Available online at www.sciencedirect.com
2212-8271 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the International Scientific Committee of the “15th Conference on Modelling of Machining Operations
doi: 10.1016/j.procir.2015.03.101
Procedia CIRP 31 ( 2015 ) 310 – 315
ScienceDirect
15th CIRP Conference on Modelling of Machining Operations
Influence of the built-up edge on the stress state in the chip formation zone
during orthogonal cutting of AISI1045
Eckart Uhlmanna, Steffen Henzea*, Katrin Brömmelhoffb
aInstitute for Machine Tools and Factory Management, Berlin University of Technology, Pascalstr. 8-9, 10587 Berlin, Germany
b Institute for Materials Science and Technology-Metallic Material, Berlin University of Technology, Ernst-Reuter-Platz 1, 10587 Berlin, Germany
* Corresponding author. Tel.: +49-30-314-23624; fax: +49-30-314-25895. E-mail address: [email protected]
Abstract
In-situ strain measurements with high energy synchrotron radiation during orthogonal cutting of AISI1045 were carried out. Thereby it was
possible to determine the stress state in the chip formation zone during the cutting process. As such, observations regarding the formation of
built-up edges during the cutting process have been made. The formation of a built-up edge on the cutting tool is a common phenomenon
during cutting of mild steel and other ductile materials, in particular at low cutting speeds. This may result in increased tool wear and a decrease
in the resulting surface quality. By analyzing the chip roots of the in-situ experiments, it was possible to determine the geometry of the built-up
edges on tools with a rake angle of J = 0° and cutting edge radii of rE = 30 μm and rE = 60 μm. Using the obtained data a simulation model
which represents the built-up edge could be established with two versions of the built-up edge: a solid one as part of the rigid tool and an elastic
one in front of the tool. Using FEM cutting simulations with and without built-up edges, it was possible to show the influence of a built-up edge
on the chip formation and the stress state in the chip formation zone. With this data, a comparison of the results of the cutting simulations with
those of the in-situ experiments was conducted.
© 2015 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of The International Scientific Committee of the “15th Conference on Modelling of Machining Operations”.
Keywords: Chip; Cutting edge; Simulation; Stress
1. Introduction
The formation of a built-up edge (BUE) is a common
phenomenon in particular during the machining of ductile
materials [1, 2]. The grade of the BUE formation depends on
the workpiece material, the tool geometry and the process
parameters. Especially during the machining of carbon steels
with cutting speeds of vc = 60 m/min and less the formation of
a BUE often occurs [3] due to the low temperatures in the chip
formation zone [4]. Thereby, the hardened workpiece material
sticks to the cutting edge and the rake face and forms a new
tool geometry with a smaller wedge angle and a bigger rake
angle [5]. Thus the chip formation and the stress state in the
chip formation zone are influenced as well as the tool wear,
the surface quality, the cutting forces and temperatures [1, 6].
The separation of the BUE from the cutting tool leads to
damage of the tool and thus to an increase of the tool wear [7].
Furthermore the undefined geometry of the tool with a BUE
and the aperiodic separation of the BUE can lead to a poor
surface quality of the workpiece and vibrations during the
cutting process [8].
Several investigations on the BUE have been undertaken in
the past. Opitz and Gappisch examined the coherence of the
BUE formation with the used workpiece material, the process
Nomenclature
BUE built-up edge
h undeformed chip thickness
le edge length of an element in the FE-Simulation
m shear friction coefficient
rE cutting edge radius
t exposure time
vc cutting speed
M plastic strain
J rake angle
μ Coulomb friction coefficient
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the International Scientifi c Committee of the “15th Conference on Modelling of Machining Operations
311
Eckart Uhlmann et al. / Procedia CIRP 31 ( 2015 ) 310 – 315
parameters and the tool geometry [5]. It was found that the
ductility of the workpiece material and the cutting speed have
a significant influence. Fang and Dewhurst analysed the BUE
formation and proposed a slip line model [1]. They
investigated the influence of the rake angle on the size of the
BUE. Childs developed a material model for the simulation of
the BUE formation [4, 9, 10] and applied it at the micro-
machining scale [9]. It was determined that the damage law,
which was implemented in the simulation is very important
for the initialisation of the BUE formation [4]. Kümmel et al.
investigated the microstructure of the BUE and concluded a
possible protecting effect for the tool [11]. In a further work
they examined the microstructure of the tool surface in order
to stabilise the BUE as a protection layer on the tool surface
[12]. Until now it was not possible to analyze the influence of
a BUE on the stress state in the chip formation zone with the
use of experimental determined data. This paper aims to
present the results of investigations, which were carried out in
this way.
2. In-situ strain measurements
By the use of high energy synchrotron radiation it was
possible to determine the strain state and thus the stress state
in the chip formation zone during orthogonal cutting [13]. A
special experimental setup for measurements at the PETRA
III storage ring at DESY, Hamburg was developed for this
purpose [14]. With this setup it was possible to position a X-
ray beam on a sample of AISI1045 during an orthogonal cut.
The beam has a size of 20 μm x 20 μm. Different measuring
positions in the chip formation zone have been defined in
order to gain detailed information regarding the stress state in
the chip formation zone. The setup of the cutting experiment
was therefore placed between the X-ray beam source and the
2D detector (type MAR345, Marresearch, Norderstedt,
Germany) which captured the diffraction patterns. The
diffraction experiments were carried out according to the
Debye–Scherrer method [15].
The cutting speed is limited to vc = 3 mm/min. This is due
to the long exposure time of t = 30 s and the need for a very
stiff cutting setup to avoid a displacement of the measuring
position during the in-situ experiment. Unfortunately this very
low cutting speed favours the formation of a BUE. The used
cutting inserts are made of cemented carbide (grade IC20,
ISCAR Germany GmbH, Ettlingen) and have the ISO-
geometry SPUN 120304 with a rake angle of J = 0° and a
cutting edge radius of rE = 6 μm. In addition cutting edge radii
of rE = 30 μm and rE = 60 μm were prepared by brushing. A
more detailed description of the experimental setup is
described by Uhlmann et al. [14].
Through the analysis of the data obtained by the in-situ
strain measurements, it was possible to develop and validate a
material model for the cutting simulation of AISI1045. The
simulations with this model showed a good qualitative and
partially quantitative accordance in comparison to the
experimentally determined data. This confirms the quality of
the material model. An investigation of the experimentally
determined stress state in the chip formation zone resulted in
new findings with regard to the shear angle model by Opitz
and Hucks [14, 16].
Fig. 1. BUE at the chip root of a tool with J = 0° and rE = 30 μm.
The analysis of the chip roots showed evidence that BUEs
appeared during the in-situ strain measurements for certain
cutting parameters. This is a common phenomenon for the
low cutting speed of vc = 3 mm/min. Tools with a cutting
edge radius of rE = 30 μm und rE = 60 μm showed remains of
a BUE in the analysis of the chip roots. Figure 1 shows a chip
root after an in-situ experiment. The used tool had a rake
angle of J = 0° and a cutting edge radius of rE = 30 μm. The
undeformed chip thickness is h = 0.06 mm. A BUE at the
cutting edge can clearly be seen.
The formation of a BUE inevitably has an influence on the
stress state in the chip formation zone. Thus a detailed
examination of the stress state under the influence of a BUE is
useful in order to investigate the results in comparison to the
experimental results for cutting parameters where the
formation of a BUE is indicated.
3. Simulation model
In order to examine the influence of the BUE on the stress
state in the chip formation zone, simulations were carried out
with the software DEFORM 2D v11.0.1, Scientific Forming
Technologies Corporation, Columbus, USA. The necessary
material model is based on yield curves, which were
determined by compression tests. For this purpose a
Rastegaev geometry was used which maintains its cylindricity
during the compression test up to plastic strains of M = 0.6
[17]. With the findings of the in-situ strain measurements the
material model was adapted and validated [14].
A hybrid friction model was used in order to reproduce the
friction condition between cemented carbide and AISI1045.
The hybrid friction model is a combination of a Coulomb
friction model and a shear friction model. The Coulomb
friction coefficient was carried out by friction tests to be
μ = 0.5 and the shear friction coefficient was set to m = 0.58
[14]. Together with the material model this combination
showed the best agreement between the stresses determined
by the experiment and those of the simulation [14].
Simulations with and without the BUE were carried out in
order to investigate the influence of the BUE on the stress
state in the chip formation zone. The process was depicted as
a rigid-plastic FEM model. Since tools with the rake angle
50 μm
BUE
312 Eckart Uhlmann et al. / Procedia CIRP 31 ( 2015 ) 310 – 315
Fig. 2. FEM-model of the cutting process in DEFORM 2D.
J = 0° and cutting edge radii of rE = 30°μm and rE = 60°μm
showed the greatest disposition for forming a BUE,
simulations with these parameters and the undeformed chip
thickness of h = 30 μm were carried out. The geometry of the
BUE was determined by the analysis of chip roots of the in-
situ experiments.
Figure 2 shows the simulation model. It consists of
approximately 7,000 elements, due to remeshing procedures
the exact number of elements varies during the simulation.
However, different mesh windows were used to define
regions with a finer mesh. The smallest elements with an edge
length of approx. le = 1.5 μm are located around the cutting
edge and the BUE.
The BUE was realised in the simulations in two different
ways. The first one was a reproduction of the BUE as a part of
the rigid tool. The second variant was an elastic BUE, which
was placed in front of the cutting edge (Figure 3). The elastic
BUE has a Young’s modulus of E = 207,000 MPa and a
Poisson ratio of Q = 0.3. The friction coefficient between the
BUE and the workpiece was set to μ = 0.15 which is a typical
value for the friction between steel and steel [18]. The
geometry of the BUE was extracted with the software Matlab
R2011a, MathWorks Inc., Natic, USA from optical
microscopy images that were taken from the chip roots as
shown in Figure 3. Normally the formation of a BUE is an
unsteady process. Nevertheless for first investigations this
behaviour is not considered. Table 1 gives an overview of the
simulations that were carried out.
4. Results
4.1. Forces and shear angles
The cutting and passive forces, Fc and Fp, that were
measured during the in-situ experiments and from the
simulations are given in Table 2 for a cutting edge radius of
rE = 30 μm. The integration of a BUE in the simulations
reduces the forces. The BUE changes the geometry of the
tool. The properties are comparable with those of a tool with a
higher rake angle and a sharper cutting edge. The grade of
reduction of the forces is higher in the simulation with the
Fig. 3. BUEs at the chip roots and the corresponding FEM-simulations with
different cutting edge radii: (a) rE = 30 μm; (b) rE = 60 μm.
Table 1. Parameters of the simulations with and without a BUE
BUE Cutting speed
vc [mm/min]
Undeformed chip
thickness h [μm]
Rake
angle J
Cutting edge
radius rE
[μm]
Solid 3 30 0° 30, 60
Elastic 3 30 0° 30, 60
None 3 30 0° 30, 60
elastic BUE. The elastic BUE reduces the forces to
approximately 50 % of the values of the simulation without a
BUE, the solid method to approximately 60 %.
Compared to the forces that were measured during the in-
situ experiments the simulation without the BUE gives the
best results. However earlier investigations showed that the
implemented simulation model with the hybrid friction model
underestimates the cutting forces, especially the passive force
Fp [14]. Nevertheless this model showed the best accordance
when comparing the stresses of the experiment and the
simulation. For this reason the simulation model with the
hybrid friction model was used for the investigations.
Table 3 shows the forces from the experiments and the
simulation for the cutting edge radius of rE = 60 μm. As
before, the BUE reduces the cutting force Fc. However, the
passive force Fp increases for the simulation with a solid
BUE. For this simulation the cutting force Fc and the passive
force Fp are equal. The elastic BUE reduces the cutting and
the passive force. In contrast to the simulation without the
BUE the passive force Fp is now higher than the cutting force
Table 2. Cutting and passive forces of the simulations and experiments with
the cutting edge radius of rE = 30 μm
rE = 30 μm Cutting Force Fc [N] Passive Force Fp [N]
Simulation with solid BUE 63 50
Simulation with elastic BUE 50 45
Simulation without BUE 100 83
Experiments 112 79
simulation:
number of elements: 7000
tool:
J
=0°
D
=11°
rb= 30 ȝm
process parameters:
vc=3 mm/min
h=0.03mm
b=1 mm
50 µm50 µm
a) b)
313
Eckart Uhlmann et al. / Procedia CIRP 31 ( 2015 ) 310 – 315
Table 3. Cutting and passive forces of the simulations and experiments with
the cutting edge radius of rE = 60 μm
rE = 60 μm Cutting Force Fc [N] Passive Force Fp [N]
Simulation with solid BUE 95 95
Simulation with elastic BUE 41 55
Simulation without BUE 114 80
Experiments 144 115
BUE and the cutting edge in the applied model. The BUE
geometry has a significant influence on the cutting process.
Further investigations with a variation of the geometry should
clarify this.
A comparison of the forces from the simulations and the
experiments shows results that are similar to those with the
cutting edge radius rE = 30 μm. The simulation without the
BUE reveals the best results. However, compared to the
experiments the forces of the simulation without the BUE are
too low.
A comparison of the shear angles is a second possibility to
evaluate the quality of the simulations (table 4). The influence
of the BUE on the shear angle is clear. Both the solid and the
elastic BUE increase the shear angles for the cutting edge
radii rE = 30 μm and rE = 60 μm. Thereby the shear angle for
rE = 30 μm is slightly higher. Furthermore the elastic BUE
increases the shear angle more than the solid BUE. The shear
angles from the in-situ experiments were measured with the
use of the optical microscopy images from the chip roots. For
each cutting edge radius three different samples were
analysed. Thus the shear angles vary between ) = 16° and
) = 21° for rE = 30 μm and between ) = 13° and ) = 18° for
rE = 60 μm. The simulation without the BUE gives shear
angles at the bottom of this range and for the elastic BUE the
shear angles are at the top of this range. The solid BUE
overestimates the shear angles.
In conclusion after the analysis of the forces and the shear
angles, the simulation without the BUE gives the best results
compared with the in-situ experiments. The BUE reduces the
forces within the simulations and increases the shear angles.
At this time it is not possible to determine if the solid BUE or
the elastic BUE gives better results.
Fig. 4. Results from the simulation without a BUE, with a solid and elastic BUE, and from the experiments with a cutting edge radius of the tool of rE = 30 μm.
simulation without BUE
simulation with solid BUE
simulation with elastic BUE
experiment
tool:
J=10 °
D=11 °
r
E
= 30 ȝm
workpiece:
AISI 1045
process parameters:
v
c
= 3 mm/min
h = 0.03 mm
b = 1 mm
measuringposition
13
400
-400
-1200
measuringposition
stress ı
11
2
MPa
45678910
200
-400
-600
measurin
g
p
osition
stress ı
12
MPa
-200
300
-600
-900
stress ı
22
-300
MPa
200
-400
-600
measurin
g
p
osition
stress ı
33
-200
MPa
-800
132 45678910
13245678910 132 45678910
50 μm
9
8
7
4
5
6
3
2
1
10
2
1
3
314 Eckart Uhlmann et al. / Procedia CIRP 31 ( 2015 ) 310 – 315
Table 4. Shear angles )
r
E = 30 μm rE = 60 μm
Simulation with solid BUE 21° 19°
Simulation with elastic BUE 24° 21°
Simulation without BUE 15° 14°
Experiments 16° - 21° 13° -18°
4.2. Stress state in the chip formation zone
With the in-situ experiments it is possible to compare the
stresses in the chip formation zone that were determined with
cutting simulations with experimental data for the first time.
Figure 4 shows the results of the simulations without the
BUE, with the solid and the elastic BUE compared with the
experimental derived data. The normal stresses V11,V22,V33
and the shear stresses V12 are given. The simulated stresses
were averaged over several points and simulation steps. Thus,
the spatially and temporally integrative character of the in-situ
strain measurements is taken into account. Earlier
investigations showed that the simulation model achieves the
best qualitative and quantitative results for the normal stresses
V11 and the shear stresses V12 [14]. The normal stress V22
cannot be reproduced by the simulation model in a good
quality.
Similar results can be seen in figure 4 for the cutting edge
radius rE = 30 μm. All simulations achieve a good accordance
for the stresses V11 and V12. For the simulations with a BUE
measuring position 9 (MP9) is outside of the workpiece
material. Thus there are no results for this MP and for these
simulations. The most interesting MPs are number 1, 2, 3 and
10. They are very close to the cutting edge and the BUE has
the biggest influence on these MPs. For V11 the simulations
with the BUE achieve a very good accordance with the
experimentally determined stress for MP1. For MP2 and 3 V11
is understimated by the simulations with the BUE. At MP10 a
negative stress V11 was measured during the in-situ
experiments. The simulation without a BUE gives a positive
stress for this MP. The simulation with a solid BUE reduces
the stress and with the elastic BUE a negative stress can be
achieved. At the other MPs the simulation without the BUE
achieves a good correlation for the stress V11. The simulations
with a BUE do not increase the correlation of the results. The
simulation without the BUE overestimates the stressesV12 for
Fig. 5. Results from the simulation without a BUE, with a solid and elastic BUE, and from the experiments with a cutting edge radius of the tool of rE = 60 μm
measuring position
13
0
-500
-1000
measuring position
stress ı
11
2
MPa
45
678910
0
-450
-600
measuring position
stress ı
12
MPa
-300
300
-600
-900
stress ı
22
-300
MPa
0
-600
-800
measuring position
stress ı
33
-400
MPa
-750
13245678910
132 45678910 1 3245678910
9
8
7
4
5
6
3
2
1
10
simulation without BUE
simulation with solid BUE
simulation with elastic BUE
experiment
tool:
J=10 °
D=11 °
r
E
= 60 ȝm
workpiece:
AISI 1045
process parameters:
v
c
= 3 mm/min
h = 0.03 mm
b = 1 mm
50 μm
2
1
3
315
Eckart Uhlmann et al. / Procedia CIRP 31 ( 2015 ) 310 – 315
the majority of the MPs. With the elastic and the solid BUE
the results can be improved for some of the MPs. As expected
from earlier investigations [14] the simulations are not able to
achieve a good correlation for the stresses V22. The integration
of the BUE does not change this behaviour.
Figure 5 shows the results for the cutting edge radius
rE = 60 μm. For the elastic BUE MP9 is again positioned
outside of the workpiece material. A good correlation for the
stresses V11 can be achieved by the simulation without the
BUE, except for the MPs 3 and 10. Especially for MP10 the
simulations with the BUE are very close to V11 determined by
the experiment. The results for the shear stress V12 with
rE = 60 μm are very similar to those that were achieved with
rE = 30 μm. For all MPs the simulation without a BUE
overestimates the stresses. The BUE reduces the stresses and
at five out of ten MPs the elastic BUE achieves a good
correlation with the experiment. Due to the BUE geometry,
which is comparable to a tool with a positive rake angle, the
shear stresses in the 12-plane are lower.
5. Conclusion and outlook
The in-situ strain measurements that were carried out with
high energy synchrotron radiation gave several indications for
the formation of BUEs during the experiments especially with
tools with a rake angle of J = 0° and cutting edge radii of
rE = 30 μm and rE = 60 μm. Thus simulations with BUEs have
been carried out. An elastic and a solid BUE as part of the
tool were implemented after determining the BUE geometry
by analysing the chip roots of the in-situ experiments. The
investigations showed that the simulations with the BUE
reduces the forces and increases the shear angles. The analysis
of the stress state in the chip formation zone gave no clear
result. For the shear stresses V12 a better correlation with the
experiments can be achieved with the integration of the BUE.
The elastic BUE gave the best results for V12. The simulation
without the BUE gave good results for the normal stresses
V11. The simulations with the BUE did not improve the
correlation. The results for the stresses V22 and V33 vary. The
grade of the correlation depends on the measuring position
and the chosen simulation. Further investigations shall be
undertaken to finally clarify the influence of the BUE on the
stress state. Since the geometry of the BUE has a big
influence on the cutting process, a variation of the BUE
geometry should taken into consideration. As a final step the
simulation of the BUE formation combined with a damage
model would be preferable.
Acknowledgements
The authors are grateful for the financial support from the
Deutsche Forschungsgemeinschaft (DFG) in the project “In-
situ Dehnungsmessung bei der Zerspanung mit geometrisch
bestimmter Schneide”, and for the granting of beamtime by
the Helmholtz-Zentrum Geesthacht. Prof. Dr. Walter Reimers
is acknowledged for the support during the the in-situ cutting
project. Nils Bergström is acknowledged for the support
during the preparation of the simulations and the data
evaluation.
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