Want to know about Plasma Arc Machining?
Then you landed in the right place. Here you will know about the plasma arc machining process, from scratch to end.
Welcome to Engineers Rail, Grab your seat and be comfortable, while I start the engine of the knowledge.
So, let’s get started…
Before I start, I have a surprise for you, you will get a PDF and PPT of this whole article at the end of this article.
Cool. Isn’t it?
Now, let’s drive into the mainstream. First, I would like to tell you What is plasma, to clarify your basics. So, here it is-
What is Plasma?
Plasma is often called the fourth state of the matter. The first three are-
So, If you first start with solid, let’s say, Ice.
When you put energy into ice, it will start melting.
Again if you put further energy into the melted ice (Liquid), it will start to evaporate and converts into Gas.
Now, if you put even more energy into the gas, it gets ionized and this ionized gas is called Plasma.
So, Plasma is essentially an ionized gas that has some interesting properties like it conducts electricity and emits light.
Now, Let’s drive into the mainstream of the article, Starting with- What is plasma arc machining and later on, the working principle.
What is Plasma Arc Machining?
When gas is heated to a temperature of about 5500C to ionize the gas, when gas is completely ionized, then the temperature of the central part of the plasma is between 11000°C to 28000°C.
When such an ionized gas is directed on the workpiece through a high-velocity jet, the metal is removed by melting.
This high velocity of hot gas is known as plasma jet and this process is known as plasma arc machining(PAM).
Working Principle of Plasma arc machining-
Here is the principle of plasma arc machining-
- In PAM Machining, constricting an electric arc through a nozzle generates the basic plasma jet. Instead of diverging into an open arc, the nozzle constricts the arc into a small cross-section.
- This action greatly increases the power of the arc so that both temperature and voltage are raised.
- After passing through the nozzle, the arc exists in the form of a high-velocity, well-illuminated and intensity hot plasma jet.
- The basic heating phenomenon that takes place at the workpiece is a combination of heating due to the energy transfer of electrons
- Recombination of dissociated molecules on the workpiece, and the convective heating from the high-temperature plasma that accompanies the arc.
- Once the material has been raised to the molten point, the high-velocity gas stream effectively blows the material away.
Plasma arc machining diagram-
Components of Plasma arc machining-
Here are the plasma arc cutting equipment and construction, given below-
- Power supply
- Gas supply
- Cooling water system
- Electrode & nozzle
1. Power supply-
Electricity supply is needed to turn the gas into plasma, the greater the current, the harder the plasma.
2. Gas Supply-
Compressed air, nitrogen and other gas provide a source for the plasma. In this example, a second inert sealed gas is used to protect the workpiece and blow off melted metal.
3. Cooling water system-
A cooling water system is used to provide the cooling effect to the plasma torch, mounted in the other body of the plasma cutter.
4. Electrode & Nozzle-
Special engineered electrodes and nozzles constrict and maintain the plasma jet concentrating it into the small area so it can be used for cutting.
The workpiece is positioned below the plasma gun in pam machining. Materials like magnesium, carbon, stainless steel, aluminium and steel alloys can be cut using this process.
Construction of Plasma arc machining-
In a tiny chamber, the tungsten electrode is picked up by the plasma arc cutting torch. These electrodes are linked to a D.C. power supply’s negative terminal, Thus, it serves as a cathode and the nozzle serves as an anode.
To provide gas to the chamber, a small entrance is constructed on one side of the flame. The water circulated around the torch to maintain its temperature.
Now, let’s discuss the working of the same.
- When the operator is ready to cut, a start signal is sent to the DC power supply.
- A circuit temporarily connects the nozzle to the positive side of the power supply with the electrode on the negative side.
- Next, the high-frequency spark ionizes the gas and makes it electrically conductive.
- This creates a current path between the electrode and nozzle and forms a Pilot arc plasma.
- When the pilot arc contacts the workpiece, the plasma arc transfers to the workpiece melting the metal.
- Then, the high-velocity gas blows the molten material away.
- And that’s the end of the working of PAM.
- Hence, let’s look out further into the Advantages, disadvantages and applications of this process in this journey.
Advantages of plasma arc machining-
Here are some advantages of the PAM machining process-
- The main advantage of PAM is the suitability for any material irrespective of hardness or heat resistant characteristics.
- PAM allows high material removal rate(up to 10000 cm3/hr) and the Material removal rate(MRR) for high strength materials are comparable with conventional turning.
- Ferrous and non-ferrous materials up to 150 mm thick can be cut.
- Plasma arc methods are also employed in special applications to replace conventional machining operations such as lathe turning, milling and planning, heat treatment and metal deposition operation, and plasma arc welding.
- The plasma arc, as an industrial tool, is the heaviest employed in sheet and plate cutting operations as an alternative to more conventional oxy-fuel torches or cutting tools.
Disadvantages of plasma arc machining-
Here are some limitations of PAM machining–
- The main disadvantage of PAM is the high electric power requirement
- Circular holes can be drilled but the size is limited by nozzle size.
- Depth of hole, tolerance and repeatability are limited.
- UV and IR radiation affect the worker’s health.
- It produces a tapered surface
- Consumption of plasma gas is high
Here are some applications of plasma arc machining-
- Mill applications
- Used in the nuclear submarine piping system
- Welding of rocket motor casing
- Stainless steel tubes & profile cutting
- For stock cutting, plate beveling, shape cutting and piercing.
- In the manufacture of automotive and railroad.
- For removal of gates and riser from casting in the foundry.
The general accuracy of plasma arc machining is approximately +/-0.040.
Plasma arc machining was initially employed to cut metals that are difficult to machine by conventional methods. However, In recent years plasma arc has also been successfully used for spraying, surfacing and welding metals like aluminium, stainless steel, titanium, etc.
However, I have shared all this above as you went through it.
I hope, you like spending time here and added some value to you. If so, consider sharing with your friends, colleagues, and especially with needy ones.
Thank you for being with me. I hope to See you in the next session.
Here are some more machining processes, you should read also-
Now, it’s time for your bonuses.
so, here it is-
An ionised pressure gas bombarded on the materials with the approx temperature of 20,000 Degree celsius.
Plasma cutting works on the principle of high heating.
Abhishek Tiwary is a blogger by passion and a Quality Engineer by profession. He completed his B.Tech degree in the year 2017. Now working in a reputed firm. He loves to share his knowledge with others.