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into the metal with a defined
rotational speed along the contact
line between the two parts
to be joined. The friction of the
tool in the metal supplies the
needed energy to heat the local
zone to the desired temperature.
Through the rotation and the
translation of the tool the material
in the weld zone is plastically
deformed to create the weld.
The process can be used for butt
welds, overlap welds, T – sections
and corner welds. For each
of these joint geometries specific
tool designs are necessary. The
process can be used in all positions
i.e. horizontal, vertical,
overhead and orbital.
The process can be used for
welds up to 50 mm thickness
from one side and up to 100 mm
from two sides. Advantages are:
• High productivity, i.e. low cost
potential
• Low distortion, even in long
welds
• Excellent mechanical properties
as proven by fatigue, tensile
and bend tests
• No fume
• No porosity
• No spatter
• Low shrinkage
• Can operate in all positions
• Energy efficient
• No consumable tool ( one tool
typically can be used for up to
1000 m of weld length in 6000
series alloys)
• No filler wire
• No gas shielding
• No welder certification
• Some tolerance to imperfect
weld preparations – thin oxide
layers can be accepted
• No grinding, brushing or pickling
required in mass production
8. FSW - Friction Stir Welding
Friction Stir Welding
120
ALUMINIUM IN COMMERCIAL VEHICULES CHAPTER VIII WELDING 120 | 121
The limitations of the FSW process
are continuously reduced by intensive
research and development.
However, the main limitations of
the FSW process are at present:
The relatively high investment
requires a high degree of
repeatability in order to materialize
the cost saving potential
Work pieces must be rigidly
clamped
Backing bar required (except
where self-reacting tool or directly
opposed tools are used
Keyhole at the end of each weld
Cannot make joints which
require metal deposition (e.g. fillet
welds)
Up to now the dimensionally
biggest equipment can cope
with work pieces up to 20 m
long.
Friction stir welded taillift profiles
121
EUROPEAN ALUMINIUM ASSOCIATION
9. Surface preparation before welding
For quality welds it is recommended
to machine the edges
(see section 3.7) of sheet to be
welded after water jet, plasma or
laser cutting to remove this
rough surface with a thick oxide
layer and also with micro cracks
in order to avoid weld defects
such as cracks and oxide inclusions.
The same should be done
for plate with thickness over 10
mm that has been sheared.
There is a great risk of cracks in
the short transverse direction,
where a removal of 2 mm via
milling or routing is adequate.
The metal to be welded must be
dry and without contamination
of any grease or other products
that evaporate under the action
of the arc. To achieve this clean
surface, the pieces to be welded
should be brought into the workshop
two days before production.
This will allow condensation
that might occur when the temperature
in the storage area is
lower than in the workshop to
dry off.
Immediately before welding, the
edges to be joined and their surroundings
must be properly
degreased using a solvent such
as acetone or industry alcohol.
Avoid trichlorethylen, which
transforms under the effect of
the arc into the poisonous gas
phosgene. When the solvent on
the surface has evaporated, a
further cleaning with a stainless
steel wire brush (hand-operated
or rotary) is recommended.
Outdoor welding is not advisable.
If it cannot be avoided, the
welding environment must be
screened off.
Welding of tipper body (SCHMITZ)
122
ALUMINIUM IN COMMERCIAL VEHICULES CHAPTER VIII WELDING 122 | 123
10. Quality control
Quality control enables manufacturers
to judge the quality of the
products they fabricate and more
specifically to grade the quality
of a welded joint against an
acceptable level of defined
defects.
The level of acceptable defects is
determined by:
• the types and directions of
load (static and dynamic),
• the levels and variations in
stress,
• possible hazards to personnel,
• the technical and financial
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