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1、Proceedings of the ASME 2013 International Mechanical Engineering Congress and ExpositionIMECE2013November 15-21, 2013, San Diego, California, USAIMECE2013-62868FINITE ELEMENT SIMULATION OF CUTTING FORCES IN TURNING Ti6Al4V USING DEFORM 3DSatyanarayana. KosarajuResearch Scholar Mechanical Engineerin

2、g DepartmentNational Institute of Technology Warangal- 506004, Andhra Pradesh, India.Phone: satyanarayana.knitw.ac.in.Venu Gopal. AnneProfessorMechanical Engineering Department National Institute of TechnologyWarangal- 506004, Andhra Pradesh, India.Phone: venunitw.ac.in.Bangaru Babu. PopuriProfessor

3、Mechanical Engineering Department National Institute of TechnologyWarangal- 506004, Andhra Pradesh, India.Phone: bangaru.nitwABSTRACTTitanium alloys are widely used in aerospace industry due to their excellent mechanical properties though they are classified as difficult to machine materials. As the

4、 experimentalerror of 9.94% was observed when these simulation results are compared with that of experimental results.NOMENCLATUREtests are costly and time demanding, metal cutting mingA B C TDT b df h k m m n q t v syield strength hardening modulusstrain rate sensitivity coefficient current tempera

5、ture Temperature dropwidth of work piece depth-of-cutfeed rateheat transfer coefficient shear flow stressthermal softening coefficient Shear friction factor hardening coefficientaverage heat flow across the interface uncut chip thicknesscutting velocity Frictional stress Inclination angle DensityFlo

6、w stressprovides an alternative way for better understanding of machining processes under different cutting conditions. In the present work, a finite element m ing software, DEFORM 3D has been used to simulate the machining of titanium alloy Ti6Al4V to predict the cutting forces. Experiments were co

7、nducted on a precision lathe machine using Ti6Al4V as workpiece material and TiAlN coated inserts as cutting tool. L9 orthogonal array based on design of experiments was used toevaluate the effect of process parameters such as cutting speed and feed with a constant depth of cut 0.25 mm and also the

8、tool geometry such as rake angle on cutting force and temperature. These results were then used for estimation of heat transfer coefficient and shear friction factor constant, which are used as boundary conditions in the process of simulation. Uponsimulations a relative error ofum 9.07% was observed

9、when compared with experimental results. A methodology wasadopted to standardize these constants for a given process by taking average values of shear friction factor and heat transfer coefficient, which are used for further simulations within therange of parameters used during experimentation. Aum1

10、Copyright 2013 by ASMEeEffective strainmeasured using piezoelectric tool post dynamometer (Kistler, 9272).Table 1. Process parameter and their levelseEffective flow straine 0gFs Fx Fy Fz x ys 0 0 Lc TrReference plastic strain rate Shear strainForce along shear plane Axial forceRadial force Cutting f

11、orce Side rake angle Back rake angle Approach angle Shear angle Orthogonal angle length of chipRoom temperatureMelting temperature of workpiece weight of chipChip thickness Width of chipINITIAL DATA SETTINGS FOR M SIMULATIONING ANDDEFORM 3D is a Finite Element Method basedprocess simulation software

12、 designed to analyze variousfor, metal cutting, die stress analysis, rolling and heatTm Wc tc bctreatment processes used by metal forand relatedindustries. It consists of three major components: Pre-processor, Simulator and Post-processor.A. Tool and workpiece materialIn the present work, simulation

13、 studies were carried out using Ti-6Al-4V titanium as the work material. The workpiece isINTRODUCTIONTitanium alloys havereceived considerableinterestrepresented by a curved mwith 60 mm diameter which isrecently due to their wide range of applications in the aerospace,automotive, chemical, and medic

14、al industries. The most common titanium alloy is Ti-6Al-4V, which belongs to the + consistent with the experimental conditions. A segment (15degrees) of the workpiece was only med in order to keep thesize of mesh elements small. The density and the melting point temperature of the material as given

15、by the manufacturer, Mishraalloy group ands for more than 50% of the titanium alloyproduction. Despite the increased usage and production ofDhatu Nigam Limited, India MIDHANI are 4.42 gm/cm3 and 1910 K respectively. The yield strength, evaluated using 2% offset method from the stress strain curve ge

16、nerated by conducting the tensile test experiment, is 900 MPa as shown in Fig 1. Based on these values of the density, melting point temperature and the yield strength, the constants of the Johnson-titanium and its alloys, they are expensive when compared to many other metals because of the complexi

17、ty of the extraction process, difficulty of melting, and problems during fabrication and machining (1). However, most titanium parts are stillmanufacturedbyconventionalmachiningmethods.Furthermore, process parameters are mainly chosen based onCook mfor the Ti-6Al-4V material have been chosen asempir

18、ical knowledge. Experimental tests are costly and time demanding. A better analysis of the finite element method has particularly become the main tool for simulating metal cuttingshown in Table.2 (4-6). The flow stress behavior of workpiecewas m med using Eq. (1), proposed by Johnson-Cook plasticity

19、 (6-8) which describes the flow stress of the material as aprocesses. Finite element ms are widely used for simulatingfunction of strain, strain rate and temperature effects as given below:the chip formation mechanisms, forces generated duringmachining, heat generation in cutting zones, tool-chip in

20、terfacial frictional characteristics and integrity of the machined surfaces (2,3).In this paper, FEM software DEFORM 3D is used to analyze the variation in cutting forces during turning of Ti-6Al-4V with PVD coated Tungsten carbide inserts. 1+ C ln ( e ) 1-( )s = A+ B (1)ewhere A, B, C, n and m are

21、constants depending on material properties, T = current temperature (K), Tr = room temperature(K), Tm= melt temperature (K), e = strain,e = effective plasticEXPERIMENTALSIn the present work, turning experiments have beenstrain rate (1/s), e 0= plastic strain rate (1/s) and s = the flowconducted on t

22、itanium alloy (Ti-6Al-4V) cylindrical bars of diameters 40 mm. Tungsten carbide inserts, coated with Titanium Aluminum Nitrate using PVD technique, along with the tool holder PCLNR 2020 M12 (Tool geometry: approach angle: 950 and inclination angle: -70) were used in the present investigation. Experi

23、ments were conducted using L9 experimental design consisting of 9 sets of data, shown in Table1. The Cutting forces generated during machining werestress (MPa).B. Tool and tool holder set-upThe tool and tool holder geometry can be setup either by selecting the geometry directly from the tool and too

24、l holder libraries or by defining the new tool geometry for the standard nomenclature available. It can also be imported from CAD systems if the tool and tool holder geometry is complex. Further,2Copyright 2013 by ASMEParameterSymbolUnitsValuesCutting velocityvm/min45; 60; 75Feed ratefmm/rev0.25; 0.

25、3; 0.35Depth of cutdmm0.25 (constant)Back rake angleyDegrees-7; -5; -3LubricationDry conditionthe tool material can also be attributed either from the tool libraries or by defining the elastic and plastic properties.Figure 2 shows meshed surfaces of tool and workpiece for turning process.(a)(b)Figur

26、e2.Meshed surfaces: a) Tool b) WorkpieceD. Boundary conditionsIn order to simulate the forces induced using FEM, it is necessary to define the boundary conditions at the tool- workpiece interface which help the user to establish the interaction of the workpiece with the tool. These boundary conditio

27、ns are usually formulated in terms of the interface heat transfer coefficient, convection coefficient and shear friction factor.Figure 1. Stress-strain diagram for Ti-6Al-4VTable 2. Constant parameters for Johnson-Cook material mof Ti-6Al-4Vi. Convection coefficient at work surface and environment (

28、medium of cutting fluid)In the process of turning, the temperature at work surface increases. Due to this, heat transfer takes place between work surface and environment (medium of cutting fluid) in the form of convection. Thus, convection coefficient is an import nputIn the present study, tool geom

29、etry (CNMG) and tool material tungsten carbide (WC) are available in the material library. But the coating material (TiAlN) on the substrate is not available. Therefore, a coating material (TiAlN) corresponding to which the experiments were conducted was developed in the database by defining the ela

30、stic and plastic properties shown in Table.3 (9, 10). Specially designed and manufactured tool holders for conducting the experiments were also not available in the tool holder library. Therefore, new tool holders were developed in the tool holder library by defining side cutting edge angle, back an

31、d side rake angles as shown in Table.3.parameter to qufy the transfer of heat between the worksurface and environment. However, the convection coefficient has not been considered in the present work as the experiments have been carried out in dry condition (i.e. no coolant).ii. Shear friction factor

32、During the process of turning, the secondary shear i.e, the friction is generated between the chip and rake face of the tool which lead to shear of chip. Thus, shear friction is an importantinput parameter to qu of the tool.fy shear friction between chip and rakeC. Mesh generationIn this study, an i

33、ncremental Lagrangian formulation is used as this formulation simulates the process at entry, exit, intermittent and discontinuous chip formation phases (11). Cutting tool is considered as rigid plastic object, which moves at a specified cutting speed by using 30000 elements. TheFormulation to find

34、shear friction factortkm =(2)ft = s sin b cos l(3)obtworkpiece was also med as plastic object (12) whichincludes 40000 elements. The bottom surface of the workpiece is fixed in all directions. A relative fine mesh density is definedFs =(-Fx cos + Fy sin )2 + (Fy cos 0 cos - Fz sin 0)21/2(4)at the ti

35、p of the tool and cutting zone in order to manage the heat transmission between tool and chip (due to friction and plastic deformation) and to obtain fine process output distribution.3Copyright 2013 by ASMEPropertySymbolValueYield strengthA896 MPaHardening modulusB656 MPaStrain rate sensitivity coef

36、ficientC0.128Thermal softening coefficientm0.8Hardening coefficientn0.5Melting temperature of the work materialTm1933 KPlastic strain ratee 01s-1Orthogonal rake angle (0) and inclination angle ()By using the Von Mises criterion 13= cot bo + tan (bo - g o )Tan Tan 0Sin Cos =g(9)Tan Tan Cos Sin coshst

37、an l cos(b - g ) - tanh sin btanhs=0oco(10) t cos gcos g t oo tan b =c (5) t obcosh1 -sin g=cb / cos l(11) t cc oNote: as reported by Stabler, the chip flow angle c is approximately equal to the inclination angle (14)tc bc Lc = Wc(6)s3e ek = =(7)(12) Formulation to find heat transfer coefficient (h)

38、Step 1: Average heat flow across the tool-work interface (12, 14):ge =(8)3q = Fzv(13)where, q is the average heat flow across the interface (W/m2), Fz is cutting force (N), v is cutting velocity (m/s).Table 3. Tool and tool holders4Copyright 2013 by ASMETool (CNMG 120408)B (mm)T (mm)R (mm)H (mm)12.7

39、4.7630.7930.394Coating materialElastic propertiesPlastic propertiesTiAlNYoungs modulus380 GPaThermal conductivity4.63W/m KPoissons ratio0.23Heat capacity565J/kg KThermal expansion6.5 x 10-6Emissivity0.07Tool holder (PCLNR 20X20 M12)Approach angle (s)Side cutting edge angle (x)Back rake angle ( y )Si

40、de rake angle (x )95-5-3-795-5-5-795-5-7-7Step2: Heat transfer coefficientSIMULATION RESULTSSimulations were carried out according to experimental conditions shown in Table.4 using the estimated values of heat transfer coefficient and shear friction factor. Figure.3 hows one of the simulations obtai

41、ned for the experimental conditions with cutting speed, feed, depth of cut and rake angle as 75 m/min,0.25 mm/rev, 0.25 mm and -3 degrees respectively. Mean of cutting forces were considered in the region where the forces are stabilized. The same exercise is repeated for all the other eight experime

42、nts and the corresponding cutting forces were recorded.qDTh =(14)where, his heat transfer coefficient (W/m2oC), and DT is the temperature drop (oC).Table.4 shows the calculated values for heat transfer coefficient and shear friction factor for different cutting speed, feed and the rake angle at cons

43、tant depth of cut.Table 4.Heat transfer coefficients and shear friction factor(c)Figure 3. Predicted cutting forces (a) FX (b) FY (c) FZTable 5. Comparison of Experimental and Simulation results5Copyright 2013 by ASMEExpt. NovfyExperimental resultsSimulation results% Relative errorFX (N)FY (N)FZ (N)

44、FX (N)FY (N)FZ (N)FXFYFZ1450.25-7139105453133984824.326.676.022450.30-5131100415126914543.819.008.593450.35-312590376133844066.026.677.394600.25-510363311113692978.858.694.505600.30-311059278101542998.188.477.026600.35-7148108495136984568.119.267.887750.25-31045525195512638.657.274.568750.30-7122863

45、61111793979.028.149.079750.35-512082327133743439.779.764.66Sl. Nov (m/min)f (mm/rev)y(degrees)Heat transfer coefficient (N/sec- mm/C)Shear friction factor1450.25-781.060.6362450.30-582.920.6213450.35-384.570.6034600.25-586.760.6635600.30-380.170. 6436600.35-784.070.6577750.25-381.570.6018750.30-787.

46、030.6109750.35-585.560.656Average83.70.63COMPARISON OF SIMULATION AND EXPERIMENTAL RESULTSThe experimental and simulated results of cutting forces along with the percentage relative error was shown in Table.5. It can be observed from the table that the error of simulation for the three force compone

47、nts was found to be within3.81 to 9.77 of the experimental results.simulation; provides a simple procedure to implement for simulation.The methodology proposed, established by the results of validation, promotes the simulation for metal cutting experiments and thereby minimizing the cost and time.RE

48、FERENCES1.Corina, Constn., Sorin, Mihai, Croitoru., George,NEW METHODOLOGY FOR SIMULATION AND ITS VALIDATION:It may be observed from the above analysis that, it is essential to conduct experiments to evaluate the heat transfer coefficient and shear friction factor, which are required for the simulat

49、ion. This is in a way confining the process of simulation for a fresh experiment. To overcome this, it was proposed to use the average values of heat transfer coefficients and shear friction factors obtained with the 9 experiments shown in Table.4. These average values of heat transfer coefficient a

50、nd shear friction factor are further used to simulate the cutting forces with a new set of parameters within the range considered during the earlier evaluation. The experiments are also conducted with these new set of parameters and the results obtained are compared with that of the simulation resul

51、ts in order to validate the procedure evolved in the present work.The simulation results show a good agreement withConstn., Claudiu, Florinel, Bisu., 2010, “3D FEManalysis of cutting processes”, Proceedings of 3rd WSEAS International Conference on Advances in Visualization,Imazing and Simulation, Un

52、iversity of Algarve, Faro, Portugal, November 3-5,pp.41-46.Strenkowski, J. S., and Carroll, J. T., 1985, “A finite2.element mof orthogonal metal cutting”, ASMEJournal of Engineering for Industry, Vol 107, pp 346-354. Athavale, S. M., and Strenkowski, J. S., 1998, “Finite3.element m ing of machining:

53、 from proof-of concept to engineering applications, Machining Science and Technology, Vol 2 (2), pp 317-342.Lee, W.S., and Lin, C.F., 1998 “High-temperature deformation behavior of Ti6Al4V alloy evaluated by high strain-rate compression tests,” Journal of Materials Processing Technology, Vol. 75, pp

54、. 127-136.4.5.Meyer Jr. H.W., and Kleponis, D. S., 2001, “Mingthat of experimental results, shown in Fig 4. Aum errorthe high strain rate behavior of titanium undergoingof 9.94% was observed between the experimental andballistic impact and penetration,” International Journal of Impact Engineering, Vol. 26, pp. 509-521simulation results. From these studies, it can be concluded that the procedure developed in the present work is applicable to any set of process parameters within the range considered6.Moaz, H. Ali., Basim, A. Khidhir., Bashir,med,and Oshko