Plasma Arc Welding (PAW)

Plasma arc welding is an extension of or related to GTAW in which coalescence is obtained by heating with a plasma or constricted arc established between a nonconsumable electrode and the base metal.

The major difference among the PAW and GTAW is that in PAW, the welder is capable in placing the electrode in the torch’s body; so this will allow the PAW to be divided from the protecting gas.

In PAW, a tungsten electrode is contained in a specially designed nozzle that focuses a high-velocity stream of inert gas (e.g., argon or argon–hydrogen mixtures) into the region of the arc to form a high-velocity, intensely hot plasma arc stream. Argon, argon–hydrogen, and helium are also used as the arc-shielding gases.

The plasma arc method utilizes a non-consumable tungsten electrode & an arc can be formed by strengthening the plasma throughout a bore nozzle.

Temperatures in plasma arc welding reach 17,000°C  or greater, hot enough to melt any known metal. The reason why temperatures are so high in PAW (significantly higher than those in GTAW) derives from the constriction of the arc. Although the typical power levels used inPAWare below those used in GTAW, the power is highly concentrated to produce a plasma jet of small diameter and very high power density.

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This arc welding can be productively applied to every metal that can be connected with the help of the gas tungsten arc welding technique.

» Working Principle of Plasma ARC Wielding:-

  • The plasma arc welding is method wherever a coalescence is generated with the temperature which is developed from a special setup between a tungsten alloy electrode and the water-cooled nozzle (Non transferred ARC) or between a tungsten alloy electrode and the job (transferred ARC).
  • In this type of winding, there are three types of gas supplies being utilized namely
    plasma gas, shielding gas, and a back-purge gas.
  • Plasma gas supplies throughout the nozzle turn into ionized.
  • The shielding gas supplies throughout the external nozzle & protects the joint from the environment.
  • Back-Purge gas is mainly used when particular materials are being used.

» Equipment used in Plasma ARC Welding:-

The equipment used in the PAW includes the following-

  1. The power supply used in the PAW is a DC power source, and the suitable voltage for this type of welding is 70 volts otherwise above.
  2. The typical welding parameters are voltage, current, and gas flow rate. These parameter values can be ranges like the current is 500A, voltage is 30V to 250V, the speed of cutting is: 0.1 to7.5 m/min, the thickness of the plate is up to 200mm, required power is 2KW to 200KW, the rate of material removal is 150 cm3/min, and plasma velocity is 500m/sec
  3. Current limiting resistors, as well as a high-frequency generator, are used for arc ignition.
  4. The plasma torch includes an electrode as well as water-cooling arrangement, and these are used to save the nozzle & the electrode’s lifespan from dissolving due to the extreme heat generated while welding.
  5. The fixture is necessary to avoid atmospheric pollution from the molten metal beneath bead.
  6. Shielding gas is used for protecting the arc region from the atmosphere.
Also read : Metal Forming Processes

» Types of Plasma ARC Welding:- 

  1. Transferred PAW
    The transferred PAW method uses direct polarity DC current. And in this method, the tungsten electrode can be allied to the –ve terminal and the metal can be allied to the +ve terminal. The arc produces among tungsten electrode as well as work portion. In this kind of method, both arc and plasma moved toward the work portion, which will enhance the heating capacity of the method. This type of PAW can be used to join solid sheets.

  2. Non-transferred PAW
    The Non-transferred PAW method used direct polarity DC current. And in this method the tungsten electrode can be connected to the –ve and the nozzle can be connected to the +ve pole. The arc generates among the nozzle as well as tungsten electrode within the torch, which will enhance the ionization of the gas within the torch. And the torch will transfer the ionized gas for further procedure. This type of PAW can be used to join thin sheets.

» Advantages of PAW

  1. Power consumption is low
  2. Welding speed is high, so it can simply utilize to join thick and hard workpieces.
  3. Penetration rate and strong arc are high.
  4. It can function at little amperage.
  5. The arc arrangement doesn’t affect by the distance among tool as well as the workpiece.
  6. By using this method, the more steady arc can be produced.

» Disadvantages of PAW

  1. The process is noisy.
  2. Equipment cost is high.
  3. High expertise labor required.
  4. Radiation is more.

» Applications of PAW

The applications of PAW mainly include the following.

  1. PAW can be used in industries like aerospace as well as marine
  2. PAW is used to join stainless tubes and pipes
  3. This type of welding is mostly applicable for electronic industries.
  4. PAW is mainly used to fix tools, mold and die.
  5. PAW is used to coating otherwise welding on the turbine blade.

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