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Special effect Wire pulsation Cold Metal Transfer
Suitability
Thickness range (mm) 0.8 ≤ t ≤ 5 0.2 ≤ t ≤ 10 3 ≤t 2 ≤t 1 ≤ t ≤5 t ≤ 1
Manual yes no yes yes difficult no
Automatic yes yes yes yes yes yes
Industrial robot no no yes yes yes yes
3.9. Selection of welding process
3.8. Choice of filler wire or rod
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EUROPEAN ALUMINIUM ASSOCIATION
This process combines the high
melting capacity of the MIG
process with the nearly ideal
shape of the plasma arc and its
very good gas shield for the
welding pool. The result is an
extremely good quality of welds,
especially the absence of porosity.
The plasma arc is maintained
between the plasma ring nozzle
of the torch and the work piece,
the MIG arc is in the centre of
the plasma arc. Both arcs have
the same polarity where the high
kinetic energy of the plasma arc
destroys the oxide layer on the
work piece. Mechanical removal
of the oxide layer can be dispensed
with.
The process is well suited for
applications with high requirements
for tightness and surface
aspect. It is possible to carry out
butt welds of up to 10 mm thickness
in one pass with the edge
preparation in V. The welding
speed is higher than for MIG
welding.
4. Plasma MIG welding
5. Laser welding
Laser welding of aluminium
alloys is developing rapidly parallel
with the development of ever
growing power of laser sources.
There are on one side CO2 lasers
of up to 20 KW and more and
Nd:YAG lasers of 6 KW and
more. With the CO2 laser, the orientation
of the beam is limited,
whereas with the Nd:YAG laser
optical fibres allow to bring the
laser beam directly to the weld
zone. This gives high flexibility
especially for robot welding. The
high reflectivity of aluminium
makes it necessary to install the
laser equipment in a separate
room, where during operation of
the equipment, nobody without
adequate eye protection has
access. The sensor which emits
the signals necessary for the
motion control of the laser beam
must be very effective for not
being disturbed by reflections.
The process is mainly used for
thin gauge materials (1 – 4 mm)
and the pieces to be joined must
fit perfectly as is the case e.g. in
the production of tailored blanks
for the car industry.
The achievable welding speeds
are up to 12m/min with thickness
of around 1mm and still
1-3 m/min with thicknesses
between 1.5 and 3 mm.
Compared with standard arc
welding, laser welding allows the
production of components with
reduced geometrical distortions
and residual stresses, as well as
narrower heat affected zone, a
direct consequence of the high
work speed and thus the low
heat input.
The laser welding process is
preferably used with filler wire
for aluminium alloys.
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ALUMINIUM IN COMMERCIAL VEHICULES CHAPTER VIII WELDING 118 | 119
6. Laser MIG welding
The combination of a standard
arc welding process with the
laser welding process allows to
benefit from the advantages of
both processes, which are good
process stability, high welding
speed and enhanced bridging
capacity.
The laser beam runs ahead of the
MIG arc but both focus on the
same point of the metal surface.
The shielding gas is provided by
the MIG torch. Preferably a mixture
of helium (70%) and argon
(30%) is used. This process is
ideal for continuous automatic
welds up to 10 mm thickness in
one pass, where the requirements
for fit up of the pieces to
be joined is less stringent than
for pure laser welds.
The same safety measures as for
laser welding must be applied.
Laser welding
119
EUROPEAN ALUMINIUM ASSOCIATION
This technique is very common in
the automotive industry and not
so widespread in the Commercial
Vehicles industry.
For this reason, we do not give
details here.
Interested readers should refer to
the Aluminium Automotive Manual:
www.eaa.net/aam
7. Resistance welding
This is an innovative process
which had been developed by
TWI Ltd (The Welding Institute)
and is protected by patents in
Europe, USA and Australia.
Anyone using the process needs
a license from TWI.
The process operates in the solid
phase of the metal below the
melting point of the alloy. A tool
in the form of a finger with a
shoulder is rotated and moved
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