TUNGASTEN INERT GAS (TIG) OR GAS TUNGASTEN ARC WELDING (GTAW)

Welding heat is produced from an electric arc established between the tungsten electrode and
the job.
A shielding gas (argon, helium nitrogen etc) is used to avoid atmospheric contamination of the
molten weld pool. Filler metal if required is fed separately

SHIELDING GAS
Argon is normally preferred over helium because:
 It requires a lower arc voltage.
 Easy arc starting.
 Provides a smooth arc action.
 Its economical and heaviest.
Helium is used where higher heat in put is used because it can with stand higher arc voltage. At
times active gas carbon dioxide can be used its more economical. It requires slightly higher
current and normally used with Dc with positive electrodes where as both argon and helium
can be used with Ac as well as Dc welding power source.

OPERATION
It uses anon consumable tungsten electrode mounted in a special electrode holder, This holder
is also designated to furnish a flow of inert gas around the electrode and around the arc.
The work pieces to be joined are cleaned to remove dirt, grease and other oxides
chemically or mechanically to obtain a sound weld. The welding current and inert gas
supply are turned on
Welding operation is done by striking an arc between the work piece and tungsten electrode in
an atmosphere of inert gas. The arc is struck either by touching the electrode with a scrap metal
tungsten piece or using a high frequency unit. After striking the arc its allowed to impinge on
the job and a weld pool is formed or created The welding torch and the filler metal are
generally kept inclined at an angle of 70=80 degrees and 10-20 degrees respectively with the
flat work piece. Filler metal if required should be added by dipping the filler rod in the weld
pool. When doing so the tungsten electrode should be taken a little away from the weld pool
however the heated end of the filler rod as well as as the electrode should be within the inert
gas shield .both dc and ac power source can be used.

COMPONENTS OF THE TIG WELDING EQUIPMENTS

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  Welding torch, tungsten electrode and filler metal.
 Welding power source, high frequency unit dc suppressor unit and cable
 Inert gas cylinder ,pressure regulator and flow meter
 Cooling water supply
 Water and gas solenoid valve

ADVANTAGES OF TIG OR GTAW WELDING PROCCESS

 It welds more different types of metals and alloys ,carbon steel, stainless steel. Nickel
steels aluminum magnesium brass, titanium etc
 Heat affected zone is very low
 No flux is used therefore there is no danger of flux entrapment
 It can weld in all positions
 Un like metals can be welded to each other like mild steel to stainless steel and brass to
copper
 There is clear visibility of the arc and hence clear control
 Provides high quality welding of thin metals
 Requires no clean up because of absence of slag or spatter.

DISADVANTAGES

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  TIG is the most difficult process compared to all the other welding
processes.
 The welder must maintain short arc length, avoid contact between
electrode and the work piece and manually feed the filler metal with one
hand while manipulating the torch with the other hand.
 Tungsten material when gets transferred into the molten metal
contaminates the same leading to a hard and brittle joint.
 Skilled operator is required.
 Process is slower.
 Not suitable for thick metals.

APPLICATIONS
 Welding of carbon steel, stainless steel, nickel aluminum magnesium
brass copper bronze titanium
 Welding sheet metal and thinner section.
 Used in air crafts, rockets . motor chambers, transistor cases and
instrument industries.

Types of Welding Polarity

GTAW

Uses the three different types of current or polarity for welding and these are:

 Alternating current (AC),

 Direct-current electrode negative (DCEN) is also called straight Polarity.
 Direct current electrode positive is also called DCEP and Reverse Polarity

What is Direct Current Electrode Negative or DCEN Polarity?

DCEN or also known as Straight Polarity works with the electrode connected to the
negative, and the work is connected to the positive terminal as shown in the below
picture (left side).

The electrons flow from the Cathode (Welding electrode) to the Anode (workpiece). This
gives around 1/3 of the welding heat on the welding rod and 2/3 on the base material
being welded. Straight polarity due to the above reason results in high welding rod
melting. Its therefore used on applications requiring deep penetration.

What is Direct Current Electrode Positive or DCEP Polarity?

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DCEP is also called Reverse Polarity. In DCEP as you can see in the below picture-
the job is connected to the negative terminal and the welding rod is connected to the
positive terminal.

The electrons flow from the base material to the welding rod (cathode to anode flow of
electrons).

Change in these terminal points as stated above results in 2/3 heat concentration on the
welding rod and 1/3 on the base material to be welded. The tungsten electrode is
positive and the work is negative Its used for welding aluminium and heavily oxidized
aluminium castings

What is Alternating Current (AC) Polarity (ACHP)

Alternating Current (AC) polarity uses alternating current and hence there are no
negative or positive terminals. It is used for welding aluminum and magnesium which
have oxide coating that contaminates the molten AL and Mg while welding and ACHP
helps to remove these oxides

The electron flows keep alternating every 1/120 seconds from the welding rod to the
base material. AC polarity with alternating terminals brings cleaning action to the work
piece.

This action is highly beneficial for welding materials having tough oxide layers such as
aluminum & magnesium alloys welding

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How do you determine the polarity of a weld?

The polarity of a weld is determined by the direction of the current flow. In a weld, the
electrode is the positive terminal and the work piece is the negative terminal.

The polarity can be reversed by changing the leads on the welding machine, which
changes the direction of the current flow. Reversing the polarity will change the
appearance of the weld puddle.

Effect of Welding Polarity on Penetration & Heat Distribution in Welding

In GTAW, if we keep the tungsten electrode positive, it will lead to the melting of the
tungsten electrode fast. This can cause tungsten inclusion in the weld as well as
other welding defects.

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Thus, a correct selection of the welding polarity is very important. The effect of welding
polarity and heat distribution is shown in the below figure

TUNGSTEN ELECTRODES

Five types of electrodes are used in TIG /GTAW welding including their color of
identification and these are

 Pure tungsten(W) (green)

 1% Thoriated w( yellow)
 2% Thoriated w (red)
 Striped w(blue)
 Zirconium w(brown)

Pure tungsten electrodes are used only on ACHP and designed for aluminums and
magnesium welding only

1%thoriated tungsten electrodes is used for copper and copper alloys

2%thoriated tungsten is used for almost any metal

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 Striped tungsten combines pure tungsten and a stripe of 2% thoriated
tungsten.Thoriat helps to keep astablised arc and increases melting temperatuere.

Zirconium tungsten reduces the contaminationeffectsof dipping the tungsten into the
molten puddle while welding Al and Mg.

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