Plasma Arc Machine: Defination,working principle,parts,types, construction, application,advantage,disadvantage,limitation,charterstics

Introduction:-

This is used to remove materials from the workpiece.In this process a high velocity jet of high temperature gas is used to melt and remove material from the workpiece.
This velocity of hot gas is also known as plasma jet.
The temperature range is plasma zone is 11000 degree to 28000 degree centrigate.



Parts of Plasma Arc Machine:-

•Plasma Gun
•Power supply
•Cooling Mechanism
•Workpiece
•Tooling

Construction of Plasma Arc Machine:-

The schematic arrangement of plasma arc machining is shown in Fig.
• The plasma arc cutting torch carries a tungsten electrode fitted in a small chamber.
• This electrode is connected to the negative terminal of a DC power supply. So it acts as a cathode.
• The positive terminal of a D.C power supply is connected to the nozzle formed near the bottom of the chamber. So, nozzle acts as an anode.
• A small passage is provided on one side of the torch for supplying gas into the chamber.
• Since there is a water circulation around the torch, the electrode and the nozzle remains water-cooled.

Working of Plasma Arc Machine:-

•When a D.C power is given to the circuit, a strong arc is produced between the electrode (cathode) and the nozzle (anode).
•A gas usually hydrogen (H2) or Nitrogen (N2) is passed into the chamber.
•This gas is heated to a sufficiently high temperature of the order of 11,000°C to 28,000°C by using an electric arc produced between the electrode and the nozzle.
•In this high temperature, the gases are ionized and a large amount of thermal energy is liberated.
•This high velocity and high-temperature ionized gas (plasma) is directed on the workpiece surface through the nozzle.
•This plasma jet melts the metal of the workpiece and the high-velocity gas stream effectively blows the molten metal away.
•The heating of workpiece material is not due to any chemical reaction, but due. to the continuous attack of plasma on the workpiece material. So, it can be safely used for machining of any metal including those which can be subjected to the chemical reaction.

Application of Plasma Arc Machine:-

•It is used for cutting alloy steels, stainless steel, cast iron, copper, nickel, titanium, aluminum, and alloy of copper and nickel, etc.
• It is used for profile cutting.
•It is successfully used for turning and milling of hard to machine materials.
• It can be used for stack cutting, shape cutting, piercing, and underwater cutting.
•Uniform thin film spraying of refractory materials on different metals, plastics, ceramics are also done by plasma arcs.

Advantage of Plasma Arc Machine:-

• It can be used to cut any metal.
 The cutting rate is high.
•As compared to the ordinary flame cutting process, it can cut plain carbon steel four times faster.
•It is used for rough turning of very difficult materials.
•Due to the high speed of cutting, the deformation of sheet metal is reduced while •the width of the cut is minimum and the surface quality is high.
  
Disadvantage of Plasma Arc Machine:-

•It produces a tapered surface.
•The protection of noise is necessary.
•The equipment cost is high.
•Protection of eyes is necessary for the operator and persons working in nearby areas.
• Oxidation and scale formation takes place. So, it requires shielding.
•The work surface may undergo metallurgical changes.

Characteristics of Plasma Arc Machine

Metal removal technique: Heating, melting, and vaporizing by using plasma.

Work material .-All materials that conduct electricity.

Tool: Plasma jet

Velocity of plasma jet: 500 m /s

Power range: 2 to 220 kW

Current: As high as 600 amp

Voltage : 40 – 250 V

Cutting speed: 0. 1 to 7 m / min

Metal removal rate: 145 cm3 /min

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