EPT 311 Advanced Manufacturing Technology
PPK Pembuatan
Lab 2: TIG Welding Technology
Lab Outcomes:1. Student will be able to identify operational parameters for TIG welding.
2. Student will be able to identify defects in TIG welding.
Introduction:Arc welding in inert gas with infusible tungsten electrodes (or simply TIG - Tungsten Inert
Gas welding) is a process in which heat is produced by an electric arc passing between a
non-consumable electrode and the parts to be welded. The weld is achieved by fusing the
edges of the parts to be welded, adding material if necessary in the form of rods. The arc can
be triggered by an HF (high frequency) discharge, but in Selco welders it is triggered by a
high voltage discharge to minimize electromagnetic interference.
This ionizes the surrounding gas and allows current to pass. Alternatively, the arc can be
triggered by touching the electrode and the part to be welded in a LIFT start process.
During the electrode-work short-circuit phase Selco welders reduce current to avoid
damaging the electrode. TIG welding is suitable for all welding positions and can even be
used with sheet of only a few tenths in thickness.
TIG welding stands out for ease of arc control, a powerful and concentrated heat source, and
for ease of control over the amount of material added. These advantages make TIG welding
ideal for precision applications on parts of widely varying thickness, welding in position,
and
welding
fully
inside
pipes.
Thanks to the choice of DC (Direct Current) or AC (Alternating Current) power, TIG
welding can be used with any material and is best for welding ferrous materials nickel,
copper, titanium and magnesium alloys.
In simplest terms, the TIG (Tungsten Inert Gas) welding process is based on the presence of
an electric arc stricken between a non-consumable electrode (pure or alloyed tungsten with
an approximate melting temperature of 3370ºC) and the work-piece; an inert gas argon)
atmosphere protects the weld pool.
To avoid dangerous inclusions of tungsten in the joint, the electrode must never get in contact
with the workpiece; for this reason the spark is started through an H.F. power source, thus
ensuring the remote striking of the electric arc.
Page 1 of 4
EPT 311 Advanced Manufacturing Technology
PPK Pembuatan
Another type of start is also possible, with reduced tungsten inclusions: the lift start, which
does not require high frequency, but only an initial short-circuit at low current between the
electrode and the work piece; when the electrode is lifted, the arc will be started and the
current will increase until reaching the set welding value.
To improve quality of the end of the welding bead it is important to control carefully the
slope down of the current and it is necessary that the gas goes on flowing in the welding pool
some seconds after the arc blowout. Under many operational conditions, it is useful to be
able to use two preset welding currents and to be able to move easily from one to the other.
The following diagram show an equipment of TIG welding system:-
Page 2 of 4
EPT 311 Advanced Manufacturing Technology
PPK Pembuatan
The TIG-Welding process:-
TIG-welding (Tungsten Inert Gas) or GTAW-welding (Gas Tungsten Arc Welding) uses
a permanent non-melting electrode made of tungsten. Filler metal is added separately, which
makes the process very flexible. It is also possible to weld without filler material.
The most used power source for TIG-welding generates alternating current (AC). Direct
current can be used, but due to high heat generation on the tungsten electrode when DC-EP
(electrode positive) welding, that particular polarity is not feasible. In some cases DC-EN
(electrode negative) is used, however, this requires special attention before welding, due to
the arc's poor oxide cleaning action.
AC TIG-welding usually uses argon as a shielding gas. The process is a multi purpose
process, which offers the user great flexibility. By changing the diameter of the tungsten
electrode, welding may be performed with a wide range of heat input at different thicknesses.
AC TIG-welding is possible with thicknesses down to about 0.5 mm. For larger thicknesses,
> 5 mm, AC TIG-welding is less economical compared to MIG-welding due to lower
welding speed.
DC TIG-welding with electrode negative is used for welding thicknesses above 4 mm. The
negative electrode gives a poor oxide cleaning compared to AC-TIG and MIG, and special
cleaning of joint surfaces is necessary. The process usually uses helium shielding gas. This
gives a better penetration in thicker sections. DC TIG-welding is applicable for welding
thicknesses in the range 0.3 to12 mm. More and more popular is also pulsed DC TIGwelding, which makes it possible to weld uniform welds with deeper penetration at the same
heat input. Pulse frequency is usually in the range 1 to10 Hz.
Procedures:-
Page 3 of 4
EPT 311 Advanced Manufacturing Technology
PPK Pembuatan
1.
Turn ON the power supply
2.
Activate the switch at the machine
3.
Set the Argon gas pressure to 30 L/min by turning the gas regulator and nozzle .
4.
Choose types of Current :
i. Power supply for steel, mild steel and copper is Direct Current (DC).
ii. Power supply for alloy is Alternate Current (AC) .
5.
Set the current to 70A ( for mild steel ).
6.
Clamp the earth cable to work piece .
7.
Touch the electrode ( Tungsten) at 450 to the work piece.
8.
Press and release the Argon gas trigger until spark appears.
9.
Weld the work piece with feeder by moving outwards.
10.
Make sure both gas regulator and nozzle is fully closed after working.
11.
Ensure that the gas pressure is set to ZERO.
12.
Press the gas trigger to release all the gas in the pipe.
13.
Switch OFF the TIG machine and the main socket switch.
Questions:-
1) Discuss the relations between process parameter and welding quality?
 Ampere
 Gas pressure
 Torch welding polarity
 Types of workpiece material
 Types of rod
 Others related.
2) Based on your observation, what are the defects? Discuss ways to avoid it. Insert
pictures of your experiment.
3) What is the difference between TIG welding and conventional welding?
4) Give examples where welding quality is important.
5) Write your conclusion based on the experiment that you have done in this lab.
Page 4 of 4