Tweco 400i Transmig - Manual (Page 39)

TRANSMIG 400 i
July 18, 2008 5-5
5.03 Basic MIG Welding Guide
5.03.1 Setting of the Power Source
The setting of the Transmig 400 i requires some
practice by the operator, the welding Power
Source/Wirefeeder having two control settings
that have to balance. These are the Wirespeed
control and the 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 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 Wirespeed
to achieve the same current level.
A satisfactory weld cannot be obtained if the
wirespeed and voltage switch settings are not
adjusted to suit the electrode wire diameter and
dimensions of the workpiece.
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 electrode 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.
5.03.2 Position of MIG Torch
The angle of MIG torch to the weld has an effect
on the width of the weld run.
5.03.4 Electrode Wire Size Selection
The choice of electrode wire size in conjunction
with shielding gas used depends on:
• The position of welding
• Thickness of the metal to be welded
• The deposition rate required
• Capacity of the wire feed unit and power source
• The bead profile desired
• The amount of penetration required
• Type of joint
• Cost of the electrode wire
Weld metal deposition rate is proportional to
current density. Current density is defined as the
current per cross sectional area of the electrode
wire and is normally expressed as amps per mm2.
An example is tabled below.
Electrode
Wire Size
Current
(Amps)
Current
Density
(Amps/mm 2 )
Deposition
Rate
(lb/hour)
0.035”
(0.9mm)
200 380 6.3
0.034”
(1.2mm)
200 177 6.0
5.03.3 Travel Speed
Speed at which a weld travels influences the width
of the weld and penetration of the welding run.
5.03.5 Deposition Rate Comparison
This demonstrates that where the upper limit of
current is limited by machine capacity and duty
cycle, higher deposition rates and therefore
greater productivity will be achieved by using
smaller electrode wire. The TRANSMIG 400 i is a
particularly efficient MIG welder with the 0.9mm
steel wire in spray transfer mode. The savings
from decreased welding time will more than cover
the small cost penalty of the smaller electrode
wire sizes. 0.035" wire cost approximately 10%
more than 0.045", but is deposited approximately
15% faster. Higher current density (or smaller
diameter wire) also gives deeper penetration as
shown.
Wire penetration comparison using the same
current (200A) for both electrodes