Plasma Arc Welding | PAW Process |Transferred Plasma Arc Welding

Plasma is the name given to a high temperature stream of partially ionized gas flowing at near sonic velocity. It is a mixture of neutral atoms, free electrons that have disassociated from the gas atoms and positively charged gas ions.

Plasma arc welding is an arc welding process wherein coalescence is produced by the heat obtained from a constricted arc setup between a Tungsten alloy electrodes, Water cooled Nozzle and the job. The process employs two inert gases, one forms the arc plasma and the second shields the arc plasma. The tip of the plasma arc torch is constricted or reduced in cross sectional area. This constriction of arc considerably increases its temperature (upto 10000 deg Celsius) since it carries the same amount of current.

Types of Plasma Arc Welding:

1. Non-transferred arc process

2. Transferred arc process

Non-Transferred arc process:

The arc is formed between the electrode (negative) and the water cooled constricting nozzle (positive). Arc plasma comes out of the nozzle as a flame. The arc is independent of the workpiece and the workpiece does not form a part of the electrical circuit. Just as an arc flame, it can be moved from one place to another and it can be better controlled.

This mode is used for plasma spraying or for very low current applications as in non metals. The non-transferred arc plasma possesses comparatively less energy density as compared to transferred arc plasma and it is employed for welding and in applications involving ceramics or metal plating.

Transferred Arc Process:

Current is transferred from the tungsten electrode (negative) through the orifice to the workpiece (positive) and back to the power supply. A transferred arc possesses high energy density and plasma jet velocity.

This is the mode most commonly used for welding. So it is employed to cut and melt metals. It can also be used for welding at high arc travel speeds.