Page 94 - Welding of Aluminium and its Alloys

Welding design 83

rence of this feature. The corner joint is most often found in low load-
carrying applications and in sheet metal work.

5.5.5 The edge joint
The edge joint (Fig. 5.4e) is simple to assemble and to hold in position
during welding. Like the corner weld, it is weak in loading situations that
put the root in tension and is rarely used in a structural application, being
confined to non-load-carrying applications in thin sheet metal. Melting of
the corners of the edges being joined can be a problem and may result in
a shallow, low throat thickness weld.

5.5.6 The lap joint
The lap joint is perhaps the easiest joint of all to assemble. It comprises two
overlapping plates joined by a fillet weld (Fig. 5.4c). Variations in compo-
nent sizes are easily accommodated and no edge preparation is required,
although a bevel, as in Fig. 5.16, may be used to guarantee full root fusion.
The joint is uneconomical in terms of material as the overlapping mate-
rial is waste. The overlap should be at least three times the thickness of the
thinner plate. Care also needs to be taken to ensure that the weld does not
melt away the corner of the upper plate as this results in a reduction in the
effective throat thickness of the fillet.
The joint strength is set by the shear strength of the fillet weld.Weld sizes
and lengths should be specified by the designer to guarantee adequate load-
carrying capacity.

5.5.7 Spot, plug and slot welds

Arc welded plug and spot welds are illustrated in Fig. 5.17. Both the TIG
and MIG processes are capable of fully penetrating 2–3mm through the
upper sheet of a lap type joint to provide an acceptable weld. Laser and

Around 60°

A square edge as shown above may lead Bevelling the plate edge as
to difficulty in penetrating completely into above assists in achieving full
the root, resulting in a lack of fusion penetration at the root
defect and a reduction in throat thickness
5.16 Bevelling the plate edge in a lap joint to improve penetration.