Finite Element Simulation of Cutting Processes Simulation Techniques in Manufacturing Technology Lecture 8 Laboratory for Machine Tools and Production Engineering Chair of Manufacturing Technology Prof. Dr.-Ing. Dr.-Ing. E.h. Dr. h.c. Dr. h.c. F. Klocke
Outline 1 Introduction 2 Material Models 3 Boundary Conditions 4 Chip Separation 5 Simulation of serrated Chip Formation 6 FEM Software Solutions 7 Process Modells 8 Verification Seite 1
Introduction Seite 2
Phases of a Finite Element Simulation A typical finite element analysis takes place in three phases from the standpoint of the user: Data preparation with the preprocessor defining the geometry, meshing, inputting the material data and defining the boundary conditions Calculation and Evaluation of the results with the postprocessor potential sources of error in FE analyses include: discretization errors from geometry interpolation when meshing and interpolation of the state variables, incorrect input data (e.g. material data, process data, friction conditions), numerical errors (e.g. in numerical integration) Seite 3
Outline 1 Introduction 2 Material Models 3 Boundary Conditions 4 Chip Separation 5 Simulation of serrated Chip Formation 6 FEM Software Solutions 7 Process Modells 8 Verification Seite 4
Conditions in cutting operations Forces: 10 0 to 10 4 N Stresses: 10 3 N/mm 2 Strain 0,1 to 5 Strain rate 0,5 * 10 4 to 0,5 *10 6 1/s Temperatures: 1500 C Temperature gradient: > 10 3 C/mm Seite 5
Comparison of strain, strain rate and temperature for different manufacturing processes Manufacturing process strain Strain rate / s -1 T homolog a Extrusion Forging/ Rolling Sheet metal forming Cutting 2-5 0,1-0,5 0,1-0,5 1-5 10-1 - 10-2 10-10 3 10-10 2 10 3-10 6 0,16-0,7 0,16-0,7 0,16-0,7 0,16-0,9 a: T homolog = T / T melting point High demands on the material model for cutting simulations Seite 6
Principles of metal forming: Material Laws Seite 7
Conventional set-ups to determine flow stress curves tensile test compression test torsion test v w d 0 l 0 d 0 l v w l d u 0 t 0 h 0 z R r α M t γ R l M t lubricant ϕ max 0,8 to 1. ϕ 10-3 to 10 3 s -1 ϑ 20 to 1300 C ϕ max 0,8 to 1. ϕ 10-3 to 10 2 s -1 ϑ 20 to 700 C ϕ max 5. ϕ 10-4 to 30 s -1 ϑ 20 to 1300 C adapted from: Kopp Seite 8
Split-Hopkinson-Bar-Test projectile tempered chamber striker bar input bar output bar strain gages v >> 50m/s. ϕ to 10 4 s -1 specimen ϑ to 1200 C source: LFW, RWTH Aachen Seite 9
Flow stress curves parameter: k f = f (ϕ, ϕ) ϑ = const. = RT Flow stress kf 1400 N/mm 2 800 1600 N/mm 2 0 0 strain 0,5 9SMnPb36 1 0 1/s 10000 5000 strain rate ϕ Flow stress k f 800 0 0 strain ϕ 0,5 source: LFW, RWTH Aachen Ck45N 1 0 1/s 10000 5000 strain rate ϕ Seite 10
Flow stress curves in DEFORM for room temperature Flow stress [Mpa] strain Seite 11
Flow stress curves in DEFORM for high temperatures (600 C) Flow stress [MPa] strain Seite 12
Consitutive material laws for metal cutting In order to reduce the number of experiments constitutve material laws are needed The constitutive material law has to describe the plastic behaviour in dependence for a wide range of strain, strain rate and temperature For the simulation several material models have been developed, which consider strain hardening, strain rate hardening and thermal softening Most of material laws are of empircal nature Empirical material laws describe the flow stress as a function of strain, strain rate and temperature σ Flow stress = f(ε, dε/dt, T) Empirical material laws contain specific material constants, which will be determined by regression analyses or by the least squares method) based on the experimental measured flow stress curves Seite 13
Consitutive material law by Johnson and Cook σ = A ( 1 ) 0 1 ( n + Bε ) + C ln( & ε / & ε ) T T m Tr T r m plasticity viscous damping Material constants: Reference velocity: Room temperature: Melting temperature: A, B, n, C, m ε& 0 T r T m temperature function Seite 14
Thermal material properties Thermal Conductivity Conduction is the process by which heat flows from a region of higher temperature to a region of lower temperature within a medium. The Thermal Conductivity in this case is the ability of the material to conduct heat within an object's boundary. Temperature dependent! Thermal Expansion Defines the material's tendency to grow and shrink with changes in temperature. Temperature dependent! Seite 15
Thermal material properties Heat Capacity The Heat Capacity for a given material is the measure of the change in internal energy per degree of temperature change. Temperature dependent! Emissivity The emissive power (E) of a body is the total amount of radiation emitted by a body per unit area and time. The Emissivity (e) of a body is the ratio of E/E black body where E black body is the emissive power of a perfect black body. Seite 16
Outline 1 Introduction 2 Material Models 3 Boundary Conditions 4 Chip Separation 5 Simulation of serrated Chip Formation 6 FEM Software Solutions 7 Process Modells 8 Verification Seite 17
Simulation boundary conditions Setting the simulation type Lagrange (non stationary processes) In lagrangian mode the nodes of the mesh elements are connected to the material Euler (stationary processes) The Eulerian approach considers the motion of the continuum through a fixed mesh Arbitrary Lagrangian Eulerian method (ALE) The Arbitrary Lagrangian Eulerian method (ALE) is becoming more and more accepted, which is a combination of the above approaches and permits the mesh a motion independent of the material as long as the form of the domains under consideration remains the same Simulation mode Deformation Heat Transfer Coupled thermo-mechanical simulation Time integration Implicit Explicit Seite 18
Object Boundary Conditions Boundary Conditions Object Conditions Inter Object Conditions Environment Object Conditions Tool Workpiece 2D FEM Cutting Model Seite 19
Object Boundary Conditions Boundary Conditions Object Conditions Inter Object Conditions Environment Object Conditions Friction Heat Transfer Movement Tool = Object 1 Workpiece = Object 2 2D FEM Cutting Model Seite 20
Boundary Conditions Boundary Conditions Object Conditions Self Contact (Chip vs. Workpice Surface) Friction Heat Transfer Movement F N F R F R : Friction Force Workpiece = Object 2 F N : Normal Force 2D FEM Cutting Model Seite 21
Object Boundary Conditions Object Conditions Boundary Conditions Workpiece is moving in the x-direction with the prescribed velocity v c, in the y-direction the workpiece is fixed Tool is fixed in x- and y-direction! Friction Heat Transfer Tool Movement cutting speed v c in x-direction Workpiece y x Seite 22
Object Boundary Conditions Boundary Conditions Object Conditions Tool Heat Transfer Friction Heat Transfer Movement Workpice Seite 23
Object Boundary Conditions Boundary Conditions Object Conditions Inter Object Conditions Environment Object Conditions Friction Heat Transfer Tool F N F N F R Heat Transfer F N Seite 24
Normal and shear stress distribution along the rake face Normal pressure Adapted from Usui and Takeyama Adapted from Zorev Adapted from Oxley and Hatton Seite 25
Inter Object Conditions - Friction Models Seite 26
Object Boundary Conditions Boundary Conditions Object Conditions Inter Object Conditions Environment Object Conditions Tool Heat Transfer Heat Convection Heat Emissivity Heat Radiation Heat Convection Heat exchange with environment Seite 27
Outline 1 Introduction 2 Material Models 3 Boundary Conditions 4 Chip Separation 5 Simulation of serrated Chip Formation 6 FEM Software Solutions 7 Process Modells 8 Verification Seite 28
Chip separation Chip separation based on nodal distances Chip separation based on a critical indicator chip A S B S l separation criterion B S A S D S C S Tool v c l KR D S C S Tool v c X E S X X F S E S X H S,W G S,W F S,W E W D W C W B W A W H S,W G S,W F W E W D W C W B W A W d cr cutting plane d cutting plane Seite 29
Chip separation - Predefined critical elements Cutting Plane Cutting plane consists out of critical elements. If one element reaches predefined separation criterion, the element will be deleted Disadvantage: Volume loss of workpiece Seite 30
Chip separation - Without chip separation criterion by Remeshing Old Mesh New Mesh Elements are highly distorted Remeshing leads to better mesh a) Span chip Werkzeug tool b) New Mesh Seite 31
FE-Mesh Definition of an element type Mesh density can be controlled by: Meshing Windows Weighting Factors for Temperature Strain Strain rate Curvature Criteria for calling the remeshing routine: Elements are critically deformed Predefined no. of time steps Predefined no. of strokes Remeshing criteria has to fulfill the following conditions: The critical value for the remeshing increases with the distortion of the mesh If a remeshing has been conducted the value of the remeshing criteria will be reset Seite 32
Definition of element type Seite 33
Outline 1 Introduction 2 Material Models 3 Boundary Conditions 4 Chip Separation 5 Simulation of serrated Chip Formation 6 FEM Software Solutions 7 Process Modells 8 Verification Seite 34
Simulation of serrated chip formation Consistent strain distribution Continuous metallographic structure Moderately different strains over the chip dimensions caused by dynamical loads of mechanical and thermal nature distinct segments of the chip s top Very different strains over the chip dimensions caused by dynamical loads of mechanical and thermal nature discontinuous chip segments continuous chip formation segmented chip formation discontinuous chip formation Ernst, 1938 Seite 35
Simulation of serrated chip formation Serrated chips can be caused by cracks and pores, adiabatic formation of shear bands or a combination of both mechanisms. Simulation of serrated chips can be realised by two different approaches: simulation of serrated chip caused by deformation localisation based on modified material characteristics simulation of serrated chip caused by crack initiation based on breakage- and crack hypotheses (e.g. fracture criteria) combination of both approaches Seite 36
Deformation localisation based on modified material characteristics I/II rigid-viscoplastic model σ undamaged A Effective strain 10 5 0 stress σ 0 E deformation B damaged C ε cutting edge radius: r β = 10 µm cutting speed: v c = 25 m/min material: TiAl6V4 Chip formation based on manipulated flow stress data incorporating strain softening. Seite 37
Deformation localisation based on modified material characteristics I/II i ii iii force / N 200 150 100 50 6 10 5 s -1 2 10 5 s -1 dφ/dt cutting force simulation time / ms cutting force experiment feed force experiment feed force simulation 0 7,65 7,75 7,85 7,95 8,05 i: shear initiation ii: sliding iii: new segmentation material: AlSI 1045 cutting speed: v c = 1000 m/min feed: f = 0.1 mm Seite 38
Crack initiation based on breakage and crack hypotheses Phase 2.1: Shearing Initiation The Material Law does not fulfil the conditions in front of the cutting edge Strain rate hardening (damping) in extreme conditions distorts the calculated results flow Stress at 100 C / (N/mm²) 5000 2000 1000 0 0 1 2 3 4 Real Plastic Strain strain rate / s -1 4000 0,001 10000 3000 50000 100000 Phase 2.2: Crack Initiation The accelerated sliding is initialised by a crack on the workpiece material surface The crack region is characterised by uniaxial principal tensile stresses Cracks can be simulated by failure criteria considering the deformation history applying a following law ε k ( ) C = F max(σ,0) 1 0 Seite 39
Segmented Chip Simulation reveals periodic sticking zone First Contact Start of Shearing Crack Initiation Gliding strain rate 90 75 62,5 50 37,5 25 12,5 Material Speed / m/min End of Gliding New Segmentation Start of Shearing Crack initiation 0 Seite 40
Verification of Segmented Chip Simulation tertiary shear zone 800 Simulation Measurement primary shear zone secondary shear zone (sticking zone) relative cutting force F c /b [N/mm] 700 600 500 400 300 200 100 Theory of van Luttervelt & Pekelharing FEM-Simulation 0 0,0 0,4 0,8 1,2 cutting time t c / ms 0,0 0,4 0,8 1,2 cutting time t c / ms Seite 41
Outline 1 Introduction 2 Material Models 3 Boundary Conditions 4 Chip Separation 5 Simulation of serrated Chip Formation 6 FEM Software Solutions 7 Process Modells 8 Verification Seite 42
FEM Software Solution for FEM-Simulation of the Cutting Process MSC.Marc Seite 43
Outline 1 Introduction 2 Material Models 3 Boundary Conditions 4 Chip Separation 5 Simulation of serrated Chip Formation 6 FEM Software Solutions 7 Process Modells 8 Verification Seite 44
Orthogonal cutting process (2D FE-model) v r ch tool chip v r c workpiece If depth of cut a p >> uncut chip thickness h State of plane strain condition is reached Seite 45
Simulation of the High Speed Cutting Process Cutting speed v c = 3000 m/min Feed f = 0.25 mm v c Seite 46
Simulation of the High Speed Cutting Process Seite 47
Simulation of the High Speed Cutting Process Seite 48
Simulation of the High Speed Cutting Process Seite 49
Simulation of the High Speed Cutting Process Seite 50
Simulation of the High Speed Cutting Process Seite 51
Simulation of the High Speed Cutting Process Seite 52
Comparison of of different thermal properties of the tools Orthogonal truning 2D (v c = 300 m/min, f = 0,1 mm, ck45) Ceramic-Insert Thermal conductivity λ = 35 W/mK WC-Insert Thermal conductivity λ = 105 W/mK T max = 650 C T max = 550 C Seite 53
Temperature distribution in dependency of the coating and its thickness 3 µm TiN 6 µm 570 T sp Calculated temperature at the chip bottom side T Sp / C 560 550 540 530 520 510 533 539 509 539 557 TiN 6 µm Al 2 O 3 coating thickness 0 TiN 3 µm TiN 6 µm HW TiN 6 µm Al 2 O 3 6 µm heat conductivity: HW: 100 W/(mK) TiN: 26,7 W/(mK) Al 2 O 3 : 7,5 W/(mK) heat capacity: HW: TiN: Al 2 O 3 : 3,5 J/(cm³K) 3,2 J/(cm³K) 3,5 J/(cm³K) material: C45E+N tensile strength: R m = 610 N/mm² HW: HW-K10/20 Seite 54
2D FE-model for tool wear simulation Phase 1: Temperatur Thermo-mechanical FE-simulation of the cutting process till steady state solution is obtained. Phase 2: VB<VB tool life Call of the User subroutine to calculate tool wear wear rate dw/dt x time t = wear Usui s tool wear model: W / dt = σ V n S C1 exp( C T 2 ) Phase 3: Verschleiß VB [mm] Tool geometry updating in dependence of wear Wear Abort VB>VB tool life Verschleißmarkenbreite, VB [mm] (a) VB K+1 VB K A B Tool wear increase Wear growth VB Standzeit Tool life t = t K+1 - t K t K t K+1 Schnittzeit, t [min] Seite 55
Phase 4: Methodology for moving the nodes at the rake face tool node 5 µm square element tool Werkzeug workpiece v c A X ϕ n X A W ϕ ϕ AB W sin ϕ ϕ X W cos ϕ chip v c B rake B Seite 56
Phase 4: Methodology for moving the nodes at the flank face Tool node square element 5 µm Tool Workpiece v c workpiece n A n B n C A B C D n D n A = n B = n C = flank n D Seite 57
Results of the tool wear simulation γ eff = -26 Tool Time: 5 min α 0 = 7 Time: 15 min Process: Part Turning Work material: Cutting Speed: Feed: Depth of cut: Cooling: 16MnCr5 (case hardened) v c = 150 m/min f = 0,06 mm a p = 1 mm dry Time: 25 min Time: 35 min 93 µm Seite 58
Verification of the tool wear simulation for the flank wear v c = 150 m/min, f = 0.06 mm, a p = 1 mm, dry γ eff = -26 Tool Time: 5 min Flank wear width VB [mm] α 0 = 7 0,1 0,08 0,06 0,04 0,02 0 Time: 15 min Experiment Time: 25 min Simulation Time: 35 min 0 5 10 15 20 25 30 35 Cutting time t [min] 93 µm Seite 59
Longitudinal Turning, 3D FE-Model Why 3D modelling? orthogonal cut 3D turning process n workpiece created surface f major cutting edge a p v c k minor cutting edge major cutting edge f v c 3D simulation needed for the consideration of the workpiece surface Seite 60
Cutting process simulation Turning Drilling Milling Calculation of the thermo-mechanical tool-load-collective for an ideal dimensioning of the tools micro- and macrogeometry Seite 61
Input and output parameters of a FEA-based cutting model Workpiece / Tool geometries material data contact conditions boundary conditions cutting conditions Seite 62
Input and output parameters of the cutting simulation Chip Formation temperatures stresses deformations strain rate kind of chip chip flow chip breakage Tool strain stresses temperatures process forces wear Workpiece strain temperatures deformation Workpiece / Tool geometries material data contact conditions boundary conditions cutting conditions burr formation distortion prospective: residual stresses, surface qualities, like: roughness, dimensional- and formdeviation Seite 63
Setup of a 3D FE-Model 15 15 7,5 Seite 64
Setup of a 3D FE-Model - specification of the tool holder Tool holder: Rot Z =6 Z Kennametal ID: PCLNL252M12 F4 NG27 Rake angle γ 0 = -6 Relief angle α 0 = 6 Tool inclination angle λ s = -6 Rot x =-6 X Y Tool cutting edge angle κ r = 95 Seite 65
Setup of a 3D FE-Model - tool position f r tool a p r workpiece r tool =r workpiece Seite 66
Setup of a 3D FE-Model - Mesh of the workpiece Seite 67
3D Simulation v c = 300 m/min f = 0,1 mm workpiece: AISI 1045 tool: K10 Seite 68
3D FE-Model - Post Processing Temperature ( C) For better visualization the tool is hidden Seite 69
3D FE-Model - Post Processing Temperature ( C) For better visualization the tool is hidden Seite 70
3D FE-Model - Post Processing Strain distribution For better visualization the tool is cut Seite 71
3D FE-Model - Post Processing Strain Rate distribution For better visualization the tool is cut Seite 72
Models of Cutting Inserts Roughing geometry Finishing geometry CNMG120408RN CNMG120408FN Seite 73
Simulation of the chip flow Chip breaker RN Material: C45E+N Cutting material: HC P25 Insert: CNMG120408 Insert geometry: α 0 γ 0 λ S κ r 6-6 -6 95 Cutting velocity.: v c = 300 m/min Feed: f = 0,1 mm Depth of cut: a p = 1 mm Dry cutting ε 90 Chip breaker FN Seite 74
Simulation of the chip flow Chip breaker RN Material: C45E+N Cutting material: HC P25 Insert: CNMG120408 Insert geometry: α 0 γ 0 λ S κ r 6-6 -6 95 Cutting velocity.: v c = 300 m/min Feed: f = 0,1 mm Depth of cut: a p = 1 mm Dry cutting ε 90 Chip breaker FN Seite 75
Comparison of simulation and real chip flow CNMG120408 Chip breaker NF HC-P15 κ r = 95 γ n = -6 λ s = -6 C45E+N a p = 1,9 mm f = 0,25 mm v c = 200 m/min dry v f v c Seite 76
Drilling: Modelling of size effects Task: Development of a consistent 3D-calculation-model based on the FE-method for scaling the boring process in consideration of size effects n f Bohrwerkzeug drill Reibung friction Reibung friction work Werkstück piece plastic Plastische deformation Verformung separation Stofftrennung material Seite 77
Previous results: 3D FE calculation model for d = 1 10 mm Material modeling Measuring the drill geometry FE boundary conditions σ =σ( ε, ε&,t) Tool FEM-Model Strain hardening Plasticity Damping mechanism Relaxation Dynamic strain ageing Temperature influence Loss of cohesion Failure mechanism Cutting parameters Tool: rigid / elastic Friction law Heat transfer Elementsize Number of elements Remeshing strategy Degree of freedom Seite 78
FE-Simulation of the drilling process with d = 1 mm (DEFORM3D) Machining conditions Workpiece material: Tool material: Cutting speed: Feed: Feed velocity: Cooling lubricant: C45E+N HW-K20 35 m/min 0.012 mm/u 133 mm/min none Boundary Conditions Tool: rigid number of elements: 90 000 Workpiece: visco-plastic (LFW-material law), temperatur fixed at boundary nodes number of elements: 100 000 Contact: coulomb friction (µ =0,2) heat transfer (conduction & convection) Computing time and drilling depth: 2000 h; 0.18 mm (70% of the major cutting edge) Seite 79
Verification of the chip formation Experimental chip formation Chip formation in the simulation workpiece material: C45E+N cutting tool material: HW K20 cutting speed: feed: v c = 35 m/min f = 0.012 mm Seite 80
Model evaluation: scale efect of the chisel edge length Specific spezifische feed Vorschubkraft force k k f,max [kn/mm 2 ] f,max [kn/mm 2 ] 6 5 4 3 2 1 Experiment Simulation Verhältnis (d Q / d) [%] 32 30 28 26 24 22 20 1 2 3 4 5 6 7 8 9 10 Durchmesser d [mm] Diameter d [mm] k f,max = 2 * F z,max / (d * f) Workpiece: C45E+N Cutting speed: v c = 35 m/min Feed: f = 0,012 * d Cutting tool material: HW-K20 Corner radius: r n = 4 µm 0 1 2 3 4 5 6 7 8 9 10 Drill Bohrerdurchmesser diameter d [mm] d [mm] Cooling: none Seite 81
Model validation: Temperature at the major cutting edge (center) 400 Temperature at the major cutting edge T [ C] 300 200 100 Experiment Simulation d = 3 mm 0 1 3 8 10 diameter d [mm] Cutting speed: v c = 35 m/min Workpiece: C45E+N Feed: f = 0,012 * d Cutting tool material:hw-k20 Coolant: none Verrundung: r n = 4 µm Seite 82
Modelling of the face milling process Materials and cutting parameters: Work material: Quenched and tempered AISI 1045 (normalized) Tool material: coated WC Cutting parameters: tool: no. of teeth: Z = 4 diameter: D = 32 mm v f process: Engagment angle: φ A φ E = 180 n feed feed per tooth: depth of cut: f = 0.5 mm f Z = 0.125 mm a p = 0,8 mm a p κ r tool tool leading angle: κ r = 90 Work piece tool inclination angle: λ = -5 no. of rev.: n = 2250 min -1 f z Seite 83
Modelling of the face milling process Axial and radial rake angle: axial rake angle γ axial = 9 radial rake angle γ radial = 5 γ axial Seite 84
Modelling of the face milling process Depth of cut a p Feed f r tool = r Work piece Work piece geometry f View r tool a p r Work piece Seite 85
Finding the best work piece geometry 1. Simplified work piece geometry 2. Simplified work piece geometry 3. Simplified work piece geometry 1 2 Seite 86
Simulation results for the 1. simplified work piece model rough elements within the work piece simulation of chip formation not accurate enough back Seite 87
Simulation results for the 3. simplified work piece model Final work piece geometry left right Seite 88
Post Processing for the face milling operation Seite 89
Results for the face milling operation Chip formation for the left side of the work piece: at the beginning very thin chips are produced chip curling starts for higher undeformed chip thickness Seite 90
. Results for the face milling operation Simulation Experiment Full agreement Seite 91
Outline 1 Introduction 2 Material Models 3 Boundary Conditions 4 Chip Separation 5 Simulation of serrated Chip Formation 6 FEM Software Solutions 7 Process Modells 8 Verification Seite 92
Verification of the FE-model simulation experiment chip tool primary shear zone workpiece 0.05 mm max. principle stress cutting temperatures cutting forces chip geometry cutting temperatures cutting forces chip geometry comparison Seite 93
Temperature measurment technical specifications temperature range: app. 250-1200 C maximum time resolution: 2 ms measured temperature independent of surface emissivity Seite 94
Temperature measurement by a two-color pyrometer fiber workpiece chip major cutting edge technical specifications 0.5 mm temperature range: app. 250-1200 C maximum time resolution: 2 ms measured temperature independent of surface emissivity measuring spot insert quartz fiber ( 0.26 mm) Seite 95
Combination of temperature and force measurement Cutting force F c Chip temperature 500 N 300 200 100 Cutting speed aluminium steel / titanium feed 0,25 mm 0,1 mm depth of cut 2 mm 1 mm 0 Seite 96
Alternative measurement position - workpiece surface measuring point Temperature C 700 600 500 400 distance to cutting edge 1 mm 4.5 mm quartz fibre 300 200 0 20 40 60 80 100 Cutting speed m/s Seite 97
Positioning of the measurement spot Seite 98
Alternative measurement position - top of the chip cemented carbide tip quartz fibre measuring point cutting insert Seite 99
Alternative measurement position - top of the chip cemented carbide tip quartz fibre 1000 C measuring point temperature Temperatur 800 600 optic Optik Hartmetallspitze cemented carbide tip cutting insert 400 0 1000 2000 3000 4000 5000 6000 Schnittgeschwindigkeit cutting speed m/min Seite 100
Force Measurement Chip temperature [ C] 600 400 200 0 Simulation Experiment AA7075 f = 0,25 mm a p = 2 mm 0 2000 4000 6000 Cutting speed v c [m/min] Cutting force F c Simulation v c = 3000 m/min 500 400 [N] 200 100 0 Cutting force F c Experiment v c = 3000 m/min Seite 101
Verification of the simulated chip formation by in-situ photography workpiece tool tool v c microscope light barrier workpiece (etched) in-situ photography of the orthogonal cutting process, suitable for all materials cutting speed up to v c = 2000 m/min realized double exposure -> two images in a defined time range down to 4 mikroseconds -> to analyse the chip flow, chip breakage and chip velocitiy v ch Seite 102
In-situ photography of chip formation - realised setups Discontinuous cut v c,max = 5000 m/min f = free a p = free workpiece = free tool = free Continuous cut setup 1 rot. tool setup 2 rot. workpiece setup 3 rot. workpiece + etched workpiece + measurement of forces - no temperature measurement + etched workpiece + force and temperature measurement + force and temperature measurement + real world process - no etched workpiece Seite 103
Results of in-situ photography - chip geometry, first image workpiece: AISI1045 feed: f = 0,1 mm depth of cut: a p = 1 mm depth of chip root: 0.041 mm lenth of contact zone: 0.2064 mm thickness of chip root: 0.1013 mm cutting speed: v c = 460 m/min magnification: 100 maximal thickness of chip : 0.123 mm minimal thickness of chip : 0.056 mm shear angle Φ = 28 Seite 104
Results of in-situ photography - chip geometry, second image workpiece: AISI1045 feed: f = 0,1 mm depth of cut: a p = 1 mm cutting speed: v c = 460 m/min magnification: 100 depth of chip root: 0.073 mm lenth of contact zone: 0.358 mm thickness of chip root: 0.155 mm shear angle Φ = 23 maximal thickness of chip : 0.112 mm minimal thickness of chip : 0.061 mm Seite 105
Results of in-situ photography - chip geometry (Dt = 40 µs) workpiece: AISI1045 0,5 mm feed: f = 0,1 mm depth of cut: a p = 1 mm cutting speed: v c = 460 m/min magnification: 100 shear angle Φ = 23 change in shear angle F = 18% change of the contact length l k = 40% v c = 460 m/min v c = 515,5 m/min v c = 522,1 m/min Seite 106
Results of in-situ photography - compression of the segment workpiece: AISI1045 feed: f = 0,1 mm depth of cut: ap = 1 mm cutting speed: vc = 460 m/min magnification: 200 Seite 107
Results of in-situ photography - shearing of the segment workpiece: AISI1045 feed: f = 0,1 mm depth of cut: ap = 1 mm cutting speed: vc = 460 m/min shearing magnification: 200 time difference: t = 20 µs Seite 108
Outlook: Benchmark-Analysis to choose the best tool geometry Fixed input parameter material parameter, firction coefficients + cutting parameter 1 2 v c1, a p1, f 1 v c2, a p1, f 1 + tool A B C Cutting simulation # determination of the thermomechanical loadspectrum, chip flow, chip form Q, T, F i, Benchmark-Analysis Flank wear VB cutting parameter 1 cutting parameter 2 A B C tool + coating TiN TiAlN AlO 2 temp wear stress chip flow tool A + - ++ - tool B - -- o + tool C ++ ++ + + optimised tooland tool carriergeometry Seite 109
Questions What are the ranges of temperature, strain and strain rate in cutting operations? What is the range of strain rate, that can be realized by the Split-Hopkinson-Bar- Test? Name two friction models. What are the advantages and the disadvantgeas of this models? How is the strain rate effecting the flow stress curve of a material? What are the demands on a temperature measurement setup which allows the evaluation of simulation results? Explain the difference between the orthogonal cutting process and the longitudinal cutting process Explain the difference between a plastic and an elastic-plastic flow stress curve! Seite 110
Determination of flow stress depth of cut, a p cutting speed, v c rake angle, g conv. flow stress curves, k f assumptions of friction conditions, µ cutting conditions orthogonal cutting tests measurement cutting forces (F c, F p ) chip thickness (h ch ) contact length (l k ) simulation, e.g. FEM forces and stresses temperature strain strain rate calculation comparisson evaluation of the real flow stress curve k f = f(strain, strain rate, temperature) Seite 111
Chip separation criteria and breakage criteria Seite 112
FE-Mesh elastic tool ideal-plastic workpiece (AISI 1045) v c f 0.5 mm y x Seite 113
Comparison of simulated and measured results 488 C good agreement of simulated and measured temperatures assumption of material properties is suitable Seite 114