Page 167 - Welding of Aluminium and its Alloys

150 The welding of aluminium and its alloys

Over 8mm thick it is necessary to weld with a prepared edge and filler
wire although in the vertical-up (PF) position material as much as 16mm
thick can be welded.The diameter of the filler wire is the same as would be
used for TIG welding, generally 1.6 or 2.4mm diameter.

8.2.2 Plasma-MIG welding
Plasma-MIG welding utilises a MIG wire, generally 1.6mm in diameter, fed
through a plasma-arc torch. This allows a higher combined welding current
to be used than for the MIG wire alone with a high current density and a
higher deposition rate than MIG being achieved. This enables welding
speeds to be increased giving lower heat input and narrower heat affected
zones with better mechanical properties.
The process is generally used in a mechanised or automated application
although it is possible to use it in a semi-automatic manual mode.The thick-
ness that has been welded ranges from 6mm to 60mm.

8.3 Laser welding
Laser welding is being used increasingly in both the automotive and aero-
space industries for the welding of a range of materials (Fig. 8.2). The laser
welding of aluminium and its alloys has, however, presented problems to
the welding engineer. Poor coupling of the beam with the parent metal,
high thermal conductivity, high reflectivity and low boiling point alloying
elements have, until relatively recently, prevented the achievement of con-
sistent weld quality.

8.2 Laser weld of thin plate. Courtesy of TWI Ltd.