Tweco 141i Fabricator - Manual (Page 65)

Fabricator 141i
Manual 0-5145 4-5 BASIC WELDING GUIDE
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 finished 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 16 ga. (1.6mm) or 1/8" (3.2mm) mild steel plate 6” (150mm)
x 6” (150mm). Use 0.035” (0.9mm) gas shielded steel or gasless flux cored wire.
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 (refer to section 3.10.3) and the welding Voltage
Control (refer to section 3.10.9). 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 electrode
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 electrode
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