Plasma Arc Machining: Diagram, Parts, Working, Uses [PDF]

In this post, you learn what is plasma arc machining. And its working principle, advantages, limitations, and more.

What is Plasma Arc Machining?

When a flowing gas is heated to a sufficiently high temperature to become partially ionized, it is known as ‘plasma’. Plasma arc machining erodes materials using a high-temperature ionized gas plasma. This is a mixture of free electrons, positively charged ions, and neutral atoms.

Plasma arc machining is a metal removal process in which the metal is removed by focusing a high-velocity jet of high-temperature (11,000°C to 30,000°C) ionized gas on the workpiece.

It is used in aerospace and metalworking for precision in materials such as titanium and nickel alloys, which improves manufacturing capabilities.

Parts of Plasma Arc Machining

The following are the main parts of plasma arc machining:

#1 Plasma Gun

Gas must be supplied with a power supply (electricity) in order to transform into plasma; the tougher the plasma, the higher the current.

#2 Gas Supply

The plasma is a source of compressed air, nitrogen, and other gases. Here, the workpiece is shielded and the melted metal is blown off using a second inert enclosed gas.

#3 Cooling Water System

A cooling water system is utilized to cool the plasma torch, which is located on the opposite body of the plasma cutter.

#4 Electrode and Nozzle

Specially constructed electrodes and nozzles compress and retain the plasma jet, focusing it into a narrow area suitable for cutting.

#5 Workpiece

In pam machining, the workpiece is positioned underneath the plasma gun. This method can be used to cut materials such as carbon, magnesium, stainless steel, aluminum, and steel alloys.

Working Principle of PAM

In a plasma torch, known as the gun or plasmatron, a volume of gas such as H2, N2, 02, etc. is passed through a small chamber in which a high-frequency spark (arc) is maintained between the tungsten electrode (cathode) and the copper nozzle (anode), both of which are water-cooled.

Working

In certain torches, an inert gas flow surrounding the main flame is provided to shield the gas from the atmosphere.

The high-velocity electrons generated by the arc collide with the gas molecules and produce dissociation of diatomic molecules of the gas resulting in ionization of the atoms and causing large amounts of thermal energy to be liberated.

The plasma-forming gas is forced through a nozzle duct of the torch in such a manner as to stabilize the arc.

The heating of the gas takes place in the compressed zone of the nozzle duct resulting in almost high exit gas velocity and high core temperature up to 16,000 °C.

The relative plasma jet melts the workpiece material and the high-velocity gas stream effectively blows the molten metal away.

The depth of heat affected zone depends on the work material, its thickness, and cutting speed. On a workpiece of 25 mm thickness, the heat-affected zone is about 4 mm and it is less at high cutting speeds.

A typical flow rate of the gas is 2 to 11 m/hr. Direct current, rated at about 400 V and 200 kW output is normally required.

Arc current ranges between 150 and 1000 A for a cutting rate of 250 to 1700 mm/min.

Accuracy

This is a roughing operation with an accuracy of about 1.5 mm with a corresponding surface finish. Accuracy on the width of slots and diameter of holes is ordinarily from +0.8 mm on 6 to 30 mm thick plates, and + 3,0 mm on 100 to 150 mm thick plates.

Applications of Plasma Arc Machining

The following are the applications of plasma arc machining:

1. This is chiefly used to cut stainless steel and aluminum alloys.
2. Profile cutting of metals, especially of these metals and alloys, has been the common prominent commercial application of PAM.
3. On the machining side, plasma has been used successfully in the conventional turning and milling of very difficult materials.

Advantages of PAM

The following are the advantages of plasma arc machining:

1. This type of machining can work easily with hard and brittle metals, making it applicable to a wide range of metal materials.
2. Plasma arc machining has a wide range of uses since it can be applied to almost any type of metal.
3. A key advantage is the capacity to attain high cutting speeds, guaranteeing amplified productivity and effectiveness.
4. PAM is ideal for precise and complicated work, excellent at machining small cavities, and delivers high dimensional accuracy.
5. Plasma arc machining is an easy technology to use, and its effectiveness helps to speed manufacturing processes.
6. Its usefulness in vital areas like aerospace and aviation is shown by its major role in the automatic repair of jet engine blades.

Disadvantages of PAM

The following are the disadvantages of plasma arc machining:

1. PAM use needs a huge initial investment due to the need for a variety of specialized equipment, which can be costly.
2. The procedure uses a lot of inert gases, such as nitrogen or argon, which raises the expense of operation.
3. PAM can result in narrow, unneeded surfaces, which may not be desired in some applications.
4. One disadvantage is that the workpiece may have surface variations, necessitating further finishing or post-processing procedures.
5. PAM has strong light emissions that could damage human eyes.

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FAQs

Conclusion

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Read also:

1. What is Ultrasonic Machining (USM)?
2. How does an Abrasive Jet Machining (AJM) work?
3. Parts and function of Laser Beam Machining (LBM).

External resources:

Download PDF from researchgate.net