication of a
desired responses are minimum tool wear rate             blind hole..
and minimum overcut while the independent                          Mukherjee and Ray [3] presented a generic
control parameters considered are pulse on time,         framework for parameter optimization in metal
peak current and flushing pressure. In the               cutting processes for selection of an appropriate
multiobjective problem, the responses conflict           approach. In practice, a robust optimization
with each other. This research provides a Pareto         technique which is immune with respect to
optimal set of solution points where each solution       production tolerances is desirable [4]. Karthikeyan
is a non dominated solution among the group of           et al. [5] conducted general factorial experiments to
predicted solution points thus allowing flexibility      provide an exhaustive study of parameters on
in operating the machine while maintaining the           material removal rate (MRR) and tool wear rate
standard quality.                                        (TWR) while investigating performance of micro
                                                         electric discharge milling process. Taguchi method
Keywords: Micro electric discharge machining             is used for experiment design to optimize the cutting
(micro EDM), Response Surface methodology                parameters [6]. Experimental methods increase the
(RSM), Genetic Algorithm (GA), Pareto Optimal.           cost of investigation and at times are not feasible to
                                                         perform all the experiments specially when the
1. INTRODUCTION                                          number of parameters and their levels are more.
          Micro-EDM is a recently developed              RSM is employed to design the experiments with a
process which is used to produce micro-parts in the      reduced number of experimental runs to achieve
range of 50μm -100μm. In this process, metal is          optimum responses [7]. Lalwani et al. [8] applied
removed from the workpiece by melting and                RSM to investigate the effect of cutting parameters
vaporization due to pulse discharges that occur in a     on surface roughness in finish hard turning of
small gap between the workpiece and the electrode.       MDN250 steel using coated ceramic tool.
It is a novel machining process used for fabrication               Yildiz [9] compared state-of-the-art
of a micro-metal hole and can be used to machine         optimization techniques to solve multi-pass turning
hard electrically conductive materials like Titanium     optimization problems. The results show the
super alloy. The characteristic of non-contact           superiority of the hybrid approach over the other
between the tool and the work piece in this process      techniques in terms of convergence speed and
eliminates the chance of stress being developed on       efficiency. Yusup et al. [10] discussed evolutionary
the work piece by the cutting tool force.                techniques and basic methodology of each technique
          However, to achieve the desired responses,     in optimizing machining process parameters for
the independent control parameters which affect the      both traditional and modern machining. Application
responses are to be set at an optimal value. Such        of evolutionary techniques in optimizing machining
problems can be solved by first developing               process parameters positively gives good results as
mathematical models correlating the responses and        observed in the literature. Samanta and Chakraborty
the parameters. The second step is to choose a           [11] proved the applicability and suitability of



                                                                                              1986 | P a g e
Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications
           (IJERA)                   ISSN: 2248-9622            www.ijera.com
                  Vol. 2, Issue 5, September- October 2012, pp.1986-1993
evolutionary     algorithm     in    enhancing     the   Table 1 Coded and Actual control parameter values
performance measures of nontraditional machining         at different levels
processes. Jain et al. [12] used GA for optimization                     Levels
of process parameters of mechanical type advanced                        1      2    3       4      5
machining processes. Traditional optimization            Coded           -1.682 -1   0       1      1.682
methods are not suitable to solve problems where         value
the formulated objective functions and constraints       Pulse-on-       1      5    12      18     22
are very complicated and implicit functions of the       time (µs)
decision variables..                                     Peak            0.4    0.7  1.2     1.7    2.0
          Unlike       conventional      optimization    current (A)
techniques, GA is a robust, global and can be            Flushing        0.1    0.2  0.3     0.4    0.5
applied without recourse to domain-specific              pressure
heuristics. Tansela et al. [13] proposed Genetically     (Kg/cm2)
Optimized Neural Network System (GONNS) for
selection of optimal cutting conditions for micro end    Table 2 Design of experiments matrix showing
milling operation. Singh and Rao [14] presented a        coded values and observed responses
multi-objective optimization technique based on GA            Coded values of parameters Actual values of Responses
to optimize the cutting parameters in turning
processes since undertaking frequent tests or many       Sl.   Pulse    Peak      Flushin    Tool wear    Overcut
experimental runs is not economically justified. Zain    No    on       current   g          rate         (mm)
et al [15] applied GA to optimize cutting conditions           time     (A)       pressure   (mg/min)
for minimizing surface roughness in end milling                (µs)               (Kg/cm2
machining process. Ghoreishi et al [16] applied GA                                )
for solving multi-objective optimization problems in
Robust Control of Distillation Column. Hence, due
                                                         1     -1       -1        -1         0.00033      0.0510
to the multifacet advantages of GA, an attempt has
                                                         2     1        -1        -1         0.00040      0.0390
been made to optimize the micro EDM process in
                                                         3     -1       1         -1         0.00047      0.0455
this research paper using this technique. In this
present research work in order to simultaneously         4     1        1         -1         0.00136      0.0340
optimize both the conflicting objectives, multi          5     -1       -1        1          0.00149      0.0490
objective GA is used to predict the non dominated        6     1        -1        1          0.00127      0.0367
Pareto optimal set of solution while drilling            7     -1       1         1          0.00062      0.0415
microholes in a Titanium super alloy.                    8     1        1         1          0.00123      0.0297
                                                         9     -1.682   0         0          0.00062      0.0665
2. PROCESS MODELLING                                     10    1.682    0         0          0.00112      0.0503
2.1 RSM Modeling                                         11    0        -1.682    0          0.00066      0.0321
          Pradhan and Bhattacharya [17] developed        12    0        1.682     0          0.00089      0.0195
mathematical models as shown by equations 1 and 2        13    0        0         -1.682     0.00060      0.0385
below based on second order polynomial equation          14    0        0         1.682      0.00150      0.0372
for correlating the interactions of micro EDM            15    0        0         0          0.00081      0.0402
control parameters, such as pulse on time, peak          16    0        0         0          0.00074      0.0382
current and flushing pressures and their effects on      17    0        0         0          0.00077      0.0399
some responses, such as tool wear rate and overcut       18    0        0         0          0.00078      0.0400
during micro hole machining of titanium alloy (Ti–       19    0        0         0          0.00082      0.0410
6Al–4V).                                                 20    0        0         0          0.00078      0.0412
          Table 1 lists the values for process control
parameters of pulse on time, peak current and            The mathematical model correlating the tool wear
flushing pressures with five levels for each             rate with the process control parameters is
parameter. A sum of twenty experimental runs is          developed as:
designed using Center composite design. The
combinatorial effects of process control parameters      Yu(twr) = 0.000708 + 0.000070(x1) - 0.000058(x2) +
at different levels on the measured response are         0.000296(X3) + 0.000011(x12) -
listed in Table 2.
                                                         0.000004(x22)+0.000095(x32)+0.000112(x1x2)-
                                                         0.000038(x1x3)–0.000252(x2x3).    (1)

                                                         Similarly, the mathematical model for overcut is
                                                         developed as:




                                                                                             1987 | P a g e
Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications
           (IJERA)                   ISSN: 2248-9622            www.ijera.com
                  Vol. 2, Issue 5, September- October 2012, pp.1986-1993
Yu(oc) = 0.044513 - 0.006398(x1) - 0.0035(x2) -
                                                                                                                        -3
0.001071(x3)+0.001980(x12)-0.005609(x22)-                                                                          x 10              Best: 0.00082663 Mean: 0.0031704




                                                                                    minimum overcut (mg/min)
        0.000841(x32)       +     0.000054(x1x2)-                                                              6
                                                                                                                                                                              Best fitness
0.00002(x1x3)-0.0005(x2x3).
                                                                                                                                                                              Mean fitness
(2)                                                                                                            4

         Where x1, x2 and x3 are pulse on time, peak
current and flushing pressure and Yu(twr) and                                                                  2
Yu(oc) are the responses for tool wear rate and
overcut respectively. The effects of linear, higher
order and the interaction of the independent process                                                           0
                                                                                                                   0                     5                             10                    15
variables are represented in equations (1) and (2).
                                                                                                                                                  Generation
                                                                                                                                             Current Best Individual
3. SINGLE OBJECTIVE OPTIMIZATION                                                                               1




                                                               control parameter values
3.1. Optimization using GA
          Genetic algorithm is an evolutionary
algorithm which applies the idea of survival of the
fittest amongst an interbreeding population to create                                               0.5
a robust search strategy. Initially a finite population
of solutions to a specified problem is maintained. It
then iteratively creates new populations from the old
by ranking the solutions according to their fitness
                                                                                                               0
values and interbreeding the fittest to create new                                                                               1                  2                3
offsprings which are optimistically closer to the                                                                                     Independent control parameters
optimum solution to the problem at hand. It uses
only the fitness value and no other knowledge is          Fig. 1 GA predicted plot for minimum tool wear
required for its operation. It is a robust search         rate and the control parameter values
technique different to the problem solving methods                  The results predicted using GA for
used by more traditional algorithms which tend to         minimum tool wear rate is listed in Table 3. Trial
be more deterministic in nature and get stuck up at       and error method for the selection of initial
local optima. As each generation of solutions is          population size found the best result when the initial
produced, the weaker ones fade away without               population size of 20 was chosen.
producing offsprings, while the stronger mate,            Table 3 GA predicted results for minimum tool
combining the attributes of both parents, to produce      wear rate
new and perhaps unique offsprings to continue the
cycle. Occasionally, mutation is introduced into one                                                                   Control parameters
of the solution strings to further diversify the          Trial                                                                                                 Tool wear
population in search for a better solution.               number                                                       Pulse   Peak           Flushing          rate
          The present research work optimizes the                                                                      on      current        pressure             (mg/min)
desired response and control parameters by writing                                                                     time    (A)
the mathematical models as developed in equations                                                                      (µs)                   (Kg/cm2)
1 and 2 as .M-files and then solved by GA using the
MATLAB software. The initial population size              1                                                            18      1.7            0.4               0.00195386
considered while running the GA is 20. A test of 10       2                                                            18      1.7            0.4               0.00199364
runs has been conducted and the results are listed in     3                                                            18      1.7            0.4               0.00225604
Tables 3 and 4 for minimum tool wear rate and             4                                                            12      1.2            0.3               0.00285234
minimum overcut respectively.                             5                                                            12      1.2            0.3               0.00452525
          The GA predicted value of minimum tool          6                                                            12      1.2            0.3               0.00625264
wear rate and the corresponding control parameter         7                                                            5       0.7            0.2               0.00975433
values are shown in Figure 1. It is observed from the     8                                                            5       0.7            0.2               0.00094524
figure that the best minimum tool wear rate               9                                                            1       0.4            0.1               0.00089732
predicted using GA is 0.00082663 mg/min with the          10                                                           1       0.4            0.1               0.00082663
corresponding control parameter values of 1µs for
pulse on time, 0.4 A for peak current and 0.1
kg/cm2.                                                            Similarly, the GA predicted value of
                                                          minimum overcut and the corresponding control
                                                          parameter values are shown in Figure 2. The GA
                                                          predicted value of minimum overcut and the
                                                          corresponding control parameter values are shown
                                                          in Figure 2. It is observed from the figure that the


                                                                                                                                                          1988 | P a g e
Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications
                                                (IJERA)                   ISSN: 2248-9622            www.ijera.com
                                                       Vol. 2, Issue 5, September- October 2012, pp.1986-1993
                                     minimum overcut         predicted using GA is
                                     0.00098289 mm with the corresponding control                        Table 4 GA predicted results for minimum overcut
                                     parameter values of 1.5µs for pulse on time, 1.9 A
                                     for peak current and 0.5 kg/cm2. The results                                   Control parameters
                                     predicted using GA for minimum overcut is listed in                 Trial                                     Overcut
                                     Table 4.                                                            number     Pulse   Peak      Flushing     (mg/min)
                                                                                                                    on      current   pressure
                                                                                                                    time    (A)
                                               Best: 0.0098289 Mean: 0.011419
                                                                                                                    (µs)              (Kg/cm2)
                           0.4
minimum overcut (mm)




                                                                                     Best fitness
                           0.3                                                       Mean fitness
                                                                                                         1          18      0.7       0.1          0.0526562
                                                                                                         2          18      0.7       0.1          0.0517556
                           0.2                                                                           3          12      0.7       0.2          0.0462829
                                                                                                         4          12      1.2       0.2          0.0482794
                           0.1                                                                           5          12      1.2       0.3          0.0358922
                                                                                                         6          5       1.2       0.3          0.0278363
                            0                                                                            7          5       1.2       0.4          0.0265262
                                 0                5                             10                  15   8          1       1.7       0.4          0.0144687
                                                           Generation
                                                                                                         9          1       1.7       0.5          0.0128623
                                                      Current Best Individual
                                                                                                         10         1.5     1.9       0.5          0.0098289
                            2
control parameter values




                           1.5                                                                           3.2 Validity of GA predicted results
                                                                                                                  Validation of the simulation results with
                            1
                                                                                                         the experimental results is done in order to conform
                                                                                                         the simulation results to the actual working
                           0.5                                                                           conditions and to know how much is it varying with
                                                                                                         the actual experimental results which is measured by
                            0                                                                            the percentage of prediction error.
                                           1                 2                3                          The percentage of prediction error is calculated as
                                               Independent control parameters                            Prediction error%
                                                                                                              Experiment al result - GA predicted result
                                     Fig. 2 GA predicted plot for minimum overcut and                                                                   100
                                     the control parameter values                                                      Experiment al result

                                                                                                                  In order to validate the test results
                                                                                                         predicted by GA, five random experimental results
                                                                                                         are compared with the GA predicted results as
                                                                                                         shown in Table 5.

                                     Table 5 Comparison of Experimental and GA predicted results
                                              Experimental result            GA predicted result                             Prediction error %
                                     Sl.no.
                                              Tool wear rate     overcut     Tool wear rate    overcut                       Tool wear rate       overcut
                                     1        0.00112            0.0665      0.00109           0.06483                       2.678                2.511
                                     2        0.00136            0.0503      0.00128           0.0542                        5.882                7.195
                                     3        0.00089            0.0321      0.00083           0.0315                        6.741                1.869
                                     4        0.00152            0.0195      0.00148           0.0191                        2.631                2.051
                                     5        0.00082            0.0402      0.0008263         0.0413                        0.762                2.663
                                     Average percentage of error                                                             3.738                3.257

                                      It is observed from the table that average prediction              Multiobjective optimization problems are also found
                                      percentage error is well within acceptable limits                  in     machining    processes.    For     nontrivial
                                      thus establishing the results predicted using GA to                multiobjective problems, such as minimizing tool
                                      be valid.                                                          wear rate and minimizing overcut while drilling
                                                                                                         microholes by microEDM on a Titanium alloy, it is
                                     4. MULTI OBJECTIVE OPTIMIZATION                                     difficult to identify a single solution that
                                               Multi-objective optimization is the process               simultaneously optimizes each objective. While
                                     of simultaneously optimizing two or more                            searching for solutions, one reaches points where
                                     conflicting objectives subject to certain constraints.              upon an attempt to improve an objective further
                                                                                                         deteriorates the second objectives. A tentative


                                                                                                                                              1989 | P a g e
Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications
           (IJERA)                   ISSN: 2248-9622            www.ijera.com
                  Vol. 2, Issue 5, September- October 2012, pp.1986-1993
solution during such cases is called non-dominated,    4.1 Multiobjective Optimization using Genetic
Pareto optimal, if it cannot be eliminated by          Algorithm
replacing it with another solution which improves an             GA is run in MATLAB for generating
objective without worsening the other. The main        Pareto optimal solution points for minimizing tool
objective when setting up and solving a                wear rate and overcut while drilling micro holes by
multiobjective optimization problem is to find such    micro EDM in Titanium super alloy. Equation for
non-dominated solutions.                               creating a fitness function for the multi objective
          Friedrich et al [18] performed runtime       optimization is written in a .M file. The range of the
analyses and observed that a fair Multi Objective      process parameters is placed as bounds on the three
Evolutionary Algorithm has a marked preference for     input control variables and the following algorithm
accepting quick small improvements. This helps to      options are set.
find new solutions close to the current population     Selection function                    : Tournament of
quicker. Different types of multi objective GA         size 2
developed for specific purpose differ from each        Crossover function                    : scattered
other mainly by using specialized fitness functions    Mutation function                     :        Adaptive
and introducing methods to promote solution            feasible
diversity. An elitist multiobjective GA ensures that   Direction of migration      : Forward with migration
the best solution does not deteriorate in the                                           function 0.2
succeeding generations. This approach uses a           Distance measure function             :         distance
priority-based encoding scheme for population          crowding
initialization.                                        Population size             : 75
          Eiben and Smit [19] observed that adoption             The variant of GA used to solve this
of parameter tuners would enable better                multiobjective optimization problem is a controlled
evolutionary algorithm design. Using tuning            elitist genetic algorithm (a variant of NSGA-II).
algorithms one can obtain superior parameter values    Elitist GA favors individuals with better fitness
as well as information about problem instances,        value. A controlled elitist GA maintains the
parameter values, and algorithm performance. This      diversity of population for convergence to an
information can serve as empirical evidence to         optimal Pareto front.
justify design decisions. Lianga and Leung [20]                  Weighted average change in the fitness
integrated GA with adaptive elitist-population         function value over 150 generations is used as the
strategies for multimodal function optimization.       criteria for stopping the algorithm. The optimized
Adaptive Elitist GA is shown to be very efficient      pareto front achieved after 50 iterations is shown in
and effective in finding multiple solutions of         Figure 1. Input control parameters corresponding to
complicated benchmark and real-world multimodal        each of the pareto optimal set of solutions are
optimization problems.                                 tabulated in Table 6 .
          Zio and Bazzo [21] proposed a clustering
procedure for reducing the number of representative
solutions in the Pareto Front of multiobjective                                    -3
                                                                                x 10
optimization problems. The procedure is then                              9.8
applied to a redundancy allocation problem. The                                                                                         Pareto front
results show that the reduction procedure makes it                        9.7
easier for the decision maker to select the final
                                                                          9.6
solution and allows him or her to discuss the
outcomes of the optimization process on the basis of                      9.5
his or her assumed preferences. The clustering
                                                           Overcut (mm)




technique is shown to maintain the Pareto Front                           9.4
shape and relevant characteristics. Su and Hou [22]
showed that the integrated multi population                               9.3
intelligent GA approach can generate the Pareto-
optimal solutions for the decision maker to                               9.2
determine the optimal parameters to assure a stable
                                                                          9.1
process and product qualities in the nano-particle
milling process.
                                                                           9
          The chief advantage of GA when applied to
solve multi-objective optimization problems is the                        8.9
computation of an approximation of the entire                               7.8         8   8.2   8.4      8.6     8.8     9    9.2   9.4   9.6        9.8
                                                                                                        tool wear rate (mg/min)                        -4
Pareto front in a single algorithm run. Thus,                                                                                                     x 10
considering the advantages of GA for solving
multiobjective problems, it is applied to optimize     Fig. 3 Pareto-optimal set of solutions obtained for
the process of microhole drilling by micro EDM.        multi objective optimization



                                                                                                                     1990 | P a g e
Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications
           (IJERA)                   ISSN: 2248-9622            www.ijera.com
                  Vol. 2, Issue 5, September- October 2012, pp.1986-1993
                                                                    From the table, it is observed that an
The two conflicting responses of minimizing tool           improvement in minimizing tool wear rate
wear rate and overcut are marked along x-axis and          deteriorates the quality of overcut and vice versa.
y-axis respectively as shown in Figure 3. The              Thus, each solution point is a unique non dominated
individual star marks between these axes depict            solution point.
individual non dominated solution point among the
pareto optimal set of all the star points which form       Table 6 Process decision variables corresponding
the pareto front. The observed responses and the           to each of the pareto optimal solution point
corresponding control parameter values are listed in       and the predicted responses using GA
Table 6.

Sl    Control parameters                                                Responses
no.   Pulse on time (µs) Peak current           Flushing    pressure    Tool     wear         rate   Overcut
                         (A)                    (Kg/cm2)                (mg/min)                     (mm)
1     13.722             0.752                  0.1                     0.000786                     0.00965
2     13.730             0.760                  0.108                   0.00079                      0.0096
3     13.736             0.768                  0.115                   0.000798                     0.00958
4     13.743             0.775                  0.122                   0.000799                     0.00952
5     13.756             0.780                  0.128                   0.000804                     0.0095
6     13.766             0.787                  0.132                   0.000805                     0.00948
7     13.773             0.796                  0.139                   0.000806                     0.00946
8     13.782             0.80                   0.142                   0.000816                     0.00944
9     13.788             0.806                  0.148                   0.000817                     0.00942
10    13.792             0.810                  0.153                   0.000821                     0.0094
11    14.805             0.817                  0.159                   0.000823                     0.00938
12    14.808             0.825                  0.164                   0.000826                     0.00936
13    14.818             0.836                  0.169                   0.000827                     0.00934
14    14.824             0.844                  0.173                   0.00083                      0.0093
15    14.830             0.853                  0.182                   0.000836                     0.00929
16    14.842             0.862                  0.192                   0.00084                      0.00928
17    14.848             0.868                  0.198                   0.000844                     0.00926
18    14.858             0.870                  0.2                     0.000846                     0.00924
19    14.862             0.877                  0.204                   0.00085                      0.0092
20    14.873             0.885                  0.209                   0.000856                     0.00919
21    15.878             0.894                  0.214                   0.000859                     0.00918
22    15.885             0.898                  0.218                   0.000861                     0.00917
23    15.886             0.90                   0.225                   0.000862                     0.00916
24    15.894             0.906                  0.229                   0.000869                     0.00915
25    15.902             0.914                  0.234                   0.00087                      0.0091
26    15.906             0.918                  0.238                   0.000881                     0.00908
27    15.918             0.926                  0.242                   0.000884                     0.00906
28    15.927             0.935                  0.249                   0.0009                       0.00903
29    15.931             0.943                  0.253                   0.000901                     0.00901
30    15.957             0.953                  0.259                   0.000924                     0.00898
31    15.958             0.960                  0.264                   0.000932                     0.00897
32    15.959             0.972                  0.269                   0.000944                     0.00896
33    15.96              0.998                  0.274                   0.000954                     0.00895

5. RESULT AND ANALYSIS                                     corresponding control parameter values of 1µs for
         While drilling micro holes by micro EDM           pulse on time, 0.4 A for peak current and 0.1
in a Titanium (Ti-6Al-4V) super alloy, two                 kg/cm2. It is observed that the all three of the control
objectives, tool wear rate and overcut are considered      parameters are to be set at low values in order to
to be important as they affect the machining               obtain minimum tool wear rate.
efficiency and the quality of the product                           Similarly, the minimum overcut predicted
respectively. While optimizing the responses               using GA is 0.00098289 mm with the corresponding
individually, the GA predicted value of minimum            control parameter values of 1.5µs for pulse on time,
tool wear rate is 0.00082663 mg/min with the               1.9 A for peak current and 0.5 kg/cm2.. It is
                                                           observed that pulse on time is to be set at low value



                                                                                                 1991 | P a g e
Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications
               (IJERA)                      ISSN: 2248-9622           www.ijera.com
                        Vol. 2, Issue 5, September- October 2012, pp.1986-1993
while the peak current and flushing pressure are to    6. CONCLUSION
be set at maximum values to obtain minimum                           Titanium super alloy has a wide range of
overcut.                                                   applications in engineering due to its characteristic
          Also, the average percentage prediction          of high strength to weight ratio. Micro EDM offers a
error of GA when compared with the experimental            suitable process for drilling microholes in Titanium
results as shown in Table 5 is 3.738 % and 3.257%          alloy mainly due to its characteristic of non contact
for tool wear rate and overcut respectively . Thus,        between the tool and the work piece. The qualities
the GA predicted results are within acceptable limits      required during micro hole drilling in Titanium alloy
establishing the validity of the GA as an appropriate      is to decrease the tool wear rate and overcut while
optimization technique for the micro EDM process.          drilling a microhole. The tool wear rate can be
The two objectives are conflicting in nature. This         considered as a measure of machining efficiency
multi objective problem is then optimized using the        and the overcut a measure of the quality of the hole
multiobjective GA in MATLAB software. The                  produced. Thus, it is a min-min two objective
solution obtained is a set of pareto optimal points as     optimization problem. Also, the two objectives are
shown in Fig. 3 where each point is non dominated.         conflicting in nature. Solution to such optimization
The observed responses were obtained in a single           problems is best described by a set of pareto optimal
process parametric combination setting. Table 6            non dominated points as presented in this research
records the range of values for responses at different     work . The decision maker is left with the choice of
parametric combination. It is observed that an             trade off between these two objectives which further
increase in peak current increases the available           increase the flexibility to select the optimal cutting
discharge energy, hence the tool wear rate also            parameters.
increases. While the peak current decreases, the
available discharge energy also decreases. This            REFERENCES
results in increase of the machining time which in           [1]    Hung, J-C., Wu, W-C, Yan B-H, Huang F-
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to predict a single solution point that optimizes both       [5]    G.        Karthikeyan,         J.Ramkumar,
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problems. This result is helpful as it provides a wide              performance:         An         experimental
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responses.                                                          conditions for effective turning of E0300
                                                                    alloy steel,” Journal of materials




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                                                                                          1993 | P a g e

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Ll2519861993

  • 1. Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1986-1993 Process Parameters Optimization Of Micro Electric Discharge Machining Process Using Genetic Algorithm Ruben Phipon* and B.B.Pradhan Department of Mechanical Engineering, Sikkim Manipal Institute of Technology, P.O. Majitar 737136, Sikkim, India. ABSTRACT Micro Electric Discharge Machining suitable optimization technique to search for correct (micro EDM) is a non-traditional machining parameter values for the desired responses. process which can be used for drilling micro Hung et al. [1] while using a helical micro-tool holes in high strength to weight ratio materials electrode with Micro-EDM combined with like Titanium super alloy. However, the process ultrasonic vibration found that it can substantially control parameters of the machine have to be set reduce the EDM gap, variation between entrance at an optimal setting in order to achieve the and exit and machining time, especially during deep desired responses. This present research study micro-hole drilling. Jeong et al. [2] proposed a deals with the single and multiobjective geometric simulation model of EDM drilling optimization of micro EDM process using process with cylindrical tool to predict the Genetic Algorithm. Mathematical models using geometries of tool and drilled hole matrix. The Response Surface Methodology (RSM) is used to developed model can be used in offline correlate the response and the parameters. The compensation of tool wear in the fabrication of a desired responses are minimum tool wear rate blind hole.. and minimum overcut while the independent Mukherjee and Ray [3] presented a generic control parameters considered are pulse on time, framework for parameter optimization in metal peak current and flushing pressure. In the cutting processes for selection of an appropriate multiobjective problem, the responses conflict approach. In practice, a robust optimization with each other. This research provides a Pareto technique which is immune with respect to optimal set of solution points where each solution production tolerances is desirable [4]. Karthikeyan is a non dominated solution among the group of et al. [5] conducted general factorial experiments to predicted solution points thus allowing flexibility provide an exhaustive study of parameters on in operating the machine while maintaining the material removal rate (MRR) and tool wear rate standard quality. (TWR) while investigating performance of micro electric discharge milling process. Taguchi method Keywords: Micro electric discharge machining is used for experiment design to optimize the cutting (micro EDM), Response Surface methodology parameters [6]. Experimental methods increase the (RSM), Genetic Algorithm (GA), Pareto Optimal. cost of investigation and at times are not feasible to perform all the experiments specially when the 1. INTRODUCTION number of parameters and their levels are more. Micro-EDM is a recently developed RSM is employed to design the experiments with a process which is used to produce micro-parts in the reduced number of experimental runs to achieve range of 50μm -100μm. In this process, metal is optimum responses [7]. Lalwani et al. [8] applied removed from the workpiece by melting and RSM to investigate the effect of cutting parameters vaporization due to pulse discharges that occur in a on surface roughness in finish hard turning of small gap between the workpiece and the electrode. MDN250 steel using coated ceramic tool. It is a novel machining process used for fabrication Yildiz [9] compared state-of-the-art of a micro-metal hole and can be used to machine optimization techniques to solve multi-pass turning hard electrically conductive materials like Titanium optimization problems. The results show the super alloy. The characteristic of non-contact superiority of the hybrid approach over the other between the tool and the work piece in this process techniques in terms of convergence speed and eliminates the chance of stress being developed on efficiency. Yusup et al. [10] discussed evolutionary the work piece by the cutting tool force. techniques and basic methodology of each technique However, to achieve the desired responses, in optimizing machining process parameters for the independent control parameters which affect the both traditional and modern machining. Application responses are to be set at an optimal value. Such of evolutionary techniques in optimizing machining problems can be solved by first developing process parameters positively gives good results as mathematical models correlating the responses and observed in the literature. Samanta and Chakraborty the parameters. The second step is to choose a [11] proved the applicability and suitability of 1986 | P a g e
  • 2. Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1986-1993 evolutionary algorithm in enhancing the Table 1 Coded and Actual control parameter values performance measures of nontraditional machining at different levels processes. Jain et al. [12] used GA for optimization Levels of process parameters of mechanical type advanced 1 2 3 4 5 machining processes. Traditional optimization Coded -1.682 -1 0 1 1.682 methods are not suitable to solve problems where value the formulated objective functions and constraints Pulse-on- 1 5 12 18 22 are very complicated and implicit functions of the time (µs) decision variables.. Peak 0.4 0.7 1.2 1.7 2.0 Unlike conventional optimization current (A) techniques, GA is a robust, global and can be Flushing 0.1 0.2 0.3 0.4 0.5 applied without recourse to domain-specific pressure heuristics. Tansela et al. [13] proposed Genetically (Kg/cm2) Optimized Neural Network System (GONNS) for selection of optimal cutting conditions for micro end Table 2 Design of experiments matrix showing milling operation. Singh and Rao [14] presented a coded values and observed responses multi-objective optimization technique based on GA Coded values of parameters Actual values of Responses to optimize the cutting parameters in turning processes since undertaking frequent tests or many Sl. Pulse Peak Flushin Tool wear Overcut experimental runs is not economically justified. Zain No on current g rate (mm) et al [15] applied GA to optimize cutting conditions time (A) pressure (mg/min) for minimizing surface roughness in end milling (µs) (Kg/cm2 machining process. Ghoreishi et al [16] applied GA ) for solving multi-objective optimization problems in Robust Control of Distillation Column. Hence, due 1 -1 -1 -1 0.00033 0.0510 to the multifacet advantages of GA, an attempt has 2 1 -1 -1 0.00040 0.0390 been made to optimize the micro EDM process in 3 -1 1 -1 0.00047 0.0455 this research paper using this technique. In this present research work in order to simultaneously 4 1 1 -1 0.00136 0.0340 optimize both the conflicting objectives, multi 5 -1 -1 1 0.00149 0.0490 objective GA is used to predict the non dominated 6 1 -1 1 0.00127 0.0367 Pareto optimal set of solution while drilling 7 -1 1 1 0.00062 0.0415 microholes in a Titanium super alloy. 8 1 1 1 0.00123 0.0297 9 -1.682 0 0 0.00062 0.0665 2. PROCESS MODELLING 10 1.682 0 0 0.00112 0.0503 2.1 RSM Modeling 11 0 -1.682 0 0.00066 0.0321 Pradhan and Bhattacharya [17] developed 12 0 1.682 0 0.00089 0.0195 mathematical models as shown by equations 1 and 2 13 0 0 -1.682 0.00060 0.0385 below based on second order polynomial equation 14 0 0 1.682 0.00150 0.0372 for correlating the interactions of micro EDM 15 0 0 0 0.00081 0.0402 control parameters, such as pulse on time, peak 16 0 0 0 0.00074 0.0382 current and flushing pressures and their effects on 17 0 0 0 0.00077 0.0399 some responses, such as tool wear rate and overcut 18 0 0 0 0.00078 0.0400 during micro hole machining of titanium alloy (Ti– 19 0 0 0 0.00082 0.0410 6Al–4V). 20 0 0 0 0.00078 0.0412 Table 1 lists the values for process control parameters of pulse on time, peak current and The mathematical model correlating the tool wear flushing pressures with five levels for each rate with the process control parameters is parameter. A sum of twenty experimental runs is developed as: designed using Center composite design. The combinatorial effects of process control parameters Yu(twr) = 0.000708 + 0.000070(x1) - 0.000058(x2) + at different levels on the measured response are 0.000296(X3) + 0.000011(x12) - listed in Table 2. 0.000004(x22)+0.000095(x32)+0.000112(x1x2)- 0.000038(x1x3)–0.000252(x2x3). (1) Similarly, the mathematical model for overcut is developed as: 1987 | P a g e
  • 3. Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1986-1993 Yu(oc) = 0.044513 - 0.006398(x1) - 0.0035(x2) - -3 0.001071(x3)+0.001980(x12)-0.005609(x22)- x 10 Best: 0.00082663 Mean: 0.0031704 minimum overcut (mg/min) 0.000841(x32) + 0.000054(x1x2)- 6 Best fitness 0.00002(x1x3)-0.0005(x2x3). Mean fitness (2) 4 Where x1, x2 and x3 are pulse on time, peak current and flushing pressure and Yu(twr) and 2 Yu(oc) are the responses for tool wear rate and overcut respectively. The effects of linear, higher order and the interaction of the independent process 0 0 5 10 15 variables are represented in equations (1) and (2). Generation Current Best Individual 3. SINGLE OBJECTIVE OPTIMIZATION 1 control parameter values 3.1. Optimization using GA Genetic algorithm is an evolutionary algorithm which applies the idea of survival of the fittest amongst an interbreeding population to create 0.5 a robust search strategy. Initially a finite population of solutions to a specified problem is maintained. It then iteratively creates new populations from the old by ranking the solutions according to their fitness 0 values and interbreeding the fittest to create new 1 2 3 offsprings which are optimistically closer to the Independent control parameters optimum solution to the problem at hand. It uses only the fitness value and no other knowledge is Fig. 1 GA predicted plot for minimum tool wear required for its operation. It is a robust search rate and the control parameter values technique different to the problem solving methods The results predicted using GA for used by more traditional algorithms which tend to minimum tool wear rate is listed in Table 3. Trial be more deterministic in nature and get stuck up at and error method for the selection of initial local optima. As each generation of solutions is population size found the best result when the initial produced, the weaker ones fade away without population size of 20 was chosen. producing offsprings, while the stronger mate, Table 3 GA predicted results for minimum tool combining the attributes of both parents, to produce wear rate new and perhaps unique offsprings to continue the cycle. Occasionally, mutation is introduced into one Control parameters of the solution strings to further diversify the Trial Tool wear population in search for a better solution. number Pulse Peak Flushing rate The present research work optimizes the on current pressure (mg/min) desired response and control parameters by writing time (A) the mathematical models as developed in equations (µs) (Kg/cm2) 1 and 2 as .M-files and then solved by GA using the MATLAB software. The initial population size 1 18 1.7 0.4 0.00195386 considered while running the GA is 20. A test of 10 2 18 1.7 0.4 0.00199364 runs has been conducted and the results are listed in 3 18 1.7 0.4 0.00225604 Tables 3 and 4 for minimum tool wear rate and 4 12 1.2 0.3 0.00285234 minimum overcut respectively. 5 12 1.2 0.3 0.00452525 The GA predicted value of minimum tool 6 12 1.2 0.3 0.00625264 wear rate and the corresponding control parameter 7 5 0.7 0.2 0.00975433 values are shown in Figure 1. It is observed from the 8 5 0.7 0.2 0.00094524 figure that the best minimum tool wear rate 9 1 0.4 0.1 0.00089732 predicted using GA is 0.00082663 mg/min with the 10 1 0.4 0.1 0.00082663 corresponding control parameter values of 1µs for pulse on time, 0.4 A for peak current and 0.1 kg/cm2. Similarly, the GA predicted value of minimum overcut and the corresponding control parameter values are shown in Figure 2. The GA predicted value of minimum overcut and the corresponding control parameter values are shown in Figure 2. It is observed from the figure that the 1988 | P a g e
  • 4. Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1986-1993 minimum overcut predicted using GA is 0.00098289 mm with the corresponding control Table 4 GA predicted results for minimum overcut parameter values of 1.5µs for pulse on time, 1.9 A for peak current and 0.5 kg/cm2. The results Control parameters predicted using GA for minimum overcut is listed in Trial Overcut Table 4. number Pulse Peak Flushing (mg/min) on current pressure time (A) Best: 0.0098289 Mean: 0.011419 (µs) (Kg/cm2) 0.4 minimum overcut (mm) Best fitness 0.3 Mean fitness 1 18 0.7 0.1 0.0526562 2 18 0.7 0.1 0.0517556 0.2 3 12 0.7 0.2 0.0462829 4 12 1.2 0.2 0.0482794 0.1 5 12 1.2 0.3 0.0358922 6 5 1.2 0.3 0.0278363 0 7 5 1.2 0.4 0.0265262 0 5 10 15 8 1 1.7 0.4 0.0144687 Generation 9 1 1.7 0.5 0.0128623 Current Best Individual 10 1.5 1.9 0.5 0.0098289 2 control parameter values 1.5 3.2 Validity of GA predicted results Validation of the simulation results with 1 the experimental results is done in order to conform the simulation results to the actual working 0.5 conditions and to know how much is it varying with the actual experimental results which is measured by 0 the percentage of prediction error. 1 2 3 The percentage of prediction error is calculated as Independent control parameters Prediction error% Experiment al result - GA predicted result Fig. 2 GA predicted plot for minimum overcut and  100 the control parameter values Experiment al result In order to validate the test results predicted by GA, five random experimental results are compared with the GA predicted results as shown in Table 5. Table 5 Comparison of Experimental and GA predicted results Experimental result GA predicted result Prediction error % Sl.no. Tool wear rate overcut Tool wear rate overcut Tool wear rate overcut 1 0.00112 0.0665 0.00109 0.06483 2.678 2.511 2 0.00136 0.0503 0.00128 0.0542 5.882 7.195 3 0.00089 0.0321 0.00083 0.0315 6.741 1.869 4 0.00152 0.0195 0.00148 0.0191 2.631 2.051 5 0.00082 0.0402 0.0008263 0.0413 0.762 2.663 Average percentage of error 3.738 3.257 It is observed from the table that average prediction Multiobjective optimization problems are also found percentage error is well within acceptable limits in machining processes. For nontrivial thus establishing the results predicted using GA to multiobjective problems, such as minimizing tool be valid. wear rate and minimizing overcut while drilling microholes by microEDM on a Titanium alloy, it is 4. MULTI OBJECTIVE OPTIMIZATION difficult to identify a single solution that Multi-objective optimization is the process simultaneously optimizes each objective. While of simultaneously optimizing two or more searching for solutions, one reaches points where conflicting objectives subject to certain constraints. upon an attempt to improve an objective further deteriorates the second objectives. A tentative 1989 | P a g e
  • 5. Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1986-1993 solution during such cases is called non-dominated, 4.1 Multiobjective Optimization using Genetic Pareto optimal, if it cannot be eliminated by Algorithm replacing it with another solution which improves an GA is run in MATLAB for generating objective without worsening the other. The main Pareto optimal solution points for minimizing tool objective when setting up and solving a wear rate and overcut while drilling micro holes by multiobjective optimization problem is to find such micro EDM in Titanium super alloy. Equation for non-dominated solutions. creating a fitness function for the multi objective Friedrich et al [18] performed runtime optimization is written in a .M file. The range of the analyses and observed that a fair Multi Objective process parameters is placed as bounds on the three Evolutionary Algorithm has a marked preference for input control variables and the following algorithm accepting quick small improvements. This helps to options are set. find new solutions close to the current population Selection function : Tournament of quicker. Different types of multi objective GA size 2 developed for specific purpose differ from each Crossover function : scattered other mainly by using specialized fitness functions Mutation function : Adaptive and introducing methods to promote solution feasible diversity. An elitist multiobjective GA ensures that Direction of migration : Forward with migration the best solution does not deteriorate in the function 0.2 succeeding generations. This approach uses a Distance measure function : distance priority-based encoding scheme for population crowding initialization. Population size : 75 Eiben and Smit [19] observed that adoption The variant of GA used to solve this of parameter tuners would enable better multiobjective optimization problem is a controlled evolutionary algorithm design. Using tuning elitist genetic algorithm (a variant of NSGA-II). algorithms one can obtain superior parameter values Elitist GA favors individuals with better fitness as well as information about problem instances, value. A controlled elitist GA maintains the parameter values, and algorithm performance. This diversity of population for convergence to an information can serve as empirical evidence to optimal Pareto front. justify design decisions. Lianga and Leung [20] Weighted average change in the fitness integrated GA with adaptive elitist-population function value over 150 generations is used as the strategies for multimodal function optimization. criteria for stopping the algorithm. The optimized Adaptive Elitist GA is shown to be very efficient pareto front achieved after 50 iterations is shown in and effective in finding multiple solutions of Figure 1. Input control parameters corresponding to complicated benchmark and real-world multimodal each of the pareto optimal set of solutions are optimization problems. tabulated in Table 6 . Zio and Bazzo [21] proposed a clustering procedure for reducing the number of representative solutions in the Pareto Front of multiobjective -3 x 10 optimization problems. The procedure is then 9.8 applied to a redundancy allocation problem. The Pareto front results show that the reduction procedure makes it 9.7 easier for the decision maker to select the final 9.6 solution and allows him or her to discuss the outcomes of the optimization process on the basis of 9.5 his or her assumed preferences. The clustering Overcut (mm) technique is shown to maintain the Pareto Front 9.4 shape and relevant characteristics. Su and Hou [22] showed that the integrated multi population 9.3 intelligent GA approach can generate the Pareto- optimal solutions for the decision maker to 9.2 determine the optimal parameters to assure a stable 9.1 process and product qualities in the nano-particle milling process. 9 The chief advantage of GA when applied to solve multi-objective optimization problems is the 8.9 computation of an approximation of the entire 7.8 8 8.2 8.4 8.6 8.8 9 9.2 9.4 9.6 9.8 tool wear rate (mg/min) -4 Pareto front in a single algorithm run. Thus, x 10 considering the advantages of GA for solving multiobjective problems, it is applied to optimize Fig. 3 Pareto-optimal set of solutions obtained for the process of microhole drilling by micro EDM. multi objective optimization 1990 | P a g e
  • 6. Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1986-1993 From the table, it is observed that an The two conflicting responses of minimizing tool improvement in minimizing tool wear rate wear rate and overcut are marked along x-axis and deteriorates the quality of overcut and vice versa. y-axis respectively as shown in Figure 3. The Thus, each solution point is a unique non dominated individual star marks between these axes depict solution point. individual non dominated solution point among the pareto optimal set of all the star points which form Table 6 Process decision variables corresponding the pareto front. The observed responses and the to each of the pareto optimal solution point corresponding control parameter values are listed in and the predicted responses using GA Table 6. Sl Control parameters Responses no. Pulse on time (µs) Peak current Flushing pressure Tool wear rate Overcut (A) (Kg/cm2) (mg/min) (mm) 1 13.722 0.752 0.1 0.000786 0.00965 2 13.730 0.760 0.108 0.00079 0.0096 3 13.736 0.768 0.115 0.000798 0.00958 4 13.743 0.775 0.122 0.000799 0.00952 5 13.756 0.780 0.128 0.000804 0.0095 6 13.766 0.787 0.132 0.000805 0.00948 7 13.773 0.796 0.139 0.000806 0.00946 8 13.782 0.80 0.142 0.000816 0.00944 9 13.788 0.806 0.148 0.000817 0.00942 10 13.792 0.810 0.153 0.000821 0.0094 11 14.805 0.817 0.159 0.000823 0.00938 12 14.808 0.825 0.164 0.000826 0.00936 13 14.818 0.836 0.169 0.000827 0.00934 14 14.824 0.844 0.173 0.00083 0.0093 15 14.830 0.853 0.182 0.000836 0.00929 16 14.842 0.862 0.192 0.00084 0.00928 17 14.848 0.868 0.198 0.000844 0.00926 18 14.858 0.870 0.2 0.000846 0.00924 19 14.862 0.877 0.204 0.00085 0.0092 20 14.873 0.885 0.209 0.000856 0.00919 21 15.878 0.894 0.214 0.000859 0.00918 22 15.885 0.898 0.218 0.000861 0.00917 23 15.886 0.90 0.225 0.000862 0.00916 24 15.894 0.906 0.229 0.000869 0.00915 25 15.902 0.914 0.234 0.00087 0.0091 26 15.906 0.918 0.238 0.000881 0.00908 27 15.918 0.926 0.242 0.000884 0.00906 28 15.927 0.935 0.249 0.0009 0.00903 29 15.931 0.943 0.253 0.000901 0.00901 30 15.957 0.953 0.259 0.000924 0.00898 31 15.958 0.960 0.264 0.000932 0.00897 32 15.959 0.972 0.269 0.000944 0.00896 33 15.96 0.998 0.274 0.000954 0.00895 5. RESULT AND ANALYSIS corresponding control parameter values of 1µs for While drilling micro holes by micro EDM pulse on time, 0.4 A for peak current and 0.1 in a Titanium (Ti-6Al-4V) super alloy, two kg/cm2. It is observed that the all three of the control objectives, tool wear rate and overcut are considered parameters are to be set at low values in order to to be important as they affect the machining obtain minimum tool wear rate. efficiency and the quality of the product Similarly, the minimum overcut predicted respectively. While optimizing the responses using GA is 0.00098289 mm with the corresponding individually, the GA predicted value of minimum control parameter values of 1.5µs for pulse on time, tool wear rate is 0.00082663 mg/min with the 1.9 A for peak current and 0.5 kg/cm2.. It is observed that pulse on time is to be set at low value 1991 | P a g e
  • 7. Ruben Phipon, B.B.Pradhan / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.1986-1993 while the peak current and flushing pressure are to 6. CONCLUSION be set at maximum values to obtain minimum Titanium super alloy has a wide range of overcut. applications in engineering due to its characteristic Also, the average percentage prediction of high strength to weight ratio. Micro EDM offers a error of GA when compared with the experimental suitable process for drilling microholes in Titanium results as shown in Table 5 is 3.738 % and 3.257% alloy mainly due to its characteristic of non contact for tool wear rate and overcut respectively . Thus, between the tool and the work piece. The qualities the GA predicted results are within acceptable limits required during micro hole drilling in Titanium alloy establishing the validity of the GA as an appropriate is to decrease the tool wear rate and overcut while optimization technique for the micro EDM process. drilling a microhole. The tool wear rate can be The two objectives are conflicting in nature. This considered as a measure of machining efficiency multi objective problem is then optimized using the and the overcut a measure of the quality of the hole multiobjective GA in MATLAB software. The produced. Thus, it is a min-min two objective solution obtained is a set of pareto optimal points as optimization problem. Also, the two objectives are shown in Fig. 3 where each point is non dominated. conflicting in nature. Solution to such optimization The observed responses were obtained in a single problems is best described by a set of pareto optimal process parametric combination setting. Table 6 non dominated points as presented in this research records the range of values for responses at different work . The decision maker is left with the choice of parametric combination. It is observed that an trade off between these two objectives which further increase in peak current increases the available increase the flexibility to select the optimal cutting discharge energy, hence the tool wear rate also parameters. increases. While the peak current decreases, the available discharge energy also decreases. This REFERENCES results in increase of the machining time which in [1] Hung, J-C., Wu, W-C, Yan B-H, Huang F- turn increases the overcut. Higher pulse on time Y and Wu K-L (2007) “Fabrication of a suggests more machining time, hence increase in micro-tool in micro-EDM combined with pulse on time increases both the overcut and the tool co-deposited Ni-Sic composites for micro- wear rate. It is also observed that larger the flushing hole machining”, J. 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