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Schematic of Globular Transfer
Large droplet
The current flows continuously because of the high voltage maintaining a
long arc and short-circuiting cannot take place. It occurs best with argon-
based gases.
In solid wire MIG, as the current is increased, dip transfer passes into spray
transfer via a transitional globular transfer mode. With metal-cored wires
there is virtually a direct transition from dip transfer to spray transfer as the
current is increased.
For metal cored wire spray transfer occurs as the current density increases
and an arc is formed at the end of the filler wire, producing a stream of small
metal droplets. Often the outside sheath of the wire will melt first and the
powder in the centre flows as a stream of smaller droplet into the weld pool.
This effect seems to give much better transfer of alloying elements into the
weld.
In spray transfer, as the current density increases, an arc is formed at the
end of the filler wire, producing a stream of small metal droplets. In solid
wire MIG this transfer mode occurs at higher currents. Flux-cored wires do
not achieve a completely true spray transfer mode but a transfer mode that
is almost true spray may occur at higher currents, and can occur at relatively
low currents depending on the composition of the flux.
Rutile flux-cored wires will operate in this almost-spray transfer mode, at
all practicable current levels. They are also able to operate in this mode for
positional welding too. Basic flux-cored and self-shielded flux-cored wires do
not operate in anything approaching true spray transfer mode.
Splatter
Workpiece
BOC Smootharc Advance III MIG 425R & 555R Operating manual
Schematic of Spray Transfer
Gas shroud
Wire
10.4 Fundamentals of MIG, FCAW and MCAW
Welding Technique
Successful welding depends on the following factors:
1
Selection of correct consumables
2
Selection of the correct power source
3
Selection of the correct polarity on the power source
4
Selection of the correct shielding gas
5
Selection of the correct application techniques
a Correct angle of electrode to work
b Correct electrical stickout
c Correct travel speed
6
Selection of the welding preparation
Selection of Correct Consumable
Chemical composition
As a general rule the selection of a wire is straightforward, in that it is only a
matter of selecting an electrode of similar composition to the parent material.
It will be found, however, that there are certain applications that electrodes
will be selected on the basis of its mechanical properties or level of residual
hydrogen in the weldmetal. Solid MIG wires are all considered to be of the
'low Hydrogen type' consumables.
The following table gives a general overview of the selection of some of the
BOC range of MIG wires for the most common materials.
Shielding gas
Droplets
Weld
Workpiece
31
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