Page 82 - Welding of Aluminium and its Alloys

Welding design 71

x For adequate access to the fillet
welds between the two upright plates
y y should always be less than x

5.1 Access requirements for welding.

Root sealing pass Face side weld

MIG torch
gas shroud Inability to achieve correct arc length

5.2 Access problems of angled plates or pipes.

requires a large diameter gas shroud and a short arc length.This means that
the welder’s view of the weld pool is more restricted than when welding a
similar configuration in steel. The sketch in Fig. 5.1 illustrates a situation
that is often encountered in practice where the designer has failed to take
into account the need for adequate access. As a rule of thumb the distance
between the plates should be as shown.A further limitation for TIG welding
is the need to add a filler wire that restricts further the welder’s view of the
arc and the ease of manipulation as both of the welder’s hands need to be
in the work area.
The welding of attachments or nozzles to plates or pipes can present
problems when the nozzle is presented to the surface at an angle less than
45°.Access into the acute angle is difficult,resulting in lack-of-fusion defects
in the root of the weld as illustrated in Fig. 5.2.

5.3 Welding speed
Aluminium is normally welded at higher travel speeds than when welding
steels, particularly when using the MIG process. The implication of this is
that abrupt changes of direction are to be avoided. It is, for example, impos-
sible to weld around a 90° corner as the MIG torch cannot be moved rapidly
enough to keep the correct lead angle. It is also difficult to weld around
small diameter bosses fixed in position. In this sort of application the boss
needs to be rotated with the torch held stationary. Such comments do not
necessarily apply when fully mechanised or robotic equipment is used.