Overview of Tungsten Inert Gas (TIG) welding process Ⓡ

TUNGSTEN INERT GAS (TIG) WELDING PROCESS 

1) Mode of Operation: Manual but can be semi-automatic 

2) Principle of operation: Small-diameter solid wire and shielding gas (inert gas) are used. The arc is produced between a non-consumable electrode (tungsten) & the workpiece. The operator must control the arc length & also add filler metal into the weld pool if needed.

 
3) Basic equipment requirements: 

a) Transformer / Rectifier (constant current (drooping) characteristic) 

b) Head / Hose assembly. 

c) Power returns cable. 

d) Torch head assembly 

e) Gas cylinder, hoses, regulators, flow meter. 

f) Visor with lens. 

g) Fume extraction. 

4) Arc Striking: The arc striking (scratch start) the core wire onto the plate and withdrawing cause contamination of the tungsten and weld metal to work on this high-frequency arc is used to cause interference. To work on this, a lift arc is used where the electrode is touched onto the plate & is withdrawn slightly. 

5) Arc and Weld Shielding: Inert gas (pure argon & helium) is used to shield arc & weld. Gas cut-off delay is used to shield weld metal at the end of a run. 

6) Weld refining & Cleaning: Very clean high quality drawn wire is used.

 
7) Process variable parameters: 

a) Voltage: Changes with change in arc length & type of gas being used. 

b) Current: Changes with change in tungsten diameter. Slope in & slope out controls the current at the start & end of the weld. 

c) Polarity: DC –ve for steels. AC for Aluminum. 

d) Inert Gas type: Pure gases argon & helium are used. Nitrogen was added for copper welding. Mixture (Arg+Heli) gives good gas cover & penetration. 

e) Gas Flow rate: Should be correct for the given joint design & position as given in approved welding procedures. 

f) Purging: Purging gas pure argon is used to reduce atmospheric root oxidation. 

g) Tungsten type: Thoriated tungsten for DC and zirconated tungsten for AC. A too-fine vertex angle will melt the tungsten tip. With AC, the tungsten end is chamfered & forms a ball end during aluminum welding.

8) Consumable: High-quality drawn wire & inert gas (pure argon or helium or a mixture of both)

 
9) Typical imperfection: 

a) Tungsten inclusions: Caused by a lack of welder skill, too high current & incorrect vertex angle. 

b) Crater pipes: Caused by poor weld finish technique or incorrect use of current decay. 

c) Weld/root oxidation: If using insufficient gas cut-off delay or purge pressure. 

10) Advantages: a) High-quality weld b) All positional c) Low inner run cleaning

 

11) Disadvantages: a) Small range of consumables. b) High ozone levels. c) Low productivity 

12) Positional capabilities: All positional.

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