Plasma arc welding (PAW) is an arc welding process similar to gas tungsten arc welding (GTAW). The electric arc is formed between an electrode (which is usually but not always made of sintered tungsten) and the workpiece. The key difference from GTAW is that in PAW, the electrode is positioned within the body of the torch, so the plasma arc is separated from the shielding gas envelope.
The plasma is then forced through a fine-bore copper nozzle which constricts the arc and the plasma exits the orifice at high velocities (approaching the speed of sound) and a temperature approaching 28,000 °C (50,000 °F) or higher.
The PAW (Plasma Arc Welding), which is a cutting method, was discovered in the year 1953 by “Robert Merrell Gage” and recognized in the year 1957. This procedure was unique as it can perform accuracy cutting on both thin and thick metal. This kind of welding is also competent for spray covering hard metal on new metals.
This welding process is used in the welding industries for bringing superior control towards the arc welding method in minor current ranges. At present, plasma holds unique benefits and is used across the industry by generating a superior control level & accuracy for generating high worth joins in miniature applications to give a long life for high production supplies. This article discusses brief information about what is plasma arc welding, working principle, different types, equipment, advantages, disadvantages, and applications.
What is Plasma Arc Welding?
The PAW (Plasma arc welding) method is related to GTAW (gas tungsten arc welding). This arc can be formed among the metal as well as an electrode. 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.
Afterward, the plasma is fed throughout a nozzle which will compress the arc to force the plasma away at high speed as well as temperature. The plasma arc method utilizes a non-consumable tungsten electrode & an arc can be formed by strengthening the plasma throughout a bore nozzle. This arc welding can be productively applied to every metal that can be connected with the help of the gas tungsten arc welding technique.
Three operating modes can be produced by varying bore diameter and plasma gas flow rate:
Micro plasma: 0.1 to 15A
The micro plasma arc can be operated at very low welding currents. The columnar arc is stable even when arc length is varied up to 20mm.
Medium current: 15 to 200A
At higher currents, from 15 to 200A, the process characteristics of the plasma arc are similar to the TIG arc, but because the plasma is constricted, the arc is stiffer. Although the plasma gas flow rate can be increased to improve weld pool penetration, there is a risk of air and shielding gas entrainment through excessive turbulence in the gas shield.
Keyhole plasma: over 100A4
By increasing welding current and plasma gas flow, a very powerful plasma beam is created which can achieve full penetration in a material, as in laser or electron beam welding. During welding, the hole progressively cuts through the metal with the molten weld pool flowing behind to form the weld bead under surface tension forces. This process can be used to weld thicker material (up to 10mm of stainless steel) in a single pass.
Construction of the Plasma Arc Welding 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 the brief overview of each components.
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 as 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 temperature.
In this welding process, we use two inert gases. We need to maintain a low pressure to avoid the 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 in high flow rate, to make the weld shield sustainable.
The inert gases which are used in this process can helium, argon, and also hydrogen as per the need, and it is totally depends on the temperature.
It is an ionized hot gas composed of nearly the same numbers of electrons and ions. It has sufficient energy to free electrons from molecules, atoms, and electron to synchronize.
It is the main energy source of this welding.
Torch Accessory Kit:
These kits are used to expanding 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 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 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, 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 wear 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.
Advantages of Plasma Arc Welding:
The advantages of Plasma Arc Welding are 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 another welding process.
Disadvantages of Plasma Arc Welding:
The disadvantages of Plasma Arc welding are:
- It produces wider welds and heat-affected zones compare 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 is:
- This welding is used in 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 mould.
- This is used for welding or coating on a turbine blade.
So, this is all about Plasma Arc Welding Machining, I hope you enjoyed this article. I also wrote articles on some other welding processes to check out those too. And moreover, do not forget to share the article on your favorite social platform.