Page 81 - Welding of Aluminium and its Alloys

70 The welding of aluminium and its alloys

addition, the designer must consider access for both welding and inspec-
tion, joint design to enable high-quality welds to be made, the effects and
minimisation of distortion and the effect of welding on stress concentra-
tions and fatigue.
The ease with which a weld can be made is crucially dependent on joint
design and this will have a direct effect on fabrication costs. It is thus essen-
tial that the designer is aware of certain fundamentals of welding practice
in order to achieve the objectives of the lightest structure capable of per-
forming its desired function at the lowest cost.
There are a number of ‘golden rules’ that the designer should keep in
mind when detailing the drawings:
• Remember that weld metal is very expensive. Do not over-specify fillet
weld throat thickness and specify the narrowest weld preparation angle
that is consistent with quality. Specify these sizes clearly.
• Keep welding to a minimum – use formed sections instead of welded
plate, keep stiffeners to a minimum. The cheapest weld of all is the one
you do not make!
• Specify welds to be made in the flat position.
• Allow adequate access for the welder – see below.

5.2 Access for welding
The two most common design faults are failing to recognise that full vision
of the weld pool is essential for manual welding and that the weld must be
at a comfortable distance from the operator, neither too close nor at a dis-
tance where the welder’s arm is at full stretch. These errors can frequently
be recognised at the design stage and the benefits of requiring an ex-
perienced welding engineer to review draft drawings cannot be over-
emphasised. The distance from the operator’s head to the weld can easily
be checked on drawings. Ideally this distance should be in the region of
200mm minimum to 450mm maximum. It should be remembered that the
diameter of the welder’s helmet is about 300mm and that this will affect
the access requirements.
For a joint to be accessible for manual welding welders must be able com-
fortably to position themselves and their equipment if high-quality welds
are to be produced. This requires sufficient space to permit free movement
of the welding torch or electrode and to enable the torch to be presented
to the weld pool at the correct angle. Detail design must also take into
account the proximity of adjacent material which should be such that the
welder is allowed an unrestricted view of the arc. The amount of space
required will depend on the size of the equipment to be used, in particular
the size of the torch. Welding aluminium with the gas shielded processes