equipment needed in plasma arc welding along with their functions are as follows: Current and gas decay control It is necessary to close the key hole properly while terminating the weld in the structure. Fixture It is required to avoid atmospheric contamination of the molten metal under bead. Materials Steel Aluminium other materials High-frequency generator and current limiting resistors A high-frequency generator and current limiting resistors are used for arc ignition. The arc-starting system may be separate or built into the system. Plasma Torch It is either transferred arc or non-transferred arc type. It is hand operated or mechanized. At present, almost all applications require automated system. The torch is water-cooled to increase the life of the nozzle and the electrode. The size and the type of nozzle tip are selected depending upon the metal to be welded, weld shapes and desired penetration depth. Power Supply A direct-current power source (generator or rectifier) having drooping characteristics and open circuit voltage of 70 volts or above is suitable for plasma arc welding. Rectifiers are generally preferred over DC generators. Working with helium as an inert gas needs open circuit voltage above 70 volts. This higher voltage can be obtained by series operation of two power sources; or the arc can be initiated with argon at normal open-circuit voltage and then helium can be switched on. Typical welding parameters for plasma arc welding are as follows: Current 50 to 350 amps, voltage 27 to 31 volts, gas flow rates 2 to 40 liters/minute (lower range for orifice gas and higher range for outer shielding gas), direct current electrode negative (DCEN) is normally employed for plasma arc welding except for the welding of aluminum in which cases water-cooled electrode is preferable for reverse-polarity welding, i.e. direct-current electrode positive (DCEP). Shielding gases Two inert gases or gas mixtures are employed. The orifice gas at lower pressure and flow rate forms the plasma arc. The pressure of the orifice gas is intentionally kept low to avoid weld metal turbulence, but this low pressure is not able to provide proper shielding of the weld pool. To have suitable shielding protection same or another inert gas is sent through the outer shielding ring of the torch at comparatively higher flow rates. Most of the materials can be welded with argon, helium, argon+hydrogen and argon+helium, as inert gases or gas mixtures. Argon is commonly used. Helium is preferred