Impax IM-MIG120 Instruction Manual page 43

TIG OPERATION
Guide for Selecting Filler Wire Diameter
Filler Wire Diameter
1.6mm
2.4mm
3.2mm
4.8mm
To avoid inclusions of tungsten in the joint, the
electrode should not contact the workpiece. For
this reason the arc is started through a Hi. Freq.
generator.
For situations requiring no Hi. Freq., Touch Start
Tig reduces the short-circuit current to keep
tungsten inclusions to the minimum.
To improve weld bead quality at the end of the
weld it is important to carefully control the
downslope of current and ensure proper gas
coverage over the weld.
Welding Polarity
DC Electrode Negative Polarity (Direct
Current Straight Polarity)
While Welding, there is a continuous flow of
electrons from the electrode to the workpiece.
This is the most used polarity, ensuring limited
wear of the electrode, since the majority of the
heat concentrates on the anode (workpiece).
Narrow and deep welds are obtained with high
travel speeds. Most materials, with the
exception of aluminum and magnesium, are
welded with this polarity (Fig.41).
Fig 41
DC Electrode Positive Polarity. (Direct
Current Reverse Polarity)
In this case, there is a continuous flow of
DC Current
electrons from the workpiece to the electrode.
Range (Amps)
The reverse polarity is used for welding alloys
20-90
covered with a layer of refractory oxide.
With this polarity the electrode functions as
65-115
anode and is subjected to a high degree of heat;
100-165
the workpiece is bombarded by positive ions
sent from the electrode which break the surface
200-350
oxide.
In Electrode Positive Polarity, high currents
cannot be used, since they would cause an
excessive wear of the electrode.
Steel TIG Welding
The TIG process is very effective for welding
both carbon steel and alloy steel, especially in
applications requiring precision results. DC
Electrode Negative Polarity is required. Since
this process does not include the removal of
impurities, proper cleaning and preparation of
the edges is required.
Filler material: The filler rods must deposit welds
with mechanical characteristics appropriate for
the application.
Copper TIG Welding
Since the TIG welding is a process characterized
by high heat concentration, it is particularly
suitable for welding materials with high thermal
conductivity, like copper. As with steel, the DC
Electrode Negative Polarity is employed, with
argon as protective gas. Considering the fluidity
of molten copper, the use of backup support
may prove useful.
Filler material: In order to avoid the oxidation of
the molten material, filler materials containing
phosphorus, silicon or other deoxidating
materials are typically used. The mechanical
properties can also be improved through the use
of silver.
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