Finite Element Modeling of Chip Formation Process: Possibilities and Drawbacks

Transcription

1 Finite Element Modeling of Chip Formation Process: Possibilities and Drawbacks Pedro-J. ARRAZOLA; Done UGARTE Mondragon University, Mondragon, Spain ( Tfno: (Ext:33); Fax: HIGH SPEED CUTTING MICRO MILLING MACHINABILITY CHIP FORMATION STUDY MONDRAGON CAD/CAM SPAIN GRINDING FINITE ELEMENT MODELLING

2 . Outline. Motivation. Possibilities 3. Drawbacks 4. Conclusions and future work 7../6

3 Why machining modelling?. Motivation Machining accounts for more than % of the total added value of all products manufactured in industrialized countries [Mer98] In the United States of America [Jaw]: The appropriate cutting tool is chosen less than in the % of the cases. The tool is employed in the optimum cutting speed the 8% of the time. Only the 38% of the tools are employed during all the life-time 7../6 3

4 . Motivation Accident triggered by a machining defect: catastrophic turbine disk breakage MD88 Accident: Pensacola (Floride), Origin : Chip couldn t exit properly when drilling (chip jamming), which promoted a thermal affected zone and a crack initiation 7../6 4

5 . Motivation MACHINING MODELLING: MULTISCALE MACRO MESO MICRO [Ort3] 7../6

6 . Motivation MACHINING MODELLING: 3D VERSUS D MACHINING 3D MACHINING D MACHINED MACHINED SURFACE: SURFACE: NOT NOT MODELLED MODELLED IN IN D D WORKPIECE MACHINED MACHINED SURFACE: SURFACE: MODELLED MODELLED IN IN D D CHIP WORKPIECE Vc DIAMETER DIAMETER OF OF MM MM 7../6 6

7 . Motivation 3D MACHINING MODELLING: ABAQUS/EXPLICIT (SHEAR FAILURE) WORKPIECE WORKPIECE Computer:,6 GHz y 8 Gb RAM memory Computational time: hours hours/,9ms of machining time (with mass scaling) Minimum Element dimension :, microns.º 7../6 7

8 . Motivation ABLE TO PREDICT THE DIFFERENCES BETWEEN TWO STEELS WITH VERY DIFFERENT MACHINABILITY RATE? C,4 Cr,44 AISI44 STEEL Mo,6 Mn,784 Si,339 S, Ca,3 Al,3 Workpiece material: AISI-44 Tool material: P Cutting speed - V : 3 m/min Undeformed chip thickness - t :. mm Rake angle - γ :6º Clearance angle - α : 6º Cutting edge radius - rh : 4μm Fe [Bit93] [Gro96] C Cr Mo Mn Si S Ca Al B.U.L.: S,Mn,4,96,8,64,8,7,4,7 AISI 44 WITH CALCIUM TREATMENT [Bel7] [Bel8] [Ler84] [Nor89] [Mae] [Ham] [Bit93] 7../6 8

9 . Motivation ABLE TO PREDICT THE SERRATED CHIP FORMATION? GEOMETRY Rake angle - γ :6º Clearance angle - α : 6º Cutting edge radius - r h : 4μm Workpiece material: AISI-44 Tool material: P Cutting speed - V : 3 m/min Undeformed chip thickness - t :. mm Deformation in all the chip γ > CONTINUOUS SERRATED γ < GEOMETRY Rake angle - γ : -6º Clearance angle - α : 6º Cutting edge radius - r h : 4μm Non-deformed material Adiabatic Shear banding: μm [Pom7][Rec64] [Kom8][Bar] /6 9

10 IS FEM OF CHIP FORMATION ABLE TO DISTINGUISH?: MACHINABILITY? SERRATED CHIP? BUILT UP EDGE? RESIDUAL STRESSES? WEAR? CHIP SHAPE? SECTORS. Motivation CUTTING S MANUFACTURERS [MAR9], [CHEN4] [MAR9], [CHEN4] (D) COMPONENTS SUPPLIERS FOR AUTOMOTIVE, AERONAUTICS SECTORS STEEL MAKERS 7../6

11 . Motivation INPUT CALCULATION OUTPUT Cutting parameters : Cutting speed Depth of cut Undeformed chip thickness. Tool geometry : Rake angle Clearance angle Cutting edge radius Workpiece and tool material : Flow stress (workpiece) Thermal Conductivity Specific heat. Inelastic heat fraction Elastic modulus Tool-chip contact : Friction coefficient Thermal resistance. Heat partition factor Friction energy transformed into heat WORKPIECE WORKPIECE CHIP CHIP Cutting and feed forces Tool-chip contact length Chip thickness Temperature Stress Hydrostatic pressure Normal stress Tangential stress Plastic strain Strain rate Chip speed Plastic and friction energies... Tool life Surface roughness Accuracy Surface integrity (Residual stresses) Stability Chip shape 7../6

12 . Motivation INPUT EXPERIMENTAL OUTPUT Cutting parameters : Cutting speed Depth of cut Undeformed chip thickness. Tool geometry : Rake angle Clearance angle Cutting edge radius Workpiece and tool material : Flow stress (workpiece) Thermal Conductivity Specific heat. Inelastic heat fraction Elastic modulus Tool-chip contact : Friction coefficient Thermal resistance. Heat partition factor Friction energy transformed into heat Cutting and feed forces Tool-chip contact length Chip thickness Temperature Stress Hydrostatic pressure Normal stress Tangential stress Plastic strain Strain rate Chip speed Plastic and friction energies... Tool life Surface roughness Accuracy Surface integrity (Residual stresses) Stability Chip shape 7../6

13 CHIP CHIP RAKE SURFACE RAKE SURFACE. Motivation CUTTING PROCESS: THERMO-MECHANICAL-CHEMICAL COUPLED PART PART Primary shear zone ε eq :- ε eq: 4 - s - T: 4-6 K T:.-.. K/s Secondary shear zone ε eq :-4 ε eq: 4 - s - T: 8- K :.-.. K/s T CUTTING EDGE CUTTING EDGE Material separation In some cases material stuck CLEARANCE SURFACE CLEARANCE SURFACE COMPLEX PROBLEM 7../6 3

14 . Possibilities ST STEP: FINITE ELEMENT MODEL SET UP WORKPIECE nd STEP: QUALITATIVE VALIDATION Temperature(ºC) 3 rd STEP:SENSITIVITY STUDY θγ =3K θγ =3K m =. m =. 7../6 4

15 . Possibilities QUALITATIVE VALIDATION: FORCES Average value Experimental 89 N AdvantEdge 6 N Abaqus 6 N FEED FORCE (F f ) V t VARIABLE VALUES Level (-) Level (+) Cutting edge radius r β (mm).. Rake angle - γ o (º) Undeformed chip thickness h (mm rev - ),,3 Cutting speed - v (m min - ) 3 4 : 6 TESTS γ r β :. mm r β :. mm r h -8% -6% -4% -% % % 4% 6% 8% % QUALITATIVE RESULTS: GOOD AGREEMENT QUANTITATIVE RESULTS: SOME REMARKABLE DIFERENCES SHOULD BE EXPECTED!!: VARYING ELEMENT DIMENSION FROM TO 4 HAS 36% INFLUENCE 7../6

16 . Possibilities QUALITATIVE VALIDATION: TEMPERATURES CUTTING SPEED - v : - 3 m/min UNDEFORMED CHIP THICKNESS - h :.3 mm RAKE ANGLE - γ : - 6º CUTTING EDGE RADIUS - r β : μm WORKPIECE MATERIAL: AISI-44 MATERIAL: P INCREASE V C 3 m min - T=K V c : m/min t =.3 mm/rev ε=.4 low range filter AVERAGE Valeur moyenne VALUE AdvantEdge_MS 3 K Abaqus 46 K Experimental K? V FEM MODEL: GOOD ENOUGH!! t γ V c :3 m/min t =.3 mm/rev ε=.6 high range filter r h -3% -% -% % % % 3% 4% QUALITATIVE RESULTS: GOOD RESULTS QUANTITATIVE RESULTS: SOME REMARKABLE DIFERENCES 7../6 6

17 . Possibilities QUALITATIVE VALIDATION: SERRATED CHIP [Arr7] Plastic strain ( ε pl ) CUTTING SPEED (V): m - UND. CHIP THICKNESS (t ):. mm CUTTING SPEED - v : - 6 m/min UNDEFORMED CHIP THICKNESS - h :.3 mm RAKE ANGLE - γ : - 6º CUTTING EDGE RADIUS - r β : μm COMPUTATIONAL TIME : 6 h/millisecond (WITH MASS SCALING OPTION) WORKPIECE MATERIAL: AISI-44 MATERIAL: P ELEMENT DIMENSION : CUTTING SPEED (V): m- UND. CHIP THICKNESS (t ):.3 mm FEM MODEL: GOOD ENOUGH!! 7../6 FASTCAM-ULTIMA APX-RS K MONOCROMO FINANCIAL SUPPORT: FEDER AND C.I.C. margune 7

18 . Possibilities QUALITATIVE VALIDATION: POSITION OF MAXIMUM TEMEPERATURE [Arr7] Temperature (K) CUTTING SPEED - v : - 6 m/min UNDEFORMED CHIP THICKNESS - h :.3 mm RAKE ANGLE - γ : 6º CUTTING EDGE RADIUS - r β : μm COMPUTATIONAL TIME : 6 h/millisecond (WITH MASS SCALING OPTION) WORKPIECE MATERIAL: AISI-44 MATERIAL: P ELEMENT DIMENSION : CUTTING EDGE FEM MODEL: GOOD ENOUGH!! RAKE SURFACE CRATER WEAR 7../6 8

19 INPUT 3. Drawbacks CALCULATION OUTPUT Cutting parameters : Cutting speed Depth of cut Undeformed chip thickness. Tool geometry : Rake angle Clearance angle Cutting edge radius Workpiece and tool material : Flow stress (workpiece) Thermal Conductivity Specific heat. Inelastic heat fraction Elastic modulus Tool-chip contact : Friction coefficient Thermal resistance. Heat partition factor Friction energy transformed into heat PARAMETERS IDENTIFICATION Parameters Unsuitable mechanical tests Models WORKPIECE WORKPIECE CHIP CHIP F.E.M. MODEL SET UP Formulation: ALE, Boundary conditions Mesh topology Element dimension LACK OF ROBUSTNESS COMPUTATIONAL TIME Cutting and feed forces Tool-chip contact length Chip thickness Temperature Stress Hydrostatic pressure Normal stress Tangential stress Plastic strain Strain rate Chip speed Plastic and friction energies... Tool life Surface roughness Accuracy Surface integrity (Residual stresses) Stability Chip shape VALIDATION Cost Uncertainty 7../6 9

20 3. Drawbacks SENSITIVITY STUDY INPUT PARAMETERS OUTPUT PARAMETERS TEMPERATURE(K)? θγ =3K MATERIAL PARAMETERS MATERIAL BEHAVIOUR: A,B,C,n, m m n θ = [ + ( ) ] [ + ( )] w θ σ A B ε C ln & ε & ε θm θ CONDUCTIVITY - k SPECIFIC HEAT - c INELASTIC HEAT FRACTION -β EXAMPLE: m =. WORKPIECE CHIP THICKNESS (mm)? θγ =6K CONTACT PARAMETERS FRICTION COEFICIENT - μ γ THERMAL CONDUCTANCE K i HEAT PARTITION COEFICIENT - Γ FRICTION ENERGY TRANSFORMED INTO HEAT -η PARAMETERS PROCESS AND NUMERICAL PARAMETERS FIXED -CHIP CONTACT LENGTH CUTTING FORCE FEED FORCE VON MISES STRESS /6

21 3. Drawbacks CONTACT INPUT PARAMETERS MATERIAL ENTRY PARAMETERS EFFETS OVER THE NUMERICAL MODEL A-(Mpa) B-(MPa) n C η K i (W m - K - ) Γ ,-, FRICTION ENERGY E F -(J) MATERIAL INPUT m.- PARAMETERS λ w (W m - K- ) μ γ.-. PROCESS v (m.min - ) -3 PARAMETERS h(m.tr - ) NUM. PAR. LESS THAN % REFERENCE VALUES PARAMETERS λ s (W m - K - ) c w (J Kg - K - ) c s (J Kg - K - ) β Num. elements RANGE TEMPER. θγ -(K) 4 BETWEN %-% VON MISES STRESS σ vm -(MPa) 348 -CHIP CONTACT LENGTH KB o -(mm).3 CHIP THICKNE SS h c (mm).3 CUTTING FORCE F v -(N) 4 BETWEN %-% FEED FORCE F f -(N) 3 TOTAL ENERGY E-(J) 6. MORE THAN % PLASTIC ENERGY E P -(J) /6

22 3. Drawbacks CONTACT INPUT PARAMETERS MATERIAL ENTRY PARAMETERS EFFETS OVER THE NUMERICAL MODEL A-(Mpa) B-(MPa) n C η K i (W m - K - ) Γ ,-, FRICTION ENERGY E F -(J) MATERIAL INPUT m.- PARAMETERS λ w (W m - K- ) μ γ.-. PROCESS v (m.min - ) -3 PARAMETERS h(m.tr - ) NUM. PAR. LESS THAN % REFERENCE VALUES PARAMETERS λ s (W m - K - ) c w (J Kg - K - ) c s (J Kg - K - ) β Num. elements RANGE TEMPER. θγ -(K) 4 BETWEN %-% VON MISES STRESS σ vm -(MPa) 348 -CHIP CONTACT LENGTH KB o -(mm).3 CHIP THICKNE SS h c (mm).3 CUTTING FORCE F v -(N) 4 BETWEN %-% FEED FORCE F f -(N) 3 TOTAL ENERGY E-(J) 6. MORE THAN % PLASTIC ENERGY E P -(J) /6

23 3. Drawbacks CONTACT INPUT PARAMETERS MATERIAL ENTRY PARAMETERS EFFETS OVER THE NUMERICAL MODEL A-(Mpa) B-(MPa) n C η K i (W m - K - ) Γ ,-, FRICTION ENERGY E F -(J) MATERIAL INPUT m.- PARAMETERS λ w (W m - K- ) μ γ.-. PROCESS v (m.min - ) -3 PARAMETERS h(m.tr - ) NUM. PAR. LESS THAN % REFERENCE VALUES PARAMETERS λ s (W m - K - ) c w (J Kg - K - ) c s (J Kg - K - ) β Num. elements RANGE TEMPER. θγ -(K) 4 BETWEN %-% VON MISES STRESS σ vm -(MPa) 348 -CHIP CONTACT LENGTH KB o -(mm).3 CHIP THICKNE SS h c (mm).3 CUTTING FORCE F v -(N) 4 BETWEN %-% FEED FORCE F f -(N) 3 TOTAL ENERGY E-(J) 6. MORE THAN % PLASTIC ENERGY E P -(J) /6 3

24 3. Drawbacks I.R. CAMERA: WORKPIECE MATERIAL INFLUENCE MACHINABILITY RATE AISI 44PLUS TO AISI 44E AISI 44PLUS ε=.6 high range filter T=4K >6% 7../6 AISI 44E ε=.6 high range filter MATERIAL: P RAKE ANGLE - γ : 6º UNDEFORMED CHIP THICKNESS (t ):.3 mm CUTTING SPEED (V ): 3 m - CUTTING EDGE RADIUS - r h : μm EMISSIVITY-(ε)=.6 MACHINING TIME: s 4

25 3. Drawbacks INPUT CALCULATION OUTPUT Cutting parameters : Cutting speed Depth of cut Undeformed chip thickness. Tool geometry : Rake angle Clearance angle Cutting edge radius Workpiece and tool material : Flow stress (workpiece) Thermal Conductivity Specific heat. Inelastic heat fraction Elastic modulus Tool-chip contact : Friction coefficient Thermal resistance. Heat partition factor Friction energy transformed into heat WORKPIECE WORKPIECE CHIP CHIP F.E.M. MODEL SET UP Formulation: ALE, Boundary conditions Mesh topology Element dimension LACK OF ROBUSTNESS COMPUTATIONAL TIME Cutting and feed forces Tool-chip contact length Chip thickness Temperature Stress Hydrostatic pressure Normal stress Tangential stress Plastic strain Strain rate Chip speed Plastic and friction energies... Tool life Surface roughness Accuracy Surface integrity (Residual stresses) Stability Chip shape 7../6

26 3. Drawbacks 3D MODEL SET UP: FORMULATIONS LAGRANGIAN FORMULATION SEPARATION LINE REMESHING [Tay74] [Str8] [Obi97] [Hua96] [Beh99] [Lei99] [Don] [Lin] [McC] [Söh] [Mam] [Kal] [Ued3] [Shi3] [Ng3]... [Sek93] [Mar9] [Fou99] [Mad] [Cer] [Mar] ADVANTEDGE, DEFORM /6 6

27 3. Drawbacks 3D MODEL SET UP: FORMULATIONS EULERIAN ARBITRARY LAGRANGIAN EULERIAN [Car88] [Str9] [Mor93] [Str97] [Ath98] [Leo99] [Mae]. [Joy94] [Pan96] [Bac] [Mov] [Olo] [Altb] [Mes] [Arra] [Adi3] [Arr7] 7../6 7

28 3. Drawbacks 3D MODEL SET UP: TIME COMSUMING NUMERICAL MODEL: D_ONE_STEP Free surface Entry material SOFTWARE : ABAQUS EXPLICIT (v6./6.3) FORMULATION : A.L.E. ELEMNT TYPE : CPE4RT WORKPIECE MATERIAL BEHAVOIUR LAW: JOHNSON-COOK (4CD4U) [Gro96] MATERIAL: P CONTACT: COULOMB MODEL (μ=,3) [Gro96] MACHINING TIME: 3ms (mm)/ 36 hours calculation time CUTTING SPEED - V : m/min-6 m/min UNDEFORMED CHIP THICKNESS - t :, /. /,3 mm RAKE ANGLE - γ : +6º/-6 CLEARANCE ANGLE - α : 6º CUTTING EDGE RADIUS - rh : μm Model X4 WITH MASS SCALING X8 WITH MASS SCALING N. Elements (h=.3mm,γ o =6º) Element dimension (mm) Min Exit chip Tool Heat transfer allowed Heat transfer not allowed Constraint on material speed Material flow allowed Constraint on mesh Constraint on material Max Workpiece Exit material Computational time (hour/millisecond) Computer: GHz y Gb RAM memory 7../6 8

29 3. Drawbacks INPUT CALCULATION OUTPUT Cutting parameters : Cutting speed Depth of cut Undeformed chip thickness. Tool geometry : Rake angle Clearance angle Cutting edge radius Workpiece and tool material : Flow stress (workpiece) Thermal Conductivity Specific heat. Inelastic heat fraction Elastic modulus Tool-chip contact : Friction coefficient Thermal resistance. Heat partition factor Friction energy transformed into heat WORKPIECE WORKPIECE CHIP CHIP Cutting and feed forces Tool-chip contact length Chip thickness Temperature Stress Hydrostatic pressure Normal stress Tangential stress Plastic strain Strain rate Chip speed Plastic and friction energies... Tool life Surface roughness Accuracy Surface integrity (Residual stresses) Stability Chip shape VALIDATION Cost Uncertainty 7../6 9

30 3. Drawbacks VALIDATION Characterisation T measurement Strain and strain rate measurement Forces, chip thickness, contact length IR IR Thermography Pyrometry Inserted Thermocouples HSF Camera Dynamometry, microscopy 7../6 3

31 TEMPERATURE MEASUREMENT: MEASURED ZONE: OUTSIDE SURFACE 94K -4K 3. Drawbacks 38K Surface where the temperature is measured >.mm CUTTING EDGE Hsm7.avi p=3mm MAXIMUM TEMPERATURE OVER RAKE SURFACE WORKPIECE MATERIAL: AISI-44 MATERIAL: P RAKE ANGLE - γ : 6º UNDEFORMED CHIP THICKNESS (t ):. mm CUTTING SPEED (V ): 3 m - CUTTING EDGE RADIUS - r h : μm [Usu78] >K difference between the border and the middle 7../6 3

32 3. Drawbacks SOME UNCERTAINTY SOURCES I.R. Temperature measurement Emissivity Experimental set-up Calibration of the camera Wavelength (not gray body) Temperature + Extrapolations? Surface roughness Process oxidation Repeteability due to emissivity measurement errors Relative positioning of the chip over the rake-face Variation of viewing angle Different filters Calibration curves 7../6 3

33 CONCLUSIONS (-): 4. Conclusions and future work -Several parameters have remarkable influence in numerical cutting results: A, B, C, m, μ γ but K i, Γ as well (temperature): all contact parameters - Experimental data: lack of proper equipment. Extrapolation 3- Inverse simulation: could not be a solution 4- Parameter identification uncertainty in order to estimate F.E.M. one - Model coefficients will depend on fitting method 6- Lack of proper models for material and contact behaviour 7- F.E.M. is not able to make the difference between standard steel and other with improved machinability 8- Lack of robustness in quantitative results: input paramenters (including numerical ones) 7../6 33

34 CONCLUSIONS (+) 4. Conclusions and future work 9- Computational time reduction: clusters, mass scaling option - Experimental validation is costly, time consuming and still high uncertainty - Abaqus: lack robustness when setting up the model 8-F.E.M. can give tips for improving machining process 9- F.E.M. of chip formation: powerful quantitative tool to develop cutting process: influence of cutting conditions on temperature, residual stresses.. NEED FOR SHARING KNOWLEDGE AND WORKING TOGETHER!!!!! 7../6 34

35 . Questions THANK YOU ARE THERE ANY QUESTIONS? WORKPIECE WORKPIECE F.E.M. MODEL 3D ABAQUS/EXPLICIT 7../6 3