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NEET 2023
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Two stainless steel foils of 0.1 mm thickness are to be joined. Which of the following processes would be best suited:
1. Gas welding
2. TIG welding
3. MIG welding
4. Plasma arc welding

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Correct Answer - Option 4 : Plasma arc welding


Plasma Arc Welding: 

  • Plasma Arc Welding is the advanced version of TIG welding. In Plasma Arc Welding process the arc is being created between tungsten electrode and the work piece. Plasma is the state of the gas when the gas is heated to high temperature and changes into positive ions, neutral atoms and negative electrons.
  • The plasma is allowed to pass through a very constricted nozzle to get a very high velocity of plasma.
  • The nozzle constrict the plasma and arc, thus constriction of arc will result into high temperature of the plasma. Thus high velocity and high temperature (30000°C) results into rapid melting of base metal.
  • The PAW is used for welding very thin foils due to very less heat affected area and intense heat generation.
  • The heat affected region in PAW is less than GTAW process, thus less amount of heat lost and high efficiency as compared to GTAW.
  • The energy density in PAW is greater than GTAW process. This result in deeper penetration in base metal and even thicker metal can be melted rapidly.
  • PAW is used in welding stainless steel, titanium, metals having very high melting points and super alloys. Also, in aeronautical industry, precision instrument industry and jet engine manufacturing.


Gas Welding: 

  • In gas welding Heat source is the flame produced by the combustion of fuel gas and oxygen. Acetylene (C2H2) is the principal fuel gas employed in this welding. No pressure is involved in this welding. Filler metal can be added in the form of a wire or rod.
  • The Gas welding process uses heat from exothermic chemical reactions.
  • Gas welding is used for joining ferrous and non-ferrous metals, e.g.,carbon steels, alloy steels, cast iron, aluminium, copper, etc.
  • Gas welding is used in automotive and Aircraft industries, sheet metal fabricating plants, etc.


TIG Welding: 

  • Tungsten Inert Gas (TIG) or Gas Tungsten Arc (GTA) welding is the arc welding process in which arc is generated between non-consumable tungsten electrode and work piece.
  • The tungsten electrode and the weld pool are shielded by an inert gas normally argon and helium.
  • TIG welding is used for welding thin materials up to a thickness of 5 mm, without using filler material.
  • TIG welds are stronger, more ductile and more corrosion resistant than welds made with ordinary shield arc welding.
  • There is little weld metal splatter or weld sparks that damages the surface of the base metal as in ordinary shield arc welding.


MIG Welding:  

  • In this process the arc is formed between a continuous, automatically fed, metallic consumable electrode and welding job in an atmosphere of inert gas, and hence this is called metal inert gas arc welding (MIG) process.
  • In MIG welding the consumable electrode is supplied in the form of a spool wire.
  • In MIG welding the thickness of base metal is limited to 40 mm.
  • It provides higher deposition rate. It is faster than shielded metal arc welding due to continuous feeding of filler metal.
  • There is no slag formation and deeper penetration is possible.
  • Practically all commercially available metals can be welded by this method.

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