Tweco VAF4 Transmig - Manual (Page 71)

TRANSMIG VAF4
Manual 0-5231 4-7 SERVICE
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
4.07 MIG (GMAW/FCAW) Welding Troubleshooting
Solving Problems Beyond the Welding Terminals
The general approach to fix Gas Metal Arc Welding (GMAW) problems is to start at the wire spool then work through
to the MIG Torch. There are two main areas where problems occur with GMAW; Porosity and Inconsistent wire feed.
Problem 1 - Porosity
When there is a gas problem the result is usually porosity within the weld metal. Porosity always stems from some
contaminant within the molten weld pool which is in the process of escaping during solidification of the molten
metal. Contaminants range from no gas around the welding arc to dirt on the work piece surface. Porosity can
be reduced by checking the following points.
FAULT CAUSE
1 Shielding gas cylinder contents and flow
meter.
Ensure that the shielding gas cylinder is not empty and the flow meter is
correctly adjusted to 15 litres per minute.
2 Gas leaks. Check for gas leaks between the regulator/cylinder connection and in the gas
hose to the Power Source.
3 Internal gas hose in the Power Source. Ensure the hose from the solenoid valve to the MIG Torch adaptor has not
fractured and that it is connected to the MIG Torch adaptor.
4 Welding in a windy environment. Shield the weld area from the wind or increase the gas flow.
5 Welding dirty, oily, painted, oxidized or
greasy plate.
Clean contaminates off the work piece.
6 Distance between the MIG Torch nozzle
and the work piece.
Keep the distance between the MIG Torch nozzle and the work piece to a
minimum.
7 Maintain the MIG Torch in good working
order.
A Ensure that the gas holes are not blocked and gas is exiting out of the torch
nozzle.
B Do NOT restrict gas flow by allowing spatter to build up inside the MIG Torch
nozzle.
C Check that the MIG Torch O-rings are not damaged.
Table 4-2 MIG (GMAW / FCAW) Welding Troubleshooting