Tweco 251 Thermal Arc Fabricator - Manual (Page 49)

FABRICATOR 251
Manual No. 0-4847 4-11 OPERATION
4.06 MIG Gun Maintenance
Remove dust and metallic particles from the gun conduit by forcing clean, dry compressed air into the conduit once a
week. This will minimize wire feeding problems.
4.07 Basic Welding Technique
Setting of the Power Supply
The setting of the Fabricator 251 requires some practice by the operator, the welding Power Supply having two control
settings that have to balance. These are the Wire Speed control and the Voltage Control switches. The welding current
is determined by the Wire Speed control, the current will increase with increased Wire Speed, resulting in a shorter
arc. Less 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.
MIG Gun Travel Speed
Speed at which a weld travels influences the width of the weld and penetration of the welding run.
Position of MIG gun
The angle of MIG gun to the weld has an effect on the width of the weld run. Refer to Figure 4-15.
Art # A-05148
Forehand Vertical
Figure 4-15: MIG Gun Angle
Distance from the MIG Gun Nozzle to the Work Piece
The electrode stick out from the MIG gun nozzle should be between 5/64" (2.0mm) to 13/64" (5.0mm). This distance
may vary depending on the type of joint that is being welded.