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© WZL/Fraunhofer IPT
Principles of Cutting
Simulation Techniques in Manufacturing Technology
Lecture 6
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
Intention of the lecture
This lecture is supposed to …
… describe the fundamental mechanisms of cutting.
… convey mechanical, thermal and chemical loads
affecting the cutting wedge.
… illustrate the resultant wear phenomena.
Seite 3 © WZL/Fraunhofer IPT
Chip Form 8
Surface Integrity 7
Tool Life 6
Force Components 5
Machinability 4
Shear Plane Model 3
Chip Formation 2
The Cutting Part 1
Outline
Seite 4 © WZL/Fraunhofer IPT
Cutting: Machining with geometrically defined cutting edge
source: DIN 8580
Manufacturing Processes
1
primary
shaping
2
secondary
shaping /
forming
3
cutting
4
joining
5
coating
6
changing
material
properties
3.2
cutting with
geometrically
defined
cutting
edges
(DIN 8598-0)
major groups
Definition (DIN 8589):
Machining is cutting, in which layers of materials
are mechanically separated from a workpiece in the
form of chips by means of a cutting tool.
Seite 5 © WZL/Fraunhofer IPT
Nomenclature at the wedge
tool shank
Direction of
primary motion
major cutting edge S
major flank Aa
minor flank Aa‘
minor cutting edge S‘
rake face Ag
corner radius
Seite 6 © WZL/Fraunhofer IPT
Tool-in-hand system (ISO 3002)
Plane of
the rake face Ag
Fix with the machine by turning,
if the cutting edge is positioned
in the centre of the spindle.
assumed working
plane Pf
tool orthogonal
plane Po
tool cutting edge
plane Ps
machine coordinate
system
rP
oPcv
fPr
ng
x
y
z
B
A
C
(DIN EN ISO 841)
sPVariable
with t
he p
rocess!
sfv
tool reference plane Pr
ev
r Tool cutting edge angle
s Tool cutting edge
inclination angle
Seite 7 © WZL/Fraunhofer IPT
Tool references systems (ISO 3002/1)
pP
rP
cv
fv
ev
fP assumed
working plane
tool reference plane
tool back
plane
cv
fv
ev
peP
reP
feP
working plane
working reference plane
working
back plane
Tool-in-hand system Tool-in-used system
Seite 8 © WZL/Fraunhofer IPT
Definition of the tool cutting edge inclination during external
cylindrical turning
Working plane
Pf
Tool reference
plane Pr
Tool cutting edge plane PS
Tool holder
Cutting insert
-
s
+
Direction of
primary motion
ap
n
Feed direction
Shoulder
Workpiece
g = 90
Seite 9 © WZL/Fraunhofer IPT
Process kinematics at the wedge
Idealised wedge in the
assumed working plane
The geometry of the idealised
cutting wedge is defined by
the rake angle gO, the wedge
angle bO and the clearance
angle aO
tool trace of the
plane of the
flank Aa
trace of the plane
of the rake face Ag
trace of the
tool back
plane Pp
trace of the tool
reference plane Pr
assumed working plane Pf
assumed direction
of primary motion
assumed
feed direction
tool orthogonal plane Po
gO
aO
bO
Seite 10 © WZL/Fraunhofer IPT
Cutting edge angle and inclination angle
Tool cutting edge angle r Tool cutting edge inclination s
trace of the
assumed
working plane
Pf tool
trace of the tool cutting
edge plane PS
trace of the
tool back
plane Pp
tool reference plane Pr
assumed feed
direction
r
re trace of the
tool reference
plane Pr tool
trace of the
assumed
working plane Pf
Tool cutting edge plane PS
major cutting edge S
assumed direction of
primary motion
s
Seite 11 © WZL/Fraunhofer IPT
Orientation of the cutting edge: process kinematics
free orthogonal cut Free oblique cut Non-free oblique cut
workpiece
tool
chv
cv
chip
chv
cv
workpiece
tool
chip
chv
cv
Tool cutting edge inclination
s = 0° and o = 90°
Tool cutting edge inclination s
not equal to 0°
Seite 12 © WZL/Fraunhofer IPT
Process kinematics at the idealised wedge
chip
trace of the plane of the flank Aa
trace of the plane
of the face Ag
trace of the plane of the
transient surface
workpiece
tool
aO
bO
gO
h
cutting
direction
The wedge geometry is
defined by the clearance
angle aO, the wedge angle bO
and the tool orthogonal rake
angle gO
The wedge penetrates the
material and causes elastic
and plastic deformations
Due to the given geometry the
deformed material is forming a
chip which flows across the
rake face
tool orthogonal plane Po
Seite 13 © WZL/Fraunhofer IPT
Process kinematics and rounded cutting edge radius
chip
workpiece bO
tool
rounded cutting edge rb
cv
cutting speed
fv
feed velocity
h
j
effective cutting
speed e v r In reality there are only
rounded cutting edges
The cutting edge radius is
usually measured in the
tool orthogonal plane PO
Feed direction and cutting
direction are enclosing the
feed motion angle j
The directions of effective
cutting speed and cutting
speed are enclosing the
effective cutting speed
angle h
tool orthogonal plane Po
Seite 14 © WZL/Fraunhofer IPT
Shearing zones in cutting processes
tool
flank Aa
face Ag
chip
workpiece
secondary
shearing zone
of the flank
primary
shearing zone secondary
shearing zone
of the face
bo
rb
Shearing is very essential
in cutting.
So-called shearing zones
might be formed.
The most important
shearing zone is called
primary shearing zone.
The zones where shearing
is caused by friction are
called secondary shearing
zones.
Under a wearless con-
sideration the secondary
shearing zone of the flank
drops out.
Seite 15 © WZL/Fraunhofer IPT
nach: Warn74
turning tool
shearing zone
0,1 mm
1 Primary shearing zone
2 Secondary shearing zone of the rake face
3 Seperative zone (stagnation point)
4 Secondary shearing zone of the flank
5 Preliminary deformation zone
Workpiece material: C53E
Cutting edge material: HW-P30
Cutting speed: vc = 100 m/min
Cross-section area of cut: ap x f = 2 x 0,315 mm2
cut surface
workpiece structure
cut surface
turning tool
flank face
rake face
shear
plane chip
structure
2
vc
1
5
3
4
Chip formation
Seite 16 © WZL/Fraunhofer IPT
Penetration of tool and work piece, cross-sectional area
workpiece
tool
rsinfh =
h
r
p
sin
ab
=
b
fv
kr
fv
A ap
f
kr
direction of rotation The cross-sectional area
is determined by the tool
cutting edge angle r , the
feed f and the depth of cut
ap
The undeformed chip
thickness h and the width
of cut b can be calculated
from the feed f and the
depth of cut ap
respectively, using the
cutting edge angle r .
Seite 17 © WZL/Fraunhofer IPT
Chip Form 8
Surface Integrity 7
Tool Life 6
Force Components 5
Machinability 4
Shear Plane Model 3
Chip Formation 2
The Cutting Part 1
Outline
Seite 18 © WZL/Fraunhofer IPT
Chip formation depending on the material behaviour
Continuous chip
1 Segmented chip
2 Shearing chip 3 Discontinuous chip 4
E0: Degree of deformation in
the shear plane
E: Elastic limit
B: Breaking limit
Z: Fraction point
Yield range
E Z B
Strain e
elastic region
plastic region Range of lamellar-
segmented and
discontinous chip
Range of
continous
chips
Degree of deformation e
e0
Sh
ear
str
en
gth
t
Sh
ear
str
en
gth
t
1
2
3 4
Seite 19 © WZL/Fraunhofer IPT
Chip formation for brittle material behaviour
source: Codron 1906
1. Bring up
gathering
2. Split up, crack
segment
formation
3. Shearing and
next bring up
4. Second segment
formation
and bring up
5. Shearing and
next crack
6. Third segment
formation
and bring up
7. Shearing and
next crack
…
t
F
Dynamic
cutting force
Seite 20 © WZL/Fraunhofer IPT
Chip Form 8
Surface Integrity 7
Tool Life 6
Force Components 5
Machinability 4
Shear Plane Model 3
Chip Formation 2
The Cutting Part 1
Outline
Seite 21 © WZL/Fraunhofer IPT
The shear plane model
shear plane
plastic deformation only in the shear plane
plane strain deformation
ideal sharpness of the cutting edge
Accounts:
Realisation: The orthogonal cut
All the force compo-
nents are in the tool
orthogonal plane Po.
tool cutting edge
angle kr= 90°
tool cutting edge
inclination s= 0°
trace of PS
F
Seite 22 © WZL/Fraunhofer IPT
Krystoff 1939: Shear angle determination
g
= Ο F
Seite 23 © WZL/Fraunhofer IPT
Ernst and Merchant 1941: Force equilibrium and shear angle
cF
og
fF
F
FFzF
gF
nFg
nFF
F
trace of the
shear plane
og
workpiece tool
o a
shear plane location is determined
by the minimum for cutting energy
Φ = 𝜋
4 +
1
2 × (γ0
− ρ)
tan 𝜌 =𝐹𝛾
𝐹γ𝑛
=𝐹𝑓 cos 𝛾 + 𝐹𝑐 sin 𝛼
𝐹𝑐 cos 𝛾 − 𝐹𝑓 sin 𝛼
𝜕𝐸𝑐
𝜕ϕ= 0
𝜕2𝐸𝑐
𝜕ϕ≠ 0 nec.: suff.:
𝑙𝑐 ∙ 𝜕 𝐹𝑐
𝜕ϕ= 0
𝜕2 𝐹𝑐
𝜕ϕ≠ 0 nec.: suff.: dadf
dffsdsafd
Seite 24 © WZL/Fraunhofer IPT
Shear plane model: force calculation
shear work
friction work at the face
Demonstration of the total force as a function of the shear stress with consideration of:
By using the circle of Thales, the total force can be substitute with the two force components
cutting force and feed force. (in the orthogonal cut)
Calculation of the force components with a physical and theoretical background!
(advantage of analytical models)
𝐹𝑧 =𝜏ϕ ∙ 𝑏 ∙ ℎ
sin ϕ ∙ cos(ϕ + 𝜌 − 𝛾0)
𝐹𝑓 =sin(𝜌 − 𝛾0)
sin ϕ ∙ cos(ϕ + 𝜌 − 𝛾0)∙ 𝜏ϕ ∙ 𝑏 ∙ ℎ 𝐹𝑐 =
cos(𝜌 − 𝛾0)
sin ϕ ∙ cos(ϕ + 𝜌 − 𝛾0)∙ 𝜏ϕ ∙ 𝑏 ∙ ℎ
Seite 25 © WZL/Fraunhofer IPT
Chip Form 8
Surface Integrity 7
Tool Life 6
Force Components 5
Machinability 4
Shear Plane Model 3
Chip Formation 2
The Cutting Part 1
Outline
Seite 26 © WZL/Fraunhofer IPT
Overview: Influencing Variables on Machinability
machinability
tool life
surface integrity
total force
chip form
Material
Workpiece
Cutting material
tool
Production conditions
tool type
geometry of the cutting edge
clamping
type of the material
chemical configuration
microstructure
strength property
surface treatment
geometry
surface integrity
clamping
type of the material
chemical configuration
microstructure
strength property
heat treatment
production processes
engagement parameter
cooling
machine tool
machine tool
machine condition
Seite 27 © WZL/Fraunhofer IPT
Chip Form 8
Surface Integrity 7
Tool Life 6
Force Components 5
Machinability 4
Shear Plane Model 3
Chip Formation 2
The Cutting Part 1
Outline
Seite 28 © WZL/Fraunhofer IPT
For the construction of
machine tools
For the definition of the
cutting conditions
For the evaluation of the
cutting edge stresses and the
explanations of the wear
process
For the evaluation of the
material‘s machinability
Resultant force and ist components in the cutting process
Fz: Resultant force
Fc: Cutting force
Ff: Feed force
Fp: Passive force
Fa: Active force
FD: Thrust force
vc: Cutting speed
vf: Feed velocity
ve: effective cutting speed
Fz
vc
Fc
Primary motion (Workpiece)
Direction of feed (Tool)
Fa
FD
Fp
Ff vf
ve The information about the
absolute values and the
directions of the force
components provide a basis:
Seite 29 © WZL/Fraunhofer IPT
Dependencies of the force components
Cutting force Fc
Feed force Ff
Passive force Fp
Feed f
Fc
Ff
Fp
Cutting speed vc
Tool cutting edge angle r
Fc
Ff
Fp
Depth of cut ap
Fc
Ff
Fp
Re
su
lta
nt
forc
e c
om
p. F
i
Re
su
lta
nt
forc
e c
om
p. F
i
Re
su
lta
nt
forc
e c
om
p. F
i
Re
su
lta
nt
forc
e c
om
p. F
i
The peaks in the cutting speed chart are traced back to the fact of built-up edge growth
The decrease in force along with increasing cutting speed is a result of the material softening
The force curves Fp and Ff have opposing trends with increasing tool cutting edge angle r, which is the angle between the main cutting edge and the direction of feed
The increase of the resultant force components dependent on the depth ap can be traced back to the higher stock removal volume
Seite 30 © WZL/Fraunhofer IPT
Cutting force measuring during the turning process
3-component-cutting-force-measuring-platform
Measurement Fc, Ff, Fp
0 5 10 15 20 25
Zeit [s]
-50
0
50
100
150
200
Kra
ft [N
]
Fx Vorschubkraft
Fy Passivkraft
Fz Schnittkraft
0 5 10 15 20 25
Zeit [s]
-50
0
50
100
150
200
Kra
ft [N
]
Fx Vorschubkraft
Fy Passivkraft
Fz Schnittkraft
Fo
rce
/
N
time tc / s
Fc
FP
Ff
Seite 31 © WZL/Fraunhofer IPT
Force approximation: Empirical models
Linear approximation: Potential approximation:
result of a curve fit
calculation of the cutting force
is statistically verified
very precise
no theoretical basis
calculation of the other force
components is not sufficiently
verified
Schlesinger (1931)
Pohl (1934)
Klein (1938)
Richter (1954)
Hucks (1956)
Thomson (1962)
Altintas (1998)
Taylor (1883/1902)
Fischer (1897)
Friedrich (1909)
Hippler (1923)
Salomon(1924)
Kronenberg (1927)
Klopstock (1932)
Kienzle (1952)
result of a curve fit
first part is based on
the shear plane theory
very easy function
not very precise
calculations are not sufficiently verified
(method is not commonly used)
researchers
𝐹𝑖 = 𝐴 ∙ 𝑏 ∙ ℎ + 𝐵 ∙ 𝑏 𝐹𝑖 = 𝑘𝑖1.1 ∙𝑏 ∙ ℎ(1−𝑚)
Seite 32 © WZL/Fraunhofer IPT
Correlation between the force and the undeformed chip thickness
Schnittkraftdiagramm
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
0 100 200 300 400 500 600 700 800
Spanungsdicke h / mm
Sch
nit
tkra
ft F
c / N
Schnittkraftdiagramm
100
10000
100
Spanungsdicke h / mm
Sc
hn
ittk
raft
Fc
/ N
Today you describe the problem by curve fitting on your computer!
Linear system with a trend line Double logarithmic system with
a trend line
Diagram of the cutting force Diagram of the cutting force
Cu
ttin
g f
orc
e
Thickness of cut Thickness of cut
Cu
ttin
g f
orc
e
Seite 33 © WZL/Fraunhofer IPT
KIENZLE Equation to calculate the static cutting forces
e
bxayi =
1'loglog'log ii FhaF =
1'loglog)log( ii Fha
b
F=
1
1')( i
mi Fhb
Fi =
im
ii hbkF
=1
1.1
)(log)(log
)('log)('log1tan
AhBh
AFBFm ii
i
==e
i = c, f, p
Linear equation:
KIENZLE equation:
Chip thickness h / mm
1
45º
1
0,1 0,2 0,4 0,6 0,8 1,0 2,0
200
400
600
800
1000
2000
Fo
rce
Fi
W
idth
of
cu
t b
=
Fi’
/ (N
/mm
)
A
B
Fi’1= 1740 N/mm2 = ki1.1
e
mi
1 - mi = 0,7265 e
Seite 34 © WZL/Fraunhofer IPT
Chip Form 8
Surface Integrity 7
Tool Life 6
Force Components 5
Machinability 4
Shear Plane Model 3
Chip Formation 2
The Cutting Part 1
Outline
Seite 35 © WZL/Fraunhofer IPT
Tool wear
Tool wear is influenced by high contact stresses, high cutting
temperatures and relative sliding velocities
These process values depend on:
tool
and
workpiece
materials
tool
geometry
machining
parameters interface
conditions
Seite 36 © WZL/Fraunhofer IPT
Thermic stress – segmenting the effective work during machining
Deformation
energy
Friction
energy
Effective
Energy
WE = Fe * le
Shear energy
Cutting energy
Friction of flank face
Friction of rake face
Latent
energy
and
heat
Quelle: Vieregge
Scherarbeit
The work transformed during the machining relates with the chip width
Especially the shearing energy increases with wider chips
Friction of flank face and cutting energy are in independent of the chip width h
The energy dedicated during the machining process is nearly completely transformed into heat
The heat emerges in the primary shearing zone and the friction zone at the tool (secondary shearing zone)
Cu
t d
ista
nc
e
Eff
ec
tive
wo
rk W
e / (
m d
aN
/m) 7000
5000
4000
3000
2000
1000
Nm
Friction of rakeface
Total energy
Chip h / mm
0 0,2 0,4 0,6 0,8 1,0
Friction of flank face and cutting energy
Shearing energy
Seite 37 © WZL/Fraunhofer IPT
Distribution of heat and temperature in workpiece, chip and tool
600
700 650
600
400
450
500
300 310
380 ºC
130
80 500
30
Workpiece
Chip
Tool
Material: steel
Yield stress: kf = 850 N/mm2
Cutting material: HW-P20
Primary speed: vc = 60 m/min
Chip width: h = 0,32 mm
Chip angle: go= 10º
Allocation of heat in the machining zone
Source: Kronenberg, Vieregge
QWp Qchip
Qtool
Qair
Heat flows emerging from the machining zone
Qair = Heat flow to environment
Qchip= Heat flow to chip
QWp = Heat flow to workpiece
Qtool = Heat flow to tool
Seite 38 © WZL/Fraunhofer IPT
Cutting forces and chip temperatures in turning
0
100
200
300
N
500
Cu
ttin
g f
orc
e F
c
Te
mp
era
ture
Cutting speed
Aluminium Steel/ Titanium
Feed 0,25 mm 0,1 mm
Depth of cut 2 mm 1 mm
Seite 39 © WZL/Fraunhofer IPT
Tool wear locations
Area of high level
of stress and
temperature, i.e. of
the order of 1200°C.
Crater Wear
Built-Up Edge
Observable for
ductile materials.
Not stable,
breaks off
frequently
Flank Wear
Mainly responsible
for the resulting
surface quality
=> used as failure
criteria.
Tool
Workpiece
Chip
Tool Wear appears at three locations at the cutting tool
Seite 40 © WZL/Fraunhofer IPT
Wear mechanisms
The total wear at the wedge is a superposition of distinct wear mechanisms
During cutting all distinct wear mechanisms occur simultaneously
Diffusion and oxidation are dependent on the tem-perature level and occur mainly at high cutting speeds
source: Vieregge
adhesion
Adhesion
Tool W
ear
Cutting Temperature
(cutting speed, feed et al.)
High Temp
Oxidation
Abrasion
Diffusive
wear
Seite 41 © WZL/Fraunhofer IPT
Wear mechanisms at the wedge: adhesion
Low cutting speeds causes low contact temperatures between chip and tool. This goes along with high contact pressure.
Low contact temperatures, high contact pressure and material affinity lead to adhesion.
Adhesion at the wedge may cause built-up edges.
Built-up edges are unstable. They peel away off the edge and slide over the flank and the face periodically.
deformed
chip
built-up edge
undeformed
bulk of the
workpiece
tool
tool
built-up edge
Seite 42 © WZL/Fraunhofer IPT
Wear mechanisms at the wedge: abrasion
Abrasion at the wedge is
caused by hard particles in
the chip, which penetrate
into the tool material and
slide and scratch over the
face.
As a result on the face a
crater is generated.
As a result on the flank a
wear land is generated.
flank wear land
crater
face
Seite 43 © WZL/Fraunhofer IPT
Catastrophic failure of the wedge
If the mechanical load at
the wedge surpasses the
resistance of the cutting
material, the cutting edge
fails.
little disruptions
at the cutting edge
face
flank
crater
Chipping and break outs
at cutting edge
Seite 44 © WZL/Fraunhofer IPT
The cutting edge influenced by thermic overload
The cutting material may heat massively through thermic load which reduces its resistance towards mechanical stress; the cutting edge may deform plastically
The plastic deformation appears basically with high speed steel
Thermic alternating load may cause comb cracks at the wedge
They appear mainly during discontinuous cuts whereas the cutting edge heats in circuit and cools down in the disruption
In order to avoid comb cracks in discontinuous cutting (e.g. during milling) the use of coolant can often be avoided
Plastic
deformation
Comb crack
Seite 45 © WZL/Fraunhofer IPT
Formation of comb cracks and parallel cracks during milling
Source: Lehwald, Vieregge
VB
42CrMo4+QT
Comb cracks
vc = 275 m/min
Comb and parallel cracks
GJS70 vc = 200 m/min
Heating
during the
cut
-y
Temperature
Cooling down
Tension
ten. + 0 – comp.
Seite 46 © WZL/Fraunhofer IPT
Wear mechanisms at the wedge: diffusion
If the temperature level of
the contact area reaches a
limit and affinity of material
is given diffusion can be
activated
The diffusion is shown by
an analogue experiment.
Here a cemented carbide
tool works on quenched
steel
During cutting only a very
short time is available for
diffusion to occur
-80 -60 -40 -20 0 20 40
Depth / µm
Ma
ss
co
nc
en
tra
tio
n / %
0
2
4
6
8
10
12
14
16
18
20
100
Material (42CrMo4) Cutting material (HT-P20)
Cr
Co
Ni
Fe
Co
Ni Fe
Seite 47 © WZL/Fraunhofer IPT
Types of wear and values for the tool wear characterization
Flank Wear
Crater Wear
VB
VB: Flank wear width
KM: Crater center distance
KF: Distance from crater to edge
KB: Crater width
KT: Crater depth
KM
KF
A
A
A-A
KB
KT
Seite 48 © WZL/Fraunhofer IPT
A
Crater
A
Cut A-A
KT
KB
KM SVa
Evaluation of crater wear
Indicators
according to DIN
ISO 3685
Crater wear
2,50 mm
0,0
-50,0
50,0
[µm]
2,50 mm
0,0
-50,0
50,0
[µm]
Measured indicators for
the evaluation of crater
wear are the crater depth
KT, the crater centre
distance KM, the crater
width KB and the
displacement of the
cutting edge SV in face
flank direction
Weakening of the cutting
edge is a result of
massive crater wear
Danger of a cutting
edge fraction
(crater edge fracture)
Seite 49 © WZL/Fraunhofer IPT
Evaluation of flank wear
A distinction is drawn between the measured indicators flank wear width VB and the
displacement of the cutting edge in flank direction SVa
The flank wear width is refered to the cutting edge without wear
Wear chamfer at the main
cutting edge
b
Flank wear width VB
VB
B m
ax.
C B N
b/4 VB
C
VB
B
A
re
VB
N
SV
a
Indicators according to DIN ISO 3685 Flank wear examined with a microscope
Seite 50 © WZL/Fraunhofer IPT
The typical course of wear
0
20
40
60
80
100
120
140
160
180
0 1 2 3 4 5 Time / min
Wid
th o
f fl
an
k w
ea
r la
nd
VB
/ µ
m
16MnCr5 (62 HRC)
CBN20
vc = 200 m/min
f = 0,08 mm
ap = 0,2 mm
I II III
Seite 51 © WZL/Fraunhofer IPT
Taylor Function
Frederick Winslow Taylor
(USA, 1856-1915)
Tool-life function in a double logarithmic system has
the shape of a straight line
bxmy =
T
Vvc
C
Ck
log
logtan ==
vc CvkT logloglog =
with
v
k
c CvT =Taylor-equation
(simple) T
k
c CTv = /1
Cv (ordinate intercept):
standardised tool life T for
vc = 1 m/min 1
10
100
10 10010 100
10
100
1
Tool life function (logarithmic scale)
Cutting speed
vc / (m/min)
To
ol li
fe T
/ m
in
tool-life straight
line
vc
CT Taylor-equation
(extended) apfzvc k
p
k
z
k
cvfa afvCT =
CT (abscissa intercept):
standardised cutting speed vc
for T = 1 min
Seite 52 © WZL/Fraunhofer IPT
Wear diagram: Flank wear
the choice of the
tool life criterion
determination of the tool life consideration of the
boundary conditions
under fixed cutting
edge geometries
and
cutting conditions
Wear diagram
Seite 53 © WZL/Fraunhofer IPT
Tool life straight line
Standzeitdiagramm
1
10
100
100 1000
Schnittgeschwindigkeit / m/min
Sta
nd
zeit
/ m
in
HW - P25
Determination of the cutting speed for a tool life of 15 minutes
T=15 min
Tool life diagram
Cutting speed / m/min
too
l li
fe
T /
min
min 170 3 , 0 15
m v VB
=
Seite 54 © WZL/Fraunhofer IPT
Tool wear modelling
Tool life by Taylor: Tool life by Hasting:
B
AT
=
v
k
c CvT =
T = Tool life
= Temperature k, A, B = Constants
Cv = T for vc = 1 m/min
Empirical
tool wear model
Physical
tool wear model
Tool wear modelling
Tool wear rate models Tool life equations
Model by Usui: Model by Takeyama: Model by Archard:
H
SFK
dt
dV
3
=
)T
C(
1chn
2
eCvσdt
dV
= R
E
eDvGdt
dVc
=
dV/dt = Wear volume per time
H = Hardness
F = Mechanical load
S = Cutting path
K, C1, C2, G, D = Constants
n = Normal pressure
vch = Sliding velocity
= Temperature
Abrasion + Diffusion Abhesion
Adhesion /
Abrasion
Seite 55 © WZL/Fraunhofer IPT
Chip Form 8
Surface Integrity 7
Tool Life 6
Force Components 5
Machinability 4
Shear Plane Model 3
Chip Formation 2
The Cutting Part 1
Outline
Seite 56 © WZL/Fraunhofer IPT
Source: F. Betz
Cutting
speed,
feed
Wear on
minor
flank,
overall
wear
Corner and
flank wear,
friction and
welds,
cooling
Tool geometry,
work material,
temperature,
tool material
Dynamic stiffness of
the system tool-work-
machine tool, cutting
forces, chip formation,
tool micro geometry,
work material,
cutting parameter
Influences on surface quality in metal cutting
Kinematic roughness Cutting roughness Additional factors
Tool
motion
Cutting
edge
Chip formation
mechanisms,
BUE
Alteration of
cut surface
Vibrations, chips,
deformation of feed
tracks
Influenced by
Factors influencing surface quality in metal cutting
Influenced by Influenced by Influenced by Influenced by
Seite 57 © WZL/Fraunhofer IPT
Kinematic (theoretical) depth of roughness
e
ee
=
=
r8
fR
:oder
4
frrR
2
t
22
t
The theoretical depth of roughness Rt can be
derived from the geometrical engagement
specifications and is a function of the feed and the
corner radius rε
Kr
f
Rt rε
f
2
__
rε rε-Rt
Feed f
Feed f
Dep
th o
f ro
ug
hn
ess R
t
rε = 0,4
rε = 0,8
rε = 1,2
or
Seite 58 © WZL/Fraunhofer IPT
Theoretical and measured depths of roughness
The illustration
demonstrates a
comparison of theoretical
and measured depths of
roughness
The divergency between
the results in the low feed
area can be traced back to
the low chip width which
grows with increasing
rounded cutting edge
radius
Source: Moll und Brammertz
4
8
12
16
20
µm
28
0,2 0,3 mm 0,6 0,4 0 0,1 0
re = 0,25
2
0,5
1
measured depth of
roughness
theoretical depth of
roughness
Dep
th o
f ro
eu
gh
ness R
t /
µm
feed f / µm
Seite 59 © WZL/Fraunhofer IPT
Chip tip theory
The geometrical ideal surface
profile is determined by the
kinematic depths of roughness
Rkin
Due to the material resilience
and the cutting edge wear,
material of the work piece is
being displaced which partially
springs back afterwards
Chip tips are created because of
this process
Due to the creation of chip tips
the real depth of roughness is
higher than the theoretical
kinematic depth of roughness
Rkin.
z
x
Cutting edge plane Ps
Pr
r
re
f
Rkin
apmin
Source: Brammertz, 1961
Working plane Pf
Seite 60 © WZL/Fraunhofer IPT
Chip Form 8
Surface Integrity 7
Tool Life 6
Force Components 5
Machinability 4
Shear Plane Model 3
Chip Formation 2
The Cutting Part 1
Outline
Seite 61 © WZL/Fraunhofer IPT
Evaluation criterion: Chip Formation
1 Ribbon chip
2 Snarled chip
3 Flat helical chip
4 Angular helical chip
5 Helical chip
6 Helical chip segment
7 Cylindrical helical chip
8 Spiral chips
9 Spiral chip segment
10 Discontinous chip
2 3 4 5 6 7 8 9 10 1
Unfavourable Acceptable Good Acceptable
Seite 62 © WZL/Fraunhofer IPT
Thanks for your attention!