Tweco 180 Portable MIG - Manual (Page 43)

OPERATION FABRICATOR 140, 180
July 20, 2007 4-7 Manual 0-4991
4.08 MIG Welding (GMAW) Variables
Most of the welding done by all processes is on carbon
steel. The following items describe the welding variables
in short-arc welding of 24 gauge (0.024”, 0.6mm) to ¼”
(6.4mm) mild sheet or plate. The applied techniques and
end results in the GMAW process are controlled by these
variables.
Pre-selected Variables
Pre-selected variables depend upon the type of material
being welded, the thickness of the material, the welding
position, the deposition rate and the mechanical
properties. These variables are:
1. Type of electrode wire
2. Size of electrode wire
3. Type of gas (not applicable to self-shielding wires
FCAW)
4. Gas flow rate (not applicable to self-shielding wires
FCAW)
Primary Adjustable Variables
These control the process after Pre-selected Variables
have been found. They control the penetration, bead width,
bead height, arc stability, deposition rate and weld
soundness. They are:
1. Arc Voltage
2. Welding Current (wire feed speed)
3. Travel Speed
Secondary Adjustable Variables
These variables cause changes in primary adjustable
variables which in turn cause the desired change in the
bead formation. They are:
1. Stickout—distance between the end of the
contact tube (tip) and the end of the electrode
wire. Keep this at about 3/8” (10mm) stickout
(as shown in Figure 4-8).
Gas Nozzle
Tip to Work
Distance
Contact Tip (Tube)
Electrode Wire
Actual Stickout
Average Arc Length
Art: A-05109
Figure 4-8: Electrode Stick-Out
2. Wire Feed Speed. Increase in wire feed speed
increases weld current. Decrease in wire feed speed
decreases weld current.
3. Nozzle Angle. (Figures 4-9 and 4-10) This refers to
the position of the welding gun in relation to the
joint. The transverse angle is usually one half the
included angle between plates forming the joint. The
longitudinal angle is the angle between the center
line of the welding gun and a line perpendicular to
the axis of the weld. The longitudinal angle is
generally called the Nozzle Angle and can be either
trailing (pulling) or leading (pushing). Whether the
operator is left-handed or right-handed has to be
considered to realize the effects of each angle in
relation to the direction of travel.
Longitudinal
Angle
Transverse
Angle
Axis of Weld
Art: A-05110
Figure 4-9: Transverse and Longitudinal Nozzle Axes
Direction of Gun Travel
90º Leading or "Pushing"
Angle (Forehand) Trailing or "Pulling"
Angle (Backhand)
Art # A-05111
Figure 4-10: Nozzle Angle, Right-Handed Operator