fe simulation of cutting processes

8/19/2019 Fe Simulation of Cutting Processes

1/92

© WZL/Fraunhofer IPT

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


2/92

Seite 2 © WZL/Fraunhofer IPT

Summary and Outlook9

Applications of the FE cutting simulation at the WZL 8

Criteria for the evaluation of FE software 7

Friction and wear models for the FE cutting simulation6

Damage models for the FE cutting simulation and multiphase simulation 5

Constitutive material laws for the FE cutting simulation4

CAD modelling for the FE cutting simulation3

Requirements of the FE cutting simulation 2

Introduction 1

Outline


3/92


Influencing factors on the cutting process

Workpiece material

structure

texture

mechanicalproperties

hardness

residual stresses

Cutting zone

chip forming

mechanisms

cooling lubricant

cutting parameters

contactconditions

e.g.: friction, wearheat transfer

Tool

cutting material

coating

geometry

tool holder

Machine

machine design

drive system

clamping device

Bildeines

Prozesses

M


4/92


Cutting process in comparison to other processes

Source: Jaspers

Process Strain Strain rate / s-1 Thomolog

Extrusion 2 – 5 10-1 – 10-2 0.16 – 0.7

Forging /

Rolling0.1 – 0.5 10 – 10+3 0.16 – 0.7

Sheet metalforming

0.1 – 0.5 10 – 10+2 0.16 – 0.7

Cutting 1 – 5 10+3 – 10+6 0.16 – 0.9

Cutting process

Extreme conditions in the cutting process


5/92


Outline








Requirements of the FE cutting simulation2

Introduction 1


6/92


Requirements to the FE cutting simulation

Reproduction of the macro/ micro geometry of the tools and kinematic of the cuttingprocess

Modelling of the thermo mechanical material behavior for the entire temperature andstrain rate range

Implementation of damage approaches, texture microstructure and phase transformation

Simulation of chip form (remeshing routine, material separation, etc.)

Consideration of friction, wear and coating

Modelling of heat generation and transfer (conduction, convection, radiation)

Consideration of the influence of cooling lubricant

Utilization of the Lagrangian solving method (instationary cutting processes)

Generation of a finely structured FE mesh and adaptive remeshing (very high element

deformation because of higher gradients of deformation, temperature and tension) Appropriate computation time (explicit time integration, parallelization, etc.)


7/92


Cutting simulation: Input- und output parameters

Tool

StrainTension

Temperature

Cutting forcesWear

Chip formation

TemperatureTension

DeformationRate of deformation

Chip typeChip flowChip crack Component

Strain

TemperaturesDeformation

Burr formationDistortionFuture: Residual stresses

Surface quality, e.g.: roughnesschanges in shape,Measurement and position

Component / tool

GeometryMaterial dataContact conditionsBoundary conditionsCutting conditions


8/92


Outline









Introduction 1


9/92


Macro- und micro tool geometry

Major clearance angle: a = 10°Twist angle: d = 35°

Cutting material: HW-K20Grain size: DK = 0.5 – 0.7 µm

Construction dimensions DIN 6539Type: N

Diameter: d = 1 mmDrill-point angle: s = 118°

Querschneide

Freifläche

Hauptschneide a

d

chisel edge

flank face

major cutting edge a

d


10/92


Definition of element type


11/92


Creation of tool models close to reality

Macrogeometry

4 mm

Drilling tool FEM-modelDetermination of the tool geometry

Microgeometry

6 µm6 µm

Real tool CAD-model


12/92


Zusammenfassung und Ausblick 9

Outline

Zusammenfassung und Ausblick Zusammenfassung und Ausblick Zusammenfassung und Ausblick Summary and Outlook9








Introduction 1


13/92


Thermo-mechanical behavior of material

i iB u


14/92


Thermo-mechanical behavior of material

Quelle: Diss-Abouridoaune

( , , )T s s

200

250

300

350

400

450

0 0.1 0.2 0.3 0.4

AA6063-T6

d

/dt=10-3

s-1

& T=20°C

, -

, M P a

300

350

400

450

10-3

10-1

101

103

AA6063-T6

=0.1 & T=20°C

d

/dt , s-1

0

150

300

450

0 100 200 300 400 500

AA6063-T6

=0.1 & d

/dt=1s-1

T , °C

StrainRateHardening StrainHardening Thermal Softening

Source: Diss- Abouridouane


15/92


Empirical models: e.g. Johnson-Cook-Modell

Micro mechanical models: e.g. enhanced Macherauch-Vöhringer-Kocks-model

Semi-empirical models: e.g. Zerilli-Armstrong-model for bcc-materials

Constitutive material modelling for the FE cutting simulation

Source: Diss-Abouridouane

n -1/2G 1 2 3 4 5σ = Δσ +C exp -C T +C Tln( ) +C +C L

Initial densityof dislocations Dislocation jam

Influence of temperatureand strain rate

Influence of grain size

m

n r 0

m r

T T(A B ) (1 Cln( / )) (1 )

T T

s

Strain hardening Strain rate sensitivity Thermal softening

1/ p1/ q

* 0a 0

0

kT1 ·ln

G

s s s Athermal processes Damping processThermal activated processes


16/92


Determination of High speed flow curves

Source: LFW

Split-Hopkinson-Pressure-Bar

AusgangsstabEingangsstab

Lager

Lager

Joch Projektil

Rohr

Zugprobe

Deckel mit

Luftanschluss

Pressluftbehälter mitSchnellöffnungsventil

AusgangsstabEingangsstab

Lager

Lager

Joch Projektil

Rohr

Zugprobe

Deckel mit

Luftanschluss

Pressluftbehälter mitSchnellöffnungsventil

Split-Hopkinson-Tension-Bar

Strain rate: 500 s-1 – 10000 s-1

Temperature range: 93 K – 1273 K

Projectile speed: 2,5 m/s – 50 m/s

Projectile mass: m = 3,15 kg

GewedaProf. El-Magd

Joke Projectile Input rodTensile specimen

Output rod

Tube Cover with airconnection

Air cylinder withquick release valve

Lager Lager Probe

Temperier-

kammer AusgangsstabEingangsstab

Rohr

Preßluftbehälter

Projektil

Auffangbehälter Collection bagSample

Input rod Output rod

Tube

Projectile

Air cylinder

Temperaturechamber

Bearing

BearingBearing

Bearing


17/92


Material law for high strain rate deformation

Source: Diss-Brodmann

dt B K a B K

k n

n

ad f

)(1

400

500

600

700

800

0 0.2 0.4 0.6 0.8

d / dt =5010 s

-1

4889 s-1

4350 s-1

4294 s

-1

3450 s-1

3439 s-1

2558 s-1

2529 s-1

0.001 s-1

o : r

K = 960 MPaB = 0.031n = 0.182 / K = 6.25·10

-6s

A A7075 T7351Druckversuche

w a

h r e

S p a n n u n g ,

M P

a

True plastic strain, -

Lines: CalculationSymbols: experiments

Pressure tests

T r u e S

t r e s s ,

M P A


18/92


Outline









Introduction 1


19/92


Failure mechanisms


Loading type

Shear stress Tensile stress

TiAl6V4

20 µm 20 µm

Shear lokalisation model

(Imperfections theory)

Pore growth model

(Hancock-Mackenzie)


20/92


Damage modelling for the FE cutting simulation (ductile fracture)

Macro mechanical failure models

– Equivalent stress/ strain model: Dσ = σv,f / Dε = εv,f

– Gosh-Model: DGosh

= (1+σ2

/σ1

) σ1

2

– Ayada-Model: dD = (σm/σv) dεv

Micro mechanical failure models (Pore growth models)

– Hancock-Mackenzie-Modell

– Gurson-Tveergard-Needleman-Model

– Johnson-Cook-Model


mf 1 2 3 4 5

v 0 m

σ ε Tε = D + D exp -D 1+ D ln 1+ Dσ ε T

mf n

v

σ3ε = ε + α exp -

2 σ

2

2V m1 1

V,M V,M

σ 3σ0 = + 2fq cosh - 1+ q f

σ 2σ

s

0s

E

εf


21/92


Failure limit at tensile stress (r: Notch radius)


0

0.5

1.0

1.5

0 0.5 1.0 1.5 2.0 2.5

glattr = 1.2 mmr = 0.8 mmr = 0.4 mmr = 0.02 mm

TiAl6V4, = 200°Cdynamisch

f

= 0.09+3.54*exp(-2.61*sm

/sv

)

0

0.5

1.0

1.5

0 0.5 1.0 1.5 2.0 2.5

glattr = 1.2 mmr = 0.8 mm

r = 0.4 mmr = 0.02 mm

TiAl6V4, = 200°Cquasistatisch

f = 0.09+5.2*exp(-2.35*s

m/s

v)

Mehrachsigkeit sm

/sv

l o k a l e p l a s t i s c h e B r u c h - V e r g l e i c h s d e h n

u n g f

0

0.2

0.4

0.6

0.8

1.0

0 0.5 1.0 1.5 2.0 2.5


TiAl6V4, = 20°Cquasistatisch

f = 0.05+2.89*exp(-2.35*s

m/s

v)

0

0.2

0.4

0.6

0.8

1.0

0 0.5 1.0 1.5 2.0 2.5


TiAl6V4, = 20°Cdynamisch

f = 0.05+2.33*exp(-2.49*s

m/s

v)

L o c a

l p

l a s

t i c

f a i l u

r e - e q u

i v a

l e n

t s t r e

s s ε

f

Multiaxiality

dynamic

dynamicquasi-static

quasi-static


22/92


Criteria for chip formation

Geometrical separationcriterion

Separation whenthe cutting edge falls below acritical distance dcr to thenext workpiece node

Without a specificseparation criterion

Separation throughcontinuous remeshing forductile material behavior

Physical separation criterion

Separation while exceedingan defined, maximumequivalent stress or atpredefined maximumtensions

Werkzeug

vc

As

Bs

Cs

DsEs

Hs,w Gs,w Fw Ew Dw Cw Bw

X X

Schnittebene

Fs

I

IKR

Trenn-kriterium

Werkzeug

vc

As

Bs

Cs

DsEs

Hs,w Gs,w Fw Ew Dw Cw Bw

X X

Schnittebene

Fs

I

IKR

Trenn-kriterium

Werkzeug

As

Bs

Cs

Ds

Es

Hs,w Gs,w Fs,w Ew Dw Cw Bw

X X

dcr

dSchnittebene

vc

Span

Werkzeug

As

Bs

Cs

Ds

Es

Hs,w Gs,w Fs,w Ew Dw Cw Bw

X X

dcr

dSchnittebene

vc

Span

Distorted gridtopology

New networkedgrid topology

Tool Tool

Tool

Separationcriterion

Tool

Chip

Sectional plane


23/92


Chip separation - without chip separation criterion by remeshing

Old Mesh

Elements are highly distorted

New Mesh

Remeshing leads to better mesh

Span Werkzeug a) b)Chip Tool

New Mesh

Microstructure-based 3D modeling for micro cutting AISI 1045


24/92


0

300

600

900

1200

0 0.5 1.0 1.5 2

True plastic strain , , -

T r u

e s t r e s s

M P a

CompressionTension

Ø 0.1x0.1 mm

Shear

0.1x0.1x0.1 mmQuasi-static

FE model

Experiment

Tension stress

Compression stress

Shear stress

Concept of the Representative Volume Element (RVE)

Macrostructure

Microstructure

RVE

Representativeness check of the RVE Capture of all significant microstructuralinhomogeneities

Pearlite

Cross section Longitudinal section

Two-phase 3D FE model(0.1 x 0.1 x 0.1 mm)

Ferrite


25/92


Microstructure-based 3D FE model: Validation

50

40

30

20

10

N22%

3% 19%7%

M i x t u r e m o

d e l

d = 1 mm, vc = 35 m/min, f = 12 µm

Test

Nmm

I s o

t r o p

i c m o

d e l

I s o

t r o p

i c m o

d e l

M i x t u r e m o

d e

l

Test

00

4

8

12

16

20Feed force

TorqueChip

Drill

Workpiece

Microstructure

Chip form

Holes

Workpiece

Drill

FerritePearlite

Two-phase FE model formicro drilling in

ferritic-pearlitic carbon steel C45N


26/92


Influence on the formation of residual stresses

The complete coupling of the various parameters influencing the formation of residualstresses has not been done

Source: Preckel

Metallurgical

state

Thermal

state

MechanicalState

Thermally-induced phasetransformation

Heat gain

Residual stresses

Input parameters for thermo-mechanical-metallurgic simulation


27/92


(residual stresses)

Microstructure, initial state of texture

Time dependent thermo-mechanical state of stress

Mathematical approach for the diffusion controlled transformation kinetics: Advanced Johnson-Mehl-Avrami-Kolmogrow-model, 1940

Mathematical approach for the phase transformation without diffusionKoistenen-Marburger-relation, 1959

TTT/TTA-diagram for not isotherm conditions (high strain rate)

Thermal material properties, depending on temperature (cp, l r …)

Mechanical material properties, depending on temperature (E, u a ...)

Elasto-viscoplastic material law

Consideration of grain orientation, texture, micro damages, inclusions, etc.

Description of the damage behavior on high strain rates Tool wear model

O


28/92


Outline


Applications of the FE-cutting-simulation at the WZL 8







Introduction 1

Friction model for FE cutting simulation

Th l l d t th k i d t l t t


29/92


Thermal load at the workpiece and tool contact zone

1 Primary shear zone2 Secondary shear zone at rake face

3 Jam and separation zone4 Secondary shear zone at flank face5 Run-up deformation zone

Structure in the workpiece

Cutting edge

Tool

Tool flankCutting surface

Shear edge

Structure in the chip

2

vc

1

5

3

4

600

700

650

600

400450500

300 310

380 ºC13080

50030

Workpiece

chip

tool

Material: steelElastic limit: kf = 850 N/mm

2 Cutting material: HW-P20Cutting velocity: v

c

= 60 m/minChip thickness: h = 0,32 mmRake angle: o = 10º

Distribution of temperature in the contact

zone(according to Kronenberg

Friction model for FE cutting simulationD f ti t th k i d t l t t


30/92


Deformation at the workpiece and tool contact zone

Turning tool

Shear zone

0,1 mm

Material: C53E

Cutting material: HW-P30Cutting velocity.: vc = 100 m/minChip section: ap x f = 2 x 0,315 mm

2

Cutting edge1 Primary shear zone2 Secondary shear zone at rake face

3 Jam and separation zone4 Secondary shear zone at flank face5 Run-up deformation zone


Cutting edge

Tool


Shear edge

Structure inthe chip

2

vc

1

5

3

4

Friction model for FE cutting simulationM h i l t t th k i d t l t t


31/92


Mechanical stress at the workpiece and tool contact zone

,

Normal stress:

Shear stress:

Tool

According to Oxley and Hatton

Contact zone

1 Primary shear zone2 Secondary shear zone at rake face

3 Jam and separation zone4 Secondary shear zone at the flank face5 Run-up deformation zone


Cutting edge

Tool


Shear edge

Structurein the chip

2

vc

1

5

3

4



32/92


k m R

N R s


Coulomb friction model :

Shear friction model:

with

Continuous passover from dynamic friction(Coulomb) to static friction (shear):

Z.B.: Usui-model

τR – shear stress from friction

s N – normal stress

k – yield stress in shear according to Mises

k f – yield stress according to Misesµ, m – friction coefficients

Coulomb friction

Shear friction

reality

Orowan / Özel

UsiuShaw /Wanheim and Bay

reality

N s

N s

R

R

3

f k k

= 1 − exp(−

)

Static frictionDynamic friction

Wear model for FE cutting simulationDifferent types of wear at the cutting blade and wear mechanisms


33/92


Different types of wear at the cutting blade and wear mechanisms

Sliding mechanisms Not-gliding mechanisms

Abrasion Adhesion Delamination Diffusion electrochemical Oxidation

Cutting

edge

Edge chippage

Crater wear

Flank abrasion

Oxidation notch

Flank wear

Crater wear

Built-up edge

Tool

Flank

Cutting-surface

Workpiece

Chip

Wear model for FE cutting simulation


34/92


Wear model for FE cutting simulation

Tool life acc. to Taylor: Tool life acc. to Hasting:

B

AT

v

k

c C v T

T = tool lifeu = temperature

k, A, B = constantCv = T für vc = 1 m/min

Empirical tool wearmodels

Physical tool wearmodels

Tool wear modelling

Differentialwear modelsTool life equations

Model acc. to Usui: Model acc. to Takeyama:Model acc. to Archard:

H

S F K

dt

dV

3

)T

C(

1chn

2

eCvσdt

dV R

E

eDv Gdt

dV c

dV/dt: wear-volume-rate

H: hardnessF: mechanical loadS: cutting length

K, C1, C2, G, D: constant

sn: normal stressVch: chip sliding speedu: temperature

Abrasion + Diffusion Adhesion

Adhesion / Abrasion

Object boundary conditions


35/92


Boundary Conditions

Inter Object Conditions Environment Object ConditionsObject Conditions

Tool

Workpiece

2D FEM Cutting Model




36/92


Boundary Conditions

Inter Object Conditions Environment Object ConditionsObject Conditions

Friction Heat Transfer

MovementTool

=

Object 1

Workpiece = Object 2



Boundary conditions


37/92


Boundary Conditions

Object Conditions


Movement

Workpiece = Object 2


FR

FN

Self Contact (Chip vs. Workpiece Surface)

FR: Friction Force

FN: Normal Force

Boundary conditions



38/92


Boundary Conditions

Object Conditions


Movement

Cutting

speed vc in

x-direction

x

y

Tool is fixed in x- and y-direction!

Tool

Workpiece

The workpiece is moving in

x-direction with the prescribed

velocity vc. It is fixed in y-direction




39/92


Boundary Conditions

Object Conditions


Movement

Tool

Workpiece

Heat Transfer




40/92


Boundary Conditions

Inter Object Conditions Environment Object Conditions


Object Conditions

Tool

Heat TransferFR

FN

j y

FN

FN



41/92


Boundary Conditions

Inter Object Conditions Environment Object Conditions

Heat Transfer

Object Conditions

Heat Convection Heat Emissivity

Tool

Heat Radiation

Heat Convection

Heat exchange withenvironment

j y

Outline


42/92



Applications of the FE-cutting-simulation at the WZL 8







Introduction 1

FEM software solution for FEM simulation of the cutting process


43/92


g

MSC.Marc

Criteria for the evaluation of FE software


44/92


Source: SIMULIA, ANSYS, LSTC, TWS, SFTC, COMSOL

Criteria

Programm ABAQUS ANSYS/ LS-DYNA AdvantEdge DEFORM COMSOL

Creation of geometries Creation of geometriesand import of CAD data Import of CAD data Creation of simplegeometries andimport of CAD data

Creation of simplegeometries andimport of CAD data

Creation of simplegeometries and importof CAD data

Material catalogue No, has to be defined Yes, expandable Yes, wide Yes, new catalogueimportable

yes

Element type Every type Every type tetrahedron,rectangle

tetrahedron, rectangle Every type

Time integration Implicit / Explicit Implicit / Explicit Explicit Implicit Implicit

Remeshing routine none none yes yes yes

use general general cuttingprocess Deforming process general

Influence on simulation

computation

High, by Python Possible, by Fortran no High, by Fortran High, by Matlab

parallelisation possible possible possible possible possible

Usage at the WZL Eigenfrequency analysis,elast. Tool behavior,elasto-plastic componentbehavior

no no Cutting simulation Thermo-elasticdeformation

Outline


45/92










Introduction 1

Applications of the FE cutting simulation at WZL


46/92


Research focus at the WZL:

Process optimization

Material modelling

Drilling Milling

2D, e.g. Planing

Turning

Simulation of the high speed cutting process


47/92


Cutting speed: vc = 3000 m/min

Feed: f = 0.25 mm

vc



48/92




49/92




50/92




51/92




52/92




53/92


Comparison of different thermal properties of the tools


54/92


Orthogonal turning 2D (vc = 300 m/min, f = 0,1 mm, C45E)

Ceramic-InsertThermal conductivity l = 35 W/mK

WC-InsertThermal conductivity l = 105 W/mK

Tmax = 650°C Tmax = 550°C

3 6TiN 570

Temperature distribution in dependency of the coating andits thickness


55/92


533

3 µm 6 µm

TiN Al2O3

TiN

6 µm 0

510

520

530

540

550

560

570

C a

l c u

l a t e d t e m p e r a

t u

r e a

t t h e

c h i p b o

t t o m

s i d e

T S p

/ ° C

Heat conductivity:HW: 100 W/(mK)TiN: 26,7 W/(mK)

Al2O3: 7,5 W/(mK)

Material: C45E+NTensile strength: Rm = 610 N/mm²

557

539

509

539

Heat capacity:HW: 3,5 J/(cm³K)TiN: 3,2 J/(cm³K)

Al2O3: 3,5 J/(cm³K)

Cutting Material: HW-K10/20

TiN3 µm

TiN6 µm

HW TiN6 µm

Al2O36 µm

CoatingThickness

Tsp

FE-Based calibration process for tool wear model


56/92


. - - -

vc = 250 m/min vc = 200 m/min vc = 150 m/min

Cutting time t

T o o

l - w e a r

V B

Wear curve

C2

lg C1

1/T

l g { w / (

n V S

) }

l g { w / (

n V S

) }

Regression analysis FE-analysis

Temperature

Normal-

tension

Sliding speed

dW/dt

Machining experiments

Determination of thespecific materialparameters C1 and C2

)T

C(

1chn

2

eCvσdt

dW

t = 1 mint = 4 min

t = 6 mint = 10 min

Modeling

2D FE model for tool wear simulation


57/92


V

e r s c h l e i ß V B [ m m ]

Tool life

Phase 3: Methodology for moving the nodes at the rake face


58/92


node square element

Rake

Tool

Tool

Workpiece vc

Chipvc

Phase 3: Methodology for moving the nodes at the flank face


59/92


nDn A nB nC

A B C D

nDn A nB nC= = =Workpiece

Flank

node square element

Tool5 µm

Verification of the tool wear simulation for the flank wearvc = 150 m/min, f = 0.06 mm, ap = 1 mm, dry


60/92


0

0,02

0,04

0,06

0,08

0,1

0 5 10 15 20 25 30 35

Experiment

Simulation

F

l a n k w e a r w i d t h

V B [ m m ]

Cutting time t [min]

eff = -26°

0 = 7°Time:

5 min

Tool

Time:

15 min

Time:

25 min

Time:

35 min

93 µm

Setup of a 3D FE model


61/92


15°

7,5°

15°

Setup of a 3D FE model - specification of the tool holder


62/92


Z

YX

RotZ=6°

Rotx=-6°

Tool ho lder:

Kennametal

ID: PCLNL252M12 F4 NG27

Rake ang le 0 = -6°

Relief ang le 0 = 6°

Tool in cl inat ion ang le ls = -6°

Tool c utt ing edge angler = 95°

Setup of a 3D FE model - Tool position


63/92


f

a p

r workpiece

r tool

r tool = r workpiece

Setup of a 3D FE model - Mesh of the workpiece


64/92


3D simulation


65/92


Workpiece: AISI 1045

Tool: K10

vc = 300 m/minf = 0,1 mm

Cutting Force Fc

Temperature

3D FE model - Post processing


66/92


Temperature (°C)

For better visualization

the tool is hidden



67/92


Temperature (°C)


the tool is hidden



68/92


Strain distribution


the tool is cut

Strain



69/92


Strain Ratedistribution

For better visualizationthe tool is cut

Strain Rate

Models of cutting inserts


70/92


Roughing geometry

CNMG120408RN

Finishing geometry

CNMG120408FN

Simulation of the chip flow

Material:Chip breaker FNChip b reaker RN


71/92


Material:

C45E+N

Cutting material:

HC P25Insert:

CNMG120408

Insert geometry:

Cutting velocity.:vc = 300 m/min

Feed:

f = 0,1 mm

Depth of cut:

ap = 1 mm

Dry cutting

a0 0 lS r 6° -6 ° 95°-6°

90°

a0 0 lS r 6° -6 ° 95°-6°

90°

Simulation of the chip flow

Chip breaker FNChip b reaker RNMaterial:


72/92


a0 0 lS r 6° -6 ° 95°-6°

90°

a0 0 lS r 6° -6 ° 95°-6°

90°

Material:

C45E+N

Cutting material:

HC P25Insert:

CNMG120408

Insert geometry:

Cutting velocity.:vc = 300 m/min

Feed:

f = 0,1 mm

Depth of cut:

ap = 1 mm

Dry cutting

Comparison of simulation and real chip flow

CNMG120408


73/92


Chip breaker NF

HC-P15

r = 95°

n = -6°

ls = -6°

C45E+N

ap = 1,9 mm

f = 0,25 mm

vc = 200 m/min

dry

vc

vf

Drilling: Modelling of size effects

Task:


74/92


Development of a consistent 3D computation model based on the FE method

for scaling the drilling process in consideration of size effects

Reibung

Werkstück

Bohrwerkzeug

PlastischeVerformung

Stofftrennung

Reibung

f

n

drill

FrictionFriction

Workpiece

Separation of materialPlasticdeformation

Previous results: 3D FE computation model for d = 1 – 10 mm

Material modeling Measuring the drill geometry FE boundary conditions


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Tool FEM-Model)T,,( ss

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

Element size

Number of elements

Remeshing strategy

Degree of freedom

FE-Simulation of the drilling process with d = 1 mm (DEFORM 3D)

Machining conditions

Workpiece material: C45E+N


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Tool:rigidnumber of elements: 90 000

Workpiece:visco-plastic (LFW-material law),temperatur fixed at boundary nodesnumber of elements: 100 000

Contact:

coulomb friction ( =0,2)heat transfer (conduction & convection)

Computing time and drilling depth:2000 h; 0.18 mm (70% of the major cutting edge)

Boundary Conditions

Workpiece material: C45E+NTool material: HW-K20Cutting speed: 35 m/minFeed: 0.012 mm/UFeed velocity: 133 mm/minCooling lubricant: none

Verification of the chip formation

Experimental chip formation Chip formation in the simulation


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Workpiece material: C45E+N

Cutting tool material: HW K20

Cutting speed:

Feed:

vc = 35 m/min

f = 0.012 mm

Model validation: Scaling effect of the chisel edge length

6

6

32 Workpiece:


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0

1

2

3

4

5

1 2 3 4 5 6 7 8 9 10

kf,max

= 2 * Fz,max

/ (d * f )

Bohrerdurchmesser d [mm]

s p e z i f i s c h e V o r s c h u b k r a f t k f , m a x

[ k

N / m m

2 ]

0

1

2

3

4

5

1 2 3 4 5 6 7 8 9 10

kf,max

= 2 * Fz,max

/ (d * f )

Bohrerdurchmesser d [mm]

s p e z i f i s c h e V o r s c h u b k r a f t k f , m a x

[ k

N / m m

2 ]

Experiment

20

22

24

26

28

30

1 2 3 4 5 6 7 8 9 10

Durchmesser d [mm]

V e r h ä l t n i s

( d Q

/ d ) [ % ]

Feed:f = 0,012 * d

Cutting speed:vc = 35 m/min

Corner radius:r n = 4 µm

Cutting tool material:

HW-K20

Workpiece:C45E+N

Cooling:None

Simulation

Diameter d [mm]

S p e c

i f i c f e e d

f o r c e

k f , m a x

[ k N / m m

2 ]

Drill diameter d [mm]

Model validation: Temperature at the main cutting edge (center)

400


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Cutting speed: vc = 35 m/min Workpiece: C45E+N

Feed: f = 0,012 * d Cutting tool material:HW-K20Coolant: None Rounding: r n = 4 µm

d = 3 mm

0

100

200

300

1 3 8 10

Diameter d [mm]

T e m p e r a

t u r e a

t t h

e

m a

j o r c u

t t i n g e

d g e T

[ ° C ]

Experiment

Simulation

Modelling of the face milling process

Materials and cutting parameters:


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Work material: Quenched and tempered AISI 1045 (normalized)

Tool material: Coated WC

Cutting parameters:

– No. of teeth: z = 4

– Diameter: D = 32 mm

– Engagement angle: φ A – φE = 180°

– Feed: f = 0.5 mm

– Feed per tooth: f Z = 0.125 mm

– Depth of cut: ap = 0.8 mm

– Tool leading angle: κr = 90°

– Tool inclination angle: λ = -5°

– No. of rev.: n = 2250 min-1

p a

z

Workpiece

Tool

r

n

f

f v


A i l d di l k l


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Axial and radial rake angle:

Axial rake angle γaxial = 9°

Radial rake angle γradial = 5°

γaxial

r tool = r Workpiece

Depth of cut ap

Feed f



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f

a p

r Workpiece

r Tool

tool Workpiece

View

Feed f

Workpiece geometry

1. Simplified

Finding the best workpiece geometry


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1 2

p

workpiece

geometry

2. Simplified work-

piece geometry

3. Simplified work-

piece geometry

Simulation results for the 1. simplified workpiece model

Rough elements within thework piece


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back

Simulation of chip formationnot accurate enough

Final workpiece geometry

Left Right

Simulation results for the 3. simplified workpiece model


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Left Right

Chip formation for the left

side of the work piece:

Results for the face milling operation


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p

at the beginning very thin

chips are produced chip curling starts for higher

undeformed chip thickness

ExperimentSimulation

Verification of the FE model


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.

Full agreement

FE based sensitivity analysis

Heat capacityVaried inputparameters:

Goal outputparameters:

Cutting force Fc

P i f F


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Thermalconductivity

Heatcapacity

Flowstress

Cutting force

Feed force

Passive force

Temperature

FrictionToolmicro-geometry

Thermal conductivity

Flow stress

Friction coefficient

Tool micro-geometry

pa a ete s pa a ete s Passive force Fp

Feed force Ff

Temperature T

Influence

low

medium

high

Legend

Outline

Introduction 1


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Summary and Outlook 9








Cutting

simulation

Fixed input

parametert i l t

Benchmark-Analysis

Cutting parameter 1

Outlook:

Benchmark-Analysis to choose the best tool geometry


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#

Determination of thethermomechanical

loadspectrum, chipflow, chip form

Q,

T,Fi,

material parameter,friction coefficients

+

Temp Wear Stress Chipflow

Tool A + - ++ -

Tool B - -- o +

Tool C ++ ++ + +

A B CTool

F l a n

k w e a r

V B

Cutting parameter 1

Cutting parameter 2

Optimised

tool-

and

tool carrier-

geometry

Tool+

A B C

Cutting parameter

vc1, ap1, f 1

1vc2, ap1, f 1

2

Coating+

TiN TiAlN AlO2

Summary

Machining process: System of complex physically coherent operations


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A holistic and comprehensive simulation of the machining has not been achieved with

conventional empirical or analytical approaches

FEM is a promising method for the holistic simulation of machining – High flexibility

– Implementation of various models that describe the aspects of machining

– Complete reproduction of the machining process

The FE cutting Simulation gives good results under the following boundary conditions: – Realistic reproduction of the tools macro/ micro geometry

– Adequate modeling of the thermo mechanical material behavior

– Exact capturing of the boundary conditions (friction, heat transfer, wear , cooling lubricant, damage,micro structure, etc.)

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?


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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 thesemodels?

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 cuttingprocess!

Explain the difference between a plastic and an elastic-plastic flow stress curve!

fe simulation of cutting processes

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