Page 71 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

A Quick Guide to Welding and Weld Inspection

has a low heat input it is best suited to the welding of thin
materials and for all positional welding due to the small weld
pool formed. The downside to this is that lack of fusion can
occur in thick section materials.
Globular transfer
Globular transfer takes place between short circuiting and
spray transfer modes at medium current and voltage levels.
The molten droplets are larger than the wire diameter and
some intermediate short circuiting can take place, leading to
the arc being unstable and producing high spatter levels. This
mode is rarely used except for some filling passes in the flat
position.
Spray transfer
Spray transfer takes place with higher currents and voltages.
As the current increases there is an increased flow of droplets
across the arc and the diameter of the droplets become
smaller. The transfer therefore takes place in the form of a
fine spray, giving a high deposition rate coupled with deep
penetration and a large weld pool. This can lead to difficulty
using spray transfer with a thin sheet owing to the risk of
burn-through. The large weld pool is also too difficult to
control and maintain during all positional welding so it is
mainly used with thick sections in the flat or horizontal–
vertical positions only. Aluminium can be welded in all
positions in the spray mode because the weld pool solidifies
quickly, maintaining a smaller more manageable pool.
Pulse transfer
The ‘all positional’ thickness limitation of the spray transfer
mode can be overcome by pulsing the arc to reduce the
overall heat input to the work and allow the weld pool to
shrink before it gets too large and collapses. This is achieved
by regulating the current and voltage to operate in the spray
mode for a set period of time, but then immediately reducing
them to a level that just keeps the wire tip molten for an
equivalent time. An example of this would be to operate on

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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200905QG Welding chap5.3d Page 56 of 66