In this article, we shall learn the Definition, types, construction, working principle, applications, advantages, and disadvantages of Plasma Arc Welding. It is a liquid-state welding process.
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
Power Supply
The plasma arc welding process needed a high-power DC supply to generate the electric spark between the tungsten electrode and welding plates. This welding can weld at a low 2 amp and the maximum current 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.
Water Re-circulator
This mechanism is used to cool the welding torch by the continuous flow of water outside of the welding torch.
Tungsten Electrode
In this machine, we use a no-consumable tungsten electrode. As we know tungsten can withstand very high temperatures.
Shielding Gas
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 used in this process can be helium, argon, and hydrogen as per the need, and it depends on the temperature.
Plasma Gas
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.
Filler Material
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
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 toward the weld area. The plasma starts between the tungsten electrode and the orifice by a low-current pilot arc. 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 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 using an outer shielding ring and the use of inert gases like argon, helium, or mixtures.
Video of the Plasma Arc Welding Process
Types of Plasma Arc Welding
There are two types of plasma welding which are as follows
- Transferred Plasma Arc Welding.
- 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 is to the positive terminal. The arc for welding is generated between the tungsten electrode and the workpiece using a DC.
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.
Based on the amperage used during welding, plasma arc welding is classified into three sub types which are as follows
- 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
- Torch design allows better control of the arc.
- This method provides more freedom to observe and control the weld.
- The higher 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 processes.
Disadvantages of Plasma Arc Welding
- It produces wider welds and heat-affected zones compared to LBW and EBW.
- Plasma welding equipment is expensive which means a high initial setup 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 100 dB.
- The torch is bulky and hence manual welding is a bit difficult and requires training as mentioned.
Applications of Plasma Arc Welding
- 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 as follows
| Plasma Arc Welding | TIG Welding |
| The tungsten electrode is suspended inside the torch nozzle in the plasma arc welding process. | 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. | 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. |
FAQ
What is the difference between plasma arc welding and plasma arc cutting?
Plasma arc welding melts and joins metal, while plasma arc cutting melts and blows away metal to create a cut. Both processes use a high-temperature plasma arc but have different outcomes.
What is the scope of Plasma Arc welder
Plasma Arc welding finds its scope in industries such as aerospace, automotive, construction, and manufacturing, which require high-quality, precise welding of materials like steel, aluminum, and other metals. It offers benefits like faster welding speeds, deeper penetration, and lower heat input, making it suitable for thick and thin materials.
What is the difference between Plasma Arc Welding and TIG welding
The main difference between Plasma Arc welding and TIG welding is the heat source. Plasma Arc welding uses a high-temperature plasma arc to melt the metal while TIG welding uses a tungsten electrode to produce an arc. Plasma Arc welding offers faster welding speeds, while TIG welding provides higher precision and control.
Conclusion
Plasma arc welding is a useful process with various applications, but it has both advantages and disadvantages. While it produces high-quality welds with precision and efficiency, it requires specialized training, expensive equipment and maintenance, and may pose health hazards. To decide if plasma arc welding is the best choice, project requirements and pros and cons must be evaluated.
References
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