Tweco VAF4HD Transmig - Manual (Page 66)

TRANSMIG VAF4HD
SERVICE 4-6 Manual 0-5269
3. Nozzle Angle. This refers to the position of the
MIG Torch in relation to the joint. The transverse
angle is usually one half the included angle be-
tween plates forming the joint. The longitudinal
angle is the angle between the centre line of the
MIG Torch and a line perpendicular to the axis
of the weld. The longitudinal angle is generally
called the Nozzle Angle and can be either trail-
ing (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.
Transverse and Longitudinal
Nozzle Axes
Art # A-08998_AB
Longitudinal
Angle
Axis of Weld
Transverse
Angle
Figure 4-9 Transverse and Longitudinal Nozzle Axes
Art # A-08999_AC Nozzle Angle, Right Handed Operator
Direction of Gun Travel
Leading or “Pushing”
Angle
(Forward Pointing)
Trailing or “Pulling”
Angle
(Backward Pointing)
90°
Figure 4-10 Nozzle Angle, Right Handed Operator
Establishing the Arc and Making Weld Beads
Before attempting to weld on a finished piece of work,
it is recommended that practice welds be made on a
sample metal of the same material as that of the fin-
ished piece.
The easiest welding procedure for the beginner to
experiment with MIG welding is the flat position. The
equipment is capable of flat, vertical and overhead
positions.
For practicing MIG welding, secure some pieces of
1.5mm or 2.0mm mild steel plate 150 x 150mm. Use
0.8mm flux cored gasless wire or a solid wire with
shielding gas.
Setting of the Power Source
Power source and Wirefeeder setting requires some
practice by the operator, as the welding plant has two
control settings that have to balance. These are the
Wirespeed control and the welding Voltage Control. The
welding current is determined by the Wirespeed control,
the current will increase with increased Wirespeed,
resulting in a shorter arc. Less wire speed will reduce
the current and lengthen the arc. Increasing the welding
voltage hardly alters the current level, but lengthens the
arc. By decreasing the voltage, a shorter arc is obtained
with a little change in current level.
When changing to a different electrode wire diameter,
different control settings are required. A thinner elec-
trode wire needs more Wirespeed to achieve the same
current level.
A satisfactory weld cannot be obtained if the Wirespeed
and Voltage settings are not adjusted to suit the elec-
trode wire diameter and the dimensions of the work
piece.
If the Wirespeed 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 wire, causing spatter. The
correct setting of voltage and Wirespeed can be seen
in the shape of the weld deposit and heard by a smooth
regular arc sound. Refer to the Weld Guide located on
the inside of the wirefeed compartment door for setup
information.
Electrode Wire Size Selection
The choice of Electrode wire size and shielding gas used
depends on the following
• Thickness of the metal to be welded
• Type of joint
• Capacity of the wire feed unit and Power Source
• The amount of penetration required
• The deposition rate required
• The bead profile desired
• The position of welding
• Cost of the wire