What is Plasma Welding?
Definition: Plasma welding (also known as Plasma Arc Welding or PAW welding) is a type of welding process in which the arc is produced between the tungsten electrode and workpiece.
Plasma welding is similar to TIG welding but the only difference is that in plasma welding, the position of electrode is inside the body of the torch, while in TIG welding, the position of electrode is outside the body of torch. (Visit TIG welding diagram to see its electrode position.)
The high temperature plasma is then forced through the fine-bored copper nozzle and this plasma exits the nozzle which is then used to weld the metal.
What is Plasma Cutting?
Definition: Plasma cutting (also known as Plasma Arc Cutting) is a process in which the accelerated hot plasma (above 20000 °C) is used to cut the metals.
During the plasma cutting process, the electric arc is stuck between tungsten electrode and the workpiece.
The hot plasma is passed through the narrow nozzle which forms a thin plasma jet with very high velocity which is capable to melt and cut the solid metal.
What is the difference between Plasma Arc Welding and Plasma Arc Cutting?
Yes, the main difference between plasma welding and cutting is the velocity of the plasma jet.
- In plasma arc welding process (PAW welding), the velocity of the plasma jet is less which is only capable of melting the metal.
- While in plasma cutting process, the velocity of the plasma jet is kept very high which can melt and even cut the metal.
Having discussed the difference between plasma Cutting and Welding, now let me explain the basic working principle of plasma arc welding process (PAW process).
Plasma welding principle (How Plasma welding works?)
The plasma welding setup diagram is shown in the above image.
The shielding gas is circulated from the nozzle to obtain a hot and ionized gas.
During this plasma welding process, more pressure is not applied to the gas.
Also the filler metal may or may not be used for plasma arc welding process.
There are basically two types of Plasma Arc.
- Transferred plasma arc
- Non-transferred plasma arc
In transferred plasma arc, the arc is obtained between the electrode (connected at -ve node) and the workpiece (connected at +ve node).
While in the Non-transferred plasma arc, the arc is obtained between the electrode (connected at -ve node) and the nozzle (connected at +ve node).
In this Non-transferred plasma arc welding, the workpiece is indirectly heated by the means of radiation.
The plasma torch contains a tungsten electrode and its position is such that the electrode is inside the body of the plasma torch (see above image).
The inert gas is passed through the torch through the outer layer as shown in the diagram.
The inert gas should possess high thermal conductivity so that it can transfer more heat.
The end of the metal cup has a smaller diameter than the diameter at the upper side. Hence this metal cup forms a nozzle.
The inner wall of the nozzle contains ceramic coating which helps the torch to resist high temperatures.
The water circulating passage is also provided in the metal cup through which cold water is circulated (see above image).
The inert gas used in plasma arc welding should have higher thermal conductivity so that it can conduct more heat which is required to weld the heavier sections.
Commonly used inert gases in plasma welding process include helium and argon.
The plasma arc can reach the temperature of around 35000 °C, which can easily weld the metal section upto 200 mm without any difficulty.
Plasma Arc welding process gives maximum penetration and it is highly beneficial.
Having said that, now let’s discuss the advantages and disadvantages of plasma arc welding.
Advantages of plasma arc welding
The advantages of plasma welding process are mentioned below.
- By using plasma welding process, almost all the metals can be welded.
- The HAZ is very narrow and hence the change in microstructure is very less.
- Plasma welding is faster process and it has higher dimensional stability.
- The arc penetration is good and deeper.
- Tungsten electrode is not contaminated with atmospheric gases, so uniform weld is obtained without any welding defects.
Limitations of plasma arc welding
The limitations/disadvantages of plasma welding process are mentioned below.
- There must be automatic control for the plasma welding and cutting process.
- Difficult to control the process for small size workpieces.
- Infrared rays and UV rays are produced during the plasma cutting and welding operation. So it may affect the operator.
- The initial cost for the plasma welding equipment is very high.
Applications of plasma arc welding
The applications of plasma welding process are mentioned below.
- Plasma Arc Welding process is widely used for welding stainless steel, nickel alloys, refractory metals, as well as many other metals.