Technical

TIG WELDING

TIG WELDING :

  • To avoid tungsten inclusion : High frequency [HF] start, Lift arc method.
  • For aluminum : AC polarity welding.
  • For Magnesium : DC polarity welding.
  • Best for TIG welding DC –ve.
  • A water cooled torch is recommended if DC +ve is used.
  • A water cooled torch is used at temp above 150 Amps.
  • Polarity change from DC +ve to DC –ve, best penetration & penetration increase
  • Co2 [carbon dioxide] is not used in TIG welding.
  • Tungsten inclusion will appear bright white spot in radiograph.
  • Device is used to avoid tungsten inclusion is slope up [or] slope in.
  • Slope out device can avoid crater cracks.
  • Working voltage 10 to 12v
  • TIG welding slag & spattern defect is not come.
  • Back purge is done to prevent root oxidation.
  • Root concavity is cause due to excessive back purging.
  • Flow rate shielding gas is 10 to 12 liters/mint.
  • Flow rate purging gas is 4 liters/mint.
  • Function of pre flow: to help welder accommodate welding conditions.
  • Function of post flow: to prevent contamination of tungsten electrode.
  • Electrode extension too small: unstable arc.
  • Electrode extension too large: over heating tungsten inclusion.
  • Travel speed increases:  reduce penetration & width vice versa.
  • Travel speed decreases: increases penetration & width.

Types of tungsten electrode:

  • Pure tungsten electrode.
  • Thoriated electrode,
  • Ceriated [or] lanthaniated electrode.
  • Zirconiated electrode.

Pure tungsten electrode:

  • AC current is used.
  • Balled end [or] chamfer end.

Thoriated electrode:

  • Electrode coating is thoria.
  • Sharp end.
  • Radio active [emitting alpha radiation]

Ceriated [or] lanthaniated electrode:

  • No radiations
  • Sharp end.

 

Zirconiated electrode :

  • AC current.
  • Balled end [or] chamfer end.
  • High integrity of weld.
  • High resistance to contamination.
  • Tungsten inclusion must be avoided.
  • Aluminum welding.