Tweco 175i Transtig - Manual (Page 43)

TRANSMIG 175i
Manual 0-5143 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 or 18 gauge (0.06” 1.5mm or 0.08” 2.0mm) mild steel plate
6” x 6” (150 x 150mm). Use 0.030” (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 (refer to section 3.06.4) and the welding
Voltage Control (refer to section 3.06.10). 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