TUNGSTEN INERT GAS WELDING (OR) GAS TUNGSTEN ARC WELDING:
Tungsten Inert Gas Welding (T.I.G) is also called as Gas Tungsten Arc Welding. (G.T.A.W).This process uses Constant Current Power Supply (or) Droping Characteristic. Polarity used Welding Process is D.C.E.N. T.I.G Welding is a process where melting is produced by heating with an arc struck between a non-consumable tungsten electrode and parent metal . the arc produced will melt the parent metal & filler wire to form weld metal.
TUNGSTEN INERT GAS WELDING
An inert gas is used to shield the electrode and weld zone to prevent oxidation of tungsten electrode and contamination of the weld pool and hot filler metal. The operator must control the arc length and also add filler metal to obtain the correct weld. Tungsten is used because it has a high melting temperature of 3370 degree centigrade which is well above any other common metal. This process is accurate and using this we can get uniform root profile.
PROCESS VARIABLE:
- Welding current
- Current type & polarity
- Travel speed
- Shielding gas flow rate
- Electrode extension
WELDING IMPERFECTIONS:
- Tungsten inclusion
- Crater cracking
APPLICATIONS:
- Autogenous welding of longitudinal seams in thin walled pipes & tubes I stainless steels and other alloys
- It is used in chemical, petroleum & power generating industries
- It is also used in aerospace industry
ADVANTAGES:
- IT PRODUCES SUPERIOR QUALITY weld
- It does not give weld spatter nor slag inclusion
- It can produce welds with a relatively high speed
- It is good for particularly controlling weld root penetration in all positions
- The heat source and filler metal addition is controlled separately
DIS-ADVANTAGES:
- IT GIVES LOW DEPOSITION RATE WHEN COMPARED TO OTHER ARC WELDING PROCESSES
- It is difficult to shield all the weld zone
- Tungsten inclusion may occur if the electrode is allowed to touch the weld pool.
DIFFERENCE BETWEEN ARGON & HELIUM GAS:
| ARGON | HELIUM |
| Used for welding thin sections | Used for welding thick sections |
| Heavier than air | Lighter than air |
| Used for flat & horizontal welding positions | Used for over head position welding |
| Obtained from atmosphere | Obtained from natural gas |
| Low cost | High cost |
| Greater availability | Lesser availability |
TYPES OF TUNGSTEN ELECTRODES:
- Pure tungsten ( used for A.C Supply)
- Thoriated electrode ( its radioactive and emits γ-rays)
- Ceriated electrode ( used for both A.C & D.C Supply)
- Zirconiated electrode ( recommended for A.C SUPPLY)
MCQ IMPORTANT POINTS
- Tungsten melting point is 3370 degree centigrade.
- Shielding gas flow rate is 10-12 liters per min
- If shielding gas flow rate is low (or) high porosity & contamination will occur.
- Back purging is done to prevent root oxidation.
- Purging gas flow rate is 4 liters per min & argon gas is used.
- Slope-in device helps in gradually increasing the current which helps to avoid Tungsten inclusion
- Slope out device helps in gradually decreasing the current which helps to is used to avoid Crater pipes
- The inert gasses used are Helium, Argon & mixture of both.
- The filler wire used must be of same composition as of parent metal.