aluminium in commercial vehicles - European Aluminium Association

EUROPEAN ALUMINIUM ASSOCIATION ALUMINIUM IN COMMERCIAL VEHICLES CHAPTER VIII 113
3.2. Automatic MIG
welding
Here, the welding torch is automatically
guided.
This is normally used for very
long straight welds where an
automatic system is profitable. A
good example is fabrication of
chassis side members consisting
of two “T” sections welded to
either edge of a central plate
which forms the web of the
built-up beam. The two welds
would normally be made automatically
and at the same time to
avoid problems of deformation.
Automatic welding is also preferred
where an attractive
appearance is desirable, e.g. for
stiffening channel welded to the
side panels of vehicle bodies.
Here the appearance and size of
the weld bead can be repeated
to achieve the impression of consistency.
Finally, automatic welding - both
TIG and MIG - provides a repeatable
welding quality provided of
course that the welding parameters
are fully defined to begin
with.
Welding of side panels
for tippers (Menci)
3.3. Smooth current MIG
Welding
This fast and economical process
allows depositing a great quantity
of filler metal per unit of time.
The energy input is such that
butt welds can only be produced
with the use of a backing bar,
either integrated into the shape
of the extrusion or as temporary
removable feature in stainless
steel, copper or even aluminium.
Due to the relatively high welding
speed, the heat affected
zone1 is narrower than with TIG
welding and thus the distortion
of the assemblies is less.
1. The extent of the heat affected zone
and the strength in the heat affected
zone are given in EN 1999-1-1.
Thin gauge material below 3 mm
is difficult to weld with this
process because of the high
energy of the arc. If no other
equipment is available, then a
thin gauge filler wire may be
used with reduced energy input,
but then the wire feed can cause
instability of the process even if a
push-pull equipment is used.
If the preassembly of structures is
carried out with stitches in the
MIG process, these short runs
must have a similar cross section
as the first weld pass and be
some 100 mm long to be sound.
Before production welding, these
stitches must be reduced in cross
section by mechanical means (no
disc grinders), so that they can
be molten up with the weld pass
and do not leave imperfections
near the root.