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How does a Plasma Cutter Work? Principle, Applications and Metal removal mechanism


What is Plasma Arc Machining??


Working Principle of Plasma Arc Machining-

The gas molecules at room temperature consist of two or more atoms. When the temperature of gas molecules is heated to 20000 degrees centigrade, the molecules separate out as atoms. If the temperature is further increased to about 30000 degree centigrade, the atoms dissociate their electrons and the gas becomes ionized (ions and electrons). The gas in this condition or state is known as plasma.
The plasma is commonly developed by direct current generation method. It consists of hot tungsten cathode and water cooled copper anode. The gas is allowed to pass around the cathode and it is made to flow out through the anode. The temperature of plasma depends on the orifice diameter of cathode. The smaller the orifice diameter, the greater is the anode. Thus the plasma arc with such high temperature on the work piece, due to which the material melts out and vaporizes. As a result, the material is removed by the stream of ionized gas. The materials which have high thermal conductivity, good oxidation cut easily by Plasma Arc Machining (PAM) process.

Process of Plasma Arc machining-

Arc cutting is the cutting process in which the metal which is to be cut is melted by the heat produced by the arc and then the molten metal is blown away.
Metal is blown by the force of the arc or by other gases like air or shielding gases. There are various processes of arc cutting, depending on the source of heat input,’ carbon Arc Cutting (CAC), Air Carbon Arc Cutting (AAC), Oxygen Arc Cutting (AOC), Shielded Metal Arc Cutting (SMAC),Gas Metal Arc Cutting (GMAC). Gas Tungsten Arc Cutting (GAC) and Plasma Arc Cutting (PAC). Among all the processes, the type of torch used for cutting is the only difference. Torch has a provision to hold the electrode and high pressure gas by itself. Among all the arc cutting processes, Carbon Arc Cutting process is the simplest process which uses Carbon electrode and the metal is blown away by the force of the arc, but produces rough edge hence, usage is less. Plasma arc cutting process produces a very high temperature of the order of 14000 degrees centigrade. 
Therefore, it is easy to melt and blow the metal In this process.

Applications of Plasma Arc Machining-

The applications of plasma arc machining are as follows:

1. It consists of multiple torch system hence can be used to cut a plate at a time.

2. Plasma Arc Machining is most commonly used to prepare ends of a pi section before the welding has been one.

3. CNC types PAM systems are used for performing operations such as punching and shape cutting. Shape cutting operations are performed on light duty plates which are complicated to machine by oxy-fuel system.

4. This system is suitable for machining materials such as stainless steel, aluminum and copper.

5. The operations which are complicated to turn or cut the material is done by using PAM method.

Mechanism of Metal Removal-

The metal to be removed gets heated up due to the heating up of anode by direct electron bombardment and also due to the convection heating from the high temperature plasma. The heat that is produced has the capacity to raise the temperature of the work piece above its melting point. The molten metal is blown away by the high velocity gas stream. It is possible to remove the metal if 45% of the electrical power is supplied to the torch. On a specific part of the work piece, the arc heat is concentrated to raise the temperature to its melting point. The metal removal mechanism involves the quality of cut with which the metal is removed depends upon the distribution of heat flow. If the heat is supplied uniformly trough out the thickness of the material then a better quality of cut can be obtained. The speed with which the metal is cut out also depends upon the distribution of heat flow. 
This is the process the Plasma cutter work.

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