Gas Tungsten Arc Welding (Gtaw/Tig) - Everlast POWER DIGITAL SERIES Operator's Manual

SECTION 3
3.1 INTRODUCTION
The Tungsten Inert Gas, or TIG process
uses the heat generated by an electric arc
struck between a non-consumable tung-
sten electrode and the workpiece to fuse
metal in the joint area and produce a mol-
ten weld pool. The arc area is shrouded in
an inert or reducing gas shield to protect
the weld pool and the non-consumable
electrode. The process may be operated
autogenously, that is, without filler, or filler
may be added by feeding a consumable
wire or rod into the established weld pool.
3.2 PROCESS
Direct or alternating current power
sources with constant current output char-
acteristics are normally employed to sup-
ply the welding current. For DC operation
the tungsten may be connected to either
output terminal, but is most often connect-
ed to the negative pole. The output charac-
teristics of the power source can have an
effect on the quality of the welds produced.
Shielding gas is directed into the arc area
by the welding torch and a gas lens within
the torch distributes the shielding gas
evenly over the weld area. In the torch the
welding current is transferred to the tung-
sten electrode from the copper conductor.
The arc is then initiated by on of several
methods between the tungsten and the
workpiece.
3.3 PROCESS VARIABLES
DCEN
When direct-current electrode –negative
(straight polarity) is used:

Electrons strike the part being welded
at a high speed.

Intense heat on the base metal is pro-
duced.

The base metal melts very quickly.

Ions from the inert gas are directed to-
wards the negative electrode at a rela-
tively slow rate.

Direct current with straight polarity
does not require post-weld cleaning to
remove metal oxides.
Use of DCEN
For a given diameter of tungsten electrode,
higher amperage can be used with straight
polarity.

GAS TUNGSTEN ARC WELDING (GTAW/TIG)

Straight polarity is used mainly for welding

Carbon steels

Stainless steels

Copper alloys
The increased amperage provides

Deeper penetration

Increased welding speed

A narrower, deeper weld bead
DCEP
The DCEP (reverse polarity) are different
from the DCEN in the following ways:

High heat is produced on the electrode
rather then on the base metal.

The heat melts the tungsten electrode
tip.

The base metal remains relatively cool
compared to the sing straight polarity.

Relatively shallow penetration is ob-
tained.

An electrode whose diameter is too
large will reduce visibility and increase
instability.
Use of DCEP

Intense heat means a larger diameter
of electrode must be used with DCEP.

Maximum welding amperage should be
relatively low (approximately six times
lower than DCEN)
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