Abrasive Water Jet Machining Of Carbon Epoxy Composite

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Defence Science Journal, Vol. 66, No. 5, September 2016, pp. 522-528, DOI : 10.14429/dsj.66.9501 2016, DESIDOCAbrasive Water Jet Machining of Carbon Epoxy CompositeAjit Dhanawade#, Shailendra Kumar#,*, and R.V. Kalmekar!#Department of Mechanical Engineering, S.V. National Institute of Technology, Surat - 395 007, India!Naval Materials Research Laboratory, Ambernath, Mumbai - 421 506, India*E-mail: skbudhwar@med.svnit.ac.inAbstractAn experimental study of abrasive water jet machining of carbon epoxy composite is presented. Processparameters namely hydraulic pressure, traverse rate, stand-off distance and abrasive mass flow rate are consideredfor this study. Taguchi approach and analysis of variance are used to study the influence of process parameterson response characteristics including surface roughness and kerf taper. It is found that hydraulic pressure andtraverse rate are most significant parameters to control surface roughness and kerf taper. Microscopic featuresof the machined surfaces are evaluated using scanning electron microscope and compared with sample surfacesmachined by conventional method using diamond edge cutter.A set of process parameters is optimised to achieveminimum surface roughness and kerf taper. Confirmation tests are performed to verify the optimum set of processparameters. Defects like delamination, fibre pull out and abrasive embedment are also studied using scanningelectron microscope.Keywords: Abrasive water jet machining, carbon epoxy composite, process parameters, surface roughness, kerftaper, delamination1.INTRODUCTIONCarbon epoxy composite is an extremely strong andlight weight fibre-reinforced polymer (FRP) which containscarbon fibres. It is used in several technological applicationsincluding marine, aerospace, sports goods, transportation,infrastructure, etc. It is used to make vessels, corvette,composite masts, propellers, propulsion shafts, etc. in marineindustries. Applications of carbon epoxy composite in marinestructures offer the potential for significant weight, cost, andsignature reductions. But its machining behaviour differs inmany aspects from metal machining due to its anisotropicand heterogeneous nature1.Although conventional machiningof carbon epoxy composite is possible using diamond edgecutter, but it results in excessive tool wear, high stresses andtemperature, delamination, fibre pull outs, impermissible kerfproperties, etc2. Abrasive water jet machining (AWJM) processis one of the most recent developed non-traditional machiningprocesses used for machining of composite materials. In AWJMprocess, machining of work piece material takes place whena high speed water jet mixed with abrasives impinges on it.This process is suitable for heat sensitive materials especiallycomposites because it produces almost no heat and chatterwith low stresses3. But high surface roughness, improperkerf geometry (Fig. 1) and abrasive embedment are notabledifficulties in AWJM.Some researchers have studied AWJM of compositesmainly glass epoxy composite, graphite epoxy composite,natural fibre composite, and ceramic matrix composite throughReceived : 09 December 2015, Revised : 19 April 2016Accepted : 21 April 2016, Online published : 30 September 2016522kerf properties such as surface roughness and kerf taper 4-12 anddelamination13,14.An experimental study of AWJM of carbon epoxycomposite to improve kerf properties is presented. The AWJMprocess is characterised by numerous process parameters butstand-off distance, jet pressure, traverse rate and abrasive massflow rate are major process variables3. Therefore, in the presentwork these four parameters are considered.2.EXPERIMENTAL WORKA flying arm AWJ machine is used for the present study.The machine is equipped with automatic abrasive feedingsystem along with abrasive metering system. The maximumpump pressure of machine is 260 MPa. The positional andrepeat accuracy of the machine is 0.04 mm. As the objectiveof present work is to minimise surface roughness and kerftaper, good quality of garnet abrasives of mesh size # 80were used for the experiments. Reverse osmosis (RO) waterpurifier tank is used to supply pure inlet water for machining.The mechanical properties of work piece material are givenin Table 1. The thickness of work piece material used in thepresent work is 22 mm.3.Experimental DesignThe levels of machining parameters namely stand-offdistance, jet pressure, traverse rate and abrasive mass flow rateare selected on the basis of literature review5,9 and availableAWJM setup. These levels are given in Table 2. Othermachining parameters namely impact angle, nozzle diameter,orifice diameter, and focusing length were kept constant as900, 0.76 mm, 0.25 mm, and 70 mm, respectively. Taguchi’s

Dhanawade, et al.: Abrasive Water Jet Machining of Carbon Epoxy CompositeTable 2. Machining parameters and their levelsMachining parameterLevel 1 Level 2 Level 3Level 411.522.5B: Jet pressure (P) (MPa)200220240260C: Traverse rate (TR)(mm/min)50100150200D: Abrasive mass flowrate (AMFR) (g/min)600700800900A: Stand-off distance(SOD) (mm)Table 3.Expt.2.3.Mechanical properties of carbon epoxy compositematerialSOD1.0SurfaceAMFR roughnessKerf lue5.2001008003.0420.950Volume fraction of carbon fibre by weight60 %6.220509002.9120.6331.5 g cm-37.2402006003.0830.75030 GPa8.2601507002.9730.733DensityShear modulus - in-plane1.5Shear strength - in-plane90 MPa9.2001509003.4711.133Compressive strength570 MPa10.2202008003.2891.033Young’s modulus2.070 GPa11.240507002.5150.4660.8 %12.2601006002.6290.500Ultimate shear strain - in-plane1.8 %13.2002007003.9981.350Ultimate tensile strain - longitudinal0.85 %14.2201506003.2391.033Ultimate tensile strain - transverse0.85 %15.2401009002.7630.833260508002.3920.433Ultimate compressive strainorthogonal array (L16) is used to plan the experiments. Total16 work piece samples were machined using AWJM set-up.Thereafter surface roughness and kerf taper of machinedsamples were measured by using surface roughness tester(Model -Mitutoyo SJ-210) and vision measurement system(Model- Sipcon SDM-TRZ 5300) respectively. The layout ofL16 orthogonal array along with measured values of surfaceroughness and kerf taper are depicted in Table 3.4.Control factors1.Figure 1. Schematic illustration of kerf geometry.Table 1.L16 orthogonal array with response measurementsINFLUENCE OF PROCESS PARAMETERS ONSURFACE ROUGHNESS AND KERF TAPERInfluence of process parameters on surface roughnessand kerf taper is investigated through analysis of variance(ANOVA) using Minitab 16 software. It is a widely usedstatistical technique to investigate and model the relationshipbetween response and control factors. Table 4 shows theANOVA for surface roughness and kerf taper. The analysis iscarried out at 95 per cent confidence level.As depicted in Table 4, the percentage contribution ofpressure and traverse rate is around 52.4 and 38.7, respectively.Therefore, pressure is the most significant factor followed bytraverse rate. Contributions of other two parameters namelystand-off distance (SOD) and abrasive mass flow rate (AMFR)are insignificant for the response characteristics.The graphs of responses (i.e. surface roughness and kerf2.516.Table 4. ANOVA table for surface roughness and kerf taperSourceDOFSurface roughnessKerf 5.12 0.02652.7919 16.52 0.02352.4559TR310.59 0.04236.9592 12.19 or33.49153.1753Total15100100DOF- degree of freedom; F- F ratio; P- P value; %P- percentage contributionof respective parameterstaper) vs significant parameters (i.e. pressure and traverse rate)generated by ANOVA are shown in Fig. 2 and Fig. 3.Figure 2 shows that the surface roughness decreases withincrease in pressure and decrease in traverse rate. The reason isthat the increase in pressure causes increase in particle velocityat nozzle exit and particle fragmentation inside the nozzle.This fragmentation reduces the size of impacting particle. Alsoan increase in pump pressure increases AWJ kinetic energy.This increased kinetic energy helps in machining the surfacewith minimum roughness. With the increase in traverse rate,523

Def. SCI. J., Vol. 66, No. 5, september 2016Figure 2. Effect of pressure and traverse rate on surface roughness.Figure 3. Effect of pressure and traverse rate on kerf taper.there is less overlapping of machining action and also reducednumber of abrasive particles to impinge on surface. It results inincrease in surface roughness.From Fig. 3, it is evident that the kerf taper decreaseswith increase in pressure and decrease in traverse rate. Theincreased kinetic energy of jet on increasing pressure cuts thematerial at bottom region of work piece. This results in surfacewith minimum taper. The reason of influence of traverse rateon kerf taper is that high traverse rate causes less overlappingof machining action and less abrasive particles to impinge onthe work piece surface which reduces the cutting ability of jet.It results in increase in kerf taper angle.Critical observation of machined surfaces reveal threedistinct regions – top (damaged), middle (smooth), and bottom(rough). Two workpiece samples are machined by using thefollowing combination of process parameters (i) SOD - 2.0 mm, P - 260 MPa, TR – 50 mm/min, AMFR –800 g/min(ii) SOD - 2.0 mm, P – 200 MPa, TR – 200 mm/min, AMFR– 800 g/minThese machined samples are examined using scanningelectron microscope (SEM) to evaluate the microscopicfeatures. It is observed that fibres are cut smoothly, withoutfracture and pull-off, and negligible abrasives embedment inthe first sample as shown in Fig. 4(a). However, fibres are524fractured and pulled off that resulted in rough surface in thesecond sample as depicted in Fig. 4(a). This is because the jetwith low pressure tends to deflect upward after impinging onthe workpiece and hence results in fibre fracture with roughsurface. Also high traverse rate decreases number of abrasiveparticles impinging on the surface. In the middle region of bothsamples smooth surface is observed. However fibre fractures areobserved with fibres pull off with some abrasives embedmentin the second sample. The low pressure decreases the kineticenergy of jet and reduces its capability of material removal. Asa result the surface roughness increases with decrease in jetpressure. Thereafter the surface of bottom region deterioratesdue to the jet energy loss during particle impact and jet-materialinteraction. It is observed that the surface is more deterioratedin the second sample as compared to the first sample. This isdue to low kinetic energy of jet in second sample.For comparison with samples machined by conventionalmethods, two samples of carbon epoxy composite are machinedby diamond edge cutter. Figure 4(b) shows machined samplesurfaces. On measuring, it is found that the surface roughness(Ra value) of these surfaces varies from 4.862 to 6.632 whichis comparatively higher than that of sample surfaces machinedby AWJM. Also it is observed that fibres are fractured withmatrix pull out in machining with diamond edge cutter.Damages are observed on entire machined surface of samples

Dhanawade, et al.: Abrasive Water Jet Machining of Carbon Epoxy Composite(a)(b)Figure 4. Machined surfaces of (a) sample 1 and sample 2, (b) sample 3 and sample 4 (Horizontal surface at 1000x).in case of diamond edge cutter. However in AWJM, damagesoccur only at the bottom region of machined surface. Defectsproduced on machined surfaces are mostly in the form ofstreaks. These streaks characterise tool trajectory and twistedareas on machined surface. This is due to the cutting face ofdiamond edge cutter. Tool trajectory plays vital role in courseof defects. Also due to matrix and fibre pull out, possiblities ofdelamination are more in machining with diamond edge cutter.Similar results have been observed by Haddad10, et al.Figure 5 shows top and bottom kerf quality of AWJmachined samples. Kerf quality varies due to loss in kineticenergy of AWJ. High pressure jet cuts the material throughlaminates with high kinetic energy but during erosion ofmaterial, it also damages surface. This initial damage regionspreads on the top edge. Further as machining advances, jetloses its kinetic energy. The loss in kinetic energy results inirregularity of kerf edge at bottom region. Meanwhile roundingof abrasives takes place which reduces cutting ability of jet. Inaddition, striation occurs at bottom region due to jet with lesskinetic energy which finds the path of least resistance.A set of process parameters is optimised by using ANOVAto minimise surface roughness and kerf taper.(i) Optimum levels for minimum surface roughness:SOD-2.0 mm, P-260 MPa, TR-50 mm/min, AMFR 800 g/min(ii) Optimum levels for minimum kerf taper:Figure 5. Top and bottom kerf edges.SOD-1.0 mm, P-260 MPa, TR-50 mm/min, AMFR-600g/minThe confirmation tests on four samples are carried outusing these optimum levels of process parameters. The resultsof the confirmation tests are given in Table 5. The surfaceroughness and kerf taper of machined samples are minimal onsetting optimum values of process parameters.5. DEFECTS IN MACHINED SAMPLESAll the machined samples were observed using SEMto study the defects occurred on the surfaces. Defects likedelamination, fibre pull out and abrasive embedment areobserved as shown in Figs. 6 (a) and 6 (b). Delamination is amode of failure for laminated composite materials, in which,repeated cyclic stresses, impact etc. can cause layers to separate525

Def. SCI. J., Vol. 66, No. 5, september 2016Table 5. Confirmation tests of optimum levelsSampleIn few samples this defect is also observed at top region ofwork piece. It is due to deflection of jet when it impinges onwork piece. It causes lateral flow of jet which penetrates intoweak interface between the composite layers and hence resultsin delamination. The maximum delamination at top region islimited within the region damaged by jet deflection. Shearingaction of the abrasive particles plays vital role in erosionmechanism. Therefore delamination is prominent in machinedsamples cut with low AMFR and high traverse rate as shown inFig. 6(a). This is because of easy penetration of jet into epoxyresin, but it gets deflected while penetrating into fibre andresin interface. If the interfacial bond is weak, the oncomingcrack can experience interface debonding, followed by crackdeflection, crack bridging, fiber breakage, and finally fiberOptimum cutting parametersSurface roughness (Ra)Kerf taper ith significant loss of mechanical toughness. It is observedthat delamination generally occurs at the bottom region ofmachined sample, because the layers at the bottom of the workpiece deform elastically and then plastically by jet pressure.(a)(b)Figure 6. (a) Delamination in machined samples and (b) Fibre pull out and abrasive embedment.526

Dhanawade, et al.: Abrasive Water Jet Machining of Carbon Epoxy Compositepull-out. During AWJM, high directional impact of abrasiveparticles on workpiece results in fibres pull out as shown inFig. 6(b). Primary function of abrasives is to cut the materialwith erosion. But increase in AMFR increases number ofabrasive particles impinging on the work piece surface. Theexcessive abrasives penetrate into the layers of materialwhich result in abrasive embedment. Abrasive embedment ismainly observed at high AMFR and low SOD. At high AMFR,abrasives collide with each other and fail to cut the material.These stray abrasive particles penetrate into the machinedsurface. At low SOD, abrasives cannot accelerate with highspeed water jet which causes abrasives to impinge on materialwith low kinetic energy. These abrasives penetrate into thelayers and machined surface.6. CONCLUSIONSPlausible trends of surface roughness and kerf taper withthe variation in process parameters have been analysed in thepresent work. The following conclusions are drawn from thepresent work.(i) Hydraulic pressure and traverse rate are most significantparameters to control surface roughness and kerf taper.(ii) Surface roughness and kerf taper decrease with increasein hydraulic pressure and decrease in traverse rate.(iii) Delamination defect is prominent in machined samplescut with low abrasive mass flow rate and high traverserate. Fibres pull out occurs at low pressure and high standoff distance. Abrasive embedment is mainly observed athigh abrasive mass flow rate and low stand-off distance.A set of process parameters is optimised by using ANOVAto minimise surface roughness and kerf taper. Confirmationtests show that the surface roughness and kerf taper ofmachined samples are minimal on setting optimum values ofprocess parameters.REFERENCES1. Azmir, M. & Ahsan, A. Investigation on glass/epoxycomposite surfaces machined by abrasive water jetmachining. J. Mater. Proces. Technol., 2008, 198, 122–128.doi:10.1016/j.jmatprotec.2007.07.0142. Teti R. Machining of composite materials. CIRP Annalsmanufacturing Technol., 2002, 51(2), 611–634.doi: 10.1016/S0007-8506(07)61703-X3. Trivedi, P.; Dhanawade, A. & Kumar, S An experimentalinvestigation on cutting performance of abrasive waterjet machining of austenite steel (AISI 316L). Adv. Mater.Processing Technol., 2016, 1, 263-274.doi: 10.1080/2374068X.2015.1128176.4. Ramulu, M. & Arola, D. The influence of abrasive waterjetcutting conditions on the surface quality of graphite/epoxy laminates. Int. J. Mach. Tools Manufacture,1994,343, 295–313. doi:10.1016/0890-6955(94)90001-95. Arola, D. & Ramulu, M. A study of kerf characteristics inabrasive water jet machining of graphite/epoxy composite.J. Eng. Mater. Technol.,1996, 1182, 256-265.doi: 10.1115/1.28048976. Wang, J. Abrasive Waterjet machining of polymer matrixcomposites - cutting performance. erosive processand predictive models. Int. J. Adv. ManufacturingTechnol.,1999, 1510, 757–768.doi: 10.1007/s0017000501297. Wang, J. & Liu, H. Profile cutting on alumina ceramicsby abrasive waterjet Part 1 : experimental investigation.Proc. Inst. Mech. Eng., 2006, 2205, 703-714.doi: 10.1243/09544062JMES207A8. Azmir, M.; Ahsan, A.; Rahmah, A. & Islamic, I.Investigation on abrasive waterjet machining of kevlarreinforced phenolic composite using taguchi approach.In the Proceedings of the International Conference onMechanical Engineering 2007, Dhaka, Bangladesh, 2007.9. Azmir, M. & Ahsan, A. A study of abrasive water jetmachining process on glass/epoxy composite laminate.J. Mater. Proces. Technol., 2009, 209, . Haddad, M.; Zituone, R.; Bougherara, H.; Eyma, F.& Castanie, B. Study of trimming damages of CFRPstructures in function of the machining processes andtheir impact on the mechanical behavior. Composites PtB, 2014, 57, 136–143.doi:10.1016/j.compositesb.2013.09.05111. Hussein, M. A.; Asif, I. & Majid, H. Numerical optimizationof hole making in GFRP composite using abrasive waterjet machining process. J. Chinese Inst. Engineers, 2015,38(1), 66–76.doi:10.1080/02533839.2014.95324012. Jani, S.; Senthilkumar, A.; Khan, M. & Uthayakumar, M.Machinablity of hybrid natural fibre composite with andwithout filler as reinforcement. Mater. ManufacturingProces., 2015.doi: 10.1080/10426914.2015.1117633.13. Miron, A.V.; Balc, N.; Popan, A.; Stefana, C.& Bere, P.Studies on water jet cutting of 2d parts made from carbonfibre composite materials. Academic J. ManufacturingEng., 2013, 112, 87–92.14. Shanmugam, D.K.; Nguyen, T. & Wang, J. A studyof delamination on graphite/epoxy composites inabrasive water jet machining. Compos. Part A: Appl. Sc.Manufacturing, 2008, 396, NOWLEDGEMENTAuthors acknowledge the financial support being providedby Naval Research Board (NRB), Govt. of India, for the project‘Investig

Abrasive water jet machining (AWJM) process is one of the most recent developed non-traditional machining processes used for machining of composite materials. In AWJM process, machining of work piece material takes place when a high speed water jet mixed with abrasives impinges on it. This process is suitable for heat sensitive materials especially composites because it produces almost no heat .

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