A Study of Hole Drilling on Stainless Steel AISI 431 by EDM Using ...

2011 International Transaction Journal <strong>of</strong> Engineering, Management, & Applied Sciences & Technologies.International Transaction Journal <strong>of</strong> Engineering,Management, & Applied Sciences & Technologieshttp://www.TuEngr.com,http://go.to/ResearchA <strong>Study</strong> <strong>of</strong> <strong>Hole</strong> <strong>Drilling</strong> on Stainless Steel AISI 431 by EDM UsingBrass Tube ElectrodePichai Janmanee a , and Apiwat Muttamara a*a Department <strong>of</strong> Industrial Engineering Faculty <strong>of</strong> Engineering, Thammasat University, THAILANDA R T I C L E I N F OArticle history:Received 23 August 2011Received in revised form23 September 2011Accepted 27 September 2011Available online27 September 2011Keywords:EDM, AISI 431,Electrode,Brass,TaperA B S T R A C TWhen a depth hole is drilled by EDM, taper is occurredwhich is not desired in the process. This research was focused oninfluence <strong>of</strong> EDM parameters on material removal rate (MRR),electrode wear rate (EWR) and tapered hole <strong>of</strong> martensiticstainless steel AISI 431. The considered factors consist <strong>of</strong>electrical current, on-time, duty factor, water pressure and servorate. The experimental results reveal that MRR increases whenincreasing <strong>of</strong> servo rate. The taper <strong>of</strong> hole increases withincreasing <strong>of</strong> electrical current and servo rate. However, it isreverse proportion to water pressure and duty factor.2011 International Transaction Journal <strong>of</strong> Engineering, Management, &Applied Sciences & Technologies.1 IntroductionNowadays, stainless steel AISI 431 is a popular material used in many industries such aswater pump, kitchenware, and fittings manufacturing industries(Jeong and Min, 2007).Because <strong>of</strong> its durability to environment. However, as drilling a hole on stainless steel isdifficult due to its properties. Therefore, various meso or micro machining methods have beenintroduced, such as machining, ultrasonic, electrochemical, laser, electrical dischargemachining. Especially an electrical discharge machining (EDM) is one <strong>of</strong> non-contact thermalprocess, which has advantages such as high-precision machining <strong>of</strong> conductive materials and*Corresponding author (A. Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:mapiwat@engr.tu.ac.th. 2011. International Transaction Journal <strong>of</strong> Engineering,Management, & Applied Sciences & Technologies. Volume 2 No.4. ISSN 2228-9860.eISSN 1906-9642. Online Available at http://TuEngr.com/V02/471-481.pdf471

insulating materials regardless <strong>of</strong> material hardness, (Muttamara et al, 2009&2010). However,the important type <strong>of</strong> defect from hole drilling during EDM process is hole taper and holeaccuracy (Ali et al.2009). Therefore, in order to improve hole quality, Sharma et al.(2002) andBilgi et al.(2007) investigated optimum values <strong>of</strong> the process parameters experimentally suchas voltage, feed rate, pulse on time, duty cycle, and the length <strong>of</strong> un–insulate tool.Figure 1: Characteristic <strong>of</strong> taper on EDMIn the EDM sparking hole drilling process, the viscous resistance in the narrow dischargegap causes difficulty in the removal <strong>of</strong> debris and bubbles from the working area, abnormaldischarges are occurred and resulting in extensive electrode wear (Yu et al. 2009). Moreover,the debris moved by pressure flow <strong>of</strong> dielectric fluid make taper on the workpiece. The holetaper <strong>of</strong> workpiece from EDM process, which as shows in Figure 1, can be calculated byequation (1). tan(1)WhereD is hole entrances,d is hole exits, andL is hole length.This research focuses on influence <strong>of</strong> machining variables affecting material removal rate(MRR), electrode wear rate (EWR), and taper on martensitic stainless steel AISI 431.2 Experimental ProcedureThe experiments were carried out on 35 mm <strong>of</strong> hole depth <strong>of</strong> martensitic stainless steelAISI 431with ZNC-EDM model JM325DZ manufactured by Joemars company, as shown inFigure2(a). The EDM was carried out on meso-scale machining with a brass tube electrode as472 Pichai Janmanee, and Apiwat Muttamara

outside diameter <strong>of</strong> 1 mm, inner hole diameter <strong>of</strong> 0.3 mm for flushing by dielectric fluid toremove wear debris and heat ventilation size as shown in Figure 2(b). Principle <strong>of</strong> tubeelectrode drilling is shown in Figure 2(c). The experiments were carried out in the de-ionised,because <strong>of</strong> the advantage <strong>of</strong> material removal rate (Diver et al. 2004). The chemicalcompositions and essential physical properties are shown in Table 1 and Table 2, respectively.Table 3 shows the physical properties <strong>of</strong> an electrode. The experiment conditions arecontained in Table 4.(a) EDM super drill model JM325DZ(b) Brass (Cu-Zn40) tube electrode(c) ZNC-EDM drilling processFigure 2: Experimental EDM .*Corresponding author (A. Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:mapiwat@engr.tu.ac.th. 2011. International Transaction Journal <strong>of</strong> Engineering,Management, & Applied Sciences & Technologies. Volume 2 No.4. ISSN 2228-9860.eISSN 1906-9642. Online Available at http://TuEngr.com/V02/471-481.pdf473

Table 1: Chemical compositions <strong>of</strong> stainless steel AISI 431.Element C Si Mn Cr Ni S PWeight (%) 0.17 0.6 1.0 17.0 2.0 0.03 0.04Table 2: Essential physical properties <strong>of</strong> stainless steel AISI 431.PropertiesValueCondition Temp.( o C)Density(x1000 Kg/m 3 ) 7.8 25Elastic modulus(GPa) 200 25Tensile strength (MPa) 965 -Thermal conductivity(W/m – K) 20.2 100Electrical resistivity(10 -9 Ω – m ) 720 25Table 3: Physical properties <strong>of</strong> brass tube electrode.Properties Cu-Zn (60-40)Melting point ( o C) 910Density (g/cm 3 ) 10.98 g / cm 3Electrical conductivity(I.A.C.S% at 20 o C) 78~85Hardness(HRB) 93Elastic modulus (GPa) 648Table 4: Experimental conditions.ParametersValuesPolarity (Electrode) +Current (A) 1-9On-time (μs) 10,30,50,90Duty factor (%) 10-90Servo rate (mm/sec) 2-10Water pressure (Kg/cm 2 ) 20-60Spindle speed (rpm) 100Dielectric fluidDe-ionised water3 Results and DiscussionAs for the experiments were conducted under five process factors such as ; electricalcurrent, on-time, duty factor, water pressure and servo rate, the data were analyzed as follows:474 Pichai Janmanee, and Apiwat Muttamara

3.1 Analysis <strong>of</strong> Water PressureThe experiments were conducted by varying the water pressure 20, 30, 40, 60 kg/cm 2 andfixing parameter <strong>of</strong> current at 9 A, on-time at 10 μs, duty factor at 75 %, and servo rate at 2 mm/sec. High water pressure has influence to cutting process makes gain <strong>of</strong> the drilling speed. Itincreases electrode wearing ratio but reduces taper <strong>of</strong> drilling wall as shown in Figure3(a-c).Because high water pressure make debris dispose out from clearance space between aworkpiece and electrode surfaces. Consequently, complete spark <strong>of</strong>ten occurred and thus thematerial removal rate increased (Diver et al. 2004).(a) Effect <strong>of</strong> water pressure to MRR(b) Effect <strong>of</strong> water pressure to EWR(c) Effect <strong>of</strong> water pressure to taperFigure 3: Variations <strong>of</strong> water pressure with meso-hole results.3.2 Analysis <strong>of</strong> currentIn this experiment, we consider <strong>of</strong> each parameter by varying current 1, 2, 3, 5, 7, 9A andfixing <strong>of</strong> parameter <strong>of</strong> on-time at 10μs, duty factor at 75%, servo rate at 2 mm/sec, and waterpressure at 40kg/cm 2 . As the results in Figure 4(a), it indicates that the increase <strong>of</strong> materialremoval rate resulted from the raise in current. High current increases material removal rateratio and electrode wear ratio as shown in Figure 4(b) (Han et al. 2004). From Figure 4(c),*Corresponding author (A. Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:mapiwat@engr.tu.ac.th. 2011. International Transaction Journal <strong>of</strong> Engineering,Management, & Applied Sciences & Technologies. Volume 2 No.4. ISSN 2228-9860.eISSN 1906-9642. Online Available at http://TuEngr.com/V02/471-481.pdf475

taper <strong>of</strong> drilled hole is increased because the discharges produce thermal energy according to anelectrical current (Fukuzawa et al. 2004). As estimation <strong>of</strong> the current increasing while thecross section is still constant, it makes gain <strong>of</strong> the density <strong>of</strong> current per cross section area (Senand Shan, 2005), (Guitrau,1997).(a) Effect <strong>of</strong> current to MRR(b)Effect <strong>of</strong> current to EWR(c) Effect <strong>of</strong> current to taperFigure 4: Variations <strong>of</strong> current with meso-hole results.3.3 Analysis <strong>of</strong> servo rateIn this experiment, we consider factor <strong>of</strong> servo rate 2, 4, 6, 8, 10 mm/sec and fix parameter<strong>of</strong> current 9 A, on-time at 10 μs, duty factor at 75 %, and water pressure at 40 kg/cm 2 . Asshown in Figure 5(a), it was found that the increasing <strong>of</strong> servo rate lead to decreasing <strong>of</strong> MRRbecause the spark requires an appropriate gap. If servo rate is set up over the required value,narrow gap will be occurred thus the spark is incomplete or short circuit (Choi and Kim, 1998),(Han et al. 2004). When servo rate increases, electrode wear and taper increases as shown inFigure 5(b-c). It can be explained that EDM sparking on servo rate in the narrow discharge gapchanges the contact angle <strong>of</strong> hole’s wall and the edge <strong>of</strong> electrode, observed in Figure 5(c).476 Pichai Janmanee, and Apiwat Muttamara

Figure 5(d) shows the phenomena <strong>of</strong> EDM drilling on shallow and deep holes (Yu et al. 2009).3.4 Analysis <strong>of</strong> Duty Factor and On­TimeThe duty factor, which means the ratio between pulse duration and pulse cycle time exertsan important role on the performance <strong>of</strong> EDM as shown in Figure6 (a). In this experiment, weconsideration <strong>of</strong> each parameters by varying duty factor 10, 15, 20, 35, 45, 60, 75, 90 %, ontime 10, 30, 50, 90 μs, and fixing parameters <strong>of</strong> current at 9 A, servo rate at 2 mm/sec, and waterpressure at 40 kg/cm 2 , respectively. As can be seen in Figure6 (b-c), the results were found thatthe each on-time was suitable for only a specific duty factor. MRR increases with increasing <strong>of</strong>duty factor <strong>of</strong> each on-time. However, increasing <strong>of</strong> duty factor leads to decreasing <strong>of</strong> EWR andtaper. Moreover, if increasing <strong>of</strong> on-time less than 30 µs, it still affects to MRR increases. At 75% <strong>of</strong> duty factor for on-time 30 and 50 µs, they give same values <strong>of</strong> MRR. However, theseparameters results in low EWR and taper.(a) Effect <strong>of</strong> servo rate with MRR(b) Effect <strong>of</strong> servo rate with EWR(c) Effect <strong>of</strong> servo rate with taper(d) Edge wear influence to high servo rateFigure 5: Variations <strong>of</strong> servo rate with meso-hole results.*Corresponding author (A. Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:mapiwat@engr.tu.ac.th. 2011. International Transaction Journal <strong>of</strong> Engineering,Management, & Applied Sciences & Technologies. Volume 2 No.4. ISSN 2228-9860.eISSN 1906-9642. Online Available at http://TuEngr.com/V02/471-481.pdf477

(a) Relations <strong>of</strong> duty factor and cycle time(b) Effect <strong>of</strong> duty factor to MRR(c) Effect <strong>of</strong> duty factor to EWR(d) Effect <strong>of</strong> duty factor to taperFigure 6: Variations <strong>of</strong> duty factor with meso-hole results.478 Pichai Janmanee, and Apiwat Muttamara

Figure 7 shows impressions <strong>of</strong> the result from the experiment test with current at 9A,on-time at 10μs, duty factor at 75%, servo rate at 2 mm/sec, and water pressure at 40 kg/cm 2 ,respectively. It shows the feature <strong>of</strong> taper could be achieved. Diameter at electrode entry wasbetween 1.08 mm and 0.97 mm as shown in Figure 7(a). Figure 7(b) shows result meso-holemachined exit. Figure 8 shows an image <strong>of</strong> a section meso-hole machined using the samecondition.(a) <strong>Hole</strong> entrance(b) <strong>Hole</strong> exitFigure 7: Characteristic <strong>of</strong> meso-hole and electrode results.Figure 8: SEM image <strong>of</strong> section meso-hole.4 ConclusionAs the results <strong>of</strong> the material removal rate, electrode wear, taper in the drill hole meso-scaleby brass tube electrode, it can conclude that:1. The MRR is lower when increasing <strong>of</strong> servo rate.2. The taper <strong>of</strong> hole increases with increasing <strong>of</strong> electrical current and servo rate.*Corresponding author (A. Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:mapiwat@engr.tu.ac.th. 2011. International Transaction Journal <strong>of</strong> Engineering,Management, & Applied Sciences & Technologies. Volume 2 No.4. ISSN 2228-9860.eISSN 1906-9642. Online Available at http://TuEngr.com/V02/471-481.pdf479

However, it is reverse proportion to water pressure and duty factor.5 AcknowledgementThis work was supported by the National Research University Project <strong>of</strong> Thailand Office<strong>of</strong> Higher Education Commission and the National Research Council <strong>of</strong> Thailand (NRCT).6 ReferencesAli S., Hinduja S., Atkinson J., Pandya M. (2009). Shaped tube electrochemical drilling <strong>of</strong> goodquality holes. CIRP Annals - Manufacturing Technology , 58, 185-188.Bilgi D.S., Jain V.K., Shekhar R., Kulkarni A. (2007). <strong>Hole</strong> quality and inter-electrode gapdynamics during pulse current electrochemical deep hole drilling. International Journal<strong>of</strong> Advanced Manufacturing Technology, 34, 79-95.Choi I-H.,Kim J-D. (1998). A study <strong>of</strong> the characteristics <strong>of</strong> the electrochemical deburring <strong>of</strong> agovernor-shaft cross hole. Journal <strong>of</strong> Material Processing Technology, 75, 198-203.Diver C., Atkinson J., Helml H.J., Li L. (2004). Micro-EDM drilling <strong>of</strong> tapered hole forindustrial applications. Journal <strong>of</strong> Material Processing Technology, 149, 296-303.Fukuzawa Y., Mohri N., Tani T. and Muttamara A. (2004). Electrical discharge machiningproperties <strong>of</strong> noble crystals. Journal <strong>of</strong> Materials Processing Technology, 149(1-3), 393-397.Guitrau E.B. (1997). The EDM Handbook. Handser Gardner publication Cincinnati, 19-54.Han F., Wachi S., Kunieda M. (2004). Improvement <strong>of</strong> machining characteristics <strong>of</strong> micro-EDM using transistor type isopulse generator and servo feed control. PrecisionEngineering, 28, 378–385.Jeong Y. H., Min B. K. (2007). Geometry prediction <strong>of</strong> EDM-drilled holes and tool electrodeshapes <strong>of</strong> micro-EDM process using simulation. International Journal <strong>of</strong> Machine Tooland Manufacture , 47, 187-1826.Muttamara A., Fukuzawa Y., Mohri N., and Tani T. (2009). Effect <strong>of</strong> electrode Materials onEDM <strong>of</strong> Alumina. Journal <strong>of</strong> Materials Processing Technology, 209, 2545-2552.Muttamara A., Janmanee P., and Fukuzawa Y.(2010). A <strong>Study</strong> <strong>of</strong> Micro–EDM on SiliconNitride Using Electrode Materials. International Transaction Journal <strong>of</strong> Engineering,Management, & Applied Sciences & Technologies, 1(1), 1-7.Rajasekhar A., Madhusudhan Reddy G., Mohandas T. (2009). V.S.R. Murti. Influence <strong>of</strong>austenitizing temperature on microstructure and mechanical properties <strong>of</strong> AISI 431martensitic stainless steel electron beam welds. Materials and Design, 30, 1612-1624.480 Pichai Janmanee, and Apiwat Muttamara

Sen M., Shan H.S.(2005). A review <strong>of</strong> electrochemical macro- to micro-hole drilling processes.International Journal <strong>of</strong> Machine Tool and Manufacture,45, 137-152.Sharma S., Jain V.K., Shekhar R. (2002). Electrochemical drilling <strong>of</strong> inconel super alloy withacidified NaCl electrolyte. International Journal <strong>of</strong> Advanced ManufacturingTechnology, 19, 492-500.Yu Z.Y., Zhang Y., Li J., Luan J., Zhao F., Guo D. (2009). High aspect ratio micro-hole drillingaided with ultrasonic vibration and planetary movement <strong>of</strong> electrode by micro-EDM.CIRP Annals - Manufacturing Technology, 58, 213-216.Pichai Janmanee is an Assistant Pr<strong>of</strong>essor in the Department <strong>of</strong> Industrial Engineering at RajamangalaUniversity <strong>of</strong> Technology Krungthep (RMUTK), Bangkok, Thailand. He received a BE in IndustrialEngineering from Rajamangala University <strong>of</strong> Technology and ME in Production Engineering from King’sMongkut University <strong>of</strong> Technology North Bangkok(KMUT’NB). His areas <strong>of</strong> research include machiningand electrical discharge machining <strong>of</strong> hard materials.9Dr.Apiwat Muttamara is an Assistant Pr<strong>of</strong>essor <strong>of</strong> Department <strong>of</strong> Industrial Engineering at ThammasatUniversity. He received his B.Eng. from Kasetsart University and the D.Eng. in Materials Science fromNagaoka University <strong>of</strong> Technology, Japan. His areas <strong>of</strong> research include machining and electrical dischargemachining <strong>of</strong> hard materials.Peer Review: This article has been internationally peer-reviewed and accepted for publicationaccording to the guidelines given at the journal’s website.*Corresponding author (A. Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:mapiwat@engr.tu.ac.th. 2011. International Transaction Journal <strong>of</strong> Engineering,Management, & Applied Sciences & Technologies. Volume 2 No.4. ISSN 2228-9860.eISSN 1906-9642. Online Available at http://TuEngr.com/V02/471-481.pdf481