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Process optimization on CNC WEDM for Al-6061 Material usingTaguchi Technique to Enhance Surface Finish and Machining Time ...
machining power supply which applies            according to the material and height of theelectrical energy to the wire e...
Properties of Aluminium-6061:                  Taguchi Method:Properties                                         It is a q...
the number of parameters and the levels of       Table1: Taguchi L9 Orthogonal Arrayvariation for each parameter, and will...
Table4: Experimental Results and                               A sample calculation is shown for factorCalculations of Var...
publishing Company Limited, New Delhi,                                                    (1999).Table 8: Response Table f...
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Process optimization on CNC WEDM for Al-6061 Material using Taguchi Technique to Enhance Surface Finish and Machining Time

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Process optimization on CNC WEDM for Al-6061 Material using Taguchi Technique to Enhance Surface Finish and Machining Time

  1. 1. Process optimization on CNC WEDM for Al-6061 Material usingTaguchi Technique to Enhance Surface Finish and Machining Time Rajesh.S1, Vinitesh.K.V1, Lingaraju.K.N, 1 Ramesh Babu.K2 [1] Dept. of Mechanical Engineering, Govt. Engineering College. Chamarajanagar-571313, [2] Dept. of PG Studies, Govt. Tool Room and Training Centre, plot no. 93 & 94, K.R.S road Mysore-16.ABSTRACT Electro Discharge Machining (EDM) is an electro-thermal non-traditional machiningprocess, in which material removal takes place through the process of controlled sparkgeneration between a pair of electrodes which are submerged in a dielectric medium. In thispaper, wire-cut electric discharge machining (WEDM) of Al-6061 material has been considerusing WEDM with a brass wire electrode by using Taguchi technique has been reported. TheTaguchi Technique is used to formulate the experimental data by using Taguchi’s orthogonalarrays under different parameter condition like voltage, power, voltage gap and wire tensionand analyzed the effect of each parameter on the machining characteristics to predict theoptimal choice for each and It is found that these parameters have a significant influence onmachining characteristic such as Surface finish, Electrode wear rate and Machining time.KEYWORDS: WEDM, Taguchi method, DOE, Orthogonal array, machining time, Surface finish.Introduction Electrical discharge machining (EDM) is better stability and higher productivity of thea non-traditional, thermo-electrical process, WEDM. The wire cut EDM uses a very thinwhich erodes materials from the work piece wire 0.2 to 0.3 mm in diameter as anby a series of discrete sparks between the electrode and machines a work piece withwork and tool electrode immersed in a liquid electrical discharge like a band saw bydielectric medium. These electrical moving either the work piece or wire.discharges melt and vaporize minute Erosion of the metal utilizing theamounts of the work material, which are phenomenon of spark discharge that is thethen ejected and flushed away by the very same as in conventional EDM. Thedielectric. A wire EDM (WEDM) generates prominent feature of a moving wire is that aspark discharges between a small wire complicated cutout can be easily machinedelectrode and a work piece with de-ionized without using a forming electrode. Wire cutwater as the dielectric medium and erodes EDM machine basically consists of athe work piece to produce complex two and machine proper composed of a work piecethree dimensional shapes according to a contour movement control unit (NC unit orcomputer numerically controlled (CNC) copying unit), work piece mounting tablepath. The main goals of WEDM and wire driven section for accuratelymanufacturers and users are to achieve a moving the wire at constant tension, a
  2. 2. machining power supply which applies according to the material and height of theelectrical energy to the wire electrode and a work piece and tool material from a manualunit which supplies a dielectric fluid provided by the WEDM manufacturer. it has(distilled water) with constant specific several special features.resistance. For the optimal selection of Principle of CNC WEDM:process parameters, the Taguchi method has In wire EDM, the conductive materialsbeen extensively adopted in manufacturing are machined with a series of electricalto improve processes with single discharges (sparks) that are producedperformance characteristic. between an accurately positioned moving wire (the electrode) and the work piece. High frequency pulses of alternating orExperimental Process: direct current is discharged from the wire to Figure 1 depicts schematically the the work piece with a very small spark gapexperimental set up. through an insulated dielectric fluid (water). Many sparks can be observed at one time. This is because actual discharges can occur more than one hundred thousand times per second, with discharge sparks lasting in the range of 1/1,000,000 of a second or less. The volume of metal removed during this short period of spark discharge depends on the desired cutting speed and the surface finish required. The heat of each electrical spark, estimated at around 15,000° to 21,000° Fahrenheit, erodes away a tiny bit of material that is vaporized and melted Fig: 1 Experimental set up from the work piece. (Some of the wireWire EDM uses deionized water as a material is also eroded away) These particlesdielectric fluid in this experiment. Diameter (chips) are flushed away from the cut withof electrode and thickness of work piece is stream of de-ionized water through the topmeasured by digimatic micrometer. (Make: and bottom flushing nozzles. The water alsoMitutoyo, Least count: 0.001 mm). Weight prevents heat build-up in the work piece.of work piece is measured by Precisa-make Without this cooling, thermal expansion ofweighing machine (Accuracy: 0.1mg). the part would affect size and positional The experiments were performed on accuracy. Keep in mind that it is the ON andFA10S MITSUBISHI high precision CNC OFF time of the spark that is repeated overWEDM, The basic parts of the WEDM and over that removes material, not just themachine consists of a wire, a work table, a flow of electric current. Al-6061 materialservo mechanism, a power supply and was the target material used in thisdielectric supply system. It allows the Investigation.operator to choose input parameters
  3. 3. Properties of Aluminium-6061: Taguchi Method:Properties It is a quality control methodology thatDensity (g/cm3 ) 2.7 combines control chart and process controlMelting Point (°C) 580 with product and process design to achieve aModulus of Elasticity 70-80 robust total design. It aims to produce(GPa) product variability with a system forThermal Conductivity 173(W/m.K) developing specifications and designingElectrical Resistivity 3.7 – 4.0 x10-6 them into a product or process. Taguchi(Ω.cm) methods focus on design – the developmentCo-Efficient of Thermal 23.5x10-6 of superior performance designs (ofExpansion (m/m.°C) products and manufacturing processes) to deliver quality.Design of Experiments: Two major tools used in Taguchi’s Design of experiments (DOE) or method are one is signal(S) to noise (N)experimental design is the design of any ratio i.e. S/N ratio to measure the quality andinformation gathering exercises where the other is orthogonal arrays tovariation is present, whether under the full accommodate many factors simultaneouslycontrol of the experimenter or not. to evaluate the machining performances.Design process should be seen as three The ability of orthogonal arrays lies instages: evaluating the machining performance with Systems design a less number of experiments when Parameter design compared to full factorial experiments Tolerance design. which reduces the number of trials. This System design identifies the basic greatly reduces the time required inelements of the design, design at the conducting the experiments and also inconceptual level, involving creativity and evaluating the significant and insignificantinnovation. parameters. Parameter design determines the most The general steps involved in the Taguchiappropriate, optimizing set of parameters Method are as follows:covering these design elements by 1. Define the process objective, or moreidentifying the settings of each parameter specifically, a target value for a performancewhich will minimize variation from the measure of the process.target performance of the product. 2. Determine the design parameters affecting Tolerance design finally identifies the the process. Parameters are variables withincomponents of the design which are the process that affect the performancesensitive in affecting the quality of the measureproduct and establishes tolerance limits 3. Create orthogonal arrays for thewhich will give the required level of parameter design indicating the number andvariation in the design. conditions for each experiment. The selection of orthogonal arrays is based on
  4. 4. the number of parameters and the levels of Table1: Taguchi L9 Orthogonal Arrayvariation for each parameter, and will be Design Matrixexpounded below.4. Conduct the experiments indicated in the Exp. No. Factor 1 Factor 2 Factor 3 Factors 4 01 1 1 1 1completed array to collect data on the effect 02 1 2 2 2on the performance measure. 03 1 3 3 35. Complete data analysis to determine the 04 2 1 2 3effect of the different parameters on the 05 2 2 3 1 06 2 3 1 2performance measure. 07 3 1 3 2 08 3 2 1 3DOE for CNC WEDM of Al-6061 09 3 3 2 1Material: Responses measured:-The design of experiment chosen for the 1) Machining time (MT),WEDM of Al-6061 was a Taguchi L9 2) Surface Roughness (SR).orthogonal array, by carrying out a totalnumber of 9 experiments along with 2 Table2: Level values of input factorsverification experiments (optional). TestingL9 Orthogonal Array: Symbols Level1 Level2 Level3 parameters In L9 (34) array 9 rows represent the 9 A Voltage (V) 7 12 16experiment to be conducted with 3 columns B Current(I) 3 6 12at 3 levels of the corresponding factor. The Voltage gap C 51 59 75matrix form of these arrays is Shown, where (Vg) Wire tension1, 2, 3 in the table represents the level of D 7 8 10 (WT)each parameters. Table 3: L9 Design MatrixInput Factors:- Parameter level 1) Voltage (v) Exp no. 2) Current (Ip) A B C D 3) Voltage gap (Vg) 1 7 3 51 7 4) Wire tension (WT) 2 7 6 59 8 3 7 12 75 10 4 12 3 59 10 5 12 6 75 7 6 12 12 51 8 7 16 3 75 8 8 16 6 51 10 9 16 12 59 7
  5. 5. Table4: Experimental Results and A sample calculation is shown for factorCalculations of Various Response Factors B [current]:based on Taguchi L9 Orthogonal Array Exp no. MT in min SR in µm Sn1 = = 38.99 1 2 1 2 1 4.8 4.86 16.9 17.1 Sn2 = = 32.718 2 4.7 4.63 15.8 16.3 3 4.92 5 16.7 17.1 Sn3 = = 35.057 4 4.24 4.4 36.3 35.8 5 5.2 5 34.8 35.3 Δ = 38.99 – 32.718 = 6.272 6 4.83 4.72 16.7 17 7 4.62 4.58 15.8 16.32 Table 6: Response Table for Signal to 8 4.9 5.2 35.2 34.9 Noise Ratios for MT 9 4.44 4.63 35 35.1 leve A B C D l [voltag [current] [voltag [wireFor machining time: e]in v in amp e gap] tensionSm1= = 46.6578 ] 1 39.823 38.99 34.806 34.272St1 = (4.82+4.862) = 46.6596 2 32.843 32.718 33.889 39.823 3 34.102 35.057 35.073 32.672Se1 = St1 – Sm1 = 1.8×10-3 Δ 6.9794 6.272 4.1847 7.151 rank 2 3 4 1ve = = = 1.8×10-3 Therefore, wire tension (WT) has the maximum effect on machining time.S n1 =10log [ ] = 41.126 Table 7: Calculation of Signal to NoiseTable 5: Calculation of Signal to Noise ratio for SRratio for MT Exp Parameters SR in µm SN Parameters level MT in min SNExp no. levelno. A B C D 1 2 A B C D 1 2 1 1 1 1 1 16.9 17.1 41.5981 1 1 1 1 4.8 4.86 41.1262 1 2 2 2 4.7 4.63 39.485 2 1 2 2 2 15.8 16.3 33.1393 1 3 3 3 4.92 5 38.8578 3 1 3 3 3 16.7 17.1 35.5264 2 1 2 3 4.24 4.4 31.63 4 2 1 2 3 36.3 35.8 40.1685 2 2 3 1 5.2 5 31.13946 2 3 1 2 4.83 4.72 35.7613 5 2 2 3 1 34.8 35.3 39.9247 3 1 3 2 4.62 4.58 44.244 6 2 3 1 2 16.7 17 37.9908 3 2 1 3 4.9 5.2 27.5298 7 3 1 3 2 15.8 16.3 32.8049 3 3 2 1 4.44 4.63 30.522 8 3 2 1 3 35.2 34.9 44.362 9 3 3 2 1 35 35.1 53.904
  6. 6. publishing Company Limited, New Delhi, (1999).Table 8: Response Table for Signal to 2. Phadke M.S, Quality Engineering UsingNoise ratios for SR Robust Design, Prentice- Hall, Englewood Cliffs,NJ, (1989).leve A B C D 3. Williams, R.E., Rajurkar, K.P., Study of l [voltage [current] [voltage [wire Wire Electrical Discharge Machining ] in v in amp gap] tension] Surface Characteristics, Journal of 1 36.754 38.19 41.32 45.142 Materials Processing Technology, Vol. 28, 2 39.36 39.1415 42.4036 34.65 pp.486-493, (1991). 3 43.6898 42.48 36.0846 40.108 4. R.E. Williams, K.P. Rajurkar, Study of Δ 6.9358 4.29 6.32 10.49 wire electrical discharge machined surfacedrank 2 4 3 1 characteristics, J. Mater. Process. Technol. 28 (1991) 127–138. 5. R .Ramakrishnan, L .Karunamoorthy, Therefore wire tension (WT) has the “Surface roughness model for CNC wirelargest effect on surface roughness. electro discharge machining”, J ManufCONCLUSION: Technol Today, 2004, Vol. 3(5), pp. 8-11. 6. Phillip J. Ross. Taguchi techniques for The machining time (MT) mainlyaffected by wire tension (WT).voltage (V) quality engineering, McGraw-Hill Book company, New Yorkhas less effect on it. Voltage gap (Vg) and 7. Dr. S. S. Khandare & Mitesh a. Popat,current (I) has a least effect on MT. The Experimental Investigations of EDM tosurface roughness (SR) is mainly influenced optimize Material Removal Rate & Surfaceby wire tension (WT). The effect of voltage Roughness through Taguchi’s Technique ofgap (Vg) and voltage (V) is less on SR and Design of Experiments. IEEE explore,current (I) has least effect on it. ICETET-09, pg 476 – 482 Print ISBN: 978- Some portion of the material is 1-4244-5250-7, (2009).conductive and some portion is non-conductive wherein CNC WEDM requires 8. T.A. Spedding and Z.Q. Wang. Parametric optimization and surfaceconductive work piece. So the composite characterization of wire electrical dischargeproperties of the work piece also lead to machining process. Precis. Eng. 20(1): pp.5-some observations which contradict thetheoretical belief. 15, 1997. 9. R. E. Williams and K. P. Rajurkar, Study of wire electrical discharged machineREFERENCES surface characteristics, Journal of Materials1.Pandey P C , Shan H S, Modern Processing Technology,28(1991) pp.Machining Processes, Tata McGraw-Hill 127-13

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