Instructions / Assembly

58
www.lincolnelectric.com
GMAW
P
ower Supplies and Wire Drives for Aluminum
GMAW
Keywords:
Constant Current (CC)
Constant Voltage (CV)
S
ynergic
Push-Pull System
P
ush System
The history of the development of power sources for aluminum
GMAW welding relates to the development of CC, constant
current, or CV, constant voltage output characteristics. Prior to
the development of CV power sources the use of CC or "drooper"
type power sources were used exclusively for welding aluminum.
Special techniques were required for arc striking and special
variable speed wire drives were developed as a solution for the
unstable arc length associated with CC.
Constant current power sources provided excellent penetration
uniformity, and they reacted slowly to changing conditions. The
slower dynamic response to changes in arc length were desirable
for welding thicker sections of aluminum with electrodes diameters
3/32" (2.4 mm) and larger. The primary disadvantage of CC
power sources is arc starting and the ability to regulate arc
length.
In the late 1950s, when selenium rectifiers were employed to
provide the CV output characteristic, many aluminum fabricators
soon realized there was a problem. The output of the early CV
power sources produced wide welding current fluctuations due
to changes in arc length, and this was compounded by changes
in output due to fluctuations in input power. Because of the
higher thermal conductivity of aluminum the current changes
that occurred produced variations in weld penetration.
Incomplete fusion defects often accompanied the penetration
problems. Because of this, many aluminum fabricators went
back to CC power supplies for consistent penetration. As a
result of these early difficulties, much of the available aluminum
welding literature continues to advocate the use of CC supplies.
Constant voltage power supplies produced since the 1990s
demonstrate more consistent output. These newer CV power
sources are line voltage compensated, which assures consistent
delivery of output. CV enjoys widespread use, and is highly
recommended for aluminum gas metal arc welding.
GMAW-P Power Supplies for Aluminum Welding
Pulsed arc power supplies have become much more sophisti-
cated than those of only a few years ago. Early pulsed power
supplies had a fixed pulsing frequency based upon multiples of
input frequencies, and they usually were 60 and 120Hz. These
systems were non-synergic, and they were difficult to set up.
The 1990s introduced newer pulsed power sources that provided
synergic control (one knob control) with a high speed amplifier
used to control output. (See Waveform Control Technology™
Section on page 18). In the newer pulsed arc power sources,
either an inverter transformer or related Chopper Technology™
provide power for the arc, and software is used to direct the
output of the power source.
T
he software developed specifically for these newer power
s
ources provides a wide selection for a range of filler types,
diameters, and shielding gas compositions. In most cases the
newer power sources provide a wide selection of pulsed spray
transfer, synergic CV, and special Pulse on Pulse™ programs
f
or use with aluminum electrodes.
Wire Drives and Controls
R
eliable feeding of the softer aluminum solid wire electrodes
t
hrough a welding torch presents more of a challenge than
feeding carbon steel electrodes. First of all, the aluminum is
much less rigid than steel wire and it is harder to push through a
GMAW torch. Special wire drives and GMAW guns are available
t
o enhance the feedability of aluminum electrode. They fall into
four main categories:
1. Push Type Feeders
Standard wire feeders, employed for carbon steel solid wire
electrodes, can also be referred to as "push type feeders." In
this type of equipment, a spool of wire electrode is mounted on
a spindle located to the rear of the drive. A shielding gas
pre-flow and post-flow timer/control should be available. There
is a set of drive rolls (two-roll or four-roll), on the feeder which
pushes the wire through from the spool mounting device
through the torch cable and then through the contact tip.
For
aluminum electrode the use of highly polished "U" groove
drive rolls, is recommended
. In all of the ensuing scenarios
the use of hard shell nylon or Teflon type liners is strongly
recommended. This type of system, with some modifications
described below, can also be used to feed softer aluminum wire
under the following circumstances:
• The gun cable must be kept short. 10 - 12 ft. (3.0 - 3.6 m) is
the practical maximum length – the shorter the GMAW gun
cable the better the overall performance. Teflon or hard
shelled nylon electrode liners must also be employed.
• If 1/16” (1.6 mm) diameter wire is used, either 4043 or 5356
filler alloys can be pushed. The thicker electrodes have higher
column strength. Again, Teflon or hard shell nylon electrode
liners must be employed.
• 3/64” (1.2 mm) 5356 filler metal can generally be pushed, but
3/64” (1.2 mm) 4043 filler metal will usually result in wire
feeding problems if pushed.
• Plastic or aluminum specific inlet and outlet guides and
special aluminum contact tips are highly recommended.
• U-grooved type drive rolls should be used. See optional
accessories for wire drive systems on page 27.
2. Push–Pull Type Feeders
A solution to the problem of feeding either small diameter or
softer aluminum wire is to use a "push–pull" feeder. These feed-
ers combine a push motor in the cabinet which holds the wire
spool with a pull motor in the handle of the welding torch.
Figure 37 shows the feeder cabinet and slave type push drive
system. Figure 38 shows a push-pull torch. The bulged area
houses the pull drive motor. Wire feed speed is controlled by
the motor on the torch handle, and the cabinet contains a slave
motor system designed to provide a slack wire reducing effect
on the electrode. The push-pull type of aluminum wire drive
provides the most consistent daily performance when compared
to the other type systems.