P-20 - YMCA University of Science & Technology

Proceedings of the National Conference onTrends and Advances in Mechanical Engineering,YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012Experimental Evaluations on Surface Quality Improvement in AluminiumPowder Mixed AEDM of Nickel Based Super Alloy 718 with CryogenicallyTreated Copper ElectrodeAnil Kumar*, Naveen Beri, Harish PungotraDepartment of Mechanical Engineering, Beant College of Engineering and Technology, Gurdaspur, Punjab,*Corresponding Author E-mail ID: ak_101968@yahoo.comAbstractIn this experimental study attempt has been made to realize potential in enhancing surface quality with finealuminum additives powders in AEDM of nickel based super alloy Inconel 718. L 36 Orthogonal Array has beenselected to conduct and analyze experiments based on Taguchi methodology. Peak current, pulse on time, dutycycle, gap voltage, retract distance, concentration of fine aluminum powder added into the dielectric fluid arechosen as input process variables to study performance in terms of surface roughness using copper and deepcryogenically treated copper electrode. It is observed that addition of 6g/l of fine aluminium powder andcryogenically treated copper electrode improves the surface finish appreciably. The recommended bestparametric settings for minimum surface roughness have been verified by conducting confirmation experiments.Keywords: AEDM, Taguchi methodology, Orthogonal Array, cryogenic treatment, surface roughness.1. IntroductionToday’s manufacturing industry is facing challenges like difficulty in machining of advance extra hard and toughmaterials (super alloys, ceramics, and composites), stringent design requirements (high precision, complexshapes and high surface quality) and machining costs. The greatly-improved thermal, chemical, and mechanicalproperties of the material such as improved strength, heat resistance, wear resistance, and corrosion resistance,while having yielded enormous economic benefits to manufacturing industries through improved productperformance and product design, are making traditional machining processes unable to machine them or unableto machine them economically. EDM has proven to be applicable to all electrically conductive materialsregardless of their physical and metallurgical properties. In EDM, material removal is achieved by preferentialerosion of the work piece electrode as controlled discrete discharges are passed between the electrode and thework piece in dielectric medium. EDM is a widespread technique used in industry for high precision machiningof all types of conductive materials such as: metals, metallic alloys, graphite or even some ceramic materials andsuper alloys such as Inconel, of any hardness [1]. Since the invention of EDM in 1940s researchers have made alot of efforts to improve the machining performance. A number of variants have emerged to manifolds theapplication of EDM process in industry. In traditional EDM process surface roughness is more and materialremoval rate is relatively less. To fulfill the objectives of improving manufacturing efficiency and quality ofshaping and finishing processes researchers have taken many directions. A relatively new advancement in thisdirection is to use some additives powders suspended in the dielectric fluid of EDM to fulfill the requirement ofminimum surface damage, enhance machining rates and improving surface properties. This new hybridmachining process is called additive mixed electrical discharge machining [2-5].The machining mechanism of AEDM is different from conventional EDM process [6-7]. In AEDM when avoltage of 80-320V is applied across work piece and electrode electrical intensity in the range of 10 5 to 10 7 V/mis generated. Under the influence this electric intensity additives powder particles get energized and behave in azigzag fashion. These additives particles arrange themselves in the form of chain at different places under thesparking area leading to bridge formation. This bridging effect promotes early explosion in the gap. As a result,the series discharge starts under the electrode area. Due to increase in frequency of discharging, faster erosiontakes place from the work piece surface. Therefore gap contamination with fine abrasive conductive particlesfacilitates ignition process and increases maching rates and due to better distribution of spark energy resulting inimproved surface roughness. Process performance of AEDM depends upon electrical parameters (like pulsefrequency, duty cycle, pulse on time, spark gap, current, and voltage), material properties of electrode, workpiece and dielectric fluid, and properties of abrasive powders (like melting point, specific heat, thermalconductivity, grain size, and concentration). Therefore, promoting the process performance by developing athorough understanding of the relationship between these parameters has become a major research concern [8-11].Erden and Belgin [12] were the first who studied the effect of impurities (copper, aluminium, iron and carbon) inelectrical discharge machining of brass steel and copper steel pair and reported increase in machining rates with482

Proceedings of the National Conference onTrends and Advances in Mechanical Engineering,YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012increase in concentration of impurities. It was reported that machining becomes unstable at an excessive additivepowder concentration due to the occurrence of short-circuits and occurrence of discharges at same spot. Sincethen a lot of research work has been done in the area of additive mixed electrical discharge machining and haveshown great effect on process performance in terms of material removal rate, surface characteristics, wear ratioetc.Jeswani [13] investigated the effect of suspended fine graphite powder in dielectric medium of electricaldischarge machining on tool steel and reported that addition of about 4 g/l of fine graphite powder (10 μm inaverage size) in kerosene increased metal removal rate (MRR) by 60% and tool wear rate by 15%. This wasattributed to better electrical discharge distribution between spark gap.Mohri and co worker [14] studied the effect of silicon powder in dielectric medium and reported significantimprovement in machining performance. Kumar and Beri studied the effect of graphite powder on surfacequality and reported improved surface finish [15]. The aim of the present research work was to experimentallyevaluate on surface quality improvement in aluminium powder mixed AEDM of Nickel Based Super Alloy 718with cryogenically treated copper electrode and to find best parametric settings to minimize SR.2. Experimental Planning and ProcedureTaguchi methodology has been applied to plan and analyze the experiments. The Taguchi method can optimizeperformance characteristics through the settings of process parameters and reduce the sensitivity of the systemperformance to sources of variation.Table 1 Process parameters and their levelsSymbol Process parameters units Levels1 2 3A Polarity +ve -veB Types of electrode Copper Cryogenicallytreated copperC Peak current amps 0.5 3 6D Pulse on time µs 50 100 150E Duty cycle τ 0.7 0.8 0.9F Gap voltage volts 40 60 80G Retract distance mm 1 2 3H Concentration of Powder(300 Mesh size)g/l 0 6 12The experimental parameters and their levels selected for present study are tabulated in Table 1 keeping otherparameters constant based on trial experiments and previous studies. In the present study experiments werecarried out on Electronica make electrical discharge machine; model SMART ZNC (S50).A copper electrode of 8mm φ was subjected to deep cryogenic treatment which consists of a slow cool-down rate(2.5°C/min) from ambient temperature to the temperature of liquid nitrogen. When the material reachedapproximately at −193.15°C it was soaked for 24 hours.Experiments were performed with O.A L 36 (2 2 x3 6 ). The results were analyzed for minimum surface roughnesswith “smaller the better” quality characteristic with Minitab software 15.1.1.The SR was measured in terms ofarithmetic mean roughness of the evaluated roughness profile (Ra in µm) by using a Mitutoyo SJ 400 surfacetesting analyzer.3. Results and DiscussionsThe S/N ratios of SR for each trial run have been calculated from experimental data and response table forsmaller the better are summarized in Table 2 giving relative importance of each parameter on desired response.The individual effects of input parameters on the S/N ratios for SR are shown in main effect plot (Fig.2).483

Proceedings of the National Conference onTrends and Advances in Mechanical Engineering,YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012Main Effects Plot for SN ratios (SR)Data MeansPolarityElectrode ty pePeak C urrent-8-10-12Mean of SN ratios-8-10-12-8-10-12-V e+v ecopper cry ogenic 0.5 3.0 6.0Ton Time Duty C y cle Gap V olt.50 100 150 0.7 0.8 0.9 40 6080Retarct distanceC oncentration1230612Signal-to-noise: Smaller is betterFig.2 Main Effect plot for S/N ratios for SRTable 2 Response Table for Signal to Noise RatiosFrom main effect plot Fig.2 it is observed that polarity, peak current, pulse on time retract distance significantlyLevelPolarityElectrodeBPeakcurrentCPulse ontimeDDutycycleEGapvoltageFRetractdistanceGConcentrationof powderHA1 -8.992 -10.511 -6.876 -8.069 -10.063 -10.236 -9.095 -9.9722 -11.541 -10.022 -10.816 -10.197 -10.852 -9.467 -11.014 -9.8913 -13.108 -12.535 -9.885 -11.097 -10.691 -10.938Delta 2.549 0.489 6.232 4.466 0.967 1.630 1.920 1.047Rank 3 8 1 2 7 5 4 6effect the surface roughness as these are having steeper slopes in main effect plots. Although slope of effect oftypes of electrodes and concentration of fine abrasives aluminium powder are not steep, still these affect thedesired objective in positive manner. Positive polarity, higher peak current, higher pulse on time contribute morespark energy leading to deeper and wider craters on the machined surfaces, thereby contributing for higher SR.whereas uniformly distributed fine abrasive powders particles under sparking area results in distributed sparkingenergy give more sparks and shallow craters on the surface. Response for Signals to Noise ratios at differentlevels are presented in Table 2. Higher the delta value in response table more the effect of parameters on thedesired objective. Rank gives the relative importance of selected parameters on SR. Main effect plots suggestthat negative electrode polarity , cryogenically treated copper electrode , 0.5 peak current , 50 µs pulse on time ,0.9 duty cycle 60 V gap voltage, 1mm retract distance and 6g/l of fine aluminium abrasive powder are bestparametric setting for minimum SR. At these settings confirmation experiments were performed and 6.5%improvement was observed in SR.Provide a space of 60 pts before the title of the paper. It may be created using“Format – Paragraph – Indent and Spacing – Spacing: Before 60 pt” option.4. ConclusionsFrom present investigations following conclusions are drawn.1) AEDM is possible option with cryogenically treated copper electrode on Inconel 718.2) Polarity, peak current and pulse on time effect surface roughness drastically.3) Cryogenically treated copper electrode and concentration of fine aluminium abrasive powder particleseffects the SR in positive manner and enhance SR appreciably.484

Proceedings of the National Conference onTrends and Advances in Mechanical Engineering,YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 20124) The optimum parametric setting s for minimum SR are negative electrode polarity , cryogenicallytreated copper electrode , 0.5 peak current , 50 µs pulse on time , 0.9 duty cycle, 60 V gap voltage, 1mmretract distance and 6g/l of fine aluminium abrasive powder.AcknowledgementsThe authors would like to acknowledge the support of department of mechanical engineering, Beant College ofEngineering and Technology, Gurdaspur, Punjab, India, University School of Engineering and TechnologyGGSIPU, Delhi, India and All India Council for Technical Education New Delhi, India for supporting and fundingthe research work under research promotion scheme in this direction vide file No.: 8023/BOR/RID/RPS-144/2008-09 and 8023/BOR/RID/RPS-86/2009-10.References1) Kumar, A., Maheshwari, S., Sharma, C. and Beri, N. (2010) , Materials and Manufacturing processes, Vol.25, No. 10, pp. 1166–1180.2) Klocke, F.; Lung, D.; Antonoglou, G.; Thomaidis, D. Journal of Materials Processing Technology 2004,149,191–197.3) Abbas, N.M.; Solomon, D.G.; Bahari, M.F. International Journal of Machine Tools and Manufacture 2007,47(7-8), 1214-1228.4) Kumar, A.; Maheshwari, S.; Sharma, C.; Beri N. Journal of Mechanical Engineering 2009, 60(5-6), 298-304.5) K.P. Rajurkar, Handbook of Design Manufacturing and Automation Chapter 13: NontraditionalManufacturing Processes, Wiley, USA, 1994.6) Kansal, H.K.; Singh, S.; Kumar, P. Journal of Materials Processing Technology 2007, 184, 32-41.7) Kumar, A.; Maheshwari, S.; Sharma, C.; Beri N. Proc. of. Int. Conf. on Advances in MechanicalEngineering, Trivandrum, Kerala, India, Dec, 2010, pp. 51-53. (Chapter No. 6)8) W.S. Zhao, Q.G. Meng and Z.L. Wang,. Journal of Materials Processing Technology, vol. 129(1-3), 30-33.2002.9) S. Singh, S. Maheshwari and P.C. Pandey, Journal of Mechanical Engineering, vol. 57, no.1, pp.13-33,2006.10) Kumar, A.; Maheshwari, S.; Sharma, C.; Beri N. Materials and Manufacturing processes, (In press 2010).11) Ho, K.H.; Newman, S.T. International Journal of Machine Tools and Manufacture 2003, 43, 1287-1300.12) Erden, A., and Bilgin, S., Proceedings of the 21 th International Machine Tool Design and ResearchConference, Macmillan, London, 1980, pp. 345-350.13) Jeswani, M.L. Wear, 1981, 70(2), 133-139.14) Mohri, N., Saito, N., Higashi, M.A. Annals CIRP, 1991, 40(1), 207-210.15) Kumar, A., Maheshwari, S., Sharma, C. Advanced Materials Research, Vol. 410 (2012) pp 236-239485