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Fig. 2: Forces acting on the reinforcing element
metallic wires as reinforcement. The
figure also shows the manufactured
profile with embedded wires.
Extrusion experiments
To improve the lightweight potential,
current investigations are aimed at
increasing the reinforcement volume
of the extruded profile. There are
three possibilities to achieve a higher
reinforcement volume, to embed
more elements or to change the element
form and to reduce the profile
wall thickness. Due to the increase in
reinforcement volume, the complexity
of the material flow, of the process
control and the tool design increase
simultaneously. For the introduction
of further elements additional supports
are required which lead the elements
into the welding chamber of
the die. Additional supports change
the die geometry and the depending
material flow. A significant influence
of the material flow on the position of
the reinforcing wires could be verified
in principle [5].
Reduction of the profile wall thickness
The effect of the reinforcement on
the material flow was analysed on the
basis of a thin profile with a double-
Table 1: Reinforced double-T-profiles
ALUMINIUM · 4/2010
ALUMINIUM EXTRUSION INDUSTRY
T-profile section. Therefore, the bearing
length of the extrusion tool and
the number of the applied wires was
varied stepwise. Overall seven steel
wires (X10CrNi18-8) with a diameter
of d r = 1 mm each were embedded
in the middle bar of the profile. The
profile has a thickness of h = 2 mm,
the billet material was AlMgSi0.5 (EN
AW-6060). The wires led to disturbances
of the material flow, because
they generated striations which were
noticed on the profile surface above
the wire position. During the extrusion,
the wires were cut one after another,
and a distinct correlation between
the appearing disturbances and
the inserted wires was found. For the
feed-in of the reinforcing elements,
no external forces were necessary, as
the wires bond with the aluminium
matrix inside the die and the leaving
reinforced profile leads to tensional
stress on the wires. For this reason,
the wires were pulled with the profile
speed through the slower material
flow inside the welding chamber
(Fig. 2).
The faster reinforcing elements are
pulling the ambient aluminium material
through the welding chamber.
Around the wire, the material flow has
a slower velocity, so that shear forces
between the aluminium near the wire
and the ambient
aluminium
are generated.
Limited by
the lower flow
stresses, the
aluminium is
sheared in the
area with the
highest differences
in mate-
rial speed and creates the striation
on the profile surface. This effect was
not observed on thicker profiles as a
result of the lower velocity gradient.
To reduce the differences in velocity,
the bearing length in the press channel
was increased. The higher friction
should compensate the negative
influence of the wires on the material
flow. Therefore, the bearing length
was changed from l b,1 = 4 mm to l b,2 =
12 mm. In further experimental investigations,
it was possible to manufacture
profiles without surface defects
due to the longer bearing length of the
die in a stable process (Table 1).
Embedding a higher number
of reinforcing elements
The number of reinforcing elements
was increased up to fourteen wires.
The wires were positioned in the upper
and lower band of a thick double-
T-profile. Fig. 3 shows the required
extrusion forces depending on the
number of reinforcing elements (RE).
The ram force rises with increasing
number of introduced wires. The
necessary forces for the extrusion of a
profile without reinforcement are approximately
2 MN lower as compared
to a profile with fourteen elements.
The higher extrusion forces can be
led back to the additional shear forces
due to the wires which are pulled
through the slower material flow. An
effect on the profile surface was not
detected. The profile has a thickness
of h = 5 mm and the material flow,
which is influenced by the wires, has
no effect on the profile surface because
of the great distance between
surface and wire. Furthermore, unilateral
inserted wires in the profile
cross-section lead to curved profile
geometry. The material in the nonreinforced
part of the profile flows
faster than in the reinforced one. The
profile bends in direction of the reinforced
profile part.
The aluminium samples for further
machining investigations were produced
on a 10 MN direct hot extrusion
press. The aluminium base material is
the regular alloy AlMgSi0.5 (EN AW-
6060). The reinforcing elements are
stainless steel wires (X10CrNi18-8)
with a diameter of d r = 1 mm. The pro-
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