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International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:18 No:03 18
181403-6262-IJMME-IJENS © June 2018 IJENS I J E N S
Abstract— The objective of this study is to redesign the
blade used for severing the butt ends of aluminium billets in
order to eliminate the quality and production problems
during the extrusion process. During the end of the cutting
process, material from the mold may be detached and gaps
between the mold and the next billet occur. This
phenomenon creates blisters in the extruded aluminum
profiles and many profiles are considered scrap. By
alleviating such problem, many quality control
complications could be resolved while extrusion’s scrap
percentage could be significantly reduced. Various different
factors that can affect the cut process are studied herein,
with an emphasis given on the angle of the cutting blade
and the lubricant used in order to make the severing more
efficient. Also, a new design of the blade is proposed in
order to improve the cutting process, while the simulations
of the process performed investigate the behavior of the
system in detail.
Index Term-- Finite Element Analysis, Severing butt ends of
Aluminium Billets, Extrusion
I. INTRODUCTION
Aluminum extrusion is a metal forming process used for mass
production of aluminum products with constant cross section
profiles such as rods, tubes, beams, wires, multi-porting tubes
etc. The most commonly and widely practiced type of
extrusion in the industry today is the direct extrusion process,
also known as the billet-on-billet extrusion. In the direct
extrusion process the hot aluminum billet is pushed through
the profile opening of a die by the ram in a hydraulic press
1.During the extrusion process, as the ram and the dummy
block press the billet through the container, the actual flow of
alloy into the die is tapered. A dead metal zone remains at the
end of the container, surrounding the cone-shaped section of
flowing metal. Oxides, impurities and other inclusions from
the skin of the billet accumulate in this area. Care must
therefore be taken to ensure that extrusion is stopped before
this contaminated alloy is carried through the die and into the
product 2. This residue then forms the butt that sticks to the
back of the die stack. Hot aluminium extrusion involves
complex thermomechanical and chemical interactions between
.
aluminium and tool-steel tooling (mainly extrusion die and
container). Furthermore, the local contact conditions at the
workpiece/tooling interfaces are of great influence on process
parameters, such as productivity, product quality and scrap
rate. Finite-element (FE) simulations have been extensively
used in scientific research and industrial practice to analyze the
extrusion process and to aid in process optimization 3.
During the extrusion process after each billet has been
extruded, the container is opened to expose the butt. This must
then be sheared off before the container is closed, and the next
billet is loaded. If this operation is not performed cleanly and
efficiently, part of the butt can ‘hang up’ or continue to adhere
to the back of the die stack as illustrated in Figure 1 [4]. One
of the biggest problems that may occur during the cutting
process of the butts is the detachment of material from the
interior part of the die. This can cause serious problems during
the extrusion process, as material from the next billet cannot
cover this gap and blisters will appear in the extruded
aluminium profiles, raising the production scrap with several
degrees. Figure 2 shows both detached butts and extruded
aluminium profiles with blisters. This problem may be even
bigger as soon as multi-hole dies are used. Across the
aluminium extrusion industry, multi-hole dies are extensively
used to produce several solid profiles simultaneously for
increases productivity. A multi-hole die may sometimes also
be useful in the try to avoid a high reduction ratio, if a single-
hole die is used, which requires an excessively high
breakthrough pressure. It is important that the multiple
extruded profiles coming out of the multi-hole die are at the
same velocity and straight (without distortions).
Synchronization and flow uniformity are affected by the shape
and sizes of the profiles and the number and layout of die
orifices, in addition to operational parameters such as
extrusion speed and temperature. These can, in principle, be
achieved by adjusting the die bearing angle and length, which
is delicate manual work of the die corrector 5. However, as
much more holes exist in the die, the possibility to have more
gaps, that will trap air in them, is increased.
The finite element analysis approach has been chosen in order
to simulate the cutting process of the aluminium billet. The
stress, strain and deformation results are compared for various
cases, while the shape of the detachment is compared with
experimental findings. Emphasis is given on the angle of the
cutting blade and the lubricant that can be used in order to
E. GIARMAS1, D. TZETZIS2
1 Alumil S.A., Department of Production Planning, 611 00 Kilkis, Greece 2International Hellenic University, School of Science and Technology 14th km Thessaloniki-Moudania,
57001 Thermi, Greece
Experimental and Finite Element Analysis
of Severing the Butt Ends of Aluminum Billets
During the Extrusion Process
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:18 No:03 19
181403-6262-IJMME-IJENS © June 2018 IJENS I J E N S
make the severing more efficient. A new design of the blade is
proposed in order to improve the cutting process.
Fig. 1. Severing the butt end
Fig. 2. (a) Detached butt end and (b) Extruded profile with blisters
II. MATERIALS AND METHODS
Alumimium alloy 6061 T6 (6005) has been chosen for the
material of the billet. Detail material properties that have been
used for the analysis are shown in Table 1. The diameter of the
billet is at 178 mm (extrusion machine 1800tn). The material
of the cutting blade is ORVAR 2 46-48 HRC. This is a
chromium-molybdenum-vanadium-alloyed steel which is
characterized by high level of resistance to thermal shock and
thermal fatigue, good high-temperature strength, excellent
toughness and ductility in all directions, good machinability
and polishability, excellent through-hardening properties and
good dimensional stability during hardening [6]. The
increasing global interest in the manufacture of products of a
precise shape, or one which is close to the shape of ready
components, has led to a significant development of the hot
and cold die forging technology that is used for the
construction of tools such as the cutting blade of the butt ends
in extrusion lines. Die forging, due to its advantages, is
currently the most advanced production technique used in the
mass production of responsible components as in the current
case the cutting blade 7.
Table I
Material Properties for AL6061-T6 and ORVAR 2_46-48 HRC
Property AL 6061-T6 ORVAR 2_46-48
HRC
Density (kg/m3) 2700 7800
Young's Modulus (GPa) 71 210
Poisson's Ratio 0,33 0,31
Bulk Modulus (GPa) 69,6 184,2
Shear Modulus (GPa) 26,69 80,15
Tensile Yield Strength (MPa) 280 1420
Compressive Yield Strength (MPa) 280 -
Tensile Ultimate strength (MPa) 310 -
III. FINITE ELEMENT ANALYSIS MODEL
The CAD model has been created in Solidworks and then was
inserted in ANSYS software. The ANSYS workbench has
been used and specifically the explicit dynamics method.
Multilinear Isotropic Hardening was selected for the material
model in order to ensure that plastic deformation will be
achieved in the course of the severing procedure [8]. The built
mesh is shown Figure 3a. The table of the billet and the back
side of it, have been chosen as fixed supports. The vertical
movement of the cutting blade has also been selected, while
the displacement of the two surfaces of the billet have been
calculated accordingly.
The two most important factors that are studied in this paper
are the angle of the cutting blade and the lubricant that can be
used in order to make the severing more efficient. Some
factors such as the velocity of the cutting blade and the
temperature do not play an important role in the studied
model. The velocity is something that cannot be modified
during the actual test, so it is not taken into account as a
parameter in this study. Thereby, it was kept constant in all
simulations. The temperature of the billet is around 400 °C and
it is very important to keep it constant during the extrusion
process. The temperature of the cutting blade cannot affect the
cutting results, because both the size of contact surfaces and
the contact time cannot permit important heat transfer
phenomena during the cutting process.
Simulations with the existent cutting parameters and
comparison with the actual testing results (taken by extrusion
machines) were made and a validation study was performed.
Additionally, three different angles for the cutting blade and a
new lubricant were simulated with finite elements. The results
are presented and evaluated in order to give a final solution.
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:18 No:03 20
181403-6262-IJMME-IJENS © June 2018 IJENS I J E N S
Fig. 3. a) The FEA model and b) Shape of the butt end (15mm) in simulation
and reality
IV. VALIDATION OF THE MODEL
The simulation with the existent cutting parameters in the
production line and comparison with the actual situation is
presented in this section. This comparison is very important as
it is the only way to detect whether the model can give results
that keep up with reality. Three factors are compared. First of
all the shape of the cut butt end, the deformation of the butt
end and the point from where the detachment occurs. The
shapes of the butt end (from the simulation of cutting process
and the actual test) that occurred with the existent blade are
illustrated in Figure 3b. The width of the butt end is 15mm. It
is very important to emphasize that from the first view the
results of are almost the same.
This is very good evidence that the model has been built
correctly and further analysis can optimize the process
operation through dimensional changes of the cutting blade so
to ameliorate the production process in general. Further
measurements of the butt-end with a micrometer was
performed in order to compare the measurement values with
the total deformation obtained from the simulation. The results
revealed that the model has been built in a way that predicts
the deformation with high accuracy. The measured
deformation was 95,86 mm while the model has shown a
deformation of 95,87 mm (Figure 4). The time and the area
from where the detachment starts give more information
regarding the accuracy of the calculations. The actual
detachment in the model was calculated from the percentage
detachment which was 74,35% ((1-0,7435)*178 =45,66mm
(Figure 5). The accuracy of the model is confirmed from such
results since the detachment value is almost identical with the
measured one (Figure 5). The detachment has been calculated
with the aid of the animation that ANSYS give to the user. At
the point that the bottom part of the butt end starts to move
without being cut, the phenomenon of detachment has been
started. With very simple calculations the percentage of the
total billet diameter that has been covered until that moment
can be found. Another important test in order to ensure the
validation of the results of the FEA model was to measure the
detachment area according to the thickness of the butt-end.
From the actual production process and the measurements that
have been made, the detachment starts earlier for a larger butt-
end. Specifically, the detachment area is at around 22,88%
larger for a butt end at 30mm. Figure 6 illustrates the results
from the measurement and the model. The method that has
been used in order to define the detachment is the same as
previously. The detachment was at the 68,6% of the process,
which results to (1-0,686)*178 =55,89mm of actual
detachment (Figure 6). Clearly, such value is almost identical
with the measured one and shows that the model is capable of
predicting correctly the behavior of severing the butt-end of
aluminum billets.
Fig. 4. Deformation (m) at 95,87mm in ANSYS and reality
Fig. 5. Predicted detachment of 45,66 and reality
Fig. 6. Detachment of 55,89mm and reality
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:18 No:03 21
181403-6262-IJMME-IJENS © June 2018 IJENS I J E N S
V. OPTIMIZATION OF THE PROCESS
The optimization of the cutting process has been made for the
blade’s angle and the lubrication of the process. With the aid
of the finite element analysis the deformation, the stresses, the
strain and the detachment of the butt end during the cutting
process have been examined. In addition, the maximum shear
stresses that the cutting blade faces are presented below.
Blade’s Angle
The blade’s angle is the first and one of the most important
factors that can affect the cutting process. The angle of the
blade affects not only the deformation of the butt end but the
plastic strain and the detachment of it as well. The dimensions
of the existent blade and for the two alternatives are given in
Figure 7. The deformation of the butt end plays an important
role in the studied process. Despite the fact that it is important
in order to be easier for the blade to penetrate the billet deeply,
very large deformation may cause earlier the detachment of the
butt end. Figure 8 represents the deformation of the butt end
for the 3 blades.
Fig. 7. Schematic of the blade with the various angles under study
Fig. 8. Deformation (m) for (a) existent Blade, (b) Blade No2 and (c)Blade
No3
Fig. 9. Detachment of: a) 45,66mm for blade No1, b) 36,6mm for blade No2
and c) 27,7mm for blade No3
Fig. 10. Equivalent plastic train for (a) existent Blade, (b) Blade No2 and (c)
Blade No3
It is clear from the view of the butt end that the deformation
decreases as the blade’s angles decreases as well. Total
deformation started from 95,86 mm for the existent blade and
resulted in 66 mm and 56 mm for the two other blades (-
31,14% and -41,6% respectively) under study. The detachment
of the butt end is certainly the most important factor that
should be investigated. The variation of the detachment in
relation to the blade’s angle is illustrated in Figure 9. The
detachment occurs when bottom parts of the butt end start
moving before the blade severe it. It is easily noticeable that
smaller angles for the cutting blades can provide much better
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:18 No:03 22
181403-6262-IJMME-IJENS © June 2018 IJENS I J E N S
production results. From 45,66 mm the detachment decreases
to 36,6mm (-19,84%) and 27,7mm (-39,33%) with the use of
blades No2 and No3 respectively.
The plastic strain in the butt end gives very important
information about the detachment that occurs during the
cutting process. High values for the plastic strain indicate
bigger detachment in the model. Figure 10 shows the
simulated data for the equivalent plastic strain in the detached
area. It is clear that as the angles of the blade decrease, the
plastic deformation decreases as well. This observation comes
to confirm the previous analysis that has already shown a clear
improvement in the process of severing the butt end as the
angles of the cutting blade decrease. In detail, the plastic strain
in the detached area decreases from 0,82 to 0,74 (-9,7%) and
0,7 (-14,63%) with the use of blades No2 and No3
respectively.
Lubrication
In the current study, Boron Nitride has been tested as
preferable lubricant for the extrusion process since such
material is the ultimate lubricant to facilitate butt shear. The
lubricants that are often used are not suitable since they are
suited for up to 200 °C. However, the billet’s temperature is
around 400 °C. Boron nitride is the ideal lubricant, not only
for its unmatched lubricity, but also for its ease and economy
of application [9]. Environmental problems are eliminated and
scrap due to blisters is reduced. The friction coefficient that
this lubricant can give is 0,3 [10].
In order to test the new lubricant, an analysis has been made
with the existent blade, as it is important to investigate the way
that a Boron Nitride lubricant can ameliorate the cutting
process. Boron nitride has been extensively applied in the
fields of electronics, physics, and aerospace as a sealing
material, taking advantage of its structural stability and
excellent anti‐oxidation properties. In a study reported by Wan
et. al. [11 lubricant oils containing Boron Nitride
nanoparticles with different concentration were formulated and
showed good stability for more than two weeks. In addition,
their tribological performances and viscosities were studied.
The viscosities of both the nano-Boron Nitride oils and base
oil decreased sharply with increasing temperature and no
significant distinct between them were found. The nano-Boron
Nitride oils could significantly improve the anti-wear and anti-
friction properties of the base oil, and lower nanoparticle
concentration exhibited better tribological performance. The
patching mechanism of the Boron Nitride nanoparticles on the
worn surface were confirmed by the Energy Dispersive X-ray
Spectrometer (EDS) results and an effective concentration was
proposed to be around 0.1wt.% [11.
Figure 11 shows the results of this simulation. By comparing
the above results, it is evident that with the use of boron nitride
as lubricant, the total deformation decreases from 95,8mm to
88,2mm (-8%), the plastic strain in the area of the detachment
decreases from 0,78 to 0,74 (-5,1%) and the size of
detachment area decreases from 45,66mm to 38,94mm (-
14,7%). As a result, the use of boron nitride only can improve
the cutting procedure and minimize any defects caused.
Fig. 11. (a) Total Deformation, (b) Equivalent plastic train and (c)
Detachment of 38,94 mm for existent Blade and use of Boron Nitride as
Lubricant
Shear and Maximum shear Stresses on the Blade
Figure 12 illustrates the fluctuation of the shear stresses on the
blade in the 20% of the cutting process. Due to the vertical
movement of the blade and the shear cutting of the billet, these
stresses are considerably important. From the actual cutting
process, it easily noticed that the butt end curves and a gap
between the blade and the butt end is created in the middle
(Figure 13). The maximum shear stresses that the blades
withstand during the cutting process are presented in Figure 14.
It easily understandable that the use of the proper lubricant can
decrease the maximum shear stresses. In addition, as the
blade’s angles decrease, the maximum stresses increase and
the possibility of blade fracture and catastrophic failure is
increased. The stresses are lower in the center of the blade due
to the curvature of the butt end that created during the cutting
process. However, due to the spherical section of the billet, the
central part of the blades is in contact with material for longer
time and the failures that have been observed practically are
mainly located in that region.
Fig. 12. Shear Stresses on the cutting blade
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:18 No:03 23
181403-6262-IJMME-IJENS © June 2018 IJENS I J E N S
Fig. 13. The curved butt end from the actual process
Fig. 14. Maximum Shear Stresses over time for (a) the existent Blade without
and (b) with the use of Boron Nitride, (c) Blade No2 and (d) Blade No3
VI. NEW DESIGN STUDY
A new design of the blade is proposed in order to improve the
cutting process as shown in Figure 15. Figure 16 shows the
deformation and detachment of the newly designed blade No4
as well as the equivalent plastic strain and the maximum shear
stresses. By comparing these results with those of the blade
No1 (existent blade) it is evident that the total deformation
decreases from 95,8mm to 59,4mm (-38%), the plastic strain in
the area of the detachment decreases from 0,78 to 0,69 (-
11,54%) and the size of detachment area decreases
dramatically from 45,66mm to 25,22mm (-44,77%). Finally,
the maximum shear stresses in Blade Nο 4 are slightly smaller
in comparison to blade No1 but with extremely smoother
dispersion across the blade. As a result, taking all the above
under consideration, the use of Blade Nο 4 is a very promising
design approach, as the detachment decreases in a great grade
and the shear stresses on the blade remain in normal levels
without the risk of material failure, as the maximum shear
stress over time is 736 MPa with the yield strength of Blade’s
material at 1280 MPa.
Fig. 15. Technical Drawing of Blade No4
Fig. 16. Deformation (a), Detachment at 25,22 mm (b), Equivalent plastic
strain (c) and Maximum Shear Stresses over time (d) for Blade No4
VII. CONCLUSIONS
The current paper presents a study towards the optimization of
the cutting process of the butt ends of aluminium billets. A
reduction in the blade’s angles seems to reduce the detachment
area up to 39,33% for the blade Nο3. However, this type of
Blade is too thin and the risk of failure is higher because of
fatigue. On the other hand, the use of Blade Nο2 reduces the
detachment area up to 19,84% by having smoother stress
distribution. Furthermore, the use of Blade Nο4 seems to offer
the best possible solution for the studied problem. The
detached area decreases up to 44,77% with simultaneous
normal shear stresses distribution. Finally, the use of Boron
Nitride as lubricant could smooth out the shear stresses on the
blade, as the simulations have clearly shown. Future tests in
the extrusion production lines can clarify these predictions as
far as the optimal use of Blade Nο2 and Nο4 with Boron
Nitride preferably as lubricant.
International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:18 No:03 24
181403-6262-IJMME-IJENS © June 2018 IJENS I J E N S
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