finite element simulation of cutting processes€¦ · lecture 8 laboratory for machine tools and...

© 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

Seite 2 © WZL/Fraunhofer IPT

Summary and Outlook 9

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 simulation 6

Damage models for the FE cutting simulation and multiphase simulation 5

Constitutive material laws for the FE cutting simulation 4

CAD modelling for the FE cutting simulation 3

Requirements of the FE cutting simulation 2

Introduction 1

Outline


Influencing factors on the cutting process

Workpiece material

structure

texture

mechanical

properties

hardness

residual stresses

Cutting zone

chip forming

mechanisms

cooling lubricant

cutting parameters

contact

conditions

e.g.: friction, wear

heat transfer

Tool

cutting material

coating

geometry

tool holder

Machine

machine design

drive system

clamping device

Bild

eines

Prozesses

M


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 /

Rolling 0.1 – 0.5 10 – 10+3 0.16 – 0.7

Sheet metal

forming 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


Outline









Introduction 1


Requirements to the FE cutting simulation

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

process

Modelling of the thermo mechanical material behavior for the entire temperature and

strain 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.)


Cutting simulation: Input- und output parameters

Tool

Strain

Tension

Temperature

Cutting forces

Wear

Chip formation

Temperature

Tension

Deformation

Rate of deformation

Chip type

Chip flow

Chip crack Component

Strain

Temperatures

Deformation

Burr formation

Distortion

Future:

Residual stresses

Surface quality, e.g.: roughness,

changes in shape,

Measurement and position

Component / tool

Geometry

Material data

Contact conditions

Boundary conditions

Cutting conditions


Outline









Introduction 1


Macro- und micro tool geometry

Major clearance angle: a = 10°

Twist angle: d = 35°

Cutting material: HW-K20

Grain size: DK = 0.5 – 0.7 µm

Construction dimensions DIN 6539

Type: N

Diameter: d = 1 mm

Drill-point angle: s = 118°

Querschneide

Freifl ä che

Hauptschneide a

d

chisel edge

flank face

major cutting edge a

d


Definition of element type


Creation of tool models close to reality

Macro

geometry

4 mm

Drilling tool FEM-model Determination of the tool geometry

Micro

geometry

6 µm 6 µm

Real tool CAD-model


Zusammenfassung und Ausblick 9

Outline

Zusammenfassung und Ausblick Zusammenfassung und Ausblick Zusammenfassung und Ausblick Summary and Outlook 9








Introduction 1


Thermo-mechanical behavior of material

i iB u


Thermo-mechanical behavior of material

Quelle: Diss-Abouridoaune

( , , )Ts 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

, -

s ,

M

Pa

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

Strain Rate HardeningStrain Hardening Thermal Softening

Source: Diss- Abouridouane


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 -1/2

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

Initial density

of dislocations Dislocation jam

Influence of temperature

and strain rate Influence of grain size

m

n r0

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 process

Thermal activated processes


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

Geweda

Prof. El-Magd Joke Projectile Input rod

Tensile specimen Output rod

Tube Cover with air

connection

Air cylinder with

quick release valve

Lager LagerProbe

Temperier-

kammerAusgangsstabEingangsstab

Rohr

Preßluftbehälter

Projektil

AuffangbehälterCollection bag Sample

Input rod Output rod

Tube

Projectile

Air cylinder

Temperature

chamber

Bearing

Bearing Bearing

Bearing


Material law for high strain rate deformation

Source: Diss-Brodmann

dtBKa

BKk

n

n

adf

)(1

4 0 0

5 0 0

6 0 0

7 0 0

8 0 0

0 0 . 2 0 . 4 0 . 6 0 . 8

d / d t = 5 0 1 0 s

- 1

4 8 8 9 s - 1

4 3 5 0 s - 1

4 2 9 4 s - 1

3 4 5 0 s - 1

3 4 3 9 s - 1

2 5 5 8 s - 1

2 5 2 9 s - 1

0 . 0 0 1 s - 1

o : r

K = 9 6 0 M P a B = 0 . 0 3 1 n = 0 . 1 8 2

/ K = 6 . 2 5 · 1 0 - 6

s

A A 7 0 7 5 T 7 3 5 1 D r u c k v e r s u c h e

w

a h r e

S p a n n u n g , M

P a

True plastic strain, -

Lines: Calculation

Symbols: experiments

Pressure tests

Tru

e S

tress,

M

PA


Outline









Introduction 1


Failure mechanisms


Loading type

Shear stress Tensile stress

TiAl6V4

20 µm 20 µm

Shear lokalisation model

(Imperfections theory)

Pore growth model

(Hancock-Mackenzie)


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) σ12

– Ayada-Model: dD = (σm/σv) dεv

Micro mechanical failure models (Pore growth models)

– Hancock-Mackenzie-Modell

– Gurson-Tveergard-Needleman-Model

– Johnson-Cook-Model


m

f 1 2 3 4 5

v 0 m

σ ε Tε = D + D exp -D 1+ D ln 1+ D

σ ε T

m

f 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


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*s

m/s

v)

0

0.5

1.0

1.5

0 0.5 1.0 1.5 2.0 2.5


TiAl6V4, = 200°Cquasistatisch

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

m/s

v)

Mehrachsigkeit sm

/sv

lokal

e pla

stis

che

Bru

ch-V

ergle

ichsd

ehnung

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)

Local pla

stic f

ailu

re-e

quiv

ale

nt

str

ess ε

f

Multiaxiality

dynamic

dynamic quasi-static

quasi-static


Criteria for chip formation

Geometrical separation

criterion

Separation when

the cutting edge falls below a

critical distance dcr to the

next workpiece node

Without a specific

separation criterion

Separation through

continuous remeshing for

ductile material behavior

Physical separation criterion

Separation while exceeding

an defined, maximum

equivalent stress or at

predefined maximum

tensions

Werkzeug

As

Bs

Cs

Ds

Es

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

X X

dcr

dSchnittebene

vc

Span

Werkzeug

vc

As

Bs

Cs

Ds

Es

Hs,w Gs,w Fw Ew Dw Cw Bw

X X

Schnittebene

Fs

I

IKR

Trenn-

kriterium

Werkzeug

As

Bs

Cs

Ds

Es


X X

dcr

dSchnittebene

vc

Span

Werkzeug

vc

As

Bs

Cs

Ds

Es


X X

Schnittebene

Fs

I

IKR

Trenn-

kriterium

Geometrischen Trennkriterium Physikalisches Trennkriterium

Werkzeug

As

Bs

Cs

Ds

Es


X X

dcr

dSchnittebene

vc

Span

Werkzeug

vc

As

Bs

Cs

Ds

Es


X X

Schnittebene

Fs

I

IKR

Trenn-

kriterium

Werkzeug

As

Bs

Cs

Ds

Es


X X

dcr

dSchnittebene

vc

Span

Werkzeug

vc

As

Bs

Cs

Ds

Es


X X

Schnittebene

Fs

I

IKR

Trenn-

kriterium

Geometrischen Trennkriterium Physikalisches Trennkriterium

Distorted grid

topology

New networked

grid topology

Tool Tool

Tool

Separation

criterion

Tool

Chip

Sectional plane


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


0

300

600

900

1200

0 0.5 1.0 1.5 2.0

True plastic strain , , -T

rue

str

ess

M

Pa

CompressionTension

Ø 0.1x0.1 mm

Shear

0.1x0.1x0.1 mmQuasi-static

FE model

Experiment

Tension stress

Compression stress

Shear stress

Microstructure-based 3D modeling for micro cutting AISI 1045

Concept of the Representative Volume Element (RVE)

Macrostructure

Microstructure

RVE

Representativeness check of the RVE Capture of all significant microstructural

inhomogeneities

Pearlite

Cross section Longitudinal section

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

Ferrite


Microstructure-based 3D FE model: Validation

50

40

30

20

10

N 22%

3% 19% 7%

Mix

ture

mo

de

l

d = 1 mm, vc = 35 m/min, f = 12 µm

Test

Nmm

Iso

trop

ic m

od

el

Iso

trop

ic m

od

el

Mix

ture

mo

de

l

Test

0 0

4

8

12

16

20 Feed force

Torque Chip

Drill

Workpiece

Microstructure

Chip form

Holes

Workpiece

Drill

Ferrite Pearlite

Two-phase FE model for

micro drilling in

ferritic-pearlitic carbon steel C45N


Influence on the formation of residual stresses

The complete coupling of the various parameters influencing the formation of residual

stresses has not been done

Source: Preckel

Metallurgical

state

Thermal

state

Mechanical

State

Thermally-induced phase

transformation

Heat gain

Residual stresses


Input parameters for thermo-mechanical-metallurgic simulation

(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 diffusion

Koistenen-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


Outline


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







Introduction 1


Friction model for FE cutting simulation

Thermal load at the workpiece and tool contact zone

1 Primary shear zone

2 Secondary shear zone at rake face

3 Jam and separation zone

4 Secondary shear zone at flank face

5 Run-up deformation zone

Structure in the workpiece

Cutting edge

Tool

Tool flank

Cutting surface

Shear edge

Structure in the chip

2

vc

1

5

3

4

600

700 650

600

400

450

500

300 310

380 ºC

130

80 500

30

Workpiece

chip

tool

Material: steel

Elastic limit: kf = 850 N/mm2

Cutting material: HW-P20

Cutting velocity: vc = 60 m/min

Chip thickness: h = 0,32 mm

Rake angle: o = 10º

Distribution of temperature in the contact

zone (according to Kronenberg)



Deformation at the workpiece and tool contact zone

Turning tool

Shear zone

0,1 mm

Material: C53E

Cutting material: HW-P30

Cutting velocity.: vc = 100 m/min

Chip section: ap x f = 2 x 0,315 mm2

Cutting edge 1 Primary shear zone



4 Secondary shear zone at flank face



Cutting edge

Tool

Tool flank

Cutting surface

Shear edge

Structure in

the chip

2

vc

1

5

3

4



Mechanical stress at the workpiece and tool contact zone

𝜏

𝜎𝑛

𝑥

𝜏, 𝜎

Normal stress:

Shear stress:

Tool

According to Oxley and Hatton

Contact zone

1 Primary shear zone



4 Secondary shear zone at the flank face



Cutting edge

Tool

Tool flank

Cutting surface

Shear edge

Structure

in the chip

2

vc

1

5

3

4


kmR

NR 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

sN – normal stress

k – yield stress in shear according to Mises

kf – yield stress according to Mises

µ, m – friction coefficients

Coulomb friction

Shear friction

reality

Orowan / Özel

Usiu

Shaw /

Wanheim and Bay

reality

Ns

Ns

R

R

3

fkk

𝜏𝑅 = 𝑘 1 − exp(−𝜇𝜎𝑁𝑘)

Static friction Dynamic friction


Wear model for FE cutting simulation

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

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

B

AT

v

k

c CvT

T = tool life

u = temperature k, A, B = constant

Cv = T für vc = 1 m/min

Empirical tool wear

models

Physical tool wear

models

Tool wear modelling

Differential

wear models Tool life equations

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

H

SFK

dt

dV

3

)T

C(

1chn

2

eCvσdt

dV

R

E

eDvGdt

dVc

dV/dt: wear-volume-rate

H: hardness

F: mechanical load

S: cutting length

K, C1, C2, G, D: constant

sn: normal stress

Vch: chip sliding speed

u: temperature

Abrasion + Diffusion Adhesion

Adhesion /

Abrasion


Boundary Conditions

Inter Object Conditions Environment Object Conditions Object Conditions

Tool

Workpiece

2D FEM Cutting Model

Object boundary conditions


Boundary Conditions

Inter Object Conditions Environment Object Conditions Object Conditions

Friction Heat Transfer

Movement Tool

=

Object 1

Workpiece = Object 2




Boundary Conditions

Object Conditions


Movement

Workpiece = Object 2


FR

FN

Self Contact (Chip vs. Workpiece Surface)

FR: Friction Force

FN: Normal Force

Boundary conditions


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



Boundary Conditions

Object Conditions


Movement

Tool

Workpiece

Heat Transfer



Boundary Conditions

Inter Object Conditions Environment Object Conditions


Object Conditions

Tool

Heat Transfer FR

FN


FN

FN


Boundary Conditions

Inter Object Conditions Environment Object Conditions

Heat Transfer

Object Conditions

Heat Convection Heat Emissivity

Tool

Heat Radiation

Heat Convection

Heat exchange with

environment



Outline


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







Introduction 1


FEM software solution for FEM simulation of the cutting process

MSC.Marc


Criteria for the evaluation of FE software

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

Criteria

Programm ABAQUS ANSYS/ LS-DYNA AdvantEdge DEFORM COMSOL

Creation of geometries Creation of geometries

and import of CAD data

Import of CAD data

Creation of simple

geometries and

import of CAD data

Creation of simple

geometries and

import of CAD data

Creation of simple

geometries and import

of CAD data

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

importable

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 component

behavior

no no Cutting simulation Thermo-elastic

deformation


Outline









Introduction 1


Applications of the FE cutting simulation at WZL

Research focus at the WZL:

Process optimization

Material modelling

Drilling Milling

2D, e.g. Planing

Turning


Cutting speed: vc = 3000 m/min

Feed: f = 0.25 mm

vc

Simulation of the high speed cutting process


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

Ceramic-Insert

Thermal conductivity l = 35 W/mK WC-Insert

Thermal conductivity l = 105 W/mK

Tmax = 650°C Tmax = 550°C

Comparison of different thermal properties of the tools


533

3 µm 6 µm

TiN Al2O3

TiN

6 µm 0

510

520

530

540

550

560

570

Ca

lcu

late

d t

em

pe

ratu

re a

t th

e

chip

bottom

sid

e T

Sp / °

C

Heat conductivity:

HW: 100 W/(mK)

TiN: 26,7 W/(mK)

Al2O3: 7,5 W/(mK)

Material: C45E+N

Tensile 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

TiN

3 µm

TiN

6 µm

HW TiN

6 µm

Al2O3

6 µm

Coating

Thickness

Tsp

Temperature distribution in dependency of the coating and

its thickness


FE-Based calibration process for tool wear model

Verschleißmarkenbreite über die Schnittzeit

16MnCr5 (einsatzgehärtet), Stegbreite = 1 mm, cBN bestückte Einstechplatte der Sorte N151.2-600-50E-G

Schnittgeschwindigkeit vc = 150, 200, 300 m/min und Vorschub f = 0,06 mm

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40

Schnittzeit t [min]

Ve

rsc

hle

ißm

ark

en

bre

ite

VB

[µ

m]

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

Cutting time t

To

ol-w

ear

VB

Wear curve

C2

lg C1

1/T

lg{w

/(n

VS)}

slg

{w/(

nV

S)}

sRegression analysis FE-analysis

Temperature

Normal-

tension

Sliding speed

dW/dt

Machining experiments

Determination of the

specific material

parameters C1 and C2

)T

C(

1chn

2

eCvσdt

dW

t = 1 min

t = 4 min t = 6 min

t = 10 min

Modeling


Ve

rsc

hle

iß V

B [

mm

]

2D FE model for tool wear simulation

Tool life


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

node square element

Rake

Tool

Tool

Workpiece vc

Chip vc


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

nD nA

nB nC

A B C D

nD nA nB nC = = = Workpiece

Flank

node square element

Tool 5 µm


Verification of the tool wear simulation for the flank wear

vc = 150 m/min, f = 0.06 mm, ap = 1 mm, dry

0

0,02

0,04

0,06

0,08

0,1

0 5 10 15 20 25 30 35

Time [min]

Fla

nk W

ear

Wid

th V

B/

[mm

]

Experiment

Simulation

Fla

nk w

ear

wid

thV

B [

mm

]

Cutting time t [min]

eff = -26°

a0 = 7°Time:

5 min

Tool

Time:

15 min

Time:

25 min

Time:

35 min

93 µm


15°

7,5°

15°

Setup of a 3D FE model


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

Z

YX

RotZ=6°

Rotx=-6°

Tool holder:

Kennametal

ID: PCLNL252M12 F4 NG27

Rake angle 0 = -6°

Relief angle a0 = 6°

Tool inclination angle ls = -6°

Tool cutting edge angle r = 95°


f

a p

r workpiece

r tool

r tool = r workpiece

Setup of a 3D FE model - Tool position


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


3D simulation

Workpiece: AISI 1045

Tool: K10

vc = 300 m/min

f = 0,1 mm

Cutting Force Fc

Temperature


Temperature (°C)

For better visualization

the tool is hidden

3D FE model - Post processing


Temperature (°C)


the tool is hidden




Strain distribution


the tool is cut

Strain



Strain Rate

distribution


the tool is cut

Strain Rate


Roughing geometry

CNMG120408RN

Finishing geometry

CNMG120408FN

Models of cutting inserts


Simulation of the chip flow

Material:

C45E+N

Cutting material:

HC P25

Insert:

CNMG120408

Insert geometry:

Cutting velocity.:

vc = 300 m/min

Feed:

f = 0,1 mm

Depth of cut:

ap = 1 mm

Dry cutting

Chip breaker FN Chip breaker RN

a0 0 lS r

6° -6 ° 95°-6°

90°

a0 0 lS r

6° -6 ° 95°-6°

90°


Simulation of the chip flow

a0 0 lS r

6° -6 ° 95°-6°

90°

a0 0 lS r

6° -6 ° 95°-6°

90°

Chip breaker FN Chip breaker RN Material:

C45E+N

Cutting material:

HC P25

Insert:

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

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:

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

Plastische

Verformung

Stofftrennung

Reibung

f

n

drill

Friction Friction

Workpiece

Separation of material Plastic

deformation


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

Material modeling Measuring the drill geometry FE boundary conditions

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)

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 ( =0,2)

heat transfer (conduction & convection)

Computing time and drilling depth:

2000 h; 0.18 mm (70% of the major cutting edge)

Boundary Conditions

Machining conditions

Workpiece material: C45E+N

Tool material: HW-K20

Cutting speed: 35 m/min

Feed: 0.012 mm/U

Feed velocity: 133 mm/min

Cooling lubricant: none


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:

vc = 35 m/min

f = 0.012 mm


Model validation: Scaling effect of the chisel edge length

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8 9 10

kf,max

= 2 * Fz,max

/ (d * f)

Bohrerdurchmesser d [mm]

sp

ezifis

ch

e V

ors

chub

kra

ft k

f,m

ax [kN

/mm

2]

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8 9 10

k

f,max = 2 * F

z,max / (d * f)

Bohrerdurchmesser d [mm]

sp

ezifis

ch

e V

ors

chub

kra

ft k

f,m

ax [kN

/mm

2]

Experiment

20

22

24

26

28

30

32

1 2 3 4 5 6 7 8 9 10

Durchmesser d [mm]

Ve

rhä

ltnis

(d

Q / d

) [

%]

Feed:

f = 0,012 * d

Cutting speed:

vc = 35 m/min

Corner radius:

rn = 4 µm

Cutting tool material:

HW-K20

Workpiece:

C45E+N

Cooling:

None

Simulation

Diameter d [mm]

Sp

ecific

fe

ed

fo

rce

kf,

max [kN

/mm

2]

Drill diameter d [mm]


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

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

Feed: f = 0,012 * d Cutting tool material:HW-K20

Coolant: None Rounding: rn = 4 µm

d = 3 mm

0

100

200

300

400

1 3 8 10

Diameter d [mm]

Te

mp

era

ture

at th

e

ma

jor

cu

ttin

g e

dg

e T

[°C

]

Experiment

Simulation


Modelling of the face milling process

Materials and cutting parameters:

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: φA – φE = 180°

– Feed: f = 0.5 mm

– Feed per tooth: fZ = 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



Axial and radial rake angle:

Axial rake angle γaxial = 9°

Radial rake angle γradial = 5°

γaxial


f

a p

r Workpiece

r Tool

r tool = r Workpiece

View

Depth of cut ap

Feed f

Workpiece geometry



1 2

1. Simplified

workpiece

geometry

2. Simplified work-

piece geometry

3. Simplified work-

piece geometry

Finding the best workpiece geometry


back

Simulation results for the 1. simplified workpiece model

Rough elements within the

work piece

Simulation of chip formation

not accurate enough


Final workpiece geometry

Left Right

Simulation results for the 3. simplified workpiece model


Chip formation for the left

side of the work piece:

Results for the face milling operation

at the beginning very thin

chips are produced

chip curling starts for higher

undeformed chip thickness


.

Full agreement

Experiment Simulation

Verification of the FE model


FE based sensitivity analysis

Thermal

conductivity

Heat

capacity

Flow

stress

Cutting force

Feed force

Passive force

Temperature

Friction Tool

micro-geometry

Heat capacity

Thermal conductivity

Flow stress

Friction coefficient

Tool micro-geometry

Varied input

parameters:

Goal output

parameters: Cutting force Fc

Passive force Fp

Feed force Ff

Temperature T

Influence

low

medium

high

Legend


Outline









Introduction 1


#

Cutting

simulation

Determination of the

thermomechanical

loadspectrum, chip

flow, chip form

Q,

T,

Fi,

Fixed input

parameter material parameter,

friction coefficients

+

Temp Wear Stress Chip

flow

Tool A + - ++ -

Tool B - -- o +

Tool C ++ ++ + +

A B C

Tool

Benchmark-Analysis

Fla

nk w

ear

VB

Cutting parameter 1

Cutting parameter 2

Optimised

tool-

and

tool carrier-

geometry

Tool +

A B C

Cutting parameter

vc1, ap1, f1

1

vc2, ap1, f1

2

Outlook:

Benchmark-Analysis to choose the best tool geometry

Coating +

TiN TiAlN AlO2


Summary

Machining process: System of complex physically coherent operations

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?

Name two friction models. What are the advantages and the disadvantgeas of these

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!

finite element simulation of cutting processes€¦ · lecture 8 laboratory for machine tools and...

Documents