Plasma Arc Welding is a liquid state welding process. Here in this paper, you are going to learn the Definition of Plasma Arc Welding, the Components, and the Working Principle of the Machine, along with the Applications, Advantages, and Disadvantages of this Welding. So now let’s get started with the definition of PAW!
What is Plasma Arc Welding?
Plasma Arc Welding (PAW) is a liquid state welding process in which the metal-to-metal joint forms in a molten state with the help of hot ionized gases known as Plasma. These hot ionized gases are used to heat the work plates, and the joint is created due to fusion.
Construction of the Machine:
The Plasma Arc Welding setup consists of the following components:
- Power Supply
- Plasma Welding Torch
- Water re-circulator
- Tungsten Electrode
- Shielding Gas
- Plasma Gas
- Torch Accessory Kit (Tips, ceramics, collets, electrodes set-up gages)
- Filler Material
Let me give you a brief overview of each component.
The plasma arc welding process needed a high-power DC supply to generate the electric spark in between the tungsten electrode and welding plates.
This welding can weld at a low 2 amp and the maximum current which it can handle is about 300 amp. It needs about 80 volts for proper working.
The power source consists of a transformer, rectifier, and control console.
Plasma Welding Torch:
This is the most important part of the plasma welding process.
This torch is quite similar to that used in TIG welding.
PAW torches are water-cooled because the arc is contained inside the torch which produces high heat, so a water jacket is provided outside the torch.
This mechanism is used to cool the welding torch by the continuous flow of water outside of the welding torch.
In this machine, we use a no-consumable tungsten electrode. As we know tungsten can withstand very high temperatures.
In this welding process, we use two inert gases. We need to maintain a low pressure to avoid turbulence while welding due to this low-pressure gas welding shield is formed weekly, that’s why we need to charge another inert gas through the outer portion of the welding force at a high flow rate, to make the weld shield sustainable.
The inert gases which are used in this process can be helium, argon, and also hydrogen as per the need, and it totally depends on the temperature.
It is an ionized hot gas composed of nearly the same number of electrons and ions. It has sufficient energy to free electrons from molecules, atoms, and electrons to synchronize.
It is the main energy source of this welding.
Torch Accessory Kit:
These kits are used to expand the performance of the welding torch.
In Plasma welding there is no filler material is used. If the filler material is used, then it is directly fed into the weld zone.
Working Principle of Plasma Arc Welding Machining:
This is an arc welding process, a concentrated plasma arc is produced with the help of a high-frequency unit of the machine and directed towards the weld area.
The plasma starts between the tungsten electrode and the orifice by a low current pilot arc. The plasma arc welding is concentrated because it is forced through a relatively small orifice or nozzle to increase its pressure, temperature, and heat.
Because of the above characteristic, the arc will now become very stable and improved in shape and heat transfer rate.
The temperature of the arc is as high as 33,000°C due to this phenomenon heat the nozzle is surrounded by a water cooling system to avoid wearing out of the nozzle due to heat.
Operating currents usually are less than 100 amp. This makes Plasma Welding different from other types of welding.
When filler metal is used it is fed into the arc as is done in Gas Tungsten-arc Welding. Arc and weld-zone shielding are supplied by means of an outer shielding ring and the use of inert gases like argon, helium, or mixtures.
You may watch this video for a better understanding of the Plasma Arc Welding Process:
Types of Plasma Arc Welding
Broadly, there are two types of plasma arc welding. They are:
- Transferred Plasma Arc Welding, and
- Non-transferred Plasma Arc Welding
Transferred Plasma Arc Welding: In this type of plasma arc welding process, the tungsten electrode is fixed to the negative terminal while the workpiece to the positive terminal. The arc for welding is generated between the tungsten electrode and the workpiece using a DC current.
Widely used for welding thick metal sheets, the transferred plasma arc welding process transfer both the plasma and arc to the workpiece which improves the heating capacity.
Non-transferred Plasma Arc Welding: In this type of plasma arc welding process, the tungsten electrode is connected to the negative terminal and the nozzle is fixed to the positive pole. In the non-transferred plasma arc welding process, the arc is generated between the nozzle inside the torch and the tungsten electrode. This increases the gas ionization inside the torch which is then transferred for further processing. This type of welding is mainly used for joining thin metal sheets.
Again, based on the amperage used during the welding, plasma arc welding is classified into three classes. They are:
- Microplasma Welding (0.02 to 15 amperes)
- Plasma welding with the melt-in technique (15 to 100 amperes)
- Plasma welding using the keyhole technique (15 to 350 amperes)
Advantages of Plasma Arc Welding:
The advantages of Plasma Arc Welding are the following:
- Torch design allows better control of the arc.
- This method provides more freedom to observe and control the weld.
- The higher the heat concentration and plasma jet allow faster travel speeds.
- The high temperature and high heat concentration of plasma allow the keyhole effect.
- This provides complete penetration with the single-pass welding of many joints.
- The heat-affected zone is smaller compared to GTAW (Gas tungsten arc welding).
- It uses less current input as compared to other welding process.
Disadvantages of Plasma Arc Welding:
The disadvantages of Plasma Arc welding are:
- It produces wider welds and heat-affected zones compared to LBW and EBW.
- Plasma welding equipment is very costly. Hence it will have a higher startup cost.
- It requires training and specialization to perform plasma welding.
- It produces ultraviolet and infrared radiation.
- The method produces higher noise on the order of about 100dB.
- The torch is bulky and hence manual welding is a bit difficult and requires training as mentioned.
Applications of Plasma Arc Welding:
The application of Plasma Arc welding are:
- This welding is used in the marine and aerospace industries.
- This is used to weld pipes and tubes of stainless steel or titanium.
- It is mostly used in electronic industries.
- Also, this is used to repair tools, die, and mold.
- This is used for welding or coating a turbine blade.
Difference between Plasma Arc Welding and TIG Welding
The main differences between the plasma arc welding and tungsten inert arc welding process are tabulated below:
|Plasma Arc Welding||TIG Welding|
|In the plasma arc welding process the tungsten electrode is suspended inside the torch nozzle.||Whereas, In the tungsten inert gas welding process the arc formed by the tungsten electrode is maintained in a shielding gas that protects the electrode and weld pool from contamination.|
|Plasma arc welding is suitable for welding both thin and thick metal pieces.||On the other hand, TIG welding is best for welding thin metal pieces.|
|The main advantage of the plasma arc welding process is the possibility to create a variety of welds.||The main advantage of TIG welding is the control of the arc.|
|Plasma arc welding is much faster than TIG welding.||TIG welding is a comparatively slow process.|
|The temperature of the plasma arc is much higher than the temperature generated during Tig welding.||In TIG welding the generated temperature is lower than PAW.|
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- Image 1: By Chocolateoak – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=12260232
- Image 2: By Rudolfensis at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=45785285
- Image 3: By Saubhik Roy- Design Team Learn Mechanical
- Feature Image: By Saubhik Roy- Modified by Author
- Video: By Chip CM