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the formation of cracks at
points of deep deformation.
Shaping is carried out on the
5754, 5086 and 5083 grades
(and on other alloys in the same
family) in the annealed or H111
condition. In some cases shaping
may call for inter-stage annealing1,
and this can be done as
described before using an
annealing torch and tallow as
temperature indicator.
Inter-stage annealing can be
carried out several times in the
course of the shaping operation;
however care should be
taken to avoid annealing a
metal that is only slightly workhardened
to prevent the risk of
grain enlargement.
Plasma cutting (Benalu)
1. For 5000 alloys with Mg content
above 3%, this must be done very carefully
to prevent sensitization to intergranular
corrosion. See also Chapter XI,
section 2.2.6.
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EUROPEAN ALUMINIUM ASSOCIATION
Extrusions are usually individually
protected in packing cases to
prevent problems such as fretting
in transit.
3.1. Storage
Extrusions are best left in their
original packing cases until
required. As with aluminium
sheets, they should never be set
down directly on the ground,
even if concreted, and should be
kept away from splash water,
condensation and hostile environments
to prevent possible
corrosion during storage.
3.2. Cutting
The processes of sawing
described above are also suitable
for cutting aluminium extrusions
.
3.3. Bending
The bending of extrusions on an
industrial scale may be carried
out with different methods and
means.
3. Fabrication of products from extrusions
3-point press bending (Benalu)
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ALUMINIUM IN COMMERCIAL VEHICULES CHAPTER VII FABRICATION 98 | 99
3.3.1. Bending by 3-point
press-bending
This may be done when the bend
radius is small compared to the
height of the extrusion section,
and when the accuracy (springback)
of the bend as well as the
optics are not so important. It is
typically performed in a simple
tool in a (mostly) hydraulic press.
3.3.2. Bending by 3-point
press-bending with rotating
dies
This process is typically using a
tool in a press or a bending
machine. The rollers may be
kinder to the extrusion work piece
than by the method in 3.2.1 due
to less abrasive sliding action
between tools and work piece.
3.3.3. Bending by
compression bending
A sliding tool forces the extrusion
to follow a circular die. The
extrusion is not moving lengthwise
relative to the die.
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EUROPEAN ALUMINIUM ASSOCIATION
3.3.4. Bending by
compression roll-forming
It is identical with 3.3.3, but with
a rotating wheel instead of the
sliding tool. Very severe reforming
may be made. It is usually performed
in roll-forming machines
with purpose-built tools.
3.3.5. Bending by rotary
draw bending
It is mostly performed in standard
tube-bending machines.
3.3.6. Stretch-bending over a
fixed tool (“swing arm
stretch-bending”)
The ends of the profile are gripped
to stretch-bend the profile against
a fixed last which has the form of
the finished product. In many
cases this form may be a bending
sweep built-up by compounded
radii. Nearly all of the cross section
of the extrusion will be subjected
to tensile stress above the yield
stress limit, and this applies to the
full length of the work piece. This
means that the spring-back effect
on global shape will be little, constant
and predictable. When a
closed extrusion is formed in this
way, the outer wall may be subjected
to sagging. This may be
countered by using a basic extrusion
with an outer wall which is
barrel-shaped outward or by
inserting a suitable elastic material
(e.g. rubber). The operation may
be performed by a dedicated tool
in a press or in a stretch-bending
machine.
Bending over rotating tools
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ALUMINIUM IN COMMERCIAL VEHICULES CHAPTER VII FABRICATION 100 | 101
3.3.7. Stretch bending
by rotating dies (rotary
stretch bending)
By this method the extrusion is
gripped at its ends and bent over
one ore two (normally two)
rotating dies having a contour
corresponding to the final product
shape. The stretching comes
as a result of the rotation and
may effectively be controlled by
the location of the rotary axes.
As opposed to the situation in
conventional stretch bending
method (3.3.6), the bending
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