Finite Element Simulation of Cutting Processes

Transcription

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
© WZL/Fraunhofer IPT
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
6
7
Process Modells
8
Verification
Seite 4
Conditions in cutting operations
Forces:
100 to 104 N
Stresses:
103 N/mm2
Strain
0,1 to 5
Strain rate
0,5 * 104 to 0,5 *106 1/s
Temperatures:
≈ 1500 °C
Temperature gradient:
> 103 °C/mm
Seite 5
Comparison of strain, strain rate and temperature for different
manufacturing processes
Manufacturing process
Extrusion
Forging/ Rolling
Sheet metal forming
Cutting
strain
2-5
0,1 - 0,5
0,1 - 0,5
1 - 5
Strain rate / s-1
T homolog a
10-1 - 10-2
10 - 103
10 - 102
103 - 106
0,16 - 0,7
0,16 - 0,7
0,16 - 0,7
0,16 - 0,9
a: Thomolog = T / Tmelting 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
compression test
tensile test
vw
d0
t0
u0
vw
torsion test
r
∆l
Mt
R
d0
z
h0
l
l0
Mt
d
α
γR
l
lubricant
ϕmax ≈ 0,8 to 1
ϕmax ≈ 0,8 to 1
.
ϕ ≈ 10-3 to 103 s-1
.
ϕ≈
ϑ ≈ 20 to 1300 °C
ϑ≈ 20 to 700 °C
10-3
to
102
ϕmax ≈ 5
s-1
.
ϕ ≈ 10-4 to 30 s-1
ϑ ≈ 20 to 1300 °C
adapted from: Kopp
Seite 8
Split-Hopkinson-Bar-Test
tempered chamber
projectile
output bar
input bar
strain gages
striker bar
v >> 50m/s
.
ϕ ≈ to 104 s-1
specimen
ϑ ≈ to 1200 °C
source: LFW, RWTH Aachen
Seite 9
Flow stress curves
1400
parameter:
kf = f (ϕ,
ϕ, ϕ)
ϑ = const. = RT
Flow stress k f
N/mm 2
800
1/s
10000
0
0
1600
9SMnPb36
strain
N/mm2
5000
0,5
Flow stress k f
1
0
strain rate ϕ
800
0
1/s
10000
0
strain ϕ
0,5
source: LFW, RWTH Aachen
Ck45N
5000
1
0
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
σFlow 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
  T − T m 

r
σ = A + Bε n ⋅ (1 + C ln(ε& / ε&0 )) ⋅ 1 − 
  Tm − Tr  


(
)
viscous damping
plasticity
Material constants:
Reference velocity:
Room temperature:
Melting temperature:
A, B, n, C, m
ε&0
temperature function
Tr
Tm
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/Eblack body where Eblack 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
6
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
Boundary Conditions
Object Conditions
Friction
Heat Transfer
Tool
Movement
=
Object 1
Workpiece = Object 2
Seite 20
Boundary Conditions
Boundary Conditions
Self Contact (Chip vs. Workpice Surface)
Object Conditions
Friction
Heat Transfer
FN
Movement
FR
FR: Friction Force
Workpiece = Object 2
FN: Normal Force
Seite 21
Boundary Conditions
Object Conditions
Workpiece is moving in the
x-direction with the prescribed
velocity vc, in the y-direction the
workpiece is fixed
Tool is fixed in x- and y-direction!
Friction
Heat Transfer
Tool
Movement
cutting
speed vc
y
in
x-direction
Workpiece
x
Seite 22
Boundary Conditions
Tool
Object Conditions
Heat Transfer
Friction
Heat Transfer
Movement
Workpice
Seite 23
Boundary Conditions
Object Conditions
Friction
Heat Transfer
Tool
FN
FN
Heat Transfer
FR
FN
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
Boundary Conditions
Object Conditions
Heat Transfer
Tool
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
6
7
Process Modells
8
Verification
Seite 28
Chip separation
Chip separation based
on nodal distances
Chip separation based
on a critical indicator
l
AS
chip
BS
CS
DS
vc
HS,W
GS,W
FS,W
dcr
cutting plane
d
CS
DS
Tool
X
EW
BS
lKR
ES
X
AS
separation
criterion
DW
CW
BW
AW
X
FS
HS,W GS,W
vc
Tool
ES
X
FW
EW
DW
CW
BW
AW
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
6
7
Process Modells
8
Verification
Seite 34
Simulation of serrated chip formation
Consistent strain distribution
Continuous metallographic
structure
continuous chip formation
Moderately different strains
over the chip dimensions
caused by dynamical loads
of mechanical and thermal
nature
Very different strains over the
chip dimensions caused by
dynamical loads of
mechanical and thermal
nature
distinct segments of the chip’s
top
discontinuous chip segments
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
undamaged
10
5
stress
Effective strain
σ
A
B
σ0
damaged
E
C
0
cutting edge radius: rβ = 10 µm
cutting speed:
vc = 25 m/min
material:
TiAl6V4
deformation
ε
Chip formation based on manipulated flow stress
data incorporating
strain softening.
Seite 37
Deformation localisation based on modified material
characteristics I/II
i
iii
ii
6•105 s-1
i: shear initiation
ii: sliding
iii: new segmentation
2•105 s-1
dφ/dt
200
cutting force
simulation
cutting force
experiment
material:
AlSI 1045
force / N
150
cutting speed:
vc = 1000 m/min
100
feed force
experiment
50
feed force
simulation
0
7,65
7,75
7,85
7,95
feed:
f = 0.1 mm
8,05
time / ms
Seite 38
Crack initiation based on breakage and crack hypotheses
flow Stress at 100°C / (N/mm²)
Phase 2.1: Shearing Initiation
Phase 2.2: Crack Initiation
The Material Law does not fulfil the
conditions in front of the cutting edge
The accelerated sliding is initialised by a
crack on the workpiece material surface
Strain rate hardening (damping) in extreme
conditions distorts the calculated results
The crack region is characterised by uniaxial
principal tensile stresses
5000
strain rate / s-1
0,001
10000
4000
Cracks can be simulated by failure criteria
considering the deformation history applying
a following law
50000
100000
3000
2000
εk
C = F (max(σ1,0))
∫
0
1000
0
0
1
2
3
Real Plastic Strain
4
Seite 39
Segmented Chip Simulation reveals periodic sticking zone
First Contact
Start of Shearing
Crack Initiation
Gliding
Start of Shearing
Crack initiation
strain rate
75
62,5
50
37,5
25
12,5
Material Speed / m/min
90
End of Gliding New Segmentation
0
Seite 40
Verification of Segmented Chip Simulation
tertiary shear zone
800
relative cutting force Fc/b [N/mm]
primary shear zone secondary shear zone
(sticking zone)
700
600
500
400
300
200
100
0
0,0
Theory of
FEM-Simulation
van Luttervelt & Pekelharing
Measurement
Simulation
0,4
0,8
1,2 0,0
cutting time tc / ms
0,4
0,8
1,2
cutting time tc / ms
Seite 41
Outline
1
Introduction
2
Material Models
3
Boundary Conditions
4
Chip Separation
5
6
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
6
7
Process Modells
8
Verification
Seite 44
Orthogonal cutting process (2D FE-model)
r
vch
tool
chip
r
vc
workpiece
If depth of cut ap >> uncut chip thickness h
State of plane strain condition is reached
Seite 45
Simulation of the High Speed Cutting Process
Cutting speed
Feed
vc = 3000 m/min
f = 0.25 mm
vc
Seite 46
Seite 47
Seite 48
Seite 49
Seite 50
Seite 51
Seite 52
Comparison of of different thermal properties of the tools
Orthogonal truning 2D (vc = 300 m/min, f = 0,1 mm, ck45)
Ceramic-Insert
Thermal conductivity λ = 35 W/mK
Tmax = 650°C
WC-Insert
Thermal conductivity λ = 105 W/mK
Tmax = 550°C
Seite 53
Temperature distribution in dependency of the coating and
its thickness
TiN
6 µm
Tsp
TiN
570
Calculated temperature at the
chip bottom side TSp / °C
3 µm
6 µm
557
560
550
539
540
539
533
530
520
509
510
Al2O3
0
coating
thickness
TiN
3 µm
TiN
6 µm
heat conductivity:
HW:
100 W/(mK)
TiN:
26,7 W/(mK)
Al2O3: 7,5 W/(mK)
HW
TiN
6 µm
Al2O3
6 µm
heat capacity:
HW:
3,5 J/(cm³K)
TiN:
3,2 J/(cm³K)
Al2O3: 3,5 J/(cm³K)
material: C45E+N
HW: HW-K10/20
tensile strength: Rm = 610 N/mm²
Seite 54
2D FE-model for tool wear simulation
Temperatur
Phase 1:
Thermo-mechanical
FE-simulation of the cutting
process till steady state
solution is obtained.
VB<VBtool life
Phase 2:
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 n ⋅ VS ⋅ C1 ⋅ exp( −
C2
)
T
Verschleiß VB [mm]
Phase 3:
Tool wear
Wear
increase
growth
Tool geometry updating in
dependence of wear
Wear
VB>VBtool life
Abort
Verschleißmarkenbreite, VB [mm]
(a)
VBStandzeit
Tool life
VBK+1
VBK
A
tK
B
∆t = tK+1 - tK
tK+1
Schnittzeit, t [min]
Seite 55
Phase 4: Methodology for moving the nodes at the rake face
tool
node
square element
5 µm
tool
Werkzeug
workpiece
vc
ϕ
A
nX
X
B
A
∆W
ϕ‘
ϕ
AB
ϕ‘
X
∆W sin ϕ‘
chip
rake
vc
∆W cos ϕ‘
B
Seite 56
Phase 4: Methodology for moving the nodes at the flank face
Tool
node
square element
5 µm
Tool
Workpiece
vc
nB
nA
A
workpiece
B
nC
C
nD
flank
D
nA = nB = nC = nD
Seite 57
Results of the tool wear simulation
γeff = -26°
Tool
Time:
5 min
α0 = 7°
Time:
15 min
Process:
Part Turning
Work material:
Cutting Speed:
16MnCr5 (case hardened) Time:
vc = 150 m/min
25 min
Feed:
f = 0,06 mm
Depth of cut:
ap = 1 mm
Cooling:
dry
Time:
35 min
93 µm
Seite 58
Verification of the tool wear simulation for the flank wear
vc = 150 m/min, f = 0.06 mm, ap = 1 mm, dry
γeff = -26°
Tool
Flank wear width VB [mm]
Time:
5 min
α0 = 7°
Time:
15 min
Time:
25 min
Time:
35 min
93 µm
0,1
Experiment
0,08
0,06
Simulation
0,04
0,02
0
0
5
10
15
20
25
30
35
Cutting time t [min]
Seite 59
Longitudinal Turning, 3D FE-Model
Why 3D modelling?
orthogonal cut
3D turning process
n
workpiece
created surface
ap
vc
k
f
major cutting edge
minor cutting edge
major cutting edge
f
vc
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
Workpiece / Tool
geometries
material data
contact conditions
boundary conditions
cutting conditions
Tool
strain
stresses
temperatures
process forces
wear
Workpiece
strain
temperatures
deformation
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 γ0 = -6°
Relief angle α0 = 6°
Tool inclination angle λs = -6°
Rotx =-6°
X
Y
Tool cutting edge angle κr = 95°
Seite 65
Setup of a 3D FE-Model - tool position
f
r
tool
ap
r
r
tool
=r
workpiece
workpiece
Seite 66
Setup of a 3D FE-Model - Mesh of the workpiece
Seite 67
3D Simulation
vc = 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
Temperature (°C)
the tool is hidden
Seite 70
Strain distribution
the tool is cut
Seite 71
Strain Rate
distribution
the tool is cut
Seite 72
Models of Cutting Inserts
Roughing geometry
CNMG120408RN
Finishing geometry
CNMG120408FN
Seite 73
Simulation of the chip flow
Chip breaker FN
Chip breaker RN
Material:
C45E+N
Cutting material:
HC P25
Insert:
CNMG120408
Insert geometry:
α0 γ0
λS
κr
ε
6° -6 ° -6° 95° 90°
Cutting velocity.:
vc = 300 m/min
Feed:
f = 0,1 mm
Depth of cut:
ap = 1 mm
Dry cutting
Seite 74
Simulation of the chip flow
Chip breaker FN
Chip breaker RN
Material:
C45E+N
Cutting material:
HC P25
Insert:
CNMG120408
Insert geometry:
α0 γ0
λS
κr
ε
6° -6 ° -6° 95° 90°
Cutting velocity.:
vc = 300 m/min
Feed:
f = 0,1 mm
Depth of cut:
ap = 1 mm
Dry cutting
Seite 75
Comparison of simulation and real chip flow
CNMG120408
Chip breaker NF
HC-P15
κr = 95°
γn = -6°
λs = -6°
C45E+N
ap = 1,9 mm
f = 0,25 mm
vc = 200 m/min
dry
vf
vc
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
drill
f Bohrwerkzeug
friction
Reibung
Reibung
friction
work
piece
Werkstück
plastic
Plastische
Verformung
deformation
Stofftrennung
separation
of material
Seite 77
Previous results: 3D FE calculation model for d = 1 – 10 mm
Material modeling
σ = σ(ε, ε&, T)
Measuring the drill geometry
Tool
FE boundary conditions
FEM-Model
Strain hardening
Cutting parameters
Plasticity
Tool: rigid / elastic
Damping mechanism
Friction law
Relaxation
Heat transfer
Dynamic strain ageing
Elementsize
Temperature influence
Number of elements
Loss of cohesion
Remeshing strategy
Failure mechanism
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 speed: vc = 35 m/min
cutting tool material: HW K20
feed:
f = 0.012 mm
Seite 80
Model evaluation: scale efect of the chisel edge length
6
Verhältnis (dQ / d) [%]
2
2]
spezifische
kf,max [kN/mm
]
Specific
feedVorschubkraft
force kf,max [kN/mm
32
5
4
Workpiece:
C45E+N
30
28
26
Cutting speed:
vc = 35 m/min
24
22
20
1
2
3
4
5
6
7
8
9 10
Durchmesser d [mm]
Diameter
d [mm]
3
Feed:
f = 0,012 * d
Cutting tool material:
HW-K20
2
Experiment
1
Simulation
kf,max = 2 * Fz,max / (d * f)
0
1
2
3
4
5
6
7
DrillBohrerdurchmesser
diameter d [mm] d [mm]
8
9
10
Corner radius:
rn = 4 µm
Cooling:
none
Seite 81
Model validation: Temperature at the major cutting edge (center)
Temperature at the
major cutting edge T [°C]
400
Experiment
Simulation
d = 3 mm
300
200
100
0
1
3
8
10
diameter d [mm]
Cutting speed:
Feed:
Coolant:
vc = 35 m/min
f = 0,012 * d
none
Workpiece:
C45E+N
Cutting tool material:HW-K20
Verrundung:
rn = 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:
n
Engagment 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
tool
κr
ap
Work piece
f
z
Seite 83
Axial and radial rake angle:
• axial rake angle
γaxial = 9°
• radial rake angle
γradial = 5°
γaxial
Seite 84
Depth of cut ap
r
Feed f
Work piece geometry
tool
= r Work piece
f
r tool
View
ap
rWork piece
Seite 85
Finding the best work piece geometry
1. Simplified
work piece
geometry
2. Simplified work
piece geometry
1
2
3. Simplified work
piece geometry
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
Experiment
.
Simulation
Full agreement
Seite 91
Outline
1
Introduction
2
Material Models
3
Boundary Conditions
4
Chip Separation
5
6
7
Process Modells
8
Verification
Seite 92
Verification of the FE-model
experiment
simulation
tool
primary
shear zone
workpiece
max. principle stress
chip
0.05 mm
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
workpiece
fiber
chip
measuring spot
major
cutting
edge
insert
0.5 mm
technical specifications
quartz fiber
(∅
∅ 0.26 mm)
temperature range: app. 250 -1200 °C
maximum time resolution: 2 ms
measured temperature independent of surface emissivity
Seite 95
Combination of temperature and force measurement
Chip temperature
aluminium
feed
0,25 mm
depth of cut
2 mm
steel / titanium
0,1 mm
1 mm
Cutting speed
Cutting force Fc
500
N
300
200
100
0
Seite 96
Alternative measurement position - workpiece surface
°C
700
measuring point
Temperature
distance to cutting edge 1 mm
quartz fibre
600
500
4.5 mm
400
300
200
0
20
40
60
Cutting speed
80
100 m/s
Seite 97
Positioning of the measurement spot
Seite 98
Alternative measurement position - top of the chip
quartz fibre
cemented
carbide tip
measuring point
cutting insert
Seite 99
Alternative measurement position - top of the chip
1000
°C
quartz fibre
measuring point
Temperatur
temperature
cemented
carbide tip
800
optic
Optik
600
400
cutting insert
Hartmetallspitze
cemented
carbide tip
0
1000 2000 3000 4000 5000 6000 m/min
Schnittgeschwindigkeit
cutting speed
Seite 100
Chip temperature
[°C]
Force Measurement
Simulation
600
400
AA7075
f = 0,25 mm
ap = 2 mm
200
0
0
Cutting force Fc
500
Experiment
2000
4000
6000
Cutting speed vc [m/min]
Cutting force Fc
400
[N]
200
Simulation
vc = 3000 m/min
100
0
Experiment
vc = 3000 m/min
Seite 101
Verification of the simulated chip formation by in-situ photography
workpiece
tool
tool
vc
microscope
workpiece (etched)
light barrier
• in-situ photography of the orthogonal cutting process, suitable for all materials
• cutting speed up to vc = 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 vch
Seite 102
In-situ photography of chip formation - realised setups
Discontinuous cut
Continuous cut
+ etched workpiece
+ measurement of forces
- no temperature
measurement
+ etched workpiece
+ force and temperature
measurement
setup 3
rot. workpiece
setup 2
rot. workpiece
setup 1
rot. tool
vc,max = 5000 m/min
f = free
ap = free
workpiece = free
tool = free
+ 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: ap = 1 mm
cutting speed:
vc = 460 m/min
lenth of contact zone: 0.2064 mm
depth of chip root: 0.041 mm
thickness of chip root: 0.1013 mm
maximal thickness of chip : 0.123 mm
minimal thickness of chip : 0.056 mm
magnification: 100
shear angle Φ = 28°
Seite 104
Results of in-situ photography - chip geometry, second image
workpiece: AISI1045
feed: f = 0,1 mm
cutting speed:
vc = 460 m/min
lenth of contact zone: 0.358 mm
depth of chip root: 0.073 mm
magnification: 100
thickness of chip root: 0.155 mm
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
cutting speed:
vc = 460 m/min
vc = 515,5 m/min
vc = 460 m/min
vc = 522,1 m/min
magnification: 100
change in shear angle
∆F = 18%
change of the contact
length ∆lk = 40%
Seite 106
Results of in-situ photography - compression of the segment
workpiece: AISI1045
feed: f = 0,1 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
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 2
vc2, ap1, f1
+
tool
B
C
determination of the
thermomechanical
loadspectrum, chip
flow, chip form
A
coating
TiN TiAlN AlO2
B
C
tool
temp
+
Flank wear VB
Q,
T,
Fi,
cutting parameter
1
2
A
cutting parameter 1
#
+
vc1, ap1, f1
Benchmark-Analysis
Cutting
simulation
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-BarTest?
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
• conv. flow stress curves, kf
• assumptions of friction conditions, µ
• cutting conditions
• depth of cut, ap
• cutting speed, vc
• rake angle, g
orthogonal cutting tests
simulation, e.g. FEM
measurement
• cutting forces (Fc, Fp)
• chip thickness (hch)
• contact length (lk)
calculation
• forces and stresses
• temperature
• strain
• strain rate
comparisson
evaluation of the real flow stress curve
kf = f(strain, strain rate, temperature)
Seite 111
Chip separation criteria and breakage criteria
Seite 112
FE-Mesh
elastic tool
ideal-plastic
workpiece (AISI 1045)
f
vc
y
0.5 mm
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

Finite Element Simulation of Cutting Processes

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