Use and Care Manual

26
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GMAW
Power sources designed for GMAW require a feature for
providing inductance. Inductance is a necessary component for
short-circuiting transfer and low wire feed speed globular
transfer. It is of little use for spray arc transfer and the advanced
processes such as Surface Tension Transfer™ or GMAW-P.
A variable inductance control is important for short-circuiting
transfer because it will permit fine-tuning of the arc to minimize
spatter and improve weld toe wetting.
The traditional GMAW power source will provide either analog or
digital meters used to quantify voltage and current. These are
essential variables and their accuracy is central to the quality of a
finished weld.
Developments in transformer design permit the use of smaller
inverter transformers, which increases the portability and
reduces the required space needed for the power source. This
in turn provides relief for valuable manufacturing space. Inverter
designs characteristically provide smooth efficient output to the
arc. Many of the designs incorporate the use of welding
software to drive the output and quality of the arc, see
Waveform Control Technology™ section on page 18.
FIGURE 24: Unaffected Arc Length with Constant Voltage
P
ower Sources
GMAW Wire Drives
The Wire Drive and Accessories
GMAW wire drive designs provide for the use of a wide range of
solid or metal-cored electrodes, 0.025” – 1/16” (0.6 – 1.6 mm).
The wire feed speed may be pre-settable via a digital readout or
a
calibrated marking system on the wire feed speed control.
The ability to provide a precise wire speed is important to good
welding procedure control. Most standard wire drives for
GMAW provide a permanent magnet motor, which in turn
provides for fast starting and stopping of the feed system.
The effective range of wire feed speed is important, and most
w
ires drives will provide a range of 70 – 800 ipm (inches per
minute), (2 – 20 M/min.) of wire feed speed. Higher wire feed
speed wire drives are available for applications requiring the
delivery of wire feed speed up to 1200 ipm (30 M/min.).
Optional considerations for wire drive controls include
timers for setting pre-flow and post-flow for the shielding gas. A
burn-back control may be added to prevent the electrode from
sticking to the crater at the end of the weld. Some wire drives
may provide a cold inch control for safely inching wire electrode
through a GMAW torch to the work. An optional purge control
for the shielding gas system, provides gas flow in advance of the
arc, and displaces the air that may have entered the system.
The wire drive system provides a gas solenoid, which activates
when the GMAW torch trigger is depressed. Shielding gas
pre-flow and post-flow conditions control the solenoid circuit
and add gas before and after the arc is established. Optional
water connections are available for use with water-cooled
GMAW guns.
LN-15
LF-72 Series and LF-74
Gun
Arc Length
Arc Length
Gun
CTWD
1” (25mm)
CTWD
3/4” (19mm)
LN-10