Instructions / Assembly

20
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GMAW
Keywords:
Scale Factor
A
daptive Loop
Arc Length Regulation
Constant Current
I
n a constant current scenario, as the CTWD is increased, the
arc length also increases. As the CTWD decreases, the arc
length also decreases. To control the length of the arc despite
changes in CTWD, an adaptive control is necessary. The
adaptive control will add energy to the arc as the CTWD
decreases, and it will take energy out of the waveform as the
CTWD is increased. This provides stability to the arc length, and
increases the overall usability of the waveform.
Frequency, background current, peak time, and peak current
are the typical components of the waveform used to regulate the
arc length. Scale factor is the term attached to arc length
regulation, and percentage is the term applied for its relative
magnitude. If the background current is set to a value of 100
amps and the corresponding scale factor is expressed as 10%,
then as the CTWD decreases, 10% more background current
will be added to the present level for background current. If the
CTWD increases, then up to 10% background current will
decrease from the original 100 amps. This is how the arc length
regulation operates, and it is coordinated to include the values
for the other scale factor components detailed above. The
regulation of the arc length occurs automatically, and it is
functional within limits of the CTWD. The effective CTWD range
for the adaptive loop is 0.50” – 1.25” (12 – 30 mm).
The adjustment of trim relates directly to the scale factors
employed in the adaptive loop. As the trim decreases from a
nominal value of 1.00, then the scale factors apply themselves
together to decrease the arc length. As the trim is increased to a
value greater than 1.00, then the scale factors work together to
increase the arc length. Additionally, the "arc control" feature in
the GMAW-P mode is directly tied to the adaptive loop. As the
arc control is moved to +1 through +10, then frequency
increases while background current decreases. The result is that
the arc column narrows. If the "arc control" feature is moved to
–1 through –10, then the result is a wider arc column and a
wider finished weld.
The absence of the use of scale factors assumes that the arc is
stable for a given wire feed speed or for a wide range of wire
feed speeds. Arc stability means that the arc will not vary in
length with a consistent CTWD. In this scenario, the welding
program is non-adaptive, and only by adjusting the length of the
CTWD, will there be a variance in arc length. When using a true
non-adaptive program, trim and arc control will produce no
changes in arc performance or level of arc energy.
Advanced Waveform Control Technology
S
urface Tension Transfer™ (STT™)
K
eywords:
Peak Current
Background Current
Tail-Out Current
Reactive Power Source
Sensing Lead
The Surface Tension Transfer (STT) welding mode of metal
transfer is a low heat input welding mode. It specializes in its
ability to provide smooth even rippled weld beads, free of weld
spatter, and with consistently good fusion. It is ideal for sheet
metal applications requiring excellent weld bead appearance
and it is successfully applied for root pass welding of open root
pipe joints.
The STT welding mode is reactive. The power source monitors
the arc and responds instantaneously to the changes in the arc
dynamics. A sensing lead attaches to the work piece to provide
feedback information to the power source. Uniquely, the STT
power source provides current to the electrode independent of
the wire feed speed. This feature permits the ability to add or
reduce current to meet application requirements.
The power source that supports STT is neither constant current
nor constant voltage. It provides controls for the essential
components of the STT waveform. Among these are controls
for peak current, background current, and tail-out current.
See Figure 14 on page 21.
The Adaptive Loop