NIKUNJ LIMBACHIYA (M.TECH AMT)

Introduction of Plasma The plasma arc employs a restricted arc through

which a selected gas is made to flow. Plasma is generated by exposing a gas stream to the electrons from an electric arc. High velocity electrons generated by the arc impact gas molecules, and ionize them. The gas is forced through the nozzle, and the jet heats the metal, and blasts the molten metal away.

BASIC PRINCIPAL OF (PAW) If a high voltage is applied between the

electrode and the while the plasma gas is flowing, the gas is ionized and becomes conductive, then a plasma arc is generated. Since The plasma arc is restricted by the nozzle, it

had higher energy density, compared to MAG and TIG and can be used as a heat source of ultra high temperature (above 20,000C) having high heat concentrating performance.

PAM System and Basic Theory

effective cooling by a constant stream of water is

essential to keep the anode from evaporating. In

this configuration the maximum cathode amperage is about 3 000 A, at a voltage of 200 V the maximum electrical power input would be 600 kW.

The work piece to be coated remains relatively

cool and rarely exceeds 200.

Gases UsePrimary Gases:Gases that are used to create the plasma arc. Examples are nitrogen, argon, hydrogen, hydrogen, or mixture of them

Secondary Gases or Water:Surrounds the electric arc to aid in confining it and removing the molten material.

1. Transferred ArcThe generated arc is between the electrode and the work-piece.

2. Non transferred

ArcThe generated arc is between the electrode and the nozzle and heat is carried to the work-piece by the plasma gas

Transfer arc

Non transfer arc

(paw) terminology

ORIFICE GAS:This gas, referred to earlier as carrier gas, is an inert gas which is fed through the torch to surround the electrode and to enter the arc through the plenum chamber.

ELECTRODE SET BACK:This is the distance between the electrode tip and the outer bottom edge of the constricting nozzle.

PLENUM CHAMBER:This has been referred to under orifice gas.

It is the space between the inside wall of the constricting nozzleand the electrode.

SHIELDING GAS:The shielding gas is provided additionally through the outer gas nozzle , in the same manner as in TIG PROCCES. To protect the area of the work piece , over which the arc plasma impinges. Its composition is the same as the orifice gas, i.e argon or argonhelium mixture.

NozzleThe nozzle, sometimes called the cup, is made of ceramic or any other high-temperature-resistant substance. This helps prevent the internal electrical parts from accidental shorting and provides control of the shielding gas or water injection if they are used.

KEY HOLES IN PLASMA to the melt-in In additionmode adopted in conventional arc welding processes (such as GTAW), the keyholing mode can also be used in PAW in certain ranges of metal thickness (e.g., 2.5 6.4mm).With proper combinations of the orifice gas flow, the travel speed, and the welding current, keyholing is possible.

Figure 1. Plasma arc welding: (a) overall process (b) welding area enlarged and shown with key holing.

How to weld developed ?

properties

specification- Mechanics of material removal - melting - Medium - plasma - Tool - plasma jet - Maximum temperature = 16,000 - Maximum velocity of plasma jet = 500 m/sec - Maximum mrr = 150 cm3/min - Specific energy = 1000 W/cm3/min - Power range = 2 to 200 KW - Maximum plate thickness = 200 mm (depends on material)

specification- Cutting speed = 0.1 to 7.5 m/min - Voltage 30 to 250 V - Current