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SESSION SOFTWARE & SIMULATION
Fig. 3: Visualization <strong>of</strong> flow lines from <strong>the</strong> experiment and <strong>the</strong> simulation
block was also not considered in <strong>the</strong> Deform
model. Fur<strong>the</strong>rmore, only a quarter model was
setup and a constant punch speed <strong>of</strong> 10 mm/s
was chosen.
Flow lines were calculated based on <strong>the</strong>
velocity field out <strong>of</strong> <strong>the</strong> HyperXtrude simulation.
The integration time was set to <strong>the</strong> press
time to make a qualitative validation with <strong>the</strong>
experimental directly visible. Due to <strong>the</strong> results,
a high strain distribution occurs in <strong>the</strong>
area <strong>of</strong> <strong>the</strong> welding chamber which is shown
by <strong>the</strong> plastification <strong>of</strong> <strong>the</strong> contrast material
(Fig. 3). The calculated vertical flow is in accurate
agreement with <strong>the</strong> visioplastic result.
Additionally, it can be seen that <strong>the</strong> material
sticks on to <strong>the</strong> die wall. This effect is also
shown by <strong>the</strong> finite element model. It can be
seen that <strong>the</strong> material shears near <strong>the</strong> die wall.
Outside this area, <strong>the</strong> velocity is mainly constant
in <strong>the</strong> feeders. Errors occur due to <strong>the</strong> fact
that HyperXtrude is not able to calculate <strong>the</strong>
billet upsetting <strong>of</strong> <strong>the</strong> block at <strong>the</strong> beginning <strong>of</strong>
<strong>the</strong> process. The error can be established by <strong>the</strong>
decreasing error in press direction in <strong>the</strong> billet
as well as in <strong>the</strong> increasing error radial from
<strong>the</strong> billet center to <strong>the</strong> container.
Additionally <strong>the</strong> friction modeling in Deform
was analyzed. The shear friction model
according to Tresca with m = 1 was used in
<strong>the</strong> calculations. Physically, this corresponds
Fig. 4: Qualitative comparison <strong>of</strong> HyperXtrude and Deform3D results
to sticking between material and tool surface,
since <strong>the</strong> friction stress equals <strong>the</strong> shear yield
stress <strong>of</strong> <strong>the</strong> material. In order to evaluate <strong>the</strong>
impact <strong>of</strong> <strong>the</strong> friction boundary conditions on
<strong>the</strong> material flow and <strong>the</strong> flow grid pattern,
respectively, friction was also modeled using
<strong>the</strong> sticking condition solely as well as with <strong>the</strong>
sticking condition in conjunction with m = 1.
The movement <strong>of</strong> nodes on a contact surface
is prevented when <strong>the</strong> sticking condition is applied.
The results revealed that <strong>the</strong> flow lines
partially debond in case <strong>of</strong> <strong>the</strong> shear friction
model. Fur<strong>the</strong>rmore, <strong>the</strong> material slides along
<strong>the</strong> die wall in <strong>the</strong> feeder, which is also clearly
shown by <strong>the</strong> depicted velocity pr<strong>of</strong>ile. These
effects do not match <strong>the</strong> experimental results.
Here, full sticking between material and die
can be observed, so that shearing in <strong>the</strong> subsurface
<strong>layer</strong>s occurs. This flow characteristic
is qualitatively achieved by an activation <strong>of</strong>
<strong>the</strong> sticking option. The difference between
sticking and sticking in conjunction with shear
friction turned out to be insignificant. Due to
<strong>the</strong> presented results, <strong>the</strong> model incorporating
volume compensation as well as sticking condition
was determined to give best results.
The Deform results were validated using
<strong>the</strong> HyperXtrude results, which already had
turned out to be reliable. Hence, a flow net
with equally spaced lines was computed with
both Deform3D and
HyperXtrude. It can be
shown that <strong>the</strong> results
computed by HyperXtrude
and Deform3D
are in good accordance
in terms <strong>of</strong> flow
line pattern as well as
flow velocity prediction
(Fig. 4).
The hints regarding an
appropriate modeling <strong>of</strong>
<strong>the</strong> material flow in port-
hole dies, which where gained by <strong>the</strong> visioplastic
analysis will also be incorporated into <strong>the</strong>
DEFORM models <strong>of</strong> <strong>the</strong> industrial extrusion
tests, which were conducted by <strong>the</strong> collaborating
companies <strong>of</strong> this project. First results <strong>of</strong>
<strong>the</strong> numerical process simulation are already
in good correlation with <strong>the</strong> experimental results.
In particular <strong>the</strong> simulation <strong>of</strong> <strong>the</strong> pr<strong>of</strong>ile
exhibiting different wall thicknesses shows
some significant characteristics. The different
wall thicknesses <strong>of</strong> <strong>the</strong> pr<strong>of</strong>ile generate an inhomogeneous
velocity distribution at <strong>the</strong> die
orifice which, in turn, causes a curved shape
<strong>of</strong> <strong>the</strong> exiting pr<strong>of</strong>ile. A higher flow velocity
is predicted at <strong>the</strong> thicker walls. Fur<strong>the</strong>rmore,
<strong>the</strong> extruded pr<strong>of</strong>iles showed slight underfillings
at <strong>the</strong> outer face. The process simulation
is also capable <strong>of</strong> representing <strong>the</strong>se failures.
It should be mentioned here that <strong>the</strong> numerical
analysis <strong>of</strong> this process still requires some
effort since <strong>the</strong> material flow is not symmetric.
Therefore, <strong>the</strong> material and <strong>the</strong> mesh, respectively,
has to be merged manually at <strong>the</strong> welding
lines when Deform s<strong>of</strong>tware is used.
Acknowledgement
This paper is based on investigations <strong>of</strong> <strong>the</strong>
subprojects B1 – ‘Integral design, simulation
and optimization <strong>of</strong> extrusion dies’ and T6 –
‘Efficient industrial extrusion simulation’ <strong>of</strong>
<strong>the</strong> Transregional Collaborative Research
Center / Transregio 10, which is kindly supported
by <strong>the</strong> German Research Foundation
(DFG).
Additionally, <strong>the</strong> support <strong>of</strong> our industrial
partners Audi AG, Altair Engineering GmbH,
F.W. Brökelmann Aluminiumwerk GmbH &
Co. KG, Daimler AG, Gesamtverband der
Aluminiumindustrie e.V., Honsel AG, Kistler-
IGel GmbH, and S+C ETS GmbH is greatly
acknowledged. Particularly, we want to thank
Wilke Werkzeugbau GmbH for <strong>the</strong> die manufacture.
We also want to thank <strong>the</strong> Institute for Innovative
Mechanics and Management <strong>of</strong> <strong>the</strong>
University <strong>of</strong> Padova in Italy for <strong>the</strong> experimental
tests for <strong>the</strong> flow curve evaluation.
Literature
[1] L. Donati, L. Tomesani, M. Schikkora, N. Ben
Khalifa and A.E. Tekkaya: Friction model selection
in FEM simulations <strong>of</strong> aluminum extrusion, Int. j.
Surface Science and Engineering, Vol. 4, No. 1 (2010)
[2] H. S. Valberg: Applied metal forming: including
FEM analysis, Cambridge University Press (2010)
[3] H. S. Valberg: Experimental techniques to characterize
large plastic deformations in unlubricated
hot aluminum extrusion, Key Engineering Materials
Vol. 367, pp. 17-24 (2008)
74 ALUMINIUM · EAC Congress 2011