Experimental Investigation of Micro-EDM Process on Brass using Taguchi Technique

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1 Experimental Investigation of Micro-EDM Process on Brass using Taguchi Technique Ananya Upadhyay Vijay Pandey Vinay Sharma Ved Prakash CSIR- Central Mechanical Engineering Research Institute, Durgapur Abstract: Micro-EDM is an unconventional machining process, which is in high demand due to precise and accurate machining. This process is basically used in micro nozzles, aerospace industries, MEMS etc. This is a non-contact process so the machining forces between electrode and workpiece are absent. This gives freedom to select material for workpiece and tool irrespective of their hardness. The material removal takes place by melting and vaporization of metal due to the spark generated between workpiece and electrode. This paper discusses the experimental study of Micro-EDM process with a tungsten electrode on a brass workpiece using additives in the dielectric fluid. The additives used are Aluminum and Silicon carbide. The process parameters taken into consideration are capacitance, voltage, tool diameter and additive. The significant process parameters are being suggested using orthogonal array. The model is found to be valid for a range of parameters, the capacitance value from 4 pf to 6 pf and peak voltage from 105V to 115V. Keywords- Micro-EDM, Taguchi technique, ANOVA, Material Removal Rate, Surface Roughness I. INTRODUCTION The rapidly changing technologies in the field of manufacturing industries have always pushed researchers, scientist and technicians to keep exploring, developing and updating the traditional processes of manufacturing. Manufacturing process is a value addition process. [1] One of the most expensive manufacturing processes is machining. Machining is a in which substantial amount of material is removed as chips for achieving close tolerances with the required dimensions. So selection of machining process is itself is a critical decision as it is a subtractive manufacturing technique. Any machining process requires a machine tool and a work material from which material is to be removed. Machining process is broadly classified as conventional and unconventional machining processes. The conventional machining processes are those which have a machine tool and work material with difference in hardness. The machine tool has to be harder than work material to remove material from the workpiece. In these cases the unconventional machining processes can be a right choice. The unconventional machine processes use energy source to remove material [2]. The energy is used in its direct form. The importance of these processes is highly realized in case of precision machining and ultra precision machining. In this paper the area of concern is just constrict to thermo- electric processes. One of the thermo-electric processes is electro-discharge machining (EDM) process. [3] The working principle of this process is the electrical energy is converted into thermal energy. Due to this high energy plasma is generated which has a temperature upto 20,000 [4]. The high temperature of plasma melts away the material on the workpiece and electrode. Then the dielectric floods between the gap, evaporates and flushes away the removed material. The high demand of miniaturization of components has moved the interest of scientist and researchers towards micromanufacturing techniques. [5] The need for nano surface finish, 3D complex shapes, miniature features can be fulfilled only by micro-machining processes. The machining of products in the range of 1µm to 999µm is defined as micro machining process. The need for advanced micro-machining is when precision and ultra-precision machining of micro features is required. Micro-EDM has proved to be one of the promising processes regarding micro-machining of

2 materials.[6]the electro-thermal process relies on the discharge energy through the dielectric fluid which supplies heat energy to the workpiece and electrode.[7] 2% to 10% of discharge power is dissipated in the plasma channel. Workpiece is heated beyond melting point and cooled by dielectric fluid following quenching process. Electrode heating effects in micro-edm is less as mass and area to take away heat is limited so the amount of energy supplied should be high.[8] Machining of doped ceramics and insulating ceramics is studied in this paper using milling operation. As they are not conducting so assisting electrodes are used for machining. Also it has been concluded that micro-edm can be proved efficient for post processing of ceramics. Assisting electrode is a technique in which a conducting film is applied over workpiece so the machining can take place easily. This technique was first mentioned Mohri et.al.[9,10]. [11] In this paper powder mixed micro-edm mechanisms is discussed. The major highlights of the paper are that powder mixed micro-edm helps to reduce machining time. The problem of short circuiting is solved by mixing powder in dielectric as the gap between electrode and workpiece increases. [12] In this paper effect of powder suspension on titanium alloy is discussed. Titanium alloy is important for aerospace industries due to its high strength and corrosion resistance. The use of powder mixed dielectric enhances the MRR and decreases the Tool Wear Rate. In this work the selection of process parameters is done using Taguchi Technique and the analysis is done using S/N analysis. S/N ratio helped to find significant process parameters and their effects on performance parameter. II. EXPERIMENTAL INVESTIGATION ON EFFECT OF PROCESS PARAMETER A. Process Parameters Considered For The Experiments: In order to understand the effect of different process parameters on the performance parameters only essential process parameters are selected to be studied: Voltage Capacitance Electrode Diameter Additives B. Selection Of Values Of Process Parameters: Taguchi methodology of investigation is considered to understand the effect of process parameters. The selection of parameters and there range are selected based on literature review and initial investigations. Voltage: The range of voltage that DT-110 MIKROTOOL model has is 80 to 130 volts. The range that is suitable for carrying out operations drilling and milling are 105 to 115 volts. The lowest range is 105 volts as below that MRR recorded is very low and above 115 volts the deposition of material on electrode is high. Capacitance: In case of capacitance the range of machine is 0 to 6 pf. Below 4 pf the MRR is very low so the range is kept between 4 to 6 pf. Electrode Diameter: The flow of dielectric is from only one direction. The constant forces from one direction can bent or deflect the electrode so the diameter range is decided in a range of 0.4 to 0.6 mm. Additives: Thee types of condition are taken no additive, conductive additive and semi-conducting additives. As a conductive additive, Aluminum powder in a concentration 4g/l. it increases the tool gap. As semi-conductive, silicon carbide concentration 2g/l. C. Test Specimen: A brass sheet test specimen with dimensions mm and thickness of 0.2 mm. Milling operation performed with depth of 0.03 mm and 2 mm in length with different parameter setting as shown in table I with a bass electrode. Machining time is calculated with the help of stopwatch. Surface roughness is measured by Taylor Hobson machine, Surtronic 4+ model. The workpiece is examined under Moticam 352 camera at zoom level 1.5x. III. EXPERIMENTAL SETUP FOR MILLING OPERATION Milling is performed on Mikrotool DT-110 model hybrid µedm machine. Different arrangement is done to perform milling when using powder mix dielectric. For powder mix dielectric milling operation, the arrangement for flushing is not feasible. As in the machine the dielectric flushing through the machining zone contains debris which has to pass through the filter channel. The filter section pumps the fresh dielectric without the debris. So if the powder is used in the filter tank and let it to flush through the filter channel of machine then all the powder s particles would be barred to enter the dielectric tank again. So it is impossible to examine the effect of powder using given arrangement.

3 So in order to carry out the experiments with powder, an auxiliary arrangement is to be made. For this purpose, a separate flushing system is arranged. A separate jar is kept to store the dielectric which comes after machining zone. Submersible pumps are put in dielectric tank and jar respectively. The pump of dielectric tank pumps the liquid captaining powder to the jar and jar pumping the liquid containing powder from jar to EDM tank. This way the flow of powder mix dielectric is circulated. IV. EXPERIMENTAL INVESTIGATION For performing the experiment L27 orthogonal array has been adopted. The experimental design has 3 levels and four factors. L27 is selected because the aim of experimental investigation is not only examine the dominant factors among the fours, but also the interaction among the factors which effect the output parameters. From L27 orthogonal array the maximum number of interaction can be generated. Table I: Process Parameters Parameters Units Values Voltage (A) Volts (V) 105,110,115 Capacitance PicoFaraday 4,5,6 (B) Electrode Dia. (C) Additives (D) (pf) Milimeter (mm) 0.4, 0.5,0.6 mm No additive, Conductive and non-conductive Table II: Levels Parameters Voltage (A) Capacitance (B) Electrode Dia. ( D) Additives (C ) No Additives SiC Experiments are conducted as per L27 orthogonal array and for each combination the experiments are done. Thereafter analysis of variance is performed for the mean and S/N ratio. To know the maximum interaction between process parameters, beside four input parameters, interactions between the process parameters are considered. The interaction is as follows: A B,B D,A C,B C,A D,C D Al A B A B Table III: L27 orthogonal array E C B A B D A B D C C D C e C D V. Analysis of effect of µedm parameters To analyze the effect of process parameters on MRR and surface finish, Taguchi method is implemented by customizing the full factorial design to determine the effect of machining parameters on the µedm process. In DOE, Taguchi method is very useful in process optimization and for finding the optimal combination of parameters which affects the given responses. The Signal to Noise (S/N) ratio calculates the variation present in the process and is used to measure the effect of noise factor on the performance characteristics. The Signal to Noise ratios are of three types: smaller the better, nominal the better and larger the better. The analysis of Variance (ANOVA) is used to find out the significant effects of each factor and their interactions on process responses. (1) (2)

4 Equation 1 represents for larger the better and equation 2 is smaller the better. Where, S/N signal to Noise and Yi is the experimental observed value and n number of repetitions of each experiment. The experimental data are analyzed using MINITAB 15 software dedicated for DOE. For measuring the quality of the performance characteristics, the experimental data are transformed into S/N ratios. The input parameters considered are capacitance, discharge voltage, electrode diameter and additive and the responses include MRR and Surface roughness. VI. RESULT AND DISCUSSIONS Table IV: MRR and Ra values as per calculations Runs MRR Ra A. Analysis Using S/N Ratio In this experimental study, the main objective is to find out the significant factors that influence µedm machining of brass. The S/N ratio is used to analyze the response for a given set of input parameters. The ranking of process parameters affecting the MRR and surface roughness using S/N ratios is obtained as shown in the table V and VI below. Table V: MRR response table for S/N ratio (Larger the better) Levels B A C D B C (Capacitance) (Additive) Delta Rank Table VI: Ra- Response table for S/N ratio (Smaller the better) Levels B A C D B C (Capacitance) (Additive) Delta Rank VII. Conclusion From the research work carried out following conclusions can be made: The factor that largely influenced the output responses is capacitance. In case of MRR the second most influencing process parameter is interaction between A and C i.e., between voltage and electrode diameter. Third most influencing factor that affect MRR is additive. For surface roughness after capacitance the most influencing parameter are the interaction between voltage and additive. For optimal MRR, capacitance should be 5pF, Voltage 105V, electrode diameter 0.6mm and aluminum powder is used as additive. For minimum surface roughness capacitance should be 6 pf, voltage 105 V, electrode diameter 0.6mm and no additive is used. REFERENCES [1] P.N.Rao, Introduction, in Manufacturing Technology, Vol. 2,2 nd Ed., New Delhi, Tata McGraw-Hill, 2009, pp. 1-5 [2] V.K. Jain, Introduction, in Advanced Machining Processes, New Delhi, Allied Publishers,2012,pp. 2-3 [3] M.P. Jahan, Micro-Electro Discharge Machining, in Non-Traditional Machining Processes, J.P. Davim,London: Springer-Verlang.

5 [4] G. Boothroyd and A.K.Winston, Non-conventional Machining processes, in Fundamentals of Machining & Machine Tools, New York, Marcel Dekker Inc.,1989,pp. 491 [5] V.K. Jain, Micromachining Processes: An Introduction, in Introduction to Micromachining, 2 nd Ed., New Delhi,Narosa Publishing House, 2014, pp [6] Z. Katz and C.J. Tibbles, Analysis of micro- scale EDM process, International Journal of Advanced Manufacturing Technology, 25, pp ,2005. [7] J.H.Lienhard, A heat transfer Textbook, 2 nd Ed., Englewood Cliffs,New Jersy Prentice-Hall,1987. [8] A. Schubert, H. Zeidler, R.Kuhn and M.H. Oschatzchen, Microelectrical Discharge Machining : A suitable process for machining ceramics, in Journal Of Ceramics, 2015, pp.1-9. [9] N. Mohri, Y. Fukuzawa, T.Tani, N. Saito and K. Furutani, Assisting Electrode method for machining insulating ceramics,cirp Annals- Manufacturing Technology, 45 (1),pp , [10] N. Mohri, Y. Fukuzawa, T.Tani and T. Sata, Some considerations to machining characteristics of insulating ceramics- towards practical use in industry, CIRP Annals- Manufacturing Technology, 51 (1), pp , [11] S.P. Gunwana, S. Tutik and M. Muslim, Improvement of machining time in Micro-EDM with workpiece vibration & graphite powder mixed in dielectric fluid, Indian Journal of Engineering & Materials Sciences, 19, pp , 2012 ELK Asia Pacific Journals