22-12-2012, 01:39 PM
Plasma arc machining
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Plasma arc machining (PAM):-
PAM is a method of cutting metal with a plasma-arc, or tungsten inert-gas-arc, torch. The torch produces a high-velocity jet of high-temperature ionized gas (plasma) that cuts by melting and displacing material from the workpiece. Temperatures obtainable in the plasma zone range from 20,000° to 50,000° F (11,000° to 28,000° C). The process may be used for cutting most metals.
Principle of PAM:-
The plasma arc welding process is normally compared to the gas tungsten arc process.But in the TIG-process, the arc is burning free and unhandled, whereas in the plasma-arc system, the arc is necked by an additional water-cooled plasma-nozzle. Plasma gas-almost always 100 % argon flows between the tungsten electrode and the plasma nozzle.
The welding process involves heating a gas called plasma to an extremely high temperature and then ionizing it such that it becomes electrically conductive. The plasma is used to transfer an electric arc called pilot arc to a work piece which burns between the Tungsten electrode and the plasma nozzle. By forcing the plasma gas and arc through a constricted orifice the metal, which is to be welded is melted by the extreme heat of the arc. The weld pool is protected by the shielding gas, flowing between the outer shielding gas nozzle and the plasma nozzle. As shielding gas pure argon-rich gas-mixtures with hydrogen or helium are used.
The high temperature of the plasma or constricted arc and the high velocity plasma jet provide an increased heat transfer rate over gas tungsten arc welding when using the Same current. This results in faster welding speeds and deeper weld penetration. This method of operation is used for welding extremely thin material and for welding multi pass groove and welds and fillet weld.
Equipment:-
A plasma arc cutting torch has four components:
1.The electrode carries the negative charge from the power supply.
2.The swirl ring spins the plasma gas to create a swirling flow pattern.
3.The nozzle constricts the gas flow and increases the arc energy density.
4.The shield channels the flow of shielding gas and protects the nozzle from metal spatter.