The plasma arc welding process uses an inert gas with non- consumable electrode and during the welding process utilize a transferred constricted arc.
Plasma is defined as gas is heated with sufficient high temperature. That transfer into an ionized condition and it able to conduct electric current.
The plasma arc welding consists of the nozzle having two passages. One for shielding gas flow and another plasma gas flow the arc is provided due to current supply passed between work piece (+) and electrode (-) is known as transferred arc or between nozzle (+) and electrode (-) is known as non- transferred. Now the plasma gas is supplied through nozzle orifice.
The orifice gas (plasma gas) is passed to the work piece by using torch; it heated by arc and get ionized. When the gas mixture of argon to use avoid reaction with the tungsten electrode.
In this process the ionization created for more energy to the gas. After ionization the gas is known as plasma. The plasma is passed through the nozzle. When the pressure, energy (due to collision of ions) increased and temperature at 20000⁰c. The plasma strike will be melt the work piece. In this plasma welding a DC power source voltage range of above 70 volts and current 50 to 350 amps.
For ferrous and Nonferrous metal can be welded by this plasma arc welding and thickness of work piece as up to 6 mm. The welding speed and penetration is more them TIG welding.
Since the powerful plasma caused by turbulence in Melton puddle. The softer metal can be welded by limit the gas flow through nozzle. This flow may not be adequate to protect molten puddle from the atmosphere contamination and auxiliary gases are developed through outer gas cup on torch.
Gases used in plasma arc welding process:
Two separate flow gas used
- Plasma gas
It flow through orifice and become ionized.
- Shielding gas:
The flow through outer nozzle and shields the molten weld from atmosphere.
- Back- purge and trailing gas:
It require for some of material and application.
Advantages of plasma arc welding process:
- It having more energy concentration than TIG welding.
- More heat content
- No tungsten contamination
- Plasma velocity is high
- Less sensitivity to variation of arc length
- It used to join all metal
Disadvantages of plasma arc welding process:
- Torch maintenance is critical
- It require complex equipment and expensive as compared to TIG.