Instructions / Assembly

10
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GMAW
Pulsed Spray Transfer
Keywords:
P
eriod
Peak Current
Background Current
F
requency
Pulsed spray metal transfer, known by the acronym GMAW-P,
i
s a highly controlled variant of axial spray transfer, in which the
welding current is cycled between a high peak current level to a
low background current level. Metal transfer occurs during the
high energy peak level in the form of a single molten droplet.
GMAW-P was developed for two demanding reasons: control of
weld spatter and the elimination of incomplete fusion defects
common to globular and short-circuiting transfer. Its earliest
application included the welding of high strength low alloy base
material for out-of-position ship hull fabrication. The advantages
that it brought to the shipbuilding industry included: higher
efficiency electrodes than FCAW, and the ability to deliver lower
hydrogen weld deposits. The mode employs electrode diameters
from 0.030” – 1/16” (0.8 – 1.6 mm) solid wire electrodes and
metal-cored electrodes from 0.045” – 5/64” (1.1 – 2.0 mm)
diameter. It is used for welding a wide range of material types.
Argon based shielding gas selection with a maximum of 18%
CO
2
supports the use of pulsed spray metal transfer with
carbon steels.
The welding current alternates between a peak current and a
lower background current, and this controlled dynamic of the
current results in a lower average current than is found with axial
spray transfer. The time, which includes the peak current and
the background current, is a period, and the period is known as
a cycle (Hz). The high current excursion exceeds the globular to
spray transition current, and the low current is reduced to a
value lower than is seen with short-circuiting transfer. Ideally,
during the peak current, the high point of the period, a single
droplet of molten metal is detached and transferred across the
arc. The descent to the lower current, known as the background
current, provides arc stability and is largely responsible for the
overall heat input into the weld. The frequency is the number of
times the period occurs per second, or cycles per second. The
frequency of the period increases in proportion to the wire feed
speed. Taken together they produce an average current, which
leverages its use in a wide material thickness range.
1
2
4
3
5
8
9
6
7
C
U
R
R
E
N
T
T
IME (mS)
(1) Front Flank Ramp-up Rate
(2) Overshoot
(3) Peak Current
(4) Peak Time
(5) Tail-out
(6) Tail-out Speed
(7) Step-off Current
(8) Background Current
(9) Period and Frequency
FIGURE 5: A Single Pulsed Event
Time (mS)
Current
(4)
(2)
(3)
(5)
(6)
(7)
(8)
(9)
(1)
Advantages of Pulsed Spray Transfer
• Absent or very low levels of spatter.
• More resistant to lack of fusion defects than other modes of
GMAW metal transfer.
• Excellent weld bead appearance.
• High operator appeal.
• Offers an engineered solution for the control of weld fume
generation.
• Reduced levels of heat induced distortion.
• Ability to weld out-of-position.
• Lower hydrogen deposit.
• Reduces the tendency for arc blow.
• Handles poor fit-up.
• When compared to FCAW, SMAW, and GMAW-S, pulsed
spray transfer provides a low cost high-electrode efficiency
of 98%.
• Lends itself to robotic and hard automation applications.
• Is combined for use with Tandem GMAW Twinarc™ or other
multiple arc scenarios.
• Capable of arc travel speeds greater than 50 inches per
minute (1.2 M/min.).
Limitations of Pulsed Spray Transfer
• Equipment to support the process is more expensive than
traditional systems.
• Blends of argon based shielding gas are more expensive than
carbon dioxide.
• Higher arc energy requires the use of additional safety
protection for welders and bystanders.
• Adds complexity to welding.
•
Requires the use of windscreens outdoors.
Pulsed Spray Transfer
Surface Tension Transfer
™
Axial Spray Transfer
Short-Circuit Transfer
GMAW Mode of Metal Transfer Selector
Material Thickness Range
UT
(1)
19.0mm 12.5mm 6.4mm 3.2mm 1.6mm 0.9mm
3/4” 1/2” 1/4” 1/8” 1/16” 0.035”
(1)
UT = Unlimited Base Material Thickness.