Tweco 180 Portable MIG - Manual (Page 41)

OPERATION FABRICATOR 140, 180
July 20, 2007 4-5 Manual 0-4991
GAS METAL ARC WELDING (GMAW)
This process, also known as MIG welding, CO
2
welding,
Micro Wire Welding, short arc welding, dip transfer
welding, wire welding etc., is an electric arc welding
process which fuses together the parts to be welded by
heating them with an arc between a solid, continuous,
consumable electrode and the work. Shielding is obtained
from an externally supplied gas or gas mixture. The
process is normally applied semi-automatically; however
the process may be operated automatically and can be
machine operated. The process can be used to weld thin
and fairly thick steels, and some non-ferrous metals in all
positions.
Base Metal
Arc
Electrode
Nozzle
Shielding Gas
Weld Metal
Solidified Weld
Metal
Art: A-05103
Figure 4-2: GMAW Process
FLUX CORED ARC WELDING (FCAW)
This process also known as Dual-Shielded, Innershield,
FAB Shield, FabCO, etc., is an electric arc welding process
which fuses together the parts to be welded by heating
them with an arc between a continuous flux filled electrode
wire and the work. Shielding is obtained through
decomposition of the flux within the tubular wire.
Additional shielding may or may not be obtained from an
externally supplied gas or gas mixture. The process is
normally applied semi-automatically; however the process
may be applied automatically or by machine. It is
commonly used to weld large diameter electrodes in the
flat and horizontal position and small electrode diameters
in all positions. The process is used to a lesser degree for
welding stainless steel and for overlay work.
Arc
Flux Cored
Electrode
Nozzle (optional) Gas (optional)
Molten Metal
Molten
Slag
Solid Weld
Metal
Slag
Art: A-05104
Figure 4-3: FCAW Process
4.06 Basic Welding Technique
General
Two different welding processes are covered in this
section, with the intention of providing the very basic
concepts in using the semi-automatic mode of welding.
In this mode, the welding gun is hand-held. The electrode
(welding wire) is then fed into a weld puddle and the arc
is shielded by a gas or gas mixture.
Setting of the Power Supply
The settings of the Fabricator requires some practice by
the operator in that the welding Power Supply has two
control settings that need to balance. These are the Wire
Speed control and the Voltage Control switches. The
welding current is determined by the Wire Speed control
(i.e., the current will increase with increased wire speed,
resulting in a shorter arc). Slower wire speed will reduce
the current and lengthen the arc. Increasing the welding
voltage hardly alters the welding current level, but
lengthens the arc. By decreasing the voltage, a shorter
arc is obtained with little change in welding current.
When changing to a different electrode wire diameter,
different control settings are required. A thinner electrode
wire needs more wire speed to achieve the same current
level.
A satisfactory weld cannot be obtained if the wire speed
and voltage switch settings are not adjusted to suit the
electrode wire diameter and dimensions of the work piece.
If the wire speed is too high for the welding voltage,
“stubbing” will occur as the wire dips into the molten
pool and does not melt. Welding in these conditions
normally produces a poor weld due to lack of fusion. If
however, the welding voltage is too high, large drops will
form on the end of the electrode wire, causing spatter.
The correct setting of voltage and wire speed can be seen
in the shape of the weld deposit and heard by a smooth
regular arc sound.