Different types of Liquid State Welding

Tungsten Arc Welding:

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  • The tungsten arc welding technique is used for the welding of aluminum, magnesium and its alloys.
  • Arc is generated between the non-consumable tungsten electrode and the work piece material.
  • For welding of 5mm thickness material there is no requirement for the supply of the filler material, and the joints can be produced by melting the base material itself.
  • For welding of high thickness materials filler materials can be supplied externally and the movements are controlled manually due to the non-uniform weld bead that is form.
  • Molten liquid metal in the weld pool is protected by creating inert gas atmosphere
  • For welding of all materials except Al, Mg alloys the direct current straight polarity is needed.
  • For welding of Al, Mg alloys AC power supply is preferred. In this process 1st half of the cycle, ore heat is generated on the work piece and oxides are formed on the surface of the work piece.
  • In the next half of the cycle by moving the electrons from work piece to the electrode metal oxides break and they are later cleaned from the surface of the object. This is known as cathode cleaning
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Tungsten Arc Welding

Applications:

  • Used for the welding of Al. Mg and its alloys in automobile and aero scope industries

Advantages:

  • This process is applicable for a wide range of materials
  • For thin section this process is good
  • By using this one can produce high quality output and also appearance is maintained
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Disadvantage:

  • The process is restricted to horizontal or flat welding.

Resistance welding:

  • For welding of sheet materials this technique is preferred
  • The two sheets which are to be welded are kept between 2 copper electrodes
  • High frequency and high rate of current is supplied to the work piece through the copper electrodes
  • Due to contact resistance more amount of heat is generated at the contact of two work piece surfaces.
  • After attaining sufficient heat, power is switched off and external energy is supplied onto the work pieces through the copper electrodes.
  • Due to these pressures forged joint will be produced at the contact of the two work pieces below the electrodes. This is known as nugget
  • Under ideal case this is extended throughout the thickness on the both sheets.
  • Resistance welding

Applications:

  • This technique will be used for welding of sheet metals in automobile industry where the joint is not exposed to air.

Limitations:

  • Welding speed is very less
  • League proof joint is not possible
  • There is a possibility of indentation marks on the sheets

Plasma arc welding:

  • For the welding of high thickness and high melting point materials like cobalt, molybdenum based alloys; stainless steel and nickel based alloys can be joined.
  • Arc is generated in between the tungsten electrode and the work piece.
  • Through the ceramic nozzle high power arc is supplied.
  • Due to squeezing action of the arc along with the plasma high energy plasma arc is produced, which is focused on to the work piece at a given point.
  • By forming the key hole, high melting point material will be melted and the depth of penetration is maximized.
  • Liquid metal in the weld pool is protected providing inert gas atmosphere. The same technique can be used for high melting point and high thickness material.
  • The weld bead must be very small
  • Direct current straight polarity can be used in this technique.

Plasma arc welding

Advantages:

  • If the welding process is in control, it gives quality product during the welding
  • For better control of the arc the torch must be designed
  • To avoid tolerance standoff distance must be maintained
  • By using the process we can see the smoothness and clean weld

Limitations:

  • The initial setup cost is very high
  • Equipment cost is also very high
  • Experts are required to perform the operation.

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