WELDING (ARC, TIG, MIG, RESISTANCE, SPOT, ELECTROSLAG)

  • ARC WELDING
  1. Selection of electrode diameter depends upon Thickness of material.
  2. Selection of electrode diameter depends on Thickness of material.
  3. Electric current value depends upon electrode diameter.
  4. For welding Non-ferrous metal, DC is preferred.
  5. Direct Current is preferred for sheet metal welding.
  6. Alternative Current is preferred for thick section material.
  7. Voltage required for welding: Open circuit – 40 to 95 volt. Close circuit – 18 to 40 volt.
  8. Temperature produce during welding is 55000c (or 6000-7000 degree centigrade).
  9. In Arc welding heat is developed due to contact resistance.
  10. Rays produce in arc welding is- uv rays and Infra-red.
  11. In metallic arc welding, the metal transfer from electrode due to molecular attraction and surface tension.
  12. Arc is created between electrode and work by contact resistance.
  13. Arc stability is better with - AC.
  14. During Arc welding, electrode material melts first then coating melts.
  15. For welding a material by carbon electrode, DC welding set with straight polarity is used.
  16. STRAIGHT POLARITY: -
Straight Polarity
Fig. 1 | Straight Polarity

  • Electrode holder is negative and work piece is positive.
  • It is preferred for sheet metal working, shallow penetration.


17. REVERSE POLARITY: -

Reverse Polarity
Fig. 2  | Reverse Polarity


  • Electrode holder is positive and work piece is negative.
  • Deeper penetration is possible.

  • TIG OR GAS TUNGSTEN ARC WELDING: -
  1. Used for welding AL, SS, Mg, pure titanium.
  2. Non consumable tungsten electrode is used.
  3. Inert Gas used: - Helium, Argon, Neon, Nitrogen and Carbon di oxide. N2 is preferred for welding copper.


  • MIG (METALLIC INERT GAS): -
  1. Consumable electrode is used.
  2. Metal is transferred in the form of fine spray.
  3. MIG permits use of large currents, i.e. higher deposition over TIG.


  • RESISTANCE WELDING: -
  1. Resistance welding is the joining of metals by applying pressure and passing current for a length of time through the metal area which is to be joined.
  2. Pressure is released after the weld cool.
  3. Electrode use is made of copper.


  • SPOT WELDING: -
  1. Spot welding is one form of resistance welding, which is a method of welding two or more metal sheets together without using any filler material by applying pressure and heat.
  2. For welding, two sheet of different thickness always use smaller electrode tip diameter on the thicker side.
  3. Copper is very difficult to be spot welded
  4. Electrode tip diameter (D) = √ t   (t = thickness of sheet)


  • PROJECTION WELDING: -
  1. It is multi spot welding.

  • SEAM WELDING: -  It is continuous spot welding.

  • ELECTROSLAG WELDING: -
  1. Pool of molten metal is used to weld thick metal.
  2. Great thickness is welded in a single pass.
  3. High welding speed.
  4. Little distortion and good stress distribution.
  5. Protected from contamination.