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BASIC TIG WELDING GUIDE
PROCESS CHARACTERISTICS
In the TIG process the arc is formed between a pointed tungsten electrode and the workpiece in an inert
atmosphere of argon. The small intense arc provided by the pointed electrode is ideal for high quality and
precision welding. Because the electrode is not consumed during welding, the welder does not have to
balance the heat input from the arc as the metal is deposited from the melting electrode. When filler metal is
required, it must be added separately to the weldpool.
POWER SOURCE
TIG must be operated with a constant current power source. A constant current power source is essential
to avoid excessively high currents being drawn when the electrode is short-circuited onto the workpiece
surface. This could happen either deliberately during arc starting or inadvertently during welding. If, as in
MIG welding, a flat characteristic power source is used, any contact with the workpiece surface would
damage the electrode tip or fuse the electrode to the workpiece surface. In DC, because arc heat is
distributed approximately one- third at the cathode (negative) and two-thirds at the anode (positive), the
electrode is always negative polarity to prevent overheating and melting. However, the alternative power
source connection of DC electrode positive polarity has the advantage in that when the cathode is on the
workpiece, the surface is cleaned of oxide contamination.
APPLICATIONS
TIG is applied in all industrial sectors but is especially suitable for high quality welding. In manual welding,
the relatively small arc is ideal for thin sheet material or controlled penetration (in the root run of pipe welds).
Because deposition rate can be quite low (using a separate filler rod) MMA or MIG may be preferable for
thicker material and for fill passes in thick-wall pipe welds.
WELDING
GAS SELECTION CHART
GUIDE
T
TIG
X
X
X
X
X
X
X
X
√
√
√
√
√
√
√
√
TIG WELDING
MILD STEEL
STAINLESS STEEL
LOW ALLOY STEEL
ALUMINIUM
ARGON
Ar-CO
2
-O
2
TRIGGER
WELDING WIRE
FLUX COATING
ROD
ARC
CONTACT TIP
DROPLETS
SHIELDING GAS
ARC
MOLTEN WELD METAL
SHROUD
WORK PIECE
WORK PIECE
WORK PIECE
WORK PIECE
WORK PIECE
WORK PIECE
WORK PIECE
WORK PIECE
STRAIGHT GROUND
CORRECT PREPERATION
- STABLE ARC
INCORRECT PREPERATION
- STABLE ARC
RADIAL GROUND
ARC WANDER
TUNGSTEN ELECTRODE
GAS LENS
STABLE ARC
FLAT TIP
POINTED TIP
GRINDING WHEEL
GRINDING WHEEL
FILLER WIRE
Note: Do not use wheel for other jobs or tugsten can become contaminated and cause lower weld quality
AC / DC WELDING
Alternating current (AC) is electricity that switches direction back and forth so the voltage also periodically re-
verses because the current changes direction. Typical AC currents are what you would expect to see from your
electrical outlets in your home and often used in higher voltage devices such as household appliances. AC cur-
rent changes its polarity 120 times per second with a 60-hertz current. Reversed polarity (AC) results in deeper
penetration. In Alternate Current (AC) welding, since the current and the magnetic field of the arc reverse direc-
tion many times a second, there is no net deflection of the arc.
Applications of AC Welding
AC welding can be used to weld magnetic metals. This cannot be done with DC welding. AC welding is ideal for
the following types of welds:
• Downhand heavy plate
• Fast fill
• Aluminum TIG welding with high frequency
The primary advantage of using AC welding is that it allows the weld operator to weld on magnetized
materials. In AC current, the current changes direction and is not affected by magnetism. The arc remains stable
and is easier to control.